The demonstration of αKlotho deficiency in human chronic kidney disease with a novel synthetic antibody

The inflection point: α-Klotho levels and the risk of all-cause mortality

Purpose

The controversial nature of the association between α-Klotho and mortality risk in the general population warrants further investigation. This study aims to examine the correlation between circulating α-Klotho levels and the risk of all-cause mortality.

Methods

A sample size of 13,748 individuals from the NAHNES 2005-2016 cycles was included in this study. The effect of different α-Klotho levels (divided into quartiles) on survival was assessed using Kaplan-Meier (KM) curves. Cox proportional hazards models were used to analyze the linear relationship between log α-Klotho and the risk of all-cause mortality. Restricted cubic spline Cox proportional hazards regression model was used to analyze the non-linear relationship between log α-Klotho and risk of all-cause mortality. Threshold effect analysis was performed to determine the most favorable inflection point for log α-Klotho. Stratification and sensitivity analyses were performed to assess the robustness of the results.

Results

A total of 1,569 deaths were reported during the median follow-up period of 5.33 years (2.83-7.83 years). Among the log α-Klotho quartile groups, quartile 1 had the highest mortality rate compared to quartiles 2, 3, and 4. Multifactorial Cox regression analysis revealed a weak association between log α-Klotho and a 44% reduction in the risk of all-cause mortality (p=0.0473). We also found a U-shaped non-linear association between log α-Klotho and risk of all-cause mortality, with an optimal inflection point identified at 2.89 pg/mL. The stability of the U-shaped association between log α-Klotho and mortality risk was observed in various stratification and sensitivity analyses.

Conclusion

This study identified a U-shaped association between circulating α-Klotho levels and risk of all-cause mortality, with a notable inflection point at 2.89 pg/mL. Further investigation is warranted to fully elucidate the potential mechanisms underlying the association between α-Klotho and risk of all-cause mortality in the broader population.

Controlled dietary phosphate loading in healthy young men elevates plasma phosphate and FGF23 levels

Increased dietary inorganic phosphate (Pi) intake stimulates renal Pi excretion, in part, by parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23) or dopamine. High dietary Pi may also stimulate sympathetic outflow. Rodent studies provided evidence for these regulatory loops, while controlled experiments in healthy humans examined periods of either a few hours or several weeks, and often varied dietary calcium intake. The effects of controlled, isolated changes in dietary Pi intake over shorter periods are unknown. We studied the effects of a low or high Pi diet on parameters of mineral metabolism in 10 healthy young men. Participants received a standardized diet (1000 mg phosphorus equivalent/day) supplemented with either a phosphate binder (low Pi diet) or phosphate capsules (750 mg phosphorus, high Pi diet) in a randomized cross-over trial for 5 days with a 7-day washout between diets. High Pi intake increased plasma Pi levels and 24-h excretion and decreased urinary calcium excretion. High Pi intake increased intact FGF23 (iFGF23) and suppressed plasma Klotho without affecting cFGF23, PTH, calcidiol, calcitriol, Fetuin-A, dopamine, epinephrine, norepinephrine, metanephrine, or aldosterone. Higher iFGF23 correlated with lower calcitriol and higher PTH. These data support a role for iFGF23 in increasing renal Pi excretion and reducing calcitriol in healthy young men during steady-state high dietary Pi intake. High dietary Pi intake elevated blood Pi levels in healthy young subjects with normal renal function and may therefore be a health risk, as higher serum Pi levels are associated with cardiovascular risk in the general population.

Interaction Effect of Estimated Pulse Wave Velocity and Serum Klotho Level on Chronic Kidney Disease

Objectives

Older individuals usually have greater arterial stiffness, lower serum Klotho levels and a greater incidence of chronic kidney disease (CKD). The current study aimed to evaluate the interaction effect of estimated pulse wave velocity (ePWV) and serum Klotho levels on CKD in Americans.

Methods

Data from the National Health and Nutrition Examination Survey database from 2007 to 2016 were used. Participants with data for the assessment of ePWV and serum Klotho and for the assessment of CKD were enrolled. The associations between ePWV and serum Klotho levels were analyzed via restricted cubic spline analysis and a linear regression model. The associations between exposure factors and CKD prevalence were assessed via a logistic regression model. Subgroup analysis was performed for each confounding factor to assess the robustness of the results.

Results

This study enrolled 13,273 participants, 3859 of whom were CKD patients. CKD patients had higher ePWV (9.66 ± 1.75 m/s vs. 8.48 ± 1.64 m/s, p < 0.001) and lower levels of serum Klotho (816.35 ± 290.47 pg/mL vs. 869.87 ± 315.87 pg/mL, p < 0.001). A significant negative linear association was found between ePWV and serum Klotho. According to the fully adjusted model, a significant interaction effect between ePWV and serum Klotho was observed on the risk of CKD (p < 0.001). Compared with individuals with a lower ePWV and higher serum Klotho, individuals with an increased ePWV and lower serum Klotho had a significantly elevated risk of CKD (OR: 1.847, 95% confidence interval: 1.467-2.325; p < 0.001). The subgroup analysis revealed that the results were robust.

Conclusions

The study demonstrated significant interaction effect of ePWV and serum Klotho on the prevalence of CKD. Individuals with increased ePWV and decreased serum Klotho levels had the highest risk of CKD. The assessment of the combination of ePWV and serum Klotho for CKD management should be considered routine in clinical practice.

Klotho and Clinical Outcomes in CKD: Findings From the Chronic Renal Insufficiency Cohort (CRIC) Study

RATIONALE & OBJECTIVE

Klotho deficiency may affect clinical outcomes in chronic kidney disease (CKD) through fibroblast growth factor-23 (FGF23)-dependent and -independent pathways. However, the association between circulating Klotho and clinical outcomes in CKD remains unresolved and was the focus of this study.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

1,088 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study with an estimated glomerular filtration rate (eGFR) of 20-70mL/min/1.73m2.

EXPOSURE

Plasma Klotho level at the year-1 study visit.

OUTCOMES

5-year risks of all-cause mortality, heart failure hospitalization, atherosclerotic cardiovascular events, and a composite kidney end point that comprised a sustained 50% decrease in eGFR, dialysis, kidney transplant, or eGFR<15mL/min/1.73m2.

ANALYTICAL APPROACH

We divided Klotho into 6 groups to account for its nonnormal distribution. We used Cox proportional hazards regression and subdistribution hazards models to compare survival and clinical outcomes, respectively, between Klotho groups. We sequentially adjusted for demographic characteristics, kidney function, cardiovascular risk factors, sample age, and FGF23.

RESULTS

Mean eGFR was 42mL/min/1.73m2, and median Klotho concentration was 0.31ng/mL (IQR, 0.10-3.27ng/mL). When compared with the lowest Klotho group, survival (HR, 0.77; 95% CI, 0.32-1.89), heart failure hospitalization (HR, 1.10; 95% CI, 0.38-3.17), atherosclerotic cardiovascular events (HR, 1.19; 95% CI, 0.57-2.52), and CKD progression (HR, 1.05; 95% CI, 0.58-1.91) did not differ in the high Klotho group. In contrast, FGF23 was significantly associated with mortality and heart failure hospitalization independent of Klotho levels.

LIMITATIONS

Despite adjustments, we cannot exclude the potential influence of residual confounding or sample storage on the results. A single measurement of plasma Klotho concentration may not capture Klotho patterns over time.

CONCLUSIONS

In a large, diverse, well-characterized CKD cohort, Klotho was not associated with clinical outcomes, and Klotho deficiency did not confound the association of FGF23 with mortality or heart failure hospitalization.

PLAIN-LANGUAGE SUMMARY

Klotho is a protein that is vital to mineral metabolism and aging and may protect against cardiovascular disease. Klotho levels decrease in chronic kidney disease (CKD), but the association between Klotho and clinical outcomes in CKD remains uncertain. In a prospective cohort study of more than 1,000 people with CKD, circulating Klotho levels were not associated with kidney disease progression, cardiovascular outcomes, or mortality. These results suggest that the decrease in circulating Klotho levels in CKD does not play a prominent role in the development of poor clinical outcomes.

Soluble αKlotho concentration in the inferior vena cava of patients with primary aldosteronism

INTRODUCTION

Klotho, a key aging regulator, is predominantly expressed in the kidney. Various methods now enable the measurement of soluble αKlotho blood levels in humans. Limited studies have explored the renal origin of circulating αKlotho in humans.

METHODS

Soluble αKlotho in the inferior vena cava blood was measured using an enzyme-linked immunosorbent assay kit using blood samples from patients undergoing adrenal venous catheterization for close examination of primary aldosteronism.

RESULTS

The concentration at the suprarenal inferior vena cava (476±68.2) was significantly higher than that at the infrarenal inferior vena cava (434±74.8) (p=0.018), with a rate of change of 8.12 (2.3)%.

CONCLUSIONS

We demonstrate a step-up in αKlotho concentration from the infrarenal to suprarenal vena cava in humans, supporting the kidney's origin of soluble αKlotho in the bloodstream.

Determination of the reference interval for urinary klotho to creatinine ratio of healthy dogs

For several years, alpha klotho has been considered as a candidate biomarker in chronic kidney disease (CKD), progression of CKD and CKD mineral bone disorders (CKD-MBD). The evidence on the relationship between klotho and kidney function is controversial in some areas. The aim of the study was to identify the influence of age, sex and breed on urinary alpha klotho, values in the early stages of CKD within the studied population and determine a reference interval in a group of healthy dogs. Significantly higher values were measured in older dogs over 6 years old (p = 0.026, p = 0.0007) and in the breed German Shepherd than Belgian Shepherd (p = 0.0401). On the basis of sex and in small breed dogs, no significant differences were noted. In dogs with CKD stage 2, alpha klotho values were significantly lower (p = 0.0135) than in healthy dogs. Within the studied population, a reference interval for urinary klotho to creatinine ratio (UrKl/Cr) was determined in the range of 3.94-23.55 pg/gCr. Since our findings show that alpha klotho is associated with older age, we assume that this may have influenced the results in the group of dogs with CKD stage 1 due to the presence of predominantly old dogs in this group. Future studies would be needed to consider age as a factor affecting urinary alpha klotho in dogs with CKD.

Renal aging and mitochondrial quality control

Mitochondria are dynamic organelles that participate in different cellular process that control metabolism, cell division, and survival, and the kidney is one of the most metabolically active organs that contains abundant mitochondria. Perturbations in mitochondrial homeostasis in the kidney can accelerate kidney aging, and maintaining mitochondrial homeostasis can effectively delay aging in the kidney. Kidney aging is a degenerative process linked to detrimental processes. The significance of aberrant mitochondrial homeostasis in renal aging has received increasing attention. However, the contribution of mitochondrial quality control (MQC) to renal aging has not been reviewed in detail. Here, we generalize the current factors contributing to renal aging, review the alterations in MQC during renal injury and aging, and analyze the relationship between mitochondria and intrinsic renal cells. We also introduce MQC in the context of renal aging, and discuss the study of mitochondria in the intrinsic cells of the kidney, which is the innovation of our paper. In addition, during kidney injury and repair, the specific functions and regulatory mechanisms of MQC systems in resident and circulating cell types remain unclear. Currently, most of the studies we reviewed are based on animal and cellular models, the relationship between renal tissue aging and mitochondria has not been adequately investigated in clinical studies, and there is still a long way to go.

Klotho exerts protection in chronic kidney disease associated with regulating inflammatory response and lipid metabolism

BACKGROUND

The anti-aging protein Klotho plays a protective role in kidney disease, but its potential as a biomarker for chronic kidney disease (CKD) is controversial. Additionally, the main pathways through which Klotho exerts its effects on CKD remain unclear. Therefore, we used bioinformatics and clinical data analysis to determine its role in CKD.

RESULTS

We analyzed the transcriptomic and clinical data from the Nephroseq v5 database and found that the Klotho gene was mainly expressed in the tubulointerstitium, and its expression was significantly positively correlated with estimated glomerular filtration rate (eGFR) and negatively correlated with blood urea nitrogen (BUN) in CKD. We further found that Klotho gene expression was mainly negatively associated with inflammatory response and positively associated with lipid metabolism in CKD tubulointerstitium by analyzing two large sample-size CKD tubulointerstitial transcriptome datasets. By analyzing 10-year clinical data from the National Health and Nutrition Examination Survey (NHANES) 2007-2016, we also found that Klotho negatively correlated with inflammatory biomarkers and triglyceride and positively correlated with eGFR in the CKD population. Mediation analysis showed that Klotho could improve renal function in the general population by modulating the inflammatory response and lipid metabolism, while in the CKD population, it primarily manifested by mediating the inflammatory response. Restricted cubic spline (RCS) analysis showed that the optimal concentration range for Klotho to exert its biological function was around 1000 pg/ml. Kaplan-Meier curves showed that lower cumulative hazards of all-cause mortality in participants with higher levels of Klotho. We also demonstrated that Klotho could reduce cellular inflammatory response and improve cellular lipid metabolism by establishing an in vitro model similar to CKD.

CONCLUSIONS

Our results suggest that Klotho exerts protection in CKD, which may be mainly related to the regulation of inflammatory response and lipid metabolism, and it can serve as a potential biomarker for CKD.

Association between dietary phosphate intake and skeletal muscle energetics in adults without cardiovascular disease

Highly bioavailable inorganic phosphate (Pi) is present in large quantities in the typical Western diet and represents a large fraction of total phosphate intake. Dietary Pi excess induces exercise intolerance and skeletal muscle mitochondrial dysfunction in normal mice. However, the relevance of this to humans remains unknown. The study was conducted on 13 individuals without a history of cardiopulmonary disease (46% female, 15% Black participants) enrolled in the pilot-phase of the Dallas Heart and Mind Study. Total dietary phosphate was estimated from 24-h dietary recall (ASA24). Muscle ATP synthesis was measured at rest, and phosphocreatinine (PCr) dynamics was measured during plantar flexion exercise using 7-T 31P magnetic resonance (MR) spectroscopy in the calf muscle. Correlation was assessed between dietary phosphate intake normalized to total caloric intake, resting ATP synthesis, and PCr depletion during exercise. Higher dietary phosphate intake was associated with lower resting ATP synthesis (r = -0.62, P = 0.03), and with higher levels of PCr depletion during plantar flexion exercise relative to the resting period (r = -0.72; P = 0.004). These associations remain significant after adjustment for age and estimated glomerular filtration rate (both P < 0.05). High dietary phosphate intake was also associated with lower serum Klotho levels, and Klotho levels are in turn associated with PCr depletion and higher ADP accumulation post exercise. Our study suggests that higher dietary phosphate is associated with reduced skeletal muscle mitochondrial function at rest and exercise in humans providing new insight into potential mechanisms linking the Western diet to impaired energy metabolism.NEW & NOTEWORTHY This is the first translational research study directly demonstrating the adverse effects of dietary phosphate on muscle energy metabolism in humans. Importantly, our data show that dietary phosphate is associated with impaired muscle ATP synthesis at rest and during exercise, independent of age and renal function. This is a new biologic paradigm with significant clinical dietary implications.

C-terminal fragment of fibroblast growth factor 23 improves heart function in murine models of high intact fibroblast growth factor 23

Cardiovascular disease (CVD) is the major cause of death in chronic kidney disease (CKD) and is associated with high circulating fibroblast growth factor (FGF)23 levels. It is unresolved whether high circulating FGF23 is a mere biomarker or pathogenically contributes to cardiomyopathy. It is also unknown whether the C-terminal FGF23 peptide (cFGF23), a natural FGF23 antagonist proteolyzed from intact FGF23 (iFGF23), retards CKD progression and improves cardiomyopathy. We addressed these questions in three murine models with high endogenous FGF23 and cardiomyopathy. First, we examined wild-type (WT) mice with CKD induced by unilateral ischemia-reperfusion and contralateral nephrectomy followed by a high-phosphate diet. These mice were continuously treated with intraperitoneal implanted osmotic minipumps containing either iFGF23 protein to further escalate FGF23 bioactivity, cFGF23 peptide to block FGF23 signaling, vehicle, or scrambled peptide as negative controls. Exogenous iFGF23 protein given to CKD mice exacerbated pathological cardiac remodeling and CKD progression, whereas cFGF23 treatment improved heart and kidney function, attenuated fibrosis, and increased circulating soluble Klotho. WT mice without renal insult placed on a high-phosphate diet and homozygous Klotho hypomorphic mice, both of whom develop moderate CKD and clear cardiomyopathy, were treated with cFGF23 or vehicle. Mice treated with cFGF23 in both models had improved heart and kidney function and histopathology. Taken together, these data indicate high endogenous iFGF23 is not just a mere biomarker but pathogenically deleterious in CKD and cardiomyopathy. Furthermore, attenuation of FGF23 bioactivity by cFGF23 peptide is a promising therapeutic strategy to protect the kidney and heart from high FGF23 activity.NEW & NOTEWORTHY There is a strong correlation between cardiovascular morbidity and high circulating fibroblast growth factor 23 (FGF23) levels, but causality was never proven. We used a murine chronic kidney disease (CKD) model to show that intact FGF23 (iFGF23) is pathogenic and contributes to both CKD progression and cardiomyopathy. Blockade of FGF23 signaling with a natural proteolytic product of iFGF23, C-terminal FGF23, alleviated kidney and cardiac histology, and function in three separate murine models of high endogenous FGF23.

Soluble Klotho, a Potential Biomarker of Chronic Kidney Disease-Mineral Bone Disorders Involved in Healthy Ageing: Lights and Shadows

Shortly after the discovery of Klotho, interest grew in its potential role in chronic kidney disease (CKD). There are three isoforms of the Klotho protein: αKlotho, βKlotho and γKlotho. This review will focus on αKlotho due to its relevance as a biomarker in CKD. αKlotho is synthesized mainly in the kidneys, but it can be released into the bloodstream and urine as soluble Klotho (sKlotho), which undertakes systemic actions, independently or in combination with FGF23. It is usually accepted that sKlotho levels are reduced early in CKD and that lower levels of sKlotho might be associated with the main chronic kidney disease-mineral bone disorders (CKD-MBDs): cardiovascular and bone disease. However, as results are inconsistent, the applicability of sKlotho as a CKD-MBD biomarker is still a matter of controversy. Much of the inconsistency can be explained due to low sample numbers, the low quality of clinical studies, the lack of standardized assays to assess sKlotho and a lack of consensus on sample processing, especially in urine. In recent decades, because of our longer life expectancies, the prevalence of accelerated-ageing diseases, such as CKD, has increased. Exercise, social interaction and caloric restriction are considered key factors for healthy ageing. While exercise and social interaction seem to be related to higher serum sKlotho levels, it is not clear whether serum sKlotho might be influenced by caloric restriction. This review focuses on the possible role of sKlotho as a biomarker in CKD-MBD, highlighting the difference between solid knowledge and areas requiring further research, including the role of sKlotho in healthy ageing.

Relationship between klotho and physical function in healthy aging

Epidemiological studies have reported a strong association between circulating Klotho and physical function; however, the cohorts were comprised of older adults with multiple comorbidities. Herein, we examined the relationship between Klotho and physical function in a community-based cohort of healthy adults. In this cross-sectional study, serum Klotho was measured in 80 adults who visited the Musculoskeletal Function, Imaging, and Tissue Resource Core of the Indiana Center for Musculoskeletal Health. Participants (n = 20, 10 [50%] men per group) were chosen into four age groups: 20-34, 35-49, 50-64, and ≥ 65 years, and were further grouped based on performance (low vs. high) on grip strength and chair stand tests. Klotho levels were lower in the ≥ 65 years group (703.0 [189.3] pg/mL; p = 0.022) and the 50-64 years group (722.6 [190.5] pg/mL; p = 0.045) compared to 20-34 years (916.1 [284.8] pg/mL). No differences were observed in Klotho between the low and high performers. The ≥ 65 years group walked a shorter distance during the 6-min walk test (6MWT) compared to 20-34 years (p = 0.005). Klotho was correlated with age (p < 0.001), body fat (p = 0.037), and 6MWT distance (p = 0.022). Klotho levels decline as early as the fifth decade of life, potentially before the onset of age-related impairment in exercise capacity.

Association between daily alcohol consumption and serum alpha klotho levels among U.S. adults over 40 years old: a cross-sectional study

BACKGROUND

Klotho is a hormone considered to be an anti-aging biomarker. The relationships between daily alcohol consumption and serum klotho are mainly unknown. The purpose of this study is to assess the relationship between alcohol consumption and serum alpha klotho (α-klotho) levels in the U.S.

METHODS

The data came from 11,558 participants aged ≥ 40 in the 2007-2016 National Health and Nutrition Examination Survey. Adults with reliable α-klotho plasma results were the target population. The self-report method was used to assess alcohol consumption. The relationship between daily alcohol intake and serum α-klotho levels was estimated using multivariable linear regression models. We also performed a stratified analysis of clinically important variables.

RESULTS

The mean serum α-klotho level among the 11,558 participants was 843.82 pg/mL. After full adjustment, participants with current moderate and heavy alcohol intake had lower serum α-klotho levels than those who never alcohol intake (β =  - 62.64; 95% CI: - 88.86, - 36.43; P < 0.001; β =  - 81.54; 95% CI: - 111.54, - 51.54; P < 0.001, respectively). Furthermore, the stratified analysis indicated that the association was insignificant in individuals with cardiovascular disease, chronic kidney disease, or cancer.

CONCLUSION

Daily alcohol consumption was inversely associated with serum α-klotho levels among U.S. adults over 40 years old. However, individuals with cardiovascular disease, chronic kidney disease, or cancer found no such relationship.

CKD Associates with Cognitive Decline in Middle-Aged and Older Adults with Long-Standing Type 1 Diabetes

Key Points

We found that development of both albuminuria and reduced eGFR was associated with clinically significant cognitive decline, particularly in the psychomotor and mental efficiency domain. There was also a significant interaction between worsened albuminuria and eGFR, the combination of which augmented cognitive deficits. A more comprehensive longitudinal phenotype of albuminuria showed that regressed albuminuria did not associate with worsened cognitive decline, as opposed to persistent albuminuria.

Background

Individuals with CKD or type 1 diabetes (T1D) are at risk for cognitive decline, but it is unclear whether these associations are with albuminuria, eGFR, or both.

Methods

We examined the longitudinal relationships between CKD and change in cognition in 1051 participants with T1D in the Diabetes Control and Complications Trial and its follow-up, the Epidemiology of Diabetes Interventions and Complications study. Albumin excretion rate and eGFR were measured every 1–2 years. Three cognitive domains were assessed repeatedly over a 32-year period: immediate memory, delayed memory, and psychomotor and mental efficiency. Associations between cognitive function and CKD were assessed: (1 ) longitudinally and (2 ) in models using eGFR and albuminuria measurements over the first 15–20 years with subsequent change in cognitive function over the ensuing 14 years (when decline in cognition was greatest).

Results

In fully adjusted longitudinal analyses, the magnitude of decline in the psychomotor and mental efficiency domain score was associated with eGFR <60 ml/min per 1.73 m2 (β −0.449; 95% confidence interval [CI], −0.640 to −0.259) and sustained albumin excretion rate 30 to <300 mg/24 hours (β −0.148; 95% CI, −0.270 to −0.026). This was equivalent to a decrease associated with approximately 11 and 4 years of aging, respectively. In analyses focused on changes in cognition between study years 18 and 32, eGFR <60 ml/min per 1.73 m2 was associated with reduced psychomotor and mental efficiency (β −0.915; 95% CI, −1.613 to −0.217).

Conclusions

In T1D, development of CKD was associated with a subsequent reduction on cognitive tasks requiring psychomotor and mental efficiency. These data highlight the need for increased recognition of risk factors for neurologic sequelae in patients with T1D, as well as preventive and treatment strategies to ameliorate cognitive decline.

Longevity factor klotho enhances cognition in aged nonhuman primates

Cognitive dysfunction in aging is a major biomedical challenge. Whether treatment with klotho, a longevity factor, could enhance cognition in human-relevant models such as in nonhuman primates is unknown and represents a major knowledge gap in the path to therapeutics. We validated the rhesus form of the klotho protein in mice showing it increased synaptic plasticity and cognition. We then found that a single administration of low-dose, but not high-dose, klotho enhanced memory in aged nonhuman primates. Systemic low-dose klotho treatment may prove therapeutic in aging humans.

Pathophysiological Implications and Therapeutic Approach of Klotho in Chronic Kidney Disease. A Systematic Review

The Klotho protein, known as an anti-aging protein, is expressed mainly in the kidney, and kidney disorders may contribute to disrupted expression of renal Klotho. The purpose of this systematic review was to determine if there are biological and nutraceutical therapies that increase the expression of Klotho and can help prevent complications associated with CKD. A systematic literature review was carried out through the consultation of PubMed, Scopus, and Web of Science. Records between the years 2012 and 2022 in Spanish and English were selected. Cross-sectional or prevalence and analytical studies were included that evaluated the effects of Klotho therapy. A total of 22 studies were identified after the critical reading of these selected studies. Three investigated the association between Klotho and growth factors; two evaluated the relationship between the concentration of Klotho and the type of fibrosis; three focused on the relationship between vascular calcifications and vitamin D; two assessed the relationship between Klotho and bicarbonate; two investigated the relationship between proteinuria and Klotho; one demonstrated the applicability of synthetic antibodies as a support for Klotho deficiency; one investigated Klotho hypermethylation as a renal biomarker; two investigated the relationship between proteinuria and Klotho; four linked Klotho as an early marker of CKD; one investigated Klotho levels in patients with autosomal dominant polycystic kidney disease. In conclusion, no study has addressed the comparison of these therapies in the context of their use with nutraceutical agents that raise the expression of Klotho.

Exercise and chronic kidney disease: potential mechanisms underlying the physiological benefits

Increasing evidence indicates that exercise has beneficial effects on chronic inflammation, cardiorespiratory function, muscle and bone strength and metabolic markers in adults with chronic kidney disease (CKD), kidney failure or kidney transplants. However, the mechanisms that underlie these benefits have received little attention, and the available clinical evidence is mainly from small, short-duration (<12 weeks) exercise intervention studies. The available data, mainly from patients with CKD or on dialysis, suggest that exercise-mediated shifts towards a less inflammatory immune cell profile, enhanced activity of the NRF2 pathway and reduced monocyte infiltration into adipose tissue may underlie improvements in inflammatory biomarkers. Exercise-mediated increases in nitric oxide release and bioavailability, reduced angiotensin II accumulation in the heart, left ventricular remodelling and reductions in myocardial fibrosis may contribute to improvements in left ventricular hypertrophy. Exercise stimulates an anabolic response in skeletal muscle in CKD, but increases in mitochondrial mass and satellite cell activation seem to be impaired in this population. Exercise-mediated activation of the canonical wnt pathway may lead to bone formation and improvements in the levels of the bone-derived hormones klotho and fibroblast growth factor 23 (FGF23). Longer duration studies with larger sample sizes are needed to confirm these mechanisms in CKD, kidney failure and kidney transplant populations and provide evidence for targeted exercise interventions.

The Value of Klotho in Kidney Transplantation

Kidney transplant recipients have better survival rates and improved quality of life than long-term dialysis patients. However, delayed graft function, immunosuppressive therapy nephrotoxicity, and rejection episodes may compromise graft and patient survival. The KL gene is highly expressed in kidney tubular cells and encodes the antiaging and kidney-protective protein Klotho, which has membrane-anchored and soluble forms and regulates mineral metabolism. Klotho expression decreases during acute kidney injury or chronic kidney disease, and human chronic kidney disease shares features of accelerated aging with murine Klotho deficiency. In this work, we review clinical studies on the relationship between Klotho and kidney transplantation. Specifically, we address the dynamics of serum and kidney Klotho levels in donors and kidney transplant recipients, the role of Klotho as a marker of current graft function and graft outcomes, and the potential impact of Klotho on kidney protection in the transplantation context. A better understanding of the potential biomarker and therapeutic utility of Klotho in kidney transplant recipients may provide new insights into the control of graft function and new therapeutic strategies to preserve allograft function.

Physiopathology of Phosphate Disorders

Intracellular phosphate is critical for cellular processes such as signaling, nucleic acid synthesis, and membrane function. Extracellular phosphate (Pi) is an important component of the skeleton. Normal levels of serum phosphate are maintained by the coordinated actions of 1,25-dihydroxyvitamin D3, parathyroid hormone and fibroblast growth factor-23, which intersect in the proximal tubule to control the reabsorption of phosphate via the sodium-phosphate cotransporters Npt2a and Npt2c. Furthermore, 1,25-dihydroxyvitamin D3 participates in the regulation of dietary phosphate absorption in the small intestine. Clinical manifestations associated with abnormal serum phosphate levels are common and occur as a result of genetic or acquired conditions affecting phosphate homeostasis. For example, chronic hypophosphatemia leads to osteomalacia in adults and rickets in children. Acute severe hypophosphatemia can affect multiple organs leading to rhabdomyolysis, respiratory dysfunction, and hemolysis. Patients with impaired kidney function, such as those with advanced CKD, have high prevalence of hyperphosphatemia, with approximately two-thirds of patients on chronic hemodialysis in the United States having serum phosphate levels above the recommended goal of 5.5 mg/dL, a cutoff associated with excess risk of cardiovascular complications. Furthermore, patients with advanced kidney disease and hyperphosphatemia (>6.5 mg/dL) have almost one-third excess risk of death than those with phosphate levels between 2.4 and 6.5 mg/dL. Given the complex mechanisms that regulate phosphate levels, the interventions to treat the various diseases associated with hypophosphatemia or hyperphosphatemia rely on the understanding of the underlying pathobiological mechanisms governing each patient condition.

Soluble Klotho protects against glomerular injury through regulation of ER stress response

αKlotho (Klotho) has well established renoprotective effects; however, the molecular pathways mediating its glomerular protection remain incompletely understood. Recent studies have reported that Klotho is expressed in podocytes and protects glomeruli through auto- and paracrine effects. Here, we examined renal expression of Klotho in detail and explored its protective effects in podocyte-specific Klotho knockout mice, and by overexpressing human Klotho in podocytes and hepatocytes. We demonstrate that Klotho is not significantly expressed in podocytes, and transgenic mice with either a targeted deletion or overexpression of Klotho in podocytes lack a glomerular phenotype and have no altered susceptibility to glomerular injury. In contrast, mice with hepatocyte-specific overexpression of Klotho have high circulating levels of soluble Klotho, and when challenged with nephrotoxic serum have less albuminuria and less severe kidney injury compared to wildtype mice. RNA-seq analysis suggests an adaptive response to increased endoplasmic reticulum stress as a putative mechanism of action. To evaluate the clinical relevance of our findings, the results were validated in patients with diabetic nephropathy, and in precision cut kidney slices from human nephrectomies. Together, our data reveal that the glomeruloprotective effects of Klotho is mediated via endocrine actions, which increases its therapeutic potential for patients with glomerular diseases.

Aging-suppressor Klotho: Prospects in diagnostics and therapeutics

INTRODUCTION

The protein Klotho (KL) was first discovered in KL-deficient mice, which developed a syndrome similar to premature aging in humans. Since then, KL has been implicated in multiple molecular signaling pathways and diseases. KL has been shown to have anti-aging, healthspan and lifespan extending, cognitive enhancing, anti-oxidative, anti-inflammatory, and anti-tumor properties. KL levels decrease with age and in many diseases. Therefore, it has been of great interest to develop a KL-boosting or restoring drug, or to supplement endogenous Klotho with exogenous Klotho genetic material or recombinant Klotho protein, and to use KL levels in the body as a marker for the efficacy of such drugs and as a biomarker for the diagnosis and management of diseases.

OBJECTIVE

The goal of this study was to provide a comprehensive review of KL levels across age groups in individuals who are healthy or have certain health conditions, using four sources: blood, cerebrospinal fluid, urine, and whole biopsy/necropsy tissue. By doing so, baseline KL levels can be identified across the lifespan, in the absence or presence of disease. In turn, these findings can be used to guide the development of future KL-based therapeutics and biomarkers, which will heavily rely on an individual's baseline KL range to be efficacious.

METHODS

A total of 65 studies were collected primarily using the PubMed database. Research articles that were published up to April 2022 were included. Statistical analysis was conducted using RStudio.

RESULTS

Mean and median blood KL levels in healthy individuals, mean blood KL levels in individuals with renal conditions, and mean blood KL levels in individuals with metabolic or endocrine conditions were shown to decrease with age. Similarly, CSF KL levels in patients with AD also declined compared with age-matched controls.

CONCLUSIONS

The present study confirms the trend that KL levels in blood decrease with age in humans, among those who are healthy, and even further among those with renal and endocrine/metabolic illnesses. Further, by drawing this trend from multiple published works, we were able to provide a general idea of baseline KL ranges, specifically in blood in these populations. These data add to the current knowledge on normal KL levels in the body and how they change with time and in disease, and can potentially support efforts to create KL-based treatments and screening tools to better manage aging, renal, and metabolic/endocrine diseases.

The Relationship Between Klotho and SIRT1 Expression in Renal Aging Related Disease

Background

This study focused on renal arteriosclerosis and aimed to explore the relationship between Klotho and SIRT1 by morphological staining, which will help to provide new ideas for the treatment of renal-aging-related diseases and a theoretical basis for the development of new drugs.

Methods

Kidney tissue samples were collected from patients who underwent nephrectomy. HK-2 cells were cultured. The Hematoxylin-eosin (HE) staining, Periodic Acid-Schiff (PAS) staining, Masson’s Trichrome staining, Immunohistochemistry (IHC) staining, Immunofluorescence (ICC) and bioinformatics means were used for this study.

Results

HE staining showed that glomerulosclerosis was atrophic and cast was significantly increased luminal narrowing of renal arterioles in aging group. PAS staining showed that the number of podocytes was reduced, the mesangial matrix expansion and the intimal fibrosis of renal arterioles. Masson’s trichrome staining showed that there was massive collagen proliferation in the tubulointerstitial in aging group, as well as intimal thickening and fibrin deposition in the tubular walls of arterioles. IHC staining showed that the expression of Klotho and SIRT1 protein was downregulated in aging group and the trend of the two was positively correlated (P < 0.01). Klotho and SIRT1 co-localized in HK-2 cells and kidney tissue. The GEPIA database analysis showed a significant positive correlation between Klotho and SIRT1 in multiple human tissues and tumors.

Conclusion

Glomerulosclerosis in aging group is accompanied by low expression of Klotho and SIRT1 in renal tissue, and Klotho is positively correlated with SIRT1. Klotho-SIRT1 pathway may be involved in the occurrence and development of renal-aging-related diseases.

Association of α-klotho and lead and cadmium: A cross-sectional study

Epigenetic aging is associated with harmful health effects such as oxidative stress from heavy metal exposure. We considered the relationship between genes and heavy metals in association with oxidative stress and then investigated the association between serum α- klotho and lead and cadmium exposure among adults in the United States from 2007 to 2016 participating in the National Health and Nutrition Examination Survey (NHANES). Samples included 9800 adults aged 40 to 79 years with measurements of serum α-klotho, lead and cadmium, and complete covariate data. Lead and cadmium levels were measured by inductively coupled plasma mass spectrometry and serum α-klotho levels were measured using enzyme-linked immunosorbent assay (ELISA). Multivariate linear regression analysis was used to estimate the association between serum α-klotho and blood lead, blood cadmium, and urinary cadmium. A percent increase in blood lead, blood cadmium, and urinary cadmium was associated with a statistically significant 4.0 % (p < 0.001), 2.0 %, (p = 0.003) and 1.0 % (p = 0.020) decrease in serum klotho. After adjustment, a percent increase in blood lead was associated with a statistically significant 4.0 % (p < 0.001) decrease in serum klotho; blood and urinary cadmium did not show any statistically significant associations after adjustment (β (95 % CI), p-value for blood cadmium: 0.00 (-0.02-0.01), p = 0.573; urinary cadmium: -0.01 (-0.03-0.01), p = 0.210). Mean serum klotho levels showed a statistically significant decreasing trend with increasing blood lead quartiles (unadjusted and all-adjusted geometric means and 95 % confidence intervals of serum klotho (in pg/mL) for Q1, Q2, Q3, and Q4: unadjusted: 827.49 (814.20-840.92), 811.92 (794.73-829.48), 791.48 (775.11-808.19), and 772.01 (754.23-790.29); adjusted: 830.64 (805.53-856.45), 816.07 (789.18-843.87), 800.71 (773.71-828.57), and 784.31 (757.94-811.59)). Blood lead and levels were negatively associated with serum α-klotho levels in a representative population of US adults. These results suggest that blood lead levels may be associated with the serum levels of a protein associated with cognition and aging. Further research is recommended to investigate the causality behind such relationship.

Soluble α-klotho and heparin modulate the pathologic cardiac actions of fibroblast growth factor 23 in chronic kidney disease

Fibroblast growth factor (FGF) 23 is a phosphate-regulating hormone that is elevated in patients with chronic kidney disease and associated with cardiovascular mortality. Experimental studies showed that elevated FGF23 levels induce cardiac hypertrophy by targeting cardiac myocytes via FGF receptor isoform 4 (FGFR4). A recent structural analysis revealed that the complex of FGF23 and FGFR1, the physiologic FGF23 receptor in the kidney, includes soluble α-klotho (klotho) and heparin, which both act as co-factors for FGF23/FGFR1 signaling. Here, we investigated whether soluble klotho, a circulating protein with cardio-protective properties, and heparin, a factor that is routinely infused into patients with kidney failure during the hemodialysis procedure, regulate FGF23/FGFR4 signaling and effects in cardiac myocytes. We developed a plate-based binding assay to quantify affinities of specific FGF23/FGFR interactions and found that soluble klotho and heparin mediate FGF23 binding to distinct FGFR isoforms. Heparin specifically mediated FGF23 binding to FGFR4 and increased FGF23 stimulatory effects on hypertrophic growth and contractility in isolated cardiac myocytes. When repetitively injected into two different mouse models with elevated serum FGF23 levels, heparin aggravated cardiac hypertrophy. We also developed a novel procedure for the synthesis and purification of recombinant soluble klotho, which showed anti-hypertrophic effects in FGF23-treated cardiac myocytes. Thus, soluble klotho and heparin act as independent FGF23 co-receptors with opposite effects on the pathologic actions of FGF23, with soluble klotho reducing and heparin increasing FGF23-induced cardiac hypertrophy. Hence, whether heparin injections during hemodialysis in patients with extremely high serum FGF23 levels contribute to their high rates of cardiovascular events and mortality remains to be studied.

Educational Review: The Impact of Perinatal Oxidative Stress on the Developing Kidney

Oxidative stress occurs when there is an imbalance between reactive oxygen species/reactive nitrogen species and antioxidant systems. The interplay between these complex processes is crucial for normal pregnancy and fetal development; however, when oxidative stress predominates, pregnancy related complications and adverse fetal programming such as preterm birth ensues. Understanding how oxidative stress negatively impacts outcomes for the maternal-fetal dyad has allowed for the exploration of antioxidant therapies to prevent and/or mitigate disease progression. In the developing kidney, the negative impact of oxidative stress has also been noted as it relates to the development of hypertension and kidney injury mostly in animal models. Clinical research addressing the implications of oxidative stress in the developing kidney is less developed than that of the neurodevelopmental and respiratory conditions of preterm infants and other vulnerable neonatal groups. Efforts to study the oxidative stress pathway along the continuum of the perinatal period using a team science approach can help to understand the multi-organ dysfunction that the maternal-fetal dyad sustains and guide the investigation of antioxidant therapies to ameliorate the global toxicity. This educational review will provide a comprehensive and multidisciplinary perspective on the impact of oxidative stress during the perinatal period in the development of maternal and fetal/neonatal complications, and implications on developmental programming of accelerated aging and cardiovascular and renal disease for a lifetime.

Association between Dietary Inflammatory Index and serum Klotho concentration among adults in the United States

Background

Klotho is a hormone that emerges as an antiaging biomarker. However, the influence of the dietary pattern’s inflammatory potential on serum Klotho levels in human populations, especially in a general adult population, remains unknown. This study aimed to evaluate the relationship between the dietary inflammatory index (DII) and serum Klotho concentrations in individuals living in the United States. 

Methods 

From the 2007–2016 National Health and Nutrition Examination Survey database, data of participants who completed the full 24-h dietary history and underwent serum Klotho testing were analyzed. The association between DII and serum Klotho concentrations was estimated using multivariable linear regression models. We also conducted segmented regression model to examine the threshold effect of DII on serum Klotho concentrations.

Results

A total of 10,928 participants were included, with a median serum Klotho concentration of 805.20 pg/mL (IQR: 657.58 − 1001.12) and a median DII of 1.43 (IQR: − 0.16 − 2.82). Multivariable regression showed that participants with high DII scores were associated with low serum Klotho concentrations; when classifying DII into quartiles, after full adjustment, participants in DII quartiles 3 and 4 showed a decrease in Klotho levels (25.27 and 12.44 pg/ml, respectively) compared with those in the lowest quartile (quartile 1) (95% CI: − 41.80, − 8.73 and − 29.83, 4.95, respectively; P for trend = 0.036). The segmented regression showed that the turning point value of DII was − 1.82 (95% CI: − 2.32, − 0.80). A 1-unit increase in DII was significantly associated with lower Klotho levels by − 33.05 (95% CI: − 52.84, − 13.27; P = 0.001) when DII ranges from − 5.18 to − 1.82; however, the relationship was not significant when DII ranges from − 1.82 to 5.42 (P > 0.05). Furthermore, stratified analyses indicated that the observed associations between DII and serum Klotho concentration were stronger among those aged ≥ 56 years, those with normal weight, and those without chronic kidney disease (P for interaction = 0.003, 0.015, and 0.041, respectively).

Conclusions

In summary, we indicated that there was a dose–response relationship between DII and serum Klotho concentrations, suggesting that adhering to an anti-inflammatory diet has beneficial effects on aging and health by increasing the serum Klotho concentration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-03228-8.

klotho deficiency linked to multiple premature-aging syndromes and a short lifespan

Proinflammatory cytokines, including TNF-α, IFN-γ, and IL-6, downregulate α-Klotho gene expression

Dietary Inflammatory Index was developed as a tool to determine the inflammatory potential of diet

We found that there was a dose–response relationship between DII and circulating concentrations of klotho in a nationally representative population of American adults.

Renal Clearance of Fibroblast Growth Factor-23 (FGF23) and its Fragments in Humans

Relative abundance of fibroblast growth factor-23 (FGF23) measured by the C-terminal (cFGF23, which measures both intact FGF23 and C-terminal fragments) versus intact (iFGF23, measures only intact hormone) assays varies by kidney function in humans. Differential kidney clearance may explain this finding. We measured cFGF23 and iFGF23 in the aorta and bilateral renal veins of 162 patients with essential hypertension undergoing renal angiography. Using multivariable linear regression, we examined factors associated with aorta to renal vein reduction of FGF23 using both assays. Similar parameters and with addition of urine concentrations of cFGF23 and iFGF23 were measured in six Wistar rats. Mean ± standard deviation (SD) age was 54 ± 12 years, 54% were women, and mean creatinine clearance was 72 ± 48 mL/min/100 g. The human kidney reduced the concentrations of both cFGF23 (16% ± 12%) and iFGF23 (21% ± 16%), but reduction was higher for iFGF23. Greater kidney creatinine and PTH reductions were each independently associated with greater reductions of both cFGF23 and iFGF23. The greater kidney reduction of iFGF23 compared to cFGF23 appeared stable and consistent across the range of creatinine clearance evaluated. Kidney clearance was similar, and urine concentrations of both assays were low in the rat models, suggesting kidney metabolism of both cFGF23 and iFGF23. Renal reduction of iFGF23 is higher than that of creatinine and cFGF23. Our data suggest that FGF23 is metabolized by the kidney. However, the major cell types involved in metabolization of FGF23 requires future study. Kidney clearance of FGF23 does not explain differences in C-terminal and intact moieties across the range of kidney function. © 2022 American Society for Bone and Mineral Research (ASBMR).

Soluble α-Klotho levels, glycemic control and renal function in US adults with type 2 diabetes

AIMS

Soluble Klotho (s-Klotho) is associated with chronic kidney disease (CKD) and aging, but little is known on its relationship with chronic micro- and macro-vascular complications of type 2 diabetes and glycemic control. Here, we evaluate the association between s-Klotho levels, glycemic control and renal function in patients with type 2 diabetes (T2D).

METHODS

This is a cross-sectional study including 2989 patients with T2D and available s-Klotho measurements from the 2007-2016 cycles of the National Health and Nutrition Examination Survey (mean ± SE, age: 60.0 ± 0.2 years, BMI 33.3 ± 0.2 kg/m², 46.7 ± 1.3% female). Determination of s-Klotho concentrations was performed with a sandwich ELISA test.

RESULTS

Patients with higher s-Klotho levels were younger, more frequently female and had a lower prevalence of CKD and higher HbA1c levels. In multivariable linear regression models adjusting for age, race-ethnicity and BMI, both estimated glomerular filtration rate (B = 2.21, 95% CI 1.41-3.01, p < 0.001) and hemoglobin A1c (B = 37.38, 95% CI 28.91-45.86, p < 0.001) were positively associated with s-Klotho, while no significant association was found with cardiovascular disease. Results were confirmed when analyses were performed in men and women separately. No significant differences were identified between patients with an albuminuric or non-albuminuric CKD phenotype.

CONCLUSIONS

s-Klotho levels are dependent on kidney function and glycemic control in patients with T2D. Additional studies elucidating the mechanisms linking glycemic control and s-Klotho levels and exploring their predictive ability of clinically meaningful outcomes in patients with diabetes are needed.

Improvement of Mineral and Bone Disorders After Renal Transplantation

BACKGROUND

Posttransplant mineral and bone diseases are causes of fractures, and their association with cardiovascular events is being studied.

METHODS

We analyzed the evolution of biochemical, histological, and imaging parameters pre- and 1 y post-renal transplantation in 69 patients and correlated mineral and bone findings with coronary calcifications. At inclusion and after 12 mo, clinical data and echocardiographic findings were recorded, and laboratory evaluations, radiography of the pelvis and hands, and bone biopsy were performed. Noncontrast cardiac computed tomography was performed during the second evaluation.

RESULTS

Serum levels of fibroblast growth factor 23 and sclerostin decreased in all patients, parathyroid hormone levels decreased in 89.8% of patients, bone alkaline phosphatase levels decreased in 68.1% of patients, and alpha-Klotho levels increased in 65.2% of patients. More than half of the patients presented with renal osteodystrophy at both biopsies, but histological findings improved: a significant transition from high to normal or low turnover and no significant differences in volume, mineralization defect, or cortical porosity at the 2 evaluations. Alpha-Klotho, sclerostin, and bone alkaline phosphatase shifts affect bone changes. Neither echocardiographic findings nor vascular calcification scores differed between the 2 points. Both the pretransplant period (dialysis vintage, sclerostin, and low bone volume at baseline) and the maintenance of abnormalities in the posttransplant period (high turnover posttransplant) were the most reliable predictors of the severity of the coronary calcification percentile.

CONCLUSIONS

Renal transplantation improved bone and mineral abnormalities. The pretransplant period determines the severity of calcification.

Physiologic Regulation of Systemic Klotho Levels by Renal CaSR Signaling in Response to CaSR Ligands and pH o

BACKGROUND

The kidney is the source of sKlotho and kidney-specific loss of Klotho leads to a phenotype resembling the premature multiorgan failure phenotype in Klotho-hypomorphic mice ( kl/kl mice). Klotho and the Ca-sensing receptor (CaSR) are highly expressed in the distal convoluted tubule (DCT). The physiologic mechanisms that regulate sKlotho levels are unknown.

METHODS

We measured sKlotho in WT and tubule-specific CaSR -/- (TS-CaSR -/- ) mice treated with calcimimetics, alkali, or acid, and Klotho shed from minced mouse kidneys, and from HEK-293 cells expressing the CaSR and Klotho, in response to calcimimetics, calcilytics, alkalotic and acidic pH, and ADAM protease inhibitors. The CaSR, Klotho, and ADAM10 were imaged in mouse kidneys and cell expression systems using confocal microscopy.

RESULTS

The CaSR, Klotho, and ADAM10 colocalize on the basolateral membrane of the DCT. Calcimimetics and HCO 3 increase serum sKlotho levels in WT but not in CaSR -/- mice, and acidic pH suppresses sKlotho levels in WT mice. In minced kidneys and cultured cells, CaSR activation with high Ca, calcimimetics, or alkali increase shed Klotho levels via ADAM10, as demonstrated using the ADAM10 inhibitor GI254023X and siRNA. In cultured cells, the CaSR, Klotho, and ADAM10 form cell surface aggregates that disperse after CaSR activation.

CONCLUSIONS

We identify a novel physiologic mechanism for regulation of sKlotho levels by the renal CaSR-ADAM10-Klotho pathway. We show that CaSR activators, including alkali, increase renal CaSR-stimulated Klotho shedding and predict that this mechanism is relevant to the effects of acidosis and alkali therapy on CKD progression.

Hypophosphatemia in acute liver failure of a broad range of etiologies is associated with phosphaturia without kidney damage or phosphatonin elevation

Hypophosphatemia is a common and dangerous complication of acute liver failure (ALF) of various etiologies. While various mechanisms for ALF-associated hypophosphatemia have been proposed including high phosphate uptake into regenerating hepatocytes, acetaminophen (APAP)-associated hypophosphatemia was linked to renal phosphate wasting, and APAP-induced renal tubular injury was proposed as underlying mechanism. We studied 30 normophosphatemic and 46 hypophosphatemic (serum phosphate < 2.5 mg/dL) patients from the Acute Liver Failure Study Group registry with APAP- or non-APAP-induced ALF. Since kidney injury affects phosphate excretion, patients with elevated serum creatinine (>1.2 mg/dL) were excluded. Maximal amount of renal tubular phosphate reabsorption per filtered volume (TmP/GFR) was calculated from simultaneous serum and urine phosphate and creatinine levels to assess renal phosphate handling. Instead of enhanced renal phosphate reabsorption as would be expected during hypophosphatemia of non-renal causes, serum phosphate was positively correlated with TmP/GFR in both APAP- and non-APAP-induced ALF patients (R2 = 0.66 and 0.46, respectively; both P < 0.0001), indicating renal phosphate wasting. Surprisingly, there was no evidence of kidney damage based on urinary markers including neutrophil gelatinase-associated lipocalin and cystatin C even in the APAP group. Additionally, there was no evidence that the known serum phosphatonins parathyroid hormone, fibroblast growth factor 23, and α-Klotho contribute to the observed hypophosphatemia. We conclude that the observed hypophosphatemia with renal phosphate wasting in both APAP- and non-APAP-mediated ALF is likely the result of renal tubular phosphate leak from yet-to-be identified factor(s) with no evidence for proximal tubular damage or contribution of known phosphatonins.

FGFR4 and Klotho Polymorphisms Are Not Associated with Cardiovascular Outcomes in Chronic Kidney Disease

INTRODUCTION

High plasma fibroblast growth factor 23 (FGF-23) predicts cardiovascular events in chronic kidney disease (CKD) patients. Experimental evidence suggests FGF receptor 4 (FGFR4) activation by FGF-23, and deficiency of the soluble form of its co-receptor Klotho promotes left-ventricular hypertrophy (LVH). To evaluate the clinical relevance of these findings, a Mendelian randomization study analyzed the association of genetic variants of FGFR4 and Klotho with echocardiographic parameters and cardiac events in CKD patients.

METHODS

The prospective Cardiovascular and Renal Outcome in CKD 2-4 Patients-The Fourth Homburg Evaluation study recruited CKD G2-G4 patients, of whom 519 consented to SNP genotyping (FGFR4: rs351855; Klotho: rs9536314). Echocardiographic examinations at baseline and 5 years later assessed prevalence of LVH by measurement of left-ventricular mass index (LVMI). Patients were followed for 5.1 ± 2.1 years for the primary endpoints of cardiac decompensation and atherosclerotic cardiovascular disease (ASCVD).

RESULTS

Carriers of the different alleles did neither differ in baseline LVMI (rs351855: p = 0.861; rs9536314: p = 0.379) nor in LVMI changes between baseline and follow-up (rs351855: p = 0.181; rs9536314: p = 0.995). Hundred and four patients suffered cardiac decompensation, and 144 patients had ASCVD. Time to cardiac decompensation (rs351855: p = 0.316; rs9536314: p = 0.765) and ASCVD (p = 0.508 and p = 0.800, respectively) did not differ between carriers of different alleles.

DISCUSSION/CONCLUSION

rs351855 and rs9536314 were not associated with LVMI or cardiac events. These findings do not provide evidence for a relevant clinical role of either FGFR4 stimulation or soluble form of Klotho deficiency in LVH development.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23-Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

GWAS META-analysis followed by MENDELIAN randomisation revealed potential control mechanisms for circulating α-klotho levels

BACKGROUND

The protein α-Klotho acts as transmembrane the co-receptor for fibroblast growth factor 23 (FGF-23) and is a key regulator of phosphate homeostasis. However, α-Klotho also exists in a circulating form, with pleiotropic, but incompletely understood functions and regulation. Therefore, we undertook a GWAS meta-analysis followed by Mendelian randomisation (MR) of circulating α-Klotho levels.

METHODS

Plasma α-Klotho levels were measured by ELISA in the LURIC and ALSPAC (mothers) cohorts, followed by a GWAS meta-analysis in 4376 individuals across the two cohorts.

RESULTS

Six signals at five loci were associated with circulating α-Klotho levels at genome-wide significance (p < 5 × 10-8), namely ABO, KL, FGFR1, and two post-translational modification genes, B4GALNT3 and CHST9. Together, these loci explained > 9% of the variation in circulating α-Klotho levels. MR analyses revealed no causal relationships between α-Klotho and renal function, FGF-23-dependent factors such as vitamin D and phosphate levels, or bone mineral density. The screening for genetic correlations with other phenotypes, followed by targeted MR suggested causal effects of liability of Crohn's disease risk [IVW beta = 0.059 (95% CI 0.026, 0.093)] and low-density lipoprotein cholesterol (LDL-C) levels [-0.198, (-0.332, -0.063)] on α-Klotho.

CONCLUSIONS

Our GWAS findings suggest that two enzymes involved in post-translational modification, B4GALNT3 and CHST9, contribute to genetic influences on α-Klotho levels, presumably by affecting protein turnover and stability. Subsequent evidence from MR analyses on α-Klotho levels suggest regulation by mechanisms besides phosphate-homeostasis and raise the possibility of cross-talk with FGF19- and FGF21-dependent pathways, respectively.

The intersection of Mineralocorticoid Receptor (MR) activation and the FGF23 - Klotho cascade. A Duopoly that promotes renal and cardiovascular injury

The nexus of CKD and cardiovascular disease (CVD) amplifies the morbidity and mortality of CKD, emphasizing the need for defining and establishing therapeutic initiatives to modify and abrogate the progression of CKD and concomitant CV risks. In addition to the traditional CV risk factors, disturbances of mineral metabolism are specific risk factors that contribute to the excessive CV mortality in patients with CKD. These risk factors include dysregulations of circulating factors that modulate phosphate metabolism including fibroblast growth factor 23 (FGF23) and soluble Klotho. Reduced circulating levels and suppressed renal klotho expression may be associated with adverse outcomes in CKD patients. While elevated circulating concentrations or locally produced FGF23 in the strained heart exert pro-hypertrophic mechanisms on the myocardium, Klotho attenuates tissue fibrosis, progression of CKD, cardiomyopathy, endothelial dysfunction, vascular stiffness, and vascular calcification. Mineralocorticoid receptor (MR) activation in non-classical targets, mediated by aldosterone and other ligands, amplifies CVD in CKD. In concert, we detail how the interplay of elevated FGF23, activation of the MR, and concomitant reductions of circulating Klotho in CKD, may potentiate each other's deleterious effects on kidney and the heart, thereby contributing to the initiation and progression of kidney and cardiac functional deterioration, acting through multipronged albeit complementary mechanistic pathways.

Constitutive transgenic alpha-Klotho overexpression enhances resilience to and recovery from murine acute lung injury

AIMS

Normal lungs do not express alpha-Klotho (Klotho) protein but derive cytoprotection from circulating soluble Klotho. It is unclear whether chronic supranormal Klotho levels confer additional benefit. To address this, we tested the age-related effects of Klotho overexpression on acute lung injury (ALI) and recovery.

METHODS

Transgenic Klotho-overexpressing (Tg-Kl) and wild-type (WT) mice (2 and 6 months old) were exposed to hyperoxia (95% O₂; 72 h) then returned to normoxia (21% O₂; 24 h) (Hx-R). Control mice were kept in normoxia. Renal and serum Klotho, lung histology, and bronchoalveolar lavage fluid oxidative damage markers were assessed. Effects of hyperoxia were tested in human embryonic kidney cells stably expressing Klotho. A549 lung epithelial cells transfected with Klotho cDNA or vector were exposed to cigarette smoke; lactate dehydrogenase and double-strand DNA breaks were measured.

RESULTS

Serum Klotho decreased with age. Hyperoxia suppressed renal Klotho at both ages and serum Klotho at 2-months of age. Tg-Kl mice at both ages and 2-months-old WT mice survived Hx-R; 6-months-old Tg-Kl mice showed lower lung damage than age-matched WT mice. Hyperoxia directly inhibited Klotho expression and release in vitro; Klotho transfection attenuated cigarette smoke-induced cytotoxicity and DNA double-strand breaks in lung epithelial cells.

CONCLUSIONS

Young animals with chronic high baseline Klotho expression are more resistant to ALI. Chronic constitutive Klotho overexpression in older Tg-Kl animals attenuates hyperoxia-induced lung damage and improves survival and short-term recovery despite an acute reduction in serum Klotho level during injury. We conclude that chronic enhancement of Klotho expression increases resilience to ALI.

Advances in the occurrence and biotherapy of osteoporosis

Osteoporosis (OP) is a bone metabolic disease, is characterized by degeneration of bone structure and decreased bone mass. It happens in more than 1/3 women and 1/5 men of over than 50 years old, which affects the health and lives of people. The main mechanism of OP is mainly that the dynamic balance between the bone formation and resorption is broken, so that bone resorption is more than bone formation. It is prone to result in bone metabolism disorder. There are many precipitating factor such as elder age, low hormone level, genetic factors and bad hobbies. At the same time, the occurrence of the OP and its complications has different degrees of impact on people's quality of life. Based on the current understanding of the OP, we summarized the etiology, current clinical drugs and potential targeting therapy for OP. Although the research have made many progress in explore what is the novel mechanism and how to improve the effect, there are still many problems in the treatment method that limit its application prospects and need to be solved. In this review, we mainly focus on the mechanism of OP and related research on the targeted treatment of OP. Hopefully, our summary will provide a reference to develop some novel strategies for the target therapy of OP.

In search of alternatively spliced alpha-Klotho Kl1 protein in mouse brain

Alpha‐Klotho is a multi‐functional protein essential for maintenance of a myriad of cell functions. αKlotho is a single transmembrane protein with a large extracellular segment consisting of two domains (termed Kl1 and Kl2) which is shed into the extracellular fluid by proteolytic cleavage to furnish circulating soluble αKlotho. Based on cDNA sequence, an alternatively spliced mRNA is predicted to translate to a putative soluble αKlotho protein in mouse and human with only the Kl1 domain that represents a “spliced αKlotho Kl1” (spKl1) and is released from the cell without membrane targeting or cleavage. The existence of this protein remains in silico for two decades. We generated a novel antibody (anti‐spE15) against the 15 amino acid epitope (E15; VSPLTKPSVGLLLPH) which is not present in Kl1 or full‐length αKlotho and validated its specific reactivity against spKl1 in vitro. Using anti‐spE15 and two well‐established anti‐αKlotho monoclonal antibodies, we performed immunoblots, immunoprecipitation, and immunohistochemistry to investigate for expression of spKl1 in the mouse brain. We found anti‐spE15 labeling in mouse brain but were not able to see co‐labelling of Kl1 and spE15 epitopes on the same protein, which is the pre‐requisite for the existence of a spKl1 polypeptide, indicating that anti‐spE15 likely binds to another protein other than the putative spKl1. In isolated choroid plexus from mouse brain, we found strong staining with anti‐spE15, but did not find the spliced αKlotho transcript. We conclude that using reliable reagents and inclusion of proper controls, there is no evidence of the spKl1 protein in the mouse brain.

A Decreased Level of Soluble Klotho Can Predict Cardiovascular Death in No or Mild Abdominal Aortic Calcification Hemodialysis Patients

Background: Soluble Klotho plays an important role in cardiovascular disease and death in chronic kidney disease (CKD). We assessed the relationship between serum soluble Klotho (sKL) level and outcome in MHD patients.

Methods: Soluble Klotho was detected by ELISA. Cox regression analysis and Kaplan-Meier analysis showed the relationship between sKL and cardiovascular disease (CVD) mortality in maintenance hemodialysis (MHD) patients.

Results: There were 45 cases (35.2%) of all-cause death and 36 cases (28.1%) of CVD mortality. Multivariate linear regression analysis showed that Log[iPTH] (γ = −0.224, P = 0.015) was an independent predictor of sKL level. Cox regression showed that lower sKL was associated with higher CVD mortality rate [OR = 0.401, 95% CI (0.183–0.867), P = 0.022]. Kaplan-Meier analysis showed that the CVD mortality rate increased significantly in patients with low sKL (P = 0.006). Compared with high sKL patients, low sKL patients with no or mild vascular calcification [aortic calcification score (AACs) ≤ 4] had no significant difference in all-cause mortality rate. The CVD mortality rate was significantly lower in high sKL patients (P = 0.004) than in those with low sKL. In the severe calcification group (AACs ≥ 5), all-cause and CVD mortality rates were similar between different sKL groups (P = 0.706 and 0.488, respectively). The area under the receiver-operating characteristic curve (AUC) of soluble Klotho for predicting the CVD in MHD patients with AACs ≤ 4 was 0.796 (0.647–0.946, P = 0.017), sensitivity was 0.921, and specificity was 0.50 for a cutoff value of 307.69 pg/ml.

Conclusions: Lower sKL was associated with higher CVD mortality rate. Lower sKL concentration in MHD patients with no or mild calcification can predict CVD mortality.

Targeting Premature Renal Aging: from Molecular Mechanisms of Cellular Senescence to Senolytic Trials

The biological process of renal aging is characterized by progressive structural and functional deterioration of the kidney leading to end-stage renal disease, requiring renal replacement therapy. Since the discovery of pivotal mechanisms of senescence such as cell cycle arrest, apoptosis inhibition, and the development of a senescence-associated secretory phenotype (SASP), efforts in the understanding of how senescent cells participate in renal physiological and pathological aging have grown exponentially. This has been encouraged by both preclinical studies in animal models with senescent cell clearance or genetic depletion as well as due to evidence coming from the clinical oncologic experience. This review considers the molecular mechanism and pathways that trigger premature renal aging from mitochondrial dysfunction, epigenetic modifications to autophagy, DNA damage repair (DDR), and the involvement of extracellular vesicles. We also discuss the different pharmaceutical approaches to selectively target senescent cells (namely, senolytics) or the development of systemic SASP (called senomorphics) in basic models of CKD and clinical trials. Finally, an overview will be provided on the potential opportunities for their use in renal transplantation during ex vivo machine perfusion to improve the quality of the graft.

Triiodothyronine (T3) enhances lifespan and protects against oxidative stress via activation of Klotho in Caenorhabditis elegans

Age predisposes individuals to significant diseases, and the biological processes contributing to aging are currently under intense investigation. Klotho is an anti-aging protein with multifaceted roles and is an essential component of the endocrine fibroblast growth factor. In Caenorhabditis elegans (C. elegans), there are two prospective orthologs of α-Klotho, C50F7.10, and E02H9.5, identified. The two orthologs' products are homologous to the highly conserved KL1 domain of human and mouse Klotho protein. Considering the endocrine system's major involvement in an organism's homeostasis and that thyroid disorders increase with advancing age, the molecular mechanisms underlying its impact on different endocrine components during the aging process remain poorly characterized. In this study, we sought to determine the regulatory role of Triiodothyronine (T3) on homologs genes of klotho and its impact on different parameters of aging in the C. elegans model organism. We showed that T3 could increase the mRNA expressions of the klotho homologous genes in C. elegans. Moreover, T3 could also extend a worm lifespan and modulate oxidative stress resistance and aging biomarkers significantly and positively. Further investigations employing different mutant and transgenic strains reveal that these observed effects are mediated through the EGL-17/EGL-15 pathway via Klotho activation along with the involvement of transcription factor DAF-16. In conclusion, these findings have revealed an unexpected link between T3 and Klotho and how this link can modulate the aging process in C. elegans via activation of klotho. This study will help understand the crosstalk and regulations of different endocrine components and their consequences on the aging process in multiple species.

Roles for fibroblast growth factor-23 and α-Klotho in acute kidney injury

Acute kidney injury is a global disease with high morbidity and mortality. Recent studies have revealed that the fibroblast growth factor-23-α-Klotho axis is closely related to chronic kidney disease, and has multiple biological functions beyond bone-mineral metabolism. However, although dysregulation of fibroblast growth factor-23-α-Klotho has been observed in acute kidney injury, the role of fibroblast growth factor-23-α-Klotho in the pathophysiology of acute kidney injury remains largely unknown. In this review, we describe recent findings regarding fibroblast growth factor-23-α-Klotho, which is mainly involved in inflammation, oxidative stress, and hemodynamic disorders. Further, based on these recent results, we put forth novel insights regarding the relationship between the fibroblast growth factor-23-α-Klotho axis and acute kidney injury, which may provide new therapeutic targets for treating acute kidney injury.

Shedding of Klotho: Functional Implications in Chronic Kidney Disease and Associated Vascular Disease

α-Klotho (Klotho) exists in two different forms, a membrane-bound and soluble form, which are highly expressed in the kidney. Both forms play an important role in various physiological and pathophysiological processes. Recently, it has been identified that soluble Klotho arises exclusively from shedding or proteolytic cleavage. In this review, we will highlight the mechanisms underlying the shedding of Klotho and the functional effects of soluble Klotho, especially in CKD and the associated cardiovascular complications. Klotho can be cleaved by a process called shedding, releasing the ectodomain of the transmembrane protein. A disintegrin and metalloproteases ADAM10 and ADAM17 have been demonstrated to be mainly responsible for this shedding, resulting in either full-length fragments or sub-fragments called KL1 and KL2. Reduced levels of soluble Klotho have been associated with kidney disease, especially chronic kidney disease (CKD). In line with a protective effect of soluble Klotho in vascular function and calcification, CKD and the reduced levels of soluble Klotho herein are associated with cardiovascular complications. Interestingly, although it has been demonstrated that soluble Klotho has a multitude of effects its direct impact on vascular cells and the exact underlying mechanisms remain largely unknown and should therefore be a major focus of further research. Moreover, functional implications of the cleavage process resulting in KL1 and KL2 fragments remain to be elucidated.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

αKlotho (called Klotho here) is a membrane protein that serves as the coreceptor for the circulating hormone fibroblast growth factor 23 (FGF23). Klotho is also cleaved and released as a circulating substance originating primarily from the kidney and exerts a myriad of housekeeping functions in just about every organ. The vital role of Klotho is shown by the multiorgan failure with genetic deletion in rodents, with certain features reminiscent of human disease. The most common causes of systemic Klotho deficiency are AKI and CKD. Preclinical data on Klotho biology have advanced considerably and demonstrated its potential diagnostic and therapeutic value; however, multiple knowledge gaps exist in the regulation of Klotho expression, release, and metabolism; its target organs; and mechanisms of action. In the translational and clinical fronts, progress has been more modest. Nonetheless, Klotho has potential clinical applications in the diagnosis of AKI and CKD, in prognosis of progression and extrarenal complications, and finally, as replacement therapy for systemic Klotho deficiency. The overall effect of Klotho in clinical nephrology requires further technical advances and additional large prospective human studies.

Epigenetic and non-epigenetic regulation of Klotho in kidney disease

Klotho is a novel renoprotective anti-aging protein available in membrane-bound or soluble form. Klotho is expressed in brain, pancreas, and other solid organs but shows highest expression levels in the kidney. Klotho sustains normal kidney physiology but Klotho regulation also contributes to the progression of kidney disease. Systemic and intrarenal levels of Klotho fall drastically during acute kidney injury, kidney fibrosis, diabetic nephropathy, and other forms of chronic kidney disease, etc. Moreover, exogenous supplementation or overexpression of endogenous Klotho attenuates kidney disease. The regulation of endogenous Klotho expression involves epigenetic as well as non-epigenetic mechanisms. The epigenetic modifications such as DNA methylation, post-translational histone modifications, miRNAs regulate the change in Klotho expression in kidney disease. Non-epigenetic mechanisms such as ER stress, Wnt signaling, activation of the renin angiotensin system (RAS), excessive reactive oxygen species and cytokine generation, albumin overload, and PPAR-γ signaling also contribute to Klotho regulation. Evolving evidence highlight the capacity of natural products to regulate Klotho expression in kidney disease. All these preclinical data suggest that Klotho could be a novel biomarker as well as therapeutic target. Here we review the different mechanisms of Klotho regulation in the context of Klotho as a biomarker and potential therapeutic agent.

Effects of Klotho supplementation on hyperoxia-induced renal injury in a rodent model of postnatal nephrogenesis

BACKGROUND

Hyperoxia (HO) causes kidney injury in preterm infants; however, whether these effects are modifiable is unknown. We hypothesized that administration of exogenous soluble Klotho, a kidney-derived antioxidant, would attenuate HO-induced kidney injury during postnatal nephrogenesis in rats.

METHODS

Sprague Dawley neonatal rats assigned to normoxia (21% O₂) or HO (85% O₂) groups from postnatal day (P) 1 to 21 were randomly assigned to receive alternate day intraperitoneal injections of recombinant Klotho or placebo for 3 weeks. They were recovered in normoxia for an additional 3 weeks and sacrificed at 6 weeks. Renal artery resistance and pulsatility indices, tubular injury scores, glomerular area, and renal antioxidant capacity were assessed.

RESULTS

Rodents exposed to HO during postnatal nephrogenesis had reduced kidney Klotho expression, glomerulomegaly, and higher tubular injury scores. Exogenous Klotho administration improved renal perfusion as indicated by decreases in both resistance and pulsatility indices and increased antioxidant enzyme expression.

CONCLUSIONS

HO exposure during postnatal nephrogenesis in rodents results in a decline in kidney Klotho expression, decreased renal perfusion, enlarged glomerular size, and tubular injury. The exogenous administration of Klotho attenuated HO-induced kidney injury and augmented antioxidant capacity.

Dietary vitamin D interacts with high phosphate-induced cardiac remodeling in rats with normal renal function

BACKGROUND

Vitamin D (VD) and phosphate (Pi) load are considered as contributors to cardiovascular disease in chronic kidney disease and the general population, but interactive effects of VD and Pi intake on the heart are not clearly illustrated.

METHODS

We fed normal male rats with three levels of dietary VD (100, 1100 or 5000 IU/kg chow) and Pi (0.2, 0.6 or 1.6%) (3X3 design) for 8 weeks and examined renal and cardiac function and histology.

RESULTS

High dietary Pi decreased plasma and renal Klotho and plasma 25-hydroxyvitamin D, and increased plasma Pi, fibroblast growth factor 23 and parathyroid hormone without affecting renal function, while low Pi increased plasma and renal Klotho. Both low and high VD diets enhanced high Pi-reduced Klotho expression. Low dietary VD reduced-plasma Klotho was rescued by a low Pi diet. High dietary Pi reduced-cardiac ejection fraction was not modified by a low or high VD diet, but the dietary VD effects on cardiac pathologic changes were more complex. High dietary Pi-induced cardiac hypertrophy was attenuated by a low VD and exacerbated by a high VD diet. In contrast, high dietary Pi -induced cardiac fibrosis was magnified by a low VD and attenuated by a high VD diet.

CONCLUSIONS

High Pi diet induces hypertrophy and fibrosis in left ventricles, a low VD diet accelerates high Pi-induced fibrosis, and a high VD diet exacerbated high Pi -induced hypertrophy. Therefore, cardiac phosphotoxicity is exacerbated by either high or low dietary VD in rats with normal kidney function.

Klotho, Aging, and the Failing Kidney

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in the diseasome of aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology. A range of senotherapeutic strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists and indirect approaches, via modulation of the foodome and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes within the diseasome of aging.

Molecular Mechanisms of AKI in the Elderly: From Animal Models to Therapeutic Intervention

Acute kidney injury (AKI), a critical syndrome characterized by a sudden reduction of renal function, is a common disorder among elderly patients particularly in Intensive Care Unit (ICU). AKI is closely associated with both short- and long-term mortality and length of hospital stay and is considered a predictor of chronic kidney disease (CKD). Specific hemodynamic, metabolic, and molecular changes lead to increased susceptibility to injury in the aged kidney; therefore, certain causes of AKI such as the prerenal reduction in renal perfusion or vascular obstructive conditions are more common in the elderly; moreover, AKI is often multifactorial and iatrogenic. Older patients present several comorbidities (diabetes, hypertension, heart failure) and are exposed to multiple medical interventions such as the use of nephrotoxic contrasts media and medications, which can also trigger AKI. Considering the emerging relevance of this condition, prevention and treatment of AKI in the elderly should be crucial in the internist and emergency setting. This review article summarizes the incidence, the risk factors, the pathophysiology, the molecular mechanisms and the strategies of prevention and treatment of AKI in elderly patients.