Klotho, stem cells, and aging

The interaction between klotho protein and epigenetic alteration in diabetes and treatment options

Introduction

Klotho is a membrane protein predominantly expressed in the kidneys, and its discovery was serendipitously made through gene-targeting experiments conducted on mice. Klotho has a favorable role in the regulation of multiple cellular processes, such as aging, oxidative stress, inflammation, and apoptosis. This regulation occurs through the targeting of diverse signaling molecules, cell membrane receptors, and ion channels, achieved by physical contacts or enzymatic activities of Klotho. This review examines the role of Klotho in the epigenetic regulation of molecules associated with diabetes.

Methods

Authors conducted a thorough literature search using the PubMed®, Web of Science™, and Scopus®. Relevant articles up to September 2023, published in the English language were considered. We reviewed research databases searching for studies that included keywords klotho, epigenetic, and diabetes.

Results

14 related papers about epigenetic modification of proteins involved in diabetes pathogenesis were selected to be included in this narrative review. In the studies, the kidney was the most investigated organ regarding this correlation. Also, phosphorylation and methylation were the common epigenetic modifications of proteins by Klotho.

Conclusion

Klotho has a significant role in the maturation of adipocytes and the regulation of systemic glucose metabolism, exhibiting a strong association with the pathogenesis of diabetes. Both epigenetic alterations and the modulation of protein phosphorylation by Klotho play significant roles in the regulation of Klotho expression and the modulation of other molecules implicated in the etiology of diabetes.

Ohwia caudata aqueous extract attenuates senescence in aging adipose-derived mesenchymal stem cells

Stem cells exhibit pluripotency and self-renewal abilities. Adipose-derived mesenchymal stem cells can potentially be used to reconstruct various tissues. They possess significant versatility and alleviate various aging-related diseases. Unfortunately, aging leads to senescence, apoptosis, and a decline in regenerative capacity in adipose-derived mesenchymal stem cells. These changes necessitate a strategy to mitigate the effects of aging on stem cells. Ohwia caudata (O. caudata) has therapeutic effects against several illnesses. However, studies on whether O. caudata has therapeutic effects against aging are lacking. In this study, we aimed to identify potential therapeutic anti-aging effects in the crude aqueous extract of O. caudata on adipose-derived mesenchymal stem cells. Using 0.1 μM doxorubicin, we induced aging in human adipose-derived mesenchymal stem cells (hADMSCs) and evaluated whether various concentrations of O. caudata aqueous extract exhibit anti-aging effects on them. The O. caudata extract exhibited significant antioxidant effects on hADMSCs without any toxicity. Furthermore, after treatment with the O. caudata aqueous extract, the levels of mitochondrial superoxide, DNA double-strand breaks, and telomere shortening were reduced in the hADMSCs subjected to doxorubicin-induced aging. The extract also suppressed doxorubicin-induced aging by upregulating klotho and downregulating p21 in hADMSCs. These findings indicated that the O. caudata extract exhibited anti-aging properties that modulated hADMSC homeostasis. Therefore, it could be a potential candidate for restoring the self-renewal ability and multipotency of aging hADMSCs.

Serum klotho levels and mortality patterns in frail individuals: unraveling the u-shaped association

BACKGROUND

Frailty, a clinical syndrome intricately linked with the aging process, stands as a harbinger of numerous adverse outcomes, most notably mortality. This study aimed to elucidate the association between serum α-klotho concentration and mortality patterns, including all-cause and cause-specific mortality, in patients with frailty.

METHODS

The study employed Cox proportional hazard models, smoothed curve fitting, and supplementary analyses, encompassing threshold effect analysis, subgroup and sensitivity analyses, to explore the relationship between α-klotho levels and mortality, including all-cause, CVD, and cancer-related mortality.

RESULTS

Among the 2,608 frail individuals (mean age: 60.78 [SD 10.48] years; 59.89% female), the mortality stood at 25.35% during a median follow-up period of 6.95 years. Both unadjusted and adjusted models revealed a significant inverse association between higher serum α-klotho levels and the risk of all-cause and CVD-related mortality ([mean(95% CI) 0.68 (0.55, 0.83)] for all-cause mortality; [mean(95% CI) 0.48 (0.32, 0.74)] for CVD-related mortality, all P for trend < 0.001). Notably, log2-klotho displayed a U-shaped correlation with all-cause mortality and cancer mortality, characterized by thresholds of 9.48 and 9.55, respectively. The robustness of these findings was consistently supported by subgroup and sensitivity analyses.

CONCLUSION

This study unveils a U shaped association between serum α-klotho levels and both all-cause and cancer-related mortality among middle-aged and elderly individuals with frailty in the United States. The identified serum α-klotho thresholds, at 714.8 pg/ml for all-cause mortality and 750.6 pg/ml for cancer-related mortality, hold promise as potential targets for interventions aimed at mitigating the risks of premature death and cancer within this vulnerable population.

Bibliometric study and review of Klotho research: global characteristics and trends from 2000 to 2023

BACKGROUND

Although Klotho-related research has seen a significant upsurge, the field lacks comprehensive analytical representation and in-depth exploration of pertinent areas such as prevailing research trends and key focus areas.

METHOD

This review presents a bibliometric analysis of literature data gathered from the Web of Science Core Collection databases from January 1, 2000, to April 30, 2023. Parameters such as co-authorship, co-citation, co-occurrence, and the emergence of publications, countries, categories, references, and keywords were scrutinized predominantly using Citespace software.

RESULTS

Our investigation amassed a total of 3548 papers, with the United States leading in the quantity of publications (1175, accounting for 33.12%), followed by China (867, representing 24.44%), and Japan (439, accounting for 12.37%). While the United States is preeminent in the overall volume of publications, Scotland holds prominence in terms of centrality. Out of a total of 96 subject categories, urology and nephrology (573), and endocrinology and metabolism (542) were the two leading domains of Klotho-related publications. The 2011 paper titled "FGF23 induces left ventricular hypertrophy" by Faul C et al. holds the distinction of being the most frequently cited. The keywords "fibroblast growth factor 23," "phosphate homeostasis," and "functional variants" demonstrated the highest intensity, underscoring the potential of these research areas.

CONCLUSION

As the volume of literature grows, the role of Klotho in disease management and its applicability as a marker in disease progression warrant vigilant tracking and study.

Interorgan communication networks in the kidney-lung axis

The homeostasis and health of an organism depend on the coordinated interaction of specialized organs, which is regulated by interorgan communication networks of circulating soluble molecules and neuronal connections. Many diseases that seemingly affect one primary organ are really multiorgan diseases, with substantial secondary remote organ complications that underlie a large part of their morbidity and mortality. Acute kidney injury (AKI) frequently occurs in critically ill patients with multiorgan failure and is associated with high mortality, particularly when it occurs together with respiratory failure. Inflammatory lung lesions in patients with kidney failure that could be distinguished from pulmonary oedema due to volume overload were first reported in the 1930s, but have been largely overlooked in clinical settings. A series of studies over the past two decades have elucidated acute and chronic kidney-lung and lung-kidney interorgan communication networks involving various circulating inflammatory cytokines and chemokines, metabolites, uraemic toxins, immune cells and neuro-immune pathways. Further investigations are warranted to understand these clinical entities of high morbidity and mortality, and to develop effective treatments.

Improving sleep quality is essential for enhancing soluble Klotho levels in hemodialysis patients

PURPOSE

Sleep and Klotho seem to share common physiological pathways in aging. However, studies investigating this relationship are very few and none of them was done with a specific patient group. The aim of this study was to investigate the association of sleep quality and soluble Klotho levels in hemodialysis patients.

METHODS

100 hemodialysis patients were included in this study. Soluble Klotho levels were obtained from each patient and Pittsburgh Sleep Quality Index was performed by all patients. Association of soluble Klotho with sleep quality was calculated.

RESULTS

Soluble Klotho levels were significantly inversely correlated with total sleep quality score (p < 0.001, r = - 0.444). Among the subscales, soluble Klotho levels were negatively correlated with subjective sleep quality (p < 0.001, r = - 0.365), sleep latency (p = 0.002, r = - 0.312), sleep disturbance (p = 0.002, r = - 0.303) and daytime dysfunction (p = 0.027, r = - 0.221). Patients who had good sleep quality scores were found to have higher soluble Klotho levels [4.15 (0.05-22.68) vs. 1.14 (0.32-17.63), p < 0.001]. In regression analysis, total sleep quality score, subjective sleep quality and age were found to be independent negative factors for soluble Klotho levels.

CONCLUSION

In this study, a significant association between sleep quality and soluble Klotho levels was revealed in hemodialysis patients. Improving sleep quality will lead to increased soluble Klotho levels, which may further slow down the aging process in hemodialysis patients.

Bone Dysregulation in Acute Kidney Injury

Acute kidney injury (AKI) is a highly prevalent condition with multiple acute and chronic consequences. Survivors of AKI are at risk of AKI-to-chronic kidney disease (CKD) transition, which carries significant morbidity and mortality. One retrospective analysis showed increased risk of bone fracture post-AKI in humans, which was independent of CKD development. While there are several theoretical reasons for late disturbances of bone health post-AKI, no definitive data are available to date. An important question is whether there are bone sequelae from AKI that are independent of CKD, meaning bone disease prior to the onset, or in the absence of CKD - a form of "post-AKI osteopathy." While preclinical studies examining bone health after acute stressors have focused mostly on sepsis models, multiple experimental AKI models are readily available for longitudinal bone health interrogation. Future research should be tailored to define whether AKI is a risk factor, independent of CKD, for bone disease and if present, the time course and type of bone disease. This review summarizes a fraction of the existing data to provide some guidance in future research efforts.

A prospective study of the association between serum klotho and mortality among adults with rheumatoid arthritis in the USA

BACKGROUND

While it is known that klotho has negative regulatory effects in a variety of diseases such as metabolic disorders and kidney disease, the specific role of klotho in rheumatoid arthritis (RA) and its effect on mortality are unclear. This study investigated the association between serum klotho levels and mortality in patients with RA.

METHODS

This study included 841 adults with RA from the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2016 to extract the concentrations of serum klotho. The association between klotho and RA was determined using Cox regression, Kaplan-Meier (KM) curves, and restricted cubic spline (RCS) models.

RESULTS

A total of 841 patients with RA were included in this study, who were divided into four groups based on the quartiles of serum klotho levels (Q1, Q2, Q3, and Q4). Cox regression analysis with adjustment for covariates revealed that high levels of klotho lowered the risk of both all-cause and cardiovascular mortality compared to the Q1 group. The KM curve analysis suggested that this effect was more pronounced for all-cause mortality. The RCS-fitted Cox regression model indicated a U-shaped correlation between serum klotho levels and RA mortality. The risk of all-cause mortality increased with decreasing serum klotho levels below a threshold of 838.81 pg/mL. Subgroup analysis revealed that the protective effect of klotho was more pronounced in patients with the following characteristics: male, white ethnicity, age ≥ 60 years, body mass index < 25 kg/m2, estimated glomerular filtration rate ≥ 60 mL/ (min × 1.73 m2), and 25-hydroxyvitamin D level ≥ 50 nmol/L.

CONCLUSION

Serum klotho levels had a U-shaped correlation with all-cause mortality in patients with RA, indicating that maintain a certain level of serum klotho could prevent premature death.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

The Mission of Long Non-Coding RNAs in Human Adult Renal Stem/Progenitor Cells and Renal Diseases

Long non-coding RNAs (lncRNAs) are a large, heterogeneous class of transcripts and key regulators of gene expression at both the transcriptional and post-transcriptional levels in different cellular contexts and biological processes. Understanding the potential mechanisms of action of lncRNAs and their role in disease onset and development may open up new possibilities for therapeutic approaches in the future. LncRNAs also play an important role in renal pathogenesis. However, little is known about lncRNAs that are expressed in the healthy kidney and that are involved in renal cell homeostasis and development, and even less is known about lncRNAs involved in human adult renal stem/progenitor cells (ARPC) homeostasis. Here we give a thorough overview of the biogenesis, degradation, and functions of lncRNAs and highlight our current understanding of their functional roles in kidney diseases. We also discuss how lncRNAs regulate stem cell biology, focusing finally on their role in human adult renal stem/progenitor cells, in which the lncRNA HOTAIR prevents them from becoming senescent and supports these cells to secrete high quantities of α-Klotho, an anti-aging protein capable of influencing the surrounding tissues and therefore modulating the renal aging.

Klotho promotes AMPK activity and maintains renal vascular integrity by regulating the YAP signaling pathway

The development and formation of mammalian blood vessels are closely related to the regulation of signal transduction pathways. Klotho/AMPK and YAP/TAZ signaling pathways are closely related to angiogenesis, but the internal relationship between them is not clear. In this study, we found that Klotho heterozygous deletion mice (Klotho^+/- mice) had obvious thickening of the renal vascular wall, obvious enlargement of vascular volume, and significant proliferation and pricking of vascular endothelial cells. Western blot showed that the expression levels of total YAP protein, p-YAP protein (Ser127 and Ser397), p-MOB1, MST1, LATS1, and SAV1 in renal vascular endothelial cells were significantly lower in Klotho^+/- mice than in wild-type mice. Knockdown of endogenous Klotho in HUVECs accelerated their ability to divide and form vascular branches in the extracellular matrix. Meanwhile, the results of CO-IP western blot showed that the expression of LATS1 and p-LATS1 interacting with AMPK protein decreased significantly, and the ubiquitination level of YAP protein also decreased significantly in vascular endothelial cells of kidney tissue of Klotho^+/- mice. Subsequently, continuous overexpression of exogenous Klotho protein in Klotho heterozygous deficient mice effectively reversed the abnormal renal vascular structure by weakening the expression of the YAP signal transduction pathway. Therefore, we confirmed that Klotho and AMPKα proteins were highly expressed in vascular endothelial cells of adult mouse tissues and organs; this resulted in a phosphorylation modification of YAP protein, closed the activity of the YAP/TAZ signal transduction pathway, and inhibited the growth and proliferation of vascular endothelial cells. When Klotho was absent, the phosphorylation modification of YAP protein by AMPKα was inhibited, resulting in the activation of the YAP/TAZ signal transduction pathway and finally inducing the excessive proliferation of vascular endothelial cells.

Association between serum Klotho concentration and all-cause and cardiovascular mortality among American individuals with hypertension

BACKGROUND AND AIMS

Evidence indicates that serum Klotho concentration is associated with mortality in patients with chronic kidney disease (CKD). However, evidence on this association among people with hypertension is scarce. Therefore, we aimed to examine the association between serum Klotho concentration and all-cause and cardiovascular mortality in American patients with hypertension.

METHODS AND RESULTS

We included 6,778 participants with hypertension from the National Health and Nutrition Examination Survey (NHANES) 2007-2014. A Cox proportional hazard model was used to compute the hazard ratios (HRs) and 95% confidence intervals (CIs). The correlation between serum Klotho concentration and mortality was determined using restricted cubic spline and piecewise linear regression analyses. During 36,714 person-years of follow-up, 575 deaths were documented. Lower serum Klotho concentration was associated with increased all-cause mortality, but not cardiovascular mortality after multivariate adjustment. According to spline analysis, the correlation between serum Klotho concentration and all-cause mortality was non-linear (P < 0.001), and the threshold value was 574 pg/mL. The HR below the threshold point was 0.79 (95% CI: 0.67-0.93); no significant difference was found above the threshold point.

CONCLUSION

Higher serum Klotho concentration was associated with lower all-cause mortality, but not cardiovascular mortality in patients with hypertension with or without chronic renal impairment.

The long non-coding RNA HOTAIR controls the self-renewal, cell senescence, and secretion of antiaging protein α-Klotho in human adult renal progenitor cells

The long non-coding RNAs (lncRNA) play an important role in several biological processes including some renal diseases. Nevertheless, little is known on lncRNA that are expressed in healthy kidney and involved in renal cell homeostasis and development, and even less is known about lncRNA involved in the maintenance of human adult renal stem/progenitor cells (ARPCs) that have been shown to be very important for renal homeostasis and repair processes. Through a whole genome transcriptome screening, we found that the HOTAIR lncRNA is highly expressed in renal progenitors and potentially involved in cell cycle and senescence biological processes. By CRISPR/Cas9 genome editing, we generated HOTAIR knock-out ARPC lines and established a key role of this lncRNA in ARPC self-renewal properties by sustaining their proliferative capacity and limiting the apoptotic process. Intriguingly, the HOTAIR knock-out led to the ARPC senescence and to a significant decrease of the CD133 stem cell marker expression, that is an inverse marker of ARPC senescence and can regulate renal tubular repair after the damage. Furthermore, we found that ARPCs expressed high levels of the α-Klotho anti-aging protein and especially 2.6-fold higher levels compared to that secreted by renal proximal tubular cells (RPTECs). Finally, we showed that HOTAIR exerts its function through the epigenetic silencing of the cell cycle inhibitor p15 inducing the trimethylation of the histone H3K27. Altogether, these results shed new light on the mechanisms of regulation of these important renal cells and may support the future development of precision therapies for kidney diseases.

Pathobiology of the Klotho Antiaging Protein and Therapeutic Considerations

The α-Klotho protein (henceforth denoted Klotho) has antiaging properties, as first observed in mice homozygous for a hypomorphic Klotho gene (kl/kl). These mice have a shortened lifespan, stunted growth, renal disease, hyperphosphatemia, hypercalcemia, vascular calcification, cardiac hypertrophy, hypertension, pulmonary disease, cognitive impairment, multi-organ atrophy and fibrosis. Overexpression of Klotho has opposite effects, extending lifespan. In humans, Klotho levels decline with age, chronic kidney disease, diabetes, Alzheimer’s disease and other conditions. Low Klotho levels correlate with an increase in the death rate from all causes. Klotho acts either as an obligate coreceptor for fibroblast growth factor 23 (FGF23), or as a soluble pleiotropic endocrine hormone (s-Klotho). It is mainly produced in the kidneys, but also in the brain, pancreas and other tissues. On renal tubular-cell membranes, it associates with FGF receptors to bind FGF23. Produced in bones, FGF23 regulates renal excretion of phosphate (phosphaturic effect) and vitamin D metabolism. Lack of Klotho or FGF23 results in hyperphosphatemia and hypervitaminosis D. With age, human renal function often deteriorates, lowering Klotho levels. This appears to promote age-related pathology. Remarkably, Klotho inhibits four pathways that have been linked to aging in various ways: Transforming growth factor β (TGF-β), insulin-like growth factor 1 (IGF-1), Wnt and NF-κB. These can induce cellular senescence, apoptosis, inflammation, immune dysfunction, fibrosis and neoplasia. Furthermore, Klotho increases cell-protective antioxidant enzymes through Nrf2 and FoxO. In accord, preclinical Klotho therapy ameliorated renal, cardiovascular, diabetes-related and neurodegenerative diseases, as well as cancer. s-Klotho protein injection was effective, but requires further investigation. Several drugs enhance circulating Klotho levels, and some cross the blood-brain barrier to potentially act in the brain. In clinical trials, increased Klotho was noted with renin-angiotensin system inhibitors (losartan, valsartan), a statin (fluvastatin), mTOR inhibitors (rapamycin, everolimus), vitamin D and pentoxifylline. In preclinical work, antidiabetic drugs (metformin, GLP-1-based, GABA, PPAR-γ agonists) also enhanced Klotho. Several traditional medicines and/or nutraceuticals increased Klotho in rodents, including astaxanthin, curcumin, ginseng, ligustilide and resveratrol. Notably, exercise and sport activity increased Klotho. This review addresses molecular, physiological and therapeutic aspects of Klotho.

The Role of Alterations in Alpha-Klotho and FGF-23 in Kidney Transplantation and Kidney Donation

Cardiovascular disease and mineral bone disorders are major contributors to morbidity and mortality among patients with chronic kidney disease and often persist after renal transplantation. Ongoing hormonal imbalances after kidney transplant (KT) are associated with loss of graft function and poor outcomes. Fibroblast growth factor 23 (FGF-23) and its co-receptor, α-Klotho, are key factors in the underlying mechanisms that integrate accelerated atherosclerosis, vascular calcification, mineral disorders, and osteodystrophy. On the other hand, kidney donation is also associated with endocrine and metabolic adaptations that include transient increases in circulating FGF-23 and decreases in α-Klotho levels. However, the long-term impact of these alterations and their clinical relevance have not yet been determined. This manuscript aims to review and summarize current data on the role of FGF-23 and α-Klotho in the endocrine response to KT and living kidney donation, and importantly, underscore specific areas of research that may enhance diagnostics and therapeutics in the growing population of KT recipients and kidney donors.

References Values of Soluble α-Klotho Serum Levels Using an Enzyme-Linked Immunosorbent Assay in Healthy Adults Aged 18-85 Years

α-Klotho protein is a powerful predictor of the aging process and lifespan. Although lowered circulating soluble α-Klotho levels have been observed in aged non-healthy individuals, no specific reference values across a wide range of ages and sex using an enzyme-linked immunosorbent assay (ELISA) are available for larger cohorts of healthy individuals. The present analytical cross-sectional study was aimed to establish the reference values of soluble α-Klotho serum levels in healthy adults by age and sex groups. A total of 346 (59% women) healthy individuals aged from 18 to 85 years were recruited. Subjects were divided by sex and age as: (i) young (18−34.9 years), (ii) middle-aged (35−54.9 years), and (iii) senior (55−85 years) individuals. The soluble α-Klotho levels were measured in serum using ELISA. Senior adults were the age-group that presented the lowest soluble α-Klotho serum levels (p < 0.01), with age showing a negative association with soluble α-Klotho serum levels (p < 0.001). No differences between sexes were observed. Therefore, soluble α-Klotho levels were especially decreased—regardless of sex—in our cohort of healthy individuals because of the physiological decline derived from the aging process. We recommend routine assessments of soluble α-Klotho levels using ELISA as a simple and cheap detectable marker of aging that improves quality of life in the elderly.

Klotho and Mesenchymal Stem Cells: A Review on Cell and Gene Therapy for Chronic Kidney Disease and Acute Kidney Disease

Chronic kidney disease (CKD) and acute kidney injury (AKI) are public health problems, and their prevalence rates have increased with the aging of the population. They are associated with the presence of comorbidities, in particular diabetes mellitus and hypertension, resulting in a high financial burden for the health system. Studies have indicated Klotho as a promising therapeutic approach for these conditions. Klotho reduces inflammation, oxidative stress and fibrosis and counter-regulates the renin-angiotensin-aldosterone system. In CKD and AKI, Klotho expression is downregulated from early stages and correlates with disease progression. Therefore, the restoration of its levels, through exogenous or endogenous pathways, has renoprotective effects. An important strategy for administering Klotho is through mesenchymal stem cells (MSCs). In summary, this review comprises in vitro and in vivo studies on the therapeutic potential of Klotho for the treatment of CKD and AKI through the administration of MSCs.

Interorgan crosstalk mechanisms in disease: the case of acute kidney injury-induced remote lung injury

Homeostasis and health of multicellular organisms with multiple organs depends on interorgan communication. Tissue injury in one organ disturbs this homeostasis and can lead to disease in multiple organs, or multiorgan failure. Many routes of interorgan crosstalk during homeostasis are relatively well known, but interorgan crosstalk in disease still lacks understanding. In particular, how tissue injury in one organ can drive injury at remote sites and trigger multiorgan failure with high mortality is poorly understood. As examples, acute kidney injury can trigger acute lung injury and cardiovascular dysfunction; pneumonia, sepsis or liver failure conversely can cause kidney failure; lung transplantation very frequently triggers acute kidney injury. Mechanistically, interorgan crosstalk after tissue injury could involve soluble mediators and their target receptors, cellular mediators, in particular immune cells, as well as newly identified neuro-immune connections. In this review, I will focus the discussion of deleterious interorgan crosstalk and its mechanistic concepts on one example, acute kidney injury-induced remote lung injury.

Exploiting the neuroprotective effects of α-klotho to tackle ageing- and neurodegeneration-related cognitive dysfunction

Cognitive dysfunction is a key symptom of ageing and neurodegenerative disorders, such as Alzheimer's disease (AD). Strategies to enhance cognition would impact the quality of life for a significant proportion of the ageing population. The α-klotho protein may protect against cognitive decline through multiple mechanisms: such as promoting optimal synaptic function via activation of N-methyl-d-aspartate (NMDA) receptor signalling; stimulating the antioxidant defence system; reducing inflammation; promoting autophagy and enhancing clearance of amyloid-β. However, the molecular and cellular pathways by which α-klotho mediates these neuroprotective functions have yet to be fully elucidated. Key questions remain unanswered: which form of α-klotho (transmembrane, soluble or secreted) mediates its cognitive enhancing properties; what is the neuronal receptor for α-klotho and which signalling pathways are activated by α-klotho in the brain to enhance cognition; how does peripherally administered α-klotho mediate neuroprotection; and what is the molecular basis for the beneficial effect of the VS variant of α-klotho? In this review, we summarise the recent research on neuronal α-klotho and discuss how the neuroprotective properties of α-klotho could be exploited to tackle age- and neurodegeneration-associated cognitive dysfunction.

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

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

Constitutive Expression of TERT Enhances β-Klotho Expression and Improves Age-Related Deterioration in Early Bovine Embryos

Age-associated decline in oocyte quality is one of the dominant factors of low fertility. Aging alters several key processes, such as telomere lengthening, cell senescence, and cellular longevity of granulosa cells surrounding oocyte. To investigate the age-dependent molecular changes, we examined the expression, localization, and correlation of telomerase reverse transcriptase (TERT) and β-Klotho (KLB) in bovine granulosa cells, oocytes, and early embryos during the aging process. Herein, cumulus-oocyte complexes (COCs) obtained from aged cows (>120 months) via ovum pick-up (OPU) showed reduced expression of β-Klotho and its co-receptor fibroblast growth factor receptor 1 (FGFR1). TERT plasmid injection into pronuclear zygotes not only markedly enhanced day-8 blastocysts’ development competence (39.1 ± 0.8%) compared to the control (31.1 ± 0.5%) and D-galactose (17.9 ± 1.0%) treatment groups but also enhanced KLB and FGFR1 expression. In addition, plasmid-injected zygotes displayed a considerable enhancement in blastocyst quality and implantation potential. Cycloastragenol (CAG), an extract of saponins, stimulates telomerase enzymes and enhances KLB expression and alleviates age-related deterioration in cultured primary bovine granulosa cells. In conclusion, telomerase activation or constitutive expression will increase KLB expression and activate the FGFR1/β-Klotho pathway in bovine granulosa cells and early embryos, inhibiting age-related malfunctioning.

Bovine serum albumin aggravates macrophage M1 activation and kidney injury in heterozygous Klotho-deficient mice via the gut microbiota-immune axis

Klotho expression abnormalities induces kidney injury and chronic kidney disease, however, the underlying mechanism remains unclear. Here, Klotho^+/- mice and wild-type mice were treated with low-dose bovine serum albumin (BSA). Pathological examination demonstrated that the area of glomerular collagen deposition and fibrosis in BSA-Kl^-/+ mice was significantly larger than that in BSA-WT mice. The serum levels of superoxide dismutase, malondialdehyde, creatinine, and urea in BSA-Kl^-/+ mice were significantly increased. Sequencing of gut microbiota 16S rRNA v3-v4 region indicated that BSA-Kl^-/+ mice showed a significantly higher relative abundance of the genera Dubosiella, Akkermansia, Alloprevotella, and Lachnospiraceae and a significantly lower relative abundance of the genera Allobaculum and Muribaculaceae than BSA-WT mice. KEGG analysis revealed that the metabolic pathways of signal transduction, xenobiotic biodegradation and metabolism, and lipid metabolism increased significantly in BSA-Kl^-/+ mice. Flow cytometry showed that the proportion of CD68⁺/CD11b⁺ cells in the peripheral blood was significantly higher in BSA-KL^-/+ mice than that in BSA-WT mice. qPCR and western blot suggested that Klotho and Nrf2 expression in MΦ1 cells of BSA-KL^-/+ mice was significantly decreased. Thus, the findings suggest during the immune activation and chronic inflammation induced by the gut microbiota imbalance in Klotho-deficient mice treated to BSA, disrupted expression of proteins in the Nrf2/NF-κB signaling pathway in monocyte-derived macrophage M1 cells leads to the aggravation of inflammation and kidney injury.

The role of AMP-activated protein kinase α1-mediated endoplasmic reticulum stress in alleviating the toxic effect of uremic toxin indoxyl sulfate on vascular endothelial cells by Klotho

Recently, the Klotho protein (Klotho) has received substantial attention as protective factor against cardiovascular complications of chronic kidney disease (CKD). However, the direct effect and mechanism of Klotho on endothelial cells injury are not well-known. In this study, we incubated human vein umbilical endothelial cells (HUVECs) with uremic toxin indoxyl sulfate (IS) to mimic CKD internal environment and investigated the direct effect of Klotho on the HUVECs injury induced by IS and to explore the mechanism in this process. We found IS inhibited cell viability, increased endoplasmic reticulum stress, and mediated apoptosis of HUVECs. Treatment with Klotho significantly attenuated IS-induced above effects. Furthermore, Klotho alleviated the IS toxic effect on HUVECs via promoting AMP-activated protein kinase (AMPK) α1 phosphorylation instead of directly upregulating AMPKα1, which could be partly blocked by AMPK pathway inhibitor-Compound C. In addition, Klotho also inhibited intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression induced by IS. Altogether, these results indicated that Klotho can protect HUVECs from IS-induced injury by alleviating AMPKα1-mediated endoplasmic reticulum stress.

Antiinflammatory Actions of Klotho: Implications for Therapy of Diabetic Nephropathy

Klotho was initially introduced as an antiaging molecule. Klotho deficiency significantly reduces lifespan, and its overexpression extends it and protects against various pathological phenotypes, especially renal disease. It was shown to regulate phosphate and calcium metabolism, protect against oxidative stress, downregulate apoptosis, and have antiinflammatory and antifibrotic properties. The course of diabetes mellitus and diabetic nephropathy resembles premature cellular senescence and causes the activation of various proinflammatory and profibrotic processes. Klotho was shown to exert many beneficial effects in these disorders. The expression of Klotho protein is downregulated in early stages of inflammation and diabetic nephropathy by proinflammatory factors. Therefore, its therapeutic effects are diminished in this disorder. Significantly lower urine levels of Klotho may serve as an early biomarker of renal involvement in diabetes mellitus. Recombinant Klotho administration and Klotho overexpression may have immunotherapeutic potential for the treatment of both diabetes and diabetic nephropathy. Therefore, the current manuscript aims to characterize immunopathologies occurring in diabetes and diabetic nephropathy, and tries to match them with antiinflammatory actions of Klotho. It also gives reasons for Klotho to be used in diagnostics and immunotherapy of these disorders.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

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

Echinacoside protects adenine-induced uremic rats from sciatic nerve damage by up-regulating α-Klotho

OBJECTIVES

To investigate the therapeutic effect of Echinacoside on uremia-induced sciatic nerve injury and explore the specific molecular mechanism and role of α-Klotho.

METHODS

SD rats were given continuous gavage of adenine to prepare a uremia-induced sciatic nerve injury model. The model was given either Echinacoside or α-Klotho by gavage. Histopathological changes of kidney and sciatic nerve were detected by H&E staining. The changes of creatinine, urea nitrogen, and urine protein were detected by biochemical detection. The changes of IL-1β and IL-18 were detected by ELISA. Nerve activity-related indicators were detected by biochemical detection. Changes in related mRNA and protein expression were detected by qPCR and western blot.

RESULTS

Creatinine, urea nitrogen, urine protein, and malondialdehyde (MDA) in the model group were significantly increased and inhibited by Echinacoside and α-Klotho treatment with Echinacoside dose-dependence. Meanwhile, the activities of ATP concentration, potassium adenosine triphosphate (Na+, K+ ATPase), succinate dehydrogenase (SDH), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) showed opposite trends.

CONCLUSIONS

Echinacoside can significantly relieve uremia-induced sciatic nerve injury in rats. Its specific molecular mechanism is related to the inhibition of the classical cellular pyroptosis pathway, which is likely achieved by promoting α-Klotho expression.

Anti-Ageing Protein β-Klotho Rejuvenates Diabetic Stem Cells for Improved Gene-Activated Scaffold Based Wound Healing

Skin wounds can lead to serious morbidity complications in diabetic patients due to the reduced healing potential of autologous stem cells. One reason for the low functional potency of stem cells from diabetic patients (diabetic stem cells) is attributed to their senescent-like nature. Here, we investigated if an anti-ageing protein, β-klotho, could be used to rejuvenate diabetic stem cells and to promote pro-angiogenic gene-activated scaffold (GAS)-induced functional response for wound healing applications. Human stem cells derived from the adipose tissue (adipose-derived stem cells (ADSCs)) of normal and diabetic (type 2) donors were used for the study. We report that the β-klotho priming facilitated inflammatory signal pruning by reducing interleukin-8 release by more than half while concurrently doubling the release of monocyte chemoattractant protein-1. Additionally, β-klotho priming enhanced the pro-angiogenic response of diabetic ADSCs on GAS by dampening the release of anti-angiogenic factors (i.e., pigment epithelium-derived factor, tissue inhibitor of metalloproteinase-1 and thrombospondin-1) while simultaneously supporting the expression of pro-angiogenic factors (i.e., Vascular Endothelial Growth Factor (VEGF), angiopoietin-2 and angiogenin). Finally, we show that β-klotho pre-treatment expedites the cellular expression of matrix proteins such as collagen IV and collagen VI, which are implicated in tissue maturation. Taken together, our study provides evidence that the synergistic effect of the pro-angiogenic GAS and β-klotho activation effectively accelerates the functional development of diabetic ADSCs for wound healing applications.

Cellular Senescence in Kidney Fibrosis: Pathologic Significance and Therapeutic Strategies

Age-related disorders such as chronic kidney disease (CKD) are increasingly prevalent globally and pose unprecedented challenges. In many aspects, CKD can be viewed as a state of accelerated and premature aging. Aging kidney and CKD share many common characteristic features with increased cellular senescence, a conserved program characterized by an irreversible cell cycle arrest with altered transcriptome and secretome. While developmental senescence and acute senescence may positively contribute to the fine-tuning of embryogenesis and injury repair, chronic senescence, when unresolved promptly, plays a crucial role in kidney fibrogenesis and CKD progression. Senescent cells elicit their fibrogenic actions primarily by secreting an assortment of inflammatory and profibrotic factors known as the senescence-associated secretory phenotype (SASP). Increasing evidence indicates that senescent cells could be a promising new target for therapeutic intervention known as senotherapy, which includes depleting senescent cells, modulating SASP and restoration of senescence inhibitors. In this review, we discuss current understanding of the role and mechanism of cellular senescence in kidney fibrosis. We also highlight potential options of targeting senescent cells for the treatment of CKD.

Herb-Derived Products: Natural Tools to Delay and Counteract Stem Cell Senescence

Cellular senescence plays a very important role in organismal aging increasing with age and in age-related diseases (ARDs). This process involves physiological, structural, biochemical, and molecular changes of cells, leading to a characteristic trait referred to "senescence-associated secretory phenotype (SASP)." In particular, with aging, stem cells (SCs) in situ exhibit a diminished capacity of self-renewal and show a decline in their functionality. The identification of interventions able to prevent the accumulation of senescent SCs in the organism or to pretreat cultured multipotent mesenchymal stromal cells (MSCs) prior to employing them for cell therapy is a main purpose of medical research. Many approaches have been investigated and resulted effective to prevent or counteract SC senescence in humans, as well as other animal models. In this work, we have reviewed the chance of using a number of herb-derived products as novel tools in the treatment of cell senescence, highlighting the efficacy of these agents, often still far from being clearly understood.

Roles of klotho and stem cells in mediating vascular calcification (Review)

Vascular calcification, characterized by the active deposition of calcium phosphate in the vascular walls, is commonly observed in aging, diabetes mellitus and chronic kidney disease. This process is mediated by different cell types, including vascular stem/progenitor cells. The anti-aging protein klotho may act as an inhibitor of vascular calcification through direct effects on vascular stem/progenitor cells with osteogenic differentiation potential. A better understanding of the possible effects of klotho on vascular stem/progenitor cells may provide novel insight into the cellular and molecular mechanisms of klotho deficiency-related vascular calcification and disease. The klotho protein may be considered as a promising therapeutic agent for treating vascular calcification and disease and calcification-related vascular diseases.

Klotho overexpression improves amyloid-β clearance and cognition in the APP/PS1 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent type of dementia, characterized by the presence of amyloid-β (Aβ) plaques. We previously reported that Klotho lowered Aβ levels in the brain and protected against cognitive deficits in amyloid precursor protein/presenilin 1(APP/PS1) mice. However, the underlying mechanism remains unclear. In this study, we induced intracerebral Klotho overexpression in 13-month-old APP/PS1 mice by injecting lentivirus that carried full-length mouse Klotho cDNA in the lateral ventricle of the brain. We examined the effects of Klotho overexpression on cognition, Aβ burden, Aβ-related neuropathology, microglia transformation, and Aβ transport systems in vivo. Additionally, we investigated the effects of Klotho on Aβ transport at the blood-cerebrospinal fluid barrier by knocking down Klotho in primary human choroid plexus epithelial cells (HCPEpiCs). The upregulation of Klotho levels in the brain and serum significantly ameliorated Aβ burden, neuronal and synaptic loss and cognitive deficits in aged APP/PS1 mice. Klotho treatment significantly inhibited NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) and the subsequent transformation of microglia to the M2 type that may enhance microglia-mediated Aβ clearance. Meanwhile, Klotho overexpression also regulated Aβ transporter expression, which may promote Aβ transporter-mediated Aβ clearance. Moreover, the ability of HCPEpiCs to transport Aβ in vitro was also significantly impaired by Klotho knockdown. Given the neuroprotective effect of Klotho overexpression, the present findings suggest that Klotho should be further investigated as a potential therapeutic target for AD.

Multiple genetic programs contribute to CD4 T cell memory differentiation and longevity by maintaining T cell quiescence

While memory T-cells represent a hallmark of adaptive immunity, little is known about the genetic mechanisms regulating the longevity of memory CD4 T cells. Here, we studied the dynamics of gene expression in antigen specific CD4 T cells during infection, memory differentiation, and long-term survival up to nearly a year in mice. We observed that differentiation into long lived memory cells is associated with increased expression of genes inhibiting cell proliferation and apoptosis as well as genes promoting DNA repair response, lipid metabolism, and insulin resistance. We identified several transmembrane proteins in long-lived murine memory CD4 T cells, which co-localized exclusively within the responding antigen-specific memory CD4 T cells in human. The unique gene signatures of long-lived memory CD4 T cells, along with the new markers that we have defined, will enable a deeper understanding of memory CD4 T cell biology and allow for designing novel vaccines and therapeutics.

Is Sleep Associated with the S-Klotho Anti-Aging Protein in Sedentary Middle-Aged Adults? The FIT-AGEING Study

Sleep and Klotho have both been closely related to the ageing process, both playing a substantial role in the endocrine and immune systems and, thereby, in oxidative stress and chronic inflammation. However, there are no studies elucidating the relationship between sleep and Klotho. Therefore, this study investigated the association of sleep quantity and quality with the shed form of the α-Klotho gene (S-Klotho plasma levels) in sedentary middle-aged adults. A total of 74 volunteers (52.7% women; aged 53.7 ± 5.1) were recruited for the present study. Objective sleep quality parameters (total sleep time (TST), wake after sleep onset (WASO), and sleep efficiency (SE)) were determined using a wrist-worn accelerometer over seven consecutive days, and the subjective sleep quality was assessed by the Pittsburgh Sleep Quality Index (PSQI; higher scores indicate worse sleep quality). The S-Klotho plasma levels were measured in the ethylenediaminetetraacetic acid plasma using a solid-phase sandwich enzyme-linked immunosorbent assay. Objective sleep parameters were associated with the S-Klotho plasma levels only after including the age, fat mass percentage, and lean mass index as covariates. A direct relationship was observed between the subjective sleep quality (inverse of PSQI scores) and the S-Klotho plasma levels in sedentary middle-aged adults. Improving sleep quantity and quality could be considered an anti-aging therapeutic approach for the prevention, slowing, and even reversal of the physiological decline and degenerative pathologies that are certainly related to the aging process.

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

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

Micturition defects and altered bladder function in the klotho mutant mouse model of aging

INTRODUCTION AND OBJECTIVES

Symptoms associated with detrusor underactivity (DU) or underactive bladder (UAB) can severely impact a person's quality of life, and growing old is the main etiological factor of DU and UAB. The gene Klotho has been associated with suppression of several aging phenotypes, and there is moderate klotho expression in the bladder. Given this, we hypothesized that the klotho gene is involved in regulation of bladder function. Thus, we examined a premature aging rodent genetic model with hypomorphic klotho expression for alterations in bladder function.

METHODS

Klotho mutant mice are established as a preclinical model of aging. Male and female klotho mice had micturition measured at weeks 4, 6, and 8 through metabolic cage and void spot assays. Histology was assessed at 4, 6, and 8 weeks. Lastly, bladder contraction was assessed using bladder strip tissue bath. All animals were gender- and age-matched with wild-type littermates for analysis.

RESULTS

Void spot and bladder contraction assays revealed that klotho mutant mice, similar to other aging models, have increased voiding frequency and decreased voiding volume per micturition event. The in vitro contractile response to electrical stimulation was weaker and muscarinic receptor subtype expression was reduced in the in klotho mutant mouse bladders. These data suggest that klotho mutant mouse bladders had impaired bladder function.

CONCLUSIONS

Klotho mutant mice recapitulate many characteristics of an older dysfunctional bladder, including altered bladder function. Given the short time frame to bladder dysfunction and robustness of the model, this model will provide new insights to drive aging bladder research.

Serum Klotho in Living Kidney Donors and Kidney Transplant Recipients: A Meta-Analysis

α-Klotho is a known anti-aging protein that exerts diverse physiological effects, including phosphate homeostasis. Klotho expression occurs predominantly in the kidney and is significantly decreased in patients with chronic kidney disease. However, changes in serum klotho levels and impacts of klotho on outcomes among kidney transplant (KTx) recipients and kidney donors remain unclear. A literature search was conducted using MEDLINE, EMBASE, and Cochrane Database from inception through October 2019 to identify studies evaluating serum klotho levels and impacts of klotho on outcomes among KTx recipients and kidney donors. Study results were pooled and analyzed utilizing a random-effects model. Ten cohort studies with a total of 431 KTx recipients and 5 cohort studies with a total of 108 living kidney donors and were identified. After KTx, recipients had a significant increase in serum klotho levels (at 4 to 13 months post-KTx) with a mean difference (MD) of 243.11 pg/mL (three studies; 95% CI 67.41 to 418.81 pg/mL). Although KTx recipients had a lower serum klotho level with a MD of = -234.50 pg/mL (five studies; 95% CI -444.84 to -24.16 pg/mL) compared to healthy unmatched volunteers, one study demonstrated comparable klotho levels between KTx recipients and eGFR-matched controls. Among kidney donors, there was a significant decrease in serum klotho levels post-nephrectomy (day 3 to day 5) with a mean difference (MD) of -232.24 pg/mL (three studies; 95% CI -299.41 to -165.07 pg/mL). At one year following kidney donation, serum klotho levels remained lower than baseline before nephrectomy with a MD of = -110.80 pg/mL (two studies; 95% CI 166.35 to 55.24 pg/mL). Compared to healthy volunteers, living kidney donors had lower serum klotho levels with a MD of = -92.41 pg/mL (two studies; 95% CI -180.53 to -4.29 pg/mL). There is a significant reduction in serum klotho levels after living kidney donation and an increase in serum klotho levels after KTx. Future prospective studies are needed to assess the impact of changes in klotho on clinical outcomes in KTx recipients and living kidney donors.

Klotho Deficiency Accelerates Stem Cells Aging by Impairing Telomerase Activity

Understanding the effect of molecular pathways involved in the age-dependent deterioration of stem cell function is critical for developing new therapies. The overexpression of Klotho (KL), an antiaging protein, causes treated animal models to enjoy extended life spans. Now, the question stands: Does KL deficiency accelerate stem cell aging and telomere shortening? If so, what are the specific mechanisms by which it does this, and is cycloastragenol (CAG) treatment enough to restore telomerase activity in aged stem cells? We found that KL deficiency diminished telomerase activity by altering the expression of TERF1 and TERT, causing impaired differentiation potential, pluripotency, cellular senescence, and apoptosis in stem cells. Telomerase activity decreased with KL-siRNA knockdown. This suggests that both KL and telomeres regulate the stem cell aging process through telomerase subunits TERF1, POT1, and TERT using the TGFβ, Insulin, and Wnt signaling. These pathways can rejuvenate stem cell populations in a CD90-dependent mechanism. Stem cell dysfunctions were largely provoked by KL deficiency and telomere shortening, owing to altered expression of TERF1, TGFβ1, CD90, POT1, TERT, and basic fibroblast growth factor (bFGF). The CAG treatment partially rescued telomerase deterioration, suggesting that KL plays a critical role in life-extension by regulating telomere length and telomerase activity.

Inflammaging and Complement System: A Link Between Acute Kidney Injury and Chronic Graft Damage

The aberrant activation of complement system in several kidney diseases suggests that this pillar of innate immunity has a critical role in the pathophysiology of renal damage of different etiologies. A growing body of experimental evidence indicates that complement activation contributes to the pathogenesis of acute kidney injury (AKI) such as delayed graft function (DGF) in transplant patients. AKI is characterized by the rapid loss of the kidney's excretory function and is a complex syndrome currently lacking a specific medical treatment to arrest or attenuate progression in chronic kidney disease (CKD). Recent evidence suggests that independently from the initial trigger (i.e., sepsis or ischemia/reperfusions injury), an episode of AKI is strongly associated with an increased risk of subsequent CKD. The AKI-to-CKD transition may involve a wide range of mechanisms including scar-forming myofibroblasts generated from different sources, microvascular rarefaction, mitochondrial dysfunction, or cell cycle arrest by the involvement of epigenetic, gene, and protein alterations leading to common final signaling pathways [i.e., transforming growth factor beta (TGF-β), p16 ink4a , Wnt/β-catenin pathway] involved in renal aging. Research in recent years has revealed that several stressors or complications such as rejection after renal transplantation can lead to accelerated renal aging with detrimental effects with the establishment of chronic proinflammatory cellular phenotypes within the kidney. Despite a greater understanding of these mechanisms, the role of complement system in the context of the AKI-to-CKD transition and renal inflammaging is still poorly explored. The purpose of this review is to summarize recent findings describing the role of complement in AKI-to-CKD transition. We will also address how and when complement inhibitors might be used to prevent AKI and CKD progression, therefore improving graft function.

Local Klotho Enhances Neuronal Progenitor Proliferation in the Adult Hippocampus

Klotho is an aging-related protein associated with hippocampal cognitive performance in mammals. Klotho regulates progenitor cell proliferation in non-neuronal tissues, but its role in adult hippocampal neurogenesis (AHN) has not been explored. Klotho expression in the adult mouse hippocampus was examined by immunofluorescence and polymerase chain reaction. AHN was evaluated in the hippocampus of klotho knock-out mice (KO), klotho KO/vitamin D-receptor mutant mice, and in a model of local klotho hippocampal knockdown. The recombinant Klotho effect on proliferation was measured in mouse-derived hippocampal neural progenitor cells. Hippocampal-dependent memory was assessed by a dry-land version of the Morris water maze. Klotho was expressed in the granular cell layer of the adult Dentate Gyrus. AHN was increased in klotho KO mice, but not in klotho KO/vitamin D-receptor mutant mice. Inversely, local downregulation of hippocampal Klotho diminished AHN. Recombinant Klotho increased the proliferation rate of neural progenitors. Downregulation of hippocampal Klotho correlated with a decreased performance in hippocampal-dependent memory. These results suggest that Klotho directly participates in regulating AHN. Our observations indicate that Klotho promotes proliferation, AHN and hippocampal-dependent cognition. Increased neurogenesis in klotho KO mice may be secondary to the activation of other pathways altered in the model, such as vitamin D.

Beclin 1/Bcl-2 complex-dependent autophagy activity modulates renal susceptibility to ischemia-reperfusion injury and mediates renoprotection by Klotho

Klotho- and beclin 1-driven autophagy extends life. We examined the role of beclin 1 in modifying acute kidney injury (AKI) and whether beclin 1 mediates Klotho's known renoprotective action in AKI. AKI was induced by ischemia-reperfusion injury in mice with different levels of autophagy activity by genetic manipulation: wild-type (WT) mice with normal beclin 1 expression and function, mice with normal beclin 1 levels but high activity through knockin of gain-of-function mutant beclin 1 (Becn1^F121A), mice with low beclin 1 levels and activity caused by heterozygous global deletion of beclin 1 (Becn1^+/-), or mice with extremely low beclin 1 activity from knockin of the mutant constitutively active beclin 1 inhibitor Bcl-2 (Bcl2^AAA). Klotho was increased by transgenic overexpression (Tg-Kl) or recombinant Klotho protein administration. After ischemia-reperfusion injury, Becn1^F121A mice (high autophagy) had milder AKI and Becn1^+/- and Bcl2^AAA mice (low autophagy) had more severe AKI than WT mice. Tg-Kl mice had milder AKI, but its renoprotection was partially attenuated in Becn1^+/-;Tg-Kl mice and was significantly reduced, although not completely abolished, in Bcl2^AAA;Tg-Kl mice. Recombinant Klotho protein conferred more renoprotection from AKI in WT mice than in Becn1^+/- or Bcl2^AAA mice. Klotho reduced beclin 1/Bcl-2 protein complexes and increased autophagy activity, but this effect was less prominent in mice or cells with Bcl2^AAA. Transfected Bcl2^AAA or Becn1^F123A decreased or increased autophagy activity and rendered cells more susceptible or more resistant to oxidative cytotoxicity, respectively. In conclusion, beclin 1 confers renoprotection by activating autophagy. Klotho protects the kidney partially via disruption of beclin 1/Bcl-2 interactions and enhancement of autophagy activity.

Serum Levels of FGF21, β-Klotho, and BDNF in Stable Coronary Artery Disease Patients With Depressive Symptoms: A Cross-Sectional Single-Center Study

Background: The incidence of depressive symptoms (DS) in patients with stable coronary artery disease (SCAD) is significantly higher than those in healthy population, and that DS are independent risk factors for cardiovascular events. Previous studies have reported that fibroblast growth factor 21 (FGF21), β-klotho, mature brain-derived neurotrophic factor (mBDNF), and BDNF precursor (proBDNF) play important roles in the pathogenesis and treatment of coronary heart disease and depression. With this in mind, the present study aimed to clarify the relationship between FGF21, β-klotho, mBDNF, and proBDNF and SCAD with comorbid depression, in addition to also exploring the underlying mechanisms of these disease processes. Methods: A total of 116 patients with SCAD and 45 healthy controls were recruited. Patients with SCAD were further divided into two subgroups based on the Zung Self-Rating Depression Scale (SDS), which were characterized as those with no DS (NDS) and those with DS. Baseline data were collected, and serum levels of FGF21, β-klotho, mBDNF, and proBDNF were determined. Results: In SCAD patients, Gensini scores-denoting the degree of coronary arteriostenosis-were significantly greater in the DS group than in the NDS group. There was also a positive correlation between the Gensini scores and the SDS scores. Patients in the SCAD group demonstrated a lower serum FGF21. Serum β-klotho, mBDNF, and mBDNF/proBDNF were also significantly lower in the DS group than in the NDS group. Furthermore, β-klotho and mBDNF were negatively correlated with the SDS scores. Additionally, SCAD patients were divided into lower- and higher-level groups using hierarchical cluster analysis, with the results highlighting that patients in the lower mBDNF group had a higher incidence of DS. Conclusions: The depression score was positively correlated with the severity of coronary artery stenosis, and serum FGF21, β-klotho, mBDNF, and proBDNF were closely related to the development of DS in patients with SCAD. These observations suggest FGF21, β-klotho, mBDNF, and proBDNF as potential diagnostic and/or therapeutic targets for SCAD with co-morbid depression.

The decreased SIRT1 level may account for the lipid profile in chronic kidney disease

Dysregulated lipid profile with hypertriglyceridemia and increased low-density lipoprotein (LDL) is common in chronic kidney disease (CKD) whereas the reason is unclear. A similar phenomenon is found in the elder population. Silent information regulator-1 (SIRT1) associates with many modulators regulating lipid metabolism and results in increased expression of sterol regulatory element-binding proteins (SREBPs), which functions as a key modulator in lipid synthesis. Since CKD is being viewed as a premature aging model and SIRT1 is known to decrease during the process of aging, we hypothesize that SIRT1 level is reduced in the liver when CKD develops and eventually result in dysregulated lipid profile.

Renal Klotho is Reduced in Septic Patients and Pretreatment With Recombinant Klotho Attenuates Organ Injury in Lipopolysaccharide-Challenged Mice

OBJECTIVES

To determine the applicability of recombinant Klotho to prevent inflammation and organ injury in sepsis in man and mice.

DESIGN

Prospective, clinical laboratory study using "warm" human postmortem sepsis-acute kidney injury biopsies. Laboratory study using a mouse model of endotoxemia.

SETTING

Research laboratory at a university teaching hospital.

SUBJECTS

Adult patients who died of sepsis in the ICU and control patients undergoing total nephrectomy secondary to renal cancer; male C57BL/6 and Klotho haploinsufficient mice.

INTERVENTIONS

Lipopolysaccharide (0.05 mg/kg) injection and kill after 4, 8, and 24 hours. Mice received recombinant Klotho (0.05 mg/kg) 30 minutes prior to lipopolysaccharide (1 mg/kg) injection. Mice treated with saline were included as controls.

MEASUREMENTS AND MAIN RESULTS

Quantitative reverse transcription polymerase chain reaction and immunohistochemical staining were used to quantify Klotho messenger RNA and protein expression in the kidney of sepsis-acute kidney injury patients and the kidney and brain of mice. The messenger RNA and protein expression of damage markers, inflammatory cytokine, chemokines, and endothelial adhesion molecules were also determined in mice. Renal neutrophil influx was quantified. We found significantly lower renal Klotho messenger RNA and protein levels in sepsis-acute kidney injury biopsies than in control subjects. These findings were recapitulated in the kidney and brain of lipopolysaccharide-challenged mice. Decreased Klotho expression paralleled an increase in kidney damage markers neutrophil gelatinase-associated lipocalin and kidney injury molecule-1. Administration of recombinant Klotho prior to lipopolysaccharide injection attenuated organ damage, inflammation and endothelial activation in the kidney and brain of mice. Furthermore, less neutrophils infiltrated into the kidneys of recombinant Klotho mice compared with lipopolysaccharide only treated mice.

CONCLUSIONS

Renal Klotho expression in human sepsis-acute kidney injury and in mouse models of sepsis was significantly decreased and correlated with renal damage. Recombinant Klotho intervention diminished organ damage, inflammation, and endothelial activation in the kidney and brain of lipopolysaccharide-challenged mice. Systemic Klotho replacement may potentially be an organ-protective therapy for septic patients to halt acute, inflammatory organ injury.

Cord blood alpha klotho is decreased in small for gestational age preterm infants with placental lesions of accelerated aging

BACKGROUND

Intrauterine growth restriction is often accompanied by placental vascular disease, of which histologic maternal vascular malperfusion is prominent. Maternal vascular malperfusion is characterized by accelerated villous maturation consistent with placental aging. Alpha klotho is an anti-aging protein produced by the placenta. We hypothesize that cord blood alpha klotho varies with maternal vascular malperfusion and small for gestational age infants through dysregulated angiogenesis.

METHODS

Nested case-control study of 54 preterm infants (N = 22 small for gestational age infants, 32 appropriate for gestational age infants, mean gestational age = 33.7 ± 2.7 weeks) and validation sample (N = 39) from a longitudinal birth cohort at Prentice Women's Hospital, Chicago, IL. Cord blood alpha klotho was measured via enzyme-linked immunoassay; concentrations were linked to multiplex data of cord blood angiogenic growth factors.

RESULTS

Median cord blood alpha klotho was decreased in small for gestational age infants (1200 [859, 2083] pg/mL) versus controls (3193 [1703, 3963] pg/mL; p < 0.01) and with severe maternal vascular malperfusion (1170 [760, 2645] pg/mL; P < 0.01), consistent with validation sample. Alpha klotho was decreased with maternal vascular malperfusion sublesions signifying accelerated villous maturation, including increased syncytial knots (1230 [805, 3606] pg/mL; p < 0.05) and distal villous hypoplasia (1170 [770, 3390] pg/mL; p < 0.05). Among 15 angiogenic markers, alpha klotho correlated directly with angiopoietin-2 (beta-coefficient = 2.6, p = 0.01).

CONCLUSIONS

Cord blood alpha klotho is decreased with small for gestational infants and maternal vascular malperfusion sublesions of accelerated placental villous maturation, and correlated with angiopoietin-2. Alpha klotho may play a role in vascular-mediated accelerated placental aging leading to intrauterine growth restriction.

Urine Klotho Is Lower in Critically Ill Patients With Versus Without Acute Kidney Injury and Associates With Major Adverse Kidney Events

Supplemental Digital Content is available in the text.

Klotho and fibroblast growth factor-23 were recently postulated as candidate biomarkers and/or therapeutic targets in acute kidney injury. We examined whether urine Klotho and serum intact fibroblast growth factor-23 levels were differentially and independently associated with major adverse kidney events in critically ill patients with and without acute kidney injury.

Enhanced Expression of Secreted α-Klotho in the Hippocampus Alters Nesting Behavior and Memory Formation in Mice

The klotho gene family consists of α-, β-, and γ-Klotho, which encode type I single-pass transmembrane proteins with large extracellular domains. α-Klotho exists as a full-length membrane-bound and as a soluble form after cleavage of the extracellular domain. Due to gene splicing, a short extracellular Klotho form can be expressed and secreted. Inactivation of α-Klotho leads to a phenotype that resembles accelerated aging, as the expression level of the α-Klotho protein in the hippocampal formation of mice decreases with age. Here, we show that intrahippocampal viral expression of secreted human α-Klotho alters social behavior and memory formation. Interestingly, overexpression of secreted human α-Klotho in the CA1 changed the nest-building behavior and improved object recognition, object location and passive avoidance memory. Moreover, α-Klotho overexpression increased hippocampal synaptic transmission in response to standardized stimulation strengths, altered paired-pulse facilitation of synaptic transmission, and enhanced activity-dependent synaptic plasticity. These results indicate that memory formation benefits from an augmented level of secreted α-Klotho.

Hyperoside attenuates renal aging and injury induced by D-galactose via inhibiting AMPK-ULK1 signaling-mediated autophagy

The kidney is a typical organ undergoing age and injury. Hyperoside is reported to be useful for preventing aging induced by D-galactose (D-gal). However, therapeutic mechanisms remain unclear. We thereby aimed to verify whether hyperoside, compared to vitamin E (VE), could alleviate renal aging and injury by regulating autophagic activity and its related signaling pathways. In vivo, rats were administered with either hyperoside or VE after renal aging modeling induced by D-gal. Changes in renal aging and injury markers, autophagic activity and AMPK-ULK1 signaling pathway in the kidneys were analysed. In vitro, the NRK-52E cells exposed to D-gal were used to investigate regulative actions of hyperoside and VE on cell viability, renal tubular cellular aging markers, autophagic activity and its related signaling pathways by histomorphometry, immunohistochemistry, immunofluorescence, lentiviral transfection and Western blot. Aging and injury in the kidneys and renal tubular cells induced by D-gal were ameliorated by hyperoside and VE. Hyperoside and VE inhibited autophagic activity through mTOR-independent and AMPK-ULK1 signaling pathways. Hyperoside, as a component of phytomedicine similar to VE, attenuated renal aging and injury induced by D-gal via inhibiting AMPK-ULK1-mediated autophagy. This study provides the first evidence that hyperoside contributes to the prevention of age-associated renal injury.

Modelling Sporadic Alzheimer's Disease Using Induced Pluripotent Stem Cells

Developing cellular models of sporadic Alzheimer's disease (sAD) is challenging due to the unknown initiator of disease onset and the slow disease progression that takes many years to develop in vivo. The use of human induced pluripotent stem cells (iPSCs) has revolutionised the opportunities to model AD pathology, investigate disease mechanisms and screen potential drugs. The majority of this work has, however, used cells derived from patients with familial AD (fAD) where specific genetic mutations drive disease onset. While these provide excellent models to investigate the downstream pathways involved in neuronal toxicity and ultimately neuronal death that leads to AD, they provide little insight into the causes and mechanisms driving the development of sAD. In this review we compare the data obtained from fAD and sAD iPSC-derived cell lines, identify the inconsistencies that exist in sAD models and highlight the potential role of Aβ clearance mechanisms, a relatively under-investigated area in iPSC-derived models, in the study of AD. We discuss the development of more physiologically relevant models using co-culture and three-dimensional culture of iPSC-derived neurons with glial cells. Finally, we evaluate whether we can develop better, more consistent models for sAD research using genetic stratification of iPSCs and identification of genetic and environmental risk factors that could be used to initiate disease onset for modelling sAD. These considerations provide exciting opportunities to develop more relevant iPSC models of sAD which can help drive our understanding of disease mechanisms and identify new therapeutic targets.

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.