Klotho, stem cells, and aging

Moderate aerobic exercise training decreases middle-aged induced pathologic cardiac hypertrophy by improving Klotho expression, MAPK signaling pathway, and oxidative stress status in Wistar rats

OBJECTIVES

This study aimed to investigate the effect of aerobic training on serum levels of Klotho, cardiac tissue levels of H₂O₂ and phosphorylation of ERK1/2 and P38 as well as left ventricular internal diameter (LVID), the left ventricle wall thickness (LVWT) and fibrosis in middle-aged rats.

MATERIALS AND METHODS

Forty wistar rats, including young rats (n=10, 4 month-old) and middle-aged rats (n=30, 13-15 months-old) were enrolled in this experimental study. The all young and 10 middle-aged rats were sacrificed (randomly) under deep anesthesia without any exercise training as normal young control and normal middle-aged control respectively. The remaining 20 middle-aged rats participated in 4 (n=10) or 8-week (n=10) aerobic exercise training.

RESULTS

There were significant differences in the plasmatic Klotho levels and the heart tissue levels of phosphorylated-ERK1/2 (p-ERK1/2), P-P38 and H₂O₂, LVWT, LVID and fibrosis between young and middle-aged rats (P=0.01). Plasmatic Klotho level was significantly increased after eight weeks training (P=0.011). Also, p-ERK1/2 was significantly decreased after eight weeks and p-P38 was significantly decreased in the fourth (P=0.01) and eight weeks of training (P=0.01). A similar decrease was reported for aging-induced H₂O₂ in the fourth (P=0.016) and eighth weeks (P=0.001). LVID was significantly increased in eight weeks, but LVWT and fibrosis was significantly reduced in the eighth week (P=0.011, P=0.028, P=0.001 respectively).

CONCLUSION

Moderate aerobic training attenuates aging-induced pathological cardiac hypertrophy at least partially by restoring the Klotho levels, attenuating oxidative stress, and reduction in the phosphorylation of ERK1/2, P38 and fibrosis.

Wnt signaling in bone, kidney, intestine, and adipose tissue and interorgan interaction in aging

Over the last two decades, it has become increasingly apparent that Wnt signaling plays a critical role in development and adult tissue homeostasis in multiple organs and in the pathogenesis of many diseases. In particular, a crucial role for Wnt signaling in bone development and bone tissue homeostasis has been well recognized. Numerous genome-wide association studies confirmed the importance of Wnt signaling in controlling bone mass. Moreover, ample evidence suggests that Wnt signaling is essential for kidney, intestine, and adipose tissue development and homeostasis. Recent emerging evidence demonstrates that Wnt signaling may play a fundamental role in the aging process of those organs. New discoveries show that bone is not only the major reservoir for calcium and phosphate storage, but also the largest organ with multiple functions, including mineral and energy metabolism. The interactions among bone, kidney, intestine, and adipose tissue are controlled and regulated by several endocrine signals, including FGF23, klotho, sclerostin, osteocalcin, vitamin D, and leptin. Since the aging process is characterized by structural and functional decline in almost all tissues and organs, understanding the Wnt signaling-related interactions among bone, kidney, intestine, and adipose tissue in aging may shed light on the pathogenesis of age-related diseases.

Klotho expression is a prerequisite for proper muscle stem cell function and regeneration of skeletal muscle

BACKGROUND

Klotho is a well-known anti-aging hormone, which serves as a suppressor of aging through a variety of mechanisms. Aging of skeletal muscle is concomitant with a decrease in muscle stem cell function resulting in impaired regeneration.

METHODS

Here we investigate the functional role of the anti-aging hormone Klotho for muscle stem cell function after cardiotoxin-induced injury of skeletal muscle using a klotho hypomorphic mouse line, which is characterized by a premature aging phenotype. Furthermore, we perform floating single myofiber cultures with their adjacent muscle stem cells to investigate the interplay between canonical Wnt signaling and Klotho function.

RESULTS

We demonstrate that muscle stem cell numbers are significantly decreased in klotho hypomorphic mice. Furthermore, we show that muscle stem cell function is also severely impaired upon loss of klotho expression, in culture and during regeneration in vivo. Moreover, we demonstrate that addition of recombinant Klotho protein inhibits aberrant excessive Wnt signaling in aged muscle stem cells thereby restoring their functionality.

CONCLUSIONS

The anti-aging hormone Klotho counteracts aberrant canonical Wnt signaling in muscle stem cells and might be one of the naturally occurring inhibitors of canonical Wnt signaling in skeletal muscle.

Klotho preservation by Rhein promotes toll-like receptor 4 proteolysis and attenuates lipopolysaccharide-induced acute kidney injury

Renal anti-aging protein Klotho exhibits impressive properties of anti-inflammation and renal protection, however is suppressed early after renal injury, making Klotho restoration an attractive strategy of treating renal inflammatory disorders. Here, we reported that Klotho is enriched in macrophages and Klotho preservation by Rhein, an anthraquinone derived from medicinal plant rhubarb, attenuates lipopolysaccharide (LPS)-induced acute inflammation essentially via promoting toll-like receptor 4 (TLR4) degradation. LPS-induced pro-inflammatory NF-κB signaling and cytokine expressions coincided with Klotho repression and toll-like receptor 4 (TLR4) elevation in macrophages, renal epithelial cells, and acutely- inflamed kidney. Intriguingly, Rhein treatment effectively corrected the inverted alterations of Klotho and TLR4 and mitigated the TLR4 downstream inflammatory response in a Klotho restoration and TLR4 repression-dependent manner. Klotho inducibly associated with TLR4 after LPS stimulation and suppressed TLR4 protein abundance mainly via a proteolytic process sensitive to the inhibition of Klotho's putative β-glucuronidase activity. Consistently, Klotho knockdown by RNA interferences largely diminished the anti-inflammatory and renal protective effects of Rhein in a mouse model of acute kidney injury incurred by LPS. Thus, Klotho suppression of TLR4 via deglycosylation negatively controls TLR-associated inflammatory signaling and the endogenous Klotho preservation by Rhein or possibly other natural or synthetic compounds possesses promising potentials in the clinical treatment of renal inflammatory disorders.

KEY MESSAGES

• Klotho is highly expressed in macrophages and repressed by LPS in vitro and in vivo. • Klotho inhibits LPS-induced TLR4 accumulation and the downstream signaling. • Klotho decreases TLR4 via a deglycosylation-associated proteolytic process. • Rhein effectively prevents acute inflammation-incurred Klotho suppression. • Rhein reversal of Klotho attenuates LPS-induced acute inflammation and kidney injury.

Alpha-Klotho Enrichment in Induced Pluripotent Stem Cell Secretome Contributes to Antioxidative Protection in Acute Lung Injury

Induced pluripotent stem cells (iPSCs) have been reported to alleviate organ injury, although the mechanisms of action remain unclear and administration of intact cells faces many limitations. We hypothesized that cell-free conditioned media (CM) containing the secretome of iPSCs possess antioxidative constituents that can alleviate pulmonary oxidant stress damage. We derived iPSCs from human dermal fibroblasts and harvested the CM. Addition of iPSC CM to cultured human alveolar type-1 epithelial cells mitigated hyperoxia-induced depletion of endogenous total antioxidant capacity while tracheal instillation of iPSC CM into adult rat lungs enhanced hyperoxia-induced increase in TAC. In both the in vitro and in vivo models, iPSC CM ameliorated oxidative damage to DNA, lipid, and protein, and activated the nuclear factor (erythroid 2)-related factor 2 (Nrf2) network of endogenous antioxidant proteins. Compared with control fibroblast-conditioned or cell-free media, iPSC CM is highly enriched with αKlotho at a concentration up to more than 10-fold of that in normal serum. αKlotho is an essential antioxidative cell maintenance and protective factor and an activator of the Nrf2 network. Immunodepletion of αKlotho reduced iPSC CM-mediated cytoprotection by ∼50%. Thus, the abundant αKlotho content significantly contributes to iPSC-mediated antioxidation and cytoprotection. Results uncover a major mechanism of iPSC action, suggest a fundamental role of αKlotho in iPSC maintenance, and support the translational potential of airway delivery of cell-free iPSC secretome for protection against lung injury. The targeted cell-free secretome-based approach may also be applicable to the amelioration of injury in other organs. Stem Cells 2018;36:616-625.

The age-related changes of dietary phosphate responsiveness in plasma 1,25-dihydroxyvitamin D levels and renal Cyp27b1 and Cyp24a1 gene expression is associated with renal α-Klotho gene expression in mice

In this study, we investigated the relationship between age-related changes in renal α-Klotho gene expression, vitamin D metabolism and the responsiveness of dietary phosphate in 1, 2 and 13 month-old mice fed a high phosphate (phosphate 1.2%) diet or low phosphate (phosphate 0.02%) diet for 5 days. We found that 1,25-dihydroxyvitamin D levels in plasma were significantly lower in the high phosphate group than the low phosphate group for 1 and 2 month-old mice, but not 13 month-old mice. In addition, in the high phosphate group plasma 1,25-dihydroxyvitamin D levels were decreased in 2 month-old mice relative to 1 month-old mice, but 13 month-old mice had higher levels than 2 month-old mice. In fact, plasma 1,25-dihydroxyvitamin D levels showed a significant correlation with vitamin D metabolism gene Cyp27b1 and Cyp24a1 mRNA expression in the high phosphate group. Interestingly, renal α-Klotho mRNA and protein levels were significant change with age. Furthermore, α-Klotho mRNA expression showed a significant negative correlation with plasma 1,25-dihydroxyvitamin D levels in the high phosphate group. Our results suggest that age-related alterations in renal α-Klotho expression could affect the responsiveness of dietary phosphate to vitamin D metabolism.

Biological effects of dosing aerobic exercise and neuromuscular electrical stimulation in rats

Aerobic exercise (AE) and non-aerobic neuromuscular electric stimulation (NMES) are common interventions used in physical therapy. We explored the dose-dependency (low, medium, high) of these interventions on biochemical factors, such as brain derived neurotrophic growth factor (BDNF), vascular endothelial growth factor-A (VEGF-A), insulin-like growth factor-1 (IGF-1) and Klotho, in the blood and brain of normal rats, as well as a treadmill-based maximum capacity test (MCT). A medium dose of AE produced the most improvement in MCT with dose-dependent changes in Klotho in the blood. A dose-dependent increase of BDNF was evident following completion of an NMES protocol, but there was no improvement in MCT performance. Gene expression in the hippocampus was increased after both AE and NMES, with IGF-1 being a signaling molecule that correlated with MCT performance in the AE conditions, but also highly correlated with VEGF-A and Klotho. Blood Klotho levels can serve as a biomarker of therapeutic dosing of AE, whereas IGF-1 is a key molecule coupled to gene expression of other molecules in the hippocampus. This approach provides a translatable paradigm to investigate the mode and mechanism of action of interventions employed in physical therapy that can improve our understanding of how these factors change under pathological conditions.

Acute lung injury complicating acute kidney injury: A model of endogenous αKlotho deficiency and distant organ dysfunction

The lung interfaces with atmospheric oxygen via a large surface area and is perfused by the entire venous return bearing waste products collected from the whole body. It is logical that the lung is endowed with generous anti-oxidative capacity derived both locally and from the circulation. The single-pass pleiotropic alpha-Klotho (αKlotho) protein was discovered when its genetic disruption led to premature multi-organ degeneration and early death. The extracellular domain of αKlotho is cleaved by secretases and released into circulation as endocrine soluble αKlotho protein, exerting wide-ranging cytoprotective effects including anti-oxidation on distant organs including the lung, which exhibits high sensitivity to circulating αKlotho insufficiency. Because circulating αKlotho is derived mainly from the kidney, acute kidney injury (AKI) leads to systemic αKlotho deficiency that in turn increases the risks of pulmonary complications, i.e., edema and inflammation, culminating in the acute respiratory distress syndrome. Exogenous αKlotho increases endogenous anti-oxidative capacity partly via activation of the Nrf2 pathway to protect lungs against injury caused by direct hyperoxia exposure or AKI. This article reviews the current knowledge of αKlotho antioxidation in the lung in the setting of AKI as a model of circulating αKlotho deficiency, an under-recognized condition that weakens innate cytoprotective defenses and contributes to the dysfunction in distant organs.

Recombinant α-Klotho may be prophylactic and therapeutic for acute to chronic kidney disease progression and uremic cardiomyopathy

α-Klotho is highly expressed in the kidney, and its extracellular domain is cleaved and released into the circulation. Chronic kidney disease (CKD) is a state of α-Klotho deficiency, which exerts multiple negative systemic effects on numerous organs including the cardiovascular system. Since acute kidney injury (AKI) greatly escalates the risk of CKD development, we explored the effect of α-Klotho on prevention and treatment on post-AKI to CKD progression and cardiovascular disease. Therein, ischemia reperfusion injury-induced AKI was followed by early administration of recombinant α-Klotho or vehicle starting one day and continued for four days after kidney injury (CKD prevention protocol). A CKD model was generated by unilateral nephrectomy plus contralateral ischemia reperfusion injury. Late administration of α-Klotho in this model was started four weeks after injury and sustained for 12 weeks (CKD treatment protocol). The prevention protocol precluded AKI to CKD progression and protected the heart from cardiac remodeling in the post-AKI model. One important effect of exogenous α-Klotho therapy was the restoration of endogenous α-Klotho levels long after the cessation of exogenous α-Klotho therapy. The treatment protocol still effectively improved renal function and attenuated cardiac remodeling in CKD, although these parameters did not completely return to normal. In addition, α-Klotho administration also attenuated high phosphate diet-induced renal and cardiac fibrosis, and improved renal and cardiac function in the absence of pre-existing renal disease. Thus, recombinant α-Klotho protein is safe and efficacious, and might be a promising prophylactic or therapeutic option for prevention or retardation of AKI-to-CKD progression and uremic cardiomyopathy.

The effects of aerobic and anaerobic exercises on circulating soluble-Klotho and IGF-I in young and elderly adults and in CAD patients

Different studies support the notion that chronic aerobic exercises training can influence the circulating levels of soluble-Klotho (s-Klotho) and insulin-like growth factor 1 (IGF-I). The effects of s-Klotho include improving the quality of life, alleviating the negative impact of age on the body's work capacity, and possibly increasing longevity. This review provides an overview of the latest findings in this field of research in humans. The different modes of dynamic exercise and their impact on circulating levels of s-Klotho and IGF-I in young adult athletes, untrained young adults, trained healthy older adults, untrained healthy older adults, and coronary artery disease (CAD) patients are reviewed and discussed. Together these findings suggest that long-lasting (chronic) aerobic exercise training is probably one of the antiaging factors that counteract the aging and CAD process by increasing the circulating s-Klotho and lowering the IGF-I levels. However, following anaerobic exercise training the opposite occurs. The exact metabolic and physiological pathways involved in the activity of these well-trained young and master sportsmen should be further studied and elucidated. The purpose of this review was to provide a clarification regarding the roles of s-Klotho and intensities and durations of different exercise on human health.

Renal Aging: Causes and Consequences

Individuals age >65 years old are the fastest expanding population demographic throughout the developed world. Consequently, more aged patients than before are receiving diagnoses of impaired renal function and nephrosclerosis-age-associated histologic changes in the kidneys. Recent studies have shown that the aged kidney undergoes a range of structural changes and has altered transcriptomic, hemodynamic, and physiologic behavior at rest and in response to renal insults. These changes impair the ability of the kidney to withstand and recover from injury, contributing to the high susceptibility of the aged population to AKI and their increased propensity to develop subsequent progressive CKD. In this review, we examine these features of the aged kidney and explore the various validated and putative pathways contributing to the changes observed with aging in both experimental animal models and humans. We also discuss the potential for additional study to increase understanding of the aged kidney and lead to novel therapeutic strategies.

αKlotho and Chronic Kidney Disease

Alpha-Klotho (αKlotho) protein is encoded by the gene, Klotho, and functions as a coreceptor for endocrine fibroblast growth factor-23. The extracellular domain of αKlotho is cleaved by secretases and released into the circulation where it is called soluble αKlotho. Soluble αKlotho in the circulation starts to decline in chronic kidney disease (CKD) stage 2 and urinary αKlotho in even earlier CKD stage 1. Therefore soluble αKlotho is an early and sensitive marker of decline in kidney function. Preclinical data from numerous animal experiments support αKlotho deficiency as a pathogenic factor for CKD progression and extrarenal CKD complications including cardiac and vascular disease, hyperparathyroidism, and disturbed mineral metabolism. αKlotho deficiency induces cell senescence and renders cells susceptible to apoptosis induced by a variety of cellular insults including oxidative stress. αKlotho deficiency also leads to defective autophagy and angiogenesis and promotes fibrosis in the kidney and heart. Most importantly, prevention of αKlotho decline, upregulation of endogenous αKlotho production, or direct supplementation of soluble αKlotho are all associated with attenuation of renal fibrosis, retardation of CKD progression, improvement of mineral metabolism, amelioration of cardiac function and morphometry, and alleviation of vascular calcification in CKD. Therefore in rodents, αKlotho is not only a diagnostic and prognostic marker for CKD but the enhancement of endogenous or supplement of exogenous αKlotho are promising therapeutic strategies to prevent, retard, and decrease the comorbidity burden of CKD.

TGF-β signaling in the kidney: profibrotic and protective effects

Transforming growth factor-β (TGF-β) is generally considered as a central mediator of fibrotic diseases. Indeed, much focus has been placed on inhibiting TGF-β and its downstream targets as ideal therapeutic strategies. However, pharmacological blockade of TGF-β has not yet translated into successful therapy for humans, which may be due to pleiotropic effects of TGF-β signaling. Equally, TGF-β signaling as a protective response in kidney injury has been relatively underexplored. An emerging body of evidence from experimental kidney disease models indicates multifunctionality of TGF-β capable of inducing profibrotic and protective effects. This review discusses recent advances highlighting the diverse roles of TGF-β in promoting not only renal fibrosis but also protective responses of TGF-β signaling. We review, in particular, growing evidence that supports protective effects of TGF-β by mechanisms which include inhibiting inflammation and induction of autophagy. Additional detailed studies are required to fully understand the diverse mechanisms of TGF-β actions in renal fibrosis and inflammation that will likely direct toward effective antifibrotic therapies.