Sirtuin 3-dependent mitochondrial dynamic improvements protect against acute kidney injury

Notoginsenoside Fc ameliorates renal tubular injury and mitochondrial damage in acetaminophen-induced acute kidney injury partly by regulating SIRT3/SOD2 pathway

Introduction

Mitochondria dysfunction is one of the primary causes of tubular injury in acute kidney injury (AKI). Notoginsenoside Fc (Fc), a new saponin isolated from Panax notoginseng, exhibited numerous pharmacological actions. However, the beneficial effects of Fc on renal tubular impairment and mitochondrial dysfunction in AKI have not been fully studied.

Methods

In this study, we established acetaminophen (APAP)-induced AKI model in mice to examine the therapeutic impacts of Fc on AKI.

Results

Our results showed that Fc could decrease the levels of the serum creatinine (Scr), blood urea nitrogen (BUN) and Cystatin C in mice with AKI. Fc also ameliorated renal histopathology, renal tubular cells apoptosis and restored expression of apoptosis-related proteins such as Bax, Bcl-2 and caspase3 (C-caspase3). Additionally, Fc increased the protein expression of SIRT3 and SOD2 in kidneys from mice with AKI. In vitro studies further showed Fc reduced the apoptosis of HK-2 cells exposure to APAP, attenuated the loss of mitochondrial membrane potential and decreased the formation of mitochondrial superoxide. Fc also partly restored the protein expression of Bax, Bcl-2, C-Caspase3, SIRT3, and SOD2 in HK-2 cells exposure to APAP.

Conclusion

In summary, Fc might reduce renal tubular injury and mitochondrial dysfunction in AKI partly through the regulation of SIRT3/SOD2 pathway.

Cisplatin nephrotoxicity: new insights and therapeutic implications

Cisplatin is an effective chemotherapeutic agent for various solid tumours, but its use is limited by adverse effects in normal tissues. In particular, cisplatin is nephrotoxic and can cause acute kidney injury and chronic kidney disease. Preclinical studies have provided insights into the cellular and molecular mechanisms of cisplatin nephrotoxicity, which involve intracellular stresses including DNA damage, mitochondrial pathology, oxidative stress and endoplasmic reticulum stress. Stress responses, including autophagy, cell-cycle arrest, senescence, apoptosis, programmed necrosis and inflammation have key roles in the pathogenesis of cisplatin nephrotoxicity. In addition, emerging evidence suggests a contribution of epigenetic changes to cisplatin-induced acute kidney injury and chronic kidney disease. Further research is needed to determine how these pathways are integrated and to identify the cell type-specific roles of critical molecules involved in regulated necrosis, inflammation and epigenetic modifications in cisplatin nephrotoxicity. A number of potential therapeutic targets for cisplatin nephrotoxicity have been identified. However, the effects of renoprotective strategies on the efficacy of cisplatin chemotherapy needs to be thoroughly evaluated. Further research using tumour-bearing animals, multi-omics and genome-wide association studies will enable a comprehensive understanding of the complex cellular and molecular mechanisms of cisplatin nephrotoxicity and potentially lead to the identification of specific targets to protect the kidney without compromising the chemotherapeutic efficacy of cisplatin.

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.

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.

Tubular β-catenin alleviates mitochondrial dysfunction and cell death in acute kidney injury

Mitochondria take part in a network of intracellular processes that regulate homeostasis. Defects in mitochondrial function are key pathophysiological changes during AKI. Although Wnt/β-catenin signaling mediates mitochondrial dysfunction in chronic kidney fibrosis, little is known of the influence of β-catenin on mitochondrial function in AKI. To decipher this interaction, we generated an inducible mouse model of tubule-specific β-catenin overexpression (TubCat), and a model of tubule-specific β-catenin depletion (TubcatKO), and induced septic AKI in these mice with lipopolysaccharide (LPS) and aseptic AKI with bilateral ischemia-reperfusion. In both AKI models, tubular β-catenin stabilization in TubCat animals significantly reduced BUN/serum creatinine, tubular damage (NGAL-positive tubules), apoptosis (TUNEL-positive cells) and necroptosis (phosphorylation of MLKL and RIP3) through activating AKT phosphorylation and p53 suppression; enhanced mitochondrial biogenesis (increased PGC-1α and NRF1) and restored mitochondrial mass (increased TIM23) to re-establish mitochondrial homeostasis (increased fusion markers OPA1, MFN2, and decreased fission protein DRP1) through the FOXO3/PGC-1α signaling cascade. Conversely, kidney function loss and histological damage, tubular cell death, and mitochondrial dysfunction were all aggravated in TubCatKO mice. Mechanistically, β-catenin transfection maintained mitochondrial mass and activated PGC-1α via FOXO3 in LPS-exposed HK-2 cells. Collectively, these findings provide evidence that tubular β-catenin mitigates cell death and restores mitochondrial homeostasis in AKI through the common mechanisms associated with activation of AKT/p53 and FOXO3/PGC-1α signaling pathways.

FFAR4 improves the senescence of tubular epithelial cells by AMPK/SirT3 signaling in acute kidney injury

Acute kidney injury (AKI) is a serious clinical complication with high morbidity and mortality rates. Despite substantial progress in understanding the mechanism of AKI, no effective therapy is available for treatment or prevention. We previously found that G protein-coupled receptor (GPCR) family member free fatty acid receptor 4 (FFAR4) agonist TUG891 alleviated kidney dysfunction and tubular injury in AKI mice. However, the versatile role of FFAR4 in kidney has not been well characterized. In the study, the expression of FFAR4 was abnormally decreased in tubular epithelial cells (TECs) of cisplatin, cecal ligation/perforation and ischemia/reperfusion injury-induced AKI mice, respectively. Systemic and conditional TEC-specific knockout of FFAR4 aggravated renal function and pathological damage, whereas FFAR4 activation by TUG-891 alleviated the severity of disease in cisplatin-induced AKI mice. Notably, FFAR4, as a key determinant, was firstly explored to regulate cellular senescence both in injured kidneys of AKI mice and TECs, which was indicated by senescence-associated β-galactosidase (SA-β-gal) activity, marker protein p53, p21, Lamin B1, phospho-histone H2A.X, phospho-Rb expression, and secretory phenotype IL-6 level. Mechanistically, pharmacological activation and overexpression of FFAR4 reversed the decrease of aging-related SirT3 protein, where FFAR4 regulated SirT3 expression to exhibit anti-senescent effect via Gq subunit-mediated CaMKKβ/AMPK signaling in cisplatin-induced mice and TECs. These findings highlight the original role of tubular FFAR4 in cellular senescence via AMPK/SirT3 signaling and identify FFAR4 as a potential drug target against AKI.

A novel mechanism for the protection against acute lung injury by melatonin: mitochondrial quality control of lung epithelial cells is preserved through SIRT3-dependent deacetylation of SOD2

The mitochondrial quality control of lung epithelial cells is disturbed during sepsis, which contributes to abnormal mitochondrial function and acute lung injury. Melatonin is one of the primary hormones secreted by the pineal gland, displaying favorable antioxidative actions in sepsis and cardiopulmonary disease. However, the potential roles and molecular basis of melatonin in lipopolysaccharide (LPS)-treated lung epithelial cells have not been explored and reported. Herein, we investigated whether melatonin could protect against sepsis-induced acute lung injury (ALI) and LPS-treated lung epithelial cells through the mitochondrial quality control as well as its possible molecular targets. Wild type and Sirt3 knockout mice were intratracheally instilled with LPS for 12 h to construct an in vivo acute lung injury model. Both A549 lung epithelial cells and primary alveolar type II (AT-II) cells were used to explore the possible roles of melatonin in vitro by incubating with small interfering RNA against Sirt3. To determine the involvement of the melatonin receptor, cells and mice were treated with si Mtnr1b and luzindole. Melatonin pretreatment significantly inhibited pathological injury, inflammatory response, oxidative stress, and apoptosis in LPS-treated lung tissues and LPS-treated lung epithelial cells. Furthermore, melatonin also shifted the dynamic course of mitochondria from fission to fusion, inhibited mitophagy and fatty acid oxidation in LPS-treated lung epithelial cells in vitro and in vivo. However, SIRT3 inhibition abolished the protective roles of melatonin in acute lung injury. Mechanistically, we found that melatonin increased the activity and expression of SIRT3, which further promoted the deacetylation of SOD2 at K122 and K68. More importantly, melatonin exerted pulmonary protection by activating MTNR1B but not MTNR1A during ALI. Collectively, melatonin could preserve the mitochondrial quality control of lung epithelial cells through the deacetylation of SOD2 in a SIRT3-dependent manner, which eventually alleviated sepsis-induced injury, inflammation, oxidative stress, and apoptosis. Thus, melatonin may serve as a promising candidate against ALI in the future.

Sirt3 mitigates LPS-induced mitochondrial damage in renal tubular epithelial cells by deacetylating YME1L1

Acute kidney injury (AKI) is often secondary to sepsis. Increasing evidence suggests that mitochondrial dysfunction contributes to the pathological process of AKI. In this study, we aimed to examine the regulatory roles of Sirt3 in Lipopolysaccharide (LPS)-induced mitochondrial damage in renal tubular epithelial cells (TECs). Sirt3 knockout mice were intraperitoneally injected with LPS, and cultured TECs were stimulated with LPS to evaluate the effects of Sirt3 on mitochondrial structure and function in TECs. Electron microscopy was used to assess mitochondrial morphology. Immunofluorescence staining was performed to detect protein expression and examine mitochondrial morphology. Western blotting was used to quantify protein expression. We observed that LPS increased apoptosis, induced disturbances in mitochondrial function and dynamics, and downregulated Sirt3 expression in a sepsis-induced AKI mouse model and human proximal tubular (HK-2) cells in vitro. Sirt3 deficiency further exacerbated LPS-induced renal pathological damage, apoptosis and disturbances in mitochondrial function and dynamics. On the contrary, Sirt3 overexpression in HK-2 cells alleviated these lesions. Functional studies revealed that Sirt3 overexpression alleviated LPS-induced mitochondrial damage and apoptosis in TECs by promoting OPA1-mediated mitochondrial fusion through the deacetylation of i-AAA protease (YME1L1), an upstream regulatory molecule of OPA1. Our study has identified Sirt3 as a vital factor that protects against LPS-induced mitochondrial damage and apoptosis in TECs via the YME1L1-OPA1 signaling pathway.

Magnesium Isoglycyrrhizinate Reduces the Target-Binding Amount of Cisplatin to Mitochondrial DNA and Renal Injury through SIRT3

Nephrotoxicity is the dose-limiting factor of cisplatin treatment. Magnesium isoglycyrrhizinate (MgIG) has been reported to ameliorate renal ischemia–reperfusion injury. This study aimed to investigate the protective effect and possible mechanisms of MgIG against cisplatin-induced nephrotoxicity from the perspective of cellular pharmacokinetics. We found that cisplatin predominantly accumulated in mitochondria of renal tubular epithelial cells, and the amount of binding with mitochondrial DNA (mtDNA) was more than twice that with nuclear DNA (nDNA). MgIG significantly lowered the accumulation of cisplatin in mitochondria and, in particular, the degree of target-binding to mtDNA. MgIG notably ameliorated cisplatin-induced changes in mitochondrial membrane potential, morphology, function, and cell viability, while the magnesium donor drugs failed to work. In a mouse model, MgIG significantly alleviated cisplatin-caused renal dysfunction, pathological changes of renal tubules, mitochondrial ultrastructure variations, and disturbed energy metabolism. Both in vitro and in vivo data showed that MgIG recovered the reduction of NAD+-related substances and NAD+-dependent deacetylase sirtuin-3 (SIRT3) level caused by cisplatin. Furthermore, SIRT3 knockdown weakened the protective effect of MgIG on mitochondria, while SIRT3 agonist protected HK-2 cells from cisplatin and specifically reduced platinum-binding activity with mtDNA. In conclusion, MgIG reduces the target-binding amount of platinum to mtDNA and exerts a protective effect on cisplatin-induced renal injury through SIRT3, which may provide a new strategy for the treatment of cisplatin-induced nephrotoxicity.

Low Nephron Number Induced by Maternal Protein Restriction Is Prevented by Nicotinamide Riboside Supplementation Depending on Sirtuin 3 Activation

A reduced nephron number at birth, due to critical gestational conditions, including maternal malnutrition, is associated with the risk of developing hypertension and chronic kidney disease in adulthood. No interventions are currently available to augment nephron number. We have recently shown that sirtuin 3 (SIRT3) has an important role in dictating proper nephron endowment. The present study explored whether SIRT3 stimulation, by means of supplementation with nicotinamide riboside (NR), a precursor of the SIRT3 co-substrate nicotinamide adenine dinucleotide (NAD⁺), was able to improve nephron number in a murine model of a low protein (LP) diet. Our findings show that reduced nephron number in newborn mice (day 1) born to mothers fed a LP diet was associated with impaired renal SIRT3 expression, which was restored through supplementation with NR. Glomerular podocyte density, as well as the rarefaction of renal capillaries, also improved through NR administration. In mechanistic terms, the restoration of SIRT3 expression through NR was mediated by the induction of proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α). Moreover, NR restored SIRT3 activity, as shown by the reduction of the acetylation of optic atrophy 1 (OPA1) and superoxide dismutase 2 (SOD2), which resulted in improved mitochondrial morphology and protection against oxidative damage in mice born to mothers fed the LP diet. Our results provide evidence that it is feasible to prevent nephron mass shortage at birth through SIRT3 boosting during nephrogenesis, thus providing a therapeutic option to possibly limit the long-term sequelae of reduced nephron number in adulthood.

The multifaceted role of kidney tubule mitochondrial dysfunction in kidney disease development

More than 800 million people suffer from kidney disease. Genetic studies and follow-up animal models and cell biological experiments indicate the key role of proximal tubule metabolism. Kidneys have one of the highest mitochondrial densities. Mitochondrial biogenesis, mitochondrial fusion and fission, and mitochondrial recycling, such as mitophagy are critical for proper mitochondrial function. Mitochondrial dysfunction can lead to an energetic crisis, orchestrate different types of cell death (apoptosis, necroptosis, pyroptosis, and ferroptosis), and influence cellular calcium levels and redox status. Collectively, mitochondrial defects in renal tubules contribute to epithelial atrophy, inflammation, or cell death, orchestrating kidney disease development.

From AKI to CKD: Maladaptive Repair and the Underlying Mechanisms

Acute kidney injury (AKI) is defined as a pathological condition in which the glomerular filtration rate decreases rapidly over a short period of time, resulting in changes in the physiological function and tissue structure of the kidney. An increasing amount of evidence indicates that there is an inseparable relationship between acute kidney injury and chronic kidney disease (CKD). With the progress in research in this area, researchers have found that the recovery of AKI may also result in the occurrence of CKD due to its own maladaptation and other potential mechanisms, which involve endothelial cell injury, inflammatory reactions, progression to fibrosis and other pathways that promote the progress of the disease. Based on these findings, this review summarizes the occurrence and potential mechanisms of maladaptive repair in the progression of AKI to CKD and explores possible treatment strategies in this process so as to provide a reference for the inhibition of the progression of AKI to CKD.

Sirtuins as novel pharmacological targets in podocyte injury and related glomerular diseases

Podocyte injury is a major cause of proteinuria in kidney diseases, and persistent loss of podocytes leads to rapid irreversible progression of kidney disease. Sirtuins, a class of nicotinamide adenine dinucleotide-dependent deacetylases, can promote DNA repair, modify transcription factors, and regulate the cell cycle. Additionally, sirtuins play a critical role in renoprotection, particularly against podocyte injury. They also have pleiotropic protective effects on podocyte injury-related glomerular diseases, such as improving the immune inflammatory status and oxidative stress levels, maintaining mitochondrial homeostasis, enhancing autophagy, and regulating lipid metabolism. Sirtuins deficiency causes podocyte injury in different glomerular diseases. Studies using podocyte sirtuin-specific knockout and transgenic models corroborate this conclusion. Of note, sirtuin activators have protective effects in different podocyte injury-related glomerular diseases, including diabetic kidney disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, and lupus nephritis. These findings suggest that sirtuins are promising therapeutic targets for preventing podocyte injury. This review provides an overview of recent advances in the role of sirtuins in kidney diseases, especially their role in podocyte injury, and summarizes the possible rationale for sirtuins as targets for pharmacological intervention in podocyte injury-related glomerular diseases.

Activating SIRT3 in peritoneal mesothelial cells alleviates postsurgical peritoneal adhesion formation by decreasing oxidative stress and inhibiting the NLRP3 inflammasome

Peritoneal adhesions (PAs) are a serious complication of abdominal surgery and negatively affect the quality of life of millions of people worldwide. However, a clear molecular mechanism and a standard therapeutic strategy for PAs have not been established. Here, we developed a standardized method to mimic the pathological changes in PAs and found that sirtuin 3 (SIRT3) expression was severely decreased in adhesion tissues, which was consistent with our bioinformatics analysis and patient adhesion tissue analysis. Thus, we hypothesized that activating SIRT3 could alleviate postsurgical PAs. Sirt3-deficient (Sirt3^−/−) mice exhibited many more PAs after standardized abdominal surgery. Furthermore, compared with wild-type (Sirt3^+/+) mice, Sirt3-deficient (Sirt3^−/−) mice showed more prominent reactive oxygen species (ROS) accumulation, increased levels of inflammatory factors, and exacerbated mitochondrial damage and fragmentation. In addition, we observed NLRP3 inflammasome activation in the adhesion tissues of Sirt3^−/− but, not Sirt3^+/+ mice. Furthermore, mesothelial cells sorted from Sirt3^−/− mice exhibited impaired mitochondrial bioenergetics and redox homeostasis. Honokiol (HKL), a natural compound found in several species of the genus Magnolia, could activate SIRT3 in vitro. Then, we demonstrated that treatment with HKL could reduce oxidative stress and the levels of inflammatory factors and suppress NLRP3 activation in vivo, reducing the occurrence of postsurgical PAs. In vitro treatment with HKL also restored mitochondrial bioenergetics and promoted mesothelial cell viability under oxidative stress conditions. Taken together, our findings show that the rescue of SIRT3 by HKL may be a new therapeutic strategy to alleviate and block postsurgical PA formation.

Treatment with honokiol, a compound found in magnolia tree bark, significantly reduces formation of internal scar tissue after abdominal surgery in mice. Healing of incisions in the peritoneum, the connective tissue lining the abdomen, can result in scar tissue bonds known as peritoneal adhesions (PA), causing complications such as infertility or bowel obstructions. The mechanism of PA formation is unknown, and no therapies are available. Xuqi Li at The First Affiliated Hospital of Xi’an Jiaotong University, China, and co-workers found that PA tissues in both mice and human patients had decreased levels of SIRT3, a stress-response protein. Mice lacking SIRT3 showed increased inflammation and PA formation. When mice were treated with honokiol the day after surgery in order to boost SIRT3 levels, PA formation was significantly decreased. These results suggest a possible preventative treatment for post-surgical PAs.

Resveratrol Reestablishes Mitochondrial Quality Control in Myocardial Ischemia/Reperfusion Injury through Sirt1/Sirt3-Mfn2-Parkin-PGC-1α Pathway

Resveratrol is a natural polyphenol found in various plants. It has been widely studied on cardiovascular disorders. It is known that resveratrol can activate Sirtuin proteins and participate in cellular energy metabolism through a Sirtuin-dependent pathway. Here, we hypothesized that resveratrol may protect against myocardial ischemia/reperfusion injury (MIRI) through the target of Sirt1/Sirt3 on mitochondrial dynamics, cardiac autophagy, bioenergetics and oxidative damage in hypoxia/reoxygenation (H/R)-induced neonatal rat cardiomyocytes. We observed that resveratrol could activate the Sirt1/Sirt3-FoxO pathway on myocardial mitochondria in H/R cardiomyocytes. Subsequently, we found that resveratrol repaired the fission–fusion balance, autophagic flux and mitochondrial biosynthesis compared by H/R group. These changes were followed by increased functional mitochondrial number, mitochondrial bioenergetics and a better mitochondrial antioxidant enzyme system. Meanwhile, these effects were antagonized by co-treatment with Selisistat (Ex527), a Sirtuin inhibitor. Together, our findings uncover the potential contribution of resveratrol in reestablishing a mitochondrial quality control network with Parkin, Mfn2 and PGC-1α as the key nodes.

Melatonin attenuates di-(2-ethylhexyl) phthalate-induced apoptosis of human granulosa cells by inhibiting mitochondrial fission

Di-(2-ethylhexyl) phthalate (DEHP) is one of the most used plasticizers which have contaminated environment widely, and its extensive use causes female reproductive injury. Melatonin has a substantial protective effect against female reproductive toxicity. This study was undertaken to investigate the influence of melatonin on DEHP-induced damage of human granulosa cells (GCs) in vitro and explore the potential mechanisms. Here, we found that melatonin treatment alleviated DEHP-induced human GCs apoptosis and improved mitochondrial function via inhibiting dynamin-related protein 1 (Drp1) mediated mitochondrial fission. Melatonin inhibited the expression, activation and oligomerization of Drp1, which decreased translocation of Drp1 to mitochondria in DEHP-exposed human GCs. Inhibition of mitochondrial fission reduced intracellular reactive oxygen species (ROS) production, sustained mitochondrial membrane potential and decreased cytochrome c release. Further research showed that AMPK-PGC-1α signal pathway was involved in the inhibition of melatonin on Drp1 expression and activation. Melatonin treatment promoted AMPK activation suppressed by DEHP, and activated AMPK recovered the balance of Drp1 phosphorylation at Ser616 and Ser637 sites and enhanced PGC-1α expression. Moreover, PGC-1α could prevent mitochondrial fission by decreasing Drp1 expression directly via binding to its promoter. In contrast, blocking of AMPK or PGC-1α with specific inhibitor negated the protective effects of melatonin on mitochondrial homeostasis and GCs apoptosis. In summary, our results indicated the protective effects of melatonin on improving mitochondrial function and attenuating cells injury in DEHP-exposed human GCs. Melatonin treatment may be a promising therapeutic approach against DEHP-induced reproductive disorder.

β-Hydroxybutyrate against Cisplatin-Induced acute kidney injury via inhibiting NLRP3 inflammasome and oxidative stress

Cisplatin, as a commonly used anticancer drug, can easily lead to acute kidney injury (AKI), and has received more and more attention in clinical practice. β-hydroxybutyric acid (BHB) is a metabolite in the body and acts as an inhibitor of oxidative stress and NLRP3 inflammasome, reducing inflammatory responses and apoptosis. However, the role of BHB in cisplatin-induced AKI is currently not fully elucidated. In this study, C57BL/6 male mice were randomly divided into normal control group, cisplatin-induced AKI group and AKI with BHB treatment group. Compared to the control, cisplatin-treated mice exhibited high level of serum creatinine, blood urea nitrogen and severe tubular injury, which accompanied with significantly increased expression level of NLRP3, IL-1β, IL-18, BAX, cleaved-caspase 3, as well as aggravated oxidative stress and renal tubular cell apoptosis. However, these changes were significantly improved in that of BHB treatment. In vitro, our study showed that the expression of cleaved-caspase3, IL-1β and IL-18 were significantly increased in human proximal tubular epithelial cell line (HK-2) treated with cisplatin compared with the control group, while decreased in cells treated with BHB. Furthermore, a significantly increased expression of cGAS and STING in HK-2 cells treated with cisplatin were found, whereas notably decreased in cells treated with BHB. This data indicates that BHB protects against cisplatin-induced AKI and renal tubular damage mediated by NLRP3 inflammasome and cGAS-STING pathway.

Metabolic mechanisms of acute proximal tubular injury

Damage to the proximal tubule (PT) is the most frequent cause of acute kidney injury (AKI) in humans. Diagnostic and treatment options for AKI are currently limited, and a deeper understanding of pathogenic mechanisms at a cellular level is required to rectify this situation. Metabolism in the PT is complex and closely coupled to solute transport function. Recent studies have shown that major changes in PT metabolism occur during AKI and have highlighted some potential targets for intervention. However, translating these insights into effective new therapies still represents a substantial challenge. In this article, in addition to providing a brief overview of the current state of the field, we will highlight three emerging areas that we feel are worthy of greater attention. First, we will discuss the role of axial heterogeneity in cellular function along the PT in determining baseline susceptibility to different metabolic hits. Second, we will emphasize that elucidating insult specific pathogenic mechanisms will likely be critical in devising more personalized treatments for AKI. Finally, we will argue that uncovering links between tubular metabolism and whole-body homeostasis will identify new strategies to try to reduce the considerable morbidity and mortality associated with AKI. These concepts will be illustrated by examples of recent studies emanating from the authors' laboratories and performed under the auspices of the Swiss National Competence Center for Kidney Research (NCCR Kidney.ch).

The Effect of Polyphenols on Kidney Disease: Targeting Mitochondria

Mitochondrial function, including oxidative phosphorylation (OXPHOS), mitochondrial biogenesis, and mitochondria dynamics, are essential for the maintenance of renal health. Through modulation of mitochondrial function, the kidneys are able to sustain or recover acute kidney injury (AKI), chronic kidney disease (CKD), nephrotoxicity, nephropathy, and ischemia perfusion. Therapeutic improvement in mitochondrial function in the kidneys is related to the regulation of adenosine triphosphate (ATP) production, free radicals scavenging, decline in apoptosis, and inflammation. Dietary antioxidants, notably polyphenols present in fruits, vegetables, and plants, have attracted attention as effective dietary and pharmacological interventions. Considerable evidence shows that polyphenols protect against mitochondrial damage in different experimental models of kidney disease. Mechanistically, polyphenols regulate the mitochondrial redox status, apoptosis, and multiple intercellular signaling pathways. Therefore, this review attempts to focus on the role of polyphenols in the prevention or treatment of kidney disease and explore the molecular mechanisms associated with their pharmacological activity.

Tubular Mitochondrial Dysfunction, Oxidative Stress, and Progression of Chronic Kidney Disease

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected conditions, and CKD is projected to become the fifth leading global cause of death by 2040. New therapeutic approaches are needed. Mitochondrial dysfunction and oxidative stress have emerged as drivers of kidney injury in acute and chronic settings, promoting the AKI-to-CKD transition. In this work, we review the role of mitochondrial dysfunction and oxidative stress in AKI and CKD progression and discuss novel therapeutic approaches. Specifically, evidence for mitochondrial dysfunction in diverse models of AKI (nephrotoxicity, cytokine storm, and ischemia-reperfusion injury) and CKD (diabetic kidney disease, glomerulopathies) is discussed; the clinical implications of novel information on the key role of mitochondria-related transcriptional regulators peroxisome proliferator-activated receptor gamma coactivator 1-alpha, transcription factor EB (PGC-1α, TFEB), and carnitine palmitoyl-transferase 1A (CPT1A) in kidney disease are addressed; the current status of the clinical development of therapeutic approaches targeting mitochondria are updated; and barriers to the clinical development of mitochondria-targeted interventions are discussed, including the lack of clinical diagnostic tests that allow us to categorize the baseline renal mitochondrial dysfunction/mitochondrial oxidative stress and to monitor its response to therapeutic intervention. Finally, key milestones for further research are proposed.

Sirtuins: Research advances on the therapeutic role in acute kidney injury

BACKGROUND

Acute kidney injury (AKI), a common multidisciplinary diagnostic clinical critical illness, eventually causes end-stage renal disease (ESRD). Although many clinical measures have been taken to prevent or treat AKI, high morbidity and death rates were recorded. Therefore, in-depth pathogenesis study and search for new therapeutic targets are in demand. Interestingly, the suirtuins family showed a significant protective effect in AKI. Sirtuins (SIRT1-7) is a family of seven proteins with NAD⁺-dependent type III histone deacetylase activity. Sirtuins family members were involved by AKI, and regulation of sirtuins activities significantly improved AKI-induced renal injury. Therefore, the therapeutic role and molecular mechanisms of the sirtuins family in AKI has important research implications for clinical applications or basic research.

PURPOSE

This review summarizes recent advances in the roles and functions of the sirtuins family, discusses their therapeutic effects on AKI and related molecular mechanisms, and the mechanisms of action of small molecule specific activators or inhibitors sirtuins in the prevention and treatment of AKI were discussed.

METHODS

The data in this review were retrieved from various scientific databases (PubMed, Google scholar, Science Direct, and Web of Science), till December 2021. The keywords were used as follows: "Sirtuins", "Acute kidney injury", "AKI", "Sirtuins modulators" and "Histone deacetylation". The retrieved data followed PRISMA criteria (preferred reporting items for systematic review).

RESULTS

Growing evidence indicates that members of the sirtuins family regulate the development and progression of different renal diseases, including AKI, through anti-inflammation, antioxidation, anti-apoptotic, and maintenance of mitochondrial homeostasis. The molecular mechanism of Sirtuins family on AKI mainly regulated NF-κB, JNK/ERK, and AMPK/mTOR signaling pathways, upregulated the expression of PGC-1α, HO-1, NRF2, Bcl-2, OPA1, and AMPK, and downregulated the expression of NRLP3, IL-1β, TNF-α, IL-6, ROS, MFF, Drp1, Bax, ERK, and mTOR. In addition, the active ingredients of herbs (resveratrol, thujaplicins, huperzine, and curcumin) could activate the activity of SIRT1 or SIRT3, thereby improving AKI. Meanwhile, the synthetic Sirtuins inhibitor (AK-1) inhibited SIRT2 activity, thus alleviating AKI. In the future, more specific modulators will remain needed to enhance the clinical therapeutic role of the Sirtuins family in AKI.

CONCLUSION

The sirtuins family is a promising type III histone deacetylase for AKI treatment. This review will provide insight into sirtuins family's therapeutic role in AKI and promote the clinical use of sirtuins modulators in AKI.

Inhibition of polycomb repressive complex 2 by targeting EED protects against cisplatin-induced acute kidney injury

Polycomb repressive complex 2 (PRC2) is a multicomponent complex with methyltransferase activity that catalyzes trimethylation of histone H3 at lysine 27 (H3K27me3). Interaction of the epigenetic reader protein EED with EZH2, a catalytic unit of PRC, allosterically stimulates PRC2 activity. In this study, we investigated the role and underlying mechanism of the PRC2 in acute kidney injury (AKI) by using EED226, a highly selective PRC2 inhibitor, to target EED. Administration of EED226 improved renal function, attenuated renal pathological changes, and reduced renal tubular cell apoptosis in a murine model of cisplatin‐induced AKI. In cultured renal epithelial cells, treatment with either EED226 or EED siRNA also ameliorated cisplatin‐induced apoptosis. Mechanistically, EED226 treatment inhibited cisplatin‐induced phosphorylation of p53 and FOXO3a, two transcriptional factors contributing to apoptosis, and preserved expression of Sirtuin 3 and PGC1α, two proteins associated with mitochondrial protection in vivo and in vitro. EED226 was also effective in enhancing renal tubular cell proliferation, suppressing expression of multiple inflammatory cytokines, and reducing infiltration of macrophages to the injured kidney. These data suggest that inhibition of the PRC2 activity by targeting EED can protect against cisplatin‐induced AKI by promoting the survival and proliferation of renal tubular cells and inhibiting inflammatory response.

Correlation between coenzyme Q10 content and the nutrient sensors in AKI induced by Hemiscorpius lepturus envenomation

Introduction: Acute kidney injury (AKI) may have a negative effect on mitochondrial hemostasis and bioenergetics as well as coenzyme Q₁₀ (CoQ₁₀) content. PGC-1α, AMPK, sirtuin 1 (Sirt1), and Sirt3, as the key metabolic regulators under nutritional stress, stimulate energy production via mitochondrial biogenesis during AKI. However, no report is available on the relationship between CoQ₁₀ level and nutrient sensors in the pathophysiology of AKI caused by Hemiscorpius lepturus scorpion envenomation. Methods: Three doses of venoms (1, 5, and 10 mg/kg) were administered by subcutaneous (SC) injection to male albino mice. The animals were sacrificed 1 day or 7 days after administration of venom and their kidneys were collected to analyze gene expression involved in AKI, nutrient sensors, and apoptosis signaling activation by real-time polymerase chain reaction (PCR) and the measurement of CoQ₁₀ level using the High-performance liquid chromatography (HPLC) method. Results: The data indicated a significant decrease in CoQ₁₀ level after the administration of venom in 5 and 10 mg/kg. In addition, 1 day after the treatment, a significant over-expression of Sirt1 (5 and 10 mg/kg) was observed compared with normal mice. Overexpression of Sirt3 occurred 1 day and 7 days after treatment only at the dose of 5.0 mg/kg of venom. Furthermore, over-expression of AMPK as an important mitochondrial energetic sensor happened 1 day and 7 days after the injection of venom (5 mg/kg) (P < 0.01). The significant increase in the gene expression of caspase-9 and 3 after the injection of venom (5 and 10 mg/kg) confirmed the role of cell death signaling. Conclusion: The venom-induced energy-sensing pathways have a key role in gene expression of PGC-1α, AMPK, Sirt3, and CoQ₁₀ content after venom-induced AKI.

Protective Effects of Liquiritigenin against Cisplatin-Induced Nephrotoxicity via NRF2/SIRT3-Mediated Improvement of Mitochondrial Function

Acute kidney injury (AKI) induced by cisplatin (CP), a first-line anticancer drug for chemotherapy, is common. To date, there is an urgent need to find effective treatments to reduce the nephrotoxicity caused by CP. Meanwhile, the restoration of mitochondrial dysfunction shows potential to be used as an adjunct to conventional therapeutic strategies. This study found that liquiritigenin can ameliorate mitochondrial dysfunction and acute kidney injury induced by CP in mice. The intraperitoneal injection of 15 mg/kg body weight liquiritigenin for 2 days markedly protected against CP-induced mitochondrial dysfunction, restored renal tubule and mitochondrial morphology, decreased blood Scr and BUN levels, and decreased cell apoptosis. Furthermore, the elevated expression of SIRT3 induced by liquiritigenin, which can be upregulated by NRF2, was confirmed in vivo and in vitro. The underlying protective mechanisms of liquiritigenin in CP-induced nephrotoxicity were then investigated. Molecular docking results showed that liquiritigenin has potent binding activities to KEAP1, GSK-3β and HRD1. Further results showed that liquiritigenin induced the nuclear translocation of NRF2 and increased the levels of mitochondrial bioenergetics-related protein such as PGC-1α, and TFAM, which are related to NRF2 activity and mitochondrial biogenesis. In addition, liquiritigenin was found to possibly reverse the decrease in BCL2/BAX ratio induced by CP in live cultured renal tubule epithelial cells. Collectively, these results indicated that liquiritigenin could be used as a potential nephroprotective agent to protect against cisplatin-induced acute kidney injury in a NRF2-dependent manner by improving mitochondria function.

Matrine alleviates cisplatin-induced acute kidney injury by inhibiting mitochondrial dysfunction and inflammation via SIRT3/OPA1 pathway

Cisplatin is extensively used to treat malignancies. However, its clinical use is always limited due to the serious side effects, especially the nephrotoxicity. Matrine (MAT), a tetracyclic quinolizine alkaloid found in sophora genus, exerts multiple pharmacological roles, including anti-oxidative stress, anti-inflammation and anti-apoptosis, but the role of MAT on acute kidney injury (AKI) has not been evaluated. Here, we found that MAT potently inhibited cell injury induced by cisplatin in HK2 cells in vitro, which was associated with the inhibition of oxidative injury and NF-κB-mediated inflammation. Moreover, MAT treatment could activate the SIRT3/OPA1 axis and subsequently suppress the mitochondrial fragmentation and improve mitochondrial function. More importantly, SIRT3 knockdown suppressed the deacetylation of OPA1, which blocked the protective role of MAT on cisplatin-induced cell injury. In vivo, MAT treatment alleviated renal dysfunction, histological damage and inflammation induced by cisplatin in mice. Furthermore, consistent with the founding in vitro, MAT also activated SIRT3-mediated deacetylation of OPA1 and alleviated mitochondrial dysfunction in AKI mice. Our study proved that MAT protected against cisplatin-induced AKI by synergic anti-oxidative stress and anti-inflammation actions via SIRT3/OPA1-mediated improvement of mitochondrial function, suggesting that MAT may be a novel and effective strategy for AKI.

Transition of acute kidney injury to chronic kidney disease: role of metabolic reprogramming

Acute kidney injury (AKI) is a global public health concern associated with high morbidity and mortality. Although advances in medical management have improved the in-hospital mortality of severe AKI patients, the renal prognosis for AKI patients in the later period is not encouraging. Recent epidemiological investigations have indicated that AKI significantly increases the risk for the development of chronic kidney disease (CKD) and end-stage renal disease (ESRD) in the future, further contributing to the economic burden on health care systems. The transition of AKI to CKD is complex and often involves multiple mechanisms. Recent studies have suggested that renal tubular epithelial cells (TECs) are more prone to metabolic reprogramming during AKI, in which the metabolic process in the TECs shifts from fatty acid β-oxidation (FAO) to glycolysis due to hypoxia, mitochondrial dysfunction, and disordered nutrient-sensing pathways. This change is a double-edged role. On the one hand, enhanced glycolysis acts as a compensation pathway for ATP production; on the other hand, long-term shut down of FAO and enhanced glycolysis lead to inflammation, lipid accumulation, and fibrosis, contributing to the transition of AKI to CKD. This review discusses developments and therapies focused on the metabolic reprogramming of TECs during AKI, and the emerging questions in this evolving field.

Several Alkaloids in Chinese Herbal Medicine Exert Protection in Acute Kidney Injury: Focus on Mechanism and Target Analysis

Objectives

Acute kidney injury (AKI) is a loose set of kidney diseases accompanied by a variety of syndromes, which is a serious threat to human life and health. Some alkaloids are derived from various Chinese herbs have been widely concerned in the improvement of AKI. This review provides the research progress of alkaloids in AKI experimental models and discusses the related molecular mechanisms. Key Findings. Alkaloids can protect AKI through various mechanisms including antioxidant stress, improvement of mitochondrial damage, reduction of cell death, induction of autophagy, and inhibition of inflammation. These mechanisms are mainly related to the activation of Nrf2/HO-1 signaling pathway, inhibition of ferroptosis and apoptosis, regulation of PINK1/Parkin pathway, inhibition of TLR4/NF-κB pathway and NLRP3 inflammatory bodies, upregulation of Klotho protein level and so on. In addition, there are a few alkaloids that have certain toxicity on the kidney.

Conclusion

Alkaloids have been shown to significantly improve AKI, but only in pharmacological studies. This paper summarizes the main experimental models currently used in AKI research and describes some representative alkaloids based on recent research. Their potential roles in the prevention and treatment of AKI through different mechanisms are highlighted.

Shen Shuai Ⅱ Recipe attenuates renal fibrosis in chronic kidney disease by improving hypoxia-induced the imbalance of mitochondrial dynamics via PGC-1α activation

BACKGROUND

Shen Shuai Ⅱ Recipe (SSR) is an effective Chinese herbal formula for the treatment of patients with chronic kidney disease (CKD) in the clinic and significantly improves 5/6 ablation and infarction (A/I) surgery-induced renal interstitial fibrosis (RIF) and intrarenal hypoxia in rats. However, the underlying molecular mechanisms need further elucidation.

PURPOSE

This study aims to investigate the renoprotective mechanisms of SSR in vivo and in vitro.

METHODS

CKD model was induced in rats with 5/6 (A/I) surgery. 4 weeks later, rats were treated with vehicle or SSR or Fenofibrate by daily gavage. In vitro, HK2 cells exposed to hypoxia (1% O2) were treated with SSR in the presence or absence of 100 μM MitoTEMPO or 10 μM Mitochondrial Fusion Promoter M1. The effects of SSR on RIF, mitochondrial dynamics, oxidative metabolism, and mitochondrial ROS (mtROS) were determined by immunoblotting, colorimetric, and fluorometric assays according to the experimental protocols. Furthermore, to explore the mechanisms of SSR against RIF, HK2 cells of PGC-1α or MFN2 knockdown under hypoxic stimulation were treated with 400 μg/ml of SSR and (or) 1 μM of ZLN005.

RESULTS

The results showed that treatment with SSR significantly improved mitochondrial morphology and function, up-regulated the expression of PGC-1α protein, and inhibited the production of mtROS in 5/6 (A/I) kidneys and hypoxia-treated HK2 cells, which may be closely correlated with its anti-RIF effect. In addition, compared to wild-type HK2 cells, the roles of SSR in improving mitochondrial dynamics and energy metabolism were greatly diminished in HK2 cells of PGC-1α knockdown under hypoxic exposure. More importantly, compared to ZLN005 or SSR combined with ZLN005 treatment, MFN2-deficient HK2 cells exhibited the increased protein levels of FN, α-SMA, TGF-β1 and cleaved IL-1β in response to hypoxic stimulation.

CONCLUSION

SSR exerted the renoprotective effects by improving mitochondrial dynamics under hypoxic condition via PGC-1α activation.

Honokiol ameliorates cisplatin-induced acute kidney injury via inhibition of mitochondrial fission

BACKGROUND AND PURPOSE

Mitochondrial damage and oxidative stress are the crucial contributors to the tubular cell injury and death in acute kidney injury (AKI). Novel therapeutic strategies targeting mitochondria protection and halting the progression of AKI are urgently needed. Honokiol (HKL) is a small-molecule polyphenol that exhibits extraordinary cytoprotective effects, such as anti-inflammatory and anti-oxidative properties. Thus, we wonder whether HKL could ameliorate cisplatin-induced AKI via preventing mitochondrial dysfunction.

EXPERIMENTAL APPROACH

AKI was induced by cisplatin administration. Biochemical and histological analysis were applied to determine kidney injury. The effect of HKL on mitochondrial function and morphology were evaluated by immunohistochemistry, transmission electron microscopy, immunoblot and immunofluorescence. To investigate the mechanism of HKL in mitochondrial dynamics remodeling and resistance to apoptosis, we did transfection experiments, immunoblot, immunoprecipitation and flow cytometry assay.

KEY RESULTS

We demonstrated that the prominent mitochondrial fragmentation occurred in experimental models of cisplatin-induced nephrotoxicity, which was coupled with radical oxygen species (ROS) overproduction, deterioration of mitochondrial function, release of apoptogenic factors, and consequent apoptosis. HKL treatment exhibited notable renoprotection and attenuated these perturbations. Mechanically, we show that HKL treatment recovered the expression of SIRT3 and improved AMPK activity in tubular cells exposure to cisplatin, which preserved the Drp1 phosphorylation at Ser637 and blocked its translocation to mitochondria, consequently preventing mitochondrial fragmentation and subsequent cell injury and death.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that HKL may protect against cisplatin-induced AKI by preserving mitochondrial integrity and fitness through a mechanism of SIRT3/AMPK-dependent mitochondrial dynamics remodeling.

Cardiovascular Inflammaging: Mechanisms and Translational Aspects

Aging is one of the major non-reversible risk factors for several chronic diseases, including cancer, type 2 diabetes, dementia, and cardiovascular diseases (CVD), and it is a key cause of multimorbidity, disability, and frailty (decreased physical activity, fatigue, and weight loss). The underlying cellular mechanisms are complex and consist of multifactorial processes, such as telomere shortening, chronic low-grade inflammation, oxidative stress, mitochondrial dysfunction, accumulation of senescent cells, and reduced autophagy. In this review, we focused on the molecular mechanisms and translational aspects of cardiovascular aging-related inflammation, i.e., inflammaging.

Chicoric Acid Attenuated Renal Tubular Injury in HFD-Induced Chronic Kidney Disease Mice through the Promotion of Mitophagy via the Nrf2/PINK/Parkin Pathway

As the main factor in the pathogenesis of chronic kidney disease (CKD), the excessive apoptosis of renal tubular epithelial cells (RTECs) and its underlying mechanism of action are worth further investigation. Chicoric acid (CA), a major active constituent of the Uyghur folk medicine chicory, was recorded to possess a renal protective effect. The precise effect of CA on renal tubular injury in obesity-related CKD remains unknown. In the current study, CA was proven to ameliorate metabolic disorders including overweight, hyperglycemia, hyperlipidemia, and hyperuricemia in high fat diet (HFD)-fed mice. Furthermore, the reverse effect of CA on renal histological changes and functional damage was confirmed. In vitro, the alleviation of lipid accumulation and cell apoptosis was observed in palmitic acid (PA)-exposed HK2 cells. Treatment with CA reduced mitochondrial damage and oxidative stress in the renal tubule of HFD-fed mice and PA-treated HK2 cells. Finally, CA was observed to activate the Nrf2 pathway; increase PINK and Parkin expression; and regulate LC3, SQSTM1, Mfn2, and FIS1 expression; therefore, it would improve mitochondrial dynamics and mitophagy to alleviate mitochondrial damage in RTECs of obesity-related CKD. These results may provide fresh insights into the promotion of mitophagy in the prevention and alleviation of obesity-related CKD.

Sirtuin 7 Deficiency Reduces Inflammation and Tubular Damage Induced by an Episode of Acute Kidney Injury

Acute kidney injury (AKI) is a public health problem worldwide. Sirtuins are a family of seven NAD+-dependent deacylases, Overexpression of Sirtuin 1, 3, and 5 protect against AKI. However, the role of Sirtuin 7 (Sirt7) in AKI is not known. Here, we analyzed how Sirt7 deficient mice (KO-Sirt7) were affected by AKI. As expected, wild-type and Sirt7 heterozygotes mice that underwent renal ischemia/reperfusion (IR) exhibited the characteristic hallmarks of AKI: renal dysfunction, tubular damage, albuminuria, increased oxidative stress, and renal inflammation. In contrast, the KO-Sirt7+IR mice were protected from AKI, exhibiting lesser albuminuria and reduction in urinary biomarkers of tubular damage, despite similar renal dysfunction. The renoprotection in the Sirt7-KO+IR group was associated with reduced kidney weight, minor expression of inflammatory cytokines and less renal infiltration of inflammatory cells. This anti-inflammatory effect was related to diminished p65 expression and in its active phosphorylation, as well as by a reduction in p65 nuclear translocation. Sirt7 deficient mice are protected from AKI, suggesting that this histone deacetylase promotes tubular damage and renal inflammation. Therefore, our findings indicate that Sirt7 inhibitors may be an attractive therapeutic target to reduce NFκB signaling.

Sirtuin 3: Emerging therapeutic target for cardiovascular diseases

Acetylation is one of the most important methods of modification that lead to a change in the function of proteins. In humans, metabolic enzymes commonly undergo acetylation, which regulates the activities of metabolic enzymes and metabolic pathways. Sirtuin 3 (SIRT3) is a prominent deacetylase that participates in mitochondrial metabolism, redox balance, and mitochondrial dynamics by regulating mitochondrial protein acetylation, thereby protecting mitochondria from damage. Normal mitochondrial function is essential for maintaining the metabolism and function of the heart. Therefore, mitochondrial dysfunction caused by SIRT3 consumption and defects leads to the development of a variety of cardiovascular diseases. A comprehensive understanding of the role of SIRT3 in cardiovascular disease is critical for developing new therapeutic strategies. Herein, we summarize the function of SIRT3 in mitochondria, the complex mechanisms mediating cardiovascular diseases, and the potential value of SIRT3 small-molecule agonists in future clinical treatments.

p53 in Proximal Tubules Mediates Chronic Kidney Problems after Cisplatin Treatment

Nephrotoxicity is a major side-effect of cisplatin in chemotherapy, which can occur acutely or progress into chronic kidney disease (CKD). The protein p53 plays an important role in acute kidney injury induced by cisplatin, but its involvement in CKD following cisplatin exposure is unclear. Here, we address this question by using experimental models of repeated low-dose cisplatin (RLDC) treatment. In mouse proximal tubular BUMPT cells, RLDC treatment induced p53 activation, apoptosis, and fibrotic changes, which were suppressed by pifithrin-α, a pharmacologic inhibitor of p53. In vivo, chronic kidney problems following RLDC treatment were ameliorated in proximal tubule-specific p53-knockout mice (PT-p53-KO mice). Compared with wild-type littermates, PT-p53-KO mice showed less renal damage (KIM-1 positive area: 0.97% vs. 2.5%), less tubular degeneration (LTL positive area: 15.97% vs. 10.54%), and increased proliferation (Ki67 positive area: 2.42% vs. 0.45%), resulting in better renal function after RLDC treatment. Together, these results indicate that p53 in proximal tubular cells contributes significantly to the development of chronic kidney problems following cisplatin chemotherapy.

SIRT3 deficiency exacerbates early-stage fibrosis after ischaemia-reperfusion-induced AKI

BACKGROUND

Sirtuin 3 (SIRT3) is a crucial regulator of mitochondrial function and is associated with injury and repair in acute kidney injury (AKI). To investigate whether mitochondrial damage and early renal fibrosis are associated with decreased renal SIRT3 levels, we established an in vivo model.

METHODS

In vivo, we established ischaemia-reperfusion-induced AKI (IR-AKI) models in wild-type (WT) and SIRT3-knockout (SIRT3-KO) mice. Serum creatinine (Scr) and blood urea nitrogen (BUN) were measured by an automatic biochemical analyser, and renal pathological changes were examined by haematoxylin and eosin (HE) staining. Renal fibrosis in mice was assessed by Masson's trichrome staining. The expression of SIRT3, renal fibrosis-related markers (FN and α-SMA), and mitochondrial markers (DRP1, FIS1, OPA1, and MFN1) was measured by Western blotting. Morphological changes in mitochondria in renal tubular epithelial cells were analysed by transmission electron microscopy (TEM).

RESULTS

The levels of Scr and BUN were elevated with severe renal pathological damage in the IR-AKI model, especially in SIRT3-KO mice. In the IR-AKI model, the obvious increases in FN and α-SMA protein levels suggested that there was severe fibrosis in the kidney tissue, OPA1 and MFN1 protein levels were reduced while DRP1 and FIS1 protein levels were greatly increased. TEM photomicrographs showed that mitochondrial fragmentation was increased in the renal tubular epithelial cells of mice with IR injury. SIRT3-KO mice exhibited exacerbated changes.

CONCLUSION

Our findings indicate that SIRT3 plays a significant role in early-stage fibrosis after IR-AKI by regulating mitochondrial dynamics and that SIRT3 deficiency exacerbates renal dysfunction and renal fibrosis.

NAD+ ameliorates endotoxin-induced acute kidney injury in a sirtuin1-dependent manner via GSK-3β/Nrf2 signalling pathway

Acute kidney injury (AKI) is a substantial worldwide public health concern with no specific and effective therapies in clinic. NAD⁺ is a pivotal determinant of cellular energy metabolism involved in the progression of AKI; however, its mechanism in kidney injury remains poorly understood. Sirtuin 1 (SIRT1) is an NAD⁺‐dependent deacetylase associated with renal protection and acute stress resistance. In this study, we have investigated the role of NAD⁺ in AKI and the potential mechanism(s) involved in its renoprotective effect. NAD⁺ was notably decreased and negatively correlated with kidney dysfunction in AKI, restoring NAD⁺ with NMN significantly ameliorates LPS‐induced oxidative stress and apoptosis and attenuates renal damage. We also found that the protection of NAD⁺ is associated with SIRT1 expressions and performs in a SIRT1‐dependent manner. Inhibition of SIRT1 blunted the protective effect of NAD⁺ and up‐regulated the activity of glycogen synthase kinase‐3β (GSK‐3β) that was concomitant with mitigated Nrf2 nuclear accumulation, thereby exacerbates AKI. These findings suggest that NAD⁺/SIRT1/GSK‐3β/Nrf2 axis is an important mechanism that can protect against AKI which might be a potential therapeutic target for the treatment of AKI.

Mitochondrial Pathophysiology on Chronic Kidney Disease

In healthy kidneys, interstitial fibroblasts are responsible for the maintenance of renal architecture. Progressive interstitial fibrosis is thought to be a common pathway for chronic kidney diseases (CKD). Diabetes is one of the boosters of CKD. There is no effective treatment to improve kidney function in CKD patients. The kidney is a highly demanding organ, rich in redox reactions occurring in mitochondria, making it particularly vulnerable to oxidative stress (OS). A dysregulation in OS leads to an impairment of the Electron transport chain (ETC). Gene deficiencies in the ETC are closely related to the development of kidney disease, providing evidence that mitochondria integrity is a key player in the early detection of CKD. The development of novel CKD therapies is needed since current methods of treatment are ineffective. Antioxidant targeted therapies and metabolic approaches revealed promising results to delay the progression of some markers associated with kidney disease. Herein, we discuss the role and possible origin of fibroblasts and the possible potentiators of CKD. We will focus on the important features of mitochondria in renal cell function and discuss their role in kidney disease progression. We also discuss the potential of antioxidants and pharmacologic agents to delay kidney disease progression.

DsbA-L interacts with VDAC1 in mitochondrion-mediated tubular cell apoptosis and contributes to the progression of acute kidney disease

BACKGROUND

we demonstrated that disulfide-bond A oxidoreductase-like protein (DsbA-L) was involved in the progression of renal fibrosis. However, the precise function of DsbA-L in acute kidney injury (AKI), and the mechanisms involved, have yet to be elucidated.

METHODS

We illustrate the DsbA-L interacted with VDAC1 by co-IP (co-immunoprecipitation) in vitro and vivo, and found the interaction parts of them by mutation experiment. The above findings were verified by co-localization of them. In addition, we constructed the two model of PT-DsbA-L and VDAC1 KO mice to verify the function of DsbA-L and VDAC1 in models of VAN, CLP and I/R-induced AKI.

FINDINGS

The PT-DsbA-L-KO mice showed amelioration of I/R, VAN-, and CLP-induced AKI progression via the downregulation of VDAC1. Finally, we confirmed these changes in signal molecules by examining in HK-2 cells and kidney biopsies taken from patients with ischemic or acute interstitial nephritis (AIN)-induced AKI. Mechanistically, DsbA-L interacted with amino acids 9-13 and 22-27 of VDAC1 in the mitochondria of BUMPT cells to induce renal cell apoptosis and mitochondrial injury.

INTERPRETATION

This work suggested that DsbA-L, located in the proximal tubular cells, drives the progression of AKI, by directly upregulating the levels of VDAC1.Running Title: The role of DsbA-L in AKI FUNDING: National Natural Science Foundation of China, a grant from Key Project of Hunan provincial science and technology innovation, Department of Science and Technology of Hunan Province project of International Cooperation and Exchanges, Changsha Science and Technology Bureau project, Natural Science Foundation of Hunan Province, Fundamental Research Funds for the Central Universities of Central South University, Hunan Provincial Innovation Foundation For Postgraduate China Hunan Provincial Science and Technology Department.

Tolvaptan Improves Contrast-Induced Acute Kidney Injury

OBJECTIVE

Contrast-induced acute kidney injury (CI-AKI) is a serious side effect of contrast media use. The purpose of this study was to investigate the role and mechanism of tolvaptan (TOL) in CI-AKI.

METHODS

24 Wistar male rats were randomly divided into 4 groups (n = 6). And a rat model of CI-AKI was established. Then, the blood and urine of rats in each group were collected to detect relevant parameters. HE staining was utilized for the observation of the pathological changes of rat kidney tissues, TUNEL assay for the detection of tubular cell apoptosis, biochemical detection for the confirmation of oxidative stress level in kidney tissues, and western blot for the test of the expression of apoptotic proteins and the Nrf2 signaling pathway-related proteins in kidney tissues.

RESULTS

TOL could significantly reduce the serum level of urea nitrogen, creatinine, and neutrophil gelatinase-associated lipocalin and decrease serum Cys-C and urine KIM-1 in CI-AKI rats. The result above meant that TOL could improve kidney injury and reduce tubular cell apoptosis in CI-AKI rats. In addition, TOL contributed to a reduction of oxidative stress level by downregulating myeloperoxidase level and increasing the activities of superoxide dismutase and glutathione peroxidase in the kidney tissue of CI-AKI rats. After the pretreatment of TOL, the expression of proapoptotic proteins cleaved-caspase 3 and BAX, as well as mitochondrial fusion proteins DRP1 and MFN2 was downregulated, while the expression of Bcl-2 and PINK1 was upregulated in the kidney tissue of CI-AKI rats. Further, TOL could activate the Nrf2 signaling pathway, and the Nrf2 inhibitor ML385 reversed the effect of TOL on CI-AKI.

CONCLUSION

TOL can improve CI-AKI by activating the Nrf2/HO-1 signaling pathway, inhibiting oxidative stress response, and reducing tubular cell apoptosis.

The Effect of PGC-1alpha-SIRT3 Pathway Activation on Pseudomonas aeruginosa Infection

The innate immune response to P. aeruginosa pulmonary infections relies on a network of pattern recognition receptors, including intracellular inflammasome complexes, which can recognize both pathogen- and host-derived signals and subsequently promote downstream inflammatory signaling. Current evidence suggests that the inflammasome does not contribute to bacterial clearance and, in fact, that dysregulated inflammasome activation is harmful in acute and chronic P. aeruginosa lung infection. Given the role of mitochondrial damage signals in recruiting inflammasome signaling, we investigated whether mitochondrial-targeted therapies could attenuate inflammasome signaling in response to P. aeruginosa and decrease pathogenicity of infection. In particular, we investigated the small molecule, ZLN005, which transcriptionally activates peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, antioxidant defense, and cellular respiration. We demonstrate that P. aeruginosa infection promotes the expression of inflammasome components and attenuates several components of mitochondrial repair pathways in vitro in lung epithelial cells and in vivo in an acute pneumonia model. ZLN005 activates PGC-1α and its downstream effector, Sirtuin 3 (SIRT3), a mitochondrial-localized deacetylase important for cellular metabolic processes and for reactive oxygen species homeostasis. ZLN005 also attenuates inflammasome signaling induced by P. aeruginosa in bronchial epithelial cells and this action is dependent on ZLN005 activation of SIRT3. ZLN005 treatment reduces epithelial-barrier dysfunction caused by P. aeruginosa and decreases pathogenicity in an in vivo pneumonia model. Therapies that activate the PGC-1α—SIRT3 axis may provide a complementary approach in the treatment of P. aeruginosa infection.

Overexpression of NMNAT3 improves mitochondrial function and enhances anti-oxidative stress of bone marrow mesenchymal stem cells via the NAD+-Sirt3 pathway

Oxidative stress damage is a common problem in bone marrow mesenchymal stem cell (BMSC) transplantation. Under stress conditions, the mitochondrial function of BMSCs is disrupted, which accelerates senescence and apoptosis of BMSCs, ultimately leading to poor efficacy. Therefore, improving mitochondrial function and enhancing the anti-oxidative stress capacity of BMSCs may be an effective way of improving the survival rate and curative effect of BMSCs. In this study, we have confirmed that overexpression of nicotinamide mononucleotide adenylyl transferase 3 (NMNAT3) improves mitochondrial function and resistance to stress-induced apoptosis in BMSCs. We further revealed the mechanism of NMNAT3-mediated resistance to stress-induced apoptosis in BMSCs. We increased the level of nicotinamide adenine dinucleotide (NAD+) by overexpressing NMNAT3 in BMSCs and found that it could significantly increase the activity of silent mating type information regulation 2 homolog 3 (Sirt3) and significantly decrease the acetylation levels of Sirt3-dependent deacetylation-related proteins isocitrate dehydrogenase 2 (Idh2) and Forkhead-box protein O3a (FOXO3a). These findings show that NMNAT3 may increase the activity of Sirt3 by increasing NAD+ levels. Our results confirm that the NMNAT3-NAD+-Sirt3 axis is a potential mechanism for improving mitochondrial function and enhancing anti-oxidative stress of BMSCs. In this study, we take advantage of the role of NMNAT3 in inhibiting stress-induced apoptosis of BMSCs and provide new methods and ideas for breaking through the bottleneck of transplantation efficacy of BMSCs in the clinic.

Kidney-Targeted Redox Scavenger Therapy Prevents Cisplatin-Induced Acute Kidney Injury

Cisplatin-induced acute kidney injury (CI-AKI) is a significant co-morbidity of chemotherapeutic regimens. While this condition is associated with substantially lower survival and increased economic burden, there is no pharmacological agent to effectively treat CI-AKI. The disease is hallmarked by acute tubular necrosis of the proximal tubular epithelial cells primarily due to increased oxidative stress. We investigated a drug delivery strategy to improve the pharmacokinetics of an approved therapy that does not normally demonstrate appreciable efficacy in CI-AKI, as a preventive intervention. In prior work, we developed a kidney-selective mesoscale nanoparticle (MNP) that targets the renal proximal tubular epithelium. Here, we found that the nanoparticles target the kidneys in a mouse model of CI-AKI with significant damage. We evaluated MNPs loaded with the reactive oxygen species scavenger edaravone, currently used to treat stroke and ALS. We found a marked and significant therapeutic benefit with edaravone-loaded MNPs, including improved renal function, which we demonstrated was likely due to a decrease in tubular epithelial cell damage and death imparted by the specific delivery of edaravone. The results suggest that renal-selective edaravone delivery holds potential for the prevention of acute kidney injury among patients undergoing cisplatin-based chemotherapy.

A comprehensive insight into autophagy and its potential signaling pathways as a therapeutic target in podocyte injury

As part of the glomerular filtration membrane, podocyte is terminally differentiated, structurally unique, and highly specialized in maintaining kidney function. Proteinuria caused by podocyte injury (foot process effacement) is the clinical symptom of various kidney diseases (CKD), including nephrotic syndrome. Podocyte autophagy has become a powerful therapeutic strategy target in ameliorating podocyte injury. Autophagy is known to be associated significantly with sirtuin-1, proteinuria, and podocyte injury. Various key findings in podocyte autophagy were reported in the past ten years, such as the role of endoplasmic reticulum (ER) stress in podocyte autophagy impairment, podocyte autophagy-related gene, essential roles of the signaling pathways: Mammalian Target of Rapamycin (mTOR)/ Phosphoinositide 3-kinase (PI3k)/ serine/threonine kinase 1 (Akt) in podocyte autophagy. These significant factors caused podocyte injury associated with autophagy impairment. Sirtuin-1 was reported to have a vital key role in mTOR signaling, 5'AMP-activated protein kinase (AMPK) regulation, autophagy activation, and various critical pathways associated with podocyte's function and health; it has potential value to podocyte injury pathogenesis investigation. From these findings, podocyte autophagy has become an attractive therapeutic strategy to ameliorate podocyte injury, and this review will provide an in-depth review on therapeutic targets he podocyte autophagy.

The tryptophan pathway and nicotinamide supplementation in ischaemic acute kidney injury

Background

Down-regulation of the enzymes involved in tryptophan-derived nicotinamide (NAM) adenine dinucleotide (NAD⁺) production was identified after acute kidney injury (AKI), leading to the hypothesis that supplementation with NAM may increase the kidney NAD⁺ content, rescuing tryptophan pathways and subsequently improving kidney outcomes.

Methods

Urinary measurement of tryptophan and kynurenin using liquid chromatography–mass spectrometry metabolomics was used in a cohort of 167 cardiac bypass surgery patients along with tests for correlation to the development of postoperative AKI. A mouse model of ischaemic AKI using ischaemia–reperfusion injury (bilateral clamping of renal arteries for 25 min) was also used.

Results

We identified a significant decrease in urinary tryptophan and kynurenin in patients developing AKI, irrespective of the Kidney Disease: Improving Global Outcomes (KDIGO) stage. Although a significant difference was observed, tryptophan and kynurenin moderately discriminated for the development of all AKI KDIGO stages {area under the curve [AUC] 0.82 [95% confidence interval (CI) 0.75–0.88] and 0.75 [0.68–0.83], respectively} and severe KDIGO Stages 2–3 AKI [AUC 0.71 (95% CI 0.6–0.81) and 0.66 (0.55–0.77), respectively]. Sparked by this confirmation in humans, we aimed to confirm the potential preventive effect of NAM supplementation in wild-type male and female C57BL/6 mice subjected to ischaemic AKI. NAM supplementation had no effect on renal function (blood urea nitrogen at Day 1, sinistrin–fluorescein isothiocyanate glomerular filtration rate), architecture (periodic acid–Schiff staining) and injury or inflammation (kidney injury molecule 1 and IL18 messenger RNA expression). In addition, NAM supplementation did not increase post-AKI NAD⁺ kidney content.

Conclusion

Notwithstanding the potential role of NAM supplementation in the setting of basal NAD⁺ deficiency, our findings in mice and the reanalysis of published data do not confirm that NAM supplementation can actually improve renal outcomes after ischaemic AKI in unselected animals and probably patients.

Jian-Pi-Yi-Shen Formula Alleviates Chronic Kidney Disease in Two Rat Models by Modulating QPRT/NAD+/SIRT3/Mitochondrial Dynamics Pathway

Objective

Jian-Pi-Yi-Shen formula (JPYSF) is a traditional Chinese herbal decoction and has been used for treating chronic kidney disease (CKD) in clinics for decades. However, the potential mechanisms have not been fully elucidated. This study was designed to test the efficacy of JPYSF in treating CKD and explore the underlying mechanism.

Methods

Two CKD rat models were established by 5/6 nephrectomy (5/6 Nx) and feeding with adenine-containing feed, respectively. The intervention dose of JPYSF was 10.89 g/kg/d by gastric irrigation. Renal function was assessed by serum creatinine (Scr) and blood urea nitrogen (BUN). Periodic acid-Schiff (PAS) and Masson's trichrome staining were used to evaluate renal histopathological changes. The levels of nicotinamide adenine dinucleotide (NAD⁺) were measured by using the enzyme-linked immunosorbent assay kit. The proteins expressions of renal fibrosis, quinolinate phosphoribosyltransferase (QPRT), sirtuin 3 (SIRT3), and mitochondrial dynamics were determined and quantified by Western blot analysis.

Results

The results show that administration of JPYSF significantly lowered Scr and BUN levels, improved renal tubular atrophy and interstitial fibrosis, and decreased renal extracellular matrix deposition in two CKD rat models. In addition, CKD rats exhibited suppressed QPRT/NAD⁺/SIRT3 signal, increased mitochondrial fission, and decreased mitochondrial fusion. JPYSF treatment promoted QPRT/NAD⁺/SIRT3 signal and restored mitochondrial fission/fusion balance.

Conclusion

In conclusion, administration of JPYSF effectively alleviated CKD progression in two rat models, which may be related with regulation of the QPRT/NAD⁺/SIRT3/mitochondrial dynamics pathway.

Post-translational modifications by SIRT3 de-2-hydroxyisobutyrylase activity regulate glycolysis and enable nephrogenesis

Abnormal kidney development leads to lower nephron number, predisposing to renal diseases in adulthood. In embryonic kidneys, nephron endowment is dictated by the availability of nephron progenitors, whose self-renewal and differentiation require a relatively repressed chromatin state. More recently, NAD⁺-dependent deacetylase sirtuins (SIRTs) have emerged as possible regulators that link epigenetic processes to the metabolism. Here, we discovered a novel role for the NAD⁺-dependent deacylase SIRT3 in kidney development. In the embryonic kidney, SIRT3 was highly expressed only as a short isoform, with nuclear and extra-nuclear localisation. The nuclear SIRT3 did not act as deacetylase but exerted de-2-hydroxyisobutyrylase activity on lysine residues of histone proteins. Extra-nuclear SIRT3 regulated lysine 2-hydroxyisobutyrylation (Khib) levels of phosphofructokinase (PFK) and Sirt3 deficiency increased PFK Khib levels, inducing a glycolysis boost. This altered Khib landscape in Sirt3^−/− metanephroi was associated with decreased nephron progenitors, impaired nephrogenesis and a reduced number of nephrons. These data describe an unprecedented role of SIRT3 in controlling early renal development through the regulation of epigenetics and metabolic processes.

SIRT3 protects kidneys from ischemia-reperfusion injury by modulating the DRP1 pathway to induce mitochondrial autophagy

Renal ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI) and may influence renal graft survival. In this study, we investigate the involvement of SIRT3 and DRP1 in mitochondrial autophagy and AKI in a mouse model of IRI. Autophagy was detected in the absence of SIRT3, and hypoxic reoxygenation (H/R) experiments using renal tubular epithelial cells NRK52E were performed in vitro to validate these results. We found that autophagosomes increased following IRI and that the expression of autophagy-related genes was up-regulated. The inhibition of autophagy with 3-methyladenine exacerbated IRI, whereas the DRP1 inhibitor Mdivi-1 reversed this inhibition. Mdivi-1 did not reverse the inhibition of autophagy in the absence of SIRT3. During IRI, Mdivi-1 reduced autophagy and DRP1 expression, whereas SIRT3 overexpression attenuated this condition. Rescue experiment showed that autophagy was increased when both SIRT3 or DRP1 were over- or under-expressed or just DRP1 was under-expressed but expression was reduced when just SIRT3 was under-expressed. However, the expression of DRP1-related molecules was reduced when SIRT3 was overexpressed and when DRP1 was under-expressed. Taken together, these findings indicate that SIRT3 protects against kidney damage from IRI by modulating the DRP1 pathway to induce mitochondrial autophagy.