Sirtuin 3 deficiency aggravates contrast-induced acute kidney injury

Sirtuin 3 in renal diseases and aging: From mechanisms to potential therapies

The longevity protein sirtuins (SIRTs) belong to a family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases. In mammals, SIRTs comprise seven members (SIRT1-7) which are localized to different subcellular compartments. As the most prominent mitochondrial deacetylases, SIRT3 is known to be regulated by various mechanisms and participate in virtually all aspects of mitochondrial homeostasis and metabolism, exerting significant impact on multiple organs. Notably, the kidneys possess an abundance of mitochondria that provide substantial energy for filtration and reabsorption. A growing body of evidence now supports the involvement of SIRT3 in several renal diseases, including acute kidney injury, chronic kidney disease, and diabetic nephropathy; notably, these diseases are all associated with aging. In this review, we summarize the emerging role of SIRT3 in renal diseases and aging, and highlights the intricate mechanisms by which SIRT3 exerts its effects. In addition, we highlight the potential therapeutic significance of modulating SIRT3 and provide valuable insights into the therapeutic role of SIRT3 in renal diseases to facilitate clinical application.

The protective mechanism of SIRT3 and potential therapy in acute kidney injury

Acute kidney injury (AKI) is a complex clinical syndrome with a poor short-term prognosis, which increases the risk of the development of chronic kidney diseases and end-stage kidney disease. However, the underlying mechanism of AKI remains to be fully elucidated, and effective prevention and therapeutic strategies are still lacking. Given the enormous energy requirements for filtration and absorption, the kidneys are rich in mitochondria, which are unsurprisingly involved in the onset or progression of AKI. Accumulating evidence has recently documented that Sirtuin 3 (SIRT3), one of the most prominent deacetylases highly expressed in the mitochondria, exerts a protective effect on AKI. SIRT3 protects against AKI by regulating energy metabolism, inhibiting oxidative stress, suppressing inflammation, ameliorating apoptosis, inhibiting early-stage fibrosis and maintaining mitochondrial homeostasis. Besides, a number of SIRT3 activators have exhibited renoprotective properties both in animal models and in vitro experiments, but have not yet been applied to clinical practice, indicating a promising therapeutic approach. In this review, we unravel and summarize the recent advances in SIRT3 research and the potential therapy of SIRT3 activators in AKI.

SIRT3 Activation a Promise in Drug Development? New Insights into SIRT3 Biology and Its Implications on the Drug Discovery Process

Sirtuins catalyze deacetylation of lysine residues with a NAD+-dependent mechanism. In mammals, the sirtuin family is composed of seven members, divided into four subclasses that differ in substrate specificity, subcellular localization, regulation, as well as interactions with other proteins, both within and outside the epigenetic field. Recently, much interest has been growing in SIRT3, which is mainly involved in regulating mitochondrial metabolism. Moreover, SIRT3 seems to be protective in diseases such as age-related, neurodegenerative, liver, kidney, heart, and metabolic ones, as well as in cancer. In most cases, activating SIRT3 could be a promising strategy to tackle these health problems. Here, we summarize the main biological functions, substrates, and interactors of SIRT3, as well as several molecules reported in the literature that are able to modulate SIRT3 activity. Among the activators, some derive from natural products, others from library screening, and others from the classical medicinal chemistry approach.

Diosmin ameliorates renal fibrosis through inhibition of inflammation by regulating SIRT3-mediated NF-κB p65 nuclear translocation

BACKGROUND

Renal fibrosis is considered an irreversible pathological process and the ultimate common pathway for the development of all types of chronic kidney diseases and renal failure. Diosmin is a natural flavonoid glycoside that has antioxidant, anti-inflammatory, and antifibrotic activities. However, whether Diosmin protects kidneys by inhibiting renal fibrosis is unknown. We aimed to investigate the role of Diosmin in renal interstitial fibrosis and to explore the underlying mechanisms.

METHODS

The UUO mouse model was established and gavaged with Diosmin (50 mg/kg·d and 100 mg/kg·d) for 14 days. HE staining, Masson staining, immunohistochemistry, western blotting and PCR were used to assess renal tissue injury and fibrosis. Elisa kits were used to detect the expression levels of IL-1β, IL-6, and TNF-α and the activity of SIRT3 in renal tissues. In addition, enrichment maps of RNA sequencing analyzed changes in signaling pathways. In vitro, human renal tubular epithelial cells (HK-2) were stimulated with TGF-β1 and then treated with diosmin (75 μM). The protein and mRNA expression levels of SIRT3 were detected in the cells. In addition, 3-TYP (selective inhibitor of SIRT3) and SIRT3 small interfering RNA (siRNA) were used to reduce SIRT3 levels in HK-2.

RESULTS

Diosmin attenuated UUO-induced renal fibrosis and TGF-β1-induced HK-2 fibrosis. In addition, Diosmin reduced IL-1β, IL-6, and TNF-α levels in kidney tissues and supernatants of HK-2 medium. Interestingly, Diosmin administration increased the enzymatic activity of SIRT3 in UUO kidneys. In addition, Diosmin significantly increased mRNA and protein expression of SIRT3 in vitro and in vivo. Inhibition of SIRT3 expression using 3-TYP or SIRT3 siRNA abolished the anti-inflammatory effects of diosmin in HK-2 cells. Enrichment map analysis by RNA sequencing indicates that the nuclear factor-kappa B (NF-κB) signaling pathway was inhibited in the Diosmin intervention group. Furthermore, we found that TGF-β1 increased the nuclear expression of nuclear NF-κB p65 but had little significant effect on the total intracellular expression of NF-κB p65. Additionally, Diosmin reduced TGF-β1-caused NF-κB p65 nuclear translocation. Knockdown of SIRT3 expression by SIRT3 siRNA increased the nuclear expression of NF-κB p65 and abolished the inhibition effect of Diosmin in NF-κB p65 expression.

CONCLUSIONS

Diosmin reduces renal inflammation and fibrosis, which is contributed by inhibiting nuclear translocation of NF-κB P65 through activating SIRT3.

N-acetylcysteine protects septic acute kidney injury by inhibiting SIRT3-mediated mitochondrial dysfunction and apoptosis

Objectives

To investigate the protective effect of N-acetylcysteine (NAC) on septic acute kidney injury (SAKI) via regulating Sirtuin3 (SIRT3)-mediated mitochondrial dysfunction and apoptosis.

Materials and Methods

By constructing SIRT3 knockout mice and culturing kidney tubular epithelial cells (KTECs), we assessed the changes of renal function and detected the protein expression of adenine nucleotide translocator (ANT), cyclophilin (CypD) and voltage-dependent anion channel (VDAC) using western-blotting, and simultaneously detected toll-like receptor 4 (TLR4), inhibitor of kappa B kinase (IKKβ), inhibitor of Kappa Bα (IκBα), and p65 protein expression. We observed mitochondrial damage of KTECs using a transmission electron microscope and assessed apoptosis by TdT-mediated dUTP Nick-End Labeling and flow cytometry.

Results

SIRT3 deficiency led to the deterioration of renal function, and caused a significant increase in inducible nitric oxide synthase production, a decrease in mitochondrial volume, up-regulation of TLR4, IκBα, IKKβ, and p65 proteins, and up-regulation of ANT, CypD and VDAC proteins. However, NAC significantly improved renal function and down-regulated the expression of TLR4, IκBα, IKKβ, and p65 proteins. Furthermore, SIRT3 deficiency led to a significant increase in KTEC apoptosis, while NAC up-regulated the expression of SIRT3 and inhibited apoptosis.

Conclusion

NAC has a significant protective effect on SAKI by inhibiting SIRT3-mediated mitochondrial dysfunction and apoptosis of KTECs.

NAD+-A Hub of Energy Metabolism in Heart Failure

Heart failure is a condition where reduced levels of adenosine triphosphate (ATP) affect energy supply in myocardial cells. Nicotinamide adenine dinucleotide (NAD+) plays a crucial role as a coenzyme for electron transfer in energy metabolism. Decreased NAD+ levels in myocardial cells lead to inadequate ATP production and increased susceptibility to heart failure. Researchers are exploring ways to increase NAD+ levels to alleviate heart failure. Targets such as sirtuin2 (sirt2), sirtuin3 (sirt3), Poly (ADP-ribose) polymerase (PARP), and diastolic regulatory proteins are being investigated. NAD+ supplementation has shown promise, even in heart failure with preserved ejection fraction (HFpEF). By focusing on NAD+ as a central component of energy metabolism, it is possible to improve myocardial activity, heart function, and address energy deficiency in heart failure.

NAD+ Precursors in Human Health and Disease: Current Status and Future Prospects

Significance: Nicotinamide adenine dinucleotide (NAD+) acts as a cofactor in many important biological processes. The administration of NAD+ precursors increases the intracellular NAD+ pool and has beneficial effects on physiological changes and diseases associated with aging in various organisms, including rodents and humans. Recent Advances: Evidence from preclinical studies demonstrating the beneficial effects of NAD+ precursors has rapidly increased in the last decade. The results of these studies have prompted the development of clinical trials using NAD+ precursors, particularly nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). In addition, in vivo studies of NAD+ metabolism have rapidly progressed. Critical Issues: Several studies have demonstrated that the oral administration of NAD+ precursors, such as NR and NMN, is safe and significantly increases NAD+ levels in humans. However, the efficacy of these NAD+ precursors is lower than expected from the results of preclinical studies. In addition, the identification of the contribution of the host-gut microbiota interactions to NR and NMN metabolism has added to the complexity of NAD+ metabolism. Future Directions: Further studies are required to determine the efficacy of NAD+ precursors in humans. Further in vivo studies of NAD+ metabolism are required to optimize the effects of NAD+ supplementation. There is also a need for methods of delivering NAD+ precursors to target organs or tissues to increase the outcomes of clinical trials. Antioxid. Redox Signal. 39, 1133-1149.

Neutrophil Extracellular Traps Aggravate Contrast-Induced Acute Kidney Injury by Damaging Glomeruli and Peritubular Capillaries

Background

Contrast-induced acute kidney injury (CI-AKI) is considered to be the third leading cause of hospital-acquired kidney injury. Current studies mostly suggest that contrast agents mainly harm renal tubular epithelial cells, but we hypothesized that the development of CI-AKI should be the result of the interaction of renal vascular and tubular injury.

Methods

First we constructed a CI-AKI mouse model and verified the success of the model by pathological injury and serum creatinine level. Immunohistochemistry, protein quantification and qRT-PCR were used to detect the location and level of expression of neutrophil extracellular traps (NETs) in the kidney. Then, we blocked the in vivo accumulation of NETs using GSK484 and DNase I and detected the expression of NETs and the damage of glomerular and peritubular capillaries.

Results

We first identified the presence of NETs in CI-AKI mice, and NETs were mainly accumulated in glomeruli and peritubular capillaries. The expression of NETs was positively correlated with the severity of CI-AKI kidney. After inhibition of NETs release or promotion of NETs degradation by drugs, renal vascular endothelial cell injury was reduced and renal pathological changes and creatinine levels were reversed in CI-AKI mice. In addition, inhibition of NETs reduced apoptosis and pyroptosis of renal cells and attenuated inflammation in vivo.

Conclusion

These findings suggest that NETs are involved in the development of CI-AKI by damaging glomerular and peritubular capillary endothelial cells. This study will provide a new strategy for clinical prevention and treatment of CI-AKI.

Sirt3 deficiency promotes endothelial dysfunction and aggravates renal injury

Sirtuin 3 (SIRT3), the main deacetylase of mitochondria, modulates the acetylation levels of substrates governing metabolism and oxidative stress. In the kidney, we showed that SIRT3 affects the proper functioning of high energy-demanding cells, such as tubular cells and podocytes. Less is known about the role of SIRT3 in regulating endothelial cell function and its impact on the progression of kidney disease. Here, we found that whole body Sirt3-deficient mice exhibited reduced renal capillary density, reflecting endothelial dysfunction, and VEGFA expression compared to wild-type mice. This was paralleled by activation of hypoxia signaling, upregulation of HIF-1α and Angiopietin-2, and oxidative stress increase. These alterations did not result in kidney disease. However, when Sirt3-deficient mice were exposed to the nephrotoxic stimulus Adriamycin (ADR) they developed aggravated endothelial rarefaction, altered VEGFA signaling, and higher oxidative stress compared to wild-type mice receiving ADR. As a result, ADR-treated Sirt3-deficient mice experienced a more severe injury with exacerbated albuminuria, podocyte loss and fibrotic lesions. These data suggest that SIRT3 is a crucial regulator of renal vascular homeostasis and its dysregulation is a predisposing factor for kidney disease. By extension, our findings indicate SIRT3 as a pharmacologic target in progressive renal disease whose treatments are still imperfect.

Nicotinamide Riboside, a Promising Vitamin B3 Derivative for Healthy Aging and Longevity: Current Research and Perspectives

Many studies have suggested that the oxidized form of nicotinamide adenine dinucleotide (NAD+) is involved in an extensive spectrum of human pathologies, including neurodegenerative disorders, cardiomyopathy, obesity, and diabetes. Further, healthy aging and longevity appear to be closely related to NAD+ and its related metabolites, including nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). As a dietary supplement, NR appears to be well tolerated, having better pharmacodynamics and greater potency. Unfortunately, NR is a reactive molecule, often unstable during its manufacturing, transport, and storage. Recently, work related to prebiotic chemistry discovered that NR borate is considerably more stable than NR itself. However, immediately upon consumption, the borate dissociates from the NR borate and is lost in the body through dilution and binding to other species, notably carbohydrates such as fructose and glucose. The NR left behind is expected to behave pharmacologically in ways identical to NR itself. This review provides a comprehensive summary (through Q1 of 2023) of the literature that makes the case for the consumption of NR as a dietary supplement. It then summarizes the challenges of delivering quality NR to consumers using standard synthesis, manufacture, shipping, and storage approaches. It concludes by outlining the advantages of NR borate in these processes.

Research progress on animal models of contrast-induced acute kidney injury

Contrast-induced acute kidney injury (CI-AKI) refers to acute kidney injury that occurs after intravascular contrast media is applied. It is the third most common cause for acute renal failure in hospitalized patients and can cause severe renal impairment and adverse cardiovascular outcomes. In severe cases, it can even lead to the death of the patient. Due to its complicated pathogenesis, the pathogenesis of CI-AKI has not yet been elucidated. Therefore, it is of great significance to further study the pathogenesis for the prevention of CI-AKI. Moreover, a good animal model of CI-AKI is an important tool for in-depth research on the pathogenesis of acute kidney injury induced by contrast agents.

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.

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.

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.

Strategies to protect against age-related mitochondrial decay: Do natural products and their derivatives help?

Mitochondria serve vital roles critical for overall cellular function outside of energy transduction. Thus, mitochondrial decay is postulated to be a key factor in aging and in age-related diseases. Mitochondria may be targets of their own decay through oxidative damage. However, treating animals with antioxidants has been met with only limited success in rejuvenating mitochondrial function or in increasing lifespan. A host of nutritional strategies outside of using traditional antioxidants have been devised to promote mitochondrial function. Dietary compounds are under study that induce gene expression, enhance mitochondrial biogenesis, mitophagy, or replenish key metabolites that decline with age. Moreover, redox-active compounds may now be targeted to mitochondria which improve their effectiveness. Herein we review the evidence that representative dietary effectors modulate mitochondrial function by stimulating their renewal or reversing the age-related loss of key metabolites. While in vitro evidence continues to accumulate that many of these compounds benefit mitochondrial function and/or prevent their decay, the results using animal models and, in some instances human clinical trials, are more mixed and sometimes even contraindicated. Thus, further research on optimal dosage and age of intervention are warranted before recommending potential mitochondrial rejuvenating compounds for human use.

Cellular and molecular pathways underlying the nephrotoxicity of gadolinium

Mounting evidence on the short- and long-term adverse effects associated with gadolinium [Gd (III)]-based contrast agents used in magnetic resonance imaging have emerged in the past three decades. Safety issues arise from the release of Gd (III) from chelates and its deposition in tissues, which is exacerbated in patients with renal disease, since the kidney is the major excretion organ of most of these agents. This study aimed at unveiling the cellular and molecular mechanisms of nephrotoxicity of Gd (III), using an in vitro model of human proximal tubular cells (HK-2 cell line). Cell viability declined in a concentration- and time-dependent manner after exposure to GdCl3·6H2O. The estimated inhibitory concentrations (ICs) eliciting 1 to 50% of cell death, after 24 h of exposure, ranged from 3.4 to 340.5 µM. At toxic concentrations, exposure to Gd (III) led to disruption of the oxidative status, mitochondrial dysfunction, cell death by apoptosis, switching to necrosis at higher levels, and autophagic activation. Disturbance of the lipid metabolism was already observed at low-toxicity ICs, with accumulation of lipid droplets, and upregulation of genes related to both lipogenesis and lipolysis. Gd (III)-exposure, even at the subtoxic IC01, increased the expression of modulators of various signaling pathways involved in the development and progression of renal disease, including inflammation, hypoxia and fibrosis. Our results give new insights into the mechanisms underlying the nephrotoxic potential of Gd (III) and highlight the need to further clarify the risks versus benefits of the Gd (III)-based contrast agents currently in use.

Melatonin Alleviates Contrast-Induced Acute Kidney Injury by Activation of Sirt3

Oxidative stress and apoptosis play a vital role in the pathogenesis of contrast-induced acute kidney injury (CI-AKI). The purpose of our study was to investigate the protective effects and mechanisms of melatonin against CI-AKI in a CI-AKI mouse model and NRK-52E cells. We established the CI-AKI model in mice, and the animals were pretreated with melatonin (20 mg/kg). Our results demonstrated that melatonin treatment exerted a renoprotective effect by decreasing the level of serum creatinine (SCr) and blood urea nitrogen (BUN), lessening the histological changes of renal tubular injuries, and reducing the expression of neutrophil gelatinase-associated lipid (NGAL), a marker of kidney injury. We also found that pretreatment with melatonin remarkably increased the expression of Sirt3 and decreased the ac-SOD2 K68 level. Consequently, melatonin treatment significantly decreased the oxidative stress by reducing the Nox4, ROS, and malondialdehyde (MDA) content and by increasing the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity levels. The antiapoptotic effect of melatonin on CI-AKI was revealed by decreasing the ratio of Bax/Bcl2 and the cleaved caspase3 level and by reducing the number of apoptosis-positive tubular cells. In addition, melatonin treatment remarkably reduced the inflammatory cytokines of interleukin-1β (IL-1β), tumor necrosis factor α (TNFα), and transforming growth factor β (TGFβ) in vivo and in vitro. Sirt3 deletion and specific Sirt3 siRNA abolished the above renoprotective effects of melatonin in mice with iohexol-induced acute kidney injury and in NRK-52E cells. Thus, our results demonstrated that melatonin exhibited the renoprotective effects of antioxidative stress, antiapoptosis, and anti-inflammation by the activation of Sirt3 in the CI-AKI model in vivo and in vitro. Melatonin may be a potential drug to ameliorate CI-AKI in clinical practice.

Effectiveness of N-Acetylcysteine in the Treatment of Renal Deterioration Caused by Long-Term Exposure to Bisphenol A

Human health hazards caused by bisphenol A (BPA), a precursor for epoxy resins and polycarbonate-based plastics, are well documented and are closely associated with mitochondrial impairment and oxidative imbalance. This study aimed to assess the therapeutic efficacy of N-acetylcysteine (NAC) on renal deterioration caused by long-term BPA exposure and examine the signaling transduction pathway involved. Male Wistar rats were given vehicle or BPA orally for 12 weeks then the BPA-treated group was subdivided to receive vehicle or NAC concurrently with BPA for a further 4 weeks, while the vehicle-treated normal control group continued to receive vehicle through to the end of experiment. Proteinuria, azotemia, glomerular filtration reduction and histopathological abnormalities caused by chronic BPA exposure were significantly reduced following NAC therapy. NAC also diminished nitric oxide and lipid peroxidation but enhanced renal glutathione levels, and counteracted BPA-induced mitochondrial swelling, increased mitochondrial reactive oxygen species production, and the loss of mitochondrial membrane potential. The benefit of NAC was related to the modulation of signaling proteins in the AMPK-SIRT3-SOD2 axis. The present study shows the potential of NAC to restore mitochondrial integrity and oxidative balance after long-term BPA exposure, and suggests that NAC therapy is an effective approach to tackle renal deterioration in this condition.

Boosting NAD level suppresses inflammatory activation of PBMCs in heart failure

BACKGROUNDWhile mitochondria play an important role in innate immunity, the relationship between mitochondrial dysfunction and inflammation in heart failure (HF) is poorly understood. In this study we aimed to investigate the mechanistic link between mitochondrial dysfunction and inflammatory activation in peripheral blood mononuclear cells (PBMCs), and the potential antiinflammatory effect of boosting the NAD level.METHODSWe compared the PBMC mitochondrial respiration of 19 hospitalized patients with stage D HF with that of 19 healthy participants. We then created an in vitro model of sterile inflammation by treating healthy PBMCs with mitochondrial damage-associated molecular patterns (MitoDAMPs) isolated from human heart tissue. Last, we enrolled patients with stage D HF and sampled their blood before and after taking 5 to 9 days of oral nicotinamide riboside (NR), a NAD precursor.RESULTSWe demonstrated that HF is associated with both reduced respiratory capacity and elevated proinflammatory cytokine gene expressions. In our in vitro model, MitoDAMP-treated PBMCs secreted IL-6 that impaired mitochondrial respiration by reducing complex I activity. Last, oral NR administration enhanced PBMC respiration and reduced proinflammatory cytokine gene expression in 4 subjects with HF.CONCLUSIONThese findings suggest that systemic inflammation in patients with HF is causally linked to mitochondrial function of the PBMCs. Increasing NAD levels may have the potential to improve mitochondrial respiration and attenuate proinflammatory activation of PBMCs in HF.TRIAL REGISTRATIONClinicalTrials.gov NCT03727646.FUNDINGThis study was funded by the NIH, the University of Washington, and the American Heart Association.

Protein acetylation and deacetylation: An important regulatory modification in gene transcription (Review)

Cells primarily rely on proteins to perform the majority of their physiological functions, and the function of proteins is regulated by post-translational modifications (PTMs). The acetylation of proteins is a dynamic and highly specific PTM, which has an important influence on the functions of proteins, such as gene transcription and signal transduction. The acetylation of proteins is primarily dependent on lysine acetyltransferases and lysine deacetylases. In recent years, due to the widespread use of mass spectrometry and the emergence of new technologies, such as protein chips, studies on protein acetylation have been further developed. Compared with histone acetylation, acetylation of non-histone proteins has gradually become the focus of research due to its important regulatory mechanisms and wide range of applications. The discovery of specific protein acetylation sites using bioinformatic tools can greatly aid the understanding of the underlying mechanisms of protein acetylation involved in related physiological and pathological processes.

Molecular pathophysiology of acute kidney injury: The role of sirtuins and their interactions with other macromolecular players

Acute kidney injury (AKI), a rapid drop in kidney function, displays high mortality and morbidity, and its repeated or severe status can shift into chronic kidney disease or even end-stage renal disease. How and which events cause AKI still is controversial. In addition, no specific therapies have emerged that can attenuate AKI or expedite recovery. Some central mechanisms including tubular epithelial cells injury, endothelial injury, renal cell apoptosis, and necrosis signaling cascades, and inflammation have been reported in the pathophysiology of AKI. However, the timing of the activation of each pathway, their interactions, and the hierarchy of these pathways remain unknown. The main molecular mechanisms that might be complicated in this process are the mitochondrial impairment and alteration/shifting of cellular metabolites (e.g., acetyl-CoA and NAD⁺ /NADH) acting as cofactors to alter the activities of many enzymes, for instance, sirtuins. Moreover, alteration of mitochondrial structure over the fusion and fission mechanisms can regulate cellular signaling pathways by modifying the rate of reactive oxygen species generation and metabolic activities. The aim of this review is to better understand the underlying pathophysiological and molecular mechanisms of AKI. In addition, we predicted the main other molecular players in interaction with sirtuins as energy/stresses monitoring proteins for the development of future approaches in the treatment or prevention of ischemic AKI.

CaMKII as a key regulator of contrast-induced nephropathy through mPTP opening in HK-2 cells

Contrast-induced nephropathy (CIN), refers to acute kidney injury observed after administration of contrast media during angiographic or other medical procedures such as urography, and accounting for 12% of all causes of acute renal failure, but no specific prevention or treatment strategy exists for its obscure pathophysiology. The aim of our study was to explore the influence of calcium/calmodulin-dependent protein kinase II (CaMKII) in CIN by using HK-2 cells. Knockdown of CypD was achieved by lentivirus, and CaMKII overexpression by transfection with the plasmid. In this study, we have demonstrated that CypD-mediated mPTP opening triggered mitochondrial dysfunction and tubule cells apoptosis in CIN. We also found that iohexol treatment was associated with mitochondrial ROS overloading, ATP depletion and LDH release. Inhibition of CypD with the pharmacologic inhibitor or knockdown of CypD abrogated mPTP opening, oxidative stress, mitochondria damage, and cell apoptosis induced by iohexol. In addition, we found that inhibition of the CaMKII activity alleviated iohexol-induced CypD expression, whereas also decreased mPTP opening, oxidative stress, mitochondria damage, and cell apoptosis, similarly to the inhibition of CypD did. Moreover, CaMKII overexpression enhanced iohexol-induced mPTP opening, mitochondrial damage and renal tubular epithelial cells apoptosis. These findings first identified the novel role of CaMKII in iohexol-induced tubular cells apoptosis and delineated the CaMKII-CypD/mPTP pathway during contrast-induced tubular cell damage. Hence, these results could provide a new strategy for CIN protection.

Mitochondrial Sirtuin 3: New emerging biological function and therapeutic target

Sirtuin 3 (SIRT3) is one of the most prominent deacetylases that can regulate acetylation levels in mitochondria, which are essential for eukaryotic life and inextricably linked to the metabolism of multiple organs. Hitherto, SIRT3 has been substantiated to be involved in almost all aspects of mitochondrial metabolism and homeostasis, protecting mitochondria from a variety of damage. Accumulating evidence has recently documented that SIRT3 is associated with many types of human diseases, including age-related diseases, cancer, heart disease and metabolic diseases, indicating that SIRT3 can be a potential therapeutic target. Here we focus on summarizing the intricate mechanisms of SIRT3 in human diseases, and recent notable advances in the field of small-molecule activators or inhibitors targeting SIRT3 as well as their potential therapeutic applications for future drug discovery.

tert-Butylhydroquinone Treatment Alleviates Contrast-Induced Nephropathy in Rats by Activating the Nrf2/Sirt3/SOD2 Signaling Pathway

Oxidative stress plays a critical role in the pathophysiology of contrast-induced nephropathy (CIN). Since the specific treatment of CIN remains an unmet medical need, it is imperative to find an effective strategy against the clinical management of CIN. The transcription factor Nrf2 is known to regulate antioxidative stress response. The aim of the present study was to assess the effects of tert-butylhydroquinone (t-BHQ), an activator of Nrf2, in the prevention of CIN and elucidate the underlying mechanism of its action in vitro and in vivo. We established a rat model of CIN and treated the animals with t-BHQ (25 mg/kg). The effects of t-BHQ treatment on CIN rats were elucidated by assessing renal function, HE staining, immunohistochemistry, and western blotting. We also studied the activity of oxidative stress-related markers, such as intracellular ROS level, MDA level, SOD2 activity, and GSH/GSSG ratio. We validated our results by siRNA-mediated silencing of Nrf2 in HK-2 cells exposed to the radiocontrast agent. Treatment with t-BHQ significantly ameliorated the renal function and the histopathological lesions in CIN rats. Further, pretreatment with t-BHQ significantly increased the SOD2 activity and GSH/GSSG ratio and decreased the levels of ROS and MDA in animals subjected to ioversol exposure. In addition, t-BHQ treatment increased the expression of Nrf2, Sirt3, and SOD2 and concomitantly decreased the expression of acetylated-SOD2. When Nrf2-silenced HK-2 cells were exposed to radiocontrast agent, they suffered severe cell oxidative stress, exhibited lower expression of Sirt3 and SOD2, and expressed higher levels of acetylated-SOD2; however, t-BHQ treatment did not affect the protein expression of these indicators in si-Nrf2 HK-2 cells. Our findings suggested that Nrf2 plays an important role in the regulation of the Sirt3/SOD2 antioxidative pathway, and t-BHQ may be a potential agent to ameliorate radiocontrast-induced nephropathy via activating the Nrf2/Sirt3/SOD2 signaling pathway in vitro and in vivo.

N-Acetylcysteine Attenuates the Increasing Severity of Distant Organ Liver Dysfunction after Acute Kidney Injury in Rats Exposed to Bisphenol A

Distant organ liver damage after acute kidney injury (AKI) remains a serious clinical setting with high mortality. This undesirable outcome may be due to some hidden factors that can intensify the consequences of AKI. Exposure to bisphenol A (BPA), a universal chemical used in plastics industry, is currently unavoidable and can be harmful to the liver. This study explored whether BPA exposure could be a causative factor that increase severity of remote liver injury after AKI and examined the preventive benefit by N-acetylcysteine (NAC) in this complex condition. Male Wistar rats were given vehicle, BPA, or BPA + NAC for 5 weeks then underwent 45 min renal ischemia followed by 24 h reperfusion (RIR), a group of vehicle-sham-control was also included. RIR not only induced AKI but produced liver injury, triggered systemic oxidative stress as well as inflammation, which increasing severity upon exposure to BPA. Given NAC to BPA-exposed rats diminished the added-on effects of BPA on liver functional impairment, oxidative stress, inflammation, and apoptosis caused by AKI. NAC also mitigated the abnormalities in mitochondrial functions, dynamics, mitophagy, and ultrastructure of the liver by improving the mitochondrial homeostasis regulatory signaling AMPK-PGC-1α-SIRT3. The study demonstrates that NAC is an effective adjunct for preserving mitochondrial homeostasis and reducing remote effects of AKI in environments where BPA exposure is vulnerable.