Resveratrol inhibits renal fibrosis in the obstructed kidney: potential role in deacetylation of Smad3

Nicotinamide protects against diabetic kidney disease through regulation of Sirt1

PURPOSE

To investigate the effect of nicotinamide (Nam) on diabetic kidney disease (DKD) in mice and explore its mechanism.

METHODS

Thirty DBA/2 J mice were randomly assigned to three groups. After 8 weeks of hyperglycemia induced by streptozocin (STZ), Nam and saline were administrated to STZ + Nam and STZ + NS mice, respectively, for 8 weeks. Non-diabetic mice (NDM) were used as control group. Twenty In2-/- Akita mice were randomly divided into two groups. After 8 weeks of hyperglycemia, Nam and saline were administered to Akita + Nam and Akita + NS mice, respectively, for 6 weeks. Wild-type littermates were used as control group. Markers of renal injury were analyzed, and the molecular mechanisms were explored in human proximal tubular HK2 cells.

RESULTS

Urinary albumin-to-creatinine ratio (UACR) and kidney injury molecule 1 (KIM-1) decreased in the STZ + Nam and Akita + Nam groups. Pathological analysis showed that Nam improved the structure of glomerular basement membrane, ameliorated glomerular sclerosis, and decreased the accumulation of extracellular matrix and collagen. Compared to the diabetic control group, renal fibrosis, inflammation, and oxidative stress were reduced in the Nam-treated mice. The expression of sirtuin 1 (Sirt1) in human proximal tubular HK2 cells was inhibited by high glucose and Nam treatment enhanced its expression. However, in HK2 cells with Sirt1 knockdown, the protective effect of Nam was abolished, indicating that the beneficial effect of Nam was partially dependent on Sirt1.

CONCLUSIONS

Nam has a renoprotective effect against renal injury caused by hyperglycemia and may be a potential target for the treatment of DKD.

Role of Histone Modifications in Kidney Fibrosis

Chronic kidney disease (CKD) is characterized by persistent kidney dysfunction, ultimately resulting in end-stage renal disease (ESRD). Renal fibrosis is a crucial pathological feature of CKD and ESRD. However, there is no effective treatment for this condition. Despite the complex molecular mechanisms involved in renal fibrosis, increasing evidence highlights the crucial role of histone modification in its regulation. The reversibility of histone modifications offers promising avenues for therapeutic strategies to block or reverse renal fibrosis. Therefore, a comprehensive understanding of the regulatory implications of histone modifications in fibrosis may provide novel insights into more effective and safer therapeutic approaches. This review highlights the regulatory mechanisms and recent advances in histone modifications in renal fibrosis, particularly histone methylation and histone acetylation. The aim is to explore the potential of histone modifications as targets for treating renal fibrosis.

Advance in Iron Metabolism, Oxidative Stress and Cellular Dysfunction in Experimental and Human Kidney Diseases

Kidney diseases pose a significant global health issue, frequently resulting in the gradual decline of renal function and eventually leading to end-stage renal failure. Abnormal iron metabolism and oxidative stress-mediated cellular dysfunction facilitates the advancement of kidney diseases. Iron homeostasis is strictly regulated in the body, and disturbance in this regulatory system results in abnormal iron accumulation or deficiency, both of which are associated with the pathogenesis of kidney diseases. Iron overload promotes the production of reactive oxygen species (ROS) through the Fenton reaction, resulting in oxidative damage to cellular molecules and impaired cellular function. Increased oxidative stress can also influence iron metabolism through upregulation of iron regulatory proteins and altering the expression and activity of key iron transport and storage proteins. This creates a harmful cycle in which abnormal iron metabolism and oxidative stress perpetuate each other, ultimately contributing to the advancement of kidney diseases. The crosstalk of iron metabolism and oxidative stress involves multiple signaling pathways, such as hypoxia-inducible factor (HIF) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways. This review delves into the functions and mechanisms of iron metabolism and oxidative stress, along with the intricate relationship between these two factors in the context of kidney diseases. Understanding the underlying mechanisms should help to identify potential therapeutic targets and develop novel and effective therapeutic strategies to combat the burden of kidney diseases.

Exercise alleviates renal interstitial fibrosis by ameliorating the Sirt1-mediated TGF-β1/Smad3 pathway in T2DM mice

Background

Renal interstitial fibrosis is the pathophysiological basis of type 2 diabetes mellitus (T2DM). Exercise appears to improve kidney interstitial fibrosis in T2DM, in which silent information regulator factor 2-related enzyme 1 (Sirt1) is a critical regulator. However, the role of Sirt1 in mediating exercise on renal tissue as well as its mechanism remains unknown.

Methods

T2DM mouse models were created using a high-fat diet mixed with streptozotocin, followed by 8 weeks of treadmill exercise and niacinamide (Sirt1 inhibitor) intervention. Kits for detecting biochemical indices of renal function were used. The pathological appearance and severity of renal tissue were examined using hematoxylin and eosin, Masson and immunohistochemical staining. The mRNA and protein expression of relevant signaling pathway factors were determined to use real-time reverse transcriptase-polymerase chain reaction and western blotting.

Results

T2DM can promote renal interstitial fibrosis, increase kidney index, serum creatinine, blood urea nitrogen and 24 h urinary total protein and cause pathological changes in renal tissue and affect renal function. After 8 weeks of exercise intervention, the biochemical indicators in the kidney of T2DM mice were decreased, Sirt1 expression was increased, the expression of TGF-β1, Smad3, collagen type I (COL1) and collagen type III (COL3) were decreased, and the renal interstitial fibrosis, renal tissue structural lesions and renal function were improved. However, after the nicotinamide intervention, renal interstitial fibrosis of T2DM mice was aggravated, and the improvement effect of exercise on renal interstitial fibrosis of T2DM mice was abolished.

Conclusion

The upregulation of Sirt1 expression by exercise can inhibit the transforming growth factor β1/Smad3 pathway, thereby inhibiting the expression and deposition of COL1 and COL3 in renal interstitium, thereby improving renal interstitial fibrosis in T2DM.

Therapeutic potential for renal fibrosis by targeting Smad3-dependent noncoding RNAs

Renal fibrosis is a characteristic hallmark of chronic kidney disease (CKD) that ultimately results in renal failure, leaving patients with few therapeutic options. TGF-β is a master regulator of renal fibrosis and mediates progressive renal fibrosis via both canonical and noncanonical signaling pathways. In the canonical Smad signaling, Smad3 is a key mediator in tissue fibrosis and mediates renal fibrosis via a number of noncoding RNAs (ncRNAs). In this regard, targeting Smad3-dependent ncRNAs may offer a specific therapy for renal fibrosis. This review highlights the significance and innovation of TGF-β/Smad3-associated ncRNAs as biomarkers and therapeutic targets in renal fibrogenesis. In addition, the underlying mechanisms of these ncRNAs and their future perspectives in the treatment of renal fibrosis are discussed.

GRK5 promoted renal fibrosis via HDAC5/Smad3 signaling pathway

Renal fibrosis is a common pathological feature of chronic kidney diseases (CKD), poses a significant burden in the aging population, and is a major cause of end-stage renal disease (ESRD). In this study, we investigated the role of G protein-coupled receptor kinases (GRKs) 5 in the pathogenesis of renal fibrosis. GRK5 is a serine/threonine kinase that regulates G protein-coupled receptor (GPCR) signaling. GRK5 has been shown to play a role in various diseases including cardiac disorders and cancer. However, the role of GRK5 in renal fibrosis remains largely unknown. Our finding revealed that GRK5 was significantly overexpressed in renal fibrosis. Specifically, GRK5 was transferred into the nucleus via its nuclear localization sequence to regulate histone deacetylases (HDAC) 5 expression under renal fibrosis. GRK5 acted as an upstream regulator of HDAC5/Smad3 signaling pathway. HDAC5 regulated and prevented the transcriptional activity of myocyte enhancer factor 2A (MEF2A) to repress the transcription of Smad7 which leading to the activation of Smad3. These findings first revealed that GRK5 may be a potential therapeutic target for the treatment of renal fibrosis. Inhibition of GRK5 activity may be a promising strategy to attenuate the progression of renal fibrosis.

Mitophagy in renal interstitial fibrosis

As a high energy consumption organ, kidney relies on a large number of mitochondria to ensure normal physiological activities. Under specific stimulation, mitophagy and mitochondrial dynamics (fission, fusion) cooperatively regulate mitochondrial quality and participate in many life activities such as energy metabolism, inflammatory response, oxidative stress, cell senescence and death. Mitophagy plays a key role in the progression of acute kidney injury and chronic kidney disease. The early induction of oxidative stress in renal parenchyma, the activation of pro-inflammatory cytokines and TGF-β signal pathway are closely related to renal interstitial fibrosis. Macrophage reprogramming is also considered to be an important participant in the progression of kidney fibrosis. This review summarizes the molecular mechanism of mitochondrial autophagy and its relationship with the pathway of promoting fibrosis, and discusses the possibility of restoring mitophagy balance as a pharmacological target for the treatment of renal interstitial fibrosis, so as to provide new ideas for more efficient anti-fibrosis and delay the progress of chronic kidney disease.

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

JAK/STAT signaling in diabetic kidney disease

Diabetic kidney disease (DKD) is the most important microvascular complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. The Janus kinase/signal transducer and activator of the transcription (JAK/STAT) signaling pathway, which is out of balance in the context of DKD, acts through a range of metabolism-related cytokines and hormones. JAK/STAT is the primary signaling node in the progression of DKD. The latest research on JAK/STAT signaling helps determine the role of this pathway in the factors associated with DKD progression. These factors include the renin-angiotensin system (RAS), fibrosis, immunity, inflammation, aging, autophagy, and EMT. This review epitomizes the progress in understanding the complicated explanation of the etiologies of DKD and the role of the JAK/STAT pathway in the progression of DKD and discusses whether it can be a potential target for treating DKD. It further summarizes the JAK/STAT inhibitors, natural products, and other drugs that are promising for treating DKD and discusses how these inhibitors can alleviate DKD to explore possible potential drugs that will contribute to formulating effective treatment strategies for DKD in the near future.

SIRT1 and SIRT6: The role in aging-related diseases

Aging is characterized by progressive functional deterioration with increased risk of mortality. It is a complex biological process driven by a multitude of intertwined mechanisms such as increased DNA damage, chronic inflammation, and metabolic dysfunction. Sirtuins (SIRTs) are a family of NAD⁺-dependent enzymes that regulate fundamental biological functions from genomic stability and lifespan to energy metabolism and tumorigenesis. Of the seven mammalian SIRT isotypes (SIRT1-7), SIRT1 and SIRT6 are well-recognized for regulating signaling pathways related to aging. Herein, we review the protective role of SIRT1 and SIRT6 in aging-related diseases at molecular, cellular, tissue, and whole-organism levels. We also discuss the therapeutic potential of SIRT1 and SIRT6 modulators in the treatment of these diseases and challenges thereof.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Role of sirtuins in metabolic disease-related renal injury

Poor control of metabolic diseases induces kidney injury, resulting in microalbuminuria, renal insufficiency and, ultimately, chronic kidney disease. The potential pathogenetic mechanisms of renal injury caused by metabolic diseases remain unclear. Tubular cells and podocytes of the kidney show high expression of histone deacetylases known as sirtuins (SIRT1-7). Available evidence has shown that SIRTs participate in pathogenic processes of renal disorders caused by metabolic diseases. The present review addresses the regulatory roles of SIRTs and their implications for the initiation and development of kidney damage due to metabolic diseases. SIRTs are commonly dysregulated in renal disorders induced by metabolic diseases such as hypertensive nephropathy and diabetic nephropathy. This dysregulation is associated with disease progression. Previous literature has also suggested that abnormal expression of SIRTs affects cellular biology, such as oxidative stress, metabolism, inflammation, and apoptosis of renal cells, resulting in the promotion of invasive diseases. This literature reviews the research progress made in understanding the roles of dysregulated SIRTs in the pathogenesis of metabolic disease-related kidney disorders and describes the potential of SIRTs serve as biomarkers for early screening and diagnosis of these diseases and as therapeutic targets for their treatment.

Molecular pathways that drive diabetic kidney disease

Kidney disease is a major driver of mortality among patients with diabetes and diabetic kidney disease (DKD) is responsible for close to half of all chronic kidney disease cases. DKD usually develops in a genetically susceptible individual as a result of poor metabolic (glycemic) control. Molecular and genetic studies indicate the key role of podocytes and endothelial cells in driving albuminuria and early kidney disease in diabetes. Proximal tubule changes show a strong association with the glomerular filtration rate. Hyperglycemia represents a key cellular stress in the kidney by altering cellular metabolism in endothelial cells and podocytes and by imposing an excess workload requiring energy and oxygen for proximal tubule cells. Changes in metabolism induce early adaptive cellular hypertrophy and reorganization of the actin cytoskeleton. Later, mitochondrial defects contribute to increased oxidative stress and activation of inflammatory pathways, causing progressive kidney function decline and fibrosis. Blockade of the renin-angiotensin system or the sodium-glucose cotransporter is associated with cellular protection and slowing kidney function decline. Newly identified molecular pathways could provide the basis for the development of much-needed novel therapeutics.

Mitochondrial micropeptide MOXI promotes fibrotic gene transcription by translocation to the nucleus and bridging N-acetyltransferase 14 with transcription factor c-Jun

Progressive fibrosis is a hallmark of chronic kidney disease, but we lack effective treatments to halt this destructive process. Micropeptides (peptides of no more than 100 amino acids) encoded by small open reading frames represent a new class of eukaryotic regulators. Here, we describe that the micropeptide regulator of β-oxidation (MOXI) regulates kidney fibrosis. MOXI expression was found to be up-regulated in human fibrotic kidney disease, and this correlated with the degree of fibrosis and loss of kidney function. MOXI was expressed in the cytoplasm and mitochondria of cultured tubular epithelial cells and translocated to the nucleus upon Transforming Growth Factor-β1 stimulation. Deletion of Moxi protected mice against fibrosis and inflammation in the folic acid and unilateral ureteral obstruction models. As a potential molecular therapy, treatment with an antisense MOXI oligonucleotide effectively knocked-down MOXI expression and protected against kidney fibrosis in both models. Bimolecular fluorescence complementation identified the enzyme N-acetyltransferase 14 (Nat14) and transcription factor c-Jun as MOXI binding partners. The MOXI/Nat14/c-Jun complex enhances basal and Transforming Growth Factor-β1 induced collagen I gene promoter activity. Phosphorylation at T49 is required for MOXI nuclear localization and for complex formation with Nat14 and c-Jun. Furthermore, mice with a MoxiT49A point mutation were protected in the models of kidney fibrosis. Thus, our studies demonstrate a key role for the micropeptide MOXI in kidney fibrosis and identify a new function of MOXI in forming a transcriptional complex with Nat14 and c-Jun.

NAD+ Metabolism and Interventions in Premature Renal Aging and Chronic Kidney Disease

Premature aging causes morphological and functional changes in the kidney, leading to chronic kidney disease (CKD). CKD is a global public health issue with far-reaching consequences, including cardio-vascular complications, increased frailty, shortened lifespan and a heightened risk of kidney failure. Dialysis or transplantation are lifesaving therapies, but they can also be debilitating. Currently, no cure is available for CKD, despite ongoing efforts to identify clinical biomarkers of premature renal aging and molecular pathways of disease progression. Kidney proximal tubular epithelial cells (PTECs) have high energy demand, and disruption of their energy homeostasis has been linked to the progression of kidney disease. Consequently, metabolic reprogramming of PTECs is gaining interest as a therapeutic tool. Preclinical and clinical evidence is emerging that NAD⁺ homeostasis, crucial for PTECs' oxidative metabolism, is impaired in CKD, and administration of dietary NAD⁺ precursors could have a prophylactic role against age-related kidney disease. This review describes the biology of NAD⁺ in the kidney, including its precursors and cellular roles, and discusses the importance of NAD⁺ homeostasis for renal health. Furthermore, we provide a comprehensive summary of preclinical and clinical studies aimed at increasing NAD⁺ levels in premature renal aging and CKD.

Polyphenol-rich açaí seed extract exhibits reno-protective and anti-fibrotic activities in renal tubular cells and mice with kidney failure

The main goal of this study was to evaluate the reno-protective effects of a phenolic-rich Açaí seed extract (ASE) in mice with kidney failure. Kidney failure was induced chemically with an adenine-rich diet (0.25% w/w for 4 weeks) in male CD1 Swiss mice. Mice were then provided daily with ASE (at a dose of ~ 350 mg/kg/day) in drinking water for 4 weeks. Adenine mice exhibited renal dysfunction evidenced by increased proteinuria, increased uremia, extensive tubular atrophy and kidney fibrosis associated with overexpression of pro-fibrotic genes (collagen 1a1, transforming growth factor β1, TGF-β1) and markers of tubular injury (such as Kidney injury molecule-1, KIM-1). ASE was able to beneficially counteract all these effects. ASE improved oxidative damage and fibrosis by decreasing carbonylated protein and MDA concentrations, as well as collagen deposition in renal tissue. ASE decreased the expression of TGF-β1 gene and the abundance of protein TGF-β1 in kidneys. It further decreased both expression and urinary excretion of tubular injury biomarkers, e.g., KIM-1 and Neutrophil gelatinase-associated lipocalin. CKD ASE-treated mice exhibited higher polyphenol content and total antioxidant capacity compared to control mice. ASE further prevented the expression of profibrotic genes in HK2 human tubular cells exposed to uremic toxins. Taken together, these findings suggest that ASE exerted potent reno-protective and anti-fibrotic effects through its antioxidant activity and the modulation of the TGF-β1 pathway.

The diseased kidney: aging and senescent immunology

Immunosenescence is the deterioration of the innate and adaptive immune systems associated with aging and is primarily characterized by a reduction in T cell production and accumulation of atypical subsets. Age-related immunological dysfunction leads to impaired immune protection and persistent low-grade chronic inflammation, resulting in a decreased vaccination response and increased vulnerability to infection, cancer, cardiovascular disease, and autoimmune disease in the elderly. As the elderly constitute a growing proportion of the population with renal disease, immunosenescence is a normal aging process that is prevalent among older people. In addition, immunosenescence seems to be more pronounced in patients with kidney diseases than in healthy controls, as shown by severe chronic inflammation, accumulation of immune cells with the senescent phenotype (CD28− T cells, CD14+CD16+ monocytes), and proinflammatory cytokine production. Immunosenescence inhibits immunological clearance and renal tissue regeneration, thereby increasing the risk of permanent renal damage, infection, and cardiovascular events in patients with kidney disease, lowering the prognosis, and even influencing the efficacy of renal replacement treatment. Biological drugs (senomorphics and senolytics) target the aging immune system and exert renoprotective effects. This review aims to emphasize the features of immunosenescence and its influence on kidney diseases and immunotherapy, highlighting the future directions of kidney disease treatment using senescence-focused techniques.

Renal fibrosis as a hallmark of diabetic kidney disease: Potential role of targeting transforming growth factor-beta (TGF-β) and related molecules

INTRODUCTION

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) worldwide. Currently, there is no effective treatment to completely prevent DKD progression to ESRD. Renal fibrosis and inflammation are the major pathological features of DKD, being pursued as potential therapeutic targets for DKD.

AREAS COVERED

Inflammation and renal fibrosis are involved in the pathogenesis of DKD. Anti-inflammatory drugs have been developed to combat DKD but without efficacy demonstrated. Thus, we have focused on the mechanisms of TGF-β-induced renal fibrosis in DKD, as well as discussing the important molecules influencing the TGF-β signaling pathway and their potential development into new pharmacotherapies, rather than targeting the ligand TGF-β and/or its receptors, such options include Smads, microRNAs, histone deacetylases, connective tissue growth factor, bone morphogenetic protein 7, hepatocyte growth factor, and cell division autoantigen 1.

EXPERT OPINION

TGF-β is a critical driver of renal fibrosis in DKD. Molecules that modulate TGF-β signaling rather than TGF-β itself are potentially superior targets to safely combat DKD. A comprehensive elucidation of the pathogenesis of DKD is important, which requires a better model system and access to clinical samples via collaboration between basic and clinical researchers.

Molecular mechanisms of histone deacetylases and inhibitors in renal fibrosis progression

Renal fibrosis is a common progressive manifestation of chronic kidney disease. This phenomenon of self-repair in response to kidney damage seriously affects the normal filtration function of the kidney. Yet, there are no specific treatments for the condition, which marks fibrosis as an irreversible pathological sequela. As such, there is a pressing need to improve our understanding of how fibrosis develops at the cellular and molecular levels and explore specific targeted therapies for these pathogenic mechanisms. It is now generally accepted that renal fibrosis is a pathological transition mediated by extracellular matrix (ECM) deposition, abnormal activation of myofibroblasts, and epithelial-mesenchymal transition (EMT) of renal tubular epithelial cells under the regulation of TGF-β. Histone deacetylases (HDACs) appear to play an essential role in promoting renal fibrosis through non-histone epigenetic modifications. In this review, we summarize the mechanisms of renal fibrosis and the signaling pathways that might be involved in HDACs in renal fibrosis, and the specific mechanisms of action of various HDAC inhibitors (HDACi) in the anti-fibrotic process to elucidate HDACi as a novel therapeutic tool to slow down the progression of renal fibrosis.

p53/sirtuin 1/NF-κB Signaling Axis in Chronic Inflammation and Maladaptive Kidney Repair After Cisplatin Nephrotoxicity

Chronic inflammation contributes to maladaptive kidney repair, but its regulation is unclear. Here, we report that sirtuin 1 (SIRT1) is downregulated after repeated low-dose cisplatin (RLDC) injury, and this downregulation leads to p65 acetylation and consequent NF-κB activation resulting in a persistent inflammatory response. RLDC induced the down-regulation of SIRT1 and activation of NF-κB, which were accompanied by chronic tubular damage, tubulointerstitial inflammation, and fibrosis in mice. Inhibition of NF-κB suppressed the production of pro-inflammatory cytokines and fibrotic phenotypes in RLDC-treated renal tubular cells. SIRT1 activation by its agonists markedly reduced the acetylation of p65 (a key component of NF-κB), resulting in the attenuation of the inflammatory and fibrotic responses. Conversely, knockdown of SIRT1 exacerbated these cellular changes. At the upstream, p53 was activated after RLDC treatment to repress SIRT1, resulting in p65 acetylation, NF-κB activation and transcription of inflammatory cytokines. In mice, SIRT1 agonists attenuated RLDC-induced chronic inflammation, tissue damage, and renal fibrosis. Together, these results unveil the p53/SIRT1/NF-κB signaling axis in maladaptive kidney repair following RLDC treatment, where p53 represses SIRT1 to increase p65 acetylation for NF-κB activation, leading to chronic renal inflammation.

MicroRNA-34a: A Novel Therapeutic Target in Fibrosis

Fibrosis can occur in many organs, and severe cases leading to organ failure and death. No specific treatment for fibrosis so far. In recent years, microRNA-34a (miR-34a) has been found to play a role in fibrotic diseases. MiR-34a is involved in the apoptosis, autophagy and cellular senescence, also regulates TGF-β1/Smad signal pathway, and negatively regulates the expression of multiple target genes to affect the deposition of extracellular matrix and regulate the process of fibrosis. Some studies have explored the efficacy of miR-34a-targeted therapies for fibrotic diseases. Therefore, miR-34a has specific potential for the treatment of fibrosis. This article reviews the important roles of miR-34a in fibrosis and provides the possibility for miR-34a as a novel therapeutic target in fibrosis.

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.

Resveratrol in Treating Diabetes and Its Cardiovascular Complications: A Review of Its Mechanisms of Action

Diabetes mellitus (DM) is one of the most prevalent chronic diseases worldwide. High morbidity and mortality caused by DM are closely linked to its complications in multiple organs/tissues, including cardiovascular complications, diabetic nephropathy, and diabetic neuropathy. Resveratrol is a plant-derived polyphenolic compound with pleiotropic protective effects, ranging from antioxidant and anti-inflammatory to hypoglycemic effects. Recent studies strongly suggest that the consumption of resveratrol offers protection against diabetes and its cardiovascular complications. The protective effects of resveratrol involve the regulation of multiple signaling pathways, including inhibition of oxidative stress and inflammation, enhancement of insulin sensitivity, induction of autophagy, regulation of lipid metabolism, promotion of GLUT4 expression, and translocation, and activation of SIRT1/AMPK signaling axis. The cardiovascular protective effects of resveratrol have been recently reviewed in the literature, but the role of resveratrol in preventing diabetes mellitus and its cardiovascular complications has not been systematically reviewed. Therefore, in this review, we summarize the pharmacological effects and mechanisms of action of resveratrol based on in vitro and in vivo studies, highlighting the therapeutic potential of resveratrol in the prevention and treatment of diabetes and its cardiovascular complications.

Loss of Proximal Tubular Sirtuin 6 Aggravates Unilateral Ureteral Obstruction-Induced Tubulointerstitial Inflammation and Fibrosis by Regulation of β-Catenin Acetylation

Renal fibrosis is a significant pathologic change associated with progressive kidney disease. Sirt6 is an NAD⁺-dependent deacetylase and mono-ADP ribosyltransferase known to play diverse roles in the processes attendant to aging, metabolism, and carcinogenesis. However, the role of proximal tubule-specific Sirt6 in renal fibrosis remains elusive. This study investigates the effect of proximal tubule-specific Sirt6 knockdown on unilateral ureteral obstruction (UUO)-induced renal tubulointerstitial inflammation and fibrosis. Renal fibrosis in wild type and PT-Sirt6KO (Sirt6^flox/flox; Ggt1-Cre⁺) mice was induced by UUO surgery. After seven days, histologic examination and Western blot analysis were performed to examine extracellular matrix (ECM) protein expression. We evaluated inflammatory cytokine and cell adhesion molecule expression after ureteral obstruction. The therapeutic effect of Sirt6 activator MDL-800 on UUO-induced tubulointerstitial inflammation and fibrosis was assessed. The loss of Sirt6 in the proximal tubules aggravated UUO-induced tubular injury, ECM deposition, F4/80 positive macrophage infiltration, and proinflammatory cytokine and chemokine expression. Sirt6 activator MDL-800 mitigated UUO-induced renal tubulointerstitial inflammation and fibrosis. In an in vitro experiment, MDL-800 decreases the transforming growth factor (TGF)-β1-induced activation of myofibroblast and ECM production by regulating Sirt6-dependent β-catenin acetylation and the TGF-β1/Smad signaling pathway. In conclusion, proximal tubule Sirt6 may play an essential role in UUO-induced tubulointerstitial inflammation and fibrosis by regulating Sirt6-dependent β-catenin acetylation and ECM protein promoter transcription.

The S100 calcium binding protein A11 promotes liver fibrogenesis by targeting TGF-β signaling

Liver fibrosis is a key transformation stage and also a reversible pathological process in various types of chronic liver diseases. However, the pathogenesis of liver fibrosis still remains elusive. Here, we report that the calcium binding protein A11 (S100A11) is consistently upregulated in the integrated data from GSE liver fibrosis and tree shrew liver proteomics. S100A11 is also experimentally activated in liver fibrosis in mouse, rat, tree shrew, and human with liver fibrosis. While overexpression of S100A11 in vivo and in vitro exacerbates liver fibrosis, the inhibition of S100A11 improves liver fibrosis. Mechanistically, S100A11 activates hepatic stellate cells (HSCs) and the fibrogenesis process via the regulation of the deacetylation of Smad3 in the TGF-β signaling pathway. S100A11 physically interacts with SIRT6, a deacetylase of Smad2/3, which may competitively inhibit the interaction between SIRT6 and Smad2/3. The subsequent release and activation of Smad2/3 promote the activation of HSCs and fibrogenesis. Additionally, a significant elevation of S100A11 in serum is observed in clinical patients. Our study uncovers S100A11 as a novel profibrogenic factor in liver fibrosis, which may represent both a potential biomarker and a promising therapy target for treating liver fibrosis and fibrosis-related liver diseases.

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.

Resveratrol ameliorates myocardial fibrosis by regulating Sirt1/Smad3 deacetylation pathway in rat model with dilated cardiomyopathy

Background

The aim of this study was to investigate the effects of Resveratrol (RSV) in rats with dilated cardiomyopathy (DCM).

Methods

Porcine cardiac myosin was used to set up rat model with DCM. RSV (10 mg/kg in RSV-L group and 50 mg/kg in RSV-H group) or vehicle was administered to rats with DCM once daily from the 28th day till the 90th day after the first immunization. Cardiac function of rats was evaluated by echocardiographic analysis. The deposition of fibrous tissues in the hearts was evaluated by Masson and picrosirius red staining. The mRNA levels of collagen type I (Col I), collagen type III (Col III) and silence information regulator 1 (Sirt1) were measured by quantitative real-time polymerase chain reaction (qRT-PCR). The interaction of Sirt1 with Smad3 was revealed by coimmunoprecipitation.

Results

The heart weight, heart weight/body weight ratio, left ventricular end diastolic diameter (LVEDD) and left ventricular end systolic diameter (LVESD) were significantly increased in rats with DCM, and attenuated by RSV. RSV also positively decreased fibrosis, and the expression of Col I and Col III in the myocardium. The Sirt1 mRNA was significantly decreased in myosin-immunized hearts and was positively increased by RSV. The Sirt1 combined with Smad3 directly. Acetylation of Smad3 (Ac-Smad3) was significantly increased in DCM and was markedly decreased by RSV.

Conclusion

RSV effectively ameliorated myocardial fibrosis and improved cardiac function by regulating Sirt1/Smad3 deacetylation pathway in rat model with DCM.

T Helper Cell Lineage-Defining Transcription Factors: Potent Targets for Specific GVHD Therapy?

Allogenic hematopoietic stem cell transplantation (allo-HSCT) represents a potent and potentially curative treatment for many hematopoietic malignancies and hematologic disorders in adults and children. The donor-derived immunity, elicited by the stem cell transplant, can prevent disease relapse but is also responsible for the induction of graft-versus-host disease (GVHD). The pathophysiology of acute GVHD is not completely understood yet. In general, acute GVHD is driven by the inflammatory and cytotoxic effect of alloreactive donor T cells. Since several experimental approaches indicate that CD4 T cells play an important role in initiation and progression of acute GVHD, the contribution of the different CD4 T helper (Th) cell subtypes in the pathomechanism and regulation of the disease is a central point of current research. Th lineages derive from naïve CD4 T cell progenitors and lineage commitment is initiated by the surrounding cytokine milieu and subsequent changes in the transcription factor (TF) profile. Each T cell subtype has its own effector characteristics, immunologic function, and lineage specific cytokine profile, leading to the association with different immune responses and diseases. Acute GVHD is thought to be mainly driven by the Th1/Th17 axis, whereas Treg cells are attributed to attenuate GVHD effects. As the differentiation of each Th subset highly depends on the specific composition of activating and repressing TFs, these present a potent target to alter the Th cell landscape towards a GVHD-ameliorating direction, e.g. by inhibiting Th1 and Th17 differentiation. The finding, that targeting of Th1 and Th17 differentiation appears more effective for GVHD-prevention than a strategy to inhibit Th1 and Th17 cytokines supports this concept. In this review, we shed light on the current advances of potent TF inhibitors to alter Th cell differentiation and consecutively attenuate GVHD. We will focus especially on preclinical studies and outcomes of TF inhibition in murine GVHD models. Finally, we will point out the possible impact of a Th cell subset-specific immune modulation in context of GVHD.

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.

Therapeutic and delivery strategies of phytoconstituents for renal fibrosis

Chronic kidney disease (CKD) is one of the most common diseases endangering human health and life. By 2030, 14 per 100,000 people may die from CKD. Renal fibrosis (RF) is an important intermediate link and the final pathological change during CKD progression to the terminal stage. Therefore, identifying safe and effective treatment methods for RF has become an important goal. In 2018, the World Health Organization introduced traditional Chinese medicine into its effective global medical program. Various phytoconstituents that affect the RF process have been extracted from different plants. Here, we review the potential therapeutic capabilities of active phytoconstituents in RF treatment and discuss how phytoconstituents can be structurally modified or combined with other ingredients to enhance efficiency and reduce toxicity. We also summarize phytoconstituent delivery strategies to overcome renal barriers and improve bioavailability and targeting.

P300/CBP-Associated Factor Activates Cardiac Fibroblasts by SMAD2 Acetylation

Various heart diseases cause cardiac remodeling, which in turn leads to ineffective contraction. Although it is an adaptive response to injury, cardiac fibrosis contributes to this remodeling, for which the reactivation of quiescent myofibroblasts is a key feature. In the present study, we investigated the role of the p300/CBP-associated factor (PCAF), a histone acetyltransferase, in the activation of cardiac fibroblasts. An intraperitoneal (i.p.) injection of a high dose (160 mg/kg) of isoproterenol (ISP) induced cardiac fibrosis and reduced the amount of the PCAF in cardiac fibroblasts in the mouse heart. However, the PCAF activity was significantly increased in cardiac fibroblasts, but not in cardiomyocytes, obtained from ISP-administered mice. An in vitro study using human cardiac fibroblast cells recapitulated the in vivo results; an treatment with transforming growth factor-β1 (TGF-β1) reduced the PCAF, whereas it activated the PCAF in the fibroblasts. PCAF siRNA attenuated the TGF-β1-induced increase in and translocation of fibrosis marker proteins. PCAF siRNA blocked TGF-β1-mediated gel contraction and cell migration. The PCAF directly interacted with and acetylated mothers against decapentaplegic homolog 2 (SMAD2). PCAF siRNA prevented TGF-β1-induced phosphorylation and the nuclear localization of SMAD2. These results suggest that the increase in PCAF activity during cardiac fibrosis may participate in SMAD2 acetylation and thereby in its activation.

Temporal characterization of mitochondrial impairment in the unilateral ureteral obstruction model in rats

Renal fibrosis is a well-known mechanism that favors chronic kidney disease (CKD) development in obstructive nephropathy, a significant pathology worldwide. Fibrosis induction involves several pathways, and although mitochondrial alterations have recently emerged as a critical factor that triggers renal damage in the obstructed kidney, the temporal mitochondrial alterations during the fibrotic induction remain unexplored. Therefore, in this work, we evaluated the time course of mitochondrial mass and bioenergetics alterations induced by a unilateral ureteral obstruction (UUO), a widely used model to study the mechanism involved in kidney fibrosis induction and progression. Our results show a marked reduction in mitochondrial oxidative phosphorylation (OXPHOS) in the obstructed kidney on days 7 to 28 of obstruction without significant mitochondrial coupling changes. Besides, we observed that mitochondrial mass was reduced, probably due to decreased biogenesis and mitophagy induction. OXPHOS impairment was associated with decreased mitochondrial biogenesis markers, the peroxisome proliferator-activated receptor γ co-activator-1alpha (PGC-1α), and nuclear respiratory factor 1 (NRF1); and also, with the induction of mitophagy in a PTEN-induced kinase 1 (PINK1) and Parkin independent way. It is concluded that the impairment of OXPHOS capacity may be explained by the reduction in mitochondrial biogenesis and the induction of mitophagy during fibrotic progression.

Negative regulators of TGF-β1 signaling in renal fibrosis; pathological mechanisms and novel therapeutic opportunities

Elevated expression of the multifunctional cytokine transforming growth factor β1 (TGF-β1) is causatively linked to kidney fibrosis progression initiated by diabetic, hypertensive, obstructive, ischemic and toxin-induced injury. Therapeutically relevant approaches to directly target the TGF-β1 pathway (e.g., neutralizing antibodies against TGF-β1), however, remain elusive in humans. TGF-β1 signaling is subjected to extensive negative control at the level of TGF-β1 receptor, SMAD2/3 activation, complex assembly and promoter engagement due to its critical role in tissue homeostasis and numerous pathologies. Progressive kidney injury is accompanied by the deregulation (loss or gain of expression) of several negative regulators of the TGF-β1 signaling cascade by mechanisms involving protein and mRNA stability or epigenetic silencing, further amplifying TGF-β1/SMAD3 signaling and fibrosis. Expression of bone morphogenetic proteins 6 and 7 (BMP6/7), SMAD7, Sloan-Kettering Institute proto-oncogene (Ski) and Ski-related novel gene (SnoN), phosphate tensin homolog on chromosome 10 (PTEN), protein phosphatase magnesium/manganese dependent 1A (PPM1A) and Klotho are dramatically decreased in various nephropathies in animals and humans albeit with different kinetics while the expression of Smurf1/2 E3 ligases are increased. Such deregulations frequently initiate maladaptive renal repair including renal epithelial cell dedifferentiation and growth arrest, fibrotic factor (connective tissue growth factor (CTGF/CCN2), plasminogen activator inhibitor type-1 (PAI-1), TGF-β1) synthesis/secretion, fibroproliferative responses and inflammation. This review addresses how loss of these negative regulators of TGF-β1 pathway exacerbates renal lesion formation and discusses the therapeutic value in restoring the expression of these molecules in ameliorating fibrosis, thus, presenting novel approaches to suppress TGF-β1 hyperactivation during chronic kidney disease (CKD) progression.

Redox signaling pathways in unilateral ureteral obstruction (UUO)-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is an experimental rodent model that mimics renal fibrosis associated with obstructive nephropathy in an accelerated manner. After UUO, the activation of the renin-angiotensin system (RAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and mitochondrial dysfunction lead to reactive oxygen species (ROS) overproduction in the kidney. ROS are secondary messengers able to induce post-translational modifications (PTMs) in redox-sensitive proteins, which activate or deactivate signaling pathways. Therefore, in UUO, it has been proposed that ROS overproduction causes changes in said pathways promoting inflammation, oxidative stress, and apoptosis that contribute to fibrosis development. Furthermore, mitochondrial metabolism impairment has been associated with UUO, contributing to renal damage in this model. Although ROS production and oxidative stress have been studied in UUO, the development of renal fibrosis associated with redox signaling pathways has not been addressed. This review focuses on the current information about the activation and deactivation of signaling pathways sensitive to a redox state and their effect on mitochondrial metabolism in the fibrosis development in the UUO model.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

SIRT3 Overexpression Ameliorates Asbestos-Induced Pulmonary Fibrosis, mt-DNA Damage, and Lung Fibrogenic Monocyte Recruitment

Alveolar epithelial cell (AEC) mitochondrial (mt) DNA damage and fibrotic monocyte-derived alveolar macrophages (Mo-AMs) are implicated in the pathobiology of pulmonary fibrosis. We showed that sirtuin 3 (SIRT3), a mitochondrial protein regulating cell fate and aging, is deficient in the AECs of idiopathic pulmonary fibrosis (IPF) patients and that asbestos- and bleomycin-induced lung fibrosis is augmented in Sirt3 knockout (Sirt3-/-) mice associated with AEC mtDNA damage and intrinsic apoptosis. We determined whether whole body transgenic SIRT3 overexpression (Sirt3Tg) protects mice from asbestos-induced pulmonary fibrosis by mitigating lung mtDNA damage and Mo-AM recruitment. Crocidolite asbestos (100 µg/50 µL) or control was instilled intratracheally in C57Bl6 (Wild-Type) mice or Sirt3Tg mice, and at 21 d lung fibrosis (histology, fibrosis score, Sircol assay) and lung Mo-AMs (flow cytometry) were assessed. Compared to controls, Sirt3Tg mice were protected from asbestos-induced pulmonary fibrosis and had diminished lung mtDNA damage and Mo-AM recruitment. Further, pharmacologic SIRT3 inducers (i.e., resveratrol, viniferin, and honokiol) each diminish oxidant-induced AEC mtDNA damage in vitro and, in the case of honokiol, protection occurs in a SIRT3-dependent manner. We reason that SIRT3 preservation of AEC mtDNA is a novel therapeutic focus for managing patients with IPF and other types of pulmonary fibrosis.

Silencing of miR-150-5p Ameliorates Diabetic Nephropathy by Targeting SIRT1/p53/AMPK Pathway

Diabetic nephropathy (DN) is a common complication of diabetes and an important cause of end-stage renal disease. Increasing evidence suggests that microRNAs (miRNAs) regulate the development of DN. In a preliminary study, high levels of miR-150-5p were detected in the serum and urine of patients with DN. Consequently, we investigated the effect and mechanism of action of miR-150-5p in DN in vitro and in vivo. Our results showed that inhibition of miR-150-5p reversed high glucose-induced podocyte injury and Streptozocin (STZ)-induced diabetic nephropathy in mice. Further analysis revealed that miR-150-5p targeted the 3′ untranslated region (UTR) of sirtuin 1 (SIRT1), consequently decreasing SIRT1 levels in podocytes. Importantly, we found that the silencing of miR-150-5p promoted the interaction between SIRT1 and p53, causing the suppression of p53 acetylation in podocytes and kidney tissue. This resulted in the stimulation of AMP-activated protein kinase (AMPK)-dependent autophagy. In conclusion, our study demonstrated that the silencing of miR-150-5p played a reno-protective role in DN mice through targeting SIRT1.

Serum sirtuin 1 is independently associated with intact PTH among patients with chronic kidney disease

Background

Sirtuin 1 is involved in the pathogenesis of age-related diseases.

Purpose

The aim of the study was to assess the clinical and diagnostic value of serum sirtuin 1 concentration in patients with CKD.

Patients and Methods

The serum sirtuin 1 level was evaluated using ELISA kit in 100 CKD patients stratified for five stages and in a control group of 24 healthy volunteers.

Results

Serum sirtuin 1 concentration was higher in the CKD group compared with the control group (p<0.05). Sirtuin 1 correlated with conventional CKD biomarkers and eGFR equations, intact parathyroid hormone (iPTH) and age (all p<0.05). Statins, AT₁ receptor antagonists and β-blockers use were associated with decreased sirtuin concentration (p<0.05). Sirtuin 1 was able to distinguish CKD from control group with high sensitivity and specificity (93% and 87%, respectively; AUC=0.954). Surprisingly, after adjustment only iPTH concentration was an independent predictor of sirtuin 1 level.

Conclusion

The association between sirtuin 1, eGFR equations and iPTH indicates its possible usefulness as a kidney function marker. In terms of iPTH being the only independent predictor of circulating sirtuin 1 it can be considered as an indirect cardiovascular risk biomarker regardless of renal function and provide additional information for patient management. Alternatively, sirtuin 1 is recognized as protective against vascular disease, and we demonstrated a positive correlation with iPTH, which may be related to accumulation of (7-84)-PTH having opposite biological effects to full-length PTH. Further studies are needed to explore the interplay between sirtuin 1, PTH and CKD-related vascular calcification as well as to assess its prognostic value in observational studies.

Nicotinamide mononucleotide attenuates isoproterenol-induced cardiac fibrosis by regulating oxidative stress and Smad3 acetylation

AIMS

Cardiac fibrosis is a pathological hallmark of progressive heart diseases currently lacking effective treatment. Nicotinamide mononucleotide (NMN), a member of the vitamin B₃ family, is a defined biosynthetic precursor of nicotinamide adenine dinucleotide (NAD⁺). Its beneficial effects on cardiac diseases are known, but its effects on cardiac fibrosis and the underlying mechanism remain unclear. We aimed to elucidate the protective effect of NMN against cardiac fibrosis and its underlying mechanisms of action.

MATERIALS AND METHODS

Cardiac fibrosis was induced by isoproterenol (ISO) in mice. NMN was administered by intraperitoneal injection. In vitro, cardiac fibroblasts (CFs) were stimulated by transforming growth factor-beta (TGF-β) with or without NMN and sirtinol, a SIRT1 inhibitor. Levels of cardiac fibrosis, NAD⁺/SIRT1 alteration, oxidative stress, and Smad3 acetylation were evaluated by real-time polymerase chain reaction, western blots, immunohistochemistry staining, immunoprecipitation, and assay kits.

KEY FINDINGS

ISO treatment induced cardiac dysfunction, fibrosis, and hypertrophy in vivo, whereas NMN alleviated these changes. Additionally, NMN suppressed CFs activation stimulated by TGF-β in vitro. Mechanistically, NMN restored the NAD⁺/SIRT1 axis and inhibited the oxidative stress and Smad3 acetylation induced by ISO or TGF-β. However, the protective effects of NMN were partly antagonized by sirtinol in vitro.

SIGNIFICANCE

NMN could attenuate cardiac fibrosis in vivo and fibroblast activation in vitro by suppressing oxidative stress and Smad3 acetylation in a NAD⁺/SIRT1-dependent manner.

An updated pharmacological insight of resveratrol in the treatment of diabetic nephropathy

As one of the most common complications of diabetes, nephropathy develops in approximately 40% of diabetic individuals. Although end stage kidney disease is known as one of the most consequences of diabetic nephropathy, the majority of diabetic individuals might die from cardiovascular diseases and infections before renal replacement treatment. Moreover, the routine medical treatments for diabetes hold undesirable side effects. The explosive prevalence of diabetes urges clinicians and scientists to investigate the complementary or alternative therapies. Phytochemicals are emerging as alternatives with a wide range of therapeutic effects on various pathologies, including diabetic kidney disease. Of those phytochemicals, resveratrol, a natural polyphenolic stilbene, has been found to exert a broad spectrum of health benefits via various signaling molecules. In particular, resveratrol has gained a great deal of attention because of its anti-oxidative, anti-inflammatory, anti-diabetic, anti-obesity, cardiovascular-protective, and anti-tumor properties. In the renal system, emerging evidence shows that resveratrol has already been used to ameliorate chronic or acute kidney injury. This review critically summarizes the current findings and molecular mechanisms of resveratrol in diabetic renal damage. In addition, we will discuss the adverse and inconsistent effects of resveratrol in diabetic nephropathy. Although there is increasing evidence that resveratrol affords great potential in diabetic nephropathy therapy, these results should be treated with caution before its clinical translation. In addition, the unfavorable pharmacokinetics and/or pharmacodynamics profiles, such as poor bioavailability, may limit its extensive clinical applications. It is clear that further research is needed to unravel these limitations and improve its efficacy against diabetic nephropathy. Increasing investigation of resveratrol in diabetic kidney disease will not only help us better understand its pharmacological actions, but also provide novel potential targets for therapeutic intervention.

Sirt1 inhibits renal tubular cell epithelial-mesenchymal transition through YY1 deacetylation in diabetic nephropathy

Silent information regulator 1 (Sirt1) is a deacetylase, which plays an important role in the occurrence and development of diabetic nephropathy (DN). Our previous study shows that Yin yang 1 (YY1), a widely expressed zinc finger DNA/RNA-binding transcription factor, is a novel regulator of renal fibrosis in diabetic nephropathy. Since the activity of YY1 is regulated via acetylation and deacetylation modification, this study aimed to explore whether Sirt1-induced deacetylation of YY1 mediated high glucose (HG)-induced renal tubular epithelial-mesenchymal transition (EMT) and renal fibrosis in vivo and in vitro. We first confirmed that Sirt1 expression level was significantly decreased in the kidney of db/db mice and in HG-treated HK-2 cells. Diabetes-induced Sirt1 reduction enhanced the level of YY1 acetylation and renal tubular EMT. Then, we manipulated Sirt1 expression in vivo and in vitro by injecting resveratrol (50 mg·kg^-1·d^-1. ip) to db/db mice for 2 weeks or application of SRT1720 (2.5 μM) in HG-treated HK-2 cells, we found that activation of Sirt1 reversed the renal tubular EMT and YY1 acetylation induced by HG condition. On the contrary, Sirt1 was knocked down in db/m mice or EX527 (1 μM) was added in HK-2 cells, we found that inhibition of Sirt1 exacerbated renal fibrosis in diabetic mice and enhanced level of YY1 acetylation in HK-2 cells. Furthermore, knockdown of YY1 inhibited the ameliorating effect of resveratrol on renal tubular EMT and renal fibrosis in db/db mice. In conclusion, this study demonstrates that Sirt1 plays an important role in renal tubular EMT of DN through mediating deacetylation of YY1.

Implication of cellular senescence in the progression of chronic kidney disease and the treatment potencies

Chronic kidney disease (CKD) is an increasing major public health problem worldwide. And CKD shares numerous phenotypic similarities with kidney as well as systemic ageing. Cellular senescence is mainly characterized by a stable cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Herein, the regulations and the internal mechanisms of cellular senescence will be discussed. Meanwhile, efforts are made to give a comprehensive overview of the recent advances of the implication of cellular senescence in CKD. To date, numerous studies have focused on the effects of ageing risk factors in kidney and thereby trying to interrupt the kidney ageing processes with senolytics. Interestingly, some of them showed enormous clinical application potentials. Therefore, senotherapeutics can be applied as novel potential strategies for the treatment of CKD.

Targeting energy pathways in kidney disease: the roles of sirtuins, AMPK, and PGC1α

The kidney has extraordinary metabolic demands to sustain the active transport of solutes that is critical to renal filtration and clearance. Mitochondrial health is vital to meet those demands and maintain renal fitness. Decades of studies have linked poor mitochondrial health to kidney disease. Key regulators of mitochondrial health-adenosine monophosphate kinase, sirtuins, and peroxisome proliferator-activated receptor γ coactivator-1α-have all been shown to play significant roles in renal resilience against disease. This review will summarize the latest research into the activities of those regulators and evaluate the roles and therapeutic potential of targeting those regulators in acute kidney injury, glomerular kidney disease, and renal fibrosis.

The Development of Maillard Reaction, and Advanced Glycation End Product (AGE)-Receptor for AGE (RAGE) Signaling Inhibitors as Novel Therapeutic Strategies for Patients with AGE-Related Diseases

Advanced glycation end products (AGEs) are generated by nonenzymatic modifications of macromolecules (proteins, lipids, and nucleic acids) by saccharides (glucose, fructose, and pentose) via Maillard reaction. The formed AGE molecules can be catabolized and cleared by glyoxalase I and II in renal proximal tubular cells. AGE-related diseases include physiological aging, neurodegenerative/neuroinflammatory diseases, diabetes mellitus (DM) and its complications, autoimmune/rheumatic inflammatory diseases, bone-degenerative diseases, and chronic renal diseases. AGEs, by binding to receptors for AGE (RAGEs), alter innate and adaptive immune responses to induce inflammation and immunosuppression via the generation of proinflammatory cytokines, reactive oxygen species (ROS), and reactive nitrogen intermediates (RNI). These pathological molecules cause vascular endothelial/smooth muscular/connective tissue-cell and renal mesangial/endothelial/podocytic-cell damage in AGE-related diseases. In the present review, we first focus on the cellular and molecular bases of AGE–RAGE axis signaling pathways in AGE-related diseases. Then, we discuss in detail the modes of action of newly discovered novel biomolecules and phytochemical compounds, such as Maillard reaction and AGE–RAGE signaling inhibitors. These molecules are expected to become the new therapeutic strategies for patients with AGE-related diseases in addition to the traditional hypoglycemic and anti-hypertensive agents. We particularly emphasize the importance of “metabolic memory”, the “French paradox”, and the pharmacokinetics and therapeutic dosing of the effective natural compounds associated with pharmacogenetics in the treatment of AGE-related diseases. Lastly, we propose prospective investigations for solving the enigmas in AGE-mediated pathological effects.

Mitochondrial dysfunction and the AKI-to-CKD transition

Acute kidney injury (AKI) has been widely recognized as an important risk factor for the occurrence and development of chronic kidney disease (CKD). Even milder AKI has adverse consequences and could progress to renal fibrosis, which is the ultimate common pathway for various terminal kidney diseases. Thus, it is urgent to develop a strategy to hinder the transition from AKI to CKD. Some mechanisms of the AKI-to-CKD transition have been revealed, such as nephron loss, cell cycle arrest, persistent inflammation, endothelial injury with vascular rarefaction, and epigenetic changes. Previous studies have elucidated the pivotal role of mitochondria in acute injuries and demonstrated that the fitness of this organelle is a major determinant in both the pathogenesis and recovery of organ function. Recent research has suggested that damage to mitochondrial function in early AKI is a crucial factor leading to tubular injury and persistent renal insufficiency. Dysregulation of mitochondrial homeostasis, alterations in bioenergetics, and organelle stress cross talk contribute to the AKI-to-CKD transition. In this review, we focus on the pathophysiology of mitochondria in renal recovery after AKI and progression to CKD, confirming that targeting mitochondria represents a potentially effective therapeutic strategy for the progression of AKI to CKD.

Senescence and the Aging Immune System as Major Drivers of Chronic Kidney Disease

Chronic kidney disease (CKD) presents an ever-growing disease burden for the world's aging population. It is characterized by numerous changes to the kidney, including a decrease in renal mass, renal fibrosis, and a diminished glomerular filtration rate. The premature aging phenotype observed in CKD is associated with cellular senescence, particularly of renal tubular epithelial cells (TECs), which contributes to chronic inflammation through the production of a proinflammatory senescence associated secretory phenotype (SASP). When coupled with changes in immune system composition and progressive immune dysfunction, the accumulation of senescent kidney cells acts as a driver for the progression of CKD. The targeting of senescent cells may well present an attractive therapeutic avenue for the treatment of CKD. We propose that the targeting of senescent cells either by direct inhibition of pro-survival pathways (senolytics) or through the inhibition of their proinflammatory secretory profile (senomorphics) together with immunomodulation to enhance immune system surveillance of senescent cells could be of benefit to patients with CKD.

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.

Mitochondrial dysfunction and endoplasmic reticulum stress in the promotion of fibrosis in obstructive nephropathy induced by unilateral ureteral obstruction

Obstructive nephropathy favors the progression to chronic kidney disease (CKD), a severe health problem worldwide. The unilateral ureteral obstruction (UUO) model is used to study the development of fibrosis. Impairment of renal mitochondria plays a crucial role in several types of CKD and has been strongly related to fibrosis onset. Nevertheless, in the UUO model, the impairment of mitochondria, their relationship with endoplasmic reticulum (ER) stress induction and the participation of both to induce the fibrotic process remain unclear. In this review, we summarize the current information about mitochondrial bioenergetics, redox dynamics, mitochondrial mass, and biogenesis alterations, as well as the relationship of these mitochondrial alterations with ER stress and their participation in fibrotic processes in UUO models. Early after obstruction, there is metabolic reprogramming related to mitochondrial fatty acid β-oxidation impairment, triggering lipid deposition, oxidative stress, (calcium) Ca²⁺ dysregulation, and a reduction in mitochondrial mass and biogenesis. Mitochondria and the ER establish a pathological feedback loop that promotes the impairment of both organelles by ER stress pathways and Ca²⁺ levels dysregulation. Preserving mitochondrial and ER function can prevent or at least delay the fibrotic process and loss of renal function. However, deeper understanding is still necessary for future clinically-useful therapies.

Resveratrol Modulates Transforming Growth Factor-Beta (TGF-β) Signaling Pathway for Disease Therapy: A New Insight into Its Pharmacological Activities

Resveratrol (Res) is a well-known natural product that can exhibit important pharmacological activities such as antioxidant, anti-diabetes, anti-tumor, and anti-inflammatory. An evaluation of its therapeutic effects demonstrates that this naturally occurring bioactive compound can target different molecular pathways to exert its pharmacological actions. Transforming growth factor-beta (TGF-β) is an important molecular pathway that is capable of regulating different cellular mechanisms such as proliferation, migration, and angiogenesis. TGF-β has been reported to be involved in the development of disorders such as diabetes, cancer, inflammatory disorders, fibrosis, cardiovascular disorders, etc. In the present review, the relationship between Res and TGF-β has been investigated. It was noticed that Res can inhibit TGF-β to suppress the proliferation and migration of cancer cells. In addition, Res can improve fibrosis by reducing inflammation via promoting TGF-β down-regulation. Res has been reported to be also beneficial in the amelioration of diabetic complications via targeting the TGF-β signaling pathway. These topics are discussed in detail in this review to shed light on the protective effects of Res mediated via the modulation of TGF-β signaling.