Klotho Ameliorates Vascular Calcification via Promoting Autophagy

Alternative splicing of vascular calcification: Insights, opportunities, and challenges

Vascular calcification(VC) significantly increases the risk of cardiovascular events, leading to thickening of the myocardium and arteries, coronary heart disease, heart failure, and potentially triggering myocardial infarction and sudden cardiac death. Although VC is a reversible process, there are currently no methods or medications in clinical practice that can completely reverse or cure it. The current treatment strategies primarily focus on slowing the progression of VC and exploring new diagnostic and therapeutic approaches, making the identification of early diagnostic markers for VC particularly important. Alternative splicing(AS)has extensive potential in clinical applications as a biomarker, including in disease diagnosis and therapeutic targeting. This article provides an overview of the roles played by different isoforms of biomarkers in VC, with the aim of offering insights for early diagnosis and disease monitoring of VC.

Association between adult body shape index and serum levels of the anti-aging protein Klotho in adults: a population-based cross-sectional study of the NHANES from 2007 to 2016

Purpose

Adult body shape index (ABSI) is widely recognized as a reliable indicator for evaluating body fat distribution and dysfunction. However, the relationship between ABSI and Klotho protein, known for its anti-aging biological function, has not yet been investigated. Therefore, the aim of this study was to assess the correlation between ABSI and serum Klotho levels in adults residing in the United States.

Methods

A cross-sectional study of participants was conducted based on the 2007-2016 National Health and Nutrition Examination Survey. Visceral adiposity was determined using the ABSI score, and Klotho protein concentration was measured using an enzyme-linked immunosorbent assay kit. Multiple regression models were used to estimate the association between ABSI and Klotho protein after adjusting for several potential confounding variables. Subgroup analysis of ABSI and Klotho was performed using restricted cubic splines.

Result

A total of 11,070 adults were eligible for participation, with a mean ABSI of 8.28 ± 0.45 and a mean Klotho protein concentration of 853.33 ± 309.80 pg/mL. Multivariate regression analysis showed that participants with high ABSI scores had lower serum Klotho protein concentrations. When ABSI was divided into quartiles, after full adjustment, Klotho protein levels were lower in participants in the fourth fully adjusted ABSI quartile (Q4: -0.352 pg/ml) than in those in the lowest quartile (Q1) (P<0.0001).

Conclusion

There was a negative linear correlation between ABSI score and serum Klotho concentration. Higher ABSI was associated with lower serum Klotho concentrations; however, this association did not seem to be significant in subjects with BMI ≥30 kg/m2.Further study is needed to verify the causality of this association and elucidate the underlying mechanisms.

Relationship of α-Klotho with Frailty Index and Sarcopenia: A Bidirectional Mendelian Randomization Study

Previous studies have established associations between α-Klotho and frailty or sarcopenia; however, the causal nature of these relationships remains unclear. This study investigates the causal effects of α-Klotho on frailty and sarcopenia-related traits using Mendelian randomization (MR). Genetic instruments for circulating α-Klotho concentrations, frailty index (FI), low grip strength (LGS), appendicular lean mass (ALM), and walking pace were developed based on data from large genome-wide association studies. Two-sample MR analyses were performed, supplemented by sensitivity analyses to ensure the robustness of the findings. Reverse MR analyses were also conducted to explore potential reverse causation. The findings demonstrated an inverse causal relationship of circulating α-Klotho levels with FI (β = -0.020, 95% confidence interval [95% CI] = -0.036 to -0.004; p = 0.017) and LGS (β = -0.033, 95% CI = -0.061 to -0.004; p = 0.023). However, no causal relationship was observed between circulating α-Klotho levels and ALM or walking pace. Additionally, no evidence of reverse causation was identified between FI or sarcopenia-related traits and circulating α-Klotho levels. In conclusion, this MR analysis establishes an inverse causal relationship of circulating α-Klotho levels with both FI and LGS.

Association of serum Klotho with the severity and mortality among adults with cardiovascular-kidney-metabolic syndrome

BACKGROUND

Cardiovascular-kidney-metabolic (CKM) syndrome is characterized as a systemic disease resulting from the pathophysiological interplay among metabolic risk factors, chronic kidney disease (CKD), and cardiovascular disease (CVD). The Klotho protein may serve as a novel biomarker. However, the utility of serum Klotho levels as an indicator of severity and mortality risk in CKM syndrome remains uncertain.

METHODS

This study involved 9,871 participants from the National Health and Nutrition Examination Survey (NHANES) conducted between 2007 and 2016. Serum Klotho levels were measured using an enzyme-linked immunosorbent assay kit. The optimal cutoff value was established through the maximum Youden's index. Multivariable weighted regression models were employed to calculate the odds ratio and hazard ratio, along with the 95% confidence interval, to evaluate the association between serum Klotho levels and the severity of CKM syndrome, as well as all-cause and cardiovascular mortality. Additionally, the receiver operating characteristic curve and restricted cubic spline curves were utilized to assess predictive efficacy and to explore nonlinear relationships.

RESULTS

After adjusting for potential confounding factors, a non-linear relationship was seen between the Klotho protein, and CKM syndrome. In the multivariable, piecewise logistic regression, when the Serum klotho was less than 801, the risk of CKM syndrome decreased with the increase in Serum klotho (OR = 0.82, 95%CI 0.70, 0.96; p < 0.001). Furthermore, we observed the association when the Serum klotho was greater than 801 (OR = 0.94, 95%CI 0.89, 0.99; p = 0.035). The relationship between serum Klotho levels and all-cause mortality was U-shaped, while the relationship with cardiovascular mortality was L-shaped. Specifically, low serum Klotho levels were associated with an increase in all-cause mortality by 21% and cardiovascular mortality by 76% among patients with CKM syndrome. Furthermore, serum Klotho levels demonstrated excellent predictive efficacy for both the severity and mortality associated with CKM syndrome.

CONCLUSIONS

This study indicates that low serum Klotho levels serve as reliable indicators of both the severity of CKM syndrome and the associated risk of mortality.

Relationship between arginine methylation and vascular calcification

In patients on maintenance hemodialysis (MHD), vascular calcification (VC) is an independent predictor of cardiovascular disease (CVD), which is the primary cause of death in chronic kidney disease (CKD). The main component of VC in CKD is the vascular smooth muscle cells (VSMCs). VC is an ordered, dynamic activity. Under the stresses of oxidative stress and calcium-‑phosphorus imbalance, VSMCs undergo osteogenic phenotypic transdifferentiation, which promotes the formation of VC. In addition to traditional epigenetics like RNA and DNA control, post-translational modifications have been discovered to be involved in the regulation of VC in recent years. It has been reported that the process of osteoblast differentiation is impacted by catalytic histone or non-histone arginine methylation. Its function in the osteogenic process is comparable to that of VC. Thus, we propose that arginine methylation regulates VC via many signaling pathways, including as NF-B, WNT, AKT/PI3K, TGF-/BMP/SMAD, and IL-6/STAT3. It might also regulate the VC-related calcification regulatory factors, oxidative stress, and endoplasmic reticulum stress. Consequently, we propose that arginine methylation regulates the calcification of the arteries and outline the regulatory mechanisms involved.

Molecular Interaction of Soluble Klotho with FGF23 in the Pathobiology of Aortic Valve Lesions Induced by Chronic Kidney Disease

Chronic kidney disease (CKD) is linked to greater prevalence and rapid progression of calcific aortic valve disease (CAVD) characterized by valvular leaflet fibrosis and calcification. Fibroblast growth factor 23 (FGF23) level is elevated, and anti-aging protein Klotho is reduced in CKD patients. However, the roles of FGF23 and Klotho in the mechanism of aortic valve fibrosis and calcification remain unclear. We hypothesized that FGF23 mediates CKD-induced CAVD by enhancing aortic valve interstitial cell (AVIC) fibrosis and calcification, while soluble Klotho inhibits FGF23 effect. Methods and Results: In an old mouse model of CKD, kidney damages were accompanied by aortic valve thickening and calcification. FGF23 levels in plasma and aortic valve were increased, while Klotho levels were decreased. Recombinant FGF23 elevated the inflammatory, fibrogenic, and osteogenic activities in AVICs. Neutralizing antibody or shRNA targeting FGF23 suppressed the pathobiological activities in AVICs from valves affected by CAVD. FGF23 exerts its effects on AVICs via FGF receptor (FGFR)/Yes-associated protein (YAP) signaling, and inhibition of FGFR/YAP reduced FGF23's potency in AVICs. Recombinant Klotho downregulated the pathobiological activities in AVICs exposed to FGF23. Incubation of FGF23 with Klotho formed complexes and decreased FGF23's potency. Further, treatment of CKD mice with recombinant Klotho attenuated aortic valve lesions. Conclusion: This study demonstrates that CKD induces FGF23 accumulation, Klotho insufficiency and aortic valve lesions in old mice. FGF23 upregulates the inflammatory, fibrogenic and osteogenic activities in AVICs via the FGFR/YAP signaling pathway. Soluble Klotho suppresses FGF23 effect through molecular interaction and is capable of mitigating CKD-induced CAVD.

Relationship between Serum Indoxyl Sulfate and Klotho Protein and Vascular Calcification in Patients with Chronic Kidney Disease Stages 3-5

Objective

This study aims to explore the relationships between serum indoxyl sulfate (IS) and Klotho protein levels with vascular calcification in patients with chronic kidney disease (CKD) stages 3-5.

Methods

From December 2021 to January 2023, a total of 108 CKD patients in stages 3-5 were enrolled in this cross-sectional investigation. Demographic information and routine clinical biochemistry test results were gathered. Serum levels of IS and Klotho were quantified through enzyme-linked immunosorbent assays. Furthermore, multislice spiral computed tomography was employed to evaluate vascular calcification. The association between serum IS or Klotho levels and abdominal aorta calcification was assessed using univariate analysis and logistic regression analyses.

Results

With the progression of CKD stages, serum creatinine, phosphorus, intact parathyroid hormone (iPTH), serum IS, and abdominal aortic calcification exhibited incremental trends, while serum calcium and Klotho protein levels showed a diminishing trend, with statistically significant differences (P < 0.05). Significant differences were observed in age, blood phosphorus, calcium, total parathyroid hormone, serum IS, and Klotho protein levels between patients with and without aortic calcification (P < 0.05). Logistic regression analysis demonstrated that advanced age, high IS level, and low Klotho protein level were independent risk factors for abdominal aortic calcification in CKD patients (P < 0.05).

Conclusion

This study indicates elevated serum IS levels and decreased Klotho protein levels in CKD patients. High IS level and low Klotho level were independent risk factors for abdominal aortic calcification.

Klotho activation of Nrf2 inhibits the ferroptosis signaling pathway to ameliorate sepsis-associated acute kidney injury

Background

Sepsis-associated acute kidney injury (SA-AKI) is a common complication of sepsis and greatly increases patient mortality. Recombinant human Klotho protein (Klotho) is a protective protein that can be secreted by the kidney. The aim of this study was to explore the protective effect of Klotho on SA-AKI and its molecular mechanism.

Methods

In vivo, a mouse SA-AKI model was constructed by cecum ligation perforation (CLP). In vitro, a human renal tubular cell epithelial cell line (HK2) was induced with lipopolysaccharide (LPS) in the SA-AKI model. Determine renal injury markers, inflammatory factors, oxidative stress and molecular proteins related to the ferroptosis signaling pathway.

Results

Klotho reduced the release of renal injury markers and inflammatory cytokines, decreased oxidative stress, improved renal histopathological changes, ameliorated mitochondrial damage in mouse renal tubular epithelial cells, increased HK2 cell viability and reduced reactive oxygen species (ROS) accumulation. Exogenous supplementation with Klotho increased the Klotho content in circulating blood, renal tissue and HK2 cells.

Conclusions

In the SA-AKI model, Klotho attenuated renal tissue injury, increased HK2 cell viability, decreased inflammatory factor expression and oxidative stress, restored tubular epithelial mitochondrial function, and increased its level in circulating blood, renal tissue and HK2 cells. Klotho probably exerts its protective effects by activating Nrf2 to inhibit the ferroptosis signaling pathway.

Emerging role of α-Klotho in energy metabolism and cardiometabolic diseases

BACKGROUND AND AIM

Klotho was first identified as a gene associated with aging and longevity in 1997. α-Klotho is an anti-aging protein and its role in energy metabolism, various cardiovascular diseases (CVDs), and metabolic disorders is increasingly being recognized. In this review, we aimed to outline the potential protective role and therapeutic prospects of α-Klotho in energy metabolism and cardiometabolic diseases (CMDs).

METHODS

We comprehensively reviewed the relevant literature in PubMed using the keywords 'Klotho', 'metabolism', 'cardiovascular', 'diabetes', 'obesity', 'metabolic syndrome', and 'nonalcoholic fatty liver disease'.

RESULTS

α-Klotho can be divided into membrane-bound Klotho, secreted Klotho, and the most studied circulating soluble Klotho that can act as a hormone. Klotho gene polymorphisms have been implicated in energy metabolism and CMDs. α-Klotho can inhibit insulin/insulin growth factor-1 signaling and its overexpression can lead to a 'healthy insulin resistance' and may exert beneficial effects on the regulation of glycolipid metabolism and central energy homeostasis. α-Klotho, mainly serum Klotho, has been revealed to be protective against CVDs, diabetes and its complications, obesity, and nonalcoholic fatty liver disease. Human recombinant Klotho protein/Klotho gene delivery, multiple drugs, or natural products, and exercise can increase α-Klotho expression.

CONCLUSION

Overall, α-Klotho has demonstrated its potential as a promising target for modulating energy metabolism and CMDs, and further research is needed to explore its utilization in clinical practice in the future.

Upstream and downstream regulators of Klotho expression in chronic kidney disease

Klotho is a critical protein that protects the kidney. Klotho is severely downregulated in chronic kidney disease (CKD), and its deficiency is implicated in the pathogenesis and progression of CKD. Conversely, an increase in Klotho levels results in improved kidney function and delays CKD progression, supporting the notion that modulating Klotho levels could represent a possible therapeutic strategy for CKD treatment. Nevertheless, the regulatory mechanisms responsible for the loss of Klotho remain elusive. Previous studies have demonstrated that oxidative stress, inflammation, and epigenetic modifications can modulate Klotho levels. These mechanisms result in a decrease in Klotho mRNA transcript levels and reduced translation, thus can be grouped together as upstream regulatory mechanisms. However, therapeutic strategies that aim to rescue Klotho levels by targeting these upstream mechanisms do not always result in increased Klotho, indicating the involvement of other regulatory mechanisms. Emerging evidence has shown that endoplasmic reticulum (ER) stress, the unfolded protein response, and ER-associated degradation also affect the modification, translocation, and degradation of Klotho, and thus are proposed to be downstream regulatory mechanisms. Here, we discuss the current understanding of upstream and downstream regulatory mechanisms of Klotho and examine potential therapeutic strategies to upregulate Klotho expression for CKD treatment.

Low serum Klotho reflects senile inflammation in middle-aged and elderly patients with coronary atherosclerosis

BACKGROUND

Anti-aging protein Klotho has been reported to be associated with atherosclerosis, which was considered as a chronic inflammatory disease. However, the relationship between Klotho and senile inflammation remained unclear. The present study aims to ascertain the correlation of Klotho with inflammation in middle-aged and elderly coronary atherosclerotic disease (CAD).

METHODS

A total of 302 patients with CAD were included in this study. Coronary atherosclerosis was confirmed and quantified for all patients by coronary angiography. Serum Klotho was detected by enzyme linked immunosorbent assay. Serum concentrations of IL-6 and IL-8 were quantified by chemiluminescence assay. T-lymphocyte subsets were measured using flow cytometry.

RESULTS

Multivariate linear regression analysis showed that serum Klotho was an independent predictor for circulating monocytes (standard β = -0.321, P < 0.001) and CD4+/CD8+ ratio (standard β = -0.522, P < 0.001). After adjustment, serum Klotho was still independently associated with IL-6 (standard β = -0.395, P < 0.001) and IL-8 (standard β = -0.296, P < 0.001). Moreover, circulating monocytes, CD4+ and CD8+ lymphocytes were correlated with increased serum concentrations of IL-6 and IL-8, independent of CRP (P < 0.05). In receiver operating characteristic curve analysis, CD4+/CD8+ ratio (AUC = 0.863, P < 0.001), IL-6 (AUC = 0.893, P < 0.001) and IL-8 (AUC = 0.884, P < 0.001) presented the excellent predictive performance for significant CAD.

CONCLUSIONS

Decreased concentrations in serum Klotho reflect senile inflammation, which is related to the severity of CAD in middle-aged and elderly patients.