The role of the anti-ageing protein Klotho in vascular physiology and pathophysiology

Decreased Alpha Klotho Expression in Placentas Exposed to Severe Maternal Vascular Malperfusion

BACKGROUND

Placental maternal vascular malperfusion (MVM) is characterized by accelerated villous maturation and has been associated with a decrease in the antiaging protein, alpha-klotho (AK). Our aim was to characterize AK protein and gene expression in the placenta and fetal organs.

METHODS

We utilized 2 cohorts. First, we characterized AK protein expression in an autopsy cohort where cases were defined as MVM as the cause of fetal death compared to a stillborn control population. Second, we characterized placental and umbilical cord blood AK gene expression in a liveborn population with and without MVM.

RESULTS

We found decreased protein expression in the villous trophoblastic cells of placentas exposed to severe MVM and decreased AK gene expression in placental tissue exposed to MVM. We did not see any statistically significant differences in fetal organ or umbilical cord blood AK expression based on the presence or absence of MVM. Furthermore, in liveborn infants, we also found increased odds of preterm birth with lower placental AK expression.

CONCLUSIONS

Decreased AK gene and protein expression in the placenta in the setting of MVM is consistent with the theory of placental aging in MVM and is associated with increased odds of preterm birth.

AMPK signaling inhibits the differentiation of myofibroblasts: impact on age-related tissue fibrosis and degeneration

Disruption of the extracellular matrix (ECM) and an accumulation of fibrotic lesions within tissues are two of the distinctive hallmarks of the aging process. Tissue fibroblasts are mesenchymal cells which display an impressive plasticity in the regulation of ECM integrity and thus on tissue homeostasis. Single-cell transcriptome studies have revealed that tissue fibroblasts exhibit a remarkable heterogeneity with aging and in age-related diseases. Excessive stress and inflammatory insults induce the differentiation of fibroblasts into myofibroblasts which are fusiform contractile cells and abundantly secrete the components of the ECM and proteolytic enzymes as well as many inflammatory mediators. Detrimental stresses can also induce the transdifferentiation of certain mesenchymal and myeloid cells into myofibroblasts. Interestingly, many age-related stresses, such as oxidative and endoplasmic reticulum stresses, ECM stiffness, inflammatory mediators, telomere shortening, and several alarmins from damaged cells are potent inducers of myofibroblast differentiation. Intriguingly, there is convincing evidence that the signaling pathways stimulated by the AMP-activated protein kinase (AMPK) are potent inhibitors of myofibroblast differentiation and accordingly AMPK signaling reduces fibrotic lesions within tissues, e.g., in age-related cardiac and pulmonary fibrosis. AMPK signaling is not only an important regulator of energy metabolism but it is also able to control cell fate determination and many functions of the immune system. It is known that AMPK signaling can delay the aging process via an integrated signaling network. AMPK signaling inhibits myofibroblast differentiation, e.g., by suppressing signaling through the TGF-β, NF-κB, STAT3, and YAP/TAZ pathways. It seems that AMPK signaling can alleviate age-related tissue fibrosis and degeneration by inhibiting the differentiation of myofibroblasts.

Hypertensive Heart Disease: A Narrative Review Series-Part 3: Vasculature, Biomarkers and the Matrix of Hypertensive Heart Disease

Over the last few decades, research efforts have resulted in major advances in our understanding of the pathophysiology of hypertensive heart disease (HHD). This is the third part of a three-part review series. Here, we focus on the influence of high blood pressure on the micro- and macroalterations that occur in the vasculature in HHD. We also provide an overview of circulating cardiac biomarkers that may prove useful for a better understanding of the pathophysiology, development and progression of HHD, and may play a unique role in the diagnostic and prognostic evaluation of patients with HHD, taking into account their properties showing as abnormal long before the onset of the disease. In the conclusion, we propose an updated definition of HHD and a matrix for clinical classification, which we suspect will be useful in practice, allowing an individual approach to HHD patients.

Early aging and premature vascular aging in chronic kidney disease

Aging is the progressive decline of body functions and a number of chronic conditions can lead to premature aging characterized by frailty, a diseased vasculature, osteoporosis, and muscle wasting. One of the major conditions associated with premature and accelerated aging is chronic kidney disease (CKD), which can also result in early vascular aging and the stiffening of the arteries. Premature vascular aging in CKD patients has been considered as a marker of prognosis of mortality and cardiovascular morbidity and therefore requires further attention. Oxidative stress, inflammation, advanced glycation end products, fructose, and an aberrant gut microbiota can contribute to the development of early aging in CKD patients. There are several key molecular pathways and molecules which play a role in aging and vascular aging including nuclear factor erythroid 2-related factor 2 (Nrf-2), AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), and klotho. Potential therapeutic strategies can target these pathways. Future studies are needed to better understand the importance of premature aging and early vascular aging and to develop therapeutic alternatives for these conditions.

Future treatment of vascular calcification in chronic kidney disease

INTRODUCTION

Cardiovascular disease (CVD) is one of the global leading causes of morbidity and mortality in chronic kidney disease (CKD) patients. Vascular calcification (VC) is a major cause of CVD in this population and is the consequence of complex interactions between inhibitor and promoter factors leading to pathological deposition of calcium and phosphate in soft tissues. Different pathological landscapes are associated with the development of VC, such as endothelial dysfunction, oxidative stress, chronic inflammation, loss of mineralization inhibitors, release of calcifying extracellular vesicles (cEVs) and circulating calcifying cells.

AREAS COVERED

In this review, we examined the literature and summarized the pathophysiology, biomarkers and focused on the treatments of VC.

EXPERT OPINION

Even though there is no consensus regarding specific treatment options, we provide the currently available treatment strategies that focus on phosphate balance, correction of vitamin D and vitamin K deficiencies, avoidance of both extremes of bone turnover, normalizing calcium levels and reduction of inflammatory response and the potential and promising therapeutic approaches liketargeting cellular mechanisms of calcification (e.g. SNF472, TNAP inhibitors).Creating novel scores to detect in advance VC and implementing targeted therapies is crucial to treat them and improve the future management of these patients.

Role of Chronic Kidney Disease (CKD)-Mineral and Bone Disorder (MBD) in the Pathogenesis of Cardiovascular Disease in CKD

Cardiovascular disease (CVD) is the leading cause of death in patients with chronic kidney disease (CKD). Multiple factors account for the increased incidence of cardiovascular morbidity and mortality in patients with CKD. Traditional risk factors for atherosclerosis and arteriosclerosis, including age, hypertension, dyslipidemia, diabetes mellitus, and smoking, are also risk factors for CKD. Non-traditional risk factors specific for CKD are also involved in CVD pathogenesis in patients with CKD. Recently, CKD-mineral and bone disorder (CKD-MBD) has emerged as a key player in CVD pathogenesis in the context of CKD. CKD-MBD manifests as hypocalcemia and hyperphosphatemia in the later stages of CKD; however, it initially develops much earlier in disease course. The initial step in CKD-MBD involves decreased phosphate excretion in the urine, followed by increased circulating concentrations of fibroblast growth factor 23 (FGF23) and parathyroid hormone (PTH), which increase urinary phosphate excretion. Simultaneously, the serum calcitriol concentration decreases as a result of FGF23 elevation. Importantly, FGF23 and PTH cause left ventricular hypertrophy, arrhythmia, and cardiovascular calcification. More recently, calciprotein particles, which are nanoparticles composed of calcium, phosphate, and fetuin-A, among other components, have been reported to cause inflammation, cardiovascular calcification, and other clinically relevant outcomes. CKD-MBD has become one of the critical therapeutic targets for the prevention of cardiovascular events and is another link between cardiology and nephrology. In this review, we describe the role of CKD-MBD in the pathogenesis of cardiovascular disorders and present the current treatment strategies for CKD-MBD.

ADAM10 and ADAM17, Major Regulators of Chronic Kidney Disease Induced Atherosclerosis?

Chronic kidney disease (CKD) is a major health problem, affecting millions of people worldwide, in particular hypertensive and diabetic patients. CKD patients suffer from significantly increased cardiovascular disease (CVD) morbidity and mortality, mainly due to accelerated atherosclerosis development. Indeed, CKD not only affects the kidneys, in which injury and maladaptive repair processes lead to local inflammation and fibrosis, but also causes systemic inflammation and altered mineral bone metabolism leading to vascular dysfunction, calcification, and thus, accelerated atherosclerosis. Although CKD and CVD individually have been extensively studied, relatively little research has studied the link between both diseases. This narrative review focuses on the role of a disintegrin and metalloproteases (ADAM) 10 and ADAM17 in CKD and CVD and will for the first time shed light on their role in CKD-induced CVD. By cleaving cell surface molecules, these enzymes regulate not only cellular sensitivity to their micro-environment (in case of receptor cleavage), but also release soluble ectodomains that can exert agonistic or antagonistic functions, both locally and systemically. Although the cell-specific roles of ADAM10 and ADAM17 in CVD, and to a lesser extent in CKD, have been explored, their impact on CKD-induced CVD is likely, yet remains to be elucidated.

Exposure to p-dichlorobenzene and serum α-Klotho levels among US participants in their middle and late adulthood

P-dichlorobenzene (p-DCB) is a volatile compound commonly used as pest repellent and air deodorant in the home and public buildings, leading to a widespread exposure in indoor environments. There has been an increasing concern about its metabolic and endocrine effects. In this study, we explored the relation between p-DCB exposure and serum levels of soluble α-Klotho, an anti-aging hormone, in US adults. A nationally representative subsample of 1485 adults 40-79 ages in the 2013-2016 National Health and Nutrition Examination Survey was analyzed for the association between p-DCB exposure, measured as urinary concentrations of 2,5-dichlorophenol (2,5-DCP), the major metabolite of p-DCB, and serum α-Klotho levels using multiple general linear models, adjusting for potential confounders. Age- and sex-specific analyses were further conducted. The weighted geometric mean of urinary 2,5-DCP was 2.43 μg/L and the weighted mean of serum α-Klotho was 831.97 pg/mL in the study participants during 2013-2016. After adjusting for potential confounders and urinary creatinine, urinary 2,5-DCP was significantly associated with decreased serum levels of α-Klotho (regression coefficient β = -9.88; p = 0.0133) in the total study population. When age- and sex-specific analyses being conducted, a significantly inverse association was found in older adults aged 60-79 years (β = -20.40; p = 0.0001) and in males (β = -13.81; p = 0.0097), but not in the middle ages (40-59 years) and in females. The strongest association was observed in older (60-79 years) male participants, with a 25.43 pg/mL reduction of α-Klotho levels per 1-unit increase of 2,5-DCP concentrations (p = 0.0008). This is the first study demonstrating a relation between p-DCB exposure, measured as 2,5-DCP, and decreased α-Klotho levels in older males. Additional studies would further explore these interactions and elucidate the pathogenesis of the potential effects of p-DCB exposure on aging.

VEGFR2 insufficiency enhances phosphotoxicity and undermines Klotho's protection against peritubular capillary rarefaction and kidney fibrosis

Vascular endothelial growth factor (VEGF) and its cognate receptor (VEGFR2) system are crucial for cell functions associated with angiogenesis and vasculogenesis. Klotho contributes to vascular health maintenance in the kidney and other organs in mammals, but it is unknown whether renoprotection by Klotho is dependent on VEGF/VEGFR2 signaling. We used heterozygous VEGFR2-haploinsufficient (VEGFR2+/-) mice resulting from heterozygous knockin of green fluorescent protein in the locus of fetal liver kinase 1 encoding VEGFR2 to test the interplay of Klotho, phosphate, and VEGFR2 in kidney function, the vasculature, and fibrosis. VEGFR2+/- mice displayed downregulated VEGF/VEGFR2 signaling in the kidney, lower density of peritubular capillaries, and accelerated kidney fibrosis, all of which were also found in the homozygous Klotho hypomorphic mice. High dietary phosphate induced higher plasma phosphate, greater peritubular capillary rarefaction, and more kidney fibrosis in VEGFR2+/- mice compared with wild-type mice. Genetic overexpression of Klotho significantly attenuated the elevated plasma phosphate, kidney dysfunction, peritubular capillary rarefaction, and kidney fibrosis induced by a high-phosphate diet in wild-type mice but only modestly ameliorated these changes in the VEGFR2+/- background. In cultured endothelial cells, VEGFR2 inhibition reduced free VEGFR2 but enhanced its costaining of an endothelial marker (CD31) and exacerbated phosphotoxicity. Klotho protein maintained VEGFR2 expression and attenuated high phosphate-induced cell injury, which was reduced by VEGFR2 inhibition. In conclusion, normal VEGFR2 function is required for vascular integrity and for Klotho to exert vascular protective and antifibrotic actions in the kidney partially through the regulation of VEGFR2 function.NEW & NOTEWORTHY This research paper studied the interplay of vascular endothelial growth factor receptor type 2 (VEGFR2), high dietary phosphate, and Klotho, an antiaging protein, in peritubular structure and kidney fibrosis. Klotho protein was shown to maintain VEGFR2 expression in the kidney and reduce high phosphate-induced cell injury. However, Klotho cytoprotection was attenuated by VEGFR2 inhibition. Thus, normal VEGFR2 function is required for vascular integrity and Klotho to exert vascular protective and antifibrotic actions in the kidney.

The pharmacological properties and corresponding mechanisms of farrerol: a comprehensive review

CONTEXT

Farrerol, a typical natural flavanone isolated from the traditional Chinese herb 'Man-shan-hong' [Rhododendron dauricum L. (Ericaceae)] with phlegm-reducing and cough-relieving properties, is widely used in China for treating bronchitis and asthma.

OBJECTIVE

To present the anti-inflammatory, antioxidant, vasoactive, antitumor, and antimicrobial effects of farrerol and its underlying molecular mechanisms.

METHODS

The literature was reviewed by searching PubMed, Medline, Web of Knowledge, Scopus, and Google Scholar databases between 2011 and May 2021. The following key words were used: 'farrerol,' 'flavanone,' 'anti-inflammatory,' 'antioxidant,' 'vasoactive,' 'antitumor,' 'antimicrobial,' and 'molecular mechanisms'.

RESULTS

Farrerol showed anti-inflammatory effects mainly mediated via the inhibition of interleukin (IL)-6/8, IL-1β, tumour necrosis factor(TNF)-α, NF-κB, NO, COX-2, JNK1/2, AKT, PI3K, ERK1/2, p38, Keap-1, and TGF-1β. Farrerol exhibited antioxidant effects by decreasing JNK, MDA, ROS, NOX4, Bax/Bcl-2, caspase-3, p-p38 MAPK, and GSK-3β levels and enhancing Nrf2, GSH, SOD, GSH-Px, HO-1, NQO1, and p-ERK levels. The vasoactive effects of farrerol were also shown by the reduced α-SMA, NAD(P)H, p-ERK, p-Akt, mTOR, Jak2, Stat3, Bcl-2, and p38 levels, but increased OPN, occludin, ZO-1, eNOS, CaM, IP3R, and PLC levels. The antitumor effects of farrerol were evident from the reduced Bcl-2, Slug, Zeb-1, and vimentin levels but increased p27, ERK1/2, p38, caspase-9, Bax, and E-cadherin levels. Farrerol reduced α-toxin levels and increased NO production and NF-κB activity to impart antibacterial activity.

CONCLUSIONS

This review article provides a theoretical basis for further studies on farrerol, with a view to develop and utilise farrerol for treating of vascular-related diseases in the future.

Klotho Ameliorates Vascular Calcification via Promoting Autophagy

Vascular calcification (VC) is regarded as a common feature of vascular aging. Klotho deficiency reportedly contributes to VC, which can be ameliorated by restoration of Klotho expression. However, the specific mechanisms involved remain unclear. Here, we investigated the role of autophagy in the process of Klotho-inhibiting VC. The clinical study results indicated that, based on Agatston score, serum Klotho level was negatively associated with aortic calcification. Then, Klotho-deficient mice exhibited aortic VC, which could be alleviated with the supplementation of Klotho protein. Moreover, autophagy increased in the aorta of Klotho-deficient mice and protected against VC. Finally, we found that Klotho ameliorated calcification by promoting autophagy both in the aorta of Klotho-deficient mice and in mouse vascular smooth muscle cells (MOVAS) under calcifying conditions. These findings indicate that Klotho deficiency induces increased autophagy to protect against VC and that Klotho expression further enhances autophagy to ameliorate calcification. This study is beneficial to exploring the underlying mechanisms of Klotho regulating VC, which has important guiding significance for future clinical studies in the treatment of VC.

Alveolar Epithelial Type 2 Cell Dysfunction in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and irreversible pulmonary interstitial disease that seriously affects the patient's quality of life and lifespan. The pathogenesis of IPF has not been clarified, and its treatment is limited to pirfenidone and nintedanib, which only delays the decline of lung function. Alveolar epithelial type 2 (AT2) cells are indispensable in the regeneration and lung surfactant secretion of alveolar epithelial cells. Studies have shown that AT2 cell dysfunction initiates the occurrence and progression of IPF. This review expounds on the AT2 cell dysfunction in IPF, involving senescence, apoptosis, endoplasmic reticulum stress, mitochondrial damage, metabolic reprogramming, and the transitional state of AT2 cells. This article also briefly summarizes potential treatments targeting AT2 cell dysfunction.

In Vivo Cardiac-specific Expression of Adenylyl Cyclase 4 Gene Protects against Klotho Deficiency-induced Heart Failure

Klotho is an aging-suppressor gene. Klotho gene deficiency causes heart failure in Klotho-hypomorphic mutant (KL (-/-)) mice. RNA-seq and western blot analysis showed that adenylyl cyclase type IV (AC4) mRNA and protein expression was largely decreased in cardiomyocytes of KL (-/-) mice. The objective of this study was to investigate whether in vivo cardiac-specific expression of AC4 gene protects against Klotho deficiency-induced heart failure. Interestingly, in vivo AAV-based cardiac-specific AC4 gene expression increased left ventricular fractional shortening, ejection fraction, stroke volume, and left ventricular end-diastolic volume in KL (-/-) mice, suggesting that cardiac-specific AC4 gene expression improves Klotho deficiency-induced heart dysfunction. Cardiac-specific AC4 gene expression also decreased Klotho deficiency-induced cardiac hypertrophy. Cardiac-specific AC4 gene expression alleviated Klotho deficiency-induced cardiac fibrosis and calcification. Furthermore, cardiac-specific AC4 gene expression attenuated mitochondrial dysfunction, superoxide accumulation and cardiomyocyte apoptotic cell death. Thus, downregulation of AC4 may contribute to Klotho deficiency-induced heart failure. Mechanistically, AAV2/9-αMHC-AC4 increased cardiomyocytic cAMP levels and thus regulated the PKA-PLN-SERCA2 signal pathway, which is critical in modulating calcium flux and mitochondrial function. In conclusion, cardiac-specific AC4 gene expression protects against Klotho deficiency-induced heart failure through increasing cardiomyocytic cAMP levels, which alleviates cAMP-dependent mitochondrial dysfunction, superoxide accumulation and apoptotic cell death. AC4 regulates superoxide levels via the cAMP-PKA pathway. AC4 could be a potential therapeutic target for heart failure associated with Klotho deficiency. Heart failure is the major cause of mortality in patients with chronic kidney disease (CKD). A decrease in Klotho levels is linked to CKD.

The association between metabolic syndrome and the anti-aging humoral factor klotho in middle-aged and older adults

BACKGROUND AND AIMS

The goal of the present study was to determine the association between metabolic syndrome (MetS) and serum klotho levels (pg/ml) in middle-aged and older adults.

MATERIAL AND METHODS

The National Health and Nutrition Examination Survey database from the cycles 2013-2014 and 2015-2016 were used to examine serum klotho levels in subjects with MetS and its components defined according to the 2009 Harmonizing Joint Scientific Statement. Sex-specific general linear models adjusted for potential confounders were assembled to compare mean log klotho levels between subjects with MetS and their healthy counterparts.

RESULTS

Of 5069 participants aged 40-79 years, the prevalence of MetS was 44.8% in men and 45.1% in women. Overall, older adults, men, non-Hispanic whites, smokers, alcohol users, and subjects with decreased renal function were characteristics associated with lower klotho levels. Notably, serum klotho levels in women progressively decreased as the number of MetS components increased. Multivariate models demonstrated that women with MetS had significantly lower mean log klotho levels (6.65 vs. 6.70; P < .05) than those who did not. Likewise, abdominal obesity (6.5 vs. 6.68; P < .05) and elevated triglycerides levels (6.64 vs 6.68; P < .05) were the MetS components independently correlated with lower klotho levels.

CONCLUSIONS

MetS in middle-aged and older adults was significantly and inversely associated with serum klotho levels. This association was particularly seen in women, and subjects with abdominal obesity or elevated triglycerides.

The association between serum soluble klotho levels and abdominal aorta calcification in older adults

BACKGROUND

The mutation of the mouse klotho gene leads to a syndrome resembling aging including calcification of the aorta.

OBJECTIVE

To examine the relationship between serum soluble klotho levels and abdominal aorta calcification (AAC) in subjects aged 60-79 years.

METHODS

The National Health and Nutrition Examination Survey data were analyzed using logistic regression models to examine the independent association between soluble klotho tertile levels and the Kauppila AAC-24 score.

RESULTS

A total of 1042 participants with a median klotho level of 796 pg/ml comprised the study sample. Overall, the prevalence of AAC was 39.2% and severe AAC was seen in 15.6% subjects. Participants with klotho levels ≤ 700 pg/ml were twice as likely (OR 2.21 (95% CI 1.15-4.26) to have severe AAC than their counterparts with klotho levels ≥ 906 pg/ml.

CONCLUSIONS

Soluble klotho levels were inversely associated with severe AAC in older adults.

Vascular Calcification in Chronic Kidney Disease: An Update and Perspective

Chronic kidney disease is a devastating condition resulting from irreversible loss of nephron numbers and function and leading to end-stage renal disease and mineral disorders. Vascular calcification, an ectopic deposition of calcium-phosphate salts in blood vessel walls and heart valves, is an independent risk factor of cardiovascular morbidity and mortality in chronic kidney disease. Moreover, aging and related metabolic disorders are essential risk factors for chronic kidney disease and vascular calcification. Marked progress has been recently made in understanding and treating vascular calcification in chronic kidney disease. However, there is a paucity of systematic reviews summarizing this progress, and investigating unresolved issues is warranted. In this systematic review, we aimed to overview the underlying mechanisms of vascular calcification in chronic kidney diseases and discuss the impact of chronic kidney disease on the pathophysiology of vascular calcification. Additionally, we summarized potential clinical diagnostic biomarkers and therapeutic applications for vascular calcification with chronic kidney disease. This review may offer new insights into the pathogenesis, diagnosis, and therapeutic intervention of vascular calcification.

The National Consensus statement on the management of adult patients with non-alcoholic fatty liver disease and main comorbidities

The National Consensus was prepared with the participation of the National Medical Association for the Study of the Multimorbidity, Russian Scientific Liver Society, Russian Association of Endocrinologists, Russian Association of Gerontologists and Geriatricians, National Society for Preventive Cardiology, Professional Foundation for the Promotion of Medicine Fund PROFMEDFORUM. The aim of the multidisciplinary consensus is a detailed analysis of the course of non-alcoholic fatty liver disease (NAFLD) and the main associated conditions. The definition of NAFLD is given, its prevalence is described, methods for diagnosing its components such as steatosis, inflammation and fibrosis are described. The association of NAFLD with a number of cardio-metabolic diseases (arterial hypertension, atherosclerosis, thrombotic complications, type 2 diabetes mellitus (T2DM), obesity, dyslipidemia, etc.), chronic kidney disease (CKD) and the risk of developing hepatocellular cancer (HCC) were analyzed. The review of non-drug methods of treatment of NAFLD and modern opportunities of pharmacotherapy are presented. The possibilities of new molecules in the treatment of NAFLD are considered: agonists of nuclear receptors, antagonists of pro-inflammatory molecules, etc. The positive properties and disadvantages of currently used drugs (vitamin E, thiazolidinediones, etc.) are described. Special attention is paid to the multi-target ursodeoxycholic acid (UDCA) molecule in the complex treatment of NAFLD as a multifactorial disease. Its anti-inflammatory, anti-oxidant and cytoprotective properties, the ability to reduce steatosis an independent risk factor for the development of cardiovascular pathology, reduce inflammation and hepatic fibrosis through the modulation of autophagy are considered. The ability of UDCA to influence glucose and lipid homeostasis and to have an anticarcinogenic effect has been demonstrated. The Consensus statement has advanced provisions for practitioners to optimize the diagnosis and treatment of NAFLD and related common pathogenetic links of cardio-metabolic diseases.

Calpain Inhibitor Calpeptin Alleviates Ischemia/Reperfusion-Induced Acute Kidney Injury via Suppressing AIM2 Inflammasome and Upregulating Klotho Protein

Renal ischemia/reperfusion injury is a major contributor of acute kidney injury (AKI), leading to renal cell necrosis, apoptosis, and inflammation. Calpains, a family of Ca²⁺-dependent cysteine proteases, play a pivotal role in the pathogenesis of renal diseases. Several studies have reported calpain inhibitors showing remarkable reno-protective effects against proteinuria and α-klotho deficiency-induced renal aging symptoms, particularly against glomerulus injury. However, little is known about the role of the calpain inhibitor calpeptin in acute kidney injury. The present study aims to investigate the potential mechanism of downregulation of Calpain 1 and 2 activity by calpeptin in the ischemia/reperfusion (IR)-induced AKI model. Firstly, we observed that the contents of Calpain 1 and 2 were significantly increased in the renal biopsy of clinical AKI patients, especially in the diseased tubules space. To investigate the impacts of calpain activity inhibition, we further pretreated with calpeptin in both the IR mouse model and in the HK-2 cells hypoxia model. We found that the calpain inhibitor calpeptin improved renal functional deterioration, attenuated pathological structure damage, and decreased tubular cell apoptosis in the IR injury-induced AKI mice model. Mechanistically, calpeptin significantly suppressed the AIM2 (absent in melanoma 2) and NLRP3 (NOD-like receptor protein 3) inflammasome signaling pathways and increased Klotho protein levels. Furthermore, immunofluorescence assays demonstrated that the application of calpeptin effectively inhibited Calpain 1 activation and gasdermin D (GSDMD) cleavage in the renal tubules of IR mice. Taken together, our both in vivo and in vitro experiments suggest that calpeptin conveyed reno-protection in AKI might be mediated by the inhibition of AIM2 inflammasome activation and upregulation of Klotho protein. As such, we provide new evidence that Calpain 1 and 2 activation may be closely associated with the pathogenesis of clinical AKI. The calpain-mediated AIM2 inflammasome signaling pathway and distinct interaction between calpain and Klotho may provide a potential novel preventative and therapeutic target for acute kidney injury.

Genes and Longevity of Lifespan

Aging is a complex process indicated by low energy levels, declined physiological activity, stress induced loss of homeostasis leading to the risk of diseases and mortality. Recent developments in medical sciences and an increased availability of nutritional requirements has significantly increased the average human lifespan worldwide. Several environmental and physiological factors contribute to the aging process. However, about 40% human life expectancy is inherited among generations, many lifespan associated genes, genetic mechanisms and pathways have been demonstrated during last decades. In the present review, we have evaluated many human genes and their non-human orthologs established for their role in the regulation of lifespan. The study has included more than fifty genes reported in the literature for their contributions to the longevity of life. Intact genomic DNA is essential for the life activities at the level of cell, tissue, and organ. Nucleic acids are vulnerable to oxidative stress, chemotherapies, and exposure to radiations. Efficient DNA repair mechanisms are essential for the maintenance of genomic integrity, damaged DNA is not replicated and transferred to next generations rather the presence of deleterious DNA initiates signaling cascades leading to the cell cycle arrest or apoptosis. DNA modifications, DNA methylation, histone methylation, histone acetylation and DNA damage can eventually lead towards apoptosis. The importance of calorie restriction therapy in the extension of lifespan has also been discussed. The role of pathways involved in the regulation of lifespan such as DAF-16/FOXO (forkhead box protein O1), TOR and JNK pathways has also been particularized. The study provides an updated account of genetic factors associated with the extended lifespan and their interactive contributory role with cellular pathways.

Circulating α-Klotho Levels in Relation to Cardiovascular Diseases: A Mendelian Randomization Study

BACKGROUND

Several studies have reported a protective role of circulating α-Klotho on cardiovascular diseases (CVD); however, the causality remains unclear. We aim to elucidate whether genetically predicted circulating α-Klotho levels were causally associated with the risk of coronary artery disease (CAD), atrial fibrillation (AF), heart failure (HF), stroke, ischemic stroke (IS), and IS subtypes.

METHODS

A two-sample Mendelian randomization (MR) study was designed, with 5 single-nucleotide polymorphisms associated with circulating α-Klotho levels utilized as instrumental variables. MR estimates on each CVD outcome derived from the fixed-effects inverse-variance weighted (IVW) approach in different data sources were combined by the fixed-effects meta-analysis approach, complemented by several sensitivity analyses including the simple median, the weighed median, MR-Egger regression, and MR-pleiotropy residual sum and outlier.

RESULTS

In the meta-analysis combining different data sources, suggestive inverse causal association of circulating α-Klotho concentrations with CAD [Odds ratio (OR), 0.97; 95% confidence interval (CI), 0.94, 1.00; P = 0.044] and significant inverse association of circulating α-Klotho concentrations with AF (OR, 0.96; 95% CI, 0.93, 0.99; P = 0.005) was observed. However, there was no causal association of α-Klotho with HF, any stroke, IS, or IS subtypes neither in different data sources nor in the meta-analysis. Complementary sensitivity analyses showed consistent and robust results in general.

CONCLUSION

Evidence was found for a protective effect of circulating α-Klotho on the prevention of AF risk. However, no significant causal association between genetically predicted circulating α-Klotho levels and risk of CAD, HF, stroke, IS, or IS subtypes was found.

α-Klotho, Plasma Asymmetric Dimethylarginine, and Kidney Disease Progression

Rationale & Objective

We aimed to explore the associated factors of endothelial injury in chronic kidney disease (CKD) and the relationship between endothelial dysfunction and CKD prognosis.

Study Design

A prospective observational cohort study.

Setting & Participants

77 adults with CKD stages 1-5 were enrolled January 2010 to December 2010 and followed up until December 2015.

Exposure

Serum asymmetric dimethylarginine (ADMA) level at baseline, α-klotho, sodium-phosphorus synergistic transporter, and dimethylarginine-dimethylamine hydrolase expression in kidney biopsy samples.

Outcome

Initiation of kidney replacement therapy (KRT).

Analytical Approach

Kaplan-Meier analysis was used for evaluation of the incidence rate of KRT. All tests were 2 tailed, and statistical significance was defined as P < 0.05.

Results

Mean serum ADMA level of 77 patients was 64.3 ± 34.6 ng/mL. ADMA level increased with CKD stages (P = 0.06) and declining kidney function (r = −0.267; P = 0.02). The expression of α-klotho in kidney biopsy specimens also decreased. Median follow-up time was 56 (interquartile range, 50.5-62) months. Kaplan-Meier analyses showed that during a total follow-up of 6 years, the incidence of KRT initiation in the high-ADMA group was significantly higher than that in the low group (35.9% vs 13.2%; P = 0.03). ADMA level was negatively correlated with α-klotho (r = −0.233; P = 0.04) and positively correlated with phosphorus level (r = 0.243; P = 0.04). The expression of sodium-phosphorus synergistic transporter in kidney tubules, which promoted phosphorus reabsorption, and the expression of dimethylarginine-dimethylamine hydrolase isoform 1, which regulated ADMA, were decreased. Correlation analysis also showed that ADMA level decreased while age increased at baseline (r = −0.292; P = 0.01).

Limitations

Small sample size with limited longer-term follow-up.

Conclusions

Serum ADMA levels increased as kidney function declined, and high serum ADMA level was associated with incident kidney failure. Low tissue α-klotho and high levels of plasma phosphorus or tissue expression of type II sodium/phosphate cotransporter in the kidney are associated with higher circulating ADMA levels, suggesting that they may be involved in the pathogenesis of endothelial dysfunction in patients with CKD.

Patients with Earlobe Crease May Associate with Lower Concentration of the Age-Suppressing Hormone Klotho

Objective

Earlobe crease (ELC) has been considered as a skin sign of atherosclerosis, and its pathophysiological mechanism is still unclear. Our study aims to test the hypothesis that ELC patients with lower serum levels of the age-suppressing hormone Klotho, which is not only associated with premature aging but also with endothelial dysfunction, may be associated with atherosclerosis.

Methods

A total of 135 patients aged 40–68 years underwent coronary angiography. According to the presence or absence of coronary heart disease (CAD) and ELC, they were divided into three groups: CAD group and ELC group (ELC group, n = 45); no ELC group (non-ELC group, n = 45). There was no ELC or CAD in the control group (control group, n = 45). Serum Klotho concentration was obtained by enzyme-linked immunosorbent assay (ELISA).

Results

The Klotho level in the ELC group was 365.6 ± 38.1 pg/mL, while the Klotho level in the non-ELC group was 568.8 ± 44.9 pg/mL. It is worth noting that the Klotho level of the ELC group was significantly lower than that of the non-ELC group (P < 0.001). The serum Klotho level of the control group was higher than that of the non-ELC group (593.3±45.3 vs 568.8±44.9 pg/mL, P = 0.702), but the difference was not statistically significant. Multiple logistic regression analysis showed that the Klotho level is a parameter that affects the appearance of ELC.

Conclusion

Serum Klotho levels were considerably lower in patients with ELC. We concluded that the perturbations of Klotho in patients might be associated with ELC and with CAD.

Klotho as Potential Autophagy Regulator and Therapeutic Target

The protein Klotho can significantly delay aging, so it has attracted widespread attention. Abnormal downregulation of Klotho has been detected in several aging-related diseases, such as Alzheimer’s disease, kidney injury, cancer, chronic obstructive pulmonary disease (COPD), vascular disease, muscular dystrophy and diabetes. Conversely, many exogenous and endogenous factors, several drugs, lifestyle changes and genetic manipulations were reported to exert therapeutic effects through increasing Klotho expression. In recent years, Klotho has been identified as a potential autophagy regulator. How Klotho may contribute to reversing the effects of aging and disease became clearer when it was linked to autophagy, the process in which eukaryotic cells clear away dysfunctional proteins and damaged organelles: the abovementioned diseases involve abnormal autophagy. Interestingly, growing evidence indicates that Klotho plays a dual role as inducer or inhibitor of autophagy in different physiological or pathological conditions through its influence on IGF-1/PI3K/Akt/mTOR signaling pathway, Beclin 1 expression and activity, as well as aldosterone level, which can help restore autophagy to beneficial levels. The present review examines the role of Klotho in regulating autophagy in Alzheimer’s disease, kidney injury, cancer, COPD, vascular disease, muscular dystrophy and diabetes. Targeting Klotho may provide a new perspective for preventing and treating aging-related diseases.

Understanding the Stony Bridge between Osteoporosis and Vascular Calcification: Impact of the FGF23/Klotho axis

A relationship between osteoporosis (OP) and vascular calcification (VC) is now proposed. There are common mechanisms underlying the regulation of them. Fibroblast growth factor- (FGF-) 23 and Klotho are hormones associated with the metabolic axis of osteovascular metabolism. Most recently, it was suggested that the FGF23-klotho axis is associated with increasing incidence of fractures and is potentially involved in the progression of the aortic-brachial stiffness ratio. Herein, we discussed the potential role of the FGF23/Klotho axis in the pathophysiology of OP and VC. We want to provide an update review in order to allow a better understanding of the potential role of the FGF23/Klotho axis in comorbidity of OP and VC. We believe that a better understanding of the relationship between both entities can help in proposing new therapeutic targets for reducing the increasing prevalence of OP and VC in the aging population.

Epigenetic and senescence markers indicate an accelerated ageing-like state in women with preeclamptic pregnancies

Background

Preeclampsia is a pregnancy-specific hypertensive disorder characterized by proteinuria and/or multisystem involvement. Disease-specific therapy has yet to be developed due to the lack of understanding of underlying mechanism(s). We postulate that accelerated ageing in general, and particularly cellular senescence, play a role in its pathophysiology.

Methods

We compared women with preeclampsia vs. normotensive pregnancies with respect to epigenetic markers of ageing and markers of senescence in tissues/organs affected by preeclampsia (blood, urine, adipose tissue, and kidney).

Findings

We demonstrate that preeclamptic compared to normotensive pregnant women: (i) undergo accelerated epigenetic ageing during pregnancy, as demonstrated by an “epigenetic clock”; (ii) exhibit higher levels/expression of senescence-associated secretory phenotype factors in blood and adipose tissue; (iii) display increased expression of p16^INK4A in adipose tissue and renal sections, and (iv) demonstrate decreased levels of urinary α-Klotho (an anti-ageing protein) at the time of delivery. Finally, we provide data indicating that pre-treatment with dasatinib, a senolytic agent, rescues the angiogenic potential of mesenchymal stem cells (MSC) obtained from preeclamptic pregnancies, and promotes angiogenesis, even under pro-inflammatory conditions.

Interpretation

Taken together, our results identify senescence as one of the mechanisms underpinning the pathophysiology of preeclampsia. Therapeutic strategies that target senescent cells may offer novel mechanism-based treatments for preeclampsia.

Funding

This work was supported by NIH grants, R01 HL136348, R37 AG013925, P01 AG062413, R01 DK11916, generous gifts from the Connor Fund, Robert J. and Theresa W. Ryan and from The George G. Beasley family, the Noaber Foundation, and the Henry and Emma Meyer Professorship in Molecular Genetics.

A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 2: Pathophysiology of calcium disorder and extraosseous calcification

Derangements in mineral metabolism are one of the main entities in chronic kidney disease-mineral and bone disorder (CKD-MBD). This is the second of a two-part review of the physiology and pathophysiology of calcium homeostasis in feline CKD-MBD. While dysregulation in calcium homeostasis is known to contribute to the development of vascular calcification in CKD, evidence characterising the relationship between serum calcium concentration and nephrocalcinosis and nephrolithiasis is limited. Recently, fibroblast growth factor 23 (FGF23) and α-Klotho have gained increased research interest and been shown to be important biomarkers for the prediction of CKD progression in human patients. However, conflicting evidence exists on their role in calcium homeostasis and vascular and soft tissue calcification. This review details the pathophysiology of calcium disorders associated with CKD-MBD and its implications on vascular and soft tissue mineralisation in human and feline patients. Further prospective studies investigating the clinical consequences of calcium disturbances in cats with CKD are warranted and this may provide additional insight into the pathophysiology of feline CKD-MBD.

Involvement of Sirtuins and Klotho in Cardioprotective Effects of Exercise Training Against Waterpipe Tobacco Smoking-Induced Heart Dysfunction

Despite its negative effect on the cardiovascular system, waterpipe smoking (WPS) is currently popular worldwide, especially among youth. This study investigated the effects of moderate endurance exercise on heart function of rats exposed to WPS and its possible mechanism. The animals were randomly divided into four groups: control group (CTL), the exercise group (Ex) which trained for 8 weeks, the waterpipe tobacco smoking group (S) exposed to smoke inhalation (30 min per day, 5 days each week, for 8 weeks), and the group that did exercise training and received waterpipe tobacco smoke inhalation together (Ex + S). One day after the last session of Ex and WPS, cardiac pressures and functional indices were recorded and calculated. The levels of SIRT1, SIRT3, Klotho, Bax, and Bcl-2 in the serum and heart, the expression of phosphorylated GSK3β of heart tissue, and cardiac histopathological changes were assessed. WPS reduced systolic pressure, +dP/dt max, -dP/dt max, and heart contractility indices (P < 0.001 vs. CTL) and increased cardiac tissue lesions (P < 0.05 vs. CTL) and end diastolic pressure and Tau index (P < 0.001 vs. CTL) of the left ventricle. Exercise training normalized the left ventricular end diastolic pressure, +dP/dt max, and contractility index. Also, exercise improved the levels of SIRT1, SIRT3, Klotho, and Bcl-2 and reduced Bax level in the heart. The findings showed that WPS causes left ventricular dysfunction. Moderate exercise prevented WPS-induced heart dysfunction partly through its anti-apoptotic features and activation of the sirtuins and Klotho pathways.

Klotho Protein and Cardio-Vascular System

Klotho protein affects a number of metabolic pathways essential for pathogenesis of cardio-vascular diseases and their prevention. It inhibits lipid peroxidation and inflammation, as well as prevents endothelial injury and calcification of blood vessels. Klotho decreases rigidity of blood vessels and suppresses development of the heart fibrosis. Low level of its expression is associated with a number of diseases. Cardioprotective effect of klotho is based on its ability to interact with multiple receptors and ion channels. Being a pleiotropic protein, klotho could be a useful target for therapeutic intervention in the treatment of cardio-vascular diseases. In this review we present data on pharmaceuticals that stimulate klotho expression and suggest some promising research directions.

Cellular senescence impairs the reversibility of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) in congenital cardiac shunts can be reversed by hemodynamic unloading (HU) through shunt closure. However, this reversibility potential is lost beyond a certain point in time. The reason why PAH becomes irreversible is unknown. In this study, we used MCT+shunt-induced PAH in rats to identify a dichotomous reversibility response to HU, similar to the human situation. We compared vascular profiles of reversible and irreversible PAH using RNA sequencing. Cumulatively, we report that loss of reversibility is associated with a switch from a proliferative to a senescent vascular phenotype and confirmed markers of senescence in human PAH-CHD tissue. In vitro, we showed that human pulmonary endothelial cells of patients with PAH are more vulnerable to senescence than controls in response to shear stress and confirmed that the senolytic ABT263 induces apoptosis in senescent, but not in normal, endothelial cells. To support the concept that vascular cell senescence is causal to the irreversible nature of end-stage PAH, we targeted senescence using ABT263 and induced reversal of the hemodynamic and structural changes associated with severe PAH refractory to HU. The factors that drive the transition from a reversible to irreversible pulmonary vascular phenotype could also explain the irreversible nature of other PAH etiologies and provide new leads for pharmacological reversal of end-stage PAH.

Calciprotein Particles: Balancing Mineral Homeostasis and Vascular Pathology

[Figure: see text].

Klotho alleviates chronic intermittent hypoxia-induced genioglossus myocyte apoptosis by inhibiting endoplasmic reticulum stress

Chronic intermittent hypoxia (CIH) has been shown to induce cell apoptosis in multiple organs of the human body. The present study aimed to assess the effects of exogenous klotho on CIH-induced genioglossus muscle injury, as well as the involvement of endoplasmic reticulum stress (ERS) in this process. A total of 36 adult C57BL/6 male mice were assigned to normoxia control (NC), CIH and CIH + klotho groups (n=12 mice/group). ELISA was performed to detect the level of klotho protein in the serum and in the genioglossus muscle tissue samples. Apoptosis was evaluated using the TUNEL assay. Reactive oxygen species (ROS) levels were quantified using a dihydroethidium assay kit, and the protein and mRNA levels of ERS-associated proteins (namely, glucoseregulated protein 78, C/EBP homologous protein, cleaved caspase-12 and cleaved caspase-3) in genioglossus samples were assessed using immunoblot assay and reverse transcription-quantitative PCR, respectively. Compared with the NC group, the quantities of klotho protein in the serum and genioglossus muscle tissue samples in the CIH group were significantly decreased, whereas the apoptotic rate, ROS levels and protein and mRNA levels of the ERS-associated proteins in the genioglossus muscle were significantly increased. Following supplementation with exogenous klotho protein, the klotho protein levels in the serum and genioglossus muscle tissue of mice were found to be markedly increased, and the apoptotic rate, ROS levels and protein and mRNA levels of the ERS-associated proteins in the genioglossus muscle were decreased compared with those in the CIH group. Taken together, the results of the present study have demonstrated that exogenous klotho may inhibit apoptosis of genioglossus myocytes in mice by inhibiting ROS-associated ERS.

Evaluation of serum and aqueous humor klotho levels in pseudoexfoliation syndrome, pseudoexfoliation and primary open-angle glaucoma

PURPOSE

The aim of our study was to compare klotho in the serum and aqueous humor of patients with primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma (PEXG) and pseudoexfoliation syndrome (PEX).

MATERIALS AND METHODS

18 POAG, 20 PEXG, 19 PEX and 20 control patients were included in our study. Aqueous humor and serum samples were collected at the time of cataract surgery. Samples were collected using enzyme-linked immunosorbent assay to evaluate the levels of Klotho protein.

RESULTS

Klotho levels in the serum and aqueous humor of PEXG patients (34.45 ± 3.59, 0.20 ± 0.15 ng/ml), PEX (35.85 ± 4.26, 0.23 ± 0.20 ng/ml) patients and POAG patients (35.99 ± 3.73, 0.25 ± 0.20 ng/ml) were significantly lower than control group (40.14 ± 3.85, 0.53 ± 0.39 ng/ml) (PEXG, P < 0.001, P < 0.001; PEX, P = 0.002, P = 0.003; POAG, P = 0.006, P = 0.003, respectively). Both serum and aqueous levels of klotho in the PEXG and PEX patients were lower than POAG patients, but the difference did not reach statistical significance (PEXG & POAG P = 0.149, P = 0.696), (PEX & POAG P = 0.845, P = 0.775).

CONCLUSION

Klotho levels in the serum and aqueous humor decreased in PEX, PEXG and POAG groups compared to control group, but the reduction was most significant in PEXG group.

Klotho attenuates angiotensin II‑induced cardiotoxicity through suppression of necroptosis and oxidative stress

Hyperglycemia is known to lead to cardiac injury and inflammation through the reactive oxygen species (ROS)‑Toll‑like receptor 4 (TLR4)‑necroptosis pathway. Similarly, angiotensin II (Ang II) activates the TLR4‑nuclear factor κB (NF‑κB) p65 pathway, while the protein Klotho is known to inhibit this pathway, protecting cardiac cells from Ang II‑induced injury. However, there is currently a lack of data on whether necroptosis participates in Ang II‑induced cardiac injury and whether the Klotho protein has an effect on this process. The present study aimed to explore whether inhibition of the TLR4/NF‑κB p65 necroptosis pathway is involved in the Klotho protein‑mediated protection against the Ang II‑induced cardiac injury and inflammation. H9c2 cardiac cells were incubated with 0.01 mM Ang II. Western blotting was used to assess the expression of receptor‑interacting protein kinase 3 (RIP3), mixed‑lineage kinase domain‑like protein (MLKL), TLR4 and NF‑κB p65. The present study also assessed injury indexes: Inflammatory cytokine expression, mitochondrial membrane potential (ΔΨm), apoptosis, ROS production and cell viability. The expression of TLR4, phosphorylated (p)‑NF‑κB p65, RIP3 and MLKL were increased by incubation with Ang II in H9c2 cells. The pretreatment of H9c2 cells with necrostatin‑1 (Nec‑1, an inhibitor of necroptosis) or TAK‑242 (a small molecule inhibitor of TLR4) attenuated the upregulation of RIP3 and MLKL caused by Ang II. Klotho protein cotreatment also reversed the Ang II‑induced upregulation of TLR4, p‑NF‑κB p65, RIP3 and MLKL. Furthermore, Ang II decreased cell viability and upregulated the secretion of inflammatory cytokines, ΔΨm loss and ROS generation blocked by pretreatment with Nec‑1 or Klotho protein. Thus, it was determined that Klotho can attenuate the Ang II‑induced necroptosis of cardiomyocytes through the TLR4/NF‑κB p65 pathway, which suggests that Klotho could be a potential therapeutic drug against Ang II‑induced cardiotoxicity.

Klotho Levels are Decreased and Associated with Enhanced Oxidative Stress and Inflammation in the Aqueous Humor in Patients with Exudative Age-related Macular Degeneration

PURPOSE

To evaluate anti-aging protein klotho levels in the aqueous humor and its association with oxidative stress and inflammation in patients with age-related macular degeneration (AMD).

METHODS

Levels of klotho, oxidative, and antioxidative stress markers, and proinflammatory and anti-inflammatory markers in the aqueous humor from 28 patients with exudative AMD and 35 age-matched controls were measured.

RESULTS

Patients with AMD had lower levels of klotho, which were negatively correlated with macular lesion size. Patients with AMD also exhibited increased levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and interleukin (IL)-6 but not tumor necrosis factor‑α, and decreased levels of total antioxidant status (TAS) and IL-10. Moreover, levels of klotho were negatively correlated with levels of 8-OHdG and IL-6, but positively correlated with levels of TSA and IL-10.

CONCLUSION

Klotho levels in the aqueous humor are decreased and associated with oxidative stress and inflammation in patients with exudative AMD.

Increased immunosuppression impairs tissue homeostasis with aging and age-related diseases

Abstract

Chronic low-grade inflammation is a common hallmark of the aging process and many age-related diseases. There is substantial evidence that persistent inflammation is associated with a compensatory anti-inflammatory response which prevents excessive tissue damage. Interestingly, the inflammatory state encountered with aging, called inflammaging, is associated with the anti-inflammaging process. The age-related activation of immunosuppressive network includes an increase in the numbers of myeloid-derived suppressor cells (MDSC), regulatory T cells (Treg), and macrophages (Mreg/M2c). Immunosuppressive cells secrete several anti-inflammatory cytokines, e.g., TGF-β and IL-10, as well as reactive oxygen and nitrogen species (ROS/RNS). Moreover, immunosuppressive cells suppress the function of effector immune cells by catabolizing l-arginine and tryptophan through the activation of arginase 1 (ARG1) and indoleamine 2,3-dioxygenase (IDO), respectively. Unfortunately, the immunosuppressive armament also induces harmful bystander effects in neighboring cells by impairing host tissue homeostasis. For instance, TGF-β signaling can trigger many age-related degenerative changes, e.g., cellular senescence, fibrosis, osteoporosis, muscle atrophy, and the degeneration of the extracellular matrix. In addition, changes in the levels of ROS, RNS, and the metabolites of the kynurenine pathway can impair tissue homeostasis. This review will examine in detail the harmful effects of the immunosuppressive cells on host tissues. It seems that this age-related immunosuppression prevents inflammatory damage but promotes the tissue degeneration associated with aging and age-related diseases.

Key messages

• Low-grade inflammation is associated with the aging process and age-related diseases.

• Persistent inflammation activates compensatory immunosuppression with aging.

• The numbers of immunosuppressive cells increase with aging and age-related diseases.

• Immunosuppressive mechanisms evoke harmful bystander effects in host tissues.

• Immunosuppression promotes tissue degeneration with aging and age-related diseases.

Genes and Pathways Implicated in Tetralogy of Fallot Revealed by Ultra-Rare Variant Burden Analysis in 231 Genome Sequences

Recent genome-wide studies of rare genetic variants have begun to implicate novel mechanisms for tetralogy of Fallot (TOF), a severe congenital heart defect (CHD). To provide statistical support for case-only data without parental genomes, we re-analyzed genome sequences of 231 individuals with TOF (n = 175) or related CHD. We adapted a burden test originally developed for de novo variants to assess ultra-rare variant burden in individual genes, and in gene-sets corresponding to functional pathways and mouse phenotypes, accounting for highly correlated gene-sets and for multiple testing. For truncating variants, the gene burden test confirmed significant burden in FLT4 (Bonferroni corrected p-value < 0.01). For missense variants, burden in NOTCH1 achieved genome-wide significance only when restricted to constrained genes (i.e., under negative selection, Bonferroni corrected p-value = 0.004), and showed enrichment for variants affecting the extracellular domain, especially those disrupting cysteine residues forming disulfide bonds (OR = 39.8 vs. gnomAD). Individuals with NOTCH1 ultra-rare missense variants, all with TOF, were enriched for positive family history of CHD. Other genes not previously implicated in CHD had more modest statistical support in gene burden tests. Gene-set burden tests for truncating variants identified a cluster of pathways corresponding to VEGF signaling (FDR = 0%), and of mouse phenotypes corresponding to abnormal vasculature (FDR = 0.8%); these suggested additional candidate genes not previously identified (e.g., WNT5A and ZFAND5). Results for the most promising genes were driven by the TOF subset of the cohort. The findings support the importance of ultra-rare variants disrupting genes involved in VEGF and NOTCH signaling in the genetic architecture of TOF, accounting for 11–14% of individuals in the TOF cohort. These proof-of-principle data indicate that this statistical methodology could assist in analyzing case-only sequencing data in which ultra-rare variants, whether de novo or inherited, contribute to the genetic etiopathogenesis of a complex disorder.

Klotho, Aging, and the Failing Kidney

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in the diseasome of aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology. A range of senotherapeutic strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists and indirect approaches, via modulation of the foodome and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes within the diseasome of aging.

BMP9 attenuates occurrence of venous malformation by maintaining endothelial quiescence and strengthening vessel walls via SMAD1/5/ID1/α-SMA pathway

Venous malformation (VM) is a type of vascular morphogenic defect in humans with an incidence of 1%. Although gene mutation is considered as the most common cause of VM, the pathogenesis of those without gene mutation remains to be elucidated. Here, we aimed to explore the relation of bone morphogenetic protein 9 (BMP9) and development of VM. At first, we found serum and tissue BMP9 expression in VM patients was significantly lower than that in healthy subjects, detected via enzyme-linked immunosorbent assay. Next, with wound healing assay, transwell assay and tube formation assay, we discovered BMP9 could inhibit migration and enhance tube formation activity of human umbilical vein endothelial cells (HUVECs) via receptor activin receptor-like kinase 1 (ALK1). Besides, BMP9 improved the expression of structural proteins alpha-smooth muscle actin (α-SMA) and Desmin in human umbilical vein smooth muscle cells (HUVSMCs) via activation of the SMAD1/5-ID1 pathway, determined by RNA-based next-generation sequencing, qPCR, immunofluorescence and western blotting. Intriguingly, this effect could be blocked by receptor ALK1 inhibitor, SMAD1/5 inhibitor and siRNAs targeting ID1, verifying the BMP9/ALK1/SMAD1/5/ID1/α-SMA pathway. Meanwhile, knocking out BMP9 in C57BL/6 mice embryo led to α-SMA scarcity in walls of lung and mesenteric vessels, as well as walls of small trachea. BMP9-/- zebrafish also exhibited abnormal vascular maturity, indicating a critical role of BMP9 in vascular maturity and remodeling. Finally, a VM mice model revealed that BMP9 might have therapeutic effect in VM progression. Our study discovered that BMP9 might inhibit the occurrence of VM by strengthening the vessel wall and maintaining endothelium quiescence. These findings provide promising evidences of new therapeutic targets that might be used for the management of VM.

Diabetes Mellitus and Vitamin D Deficiency:Comparable Effect on Survival and a DeadlyAssociation after a Myocardial Infarction

Survivors after a myocardial infarction (MI), especially those with diabetes mellitus (DM),remain at high risk of further events. Identifying and treating factors that may influence survivalmay open new therapeutic strategies. We assessed the impact on prognosis of DM andhypovitaminosis D (hypovitD), alone or combined. In this prospective, observational study, 1081patients were enrolled surviving an MI and divided into four groups according to their diabetic andVitD status. The primary end-point was composite of all-cause mortality, angina/MI and heartfailure (HF). Secondary outcomes were mortality, HF and angina/MI. During a follow-up of 26.1months (IQR 6.6-64.5), 391 subjects experienced the primary end-point. Patients with DM orhypovitD had similar rate of the composite end-point. Patients with only hypovitD or DM did notdiffer regarding components of composite end-point (angina p = 0.97, HF p = 0.29, mortality p = 0.62).DM and VitD deficiency had similarly adjusted risks for primary end-point (HR 1.3, 95%CI 1.05-1.61; HR 1.3, 95% CI 1.04-1.64). The adjusted HR for primary composite end-point for patients withhypovitD and DM was 1.69 (95%CI 1.25-2.29, p = 0.001) in comparison to patients with neitherhypoD nor DM. In conclusion, DM and hypovitD, individually and synergistically, are associatedwith a worse outcome after MI.

Klotho-HIV and Oxidative Stress: The Role of Klotho in Cardiovascular Disease Under HIV Infection-A Review

Combined antiretroviral therapy has improved quality and life expectancy of people living with human immunodeficiency virus (HIV). However, this therapy increases oxidative stress (OS), which in turn causes alterations in lipid and carbon metabolism, kidney disease, liver cirrhosis, and increased risk of cardiovascular disease. The Klotho gene has been implicated in cardiovascular risk increase. Klotho protein expression at X level decreases the risk of heart disease. HIV-positive people usually present low plasma levels of Klotho; thus, contributing to some extent to an increase in cardiovascular risk for these types of patients, mostly by favoring atherosclerosis. Therefore, our aim is to provide an overview of the effect of OS on Klotho protein and its consequent cardiometabolic alterations in HIV-positive patients on antiretroviral therapy.

The Role of Gut Dysbiosis in the Bone-Vascular Axis in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) are at increased risk of bone mineral density loss and vascular calcification. Bone demineralization and vascular mineralization often concur in CKD, similar to what observed in the general population. This contradictory association is commonly referred to as the 'calcification paradox' or the bone-vascular axis. Mounting evidence indicates that CKD-associated gut dysbiosis may be involved in the pathogenesis of the bone-vascular axis. A disrupted intestinal barrier function, a metabolic shift from a predominant saccharolytic to a proteolytic fermentation pattern, and a decreased generation of vitamin K may, alone or in concert, drive a vascular and skeletal pathobiology in CKD patients. A better understanding of the role of gut dysbiosis in the bone-vascular axis may open avenues for novel therapeutics, including nutriceuticals.

Serum Klotho, Cardiovascular Events, and Mortality in Nondiabetic Chronic Kidney Disease

Background: Experimental studies indicate that Klotho deficiency is a pathogenic factor for CKD-related complications, including cardiovascular disease (CVD). However, the association between serum Klotho and clinical outcomes in nondiabetic CKD patients needs to be further clarified. We aimed to determine whether serum Klotho levels are associated with CVD events and mortality in predialysis CKD patients without diabetes. Methods: A total of 336 CKD stage 2–5 predialysis patients without diabetes were recruited and followed from the end of 2014 to January 2019 for CVD events and overall mortality. Serum Klotho was detected by ELISA and divided into quartiles (lowest, middle, second highest, and highest quartiles) according to their serum Klotho category. Results: After a median follow-up of 3.52 years (IQR 3.34–3.76), Kaplan-Meier analysis showed that, compared to participants with a Klotho level in the highest quartile (the reference category), those in the lowest Klotho quartile were associated with a higher all-cause mortality risk (HR = 7.05; 95% CI 1.59–31.25) and a higher CVD event risk (HR = 3.02; 95% CI 1.45–6.30). In addition, the middle Klotho quartile was also associated with CVD event risk (HR = 2.56; 95% CI 1.21–5.41). Moreover, in the multivariate-adjusted model, the lowest Klotho quartile remained significantly associated with all-cause mortality (HR = 5.17; 95% CI 1.07–24.96), and the middle Klotho quartile maintained a significant association with CVD event risk (HR = 2.32; 95% CI 1.03–5.21). Conclusion: These results suggest that lower serum Klotho levels are independently associated with overall mortality and CVD events in nondiabetic predialysis CKD patients.

Inflammation and Premature Ageing in Chronic Kidney Disease

Persistent low-grade inflammation and premature ageing are hallmarks of the uremic phenotype and contribute to impaired health status, reduced quality of life, and premature mortality in chronic kidney disease (CKD). Because there is a huge global burden of disease due to CKD, treatment strategies targeting inflammation and premature ageing in CKD are of particular interest. Several distinct features of the uremic phenotype may represent potential treatment options to attenuate the risk of progression and poor outcome in CKD. The nuclear factor erythroid 2-related factor 2 (NRF2)-kelch-like erythroid cell-derived protein with CNC homology [ECH]-associated protein 1 (KEAP1) signaling pathway, the endocrine phosphate-fibroblast growth factor-23-klotho axis, increased cellular senescence, and impaired mitochondrial biogenesis are currently the most promising candidates, and different pharmaceutical compounds are already under evaluation. If studies in humans show beneficial effects, carefully phenotyped patients with CKD can benefit from them.

NAFLD as a driver of chronic kidney disease

Non-alcoholic fatty liver disease (NAFLD) and chronic kidney disease (CKD) are worldwide public health problems, affecting up to 25-30% (NAFLD), and up to 10-15% (CKD) of the general population. Recently, it has also been established that there is a strong association between NAFLD and CKD, regardless of the presence of potential confounding diseases such as obesity, hypertension and type 2 diabetes. Since NAFLD and CKD are both common diseases that often occur alongside other metabolic conditions, such as type 2 diabetes or metabolic syndrome, elucidating the relative impact of NAFLD on the risk of incident CKD presents a substantial challenge for investigators working in this research field. A growing body of epidemiological evidence suggests that NAFLD is an independent risk factor for CKD and recent evidence also suggests that associated factors such as metabolic syndrome, dysbiosis, unhealthy diets, platelet activation and processes associated with ageing could also contribute mechanisms linking NAFLD and CKD. This narrative review provides an overview of the literature on: a) the evidence for an association and causal link between NAFLD and CKD and b) the underlying mechanisms by which NAFLD (and factors strongly linked with NAFLD) may increase the risk of developing CKD.

Protective potential of klotho protein on diabetic retinopathy: Evidence from clinical and in vitro studies

AIMS/INTRODUCTION

The purpose of the present study was to observe the relationship between serum α-klotho (KL) protein level and diabetic retinopathy (DR), and to further examine the effects of KL protein on apoptosis induced by palmitic acid (PA) in human retinal endothelial cells.

MATERIALS AND METHODS

A total of 17 healthy people and 60 type 2 diabetes patients were included. According to the results from fundus fluorescein angiography, the diabetes patients were divided into three subgroups: without DR, non-proliferative DR and proliferative DR. Serum KL level was measured by enzyme-linked immunosorbent assay. In vitro, human retinal endothelial cells were exposed to PA with or without KL protein. Apoptosis rates were analyzed by flow cytometry analysis. Apoptotic-related protein expressions were detected by western blotting analysis.

RESULTS

Serum KL level was lower in diabetes patients than that in healthy participants (P = 0.007), and was gradually decreased among the without DR, non-proliferative DR and proliferative DR subgroups (P = 0.045). A logistic regression analysis showed that after adjusting for the other confounding factors, serum KL level was independently and negatively related with DR (P = 0.049). Furthermore, the increased apoptosis rates induced by PA were inhibited with the addition of KL protein. Consistently, KL protein reversed the expression levels of the increased pro-apoptotic protein Bax and the decreased anti-apoptotic protein Bcl-2 induced by PA. However, the anti-apoptotic effect of KL protein was attenuated by LY294002 through the phosphatidylinositol 3 kinase-serine∕threonine kinase pathway.

CONCLUSIONS

The data suggested that KL protein was probably a potential protective factor against retinopathy in type 2 diabetes patients.

Salusin-β Promotes Vascular Calcification via Nicotinamide Adenine Dinucleotide Phosphate/Reactive Oxygen Species-Mediated Klotho Downregulation

Aims: Vascular calcification (VC) is a hallmark feature of cardiovascular disease and a significant risk factor for morbidity and mortality. Salusin-β exerts cardiovascular regulating effects in hypertension, atherosclerosis, and diabetes. The present study was designed to examine the roles of salusin-β in the progression of VC and its downstream signaling mechanisms. Results: Salusin-β expression in both the aortas of VC rats induced by vitamin D3 and nicotine and vascular smooth muscle cells (VSMCs) incubated with calcifying media was increased. Salusin-β knockdown remarkably reduced VC, whereas overexpression of salusin-β exacerbated VC both in vitro and in vivo. Overexpression of salusin-β promoted the VSMC osteochondrogenic transition, decreased Klotho protein levels, enhanced Ras-related C3 botulinum toxin substrate 1 (Rac1) activity and the translocation of p47phox to the membrane, increased the expression of nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase subunits and the production of reactive oxygen species (ROS) with or without calcifying media; however, salusin-β deficiency played the opposite roles. The calcification and downregulated Klotho protein levels induced by salusin-β were restored by ROS scavenger N-acetyl-l-cysteine, diphenyleneiodonium chloride [an inhibitor of flavin-containing enzyme, including NAD(P)H oxidase], or gene knockdown of NAD(P)H oxidase (NOX)-2, p22phox, or p47phox but were not affected by NOX-1 and NOX-4 knockdown. Klotho knockdown attenuated the protective effect of salusin-β deficiency on VSMC calcification. By contrast, exogenous Klotho ameliorated the development of VC and ROS generation induced by salusin-β overexpression. Innovation: Salusin-β is a critical modulator in VC. Conclusion: Salusin-β regulates VC through activation of NAD(P)H/ROS-mediated Klotho downregulation, suggesting that salusin-β may be a novel target for treatment of VC.

The Klotho proteins in health and disease

The Klotho proteins, αKlotho and βKlotho, are essential components of endocrine fibroblast growth factor (FGF) receptor complexes, as they are required for the high-affinity binding of FGF19, FGF21 and FGF23 to their cognate FGF receptors (FGFRs). Collectively, these proteins form a unique endocrine system that governs multiple metabolic processes in mammals. FGF19 is a satiety hormone that is secreted from the intestine on ingestion of food and binds the βKlotho-FGFR4 complex in hepatocytes to promote metabolic responses to feeding. By contrast, under fasting conditions, the liver secretes the starvation hormone FGF21, which induces metabolic responses to fasting and stress responses through the activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system following binding to the βKlotho-FGFR1c complex in adipocytes and the suprachiasmatic nucleus, respectively. Finally, FGF23 is secreted by osteocytes in response to phosphate intake and binds to αKlotho-FGFR complexes, which are expressed most abundantly in renal tubules, to regulate mineral metabolism. Growing evidence suggests that the FGF-Klotho endocrine system also has a crucial role in the pathophysiology of ageing-related disorders, including diabetes, cancer, arteriosclerosis and chronic kidney disease. Therefore, targeting the FGF-Klotho endocrine axes might have therapeutic benefit in multiple systems; investigation of the crystal structures of FGF-Klotho-FGFR complexes is paving the way for the development of drugs that can regulate these axes.

Bone-Vascular Axis in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) are at increased risk of osteoporosis and vascular calcification. Bone demineralization and vascular mineralization go often hand in hand in CKD, similar to as in the general population. This contradictory association is independent of aging and is commonly referred to as the "calcification paradox" or the bone-vascular axis. Various common risk factors and mechanisms have been identified. Alternatively, calcifying vessels may release circulating factors that affect bone metabolism, while bone disease may infer conditions that favor vascular calcification. The present review focuses on emerging concepts and major mechanisms involved in the bone-vascular axis in the setting of CKD. A better understanding of these concepts and mechanisms may identify therapeutics able to target and exert beneficial effects on bone and vasculature simultaneously.