Association between KLOTHO gene and hand osteoarthritis in a female Caucasian population

Association between serum α-Klotho levels and osteoarthritis prevalence among middle-aged and older adults: an analysis of the NHANES 2007-2016

BACKGROUND

As individuals age, the prevalence of osteoarthritis tends to increase gradually. α-Klotho is a hormone renowned for its anti-aging properties. However, the precise role of serum α-Klotho in osteoarthritis is still not fully comprehended.

METHODS

We conducted a cross-sectional study utilizing data from the National Health and Nutrition Examination Survey (NHANES) spanning from 2007 to 2016. Serum α-Klotho levels were measured using an enzyme-linked immunosorbent assay (ELISA). Osteoarthritis was assessed through self-reported questionnaires. Through univariate and multivariate logistic regression analyses, smooth curve fitting, threshold effect analysis, and subgroup analyses, we delved into the potential association between them.

RESULTS

The study encompassed a cohort of 10,265 participants. In fully adjusted models of multivariate logistic regression analysis, we identified a negative correlation between serum ln α-Klotho and OA (OR = 0.77, 95% CI: 0.65-0.91, p = 0.003). When stratifying serum α-Klotho levels into tertiles, individuals in the highest tertile exhibited a 26% reduced risk of OA compared to those in the lowest tertile (OR = 0.84, 95% CI: 0.73-0.97, p = 0.014). Subsequent analyses indicated a linearly negative association. In subgroup analyses, we explored the relationship between serum ln α-Klotho and osteoarthritis across diverse populations, revealing the persistence of this association in the majority of subgroups.

CONCLUSION

Serum α-Klotho levels exhibit a significant negative linear correlation with the prevalence of osteoarthritis in middle-aged and elderly populations in the United States.

Senescence-regulatory factors as novel circulating biomarkers and therapeutic targets in regenerative medicine for osteoarthritis

Recent discoveries reveal that the chronic presence of senescent cells in osteoarticular tissues provides a focal point of disease development for osteoarthritis (OA). Nevertheless, senescence-regulatory factors associated with OA still need to be identified. Furthermore, few diagnostic- and prognostic-validated biochemical markers (biomarkers) are currently used in clinics to evaluate OA patients. In the future, alongside imaging and clinical examination, detecting senescence-regulatory biomarkers in patient fluids could become a prospective method for disease: diagnosis, monitoring, progression and prognosis following treatment. This review summarizes a group of circulating OA biomarkers recently linked to senescence onset. Remarkably, these factors identified in proteomics, metabolomic and microRNA studies could also have deleterious or protective roles in osteoarticular tissue homeostasis. In addition, we discuss their potentially innovative modulation in combination with senotherapeutic approaches, for long-lasting OA treatment.

Genetic polymorphism of WNT9A is functionally associated with thumb osteoarthritis in the Chinese population

BACKGROUND

In a recent genome-wide association study, novel genetic variations of WNT9A were reported to be involved in the etiopathogenesis of thumb osteoarthritis (TOA) in Caucasians. Our purposes were to replicate the association of WNT9A with the development of TOA in the Chinese population and to further unveil the functional role of the risk variants.

METHODS

SNP rs11588850 of WNT9A were genotyped in 953 TOA patients and 1124 healthy controls. The differences of genotype and allele distributions between the patients and healthy controls were evaluated using the Chi-square test. Luciferase Reporter Assay was performed to investigate the influence of variant on the gene expression.

RESULTS

There was significantly lower frequency of genotype AA in TOA patients than in the controls 74.9% vs. 81.9%, p < 0.001). The frequency of allele A was remarkably lower in the patients than in the controls (86.3% vs. 90.5%, p < 0.001), with an odds ratio of 0.66 (95% CI = 0.54-0.80). Luciferase Reporter Assay showed that the construct containing mutant allele G of rs11588850 displayed 29.1% higher enhancer activity than the wild allele A construct (p < 0.05).

CONCLUSIONS

Allele G of rs11588850 was associated with the increased risk of TOA possibly via up-regulation of WNT9A expression. Further functional analysis into the regulatory role of rs11588850 in WNT9A expression can shed new light on the genetic architecture of TOA.

A study of the molecular mechanism of quercetin and dasatinib combination as senolytic in alleviating age-related and kidney diseases

Aging is a significant risk factor for the majority of prevalent human illnesses. The chance of having severe chronic conditions grows dramatically with advancing age. Indeed, more than 90% of people over 65 get at least one chronic disease, including diabetes, heart disease, malignancy, memory loss, and kidney disease, whereas more than 70% have two or more of these ailments. Mouse and human aging lead to increased senescent cells and decreased klotho concentrations. Mice lacking the protein α-klotho show faster aging, similar to human aging. α-Klotho upregulation extends life and slows or suppresses the onset of many age-related illnesses and kidney diseases. Like the consequences of α-klotho deficiency, senescent cell accumulation is linked to tissue dysfunction in various organs and multiple age-related kidney diseases. In addition, α-klotho and cell senescence are negatively and presumably mechanistically linked. Earlier research has demonstrated that klotho exerts its protective effects in age-related and kidney disease by interacting with Wnt ligands, serving as an endogenous antagonist of Wnt/β-catenin signaling. In addition, decreasing senescent cell burden with senolytics, a class of drugs that remove senescent cells selectively and extend the life span of mice. In this work, we are studying the molecular mechanism of the combination of quercetin and dasatinib as senolytic in easing age-related chronic renal illness by altering the level of klotho/Wnt/β-catenin. PRACTICAL APPLICATIONS: There is an inverse relationship between the onset and the development of age-related disorders and cellular senescence and Klotho. Earlier attempts to suppress transforming growth factor-beta 1 (TGF-β1) in kidney disease with anti-TGF-β1 antibodies were ineffective, and this should be kept in mind. Senolytic medications may benefit from targeting senescent cells, which enhances the protective factor α-klotho. In addition, our study provides a unique, translationally feasible route for creating orally active small compounds to enhance α-klotho, which may also be a valuable biomarker for age-related kidney disease. Additionally, other aspects of aging can be affected by senolytics, such as limiting age-related mitochondrial dysfunction, lowering inflammation and fibrosis, blunting reactive oxygen species (ROS) generation, decreasing deoxyribonucleic acid (DNA) damage, and reinforcing insulin sensitivity. Senolytic agents have been shown to increase adipose progenitor and cardiac progenitor cell activity in aging animals and animals with cellular senescence-related diseases, such as heart, brain, and kidney disease.

Klotho Level as a Marker of Low Bone Mineral Density in Egyptian Sickle Cell Disease Patients

Bone involvement of sickle cell disease (SCD) patients varies from acute clinical manifestations of painful vaso-occlusive crises or osteomyelitis to more chronic affection of bone mineral density (BMD) and debilitating osteonecrosis and osteoporosis. Secreted klotho protein is involved in calcium (Ca) reabsorption in the kidney. This study aimed to measure serum klotho levels in children with SCD to determine the possibility of using it as a marker of low BMD in children with SCD in correlation with a dual-energy radiograph absorptiometry scan. This study included 60 sickle disease patients and 30 age-matched and sex-matched control participants without SCD. A highly statistically significant difference was found between patients with normal BMD and those with low BMD, with serum Ca and klotho levels being lower in the latter group. Klotho serum level correlated positively with both serum Ca and BMD. Serum klotho level showed 94.9% sensitivity and 95.2% specificity in the detection of low BMD. Both serum Ca and klotho serum levels may be useful markers for detection of low BMD related to SCD with high sensitivity and specificity; however, klotho may be a better indicator as it is less affected by the nutritional and endocrinal status of patients or by intake of Ca supplements.

Current Epidemiology and Risk Factors for the Development of Hand Osteoarthritis

PURPOSE OF REVIEW

Hand osteoarthritis (hand OA), the most common peripheral arthritis in the world, is less studied than osteoarthritis (OA) of the knee and hip. However, it is uniquely situated to offer novel insight into OA as a disease process by removing weight-bearing as a confounder of systemic disease mechanisms. Here we review the epidemiology of hand OA and key risk factors for its development.

RECENT FINDINGS

Mounting evidence points to obesity as an important risk factor for hand OA development, with new evidence implicating a role for leptin and serum fatty acids. Disease progression in hand OA and specifically the erosive OA subtype may be associated with diabetes. New evidence supports an association between cardiovascular disease progression and symptomatic hand OA. Alcohol use may be associated with increased synovitis and erosive hand OA. Differences in ethnical distributions of hand OA have become more apparent, with a lower prevalence in Black patients compared to White patients. Novel genetic insights implicating the WNT gene pathway and IL-1β have led to novel potential targets in hand OA pathogenesis. Hand OA is a heterogeneous disease with many modifiable and non-modifiable risk factors that can determine disease severity and shed light on disease pathogenesis.

Klotho gene G395A and C1818T polymorphisms in acromegaly: Association with clinical presentation and comorbidities

BACKGROUND

Klotho is a new identified anti-ageing gene with tumour suppressor activities. Current data suggest that there is a tight relationship between Klotho protein and growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis.

PURPOSE

This study aimed to investigate the possible association of Klotho gene polymorphisms with acromegaly and to assess whether these polymorphisms contribute to clinical characteristics, comorbidities and biochemical variables in these patients.

METHODS

The study included 52 patients with acromegaly and 52 unrelated healthy subjects. The Klotho G395A and C1818T polymorphisms were assessed by Sanger sequencing. Serum levels of sKlotho were determined by ELISA method.

RESULTS

Subjects carrying GA genotype of Klotho G395A polymorphism had 3.27 times higher risk of developing acromegaly [odds ratio (OR), 3.27; 95% confidence interval (CI): 1.37-7.81; p = .023]. The A allele of G395A was significantly associated with acromegaly risk (OR, 2.27; 95% CI: 1.1-4.72; p = .022). No association was observed between the studied polymorphisms and disease characteristics including age at acromegaly diagnosis, size of adenoma, baseline GH and IGF-1 concentrations, and final outcome. G395A polymorphism was associated with the presence of malignancy (OR, 2.24, 95% CI: 1.63-3.08; p = .019) and colorectal polyps (OR, 1.99; 95% CI: 1.02-3.88; p = .047) in patients with acromegaly. Serum sKlotho levels were significantly higher and correlated with GH and IGF-1 levels among acromegaly patients. There was no association between the studied polymorphisms and sKlotho levels.

CONCLUSIONS

Klotho G395A polymorphism is associated with acromegaly susceptibility and increased risk of malignancy and colorectal polyps in these patients.

Reduced Plasma Levels of α-Klotho and Their Correlation With Klotho Polymorphisms in Elderly Patients With Major Depressive Disorders

Background: Recent literature suggests that α-Klotho, a widely recognized anti-aging protein, is involved in longevity as well as in many diseases, including Alzheimer's disease, and depression. Although the Klotho gene encodes α-Klotho, a single transmembrane protein with intracellular and extracellular domains, the relationship between Klotho gene polymorphism and circulating α-Klotho levels in patients with major depressive disorder (MDD) is not clear. Methods: A total of 144 MDD patients and 112 age-matched healthy controls were included in this study. The Klotho genetic polymorphisms (rs9536314, rs9527025, and rs9315202) and plasma α-Klotho levels were measured by PCR and ELISA, respectively. The severity of depressive symptoms was estimated using the Hamilton Depression Scale (HAMD). Results: We found a significantly lower level of plasma α-Klotho in the MDD patients than in controls. Among them, only elderly MDD patients (first episode) showed significantly lower α-Klotho levels than the age-matched controls, while elderly recurrent and young MDD patients showed no difference in plasma α-Klotho levels from age-matched controls. The young MDD group showed a significantly earlier onset age, higher plasma α-Klotho levels, and lower HAMD scores than those in the elderly MDD group. While the plasma α-Klotho levels were higher in rs9315202 T alleles carrier regardless age or sex, the rs9315202 T allele was negatively correlated with disease severity only in the elderly MDD patients. Conclusion: The results of our study showed that only elderly MDD patients showed a decrease in plasma α-Klotho levels along with an increase in disease severity as well as an association with the number of rs9315202 T alleles, and not young MDD patients compared to age-matched controls. Our data suggest that circulating α-Klotho levels combined with Klotho genetic polymorphisms are important in elderly MDD patients, particularly carriers of the Klotho gene rs9315202 T allele.

Klotho (rs1207568 and rs564481) gene variants and colorectal cancer risk

BACKGROUND/AIMS

Whereas colorectal cancer (CRC) is the third most common cancer worldwide, klotho gene has been reported as a tumor suppressor gene. Therefore, the aim of this study was to investigate the association between klotho (rs1207568 and rs564481) variants and CRC in Egyptian patients.

MATERIALS AND METHODS

A case-control study comprising 100 patients with CRC and 100 age- and sex-matched healthy controls was conducted. Genotyping of klotho was performed by polymerase chain reaction with confronting two-pair primers.

RESULTS

The frequencies of the A allele of rs1207568 and the AC haplotype were significantly higher in patients with CRC than in the controls (p=0.019 and p=0.005, respectively).

CONCLUSION

We propose that klotho (rs1207568 and rs564481) variants play a significant role in colorectal carcinogenesis and that the klotho protein could be a target for oncotherapy.

Physical Exercise as an Immunomodulator of Chronic Diseases in Aging

BACKGROUND

The progressive dysfunction of the immune system during aging appears to be involved in the pathogenesis of several age-related disorders. However, regular physical exercise can present "antiaging" effects on several physiological systems.

METHODS

A narrative review of studies investigating the chronic effects of exercise and physical activity on the immune system and its association with age-related chronic diseases was carried out according to the guidelines for writing a narrative review.

RESULTS

There is compelling evidence suggesting that age-related immune system alterations play a key role on the pathophysiology of atherosclerosis, hypertension, chronic heart failure, type 2 diabetes, obesity, arthritis, and chronic obstructive pulmonary disease. On the other hand, the regular practice of physical activity appears to improve most of the inflammatory/immunological processes involved in these diseases.

CONCLUSION

Epidemiological, experimental, and clinical studies permit us to affirm that regular physical activity improves immunomodulation and may play a key role in the prevention and treatment of several age-related chronic diseases. However, further studies are needed to better describe the prophylactic and therapeutic effects of physical exercise in specific organs of older individuals, as well as the mechanisms involved in such response.

Loss of Klotho contributes to cartilage damage by derepression of canonical Wnt/β-catenin signaling in osteoarthritis mice

Caducity is known to be an independent risk factor in osteoarthritis (OA), yet the molecular basis behind caducity and OA remains unclear. Klotho, an anti-caducity protein, is an endogenous antagonist of the transduction of Wnt/β-catenin signal which can stimulate the articular cartilage degradation, indicating that deficiency in Klotho may increase Wnt/β-catenin activity and consequently accelerate the development of OA. We found that expression of Klotho was markedly higher in normal mouse cartilage than in the OA model, and in this model the activity of Wnt/β-catenin and its target gene was up-regulated. Decrease in Klotho expression was closely associated with the increase of β-catenin in OA, indicating that there was a negative correlation between Klotho and Wnt signal transduction. In the vitro and in vivo experiments, Klotho was found to bind to multiple Wnt, including Wnt1, Wnt4 and Wnt7a. It was additionally found that cyclic tenisle strain (CTS) inhibited the expression of Klotho and activated β-catenin. On the contrary, over-expression of Klotho would reduce the degradation of articular cartilage induced by CTS. These results suggest that Klotho is an antagonist of endogenous Wnt/β-catenin activity. In OA cartilage, decrease in expression of Klotho can activate Wnt/β-catenin signal transduction and consequently induce cartilage injury.

Secreted α-Klotho maintains cartilage tissue homeostasis by repressing NOS2 and ZIP8-MMP13 catabolic axis

Progressive loss of tissue homeostasis is a hallmark of numerous age-related pathologies, including osteoarthritis (OA). Accumulation of senescent chondrocytes in joints contributes to the age-dependent cartilage loss of functions through the production of hypertrophy-associated catabolic matrix-remodeling enzymes and pro-inflammatory cytokines. Here, we evaluated the effects of the secreted variant of the anti-aging hormone α-Klotho on cartilage homeostasis during both cartilage formation and OA development. First, we found that α-Klotho expression was detected during mouse limb development, and transiently expressed during in vitro chondrogenic differentiation of bone marrow-derived mesenchymal stem cells. Genome-wide gene array analysis of chondrocytes from OA patients revealed that incubation with recombinant secreted α-Klotho repressed expression of the NOS2 and ZIP8/MMP13 catabolic remodeling axis. Accordingly, α-Klotho expression was reduced in chronically IL1β-treated chondrocytes and in cartilage of an OA mouse model. Finally, in vivo intra-articular secreted α-Kotho gene transfer delays cartilage degradation in the OA mouse model. Altogether, our results reveal a new tissue homeostatic function for this anti-aging hormone in protecting against OA onset and progression.

G-395A polymorphism in the promoter region of the KLOTHO gene associates with frailty among the oldest-old

Frailty is characterized by a decline in physiological reserve and increased vulnerability. Previous studies have shown that KLOTHO (KL) plays a protective role in several age-related diseases. We hypothesize a probable protective effect of KL on frailty in the elderly population and included a cohort of Chinese nonagenarians and centenarians for our study. This study is part of a cross-sectional study and secondary analysis of the Project of Longevity and Aging in Dujiangyan (PLAD) study, which was conducted in Southwest China. Community-dwelling Chinese residents aged 90 years or older were included in this study. Frailty was determined using the FRAIL scale as proposed by the International Association of Nutrition and Aging. On the FRAIL scale, frailty was defined by a score of ≥3. G-395A (rs1207568) genotyping of the promoter region of the KL gene was performed using TaqMan allelic discrimination assay. A total of 632 participants (68.4% females; mean age: 93.5 ± 3.2 years) were included. KL G-395A polymorphism genotype frequencies were 1.7% AA, 25.6% GA, and 72.7% GG in our sample. GG genotype frequencies for the frailty and control groups were 83.6% and 71.2%, respectively. Frailty prevalence was significantly lower in the GA+AA group when compared to the GG genotype group (6.9% vs. 13.3%, P = 0.026). In addition, subjects with a GA+AA genotype had a significantly lower risk of frailty (odds ratio (OR): 0.47, 95% confidence interval (CI) 0.23 to 0.97, P = 0.040) compared to the GG genotype after adjusting for age, gender, education level, smoking, alcohol consumption, exercise, body mass index (BMI), cognitive impairment, and other potential factors. KL-395A allele carrying genotypes (GA and AA) is associated with a lower risk of frailty relative to GG genotypes in a sample of Chinese nonagenarians and centenarians.

Relationship between atherosclerosis and knee osteoarthritis as graded by radiography and ultrasonography in females

[Purpose] The aim of this study was to assess the relationship between atherosclerosis and knee osteoarthritis grade in women as assessed by both ultrasonography and radiography. [Subjects and Methods] Seventy women diagnosed with knee osteoarthritis were classified into two groups according to cartilage grading/radiographic grading. Patients with Kellgren-Lawrence grades 1 and 2 were included in group 1, while those with Kellgren-Lawrence grades 3 and 4 were included in group 2. Patients with cartilage grades 1-3 were included in group 1, while those with cartilage grades 4-6 were included in group 2. Patients were clinically assessed using a visual analog scale and the Western Ontario and McMaster Universities Arthritis Index. Radiographic osteoarthritis grade was scored using the Kellgren and Lawrence grading system. Using ultrasonography, symptomatic knees were graded and evaluated for distal femoral cartilage thickness. Carotid intima-media thickness and serum lipid levels were measured to assess atherosclerosis. [Results] Carotid intima-media thickness measurements were higher in group 2 than in group 1 as determined by the Kellgren-Lawrence and cartilage grading systems. Carotid intima-media thickness measurements were positively correlated with both the ultrasonographic cartilage grade and Kellgren-Lawrence. [Conclusion] The results of this study suggest that osteoarthritis as assessed by ultrasonography was successful and comparable to assessment with radiography. We showed a correlation between atherosclerosis and ultrasonographic knee osteoarthritis grade.

Severe Hand Osteoarthritis Strongly Correlates With Major Joint Involvement and Surgical Intervention

BACKGROUND

The presence of hand osteoarthritis (OA) increases the risk for developing OA in other major joints. Although genetic predisposition has been implicated in its causation, its exact role has yet to be established. The association of hand OA with symptomatic and asymptomatic major joints has not been previously studied.

METHODS

Hundred consecutive patients had a hand photo taken for visual documentation of the hand joints. Radiographs of hand and all major symptomatic joints were analyzed and classified using the Kellgren-Lawrence scale by 2 independent observers including an orthopedic radiologist.

RESULTS

Severe hand OA was present in 91% of the patients. Radiographic analysis showed that the hip was involved in 88% of the patients, of whom 85.2% (75) were symptomatic and 14.7% (13) were asymptomatic. Hip arthroplasty was required by 62.5% (55) of symptomatic hip patients. Knee involvement was present in 37% of the patients; all were symptomatic and 81.1% (30) of these required knee arthroplasty. Bilateral surgery was performed in 33% (28) and "2 joint (hip and knee)" surgery was performed in 6% (5). Spine involvement was present in 72% of the patients. There was a significant correlation between hand radiographic findings of OA and hip (r = 0.68; P = .03), knee (r = 0.58; P = .042), and spine (r = .39; P = .05) involvement.

CONCLUSION

There was a significant correlation between severe hand OA and hip, knee, and spine involvement. Severity of Hand OA can have a predictive value on multiple joint involvement and risk of surgical intervention. This study emphasizes the need to investigate the genetic predisposition in causation of OA.

The Klotho gene G-395A polymorphism and metabolic syndrome in very elderly people

BACKGROUND

To investigate the possible association of the Klotho G-395A polymorphism and metabolic syndrome (MetS) among a population of Chinese nonagenarians and centenarians.

METHODS

Subjects were from the Project of Longevity and Aging in Dujiangyan (PLAD). The genotyping of G-395A (rs1207568) in the promoter region of the Klotho gene was performed using the TaqMan allelic discrimination assay. MetS was diagnosed according to the International Diabetes Federation criteria.

RESULTS

We included 695 subjects aged 93.5 ± 3.2 years. G and A allele frequencies were 0.852 and 0.148, respectively. In the whole population, the frequency of MetS was 10.8% and 5.9% in the GG and GA + AA genotype group, respectively (p = 0.004). The -395A allele carriers had significantly lower risk of MetS in the whole population (odd ratio [OR] 0.50, 95% confidential interval [CI] 0.25 to 0.98) and in women (OR 0.51, 95% CI 0.24 to 0.97), but not in men (OR 0.42, 95% CI 0.05 to 3.85). In the whole population and women, the relationship between the Klotho G-395A SNP and MetS might due to its influence on high blood pressure (OR 0.48, 95% CI 0.34 to 0.67; OR 0.47, 95% CI 0.31 to 0.71, respectively) and hypertriglyceridemia (OR 0.66, 95% CI 0.39 to 0.95; OR 0.54, 95% CI 0.31 to 0.98, respectively). In men, this relationship might due to its influence on high blood pressure (OR 0.47, 95% CI 0.25 to 0.90) and low HDL-C (OR 0.69, 95% CI 0.27 to 0.93).

CONCLUSIONS

The -395A allele carriers of the Klotho gene were correlated with lower risk of MetS among Chinese nonagenarians and centenarians, especially in women.

G-395A polymorphism in the promoter region of the KLOTHO gene associates with reduced cognitive impairment among the oldest old

This study aimed to examine the possible association between G-395A polymorphism in the promoter region of the KLOTHO gene and cognitive impairment among Chinese nonagenarians and centenarians. This study is a secondary analysis of the Project of Longevity and Aging in Dujiangyan (PLAD) study. Community-dwelling Chinese people aged 90 years or older were included. G-395A (rs1207568) genotyping in the promoter region of the KLOTHO gene was performed using the TaqMan allelic discrimination assay. Cognitive function was assessed with the mini-mental status examination (MMSE). A total of 706 participants (68.0 % female; mean age 93.5 ± 3.6 years) were included. The KLOTHO G-395A polymorphism genotype frequencies for the whole sample were 2.0 % AA, 30.3 % GA, and 67.7 % GG. The GG genotype frequencies for the cognitive impairment and control groups were 70.2 and 62.7 %, respectively. Cognitive impairment prevalence was significantly lower in the GA+AA group than in the GG genotype group (61.4 vs. 69.0 %, p = 0.044). GA+AA genotype subjects had a significantly lower risk of cognitive impairment (odds ratio 0.66; 95 % confidence interval 0.44 to 0.98) than GG genotype individuals after adjusting for age, gender, and other relevant risk factors. KLOTHO G-395A polymorphism associates with reduced cognitive impairment in a sample of Chinese nonagenarians and centenarians.

Genetic Variants in KLOTHO Associate With Cognitive Function in the Oldest Old Group

Decline in cognitive abilities is a major concern in aging individuals. A potential important factor for functioning of the central nervous system in late-life stages is the KLOTHO (KL) gene. KL is expressed in various organs including the brain and is involved in multiple biological processes, for example, growth factor signaling. In the present study, 19 tagging gene variants in KL were studied in relation to 2 measures of cognitive function, a 5-item cognitive composite score and the Mini Mental State Examination, in 1,480 Danes 92-100 years of age. We found that heterozygotes for the previously reported KL-VS had poorer cognitive function than noncarriers. Two other variants positioned in the 5' end of the gene, rs398655 and rs562020, were associated with better cognitive function independently of KL-VS, and the common haplotype AG was associated with poorer cognition, consistently across two cognitive measures in two cohort strata. The haplotype effect was stronger than that of KL-VS. Two variants, rs2283368 and rs9526984, were the only variants significantly associated with cognitive decline over 7 years. We discuss an age-dependent effect of KL and the possibility that multiple gene variants in KL are important for cognitive function among the oldest old participants.

The effect of osteoarthritis on 1-year risk of ischemic heart disease following total knee arthroplasty

To evaluate the long-term risk of ischemic heart disease (IHD) following total knee arthroplasty (TKA), we conducted a retrospective cohort study using data from the National Health Insurance Research Database of Taiwan. We evaluated 3599 primary TKA patients and 14,396 matched control patients. We further classified all patients into those with and without osteoarthritis (OA). The incidence rate of IHD was significantly higher among the TKA patients than among the matched control patients (1.13 vs 0.69 per 1000 person-months, P<.05). However, after controlling for OA, this difference was non-significant (HR=1.18, 95% confidence interval (CI): 0.63-2.20, P>.05). Our study results indicate that underlying OA conditions are predominantly responsible for increased long-term risk of IHD in TKA patients.

Rosiglitazone increases cerebral klotho expression to reverse baroreflex in type 1-like diabetic rats

Reduced baroreflex sensitivity (BRS) is widely observed in diabetic human and animals. Rosiglitazone is one of the clinically used thiazolidinediones (TZD) known as PPARγ agonist. Additionally, the klotho protein produced from choroid plexus in the central nervous system is regulated by PPARγ. In an attempt to develop the new therapeutic strategy, we treated streptozotocin-induced diabetic rats (STZ) with rosiglitazone (STZ + TZD) orally at 10 mg/kg for 7 days. Also, STZ rats were subjected to intracerebroventricular (ICV) infusion of recombinant klotho at a dose of 3 μg/2.5 μL via syringe pump (8 μg/hr) daily for 7 days. The BRS and heart rate variability were then estimated under challenge with a depressor dose of sodium nitroprusside (50 μg/kg) or a pressor dose of phenylephrine (8 μg/kg) through an intravenous injection. Lower expression of klotho in medulla oblongata of diabetic rats was identified. Cerebral infusion of recombinant klotho or oral administration of rosiglitazone reversed BRS in diabetic rats. In conclusion, recovery of the decreased klotho in brain induced by rosiglitazone may restore the impaired BRS in diabetic rats. Thus, rosiglitazone is useful to reverse the reduced BRS through increasing cerebral klotho in diabetic disorders.

Novel bone endocrine networks integrating mineral and energy metabolism

The skeleton is an endocrine organ that regulates energy metabolism through the release of the osteoblast-derived hormone, osteocalcin (Ocn), and phosphate and vitamin D homeostasis through the secretion by osteoblasts and osteocytes of the novel hormone, FGF23 Ocn activates a widely expressed G-protein coupled receptor, GPRC6A, to regulate insulin secretion by pancreatic β-cells, testosterone secretion by testicular Leydig cells, fatty acid metabolism in the liver, and insulin sensitivity of muscle and fat, as well as other functions. FGF23 targets a limited number of tissues, including kidney, parathyroid gland, choroid plexus, and pituitary gland that co-express FGF receptors and α-Klotho complexes. Ectodomain shedding and secretion of a soluble form of Klotho also is purported to act as an anti-ageing hormone. Further elucidation of these novel endocrine networks is likely to lead to new appreciation of the cooperation between various organ systems to regulate phosphate, vitamin D, and energy metabolism.

A systems biology preview of the relationships between mineral and metabolic complications in chronic kidney disease

There are emerging data that the skeleton is connected to systemic biological functions through the release of two osteoblast-/osteocyte-derived hormones, fibroblastic growth factor 23 (FGF23) and undercarboxylated osteocalcin (Ocn). FGF23 is important in the regulation of phosphate and vitamin D metabolism, whereas Ocn participates in endocrine networks, coordinating bone and fat mass, energy metabolism, and sex hormone production. Bone remodeling and mineralization per se, along with the hormones leptin, insulin, glucocorticoids, PTH, and 1,25(OH)2D, regulate the release of FGF23 and Ocn, leading to complex cross-talk and coordination between endocrine networks previously thought to be distinct. These pathways are particularly important in chronic kidney disease, in which both FGF23 and Ocn are increased. Although these hormones initially serve an adaptive role, with progressive loss of renal function they show maladaptive effects, particularly on the cardiovascular system, through multiple mechanisms, including possible cross-talk with the renin angiotensin system. The complex interconnections between the various endocrine networks in chronic kidney disease may account for the difficulty in treating the uremic state.

The role of Klotho in energy metabolism

A disproportionate expansion of white adipose tissue and abnormal recruitment of adipogenic precursor cells can not only lead to obesity but also impair glucose metabolism, which are both common causes of insulin resistance and diabetes mellitus. The development of novel and effective therapeutic strategies to slow the progression of obesity, diabetes mellitus and their associated complications will require improved understanding of adipogenesis and glucose metabolism. Klotho might have a role in adipocyte maturation and systemic glucose metabolism. Klotho increases adipocyte differentiation in vitro, and mice that lack Klotho activity are lean owing to reduced white adipose tissue accumulation; moreover, mice that lack the Kl gene (which encodes Klotho) are resistant to obesity induced by a high-fat diet. Knockout of Kl in leptin-deficient Lep(ob/ob) mice reduces obesity and increases insulin sensitivity, which lowers blood glucose levels. Energy metabolism might also be influenced by Klotho. However, further studies are needed to explore the possibility that Klotho could be a novel therapeutic target to reduce obesity and related complications, and to determine whether and how Klotho might influence the regulation and function of a related protein, β-Klotho, which is also involved in energy metabolism.

Identification of novel small molecules that elevate Klotho expression

The absence of Klotho (KL) from mice causes the development of disorders associated with human aging and decreased longevity, whereas increased expression prolongs lifespan. With age, KL protein levels decrease, and keeping levels consistent may promote healthier aging and be disease-modifying. Using the KL promoter to drive expression of luciferase, we conducted a high-throughput screen to identify compounds that activate KL transcription. Hits were identified as compounds that elevated luciferase expression at least 30%. Following validation for dose-dependent activation and lack of cytotoxicity, hit compounds were evaluated further in vitro by incubation with opossum kidney and Z310 rat choroid plexus cells, which express KL endogenously. All compounds elevated KL protein compared with control. To determine whether increased protein resulted in an in vitro functional change, we assayed FGF23 (fibroblast growth factor 23) signalling. Compounds G-I augmented ERK (extracellular-signal-regulated kinase) phosphorylation in FGFR (fibroblast growth factor receptor)-transfected cells, whereas co-transfection with KL siRNA (small interfering RNA) blocked the effect. These compounds will be useful tools to allow insight into the mechanisms of KL regulation. Further optimization will provide pharmacological tools for in vivo studies of KL.

Evidence for FGF23 involvement in a bone-kidney axis regulating bone mineralization and systemic phosphate and vitamin D homeostasis

Bone is involved in the maintenance of phosphate and vitamin D homeostasis via its production and secretion of FGF23 and serves as a reservoir for the storage and release of calcium and phosphate into the circulation. Alterations in mineralization of extracellular matrix and the remodeling activities of the skeleton are coupled to the kidney conservation of phosphate and production of 1,25(OH)2D via the regulation of FGF23 production by osteocytes through yet-to-be defined locally derived factors. In addition, FGF23 production is regulated by 1,25(OH)2D in a feedback loop where FGF23 stimulate Cyp24 mediated degradation of 1,25(OH)2D that serves to protect the organism from the toxic effects of vitamin D excess. In this chapter, we will review the regulation and function of FGF23.

Secreted klotho and chronic kidney disease

Soluble Klotho (sKl) in the circulation can be generated directly by alterative splicing of the Klotho transcript or the extracellular domain of membrane Klotho can be released from membrane-anchored Klotho on the cell surface. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23), sKl, acts as hormonal factor and plays important roles in anti-aging, anti-oxidation, modulation of ion transport, and Wnt signaling. Emerging evidence reveals that Klotho deficiency is an early biomarker for chronic kidney diseases as well as a pathogenic factor. Klotho deficiency is associated with progression and chronic complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. In multiple experimental models, replacement of sKl, or manipulated up-regulation of endogenous Klotho protect the kidney from renal insults, preserve kidney function, and suppress renal fibrosis, in chronic kidney disease. Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.

The presence of total knee or hip replacements due to osteoarthritis enhances the positive association between hand osteoarthritis and atherosclerosis in women: the AGES-Reykjavik study

OBJECTIVE

This study examines the relationship between total knee replacements (TKR), total hip replacements (THR) or replacements of either joint (total joint replacement; TJR) due to osteoarthritis and atherosclerosis in a large population-based study.

METHODS

The participants were 2195 men and 2975 women, mean age 76 ± 6 years. The osteoarthritis data were analysed in relation to measures of atherosclerosis, including carotid artery intima media thickness and plaque severity (ultrasound), coronary and aortic calcifications (CT), cerebral white matter lesions (MRI) and a history of previous cardiac and cerebral events.

RESULTS

The prevalence of TKR was 223 (4.3%) and THR 316 (6.1%). The presence of TJR in women was associated with a non-significant trend towards increased carotid plaque severity, coronary calcifications and periventricular white matter hyperintensities (PVH) but not with a history of cardiac or cerebral events. No associations were seen in men. When TJR were grouped according to the presence or absence of hand osteoarthritis (HOA) there was a highly significant association in the order -TJR/-HOA < +TJR/-HOA < -TJR/+HOA < +TJR/+HOA, for carotid plaque severity, coronary calcifications and PVH.

CONCLUSION

The presence of TJR did not show a significant independent association with atherosclerosis but enhanced the strength of the positive association between HOA and subclinical atherosclerosis in women.

Klotho protein deficiency and aging

Aging is inevitable; however, the molecular mechanism of aging has not been fully elucidated. Investigations into aging are facing difficulties because aging is influenced by complex factors such as circumstances, living habits and genetic background. Recently, a variety of animals, such as Caenorhabditis elegans, Drosophila and mice, that have aberrations in their lifespan, have been investigated and a large number of genes related to aging have been found, one of which is alpha-klotho. The alpha-Klotho mouse (alpha-kl(-/-) mouse), which has a defect of the alpha-klotho gene expression, was established a decade ago. It is of great interest because the alpha-kl(-/-) mouse shows various phenotypes resembling human aging. The relationship between aging and alpha-klotho protein function is gradually becoming clear. This review covers the recent advance in alpha-klotho protein research.

Klotho: a novel phosphaturic substance acting as an autocrine enzyme in the renal proximal tubule

Klotho has profound effects on phosphate metabolism, but the mechanisms of how Klotho affects phosphate homeostasis is unknown. We detected Klotho in the proximal tubule cell, brush border, and urinary lumen, where phosphate homeostasis resides. Increasing Klotho in the kidney and urine chronically by transgenic overexpression or acutely by intravenous infusion caused hypophosphatemia, phosphaturia from decreased proximal phosphate reabsorption, and decreased activity and protein of the principal renal phosphate transporter NaPi-2a. The phosphaturic effect was present in FGF23-null mice, indicating a direct action distinct from Klotho's known role as a coreceptor for FGF23. Direct inhibition of NaPi-2a by Klotho was confirmed in cultured cells and in cell-free membrane vesicles characterized by acute inhibition of transport activity followed by decreased cell surface protein. Transport inhibition can be mimicked by recombinant beta-glucuronidase and is associated with proteolytic degradation and reduced surface NaPi-2a. The inhibitory effect of Klotho on NaPi-2a was blocked by beta-glucuronidase inhibitor but not by protease inhibitor. Klotho is a novel phosphaturic substance that acts as an enzyme in the proximal tubule urinary lumen by modifying glycans, which cause decreased transporter activity, followed by proteolytic degradation and possibly internalization of NaPi-2a from the apical membrane.

Association of KLOTHO gene polymorphisms with knee osteoarthritis in Greek population

Based on the fact that klotho-deficient mice exhibit multiple aging phenotypes, including osteopenia and subchondral sclerosis of joints and on the recent observation that KLOTHO gene plays an important role in calcium/phosphate homeostasis, we explored the possibility whether human KLOTHO gene polymorphisms are associated with osteoarthritis (OA). A total of 752 individuals participated in the study. The knee OA group consisted of 369 patients; 298 women (mean age 65.9 +/- 8.2; range 40-92 years) and 71 men (mean age 65.7 +/- 9.1; range 30-82 years). The control population consisted of 383 subjects; 231 women (mean age 65.8 +/- 8.4; range 35-90 years) and 152 men (mean age 61.5 +/- 9.3; range 28-87 years). Four SNPs--G395A in the promoter region, G1110C in exon 2, C1818T and C2298T in exon 4--were genotyped. A significant genotypic and allelic association was observed in SNP C2998T and knee OA, while genotype GA of SNP G395A was significantly associated (p = 0.039) with knee OA in females only. For the first time, an association was observed between SNPs G395A and C2998T of the KLOTHO gene and knee osteoarthritis implicating KLOTHO in OA pathogenesis.

How fibroblast growth factor 23 works

There is a discontinuum of hereditary and acquired disorders of phosphate homeostasis that are caused by either high or low circulating levels of the novel phosphaturic hormone fibroblastic growth factor 23 (FGF23). Disorders that are caused by high circulating levels of FGF23 are characterized by hypophosphatemia, decreased production of 1,25-dihydroxyvitamin D, and rickets/osteomalacia. On the other end of the spectrum are disorders that are caused by low circulating levels of FGF23, which are characterized by hyperphosphatemia, elevated production of 1,25-dihydroxyvitamin D, soft tissue calcifications, and hyperostosis. Knowledge of the genetic basis of these hereditary disorders of phosphate homeostasis and studies of their mouse homologues have uncovered a bone-kidney axis and new systems biology that govern bone mineralization, vitamin D metabolism, parathyroid gland function, and renal phosphate handling. Further understanding of this primary phosphate homeostatic pathway has the potential to have a significant impact on the diagnosis and treatment of disorders of bone and mineral metabolism.