Activation of SIRT1 Attenuates Klotho Deficiency-Induced Arterial Stiffness and Hypertension by Enhancing AMP-Activated Protein Kinase Activity

Effect of Salt Intervention on Serum Levels of Fibroblast Growth Factor 23 (FGF23) in Chinese Adults: An Intervention Study

Background

Fibroblast growth factor 23 (FGF23), a prominent regulator of phosphate and calcium metabolism, regulates sodium excretion in distal tubules through sodium-chloride cotransporter. This effect regulates blood pressure. Salt intake exerts effects on serum levels of FGF23 in mice. The aim of this study was to explore whether salt intervention affects serum concentrations of FGF23 in Chinese adults.

Material/Methods

We enrolled 44 participants from Lantian, a rural community of Shaanxi, China. All participants were maintained on a three-day normal diet, which was sequentially followed by a seven-day low-Na⁺ diet and seven-day high-Na⁺ diet. Serum FGF23 concentrations were assessed by ELISA.

Results

Serum FGF23 concentrations elevated during low-salt diet compared with levels at baseline (66.20±44.21 pg/mL versus 86.77±53.74 pg/mL, p<0.05) and remarkably decreased when changed from low to high salt intake (86.77±53.74 pg/mL versus 49.26±42.67 pg/mL, p<0.001). Responses of FGF23 to salt intervention were more prominent in normotensive, older than 60 years, BMI <24 kg/m² and salt-resistant individuals. Furthermore, a significant inverse correlation was observed between 24-hour urinary sodium and serum concentrations of FGF23 after adjusting age, sex, BMI and hypertension status.

Conclusions

Dietary salt intervention significantly affects serum FGF23 in Chinese adults.

Relationship between Serum Soluble Klotho Protein and Coronary Artery Calcification and Prognosis in Patients on Maintenance Hemodialysis

BACKGROUND

We aimed to investigate the relationship between serum soluble Klotho protein (sKlotho) level and coronary artery calcification (CAC) as well as prognosis in patients with maintenance hemodialysis (MHD).

METHODS

Overall, 128 adult patients with end-stage renal failure treated with MHD were collected in the Second Affiliated Hospital & Yuying Children's Hospital of Wenzhou Medical University, Zhejiang Province, China in 2013. Serum sKlotho was detected by ELISA and coronary artery calcification was measured by multi-slice spiral computed tomography (MSCT). With 36 months' follow-up, death notes such as cause of death and death time were recorded.

RESULTS

Patients were divided into low sKlotho group and high sKlotho group. Age, blood phosphorus level, hypertension incidence and incidence of diabetes mellitus of the patients in low sKlotho group was significantly higher than that of high sKlotho group (P<0.05). The coronary artery calcification score (CACs) of patients in high sKlotho group was significantly lower than that of low sKlotho group (P<0.001). Logistic regression showed that the decrease of sKlotho level (P<0.001) was an independent risk factor for CAC progression. The mortality of the patients in low sKlotho group was higher than that of high sKlotho group. Kaplan-Meier survival curve had shown that survival time of the patients in low sKlotho group was significantly lower than that of high sKlotho group (P<0.05).

CONCLUSION

SKlotho can increase the degree of CAC. Although MHD patients with low sKlotho level had shorter survival time, sKlotho is not an independent risk factor in prediction of prognosis of MHD patients.

Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults

Nicotinamide adenine dinucleotide (NAD+) has emerged as a critical co-substrate for enzymes involved in the beneficial effects of regular calorie restriction on healthspan. As such, the use of NAD+ precursors to augment NAD+ bioavailability has been proposed as a strategy for improving cardiovascular and other physiological functions with aging in humans. Here we provide the evidence in a 2 × 6-week randomized, double-blind, placebo-controlled, crossover clinical trial that chronic supplementation with the NAD+ precursor vitamin, nicotinamide riboside (NR), is well tolerated and effectively stimulates NAD+ metabolism in healthy middle-aged and older adults. Our results also provide initial insight into the effects of chronic NR supplementation on physiological function in humans, and suggest that, in particular, future clinical trials should further assess the potential benefits of NR for reducing blood pressure and arterial stiffness in this group.

Secreted Klotho Attenuates Inflammation-Associated Aortic Valve Fibrosis in Senescence-Accelerated Mice P1

Senescence-accelerated mice P1 (SAMP1) is an aging model characterized by shortened lifespan and early signs of senescence. Klotho is an aging-suppressor gene. The purpose of this study is to investigate whether in vivo expression of secreted klotho (Skl) gene attenuates aortic valve fibrosis in SAMP1 mice. SAMP1 mice and age-matched (AKR/J) control mice were used. SAMP1 mice developed obvious fibrosis in aortic valves, namely fibrotic aortic valve disease. Serum level of Skl was decreased drastically in SAMP1 mice. Expression of MCP-1 (monocyte chemoattractant protein 1), ICAM-1 (intercellular adhesion molecule 1), F4/80, and CD68 was increased in aortic valves of SAMP1 mice, indicating inflammation. An increase in expression of α-smooth muscle actin (myofibroblast marker), transforming growth factorβ-1, and scleraxis (a transcription factor of collagen synthesis) was also found in aortic valves of SAMP1 mice, suggesting that accelerated aging is associated with myofibroblast transition and collagen gene activation. We constructed adeno-associated virus 2 carrying mouse Skl cDNA for in vivo expression of Skl. Skl gene delivery effectively increased serum Skl of SAMP1 mice to the control level. Skl gene delivery inhibited inflammation and myofibroblastic transition in aortic valves and attenuated fibrotic aortic valve disease in SAMP1 mice. It is concluded that senescence-related fibrotic aortic valve disease in SAMP1 mice is associated with a decrease in serum klotho leading to inflammation, including macrophage infiltration and transforming growth factorβ-1/scleraxis-driven myofibroblast differentiation in aortic valves. Restoration of serum Skl levels by adeno-associated virus 2 carrying mouse Skl cDNA effectively suppresses inflammation and myofibroblastic transition and attenuates aortic valve fibrosis. Skl may be a potential therapeutic target for fibrotic aortic valve disease.

Vascular Senescence in Cardiovascular and Metabolic Diseases

In mammals, aging is associated with accumulation of senescent cells. Stresses such as telomere shortening and reactive oxygen species induce “cellular senescence”, which is characterized by growth arrest and alteration of the gene expression profile. Chronological aging is associated with development of age-related diseases, including heart failure, diabetes, and atherosclerotic disease, and studies have shown that accumulation of senescent cells has a causative role in the pathology of these age-related disorders. Endothelial cell senescence has been reported to develop in heart failure and promotes pathologic changes in the failing heart. Senescent endothelial cells and vascular smooth muscle cells are found in atherosclerotic plaque, and studies indicate that these cells are involved in progression of plaque. Diabetes is also linked to accumulation of senescent vascular endothelial cells, while endothelial cell senescence per se induces systemic glucose intolerance by inhibiting skeletal muscle metabolism. A close connection between derangement of systemic metabolism and cellular senescence is also well recognized. Aging is a complex phenomenon, and there is no simple approach to understanding the whole process. However, there is accumulating evidence that cellular senescence has a central role in the development and progression of various undesirable aspects of aging. Suppression of cellular senescence or elimination of senescent cells reverses phenotypic changes of aging in several models, and proof-of-concept has been established that inhibiting accumulation of senescent cells could become a next generation therapy for age-related disorders. It is clear that cellular senescence drives various pathological changes associated with aging. Accordingly, further investigation into the role of this biological process in age-related disorders and discovery of senolytic compounds are important fields for future exploration.

Effects of Klotho on fibrosis and cancer: A renal focus on mechanisms and therapeutic strategies

Klotho is a membrane-bound protein predominantly expressed in the kidney, where it acts as a permissive co-receptor for Fibroblast Growth Factor 23. In its shed form, Klotho exerts anti-fibrotic effects in several tissues. Klotho-deficient mice spontaneously develop fibrosis and Klotho deficiency exacerbates the disease progression in fibrotic animal models. Furthermore, Klotho overexpression or supplementation protects against fibrosis in various models of renal and cardiac fibrotic disease. These effects are mediated at least partially by the direct inhibitory effects of soluble Klotho on TGFβ1 signaling, Wnt signaling, and FGF2 signaling. Soluble Klotho, as present in the circulation, appears to be the primary mediator of anti-fibrotic effects. Similarly, through inhibition of the TGFβ1, Wnt, FGF2, and IGF1 signaling pathways, Klotho also inhibits tumorigenesis. The Klotho promoter gene is generally hypermethylated in cancer, and overexpression or supplementation of Klotho has been found to inhibit tumor growth in various animal models. This review focuses on the protective effects of soluble Klotho in inhibiting renal fibrosis and fibrosis in distant organs secondary to renal Klotho deficiency. We also discuss the structure-function relationships of Klotho domains and biological effects in the context of potential targeted treatment strategies.

The anti-aging protein Klotho is induced by GABA therapy and exerts protective and stimulatory effects on pancreatic beta cells

Systemic gamma-aminobutyric acid (GABA) therapy prevents or ameliorates type 1 diabetes (T1D), by suppressing autoimmune responses and stimulating pancreatic beta cells. In beta cells, it increases insulin secretion, prevents apoptosis, and induces regeneration. It is unclear how GABA mediates these effects. We hypothesized that Klotho is involved. It is a multi-functional protein expressed in the kidneys, brain, pancreatic beta cells, other tissues, and is cell-bound or soluble. Klotho knockout mice display accelerated aging, and in humans Klotho circulating levels decline with age, renal disease and diabetes. Here, we report that GABA markedly increased circulating levels of Klotho in streptozotocin (STZ)-induced diabetes. GABA also increased Klotho in the islet of Langerhans of normal mice, as well as the islets and kidneys of STZ-treated mice. In vitro, GABA stimulated production and secretion of Klotho by human islet cells. Knockdown (KD) of Klotho with siRNA in INS-1E insulinoma cells abrogated the protective effects of GABA against STZ toxicity. Following KD, soluble Klotho reversed the effects of Klotho deficiency. In human islet cells soluble Klotho protected against cell death, and stimulated proliferation and insulin secretion. NF-κB activation triggers beta-cell apoptosis, and both GABA and Klotho suppress this pathway. We found Klotho KD augmented NF-κB p65 expression, and abrogated the ability of GABA to block NF-κB activation. This is the first report that GABAergic stimulation increases Klotho expression. Klotho protected and stimulated beta cells and lack of Klotho (KD) was reversed by soluble Klotho. These findings have important implications for the treatment of T1D.

Eicosapentaenoic acid prevents arterial calcification in klotho mutant mice

BACKGROUND

The klotho gene was identified as an "aging-suppressor" gene that accelerates arterial calcification when disrupted. Serum and vascular klotho levels are reduced in patients with chronic kidney disease, and the reduced levels are associated with arterial calcification. Intake of eicosapentaenoic acid (EPA), an n-3 fatty acid, reduces the risk of fatal coronary artery disease. However, the effects of EPA on arterial calcification have not been fully elucidated. The aim of this study was to determine the effect of EPA on arterial calcification in klotho mutant mice.

METHODS AND RESULTS

Four-week-old klotho mutant mice and wild-type (WT) mice were given a diet containing 5% EPA (EPA food, klotho and WT: n = 12, each) or not containing EPA (control food, klotho and WT: n = 12, each) for 4 weeks. Calcium volume scores of thoracic and abdominal aortas assessed by computed tomography were significantly elevated in klotho mice after 4 weeks of control food, but they were not elevated in klotho mice after EPA food or in WT mice. Serum levels of EPA and resolvin E1, an active metabolite of EPA, in EPA food-fed mice were significantly increased compared to those in control food-fed mice. An oxidative stress PCR array followed by quantitative PCR revealed that NADPH oxidase-4 (NOX4), an enzyme that generates superoxide, gene expression was up-regulated in arterial smooth muscle cells (SMCs) of klotho mice. Activity of NOX was also significantly higher in SMCs of klotho mice than in those of WT mice. EPA decreased expression levels of the NOX4 gene and NOX activity. GPR120, a receptor of n-3 fatty acids, gene knockdown by siRNA canceled effects of EPA on NOX4 gene expression and NOX activity in arterial SMCs of klotho mice.

CONCLUSIONS

EPA prevents arterial calcification together with reduction of NOX gene expression and activity via GPR120 in klotho mutant mice.

Regulation of S-formylglutathione hydrolase by the anti-aging gene klotho

Klotho is an aging-suppressor gene. The purpose of this study is to investigate the binding sites (receptors) and function of short-form Klotho (Skl). We showed that Skl physically bound to multiple proteins. We found physical and functional interactions between Skl and S-formylglutathione hydrolase (FGH), a key enzyme in the generation of the major cellular anti-oxidant GSH, using co-immunoprecipitation-coupled mass spectrometry. We further confirmed the colocalization of Skl and FGH around the nucleus in kidney cells using immunofluorescent staining. Skl positively regulated FGH gene expression via Kid3 transcription factor. Overexpression of Skl increased FGH mRNA and protein expression while silencing of Skl attenuated FGH mRNA and protein expression. Klotho gene mutation suppressed FGH expression in red blood cells and kidneys resulting in anemia and kidney damage in mice. Overexpression of Skl increased total GSH production and the GSH/GSSG ratio, an index of anti-oxidant capacity, leading to a decrease in intracellular H₂O₂ and superoxide levels. The antioxidant activity of Skl was eliminated by silencing of FGH, indicating that Skl increased GSH via FGH. Interestingly, Skl directly interacted with FGH and regulated its function. Site-directed mutagenesis of the N-glycan-modified residues in Skl abolished its antioxidant activity, suggesting that these N-glycan moieties are important features that interact with FGH. Specific mutation of Asp to Ala at site 285 resulted in a loss of anti-oxidant activity of Skl, suggesting that N-glycosylation at site 285 is the key mechanism that determines Skl activity. Therefore, this study demonstrates, for the first time, that Skl regulates anti-oxidant GSH generation via interaction with FGH through N-glycosylation.

Vascular ageing: Underlying mechanisms and clinical implications

Epidemiological studies have shown that ageing is a major non-reversible risk factor for cardiovascular disease. Vascular ageing starts early in life and is characterized by a gradual change of vascular structure and function resulting in increased arterial stiffening. At the present review we discuss the role of the most important molecular pathways involved in vascular ageing, their association with arterial stiffening and possible novel therapeutic targets that may delay this otherwise irreversible degenerating process. Specifically, we discuss the role of oxidative stress, telomere shortening, and ubiquitin proteasome system in endothelial cell senescence and dysfunction in vascular inflammation and in arterial stiffening. Further, we summarize the most important molecular mechanisms regulating vascular ageing including sirtuin 1, telomerase, klotho, JunD, and amyloid beta 1-40 peptide.

Reduced body weight gain in ubiquilin-1 transgenic mice is associated with increased expression of energy-sensing proteins

Ubiquilin-1 (Ubqln1), a ubiquitin-like protein, is implicated in a variety of pathophysiological processes, but its role in mediating body weight gain or metabolism has not been determined. Here, we demonstrate that global overexpression of Ubqln1 in a transgenic (Tg) mouse reduces the animal's body weight gain. The decreased body weight gain in Tg mice is associated with lower visceral fat content and higher metabolic rate. The Ubqln1 Tg mice exhibited reduced leptin and insulin levels as well as increased insulin sensitivity manifested by homeostatic model assessment of insulin resistance. Additionally, the reduced body weight in Tg mice was associated with the upregulation of two energy-sensing proteins, sirtuin1 (SIRT1) in the hypothalamus and AMP-activated protein kinase (AMPK) in the skeletal muscle. Consistent with the in vivo results, overexpression of Ubqln1 significantly increased SIRT1 and AMPK levels in the mouse embryonic fibroblast cell culture. Thus, our results not only establish the link between Ubqln1 and body weight regulation but also indicate that the metabolic function of Ubqln1 on body weight may be through regulating energy-sensing proteins.