Endothelial sirtuin 1 deficiency perpetrates nephrosclerosis through downregulation of matrix metalloproteinase-14: relevance to fibrosis of vascular senescence

Lumican Is Both a Novel Risk Factor and Potential Plasma Biomarker for Vascular Aging, Capable of Promoting Vascular Smooth Cells Senescence Through Interacting With Integrin α2β1

Vascular aging, a common pathogenesis of senile chronic diseases, significantly increases morbidity and mortality in older adults; its intricate cellular and molecular mechanisms necessitate further investigation. Lumican (LUM) and integrin α2β1 are profibrotic extracellular matrix proteins and vital cell regulatory receptors, respectively. However, their roles in vascular aging remain unclear. This study sought to elucidate the connection between LUM and vascular aging as well as the biological mechanism of LUM/integrin α2β1 in this process. Using an enzyme-linked immunosorbent assay, we discovered that plasma LUM was elevated in vascular aging individuals and was positively correlated with brachial-ankle pulse wave velocity. Additionally, immunohistochemical and Western blot analyses confirmed LUM upregulation in arteries of older adults and aged mice, as well as in senescent vascular smooth cells (VSMCs). Wild-type and LUM semiknockout (Lum-/+) mice, along with primary VSMCs extracted from these mice, were exposed to angiotensin II to induce a stress-induced senescence model. LUM semiknockout mitigated angiotensin II-induced arteriosclerosis, hypertension, vascular aging, and remodeling in mice. Both in vitro and in vivo studies revealed that LUM deficiency suppressed p53, p21, collagen 1, and collagen 3 upregulation and synthetic phenotype formation in VSMCs stimulated by angiotensin II. Treating VSMCs with an integrin α2β1 antagonist reversed the aforementioned changes triggered by LUM proteins. Briefly, LUM functions as a potential marker and risk factor for vascular aging and promotes pathological changes by affecting integrin α2β1 in VSMCs. This study introduces a novel molecular target for the early diagnosis and treatment of vascular aging and age-related vascular diseases.

Potential Nephroprotective Effect of Kaempferol: Biosynthesis, Mechanisms of Action, and Clinical Prospects

Kidney is an essential organ that is highly susceptible to cellular injury caused by various toxic substances in the blood. Several studies have shown that untreated injuries to this organ can cause glomerulosclerosis, tubulointerstitial fibrosis, and tubular cell apoptosis, leading to kidney failure. Despite significant advancements in modern treatment, there is no fully effective drug for repairing its function, providing complete protection, and assisting in cell regeneration. Furthermore, some available medications have been reported to exacerbate injuries, showing the need to explore alternative treatments. Natural drugs are currently being explored as a new therapeutic strategy for managing kidney diseases. Kaempferol, a polyphenol found in plants, including vegetables, legumes, and fruits, has been extensively studied in various nephrotoxicity protocols. The compound has been reported to have potential as a nephroprotective agent with beneficial effects on various physiological pathways, such as CPL-induced kidney injury, DOX, LPO, ROS, RCC, and diabetic nephropathy. Therefore, this study aims to provide a brief overview of the current nephroprotective effects of kaempferol, as well as its molecular mechanisms of action, biosynthesis pathways, and clinical prospects.

SIRT-associated attenuation of cellular senescence in vascular wall

This review focuses on the vital function that SIRT1 and other sirtuins play in promoting cellular senescence in vascular smooth muscle cells, which is a key element in the pathogenesis of vascular aging and associated cardiovascular diseases. Vascular aging is a gradual process caused by the accumulation of senescent cells, which results in increased vascular remodeling, stiffness, and diminished angiogenic ability. Such physiological alterations are characterized by a complex interplay of environmental and genetic variables, including oxidative stress and telomere attrition, which affect gene expression patterns and trigger cell growth arrest. SIRT1 has been highlighted for its potential to reduce cellular senescence through modulation of multiple signaling cascades, particularly the endothelial nitric oxide (eNOS)/NO signaling pathway. It also modulates cell cycle through p53 inactivation and suppresses NF-κB mediated expression of adhesive molecules at the vascular level. The study also examines the therapeutic potential of sirtuin modulation in vascular health, identifying SIRT1 and its sirtuin counterparts as potential targets for reducing vascular aging. This study sheds light on the molecular basis of vascular aging and the beneficial effects of sirtuins, paving the way for the development of tailored therapies aimed at enhancing vascular health and prolonging life.

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

Sirtuins in kidney health and disease

Sirtuins (SIRTs) are putative regulators of lifespan in model organisms. Since the initial discovery that SIRTs could promote longevity in nematodes and flies, the identification of additional properties of these proteins has led to understanding of their roles as exquisite sensors that link metabolic activity to oxidative states. SIRTs have major roles in biological processes that are important in kidney development and physiological functions, including mitochondrial metabolism, oxidative stress, autophagy, DNA repair and inflammation. Furthermore, altered SIRT activity has been implicated in the pathophysiology and progression of acute and chronic kidney diseases, including acute kidney injury, diabetic kidney disease, chronic kidney disease, polycystic kidney disease, autoimmune diseases and renal ageing. The renoprotective roles of SIRTs in these diseases make them attractive therapeutic targets. A number of SIRT-activating compounds have shown beneficial effects in kidney disease models; however, further research is needed to identify novel SIRT-targeting strategies with the potential to treat and/or prevent the progression of kidney diseases and increase the average human healthspan.

Roles of Sirt1 and its modulators in diabetic microangiopathy: A review

Diabetic vascular complications include diabetic macroangiopathy and diabetic microangiopathy. Diabetic microangiopathy is characterised by impaired microvascular endothelial function, basement membrane thickening, and microthrombosis, which may promote renal, ocular, cardiac, and peripheral system damage in diabetic patients. Therefore, new preventive and therapeutic strategies are urgently required. Sirt1, a member of the nicotinamide adenine dinucleotide-dependent histone deacetylase class III family, regulates different organ growth and development, oxidative stress, mitochondrial function, metabolism, inflammation, and aging. Sirt1 is downregulated in vascular injury and microangiopathy. Moreover, its expression and distribution in different organs correlate with age and play critical regulatory roles in oxidative stress and inflammation. This review introduces the background of diabetic microangiopathy and the main functions of Sirt1. Then, the relationship between Sirt1 and different diabetic microangiopathies and the regulatory roles mediated by different cells are described. Finally, we summarize the modulators that target Sirt1 to ameliorate diabetic microangiopathy as an essential preventive and therapeutic measure for diabetic microangiopathy. In conclusion, targeting Sirt1 may be a new therapeutic strategy for diabetic microangiopathy.

Permissive role of vascular endothelium in fibrosis: focus on the kidney

Fibrosis, the morphologic end-result of a plethora of chronic conditions and the scorch for organ function, has been thoroughly investigated. One aspect of its development and progression, namely the permissive role of vascular endothelium, has been overshadowed by studies into (myo)fibroblasts and TGF-β; thus, it is the subject of the present review. It has been established that tensile forces of the extracellular matrix acting on cells are a prerequisite for mechanochemical coupling, leading to liberation of TGF-β and formation of myofibroblasts. Increased tensile forces are prompted by elevated vascular permeability in response to diverse stressors, resulting in the exudation of fibronectin, fibrinogen/fibrin, and other proteins, all stiffening the extracellular matrix. These processes lead to the development of endothelial cells dysfunction, endothelial-to-mesenchymal transition, premature senescence of endothelial cells, perturbation of blood flow, and gradual obliteration of microvasculature, leaving behind "string" vessels. The resulting microvascular rarefaction is not only a constant companion of fibrosis but also an adjunct mechanism of its progression. The deepening knowledge of the above chain of pathogenetic events involving endothelial cells, namely increased permeability-stiffening of the matrix-endothelial dysfunction-microvascular rarefaction-tissue fibrosis, may provide a roadmap for therapeutic interventions deemed to curtail and reverse fibrosis.

Sirtuins in kidney diseases: potential mechanism and therapeutic targets

Sirtuins, which are NAD+-dependent class III histone deacetylases, are involved in various biological processes, including DNA damage repair, immune inflammation, oxidative stress, mitochondrial homeostasis, autophagy, and apoptosis. Sirtuins are essential regulators of cellular function and organismal health. Increasing evidence suggests that the development of age-related diseases, including kidney diseases, is associated with aberrant expression of sirtuins, and that regulation of sirtuins expression and activity can effectively improve kidney function and delay the progression of kidney disease. In this review, we summarise current studies highlighting the role of sirtuins in renal diseases. First, we discuss sirtuin family members and their main mechanisms of action. We then outline the possible roles of sirtuins in various cell types in kidney diseases. Finally, we summarise the compounds that activate or inhibit sirtuin activity and that consequently ameliorate renal diseases. In conclusion, targeted modulation of sirtuins is a potential therapeutic strategy for kidney diseases. Video Abstract.

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.

DYRK1B inhibition exerts senolytic effects on endothelial cells and rescues endothelial dysfunctions

Aging is the major risk factor for chronic disease development. Cellular senescence is a key mechanism that triggers or contributes to age-related phenotypes and pathologies. The endothelium, a single layer of cells lining the inner surface of a blood vessel, is a critical interface between blood and all tissues. Many studies report a link between endothelial cell senescence, inflammation, and diabetic vascular diseases. Here we identify, using combined advanced AI and machine learning, the Dual Specificity Tyrosine Phosphorylation Regulated Kinase 1B (DYRK1B) protein as a possible senolytic target for senescent endothelial cells. We demonstrate that upon induction of senescence in vitro DYRK1B expression is increased in endothelial cells and localized at adherens junctions where it impairs their proper organization and functions. DYRK1B knock-down or inhibition restores endothelial barrier properties and collective behavior. DYRK1B is therefore a possible target to counteract diabetes-associated vascular diseases linked to endothelial cell senescence.

Mitochondrial Oxidative Metabolism: An Emerging Therapeutic Target to Improve CKD Outcomes

Chronic kidney disease (CKD) predisposes one toward end-stage renal disease (ESRD) and its associated morbidity and mortality. Significant metabolic perturbations in conjunction with alterations in redox status during CKD may induce increased production of reactive oxygen species (ROS), including superoxide (O₂^●-) and hydrogen peroxide (H₂O₂). Increased O₂^●- and H₂O₂ may contribute to the overall progression of renal injury as well as catalyze the onset of comorbidities. In this review, we discuss the role of mitochondrial oxidative metabolism in the pathology of CKD and the recent developments in treating CKD progression specifically targeted to the mitochondria. Recently published results from a Phase 2b clinical trial by our group as well as recently released data from a ROMAN: Phase 3 trial (NCT03689712) suggest avasopasem manganese (AVA) may protect kidneys from cisplatin-induced CKD. Several antioxidants are under investigation to protect normal tissues from cancer-therapy-associated injury. Although many of these antioxidants demonstrate efficacy in pre-clinical models, clinically relevant novel compounds that reduce the severity of AKI and delay the progression to CKD are needed to reduce the burden of kidney disease. In this review, we focus on the various metabolic pathways in the kidney, discuss the role of mitochondrial metabolism in kidney disease, and the general involvement of mitochondrial oxidative metabolism in CKD progression. Furthermore, we present up-to-date literature on utilizing targets of mitochondrial metabolism to delay the pathology of CKD in pre-clinical and clinical models. Finally, we discuss the current clinical trials that target the mitochondria that could potentially be instrumental in advancing the clinical exploration and prevention of CKD.

Cellular senescence and the blood-brain barrier: Implications for aging and age-related diseases

The blood-brain barrier (BBB) is a critical physiochemical interface that regulates communication between the brain and blood. It is comprised of brain endothelial cells which regulate the BBB's barrier and interface properties and is surrounded by supportive brain cell types including pericytes and astrocytes. Recent reports have suggested that the BBB undergoes dysfunction during normative aging and in disease. In this review, we consider the effect of cellular senescence, one of the nine hallmarks of aging, on the BBB. We first characterize known normative age-related changes at the BBB, and then evaluate changes in neurodegenerative diseases, with an emphasis on if/how cellular senescence is influencing these changes. We then discuss what insight has been gained from in vitro and in vivo studies of cellular senescence at the BBB. Finally, we evaluate mechanisms by which cellular senescence in peripheral pathologies can indirectly or directly affect BBB function.

The sirtuin family in health and disease

Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.

Sirtuins and chemokines as markers of replicative and induced senescence of human endotheliocytes

Background. One of the factors of the pathogenesis of atherosclerosis and other cardiovascular diseases is induced endothelial senescence. In this regard, the urgent task of molecular biology and medicine is the search for molecules that affect the process of vascular endotheliocytes senescence.The aim. To assess the expression of Sirt-1,3,6 and chemokines IL-4, CXCL11 in the replicative and induced senescence of human endotheliocytes.Materials and methods. The study was conducted on the primary culture of isolated human umbilical vein endothelial cells (HUVECs). HUVECs were cultured under conditions of replicative (natural) and lipopolysaccharide induced senescence.Results. The synthesis of Sirt-1,3,6, IL-4 and CXCL11 was evaluated using western blot analysis. We revealed a decrease in Sirt-1,3,6 synthesis by 1.6–1.8 times (р < 0.05) in the conditions of HUVEC replicative senescence. Induced senescence of endotheliocytes is characterized by a more pronounced decrease (1.7–3.4 times; р < 0.05) in the Sirt-1,3,6 synthesis. CXCL11 synthesis increases by 1.4 times (р < 0.05) in replicative and by 3.4 times (р < 0.05) in induced HUVEC senescence. IL-4 synthesis increases by 4.7 times in conditions of induced HUVEC senescence and doesn’t have changes in replicative senescence of endotheliocytes.Conclusion. These data obtained indicate that sirtuins and chemokines play an important role in the development of endothelial dysfunction observed in natural and induced senescence.

Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

Factors and Pathways Modulating Endothelial Cell Senescence in Vascular Aging

Aging causes a progressive decline in the structure and function of organs. With advancing age, an accumulation of senescent endothelial cells (ECs) contributes to the risk of developing vascular dysfunction and cardiovascular diseases, including hypertension, diabetes, atherosclerosis, and neurodegeneration. Senescent ECs undergo phenotypic changes that alter the pattern of expressed proteins, as well as their morphologies and functions, and have been linked to vascular impairments, such as aortic stiffness, enhanced inflammation, and dysregulated vascular tone. Numerous molecules and pathways, including sirtuins, Klotho, RAAS, IGFBP, NRF2, and mTOR, have been implicated in promoting EC senescence. This review summarizes the molecular players and signaling pathways driving EC senescence and identifies targets with possible therapeutic value in age-related vascular diseases.

Extracellular vesicle-associated microRNA-30b-5p activates macrophages through the SIRT1/ NF-κB pathway in cell senescence

Chronic inflammation is widely observed in aging, but it is unclear whether extracellular vesicles (EVs) play a role in chronic disease-associated senescence. In our study, LC/MS profiling revealed that senescent cell derived EVs (SEN EVs) activate the immune response pathways of macrophages. Significantly more EVs were found in the supernatant of SEN than of control (CON) cell cultures, and SEN EVs were enriched in miR-30b-5p, which directly target sirtuin1 (SIRT1). In vitro, we found that SEN EV treatment resulted in increased cellular levels of interleukin-1β (IL-1β) and IL-6 and decreased levels of SIRT1. Increased cytokine levels could be reversed by SIRT1 activation and miR-30b-5p inhibition. Furthermore, miR-30b-5p significantly increased with age in both mouse liver tissue and EVs harvested from the tissue, with differences in EVs observed both earlier and in the later magnitude of aging. Western blot and qPCR proved that miR-30b-5p downregulated the level of SIRT1 in mouse macrophages. Collectively, we propose that EVs carrying miR-30b-5p from SEN cells can induce chronic inflammation through macrophage activation. This occurs through the downregulation of SIRT1 and the corresponding activation of NF-κB pathways that enhance pro-inflammatory cytokine production. Collectively, these results demonstrate that EVs carrying pro-inflammatory signals are released by SEN cells and then activate immune cells in the SEN microenvironment, changing the inflammatory balance. Our results also explain why inflammation increases with age even though SEN cells can be immediately eliminated under rigorous immune surveillance.

SIRT6 in Vascular Diseases, from Bench to Bedside

Aging is a key risk factor for angiogenic dysfunction and cardiovascular diseases, including heart failure, hypertension, atherosclerosis, diabetes, and stroke. Members of the NAD+-dependent class III histone deacetylase family, sirtuins, are conserved regulators of aging and cardiovascular and cerebrovascular diseases. The sirtuin SIRT6 is predominantly located in the nucleus and shows deacetylase activity for acetylated histone 3 lysine 56 and lysine 9 as well as for some non-histone proteins. Over the past decade, experimental analyses in rodents and non-human primates have demonstrated the critical role of SIRT6 in extending lifespan. Recent studies highlighted the pleiotropic protective actions of SIRT6 in angiogenesis and cardiovascular diseases, including atherosclerosis, hypertension, heart failure, and stroke. Mechanistically, SIRT6 participates in vascular diseases via epigenetic regulation of endothelial cells, vascular smooth muscle cells, and immune cells. Importantly, SIRT6 activators (e.g., MDL-800/MDL-811) have provided therapeutic value for treating age-related vascular disorders. Here, we summarized the roles of sirtuins in cardiovascular diseases; reviewed recent advances in the understanding of SIRT6 in vascular biology, cardiovascular aging, and diseases; highlighted its therapeutic potential; and discussed future perspectives.

Sirtuin 1 in Chronic Kidney Disease and Therapeutic Potential of Targeting Sirtuin 1

The incidence and prevalence of chronic kidney disease (CKD) continue to increase worldwide remaining as a major public health burden. CKD eventually progresses to end-stage kidney failure and patients with CKD have high morbidity and mortality. Sirtuin 1 (SIRT1), a NAD+-dependent deacetylases, has significant renal protective effects through its regulation of fibrosis, apoptosis, and senescence, oxidative stress, inflammation and aging process. The renal protective effects of Sirt1 have been described in many kidney diseases such as diabetic kidney disease and HIV-related kidney disease. SIRT1 also has protective effects against vascular calcification and therefore could be developed as a therapy for both CKD and CKD complications. In this narrative review, we will give an overview of the recent progress on the role of SIRT1 and its downstream pathways in CKD. We will also discuss potential therapeutic approach by activating SIRT1-related pathway in patients with CKD. The purpose is to hope to provide some insights on the future direction of the research in the field of SIRT1 for CKD.

Recent Advances in Epigenetics of Age-Related Kidney Diseases

Renal aging has attracted increasing attention in today’s aging society, as elderly people with advanced age are more susceptible to various kidney disorders such as acute kidney injury (AKI) and chronic kidney disease (CKD). There is no clear-cut universal mechanism for identifying age-related kidney diseases, and therefore, they pose a considerable medical and public health challenge. Epigenetics refers to the study of heritable modifications in the regulation of gene expression that do not require changes in the underlying genomic DNA sequence. A variety of epigenetic modifiers such as histone deacetylases (HDAC) inhibitors and DNA methyltransferase (DNMT) inhibitors have been proposed as potential biomarkers and therapeutic targets in numerous fields including cardiovascular diseases, immune system disease, nervous system diseases, and neoplasms. Accumulating evidence in recent years indicates that epigenetic modifications have been implicated in renal aging. However, no previous systematic review has been performed to systematically generalize the relationship between epigenetics and age-related kidney diseases. In this review, we aim to summarize the recent advances in epigenetic mechanisms of age-related kidney diseases as well as discuss the application of epigenetic modifiers as potential biomarkers and therapeutic targets in the field of age-related kidney diseases. In summary, the main types of epigenetic processes including DNA methylation, histone modifications, non-coding RNA (ncRNA) modulation have all been implicated in the progression of age-related kidney diseases, and therapeutic targeting of these processes will yield novel therapeutic strategies for the prevention and/or treatment of age-related kidney diseases.

The effects of exercise on kidney injury: the role of SIRT1

In patients with kidney injury, muscle mass and strength decrease with altered muscle protein synthesis and degradation along with complications such as inflammation and low physical activity. A treatment strategy to maintain muscle metabolism in kidney injury is important. One of the proposed strategies in this regard is exercise, which in addition to inducing muscle hypertrophy, reducing plasma creatinine and urea and decreasing the severity of tubal injuries, can boost immune function and has anti-inflammatory effects. One of the molecules that have been considered as a target in the treatment of many diseases is silent information regulator 1 (SIRT1). Exercise increases the expression of SIRT1 and improves its activity. Therefore, studies that examined the effect of exercise on kidney injury considering the role of SIRT1 in this effect were reviewed to determine the direction of kidney injury research in future regarding to its prevalence, especially following diabetes, and lack of definitive treatment. In this review, we found that SIRT1 can be one of renoprotective target pathways of exercise. However, further studies are needed to determine the role of SIRT1 in different kidney injuries following exercise according to the type and severity of exercise, and the type of kidney injury.

Potential of Polyphenols to Restore SIRT1 and NAD+ Metabolism in Renal Disease

SIRT1 is an NAD⁺-dependent class III histone deacetylase that is abundantly expressed in the kidney, where it modulates gene expression, apoptosis, energy homeostasis, autophagy, acute stress responses, and mitochondrial biogenesis. Alterations in SIRT1 activity and NAD⁺ metabolism are frequently observed in acute and chronic kidney diseases of diverse origins, including obesity and diabetes. Nevertheless, in vitro and in vivo studies and clinical trials with humans show that the SIRT1-activating compounds derived from natural sources, such as polyphenols found in fruits, vegetables, and plants, including resveratrol, quercetin, and isoflavones, can prevent disease and be part of treatments for a wide variety of diseases. Here, we summarize the roles of SIRT1 and NAD⁺ metabolism in renal pathophysiology and provide an overview of polyphenols that have the potential to restore SIRT1 and NAD⁺ metabolism in renal diseases.

Exosomes Secreted by Mesenchymal Stem Cells Induce Immune Tolerance to Mouse Kidney Transplantation via Transporting LncRNA DANCR

Mesenchymal stem cells induce kidney transplant tolerance by increasing regulatory T (Treg) cells. Bone marrow mesenchymal stem cell exosomes (BMMSC-Ex) promote Treg cell differentiation. Long non-coding RNA differentiation antagonizing non-protein coding RNA (DANCR) is expressed in BMMSCs and can be encapsulated in exosomes. We aimed to explore the role of DANCR in BMMSC-Ex in immune tolerance after kidney transplantation and related mechanism. The isogenic/allograft kidney transplantation mouse model was established, and levels of serum creatinine (SCr) were determined. Hematoxylin-eosin staining was conducted to detect the inflammation, and immunohistochemistry was performed to detect the infiltration of CD4+ T cells. Levels of IFN-γ, IL-17, and IL-2 were examined by ELISA. Flow cytometry was conducted to determine Treg cells. In the allograft group, the inflammatory response was severe, CD4+ T cell infiltration, SCr levels, and plasma rejection-related factors were up-regulated, while injection of BMMSC-Ex reversed the results. BMMSC-Ex increased Treg cells in kidney transplantation mice. Interference with DANCR reversed the promoting effect of BMMSC-Ex on Treg cell differentiation. DANCR bound to SIRT1, promoted ubiquitination and accelerated its degradation. The injection of BMMSC-Ex (after interference with DANCR) promoted SIRT1 levels, inflammatory response, CD4+ T cell infiltration, SCr levels, and plasma rejection related factors' expression, while Treg cells were decreased. LncRNA DANCR in BMMSC-Ex promoted Treg cell differentiation and induced immune tolerance of kidney transplantation by down-regulating SIRT1 expression in CD4+ T cells.

Mechanisms of RPE senescence and potential role of αB crystallin peptide as a senolytic agent in experimental AMD

Oxidative stress in the retinal pigment epithelium (RPE) can cause mitochondrial dysfunction and is likely a causative factor in the pathogenesis of age-related macular degeneration (AMD). Under oxidative stress conditions, some of the RPE cells become senescent and a contributory role for RPE senescence in AMD pathology has been proposed. The purpose of this study is to 1) characterize senescence in human RPE; 2) investigate the effect of an αB Crystallin chaperone peptide (mini Cry) in controlling senescence, in particular by regulating mitochondrial function and senescence-associated secretory phenotype (SASP) production and 3) develop mouse models for studying the role of RPE senescence in dry and nAMD. Senescence was induced in human RPE cells in two ways. First, subconfluent cells were treated with 0.2 μg/ml doxorubicin (DOX); second, subconfluent cells were treated with 500 μM H₂O₂. Senescence biomarkers (senescence-associated beta-galactosidase (SA-βgal), p21, p16) and mitochondrial proteins (Fis1, DRP1, MFN2, PGC1-α, mtTFA) were analyzed in control and experimental groups. The effect of mini Cry on mitochondrial bioenergetics, glycolysis and SASP was determined. In vivo, retinal degeneration was induced by intravenous injection of NaIO3 (20 mg/kg) and subretinal fibrosis by laser-induced choroidal neovascularization. Increased SA-βgal staining and p16 and p21 expression was observed after DOX- or H₂O₂-induced senescence and mini Cry significantly decreased senescence-positive cells. The expression of mitochondrial biogenesis proteins PGC-1 and mTFA increased with senescence, and mini Cry reduced expression significantly. Senescent RPE cells were metabolically active, as evidenced by significantly enhanced oxidative phosphorylation and anaerobic glycolysis, mini Cry markedly reduced rates of respiration and glycolysis. Senescent RPE cells maintain a proinflammatory phenotype characterized by significantly increased production of cytokines (IFN-ˠ, TNF-α, IL1-α IL1-β, IL-6, IL-8, IL-10), and VEGF-A; mini Cry significantly inhibited their secretion. We identified and localized senescent RPE cells for the first time in NaIO3-induced retinal degeneration and laser-induced subretinal fibrosis mouse models. We conclude that mini Cry significantly impairs stress-induced senescence by modulating mitochondrial biogenesis and fission proteins in RPE cells. Characterization of senescence could provide further understanding of the metabolic changes that accompany the senescent phenotype in ocular disease. Future studies in vivo may better define the role of senescence in AMD and the therapeutic potential of mini Cry as a senotherapeutic.

Exploration the potential mechanism of the SIRT1 and its target gene FOXO1/PPARGC1A in uteropelvic junction obstruction

Background

Uteropelvic junction obstruction (UPJO) is a common surgical condition, which refers to the blockage of urine flowing through kidney into proximal upper ureter. However, the underlying mechanism of UPJO is poorly understood, especially the regulated and targeted genes of sirtuin 1 in UPJO.

Methods

We sequenced three renal tissues on the obstructed side of independent children with <20% differential renal function (DRF) and three samples with >40% DRF. Gene expression values were obtained and compared for differentially expressed genes (DEGs). Protein-protein interaction (PPI) analysis was conducted to identify the overlapping proteins of DEGs and Sirtuin 1 (SIRT1). The co-expression genes of overlapped genes were computed using Pearson correlation coefficient. The potential role of SIRT1 gene in UPJO was explored by resequencing 3 microarray data from RNA interference (RNAi) SIRT1 lines of renal tubular epithelial (NRK52E) cells in rat and three control datasets were sequenced again. The DEGs were obtained as parallel. GO/KEGG enrichment analysis and co-expression network were conducted to explore the underlying mechanism, particularly shared pathways or function in GO/KEGG enrichment analysis results.

Results

A total of 427 up-regulated genes and 1,099 down-regulated genes were identified among 3 mRNA-seq of renal tissue on the obstructed side of the independent children with <20% DRF and 3 samples with >40% DRF. According to prediction using the Search Tool for Retrieval of Interacting Genes/Proteins, 2 PPIs, FOXO1 and PPARGC1A, were identified among 2,524 DEGs, predicted as targets of SIRT1. Gene set enrichment analysis (GSEA) of their co-expression genes showed they may co-participate in biological activities including fatty acid degradation, regulation of signal transduction by p53 mediator. Moreover, GSEA results of DEGs was confirmed through RNAi SIRT1 lines of rat renal tubular epithelial (NRK52E) cells.

Conclusions

UPJO may cause abnormal phenotypic changes of renal tubular epithelial cells through SIRT1/FOXO1 mediated protein transport, establishment of protein localization, and intracellular transport. In addition, UPJO is involved in regulation of signal transduction, regulation of intracellular estrogen receptor signaling pathways, and nucleoprotein localization through SIRT1/PPARGC1A-mediated p53 mediators, causing abnormal phenotypic changes in renal tubular epithelial cells.

Sirtuins at the Service of Healthy Longevity

Sirtuins may counteract at least six hallmarks of organismal aging: neurodegeneration, chronic but ineffective inflammatory response, metabolic syndrome, DNA damage, genome instability, and cancer incidence. Moreover, caloric restriction is believed to slow down aging by boosting the activity of some sirtuins through activating adenosine monophosphate-activated protein kinase (AMPK), thus raising the level of intracellular nicotinamide adenine dinucleotide (NAD⁺) by stimulating NAD⁺ biosynthesis. Sirtuins and their downstream effectors induce intracellular signaling pathways related to a moderate caloric restriction within cells, mitigating reactive oxygen species (ROS) production, cell senescence phenotype (CSP) induction, and apoptosis as forms of the cellular stress response. Instead, it can promote DNA damage repair and survival of cells with normal, completely functional phenotypes. In this review, we discuss mechanisms of sirtuins action toward cell-conserving phenotype associated with intracellular signaling pathways related to moderate caloric restriction, as well as some tissue-specific functions of sirtuins, especially in the central nervous system, heart muscle, skeletal muscles, liver, kidneys, white adipose tissue, hematopoietic system, and immune system. In this context, we discuss the possibility of new therapeutic approaches.

Suppression of endothelial miR-22 mediates non-small cell lung cancer cell-induced angiogenesis

MicroRNAs (miRNAs) expressed in endothelial cells (ECs) are powerful regulators of angiogenesis, which is essential for tumor growth and metastasis. Here, we demonstrated that miR-22 is preferentially and highly expressed in ECs, while its endothelial level is significantly downregulated in human non-small cell lung cancer (NSCLC) tissues when compared to matched nontumor lung tissues. This reduction of endothelial miR-22 is possibly induced by NSCLC cell-secreted interleukin-1β and subsequently activated transcription factor nuclear factor-κB. Endothelial miR-22 functions as a potent angiogenesis inhibitor that inhibits all of the key angiogenic activities of ECs and consequently NSCLC growth through directly targeting sirtuin 1 and fibroblast growth factor receptor 1 in ECs, leading to inactivation of AKT/mammalian target of rapamycin signaling. These findings provide insight into the molecular mechanisms of NSCLC angiogenesis and indicate that endothelial miR-22 represents a potential target for the future antiangiogenic treatment of NSCLC.

Targeting Sirtuin1 to treat aging-related tissue fibrosis: From prevention to therapy

Fibrosis, which is characterized by excessive extracellular matrix (ECM) deposition, is a wound-healing response to organ injury and may promote cancer and failure in various organs, such as the heart, liver, lung, and kidney. Aging associated with oxidative stress and inflammation exacerbates cellular dysfunction, tissue failure, and body function disorders, all of which are closely related to fibrosis. Sirtuin-1 (SIRT1) is a class III histone deacetylase that regulates growth, transcription, aging, and metabolism in various organs. This protein is downregulated in organ injury and fibrosis associated with aging. Its expression and distribution change with age in different organs and play critical roles in tissue oxidative stress and inflammation. This review first described the background on fibrosis and regulatory functions of SIRT1. Second, we summarized the relationships of SIRT1 with other proteins and its protective action during fibrosis in the heart, liver, lung and kidney. Third, the activation of SIRT1 in therapies of tissue fibrosis, especially in liver fibrosis and aging-related tissue injury, was analyzed. In conclusion, SIRT1 targeting may be a new therapeutic strategy in fibrosis.

Fibrosis: Sirtuins at the checkpoints of myofibroblast differentiation and profibrotic activity

Fibrotic diseases are still a serious concern for public health, due to their high prevalence, complex etiology and lack of successful treatments. Fibrosis consists of excessive accumulation of extracellular matrix components. As a result, the structure and function of tissues are impaired, thus potentially leading to organ failure and death in several chronic diseases. Myofibroblasts represent the principal cellular mediators of fibrosis, due to their extracellular matrix producing activity, and originate from different types of precursor cells, such as mesenchymal cells, epithelial cells and fibroblasts. Profibrotic activation of myofibroblasts can be triggered by a variety of mechanisms, including the transforming growth factor-β signalling pathway, which is a major factor driving fibrosis. Interestingly, preclinical and clinical studies showed that fibrotic degeneration can stop and even reverse by using specific antifibrotic treatments. Increasing scientific evidence is being accumulated about the role of sirtuins in modulating the molecular pathways responsible for the onset and development of fibrotic diseases. Sirtuins are NAD⁺ -dependent protein deacetylases that play a crucial role in several molecular pathways within the cells, many of which at the crossroad between health and disease. In this context, we will report the current knowledge supporting the role of sirtuins in the balance between healthy and diseased myofibroblast activity. In particular, we will address the signalling pathways and the molecular targets that trigger the differentiation and profibrotic activation of myofibroblasts and can be modulated by sirtuins.

Correlation Between Polymorphisms of the SIRT1 Gene microRNA Target Sites and Diabetic Nephropathy

Objective: To study the correlations between the genotypic and allelic frequencies of the Sirtuin 1 (SIRT1) gene rs182180876, rs4746720, and rs2234975 loci and susceptibility to diabetic nephropathy. Methods: We used Sanger sequencing to analyze the genotypes of the rs182180876, rs4746720, and rs2234975 loci within the SIRT1 gene in 280 diabetic nephropathy patients and 280 diabetic patients without kidney disease who acted as the control group. Plasma SIRT1 levels were analyzed by enzyme-linked immunosorbent assay, and hsa-miR-126-5p, hsa-miR-2115-3p, and hsa-miR-200a-3p in plasma were detected by quantitative real-time polymerase chain reaction levels. Results: SIRT1 rs182180876 locus G allele carriers were 3.21 times more likely to suffer from diabetic nephropathy than carriers of the C allele (95% confidence interval [CI]: 2.08-4.95, p < 0.01). Carriers of the T allele at the rs2234975 locus had a higher risk of diabetic nephropathy than carriers of the C allele (odds ratio [OR] = 2.02, 95% CI: 1.36-3.01, p < 0.01). The SIRT1 three locus CCC haplotype was associated with a decreased risk of diabetic nephropathy (OR = 0.24, 95% CI: 0.13-0.46, p < 0.01), and the CTT haplotype was associated with an increased risk of diabetic nephropathy (OR = 3.19, 95% CI: 1.41-7.22, p = 0.01). The plasma SIRT1 levels of patients with diabetic nephropathy were lower than those of the control group (p < 0.001). The plasma SIRT1 levels were lower in SIRT1 rs182180876 locus G allele carriers, rs4746720 locus T allele carriers, and rs2234975 locus T allele carriers than in carriers of the alternate alleles. Diabetic nephropathy patients' plasma hsa-miR-126-5p, hsa-miR-2115-3p, and hsa-miR-200a-3p levels were higher than those of the control group (p < 0.001). Plasma SIRT1 levels were negatively correlated with hsa-miR-126-5p, hsa-miR-2115-3p, and hsa-miR-200a-3p levels (r = -0.90, -0.77, -0.92, -0.83, -0.87, -0.87). Conclusion: The SIRT1 loci rs182180876, rs4746720, and rs2234975 single nucleotide polymorphisms are significantly associated with the risk of diabetic nephropathy. Clinical Trials.gov ID: 2016-ZJ002-01.

SIRT1 attenuates renal fibrosis by repressing HIF-2α

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase belonging to class III histone deacetylases. Previous studies have shown that SIRT1 is involved in kidney physiology regulation and protects the kidney from various pathological factors. However, the underlying mechanisms behind its function have yet to be fully elucidated. In our study, we found that ablation of Sirt1 in renal interstitial cells resulted in more severe renal damage and fibrosis in unilateral ureteral obstruction (UUO) model mice. We also observed that hypoxia-inducible factor (HIF)-2α expression was increased in Sirt1 conditional knockout mice, suggesting that HIF-2α might be a substrate of SIRT1, mediating its renoprotective roles. Therefore, we bred Hif2a deficient mice and subjected them to renal trauma through UUO surgery, ultimately finding that Hif2a ablation attenuated renal fibrogenesis induced by UUO injury. Moreover, in cultured NRK-49F cells, activation of SIRT1 decreased HIF-2α and fibrotic gene expressions, and inhibition of SIRT1 stimulated HIF-2α and fibrotic gene expressions. Co-immunoprecipitation analysis revealed that SIRT1 directly interacted with and deacetylated HIF-2α. Together, our data indicate that SIRT1 plays a protective role in renal damage and fibrosis, which is likely due to inhibition of HIF-2α.

Endothelial Glycocalyx as a Regulator of Fibrotic Processes

The endothelial glycocalyx, the gel layer covering the endothelium, is composed of glycosaminoglycans, proteoglycans, and adsorbed plasma proteins. This structure modulates vessels’ mechanotransduction, vascular permeability, and leukocyte adhesion. Thus, it regulates several physiological and pathological events. In the present review, we described the mechanisms that disturb glycocalyx stability such as reactive oxygen species, matrix metalloproteinases, and heparanase. We then focused our attention on the role of glycocalyx degradation in the induction of profibrotic events and on the possible pharmacological strategies to preserve this delicate structure.

Endothelial glycocalyx as an important factor in composition of blood-brain barrier

The blood‐brain barrier is a dynamic and complex neurovascular unit that protects neurons from somatic circulatory factors as well as regulates the internal environmental stability of the central nervous system. Endothelial glycocalyx is a critical component of an extended neurovascular unit that influences the structure of the blood‐brain barrier and plays various physiological functions, including an important role in maintaining normal neuronal homeostasis. Specifically, glycocalyx acts in physical and charge barriers, mechanical transduction, regulation of vascular permeability, modulation of inflammatory response, and anticoagulation. Since intact glycocalyx is necessary to maintain the stability and integrity of the internal environment of the blood‐brain barrier, damage to glycocalyx can lead to the dysfunction of the blood‐brain barrier. This review discusses the role of glycocalyx in the context of the substantial literature regarding the blood‐brain barrier research, in order to provide a theoretical basis for the diagnosis and treatment of neurological diseases as well as point to new breakthroughs and innovations in glycocalyx‐dependent blood‐brain barrier function.

Transglutaminase 2 as a novel target in chronic kidney disease - Methods, mechanisms and pharmacological inhibition

Chronic kidney disease (CKD) is a global health problem with a prevalence of 10-15%. Progressive fibrosis of the renal tissue is a main feature of CKD, but current treatment strategies are relatively unspecific and delay, but do not prevent, CKD. Exploration of novel pharmacological targets to inhibit fibrosis development are therefore important. Transglutaminase 2 (TG2) is known to be central for extracellular collagenous matrix formation, but TG2 is a multifunctional enzyme and novel research has broadened our view on its extra- and intracellular actions. TG2 exists in two conformational states with different catalytic properties as determined by substrate availability and local calcium concentrations. The open conformation of TG2 depends on calcium and has transamidase activity, central for protein modification and cross-linking of extracellular protein components, while the closed conformation is a GTPase involved in transmembrane signaling processes. We first describe different methodologies to assess TG2 activity in renal tissue and cell cultures such as biotin cadaverine incorporation. Then we systematically review animal CKD models and preliminary studies in humans (with diabetic, IgA- and chronic allograft nephropathy) to reveal the role of TG2 in renal fibrosis. Mechanisms behind TG2 activation, TG2 externalization dependent on Syndecan-4 and interactions between TG and profibrotic molecules including transforming growth factor β and the angiotensin II receptor are discussed. Pharmacological TG2 inhibition shows antifibrotic effects in CKD. However, the translation of TG2 inhibition to treat CKD in patients is a challenge as clinical information is limited, and further studies on pharmacokinetics and efficacy of the individual compounds are required.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

The Role of Sirtuins in Kidney Diseases

Sirtuins (SIRTs) are class III histone deacetylases (HDACs) that play important roles in aging and a wide range of cellular functions. Sirtuins are crucial to numerous biological processes, including proliferation, DNA repair, mitochondrial energy homeostasis, and antioxidant activity. Mammals have seven different sirtuins, SIRT1–7, and the diverse biological functions of each sirtuin are due to differences in subcellular localization, expression profiles, and cellular substrates. In this review, we summarize research advances into the role of sirtuins in the pathogenesis of various kidney diseases including acute kidney injury, diabetic kidney disease, renal fibrosis, and kidney aging along with the possible underlying molecular mechanisms. The available evidence indicates that sirtuins have great potential as novel therapeutic targets for the prevention and treatment of kidney diseases.

Complement C3 deficiency ameliorates aging related changes in the kidney

AIMS

Complement C3 (C3) has been shown to be involved in the aging process. However, the role of C3 in kidney aging has not been fully elucidated. This study aimed to investigate the effect of C3 on senescence related kidney disorders in mice.

MATERIALS AND METHODS

Two-, 8-, and 16-month-old C3-deficient male mice (KO) (n = 6) and age-, gender-, and strain- matched wild type (WT) C57BL/6 mice (n = 6) were selected to represent young, middle-aged and aging mice. Renal, blood and urine samples were collected. Hematoxylin-eosin (HE), Masson, and immunohistochemistry (IHC) staining as well as ELISA and Western blotting were used to explore the mechanisms involved in renal aging.

KEY FINDINGS

The level of C3 was upregulated during aging in WT mice. The glomerular sclerosis index and tubulointerstitial fibrosis index were increased significantly in WT mice during aging. Renal function was not significantly different between the young and aged groups. Compared with those in WT mice, the levels of inflammation and fibrosis were decreased, while the expression of CD31 was significantly increased in the KO group.

SIGNIFICANCE

Our data demonstrated that age-related changes in renal structure occur earlier than functional changes and that complement C3 is involved in aging-related kidney disorder.

Cold Press Pomegranate Seed Oil Attenuates Dietary-Obesity Induced Hepatic Steatosis and Fibrosis through Antioxidant and Mitochondrial Pathways in Obese Mice

Aim: Obesity is associated with metabolic syndrome, hypertension, dyslipidemia, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes. In this study, we investigated whether the dietary supplementation of pomegranate seed oil (PSO) exerted a protective effect on liver lipid uptake, fibrosis, and mitochondrial function in a mouse model of obesity and insulin resistance. Method: In this in vivo study, eight-week-old C57BL/6J male mice were fed with a high fat diet (HFD) for 24 weeks and then were divided into three groups as follows: group (1) Lean; group (n = 6) (2) HF diet; group (n = 6) (3) HF diet treated with PSO (40 mL/kg food) (n = 6) for eight additional weeks starting at 24 weeks. Physiological parameters, lipid droplet accumulation, inflammatory biomarkers, antioxidant biomarkers, mitochondrial biogenesis, insulin sensitivity, and hepatic fibrosis were determined to examine whether PSO intervention prevents obesity-associated metabolic syndrome. Results: The PSO group displayed an increase in oxygen consumption, as well as a decrease in fasting glucose and blood pressure (p < 0.05) when compared to the HFD-fed mice group. PSO increased both the activity and expression of hepatic HO-1, downregulated inflammatory adipokines, and decreased hepatic fibrosis. PSO increased the levels of thermogenic genes, mitochondrial signaling, and lipid metabolism through increases in Mfn2, OPA-1, PRDM 16, and PGC1α. Furthermore, PSO upregulated obesity-mediated hepatic insulin receptor phosphorylation Tyr-⁹⁷², p-IRB tyr¹¹⁴⁶, and pAMPK, thereby decreasing insulin resistance. Conclusions: These results indicated that PSO decreased obesity-mediated insulin resistance and the progression of hepatic fibrosis through an improved liver signaling, as manifested by increased insulin receptor phosphorylation and thermogenic genes. Furthermore, our findings indicate a potential therapeutic role for PSO in the prevention of obesity-associated NAFLD, NASH, and other metabolic disorders.

Exosomes derived from GDNF-modified human adipose mesenchymal stem cells ameliorate peritubular capillary loss in tubulointerstitial fibrosis by activating the SIRT1/eNOS signaling pathway

Mesenchymal stem cells (MSCs) have emerged as ideal cell-based therapeutic candidates for the structural and functional restoration of the diseased kidney. Glial cell line-derived neurotrophic factor (GDNF) has been demonstrated to promote the therapeutic effect of MSCs on ameliorating renal injury. The mechanism may involve the transfer of endogenous molecules via paracrine factors to salvage injured cells, but these factors remain unknown.

Methods: GDNF was transfected into human adipose mesenchymal stem cells via a lentiviral transfection system, and exosomes were isolated (GDNF-AMSC-exos). Using the unilateral ureteral obstruction (UUO) mouse model and human umbilical vein endothelial cells (HUVECs) against hypoxia/serum deprivation (H/SD) injury models, we investigated whether GDNF-AMSC-exos ameliorate peritubular capillary (PTC) loss in tubulointerstitial fibrosis and whether this effect is mediated by the Sirtuin 1 (SIRT1) signaling pathway. Additionally, by using SIRT1 activators or siRNAs, the roles of the candidate mRNA and its downstream gene in GDNF-AMSC-exo-induced regulation of endothelial cell function were assessed. PTC characteristics were detected by fluorescent microangiography (FMA) and analyzed by the MATLAB software.

Results: The green fluorescent PKH67-labeled exosomes were visualized in the UUO kidneys and colocalized with CD81. GDNF-AMSC-exos significantly decreased PTC rarefaction and renal fibrosis scores in mice with UUO. In vitro studies revealed that GDNF-AMSC-exos exerted cytoprotective effects on HUVECs against H/SD injury by stimulating migration and angiogenesis as well as conferring apoptosis resistance. Mechanistically, GDNF-AMSC-exos enhanced SIRT1 signaling, which was accompanied by increased levels of phosphorylated endothelial nitric oxide synthase (p-eNOS). We also confirmed the SIRT1-eNOS interaction in HUVECs by immunoprecipitation. Furthermore, we observed a correlation of the PTC number with the SIRT1 expression level in the kidney in vivo.

Conclusion: Our study unveiled a mechanism by which exosomes ameliorate renal fibrosis: GDNF-AMSC-exos may activate an angiogenesis program in surviving PTCs after injury by activating the SIRT1/eNOS signaling pathway.

Sirtuin 1 and endothelial glycocalyx

Sirtuin1 deficiency or reduced activity comprises one of the hallmarks of diseases as diverse as chronic cardiovascular, renal, and metabolic, some malignancies, and infections, as well as aging-associated diseases. In a mouse model of endothelium-limited defect in sirtuin 1 deacetylase activity, we found a dramatic reduction in the volume of endothelial glycocalyx. This was associated with the surge in the levels of one of key scaffolding heparan sulfate proteoglycans of endothelial glycocalyx, syndecan-4, and specifically, its extracellular domain (ectodomain). We found that the defect in endothelial sirtuin 1 deacetylase activity is associated with (a) elevated basal and stimulated levels of superoxide generation (via the FoxO1 over-acetylation mechanism) and (b) increased nuclear translocation of NF-kB (via p65 over-acetylation mechanism). These findings laid the foundation for the proposed novel function of sirtuin 1, namely, the maintenance of endothelial glycocalyx, particularly manifest in conditions associated with sirtuin 1 depletion. In the forthcoming review, we summarize the emerging conceptual framework of the enhanced glycocalyx degradation in the states of defective endothelial sirtuin 1 function, thus explaining a broad footprint of the syndrome of endothelial dysfunction, from impaired flow-induced nitric oxide production, deterrent leukocytes infiltration, increased endothelial permeability, coagulation, and pro-inflammatory changes to development of microvascular rarefaction and progression of an underlying disease.

Id1 expression in kidney endothelial cells protects against diabetes-induced microvascular injury

The inhibitor of differentiation (Id) transcription regulators, which are induced in response to oxidative stress, promote cell proliferation and inhibit senescence. Inhibitor of differentiation 1 (Id1) expression is limited to endothelial cells (EC) in the normal mouse kidney and is required for a normal response to injury. Endothelial dysfunction leads to the development of diabetic nephropathy, and so, we hypothesized that endothelial Id1 may help protect against hyperglycemia-induced microvascular injury and nephropathy. Here, we tested this hypothesis by using streptozotocin to induce diabetes in Id1 knockout (KO) mice and WT B6;129 littermates and examining the mice at 3 months. Expression of Id1 was observed to be increased 15-fold in WT kidney EC, and Id1 KO mice exhibited increased mesangial and myofibroblast proliferation, matrix deposition, and albuminuria compared with WT mice. Electron microscopy demonstrated peritubular capillary EC injury and lumen narrowing, and fluorescence microangiography showed a 45% reduction in capillary perfusion area with no reduction in CD31-stained areas in Id1 KO mice. Microarray analysis of EC isolated from WT and KO control and diabetic mice demonstrated activation of senescence pathways in KO cells. Kidneys from KO diabetic mice showed increased histological expression of senescence markers. In addition, premature senescence in cultured KO EC was also seen in response to oxidative stress. In conclusion, endothelial Id1 upregulation with hyperglycemia protects against microvascular injury and senescence and subsequent nephropathy.

Dickkopf-3 in aberrant endothelial secretome triggers renal fibroblast activation and endothelial-mesenchymal transition

Background

Our laboratory has previously demonstrated that Sirt1endo-/- mice show endothelial dysfunction and exaggerated renal fibrosis, whereas mice with silenced endothelial transforming growth factor beta (TGF-β) signaling are resistant to fibrogenic signals. Considering the fact that the only difference between these mutant mice is confined to the vascular endothelium, this indicates that secreted substances contribute to these contrasting responses.

Methods

We performed an unbiased proteomic analysis of the secretome of renal microvascular endothelial cells (RMVECs) isolated from these two mutants. We cultured renal fibroblasts and RMVECs and used microfluidic devices for coculturing.

Results

Dickkopf-3 (DKK3), a putative ligand of the Wnt/β-catenin pathway, was present exclusively in the fibrogenic secretome. In cultured fibroblasts, DKK3 potently induced myofibroblast activation. In addition, DKK3 antagonized effects of DKK1, a known inhibitor of the Wnt pathway, in conversion of fibroblasts to myofibroblasts. In RMVECs, DKK3 induced endothelial-mesenchymal transition and impaired their angiogenic competence. The inhibition of endothelial outgrowth, enhanced myofibroblast formation and endothelial-mesenchymal transition were confirmed in coculture. In reporter DKK3-eGFP × Col3.6-GFPcyan mice, DKK3 was marginally expressed under basal conditions. Adriamycin-induced nephropathy resulted in upregulation of DKK3 expression in tubular and, to a lesser degree, endothelial compartments. Sulindac sulfide was found to exhibit superior Wnt pathway-suppressive action and decreased DKK3 signals and the extent of renal fibrosis.

Conclusions

In conclusion, this unbiased proteomic screen of the profibrogenic endothelial secretome revealed DKK3 acting as an agonist of the Wnt pathway, enhancing formation of myofibroblasts and endothelial-mesenchymal transition and impairing angiogenesis. A potent inhibitor of the Wnt pathway, sulindac sulfide, suppressed nephropathy-induced DKK3 expression and renal fibrosis.

Endothelium-mediated contributions to fibrosis

Fibrosis, characterized by abnormal and excessive deposition of extracellular matrix, results in compromised tissue and organ structure. This can lead to reduced organ function and eventual failure. Although activated fibroblasts, called myofibroblasts, are considered the central players in fibrosis, the contribution of endothelial cells to the inception and progression of fibrosis has become increasingly recognized. Endothelial cells can contribute to fibrosis by acting as a source of myofibroblasts via endothelial-mesenchymal transition (EndoMT), or by becoming senescent, by secretion of profibrotic mediators and pro-inflammatory cytokines, chemokines and exosomes, promoting the recruitment of immune cells, and by participating in vascular rarefaction and decreased angiogenesis. In this review, we provide an overview of the different aspects of fibrosis in which endothelial cells have been implicated.

Changes of the coronary arteries and cardiac microvasculature with aging: Implications for translational research and clinical practice

Aging results in functional and structural changes in the cardiovascular system, translating into a progressive increase of mechanical vessel stiffness, due to a combination of changes in micro-RNA expression patterns, autophagy, arterial calcification, smooth muscle cell migration and proliferation. The two pivotal mechanisms of aging-related endothelial dysfunction are oxidative stress and inflammation, even in the absence of clinical disease. A comprehensive understanding of the aging process is emerging as a primary concern in literature, as vascular aging has recently become a target for prevention and treatment of cardiovascular disease. Change of life-style, diet, antioxidant regimens, anti-inflammatory treatments, senolytic drugs counteract the pro-aging pathways or target senescent cells modulating their detrimental effects. Such therapies aim to reduce the ineluctable burden of age and contrast aging-associated cardiovascular dysfunction. This narrative review intends to summarize the macrovascular and microvascular changes related with aging, as a better understanding of the pathways leading to arterial aging may contribute to design new mechanism-based therapeutic approaches to attenuate the features of vascular senescence and its clinical impact on the cardiovascular system.

Molecular Mechanisms of the Acute Kidney Injury to Chronic Kidney Disease Transition: An Updated View

Increasing evidence has demonstrated the bidirectional link between acute kidney injury (AKI) and chronic kidney disease (CKD) such that, in the clinical setting, the new concept of a unified syndrome has been proposed. The pathophysiological reasons, along with the cellular and molecular mechanisms, behind the ability of a single, acute, apparently self-limiting event to drive chronic kidney disease progression are yet to be explained. This acute injury could promote progression to chronic disease through different pathways involving the endothelium, the inflammatory response and the development of fibrosis. The interplay among endothelial cells, macrophages and other immune cells, pericytes and fibroblasts often converge in the tubular epithelial cells that play a central role. Recent evidence has strengthened this concept by demonstrating that injured tubules respond to acute tubular necrosis through two main mechanisms: The polyploidization of tubular cells and the proliferation of a small population of self-renewing renal progenitors. This alternative pathophysiological interpretation could better characterize functional recovery after AKI.

SIRT1 Deletion Impairs Retinal Endothelial Cell Migration Through Downregulation of VEGF-A/VEGFR-2 and MMP14

Purpose

Silent information regulator protein 1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent deacetylase that is abundantly expressed in vascular endothelial cells (VECs), and it has an essential role in angiogenesis. However, its contribution to retinal vascular development remains unclear. Here we characterize its involvement in regulating this process under both physiological and pathologic conditions.

Methods

Endothelium-specific Sirt1 knockout mice were established using the Cre-lox system. VECs were isolated using magnetic beads and identified by immunostaining. Retinal whole-mount staining analyzed the retinal vascular patterns. SIRT1 was knocked down or overexpressed in human retinal microvascular endothelial cells (HRMECs) using small interfering RNA (siRNA) or lentivirus infection, respectively. Scratch assay, Transwell, and Matrigel angiogenesis assay evaluated cell migration and tube formation, respectively. Quantitative RT-PCR analyzed genes regulating VEC migration. Western blotting determined protein expression. Coimmunoprecipitation detected the interaction of hypoxia-inducible factor 1α (HIF-1α) and SIRT1 as well as acetylation status of HIF-1α.

Results

Specific deletion of Sirt1 in VECs dramatically delayed retinal vessel expansion and reduced vessel density. In the oxygen-induced retinopathy (OIR) mouse model, Sirt1 ablation markedly suppressed retinal revascularization and consequently increased retinal avascularity. SIRT1 downregulation in HRMECs inhibited cell migration and tube formation, while overexpression of SIRT1 had the opposite effects. Vascular endothelial growth factor-A (VEGF-A)/VEGF receptor-2 (VEGFR-2), and matrix metalloproteinases 14 (MMP14) expression significantly declined in Sirt1-null VECs, as well as SIRT1 siRNA-transfected HRMECs. SIRT1 downregulation upregulated the HIF-1α acetylation status. Conversely, SIRT1 overexpression decreased this response.

Conclusions

SIRT1 contributes to both physiological and pathologic retinal angiogenesis through promoting retinal VEC migration. Its underlying molecular mechanism involves SIRT1-mediated deacetylation of HIF-1α and subsequent upregulation of VEGF-A/VEGFR-2 and MMP14 expression.

Inhibition of TLR9 attenuates skeletal muscle fibrosis in aged sarcopenic mice via the p53/SIRT1 pathway

Sarcopenia is an age-related syndrome characterized by a gradual loss of muscle mass and function, but its pathophysiological mechanism remains unclear. Skeletal muscle extracellular matrix (ECM) remodeling is an important pathological change in sarcopenia, and fibrosis is the most obvious manifestation of this change. We found that the expression of the immunoreceptor Toll-like receptor 9 (TLR9) is significantly increased in skeletal muscle in aged mice and is positively related to muscle fibrosis. Moreover, in previous reports, the longevity gene Sirt1 was reported to attenuate ECM deposition and improve muscle function. In this study, we hypothesized that TLR9 modulated skeletal muscle fibrosis via Sirt1. We used TLR9 knockout (TLR9 KO) mice and C57 mice, and grip strength and body composition were compared at different ages. We found that TLR9 knockout significantly attenuated skeletal muscle fibrosis and improved muscle function in aged mice. Furthermore, silent information regulator 1 (Sirt1) activity in mice was inhibited by Ex527, which is a specific inhibitor of Sirt1. Negative Sirt1 regulation via the activation of TLR9-related signaling pathways participated in skeletal muscle fibrosis in the sarcopenic mice, and this process might mediated by the Sirt1/Smad signaling pathway. Our findings revealed that fibrosis changes in the gastrocnemius muscle in sarcopenic mice are closely related to TLR9 activation, and TLR9 modulation could be a therapeutic strategy for combating sarcopenia during aging.