Pre-emptive Short-term Nicotinamide Mononucleotide Treatment in a Mouse Model of Diabetic Nephropathy

Ability of NAD and Sirt1 to epigenetically suppress albuminuria

The time for diabetic nephropathy (DN) to progress from mild to severe is long. Thus, methods to continuously repress DN are required to exert long-lasting effects mediated through epigenetic regulation. In this study, we demonstrated the ability of nicotinamide adenine dinucleotide (NAD) and its metabolites to reduce albuminuria through Sirt1- or Nampt-dependent epigenetic regulation. We previously reported that proximal tubular Sirt1 was lowered before glomerular Sirt1. Repressed glomerular Sirt1 was found to epigenetically elevate Claudin-1. In addition, we reported that proximal tubular Nampt deficiency epigenetically augmented TIMP-1 levels in Sirt6-mediated pathways, leading to type-IV collagen deposition and diabetic fibrosis. Altogether, we propose that the Sirt1/Claudin-1 axis may be crucial in the onset of albuminuria at the early stages of DN and that the Nampt/Sirt6/TIMP-1 axis promotes diabetic fibrosis in the middle to late stages of DN. Finally, administration of NMN, an NAD precursor, epigenetically potentiates the regression of the onset of DN to maintain Sirt1 and repress Claudin-1 in podocytes, suggesting the potential use of NAD metabolites as epigenetic medications for DN.

SB-525334 ameliorates renal injury in diabetic kidney disease mouse model via suppressing inflammation

BACKGROUND

Diabetic kidney disease (DKD; also known as diabetic nephropathy) is a typical complication of diabetes mellitus characterised by renal injury due to disturbances in glucose metabolism, in which renal tubular damage caused by chronic inflammation has been shown to be closely associated with the development of end-stage renal disease (ESRD). However, there are insufficient effective therapeutic agents to halt the progression of DKD.

METHODS

In the present study, we screened differential gene expression profiles associated with DKD by mining the GEO database through differential and enrichment analyses. Furthermore, systemic in vivo and in vitro experiments were designed to explore the mechanism through which the potential therapeutic agent SB-525334 improves DKD.

RESULTS

SB-525334 ameliorated DKD-induced kidney injury by regulating inflammatory cytokines (TGF-β1, IL-6, IL-10) as well as promoting the translation of M1 (iNOS) macrophage to M2 (CD206) macrophage. In addition, SB-525334 ameliorates kidney injury caused by DKD through inhibiting inflammation through regulating the expression of key proteins in the TGF-β1 /JNK and TGF-β1 /Smad signaling pathways. For studies in vitro, inflammation induced by LPS in vitro was inhibited significantly after the administration of SB-525334 through down-regulating pro-inflammatory cytokines, promoting macrophage conversion from M1 to M2, and inhibiting the activation of TGF-β1 /JNK and TGF-β1 /Smad pathways.

CONCLUSIONS

These results highlight that the target compound SB-525334 could serve as a novel potential therapeutic agent and ameliorate DKD in an inflammation-inhibiting manner.

Nmnat1 Deficiency Causes Mitoribosome Excess in Diabetic Nephropathy Mediated by Transcriptional Repressor HIC1

Nicotinamide adenine dinucleotide (NAD) is involved in renal physiology and is synthesized by nicotinamide mononucleotide adenylyltransferase (NMNAT). NMNAT exists as three isoforms, namely, NMNAT1, NMNAT2, and NMNAT3, encoded by Nmnat1, Nmnat2, and Nmnat3, respectively. In diabetic nephropathy (DN), NAD levels decrease, aggravating renal fibrosis. Conversely, sodium-glucose cotransporter-2 inhibitors increase NAD levels, mitigating renal fibrosis. In this regard, renal NAD synthesis has recently gained attention. However, the renal role of Nmnat in DN remains uncertain. Therefore, we investigated the role of Nmnat by establishing genetically engineered mice. Among the three isoforms, NMNAT1 levels were markedly reduced in the proximal tubules (PTs) of db/db mice. We examined the phenotypic changes in PT-specific Nmnat1 conditional knockout (CKO) mice. In CKO mice, Nmnat1 expression in PTs was downregulated when the tubules exhibited albuminuria, peritubular type IV collagen deposition, and mitochondrial ribosome (mitoribosome) excess. In CKO mice, Nmnat1 deficiency-induced mitoribosome excess hindered mitoribosomal translation of mitochondrial inner membrane-associated oxidative phosphorylation complex I (CI), CIII, CIV, and CV proteins and mitoribosomal dysfunction. Furthermore, the expression of hypermethylated in cancer 1, a transcription repressor, was downregulated in CKO mice, causing mitoribosome excess. Nmnat1 overexpression preserved mitoribosomal function, suggesting its protective role in DN.

Tubular insulin-induced gene 1 deficiency promotes NAD+ consumption and exacerbates kidney fibrosis

Profibrotic proximal tubules (PT) were identified as a unique phenotype of proximal tubule cells (PTCs) in renal fibrosis by single-cell RNA sequencing (scRNA-seq). Controlling the process of renal fibrosis requires understanding how to manage the S1 subset's branch to the S3 subset rather than to the profibrotic PT subset. Insulin-induced gene 1 (Insig1) is one of the branch-dependent genes involved in controlling this process, although its role in renal fibrosis is unknown. Here, we discovered that tubular Insig1 deficiency, rather than fibroblast Insig1 deficiency, plays a detrimental role in the pathogenesis of renal fibrosis in vivo and in vitro. Overexpression of Insig1 profoundly inhibited renal fibrosis. Mechanistically, Insig1 deletion in PTCs boosted SREBP1 nuclear localization, increasing Aldh1a1 transcriptional activity, causing excessive NAD+ consumption and ER enlargement, as well as accelerating renal fibrosis. We also identified nicardipine as a selective inhibitor of Aldh1a1, which could restore NAD+ and maintain ER homeostasis, as well as improve renal fibrosis. Together, our findings support tubular Insig1 as a new therapeutic target for chronic kidney disease (CKD).

Unraveling the nexus of NAD+ metabolism and diabetic kidney disease: insights from murine models and human data

Background

Nicotinamide adenine dinucleotide (NAD+) is a critical coenzyme involved in kidney disease, yet its regulation in diabetic kidney disease (DKD) remains inadequately understood.

Objective

Therefore, we investigated the changes of NAD+ levels in DKD and the underlying mechanism.

Methods

Alternations of NAD+ levels and its biosynthesis enzymes were detected in kidneys from streptozotocin-induced diabetic mouse model by real-time PCR and immunoblot. The distribution of NAD+ de novo synthetic enzymes was explored via immunohistochemical study. NAD+ de novo synthetic metabolite was measured by LC-MS. Human data from NephroSeq were analyzed to verify our findings.

Results

The study showed that NAD+ levels were decreased in diabetic kidneys. Both mRNA and protein levels of kynurenine 3-monooxygenase (KMO) in NAD+ de novo synthesis pathway were decreased, while NAD+ synthetic enzymes in salvage pathway and NAD+ consuming enzymes remained unchanged. Further analysis of human data suggested KMO, primarily expressed in the proximal tubules shown by our immunohistochemical staining, was consistently downregulated in human diabetic kidneys.

Conclusion

Our study demonstrated KMO of NAD+ de novo synthesis pathway was decreased in diabetic kidney and might be responsible for NAD+ reduction in diabetic kidneys, offering valuable insights into complex regulatory mechanisms of NAD+ in DKD.

Metabolite accumulation from oral NMN supplementation drives aging-specific kidney inflammation

The mitochondrial-rich renal tubule cells are key regulators of blood homeostasis via excretion and reabsorption of metabolic waste. With age, tubules are subject to increasing mitochondrial dysfunction and declining nicotinamide adenine dinucleotide (NAD+) levels, both hampering ATP production efficiency. We tested two mitochondrial interventions in young (6-mo) and aged (26-mo) adult male mice: elamipretide (ELAM), a tetrapeptide in clinical trials that improves mitochondrial structure and function, and nicotinamide mononucleotide (NMN), an NAD+ intermediate and commercially available oral supplement. Kidneys were analyzed from young and aged mice after eight weeks of treatment with ELAM (3 mg/kg/day), NMN (300 mg/kg/day), or from aged mice treated with the two interventions combined (ELAM+NMN). We hypothesized that combining pharmacologic treatments to ameliorate mitochondrial dysfunction and boost NAD+ levels, would more effectively reduce kidney aging than either intervention alone. Unexpectedly, in aged kidneys, NMN increased expression of genetic markers of inflammation (IL-1-beta; and Ccl2) and tubule injury (Kim-1). Metabolomics of endpoint sera showed that NMN-treated aged mice had higher circulating levels of uremic toxins than either aged controls or young NMN-treated mice. ELAM+NMN-treated aged mice accumulated uremic toxins like NMN-only aged mice, but reduced IL-1-beta; and Ccl2 kidney mRNA. This suggests that pre-existing mitochondrial dysfunction in aged kidney underlies susceptibility to inflammatory signaling with NMN supplementation in aged, but not young, mice. These findings demonstrate age and tissue dependent effects on downstream metabolic accumulation from NMN and highlight the need for targeted analysis of aged kidneys to assess the safety of anti-aging supplements in older populations.

Circadian light/dark cycle reversal exacerbates the progression of chronic kidney disease in mice

Circadian disruption such as shift work, jet lag, has gradually become a global health issue and is closely associated with various metabolic disorders. The influence and mechanism of circadian disruption on renal injury in chronic kidney disease (CKD) remains inadequately understood. Here, we evaluated the impact of environmental light disruption on the progression of chronic renal injury in CKD mice. By using two abnormal light exposure models to induce circadian disruption, we found that circadian disruption induced by weekly light/dark cycle reversal (LDDL) significantly exacerbated renal dysfunction, accelerated renal injury, and promoted renal fibrosis in mice with 5/6 nephrectomy and unilateral ureteral obstruction (UUO). Mechanistically, RNA-seq analysis revealed significant immune and metabolic disorder in the LDDL-conditioned CKD kidneys. Consistently, renal content of ATP was decreased and ROS production was increased in the kidney tissues of the LDDL-challenged CKD mice. Untargeted metabolomics revealed a significant buildup of lipids in the kidney affected by LDDL. Notably, the level of β-NMN, a crucial intermediate in the NAD+ pathway, was found to be particularly reduced. Moreover, we demonstrated that both β-NMN and melatonin administration could significantly rescue the light-disruption associated kidney dysfunction. In conclusion, environmental circadian disruption may exacerbate chronic kidney injury by facilitating inflammatory responses and disturbing metabolic homeostasis. β-NMN and melatonin treatments may hold potential as promising approaches for preventing and treating light-disruption associated CKD.

Sirtuins in kidney health and disease

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

Nicotinamide mononucleotide induces autophagy and ferroptosis via AMPK/mTOR pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy worldwide. Herein, we investigated the role of nicotinamide mononucleotide (NMN) in HCC progression. HCC cells were treated with NMN (125, 250, and 500 μM), and then nicotinamide adenine dinucleotide (NAD+ ) and NADH levels in HCC cells were measured to calculate NAD+ /NADH ratio. Cell proliferation, apoptosis, autophagy and ferroptosis were determined. AMPK was knocked down to confirm the involvement of AMPK/mTOR signaling. Furthermore, tumor-inhibitory effect of NMN was investigated in xenograft models. Exposure to NMN dose-dependently increased NAD+ level and NAD+ /NADH ratio in HCC cells. After NMN treatment, cell proliferation was inhibited, whereas apoptosis was enhanced in both cell lines. Additionally, NMN dose-dependently enhanced autophagy/ferroptosis and activated AMPK/mTOR pathway in HCC cells. AMPK knockdown partially rescued the effects of NMN in vitro. Furthermore, NMN treatment restrained tumor growth in nude mice, activated autophagy/ferroptosis, and promoted apoptosis and necrosis in tumor tissues. The results indicate that NMN inhibits HCC progression by inducing autophagy and ferroptosis via AMPK/mTOR signaling. NMN may serve as a promising agent for HCC treatment.

Nicotinamide protects against diabetic kidney disease through regulation of Sirt1

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Nicotinamide riboside activates renal metabolism and protects the kidney in a model of Alport syndrome

Chronic kidney disease (CKD) is associated with renal metabolic disturbances, including impaired fatty acid oxidation (FAO). Nicotinamide adenine dinucleotide (NAD + ) is a small molecule that participates in hundreds of metabolism-related reactions. NAD + levels are decreased in CKD, and NAD + supplementation is protective. However, both the mechanism of how NAD + supplementation protects from CKD, as well as the cell types most responsible, are poorly understood. Using a mouse model of Alport syndrome, we show that nicotinamide riboside (NR), an NAD + precursor, stimulates renal peroxisome proliferator-activated receptor α signaling and restores FAO in the proximal tubules, thereby protecting from CKD in both sexes. Bulk RNA-sequencing shows that renal metabolic pathways are impaired in Alport mice and dramatically activated by NR in both sexes. These transcriptional changes are confirmed by orthogonal imaging techniques and biochemical assays. Single nuclei RNA-sequencing and spatial transcriptomics, both the first of their kind from Alport mice, show that NAD + supplementation restores FAO in the proximal tubules with minimal effects on the podocytes. Finally, we also report, for the first time, sex differences at the transcriptional level in this Alport model. Male Alport mice had more severe inflammation and fibrosis than female mice at the transcriptional level. In summary, the data herein identify both the protective mechanism and location of NAD + supplementation in this model of CKD.

Nicotinamide mononucleotide pretreatment improves long-term isoflurane anesthesia-induced cognitive impairment in mice

Postoperative cognitive dysfunction (POCD) is characterized by impaired cognitive function following general anesthesia and surgery. Oxidative stress is a significant pathophysiological manifestation underlying POCD. Previous studies have reported that the decline of nicotinamide adenine dinucleotide (NAD+) -dependent sirtuin 1 (SIRT1) contributes to the activation of oxidative stress. In this study, we investigated whether pretreatment of nicotinamide mononucleotide (NMN), an NAD+ intermediate, improves oxidative stress and cognitive function in POCD. The animal model of POCD was established in C57BL/6 J mice through 6 h isoflurane anesthesia-induced cognitive impairment. Mice were intraperitoneally injected with NMN for 7 days prior to anesthesia, after which oxidative stress and cognitive function were assessed. The level of oxidative stress was determined using flow cytometry analysis and assey kits. The fear condition test and the Y-maze test were utilized to evaluate contextual and spatial memory. Our results showed that cognitive impairment and increased oxidative stress were observed in POCD mice, as well as downregulation of NAD+ levels and related protein expressions of SIRT1 and nicotinamide phosphoribosyltransferase (NAMPT) in the hippocampus. And NMN supplementation could effectively prevent the decline of NAD+ and related proteins, and reduce oxidative stress and cognitive disorders after POCD. Mechanistically, the findings suggested that protection on cognitive function mediated by NMN pretreatment in POCD mice may be regulated by NAD+-SIRT1 signaling pathway. This study indicated that NMN preconditioning reduced oxidative stress damage and alleviated cognitive impairment in POCD mice.

Sirtuins in kidney diseases: potential mechanism and therapeutic targets

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

ASH2L-mediated H3K4me3 drives diabetic nephropathy through HIPK2 and Notch1 pathway

Diabetic nephropathy (DN) is one of the complications of diabetes. Long-term hyperglycemia in the kidney results in renal insufficiency, and eventually leads to end-stage renal disease. Epigenetic factor ASH2L has long been identified as a transcriptional activator, and we previously indicated that ASH2L aggravated fibrosis and inflammation in high glucose-induced glomerular mesangial cells, but the pathophysiological relevance and the mechanism of ASH2L-mediated H3K4me3 in DN is not well understood. Here we demonstrated that ASH2L is upregulated in glomeruli isolated from db/db mice. Loss of ASH2L protected glomerular injury caused by hyperglycemia, as evidenced by reduced albuminuria, preserved structure, decreased glomerular extracellular matrix deposition, and lowered renal glomerular expression of proinflammatory and profibrotic markers in db/db mice. Furthermore, we demonstrated that enrichment of ASH2L-mediated H3K4me3 on the promoter regions of ADAM17 and HIPK2 triggered their transcription, leading to aberrant activation of Notch1 signaling pathway, thereby contributing to fibrosis and inflammation in DN. The findings of this study provide compelling evidence for targeting ASH2L as a potential therapeutic strategy to prevent or slow down the progression of DN.

Nicotinamide mononucleotide attenuates airway epithelial barrier dysfunction via inhibiting SIRT3 SUMOylation in asthma

Nicotinamide adenine dinucleotide (NAD+) is an essential element in cellular metabolism that regulates fundamental biological processes. Growing evidence suggests that a decline in NAD+ is a common pathological factor in various diseases and aging. However, its role in airway epithelial barrier function in response to asthma remains underexplored. The current study aims to explore the efficacy of restoring cellular NAD+ concentration through supplementation with the NAD+ precursor, nicotinamide mononucleotide (NMN), in the treatment of allergic asthma and to investigate the role of SIRT3 in mediating the effects of NAD+ precursors. In this research, NMN alleviated airway inflammation and reduced mucus secretion in house dust mite (HDM)-induced asthmatic mice. It also mitigated airway epithelial barrier disruption in HDM-induced asthma in vitro and in vivo. But inhibition of SIRT3 expression abolished the effects of NMN. Mechanistically, HDM induced SIRT3 SUMOylation and proteasomal degradation. Mutation of these two SIRT3 SUMO modification sites enhanced the stability of SIRT3. Additionally, SIRT3 was targeted by SENP1 which acted to de-conjugate SUMO. And down-regulation of SENP1 expression in HDM-induced models was reversed by NMN. Collectively, these findings suggest that NMN attenuates airway epithelial barrier dysfunction via inhibiting SIRT3 SUMOylation in asthma. Blockage of SIRT3 SUMOylation emerges as for the treatment of allergic asthma.

HBB as a Novel Biomarker for the Diagnosis and Monitoring of Lung Cancer Regulates Cell Proliferation via ERK1/2 Pathway

Objective: Recent studies have revealed that hemoglobin beta (HBB) plays an important role not only in blood disorders but also in malignancies. The aim of this study is to investigate the clinical significance, diagnostic value, and biological function of HBB in lung cancer. Methods: HBB expression was examined in lung cancer tissues and plasma samples using quantitative real-time polymerase chain reaction, and its relationship with clinical pathological characteristics was analyzed. Receiver operating characteristic (ROC) curves were constructed to evaluate the diagnostic value of HBB in lung cancer. The proliferation of A549 and SPCA1 cells was analyzed using a cell counting kit-8 assay and protein expressions were detected by western blot. Results: The expressions of HBB were found to be down-regulated in both lung cancer tissues and plasma samples. Notably, plasma HBB levels were significantly elevated in postoperative samples when compared to their preoperative counterparts. Across 66 cases of lung cancer tissues, a correlation was observed between HBB levels and both gender and tumor, node, metastasis staging. ROC curve analysis further confirmed the high diagnostic potential of HBB expression in lung cancer. Moreover, the combination of HBB and carcinoembryonic antigen (CEA) had greater significance than HBB or CEA alone in the diagnosis of lung cancer. Knocking out or overexpressing HBB could affect lung cancer cell proliferation through the ERK1/2 signaling pathway. Conclusion: HBB can serve as a novel biomarker for the diagnosis and monitoring of lung cancer, regulating cell proliferation via the ERK1/2 pathway and playing a pivotal role in the oncogenesis and progression of the disease.

Nicotinamide Adenine Dinucleotide in Aging Biology: Potential Applications and Many Unknowns

Recent research has unveiled an expansive role of NAD+ in cellular energy generation, redox reactions, and as a substrate or cosubstrate in signaling pathways that regulate health span and aging. This review provides a critical appraisal of the clinical pharmacology and the preclinical and clinical evidence for therapeutic effects of NAD+ precursors for age-related conditions, with a particular focus on cardiometabolic disorders, and discusses gaps in current knowledge. NAD+ levels decrease throughout life; age-related decline in NAD+ bioavailability has been postulated to be a contributor to many age-related diseases. Raising NAD+ levels in model organisms by administration of NAD+ precursors improves glucose and lipid metabolism; attenuates diet-induced weight gain, diabetes, diabetic kidney disease, and hepatic steatosis; reduces endothelial dysfunction; protects heart from ischemic injury; improves left ventricular function in models of heart failure; attenuates cerebrovascular and neurodegenerative disorders; and increases health span. Early human studies show that NAD+ levels can be raised safely in blood and some tissues by oral NAD+ precursors and suggest benefit in preventing nonmelanotic skin cancer, modestly reducing blood pressure and improving lipid profile in older adults with obesity or overweight; preventing kidney injury in at-risk patients; and suppressing inflammation in Parkinson disease and SARS-CoV-2 infection. Clinical pharmacology, metabolism, and therapeutic mechanisms of NAD+ precursors remain incompletely understood. We suggest that these early findings provide the rationale for adequately powered randomized trials to evaluate the efficacy of NAD+ augmentation as a therapeutic strategy to prevent and treat metabolic disorders and age-related conditions.

Protein acetylation and related potential therapeutic strategies in kidney disease

Kidney disease can be caused by various internal and external factors that have led to a continual increase in global deaths. Current treatment methods can alleviate but do not markedly prevent disease development. Further research on kidney disease has revealed the crucial function of epigenetics, especially acetylation, in the pathology and physiology of the kidney. Histone acetyltransferases (HATs), histone deacetylases (HDACs), and acetyllysine readers jointly regulate acetylation, thus affecting kidney physiological homoeostasis. Recent studies have shown that acetylation improves mechanisms and pathways involved in various types of nephropathy. The discovery and application of novel inhibitors and activators have further confirmed the important role of acetylation. In this review, we provide insights into the physiological process of acetylation and summarise its specific mechanisms and potential therapeutic effects on renal pathology.

Cellular crosstalk of mesangial cells and tubular epithelial cells in diabetic kidney disease

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease and imposes a heavy global economic burden; however, little is known about its complicated pathophysiology. Investigating the cellular crosstalk involved in DKD is a promising avenue for gaining a better understanding of its pathogenesis. Nonetheless, the cellular crosstalk of podocytes and endothelial cells in DKD is better understood than that of mesangial cells (MCs) and renal tubular epithelial cells (TECs). As the significance of MCs and TECs in DKD pathophysiology has recently become more apparent, we reviewed the existing literature on the cellular crosstalk of MCs and TECs in the context of DKD to acquire a comprehensive understanding of their cellular communication. Insights into the complicated mechanisms underlying the pathophysiology of DKD would improve its early detection, care, and prognosis. Video Abstract.

New insights into the mechanisms of diabetic kidney disease: Role of circadian rhythm and Bmal1

It is common for diabetic kidney disease (DKD) to be complicated by abnormal blood glucose, blood lipids, and blood pressure rhythms. Thus, it is essential to examine diagnostic and treatment plans from the perspective of circadian disruption. This brief review discusses the clinical relevance of circadian rhythms in DKD and how the core clock gene encoding brain and muscle arnt-like protein 1 (BMAL1) functions owing to the importance of circadian rhythm disruption processes, including the excretion of urinary protein and irregular blood pressure, which occur in DKD. Exploring Bmal1 and its potential mechanisms and signaling pathways in DKD following contact with Sirt1 and NF-κB is novel and important. Finally, potential pharmacological and behavioral intervention strategies for DKD circadian rhythm disturbance are outlined. This review aids in unveiling novel, potential molecular targets for DKD based on circadian rhythms.

Regulation of autophagy by natural polyphenols in the treatment of diabetic kidney disease: therapeutic potential and mechanism

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes and a leading cause of end-stage renal disease worldwide. Autophagy plays an important role in maintaining cellular homeostasis in renal physiology. In DKD, the accumulation of advanced glycation end products induces decreased renal autophagy-related protein expression and transcription factor EB (TFEB) nuclear transfer, leading to impaired autophagy and lysosomal function and blockage of autophagic flux. This accelerates renal resident cell injury and apoptosis, mediates macrophage infiltration and phenotypic changes, ultimately leading to aggravated proteinuria and fibrosis in DKD. Natural polyphenols show promise in treating DKD by regulating autophagy and promoting nuclear transfer of TFEB and lysosomal repair. This review summarizes the characteristics of autophagy in DKD, and the potential application and mechanisms of some known natural polyphenols as autophagy regulators in DKD, with the goal of contributing to a deeper understanding of natural polyphenol mechanisms in the treatment of DKD and promoting the development of their applications. Finally, we point out the limitations of polyphenols in current DKD research and provide an outlook for their future research.

PCK1 Protects against Mitoribosomal Defects in Diabetic Nephropathy in Mouse Models

SIGNIFICANCE STATEMENT

Renal gluconeogenesis plays an important role in the pathogenesis of diabetic nephropathy (DN). Proximal tubular phosphoenolpyruvate carboxykinase1 (PEPCK1) is the rate-limiting enzyme in gluconeogenesis. However, the functions of PEPCK1 have not been elucidated. We describe the novel role of PEPCK1 as a mitoribosomal protector using Pck1 transgenic (TG) mice and knockout mice. Pck1 blocks excessive glycolysis by suppressing the upregulation of excess HK2 (the rate-limiting enzyme of glycolysis). Notably, Pck1 overexpression retains mitoribosomal function and suppresses renal fibrosis. The renal and mitoribosomal protective roles of Pck1 may provide important clues for understanding DN pathogenesis and provide novel therapeutic targets.

BACKGROUND

Phosphoenolpyruvate carboxykinase (PEPCK) is part of the gluconeogenesis pathway, which maintains fasting glucose levels and affects renal physiology. PEPCK consists of two isoforms-PEPCK1 and PEPCK2-that the Pck1 and Pck2 genes encode. Gluconeogenesis increases in diabetic nephropathy (DN), escalating fasting and postprandial glucose levels. Sodium-glucose cotransporter-2 inhibitors increase hepatic and renal gluconeogenesis. We used genetically modified mice to investigate whether renal gluconeogenesis and Pck1 activity are renoprotective in DN.

METHODS

We investigated the expression of Pck1 in the proximal tubule (PTs) of streptozotocin (STZ)-treated diabetic mice. We studied the phenotypic changes in PT-specific transgenic (TG) mice and PT-specific Pck1 conditional knockout (CKO) mice.

RESULTS

The expression of Pck1 in PTs was downregulated in STZ-treated diabetic mice when they exhibited albuminuria. TG mice overexpressing Pck1 had improved albuminuria, concomitant with the mitigation of PT cell apoptosis and deposition of peritubular type IV collagen. Moreover, CKO mice exhibited PT cell apoptosis and type IV collagen deposition, findings also observed in STZ-treated mice. Renal fibrotic changes in CKO mice were associated with increasing defects in mitochondrial ribosomes (mitoribosomes). The TG mice were protected against STZ-induced mitoribosomal defects.

CONCLUSION

PCK1 preserves mitoribosomal function and may play a novel protective role in DN.

NAD metabolism modulates inflammation and mitochondria function in diabetic kidney disease

Diabetes mellitus is the leading cause of cardiovascular and renal disease in the United -States. Despite the beneficial interventions available for patients with diabetes, there remains a need for additional therapeutic targets and therapies in diabetic kidney disease (DKD). Inflammation and oxidative stress are increasingly recognized as important causes of renal diseases. Inflammation is closely associated with mitochondrial damage. The molecular connection between inflammation and mitochondrial metabolism remains to be elucidated. Recently, nicotinamide adenine nucleotide (NAD+) metabolism has been found to regulate immune function and inflammation. In the present studies, we tested the hypothesis that enhancing NAD metabolism could prevent inflammation in and progression of DKD. We found that treatment of db/db mice with type 2 diabetes with nicotinamide riboside (NR) prevented several manifestations of kidney dysfunction (i.e., albuminuria, increased urinary kidney injury marker-1 (KIM1) excretion, and pathologic changes). These effects were associated with decreased inflammation, at least in part via inhibiting the activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway. An antagonist of the serum stimulator of interferon genes (STING) and whole-body STING deletion in diabetic mice showed similar renoprotection. Further analysis found that NR increased SIRT3 activity and improved mitochondrial function, which led to decreased mitochondrial DNA damage, a trigger for mitochondrial DNA leakage which activates the cGAS-STING pathway. Overall, these data show that NR supplementation boosted NAD metabolism to augment mitochondrial function, reducing inflammation and thereby preventing the progression of diabetic kidney disease.

Nicotinamide mononucleotide (NMN) ameliorated Nonylphenol-induced learning and memory impairment in rats via the central 5-HT system and the NAD+/SIRT1/MAO-A pathway

Nonylphenol (NP) exposure can trigger neurotoxicity and cause learning and memory impairment. Nicotinamide mononucleotide (NMN) has a therapeutic effect on neurodegenerative diseases, but the role of NMN on NP-induced learning and memory impairment is not known. Here, we examined the mitigative effect of NMN on the impaired learning and memory ability of rats exposed to NP. The NP impaired learning and memory in rats, while the low-dose intervention with NMN significantly prolonged the step-through latency of the PAT and improved the NAMPT and NMNAT1 content in brain tissue. At the same time, the NMN intervention also increased the content of 5-HTR_1A, 5-HTR₄, and 5-HTR₆ related to learning and memory in the hippocampus. In line with this, we found that the NMN intervention activated the SIRT1/MAO-A pathway in brain tissue. NMN intervention, especially at 125 mg/kg doses, may improve rats' NP-induced learning and memory impairment via the central 5-HT system and the NAD⁺/SIRT1/MAO-A pathway in the brain.

Gut microbiota-derived nicotinamide mononucleotide alleviates acute pancreatitis by activating pancreatic SIRT3 signalling

BACKGROUND AND PURPOSE

Gut microbiota dysbiosis induced by acute pancreatitis (AP) exacerbates pancreatic injury and systemic inflammatory responses. The alleviation of gut microbiota dysbiosis through faecal microbiota transplantation (FMT) is considered a potential strategy to reduce tissue damage and inflammation in many clinical disorders. Here, we aim to investigate the effect of gut microbiota and microbiota-derived metabolites on AP and further clarify the mechanisms associated with pancreatic damage and inflammation.

EXPERIMENTAL APPROACH

AP rat and mouse models were established by administration of caerulein or sodium taurocholate in vivo. Pancreatic acinar cells were exposed to caerulein and lipopolysaccharide in vitro to simulate AP.

KEY RESULTS

Normobiotic FMT alleviated AP-induced gut microbiota dysbiosis and ameliorated the severity of AP, including mitochondrial dysfunction, oxidative damage and inflammation. Normobiotic FMT induced higher levels of NAD⁺ (nicotinamide adenine dinucleotide)-associated metabolites, particularly nicotinamide mononucleotide (NMN). NMN administration mitigated AP-mediated mitochondrial dysfunction, oxidative damage and inflammation by increasing pancreatic NAD⁺ levels. Similarly, overexpression of the NAD⁺ -dependent mitochondrial deacetylase sirtuin 3 (SIRT3) alleviated the severity of AP. Furthermore, SIRT3 deacetylated peroxiredoxin 5 (PRDX5) and enhanced PRDX5 protein expression, thereby promoting its antioxidant and anti-inflammatory activities in AP. Importantly, normobiotic FMT-mediated NMN metabolism induced SIRT3-PRDX5 pathway activation during AP.

CONCLUSION AND IMPLICATIONS

Gut microbiota-derived NMN alleviates the severity of AP by activating the SIRT3-PRDX5 pathway. Normobiotic FMT could be served as a potential strategy for AP treatment.

Role of sirtuins in metabolic disease-related renal injury

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

Baicalin Exerts a Protective Effect in Diabetic Nephropathy by Repressing Inflammation and Oxidative Stress Through the SphK1/S1P/NF-κB Signaling Pathway

Background

Inflammation and oxidative stress contribute to the development of diabetic nephropathy (DN). Baicalin (BA) shows renal protection against DN through its anti-inflammatory and anti-oxidant properties. However, the molecular mechanism by which BA exerts the therapeutic effects on DN remains to be investigated.

Methods

The db/db mice and high glucose (HG)-induced HK-2 cells were used as the in vivo and in vitro model of DN, respectively. The effects of BA were assessed by detecting the related blood and urine biochemical parameters, kidney histopathology, inflammatory cytokine production, oxidative stress indicators, and apoptosis. Cell viability and apoptosis were detected by CCK-8 assay and TUNEL assay, respectively. Related protein levels were measured by an immunoblotting method.

Results

In db/db model mice, BA reduced serum glucose concentration, decreased blood lipid levels, ameliorated kidney functions, and decreased histopathological changes in kidney tissues. BA also alleviated oxidative stress and inflammation in db/db mice. In addition, BA blocked the activation of sphingosine kinases type 1/sphingosine 1-phosphate (SphK1/S1P)/NF-κB pathway in db/db mice. In HK-2 cells, BA hindered HG-induced apoptosis, oxidative stress and inflammation, while overexpression of SphK1 or S1P could reverse these effects. BA alleviated HG-induced apoptosis, oxidative stress and inflammation in HK-2 cells through the S1P/NF-κB pathway. Furthermore, BA blocked the NF-κB signaling by diminishing p65 nuclear translocation via the SphK1/S1P pathway.

Conclusion

Our study strongly suggests that BA protects against DN via ameliorating inflammation, oxidative stress and apoptosis through the SphK1/S1P/NF-κB pathway. This study provides a novel insight into the therapeutic effects of BA in DN.

Nicotinamide prevention in diabetes-induced alterations in the rat liver

Objective. The study was performed to elucidate whether nicotinamide (NAm) can attenuate the diabetes-induced liver damage by correction of ammonia detoxifying function and disbalance of NAD-dependent processes in diabetic rats. Methods. After four weeks of streptozotocin-induced diabetes, Wistar male rats were treated for two weeks with or without NAm. Urea concentration, arginase, and glutamine synthetase activities, NAD+ levels, and NAD+/NADH ratio were measured in cytosolic liver extracts. Expression of parp-1 gene in the liver was estimated by quantitative polymerase chain reaction and PARP-1 cleavage evaluated by Western blotting. Results. Despite the blood plasma lipid peroxidation products in diabetic rats were increased by 60%, the activity of superoxide dismutase (SOD) was reduced. NAm attenuated the oxidative stress, but did not affect the enzyme activity in diabetic rats. In liver of the diabetic rats, urea concentration and arginase activity were significantly higher than in the controls. The glutamine synthetase activity was decreased. Decline in NAD+ level and cytosolic NAD+/NADH ratio in the liver of diabetic rats was observed. Western blot analysis demonstrated a significant up-regulation of PARP-1 expression accompanied by the enzyme cleavage in the diabetic rat liver. However, no correlation was seen between mRNA expression of parp-1 gene and PARP-1 protein in the liver of diabetic rats. NAm markedly attenuated PARP-1 cleavage induced by diabetes, but did not affect the parp-1 gene expression. Conclusions. NAm counteracts diabetes-induced impairments in the rat liver through improvement of its detoxifying function, partial restoration of oxidative stress, NAD+ level, normalization of redox state of free cytosolic NAD+/NADH-couples, and prevention of PARP-1 cleavage.

Differences and Clinical Significance of Serum 25-Hydroxyvitamin D3 and Vasohibin-1 (VASH-1) Levels in Patients with Diabetic Nephropathy and Different Renal Injuries

Objective

We investigate the relationship between the changes of serum 25-hydroxyvitamin D3 (25(OH)D3) and vasohibin-1 (VASH-1) and renal function injury in patients with type 2 diabetic nephropathy.

Methods

In this study, 143 patients with diabetic nephropathy (DN) were selected as DN group, and 80 patients with type 2 diabetes mellitus were selected as T2DM group. The serum 25 (OH) D3, VASH-1, blood glucose index, inflammation index and renal function index were compared between the two groups. According to the urinary microalbumin/creatinine ratio (UACR), the DN group was divided into microalbuminuria group (UACR range≥30.0mg/g and <300.0mg/g) and macroalbuminuria group (UACR≥300.0mg/g) for stratified comparison. The correlation between 25-hydroxyvitamin D3, VASH-1 and inflammation index and renal function index was analyzed by simple linear correlation analysis.

Results

The level of 25 (OH) D3 in DN group was significantly lower than that in T2DM group (P<0.05). The levels of VASH-1, CysC, BUN, Scr, 24h urine protein, serum CRP, TGF-β1, TNF-α and IL-6 in DN group were higher than those in T2DM group (P<0.05). The level of 25 (OH) D3 in DN patients with massive proteinuria was significantly lower than that in DN patients with microalbuminuria. The level of VASH-1 in DN patients with massive proteinuria was higher than that in DN patients with microalbuminuria (P<0.05). There was a negative correlation between 25 (OH) D3 and CysC, BUN, Scr, 24h urine protein, CRP, TGF-β1, TNF-α, IL-6 in patients with DN (P<0.05). VASH-1 was positively correlated with Scr, 24h urinary protein, CRP, TGF-β1, TNF-α and IL-6 in patients with DN (P<0.05).

Conclusion

The level of serum 25 (OH) D3 in DN patients was considerably decreased, and the level of VASH-1 was increased, which was related to the degree of renal function injury and inflammatory response.

Correlation between lipoprotein(a), albuminuria, myostatin and sarcopenia in elderly patients with type 2 diabetes

AIM

To investigate the relationship of the lipoprotein(a), albuminuria, myostatin with sarcopenia in elderly patients with type 2 diabetes (T2D).

METHODS

A total of 461 elderly patients with T2D who were admitted to our hospital were selected as the research subjects. There were 34 cases in line with Asian sarcopenia diagnosis (group A), and 427 patients had no such symptoms as the control group (group C). The levels of lipoprotein(a), albuminuria, myostatin in each group were compared, and the effect factors of muscle loss in elderly patients with T2D were analyzed by univariate/multivariate logistic regression.

RESULTS

The incidence of sarcopenia in 461 elderly patients with T2D in this study was 7.37 % (34/461). However, the levels of appendicular skeletal muscle mass index (ASMI, kg/m²), albumin and epidermal growth factor receptor (eGFR) in group A were lower than those in group C (P < 0.05). The levels of lipoprotein(a), albuminuria, myostatin in group A were higher those in group C (P < 0.05). Additionally, group A had a higher morbidity in diabetic retinopathy and neuropathy. Univariate logistic regression analysis revealed that the risk factors of muscle loss are ASMI, lipoprotein(a), albuminuria, myostatin, diabetic retinopathy and neuropathy. Multivariate Logistic regression analysis showed that the risk factors of muscle loss in elderly patients with T2D were lipoprotein(a), albuminuria, myostatin and diabetic neuropathy.

CONCLUSION

The lipoprotein(a), albuminuria, myostatin and diabetic neuropathy are closely related to the occurrence and development of muscle loss in elderly patients with T2D.

Roles of NAD+ in Acute and Chronic Kidney Diseases

Nicotinamide adenine dinucleotide (oxidized form, NAD⁺) is a critical coenzyme, with functions ranging from redox reactions and energy metabolism in mitochondrial respiration and oxidative phosphorylation to being a central player in multiple cellular signaling pathways, organ resilience, health, and longevity. Many of its cellular functions are executed via serving as a co-substrate for sirtuins (SIRTs), poly (ADP-ribose) polymerases (PARPs), and CD38. Kidney damage and diseases are common in the general population, especially in elderly persons and diabetic patients. While NAD⁺ is reduced in acute kidney injury (AKI) and chronic kidney disease (CKD), mounting evidence indicates that NAD⁺ augmentation is beneficial to AKI, although conflicting results exist for cases of CKD. Here, we review recent progress in the field of NAD⁺, mainly focusing on compromised NAD⁺ levels in AKI and its effect on essential cellular pathways, such as mitochondrial dysfunction, compromised autophagy, and low expression of the aging biomarker αKlotho (Klotho) in the kidney. We also review the compromised NAD⁺ levels in renal fibrosis and senescence cells in the case of CKD. As there is an urgent need for more effective treatments for patients with injured kidneys, further studies on NAD⁺ in relation to AKI/CKD may shed light on novel therapeutics.

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.

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.

Safety evaluation of β-nicotinamide mononucleotide oral administration in healthy adult men and women

A decrease in the intracellular level of nicotinamide adenine dinucleotide (NAD+), an essential coenzyme for metabolic activity, causes various age-related diseases and metabolic abnormalities. Both in-vivo and in-vitro studies have shown that increasing certain NAD+ levels in cell or tissue by supplementing nicotinamide mononucleotide (NMN), a precursor of NAD+, alleviates age-related diseases and metabolic disorders. In recent years, several clinical trials have been performed to elucidate NMN efficacy in humans. However, previous clinical studies with NMN have not reported on the safety of repeated daily oral administration of ≥ 1000 mg/shot in healthy adult men and women, and human clinical trials on NMN safety are limited. Therefore, we conducted a randomized, double-blind, placebo-controlled, parallel-group study to evaluate the safety of 1250 mg of β-NMN administered orally once daily for up to 4 weeks in 31 healthy adult men and women aged 20–65 years. Oral administration of β-NMN did not result in changes exceeding physiological variations in multiple clinical trials, including anthropometry, hematological, biochemical, urine, and body composition analyses. Moreover, no severe adverse events were observed during the study period. Our results indicate that β-NMN is safe and well-tolerated in healthy adult men and women an oral dose of 1250 mg once daily for up to 4 weeks.

Trial registration Clinicaltrials.gov Identifier: UMIN000043084. Registered 21/01/2021. https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000049188.

Comprehensive bibliometric analysis of sirtuins: Focus on sirt1 and kidney disease

Sirtuins, as regulators of metabolism and energy, have been found to play an important role in health and disease. Sirt1, the most widely studied member of the sirtuin family, can ameliorate oxidative stress, immune inflammation, autophagy, and mitochondrial homeostasis by deacetylating regulatory histone and nonhistone proteins. Notably, sirt1 has gradually gained attention in kidney disease research. Therefore, an evaluation of the overall distribution of publications concerning sirt1 based on bibliometric analysis methods to understand the thematic evolution and emerging research trends is necessary to discover topics with potential implications for kidney disease research. We conducted a bibliometric analysis of publications derived from the Web of Science Core Collection and found that publications concerning sirt1 have grown dramatically over the past 2 decades, especially in the past 5 years. Among these, the proportion of publications regarding kidney diseases have increased annually. China and the United States are major contributors to the study of sirt1, and Japanese researchers have made important contributions to the study of sirt1 in kidney disease. Obesity, and Alzheimer’s disease are hotspots diseases for the study of sirt1, while diabetic nephropathy is regarded as a research hotspot in the study of sirt1 in kidney disease. NAD⁺, oxidative stress, and p53 are the focus of the sirt1 research field. Autophagy and NLRP3 inflammasome are emerging research trends have gradually attracted the interest of scholars in sirt1, as well as in kidney disease. Notably, we also identified several potential research topics that may link sirt1 and kidney disease, which require further study, including immune function, metabolic reprogramming, and fecal microbiota.

Nicotinamide mononucleotide ameliorates adriamycin-induced renal damage by epigenetically suppressing the NMN/NAD consumers mediated by Twist2

The activation of nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase, Sirt1, after the administration of nicotinamide mononucleotide (NMN) suppresses many diseases. However, the role of NMN and Sirt1 in focal glomerulosclerosis (FSGS) has not yet been elucidated. This study aimed to assess the protective effect of NMN treatment in mice with adriamycin (ADR)-induced FSGS.　Transient short-term NMN treatment was administered to 8-week-old ADR- or saline-treated BALB/c mice (Cont group) for 14 consecutive days. NMN alleviated the increase in urinary albumin excretion in the ADR-treated mice. NMN treatment mitigated glomerulosclerosis and ameliorated the reduced Sirt1 expression and elevated Claudin-1 expression in the kidneys of the mice. Moreover, this treatment improved the decrease in histone methylation and the expression level of Dnmt1 and increased the concentration of NAD⁺ in the kidney. Dnmt1 epigenetically suppressed the expression of the NMN-consuming enzyme nicotinamide mononucleotide adenyltransferase1 (Nmnat1) by methylating the E-box in the promoter region and repressing the NAD-consuming enzyme PARP1. Additionally, NMN downregulated the expression of Nmnat1 in the ADR-treated mice. Short-term NMN treatment in FSGS has epigenetic renal protective effects through the upregulation of Sirt1 and suppression of the NAD and NMN consumers. The present study presents a novel treatment paradigm for FSGS.

Sirtuin deficiency and the adverse effects of fructose and uric acid synthesis

Fructose metabolism and hyperuricemia have been shown to drive insulin resistance, metabolic syndrome, hepatic steatosis, hypertension, inflammation, and innate immune reactivity in experimental studies. We suggest that these adverse effects are at least in part the result of suppressed activity of sirtuins, particularly Sirtuin1. Deficiency of sirtuin deacetylations is a consequence of reduced bioavailability of its cofactor nicotinamide adenine dinucleotide (NAD+). Uric acid-induced inflammation and oxidative stress consume NAD+ and activation of the polyol pathway of fructose and uric acid synthesis also reduces the NAD+-to-NADH ratio. Variability in the compensatory regeneration of NAD+ could result in variable recovery of sirtuin activity that may explain the inconsistent benefits of treatments directed to reduce uric acid in clinical trials. Here, we review the pathogenesis of the metabolic dysregulation driven by hyperuricemia and their potential relationship with sirtuin deficiency. In addition, we discuss therapeutic options directed to increase NAD+ and sirtuins activity that may improve the adverse effects resulting from fructose and uric acid synthesis.

The significance of NAD + metabolites and nicotinamide N-methyltransferase in chronic kidney disease

Dysregulation of nicotinamide adenine dinucleotide (NAD +) metabolism contributes to the initiation and progression of age-associated diseases, including chronic kidney disease (CKD). Nicotinamide N-methyltransferase (NNMT), a nicotinamide (NAM) metabolizing enzyme, regulates both NAD + and methionine metabolism. Although NNMT is expressed abundantly in the kidney, its role in CKD and renal fibrosis remains unclear. We generated NNMT-deficient mice and a unilateral ureter obstruction (UUO) model and conducted two clinical studies on human CKD to investigate the role of NNMT in CKD and fibrosis. In UUO, renal NNMT expression and the degraded metabolites of NAM increased, while NAD + and NAD + precursors decreased. NNMT deficiency ameliorated renal fibrosis; mechanistically, it (1) increased the DNA methylation of connective tissue growth factor (CTGF), and (2) improved renal inflammation by increasing renal NAD + and Sirt1 and decreasing NF-κB acetylation. In humans, along with CKD progression, a trend toward a decrease in serum NAD + precursors was observed, while the final NAD + metabolites were accumulated, and the level of eGFR was an independent variable for serum NAM. In addition, NNMT was highly expressed in fibrotic areas of human kidney tissues. In conclusion, increased renal NNMT expression induces NAD + and methionine metabolism perturbation and contributes to renal fibrosis.

NAD+ Anabolism Disturbance Causes Glomerular Mesangial Cell Injury in Diabetic Nephropathy

The homeostasis of NAD⁺ anabolism is indispensable for maintaining the NAD⁺ pool. In mammals, the mainly synthetic pathway of NAD⁺ is the salvage synthesis, a reaction catalyzed by nicotinamide mononucleotide adenylyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase (NMNATs) successively, converting nicotinamide (NAM) to nicotinamide mononucleotide (NMN) and NMN to NAD⁺, respectively. However, the relationship between NAD⁺ anabolism disturbance and diabetic nephropathy (DN) remains elusive. Here our study found that the disruption of NAD⁺ anabolism homeostasis caused an elevation in both oxidative stress and fibronectin expression, along with a decrease in Sirt1 and an increase in both NF-κB P65 expression and acetylation, culminating in extracellular matrix deposition and globular fibrosis in DN. More importantly, through constitutively overexpressing NMNAT1 or NAMPT in human mesangial cells, we revealed NAD⁺ levels altered inversely with NMN levels in the context of DN and, further, their changes affect Sirt1/NF-κB P65, thus playing a crucial role in the pathogenesis of DN. Accordingly, FK866, a NAMPT inhibitor, and quercetin, a Sirt1 agonist, have favorable effects on the maintenance of NAD⁺ homeostasis and renal function in db/db mice. Collectively, our findings suggest that NMN accumulation may provide a causal link between NAD⁺ anabolism disturbance and diabetic nephropathy (DN) as well as a promising therapeutic target for DN treatment.

Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end stage renal disease (ESRD) in the USA. The pathogenesis of DKD is multifactorial and involves activation of multiple signaling pathways with merging outcomes including thickening of the basement membrane, podocyte loss, mesangial expansion, tubular atrophy, and interstitial inflammation and fibrosis. The glomerulo-tubular balance and tubule-glomerular feedback support an increased glomerular filtration and tubular reabsorption, with the latter relying heavily on ATP and increasing the energy demand. There is evidence that alterations in mitochondrial bioenergetics in kidney cells lead to these pathologic changes and contribute to the progression of DKD towards ESRD. This review will focus on the dialogue between alterations in bioenergetics in glomerular and tubular cells and its role in the development of DKD. Alterations in energy substrate selection, electron transport chain, ATP generation, oxidative stress, redox status, protein posttranslational modifications, mitochondrial dynamics, and quality control will be discussed. Understanding the role of bioenergetics in the progression of diabetic DKD may provide novel therapeutic approaches to delay its progression to ESRD.

Epigenetic Alterations in Podocytes in Diabetic Nephropathy

Recently, epigenetic alterations have been shown to be involved in the pathogenesis of diabetes and its complications. Kidney podocytes, which are glomerular epithelial cells, are important cells that form a slit membrane—a barrier for proteinuria. Podocytes are terminally differentiated cells without cell division or replenishment abilities. Therefore, podocyte damage is suggested to be one of the key factors determining renal prognosis. Recent studies, including ours, suggest that epigenetic changes in podocytes are associated with chronic kidney disease, including diabetic nephropathy. Furthermore, the association between DNA damage repair and epigenetic changes in diabetic podocytes has been demonstrated. Detection of podocyte DNA damage and epigenetic changes using human samples, such as kidney biopsy and urine-derived cells, may be a promising strategy for estimating kidney damage and renal prognoses in patients with diabetes. Targeting epigenetic podocyte changes and associated DNA damage may become a novel therapeutic strategy for preventing progression to end-stage renal disease (ESRD) and provide a possible prognostic marker in diabetic nephropathy. This review summarizes recent advances regarding epigenetic changes, especially DNA methylation, in podocytes in diabetic nephropathy and addresses detection of these alterations in human samples. Additionally, we focused on DNA damage, which is increased under high-glucose conditions and associated with the generation of epigenetic changes in podocytes. Furthermore, epigenetic memory in diabetes is discussed. Understanding the role of epigenetic changes in podocytes in diabetic nephropathy may be of great importance considering the increasing diabetic nephropathy patient population in an aging society.

Impaired Nicotinamide Adenine Dinucleotide Biosynthesis in the Kidney of Chronic Kidney Disease

Chronic kidney disease (CKD) is a global public health problem with high morbidity and mortality. Decreased nicotinamide adenine dinucleotide (NAD⁺) levels were found to be associated with aging, cancer, and neurodegenerative and metabolic disorders. However, the alteration of renal NAD⁺ levels and biosynthesis pathways in CKD is less known. In the present study, we aimed to evaluate renal NAD⁺ levels and tested the expression of key enzymes in three NAD⁺ biosynthesis pathways in two different types of CKD rat model. CKD rat models were established by 5/6 nephrectomy (5/6 Nx) and feeding with adenine-containing feed, respectively. Renal function was assessed by serum creatinine (Scr) and blood urea nitrogen (BUN). Renal pathology was evaluated by periodic acid-Schiff (PAS) and Masson’s trichrome staining. The expression of key enzymes in three NAD⁺ biosynthesis pathways was determined and quantified by Western blot analysis. The results showed CKD rat models were successfully established as evidenced by increased Scr and BUN levels, upregulation of neutrophil gelatinase-associated lipocalin (NGAL), glomerular hypertrophy, and renal fibrosis. Renal NAD⁺ and NADH content were both declined in two CKD rat models, and NAD⁺ levels were negatively correlated with Scr and BUN levels in CKD rats. Three key enzymes involved in NAD⁺ biosynthesis were significantly downregulated in the kidney of both of the two CKD models. They were quinolinate phosphoribosyltransferase (QPRT) in the de novo pathway, nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), and NMNAT3 in the salvage pathway. Moreover, the expression of NAD⁺-consuming enzymes sirtuin 3 (SIRT3) and CD38 decreased significantly in CKD rats. In conclusion, NAD⁺ biosynthesis was significantly impaired in CKD, which may attribute to downregulation of QPRT and NMNAT 1/3.

Sirtuins and Renal Oxidative Stress

Renal failure is a major health problem that is increasing worldwide. To improve clinical outcomes, we need to understand the basic mechanisms of kidney disease. Aging is a risk factor for the development and progression of kidney disease. Cells develop an imbalance of oxidants and antioxidants as they age, resulting in oxidative stress and the development of kidney damage. Calorie restriction (CR) is recognized as a dietary approach that promotes longevity, reduces oxidative stress, and delays the onset of age-related diseases. Sirtuins, a type of nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, are considered to be anti-aging molecules, and CR induces their expression. The sirtuin family consists of seven enzymes (Sirt1–7) that are involved in processes and functions related to antioxidant and oxidative stress, such as DNA damage repair and metabolism through histone and protein deacetylation. In fact, a role for sirtuins in the regulation of antioxidants and redox substances has been suggested. Therefore, the activation of sirtuins in the kidney may represent a novel therapeutic strategy to enhancing resistance to many causative factors in kidney disease through the reduction of oxidative stress. In this review, we discuss the relationship between sirtuins and oxidative stress in renal disease.

NAD+ Homeostasis in Diabetic Kidney Disease

The redox reaction and energy metabolism status in mitochondria is involved in the pathogenesis of metabolic related disorder in kidney including diabetic kidney disease (DKD). Nicotinamide adenine dinucleotide (NAD+) is a cofactor for redox reactions and energy metabolism in mitochondria. NAD+ can be synthesized from four precursors through three pathways. The accumulation of NAD+ may ameliorate oxidative stress, inflammation and improve mitochondrial biosynthesis via supplementation of precursors and intermediates of NAD+ and activation of sirtuins activity. Conversely, the depletion of NAD+ via NAD+ consuming enzymes including Poly (ADP-ribose) polymerases (PARPs), cADPR synthases may contribute to oxidative stress, inflammation, impaired mitochondrial biosynthesis, which leads to the pathogenesis of DKD. Therefore, homeostasis of NAD+ may be a potential target for the prevention and treatment of kidney diseases including DKD. In this review, we focus on the regulation of the metabolic balance of NAD+ on the pathogenesis of kidney diseases, especially DKD, highlight benefits of the potential interventions targeting NAD+-boosting in the treatment of these diseases.