Roles of SIRT6 in kidney disease: a novel therapeutic target

Molecular signaling pathways in doxorubicin-induced nephrotoxicity and potential therapeutic agents

Doxorubicin (DOX), an anthracycline chemotherapeutic agent, is extensively utilized in the clinical management of both solid and hematological malignancies. Nevertheless, the clinical application of this treatment is significantly limited by adverse reactions and toxicity that may arise during or after administration. Its cytotoxic effects are multifaceted, with cardiotoxicity being the most prevalent side effect. Furthermore, it has the potential to adversely affect other organs, including the brain, kidneys, liver, and so on. Notably, it has been reported that DOX may cause renal failure in patients and there is currently no effective treatment for DOX-induced kidney damage, which has raised a high concern about DOX-induced nephrotoxicity (DIN). Although the precise molecular mechanisms underlying DIN remain incompletely elucidated, prior research has indicated that reactive oxygen species (ROS) are pivotal in this process, triggering a cascade of detrimental pathways including apoptosis, inflammation, dysregulated autophagic flux, and fibrosis. In light of these mechanisms, decades of research have uncovered several DIN-associated signaling pathways and found multiple potential therapeutic agents targeting them. Thus, this review intends to delineate the DIN associated signaling pathways, including AMPK, JAKs/STATs, TRPC6/RhoA/ROCK1, YAP/TEAD, SIRTs, Wnt/β-catenin, TGF-β/Smad, MAPK, Nrf2/ARE, NF-κB, and PI3K/AKT, and to summarize their potential regulatory agents, which provide a reference for the development of novel medicines against DIN.

Epigenetic alterations and memory: key players in the development/progression of chronic kidney disease promoted by acute kidney injury and diabetes

Chronic kidney disease (CKD) is a highly prevalent global public health issue and can progress to renal failure. Survivors of acute kidney injury (AKI) have an increased risk of progressing to CKD by 8.8-fold and kidney failure by 3.1-fold. Further, 20% to 40% of individuals with diabetes will develop CKD, also known as diabetic kidney disease (DKD). Thus, preventing these kidney diseases can positively impact quality-of-life and life-expectancy outcomes for affected individuals. Frequent episodes of hyperglycemia and renal hypoxia are implicated in the pathophysiology of CKD. Prior periods of hyperglycemia/uncontrolled diabetes can result in development/progression of DKD even after achieving normoglycemia, a phenomenon known as metabolic memory or legacy effect. Similarly, in AKI, hypoxic memory is stored in renal cells even after recovery from the initial AKI episode and can transition to CKD. Epigenetic mechanisms involving DNA methylation, chromatin histone post-translational modifications, and noncoding RNAs are implicated in both metabolic and hypoxic memory, collectively known as "epigenetic memory." This epigenetic memory is generally reversible and provides a therapeutic avenue to ameliorate persistent disease progression due to hyperglycemia and hypoxia and prevent/ameliorate CKD progression. Indeed, therapeutic strategies targeting epigenetic memory are effective at preventing CKD development/progression in experimental models of AKI and DKD. Here, we review the latest in-depth evidence for epigenetic features in DKD and AKI, and in epigenetic memories of AKI-to-CKD transition or DKD development and progression, followed by translational and clinical implications of these epigenetic changes for the treatment of these widespread kidney disorders.

Exploring the role and therapeutic potential of lipid metabolism in acute kidney injury

Acute kidney injury (AKI) is a prevalent condition, yet no specific treatment is available. Extensive research has revealed the pivotal role of lipid-related alterations in AKI. Lipid metabolism plays an essential role in the sustenance of the kidneys. In addition to their energy-supplying function, lipids contribute to the formation of renal biomembranes and the establishment of the renal microenvironment. Moreover, lipids or their metabolites actively participate in signal transduction, which governs various vital biological processes, such as proliferation, differentiation, apoptosis, autophagy, and epithelial-mesenchymal transition. While previous studies have focused predominantly on abnormalities in lipid metabolism in chronic kidney disease, this review focuses on lipid metabolism anomalies in AKI. We explore the significance of lipid metabolism products as potential biomarkers for the early diagnosis and classification of AKI. Additionally, this review assesses current preclinical investigations on the modulation of lipid metabolism in the progression of AKI. Finally, on the basis of existing research, this review proposes future directions, highlights challenges, and presents novel targets and innovative ideas for the treatment of and intervention in AKI.

Sirt6 overexpression relieves ferroptosis and delays the progression of diabetic nephropathy via Nrf2/GPX4 pathway

OBJECTIVE

Sirt6, reactive oxygen species and ferroptosis may participate in the pathogenesis of Diabetic Nephropathy (DN). Exploring the relationship between Sirt6, oxidative stress, and ferroptosis provides new scientific ideas to DN.

METHODS

Human podocytes were stimulated with 30 mM glucose and 5.5 mM glucose. The mice of db/db group were randomly divided into two groups:12 weeks and 16 weeks. Collect mouse blood and urine specimens and renal cortices for investigations. HE, Masson, PAS and immunohistochemical staining were used to observe pathological changes. Western blot, RT-qPCR and immunofluorescence staining were used to evaluate expression of relevant molecules. CCK8 method was introduced to observe cell viability. The changes of podocyte mitochondrial membrane potential and mitochondrial morphology in each group were determined by JC-1 staining and Mito-Tracker.

RESULTS

The expression level of Sirt6, Nrf2, SLC7A11, HO1, SOD2 and GPX4 were reduced, while ACSL4 was increased in DN. Blood glucose, BUN, Scr, TG, T-CHO and 24h urine protein were upregulated, while ALB was reduced in diabetic group. The treatment of Ferrostatin-1 significantly improved these changes, which proved ferroptosis was involved in the development of DN. Overexpression of Sirt6 might ameliorate the oxidation irritable reaction and ferroptosis. Sirt6 plasmid transfection increased mitochondrial membrane potential and protected morphology and structure of mitochondria. The application of Sirt6 siRNA could aggravated the damage manifestations.

CONCLUSION

High glucose stimulation could decrease the antioxidant capacity and increase formation of ROS and lipid peroxidation. Sirt6 might alleviate HG-induced mitochondrial dysfunction, podocyte injury and ferroptosis through regulating Nrf2/GPX4 pathway.

Sirt6 ameliorates high glucose-induced podocyte cytoskeleton remodeling via the PI3K/AKT signaling pathway

BACKGROUND

Podocyte injury plays an important role in the occurrence and progression of diabetic kidney disease (DKD), which leads to albuminuria. Cytoskeletal remodeling is an early manifestation of podocyte injury in DKD. However, the underlying mechanism of cytoskeletal remodeling has not been clarified. Histone deacetylase sirtuin6 (Sirt6) has been found to play a key role in DKD progression, and the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/AKT) pathway directly regulates the cytoskeletal structure of podocytes. Whereas, the relationship between Sirt6, the PI3K/AKT pathway and DKD progression remains unclear.

METHODS

Renal injury of db/db mice was observed by PAS staining and transmission electron microscope. Expression of Sirt6 in the glomeruli of db/db mice was detected by immunofluorescence. UBCS039, a Sirt6 activator, was used to explore the renal effects of Sirt6 activation on diabetic mouse kidneys. We also downregulating Sirt6 expression in podocytes using the Sirt6 inhibitor, OSS_128167, and induced upregulation of Sirt6 using a recombinant plasmid, after which the effects of Sirt6 on high glucose (HG)-induced podocyte damage were assessed in vitro. Podocyte cytoskeletal structures were observed by phalloidin staining. The podocyte apoptotic rate was assessed by flow cytometry, and PI3K/AKT signaling activation was measured by Western blotting.

RESULTS

Db/db mice exhibited renal damage including elevated urine albumin-to-creatinine ratio (ACR), increased mesangial matrix, fused podocyte foot processes, and thickened glomerular basement membrane. The expression of Sirt6 and PI3K/AKT pathway components was decreased in db/db mice. UBCS039 increased the expressions of Sirt6 and PI3K/AKT pathway components and ameliorated renal damage in db/db mice. We also observed consistent Sirt6 expression was in HG-induced podocytes in vitro. Activation of the PI3K/AKT pathway via a Sirt6 recombinant plasmid ameliorated podocyte cytoskeletal remodeling and apoptosis in HG-treated immortalized human podocytes in vitro, whereas Sirt6 inhibition by OSS_128167 accelerated HG-induced podocyte damage in vitro.

CONCLUSIONS

Sirt6 protects podocytes against HG-induced cytoskeletal remodeling and apoptosis through activation of the PI3K/AKT signaling pathway. These findings provide evidence supporting the potential efficacy of Sirt6 activation as a promising therapeutic strategy for addressing podocyte injury in DKD.

The SIRT6/BAP1/xCT signaling axis mediates ferroptosis in cisplatin-induced AKI

BACKGROUND

Cisplatin is extensively utilized in clinical settings for treating solid tumors; However, its use is restricted because of the kidney damage caused by side effects. Moreover, currently, no effective medications have been approved to prevent or treat acute kidney injury induced by cisplatin. Our research indicates that sirtuin 6 (SIRT6) can inhibit ferroptosis induced by cisplatin, and the use of SIRT6 agonists can alleviate acute kidney injury caused by cisplatin.

METHODS

An animal model of cisplatin-induced acute kidney injury (AKI) was established, followed by RNA sequencing to identify potential differentially expressed genes (DEGs) and associated pathways. To explore the role of SIRT6 in this model, SIRT6 knockout mice were generated, and recombinant adeno-associated virus was employed to achieve SIRT6 overexpression in the mice. In vitro, cells were cultured in a cisplatin-containing medium to establish a cisplatin-induced cell model. The function of SIRT6 was further investigated by overexpressing or knocking down the gene using lentiviral plasmids. To elucidate the underlying molecular mechanisms, we employed RNA sequencing, performed bioinformatics analyses, and conducted chromatin immunoprecipitation assays.

RESULTS

RNA sequencing and Western blot analyses revealed a significant reduction in SIRT6 expression in mice with cisplatin-induced acute kidney injury (AKI). Enhancing SIRT6 expression improved renal function, reduced ferroptosis, and mitigated kidney damage, whereas SIRT6 knockout exacerbated kidney injury and heightened ferroptosis. Mechanistically, RNA sequencing, bioinformatics analysis, and chromatin immunoprecipitation assays demonstrated that SIRT6 inhibits ferroptosis by reducing the acetylation of histone H4K9ac at the BAP1 promoter. Furthermore, in vitro studies demonstrated that the SIRT6 agonist UBCS039 can alleviate cisplatin-induced acute kidney injury, highlighting its potential therapeutic role in mitigating cisplatin's damaging effects. However, further research is needed to fully elucidate the underlying mechanisms and to validate these findings in vivo.

CONCLUSION

Our findings underscore the critical role of the SIRT6/BAP1/xCT axis in regulating ferroptosis, particularly via the downregulation of SIRT6, in the context of cisplatin-induced acute kidney injury (AKI). This suggests that SIRT6 could be a promising therapeutic target for treating cisplatin-induced AKI. However, additional research is required to explore the specific mechanisms and fully assess the therapeutic potential of SIRT6 in this context.

Sirt6 protects retinal ganglion cells and optic nerve from degeneration during aging and glaucoma

Glaucoma is characterized by the progressive degeneration of retinal ganglion cells (RGCs) and their axons, and its risk increases with aging. Yet comprehensive insights into the complex mechanisms are largely unknown. Here, we found that anti-aging molecule Sirt6 was highly expressed in RGCs. Deleting Sirt6 globally or specifically in RGCs led to progressive RGC loss and optic nerve degeneration during aging, despite normal intraocular pressure (IOP), resembling a phenotype of normal-tension glaucoma. These detrimental effects were potentially mediated by accelerated RGC senescence through Caveolin-1 upregulation and by the induction of mitochondrial dysfunction. In mouse models of high-tension glaucoma, Sirt6 level was decreased after IOP elevation. Genetic overexpression of Sirt6 globally or specifically in RGCs significantly attenuated high tension-induced degeneration of RGCs and their axons, whereas partial or RGC-specific Sirt6 deletion accelerated RGC loss. Importantly, therapeutically targeting Sirt6 with pharmacological activator or AAV2-mediated gene delivery ameliorated high IOP-induced RGC degeneration. Together, our studies reveal a critical role of Sirt6 in preventing RGC and optic nerve degeneration during aging and glaucoma, setting the stage for further exploration of Sirt6 activation as a potential therapy for glaucoma.

Mitochondrial dysfunction in the pathophysiology of renal diseases

Mitochondria are essential organelles in the human body, serving as the metabolic factory of the whole organism. When mitochondria are dysfunctional, it can affect all organs of the body. The kidney is rich in mitochondria, and its function is closely related to the development of kidney diseases. Studying the relationship between mitochondria and kidney disease progression is of great interest. In the past decade, scientists have made inspiring progress in investigating the role of mitochondria in the pathophysiology of renal diseases. This article discusses various mechanisms for maintaining mitochondrial quality, including mitochondrial energetics, mitochondrial biogenesis, mitochondrial dynamics, mitochondrial DNA repair, mitochondrial proteolysis and the unfolded protein response, mitochondrial autophagy, mitochondria-derived vesicles, and mitocytosis. The article also highlights the cross talk between mitochondria and other organelles, with a focus on kidney diseases. Finally, the article concludes with an overview of mitochondria-related clinical research.

Cellular senescence in acute kidney injury: Target and opportunity

Acute kidney injury (AKI) is a common clinical disease with a high incidence and mortality rate. It typically arises from hemodynamic alterations, sepsis, contrast agents, and toxic drugs, instigating a series of events that culminate in tissue and renal damage. This sequence of processes often leads to acute renal impairment, prompting the initiation of a repair response. Cellular senescence is an irreversible arrest of the cell cycle. Studies have shown that renal cellular senescence is closely associated with AKI through several mechanisms, including the promotion of oxidative stress and inflammatory response, telomere shortening, and the down-regulation of klotho expression. Exploring the role of cellular senescence in AKI provides innovative therapeutic ideas for both the prevention and treatment of AKI. Furthermore, it has been observed that targeted removal of senescent cells in vivo can efficiently postpone senescence, resulting in an enhanced prognosis for diseases associated with senescence. This article explores the effects of common anti-senescence drugs senolytics and senostatic and lifestyle interventions on renal diseases, and mentions the rapid development of mesenchymal stem cells (MSCs). These studies have taken senescence-related research to a new level. Overall, this article comprehensively summarizes the studies on cellular senescence in AKI, aiming is to elucidate the relationship between cellular senescence and AKI, and explore treatment strategies to improve the prognosis of AKI.

Functioning and mechanisms of PTMs in renal diseases

Post-translational modifications (PTMs) are crucial epigenetic mechanisms that regulate various cellular biological processes. The use of mass spectrometry (MS)-proteomics has led to the discovery of numerous novel types of protein PTMs, such as acetylation, crotonylation, 2-hydroxyisobutyrylation, β-hydroxybutyrylation, protein propionylation and butyrylation, succinylation, malonylation, lactylation, and histone methylation. In this review, we specifically highlight the molecular mechanisms and roles of various histone and some non-histone PTMs in renal diseases, including diabetic kidney disease. PTMs exhibit diverse effects on renal diseases, which can be either protective or detrimental, depending on the specific type of protein PTMs and their respective targets. Different PTMs activate various signaling pathways in diverse renal pathological conditions, which could provide novel insights for studying epigenetic mechanisms and developing potential therapeutic strategies for renal diseases.

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.

The role of mammalian Sirtuin 6 in cardiovascular diseases and diabetes mellitus

Cardiovascular diseases are severe diseases posing threat to human health because of their high morbidity and mortality worldwide. The incidence of diabetes mellitus is also increasing rapidly. Various signaling molecules are involved in the pathogenesis of cardiovascular diseases and diabetes. Sirtuin 6 (Sirt6), which is a class III histone deacetylase, has attracted numerous attentions since its discovery. Sirt6 enjoys a unique structure, important biological functions, and is involved in multiple cellular processes such as stress response, mitochondrial biogenesis, transcription, insulin resistance, inflammatory response, chromatin silencing, and apoptosis. Sirt6 also plays significant roles in regulating several cardiovascular diseases including atherosclerosis, coronary heart disease, as well as cardiac remodeling, bringing Sirt6 into the focus of clinical interests. In this review, we examine the recent advances in understanding the mechanistic working through which Sirt6 alters the course of lethal cardiovascular diseases and diabetes mellitus.

Yishen Tongluo formula alleviates diabetic kidney disease through regulating Sirt6/TGF-β1/Smad2/3 pathway and promoting degradation of TGF-β1

ETHNOPHARMACOLOGICAL RELEVANCE

Yishen Tongluo formula (YSTLF) is formulated based on traditional Chinese medicine theory for the treatment of Diabetic kidney disease (DKD) and has been shown to be effective in improving the symptoms of DKD according to the clinical observation.

AIM OF THE STUDY

To explore the effect of YSTLF on DKD and figure out whether its effects were due to the regulation Sirt6/TGF-β1/Smad2/3 pathway and promoting degradation of TGF-β1.

MATERIALS AND METHODS

The extract of YSTLF at 1, 2.5 and 5 g/kg was orally administered to C57BLKS/J (db/db) mice for 8 weeks and db/db mice were given valsartan as a positive control. The littermate db/m and db/db mice were given vehicle as the control and model group, respectively. Blood urea nitrogen and serum creatinine were detected and the urinary albumin excretion, urea albumin creatinine ratio was calculated. The histopathological change of renal tissues in each group was determined. Simultaneously, the levels of fibrosis-related proteins and messenger RNA (mRNA) in kidney and high glucose (HG)-induced SV40-MES-13 cells were detected. The roles of YSTLF in regulating of Sirt6/TGF-β1/Smad2/3 signaling pathway were investigated in HG-stimulated SV40-MES-13 cells and validated in db/db mice. Furthermore, the effect of YSTLF on TGF-β1 degradation was investigated in HG-stimulated SV40-MES-13 cells.

RESULTS

YSTLF significantly improved the renal function in DKD mice. YSTLF dose-dependently attenuated pathological changes and suppressed the expression of type I collagen, alpha smooth muscle actin, type IV collagen, and fibronectin in vitro and in vivo, resulting in ameliorating of renal fibrosis. YSTLF positively regulated Sirt6 expression, while inhibited the activating of TGF-β1/Smad2/3 signaling pathway. TGF-β1 was steady expressed in HG-stimulated SV40-MES-13 cells, whereas was continuously degraded under YSTLF treatment.

CONCLUSIONS

YSTLF significantly ameliorates renal damages and fibrosis may via regulating Sirt6/TGF-β1/Smad2/3 signaling pathway as well as promoting the degradation of TGF-β1.

Sodium-Glucose Cotransporter 2 Inhibitors: A Scoping Review of the Positive Implications on Cardiovascular and Renal Health and Dynamics for Clinical Practice

Cardiorenal benefits of sodium-glucose cotransporter 2 inhibitors (SGLT2is) have been demonstrated in patients with type 2 diabetes in multiple trials. We aim to provide a comprehensive review of the role of SGLT2i in cardiovascular disease. Reducing blood glucose to provide more effective vascular function, lowering the circulating volume, reducing cardiac stress, and preventing pathological cardiac re-modeling and function are the mechanisms implicated in the beneficial cardiovascular effects of SGLT2 inhibitors. Treatment with SGLT2i was associated with a decrease in cardiovascular and all-cause mortality, acute heart failure exacerbation hospitalization, and composite adverse renal outcomes. Improved symptoms, better functional status, and quality of life were also seen in heart failure with reduced ejection fraction (HFrEF), heart failure and mildly reduced ejection fraction (HFmrEF), and heart failure with preserved ejection fraction (HFpEF) patients. Recent trials have shown a notable therapeutic benefit of SGLT2is in acute heart failure and also suggest that SGLT2is have the potential to strengthen recovery after acute myocardial infarction (AMI) in percutaneous coronary Intervention (PCI) patients. The mechanism behind the cardio-metabolic and renal-protective effects of SGLT2i is multifactorial. Adverse events may occur with their usage including increased risk of genital infections, diabetic ketoacidosis, and perhaps limited amputations; however, all of them are preventable. Overall, SGLT2i clearly has many beneficial effects, and the benefits of using SGLT2i by far outweigh the risks.

Serum SIRT6 Levels Are Associated with Frailty in Older Adults

OBJECTIVES

Frailty is one of the major health problems facing aging societies worldwide. We investigated the association between serum SIRT6 and frailty in older adults.

DESIGN

Cross-sectional analysis of associations of serum SIRT6 and frailty in older people.

SETTING

Enrolled community-dwelling and hospital outpatient clinic adults older than 65 years old in Wuhan City, Hubei Province, China.

PARTICIPANTS

A total of 540 community-dwelling older adults (age ≥ 65 years) in Wuhan were included in the study.

MEASURES

We used Frailty Phenotype criteria for classifying participants based on their frailty status. Serum SIRT6 was measured using an ELISA kit.

RESULTS

A total of 540 older adults were included in this cross-sectional study. Serum SIRT6 was lower in the slowness group (7.23±1.81 vs 5.89±1.74, p<0.001), weakness group (6.87±1.88 vs 5.68±1.64, p<0.001), and exhaustion group (6.73±1.90 vs 5.88±1.74, p<0.001) compare with the normal group. ROC curves were used to assess the efficiency of SIRT6 in predicting frailty in older adults. The AUC for SIRT6 was 0.792 (95% CI: 0.7514 to 0.8325), with the highest sensitivity of 68.0% and the specificity of 91.9%, and the optimal critical value of 4.65ng/ml according to Youden's index. Multivariate logistic regression analysis showed that serum SIRT6 level was independently associated with frailty in older people.

CONCLUSION

In conclusion, serum SIRT6 was decreased in frailty compared with robust older adults. A decreased serum SIRT6 was independently associated with an increased risk of frailty. SIRT6 may be a potential target for the treatment of patients with frailty.

Improvement of oocyte quality through the SIRT signaling pathway

Background

Oocyte quality is one of the major deciding factors in female fertility competence.

Methods

PubMed database was searched for reviews by using the following keyword "oocyte quality" AND "Sirtuins". The methodological quality of each literature review was assessed using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2020 statement.

Main Findings

Oxidative stress has been recognized as the mechanism attenuating oocyte quality. Increasing evidence from animal experiments and clinical studies has confirmed the protective roles of the sirtuin family in improving oocyte quality via an antioxidant effect.

Conclusion

The protective roles in the oocyte quality of the sirtuin family have been increasingly recognized.

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.

SIRT6 overexpression retards renal interstitial fibrosis through targeting HIPK2 in chronic kidney disease

Introduction: Renal interstitial fibrosis is a common pathophysiological change in the chronic kidney disease (CKD). Nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin 6 (SIRT6) is demonstrated to protect against kidney injury. Vitamin B3 is the mostly used form of NAD precursors. However, the role of SIRT6 overexpression in renal interstitial fibrosis of CKD and the association between dietary vitamin B3 intake and renal function remain to be elucidated.

Methods: Wild-type (WT) and SIRT6-transgene (SIRT6-Tg) mice were given with high-adenine diets to establish CKD model. HK2 cells were exposed to transforming growth factor β1 (TGF-β1) in vitro to explore related mechanism. Population data from Multi-Ethnic Study of Atherosclerosis (MESA) was used to examine the association between dietary vitamin B3 intake and renal function decline.

Results: Compared to WT mice, SIRT6-Tg mice exhibited alleviated renal interstitial fibrosis as evidenced by reduced collagen deposit, collagen I and α-smooth muscle actin expression. Renal function was also improved in SIRT6-Tg mice. Homeodomain interacting protein kinase 2 (HIPK2) was induced during the fibrogenesis in CKD, while HIPK2 was downregulated after SIRT6 overexpression. Further assay in vitro confirmed that SIRT6 depletion exacerbated epithelial-to-mesenchymal transition of HK2 cells, which might be linked with HIPK2 upregulation. HIPK2 was inhibited by SIRT6 in the post-transcriptional level. Population study indicated that higher dietary vitamin B3 intake was independently correlated with a lower risk of estimate glomerular filtration rate decline in those ≥65 years old during follow-up.

Conclusion: SIRT6/HIPK2 axis serves as a promising target of renal interstitial fibrosis in CKD. Dietary vitamin B3 intake is beneficial for renal function in the old people.

Interaction Between Intrinsic Renal Cells and Immune Cells in the Progression of Acute Kidney Injury

A growing number of studies have confirmed that immune cells play various key roles in the pathophysiology of acute kidney injury (AKI) development. After the resident immune cells and intrinsic renal cells are damaged by ischemia and hypoxia, drugs and toxins, more immune cells will be recruited to infiltrate through the release of chemokines, while the intrinsic cells promote macrophage polarity conversion, and the immune cells will promote various programmed deaths, phenotypic conversion and cycle arrest of the intrinsic cells, ultimately leading to renal impairment and fibrosis. In the complex and dynamic immune microenvironment of AKI, the bidirectional interaction between immune cells and intrinsic renal cells affects the prognosis of the kidney and the progression of fibrosis, and determines the ultimate fate of the kidney.

Sirtuins and Hypoxia in EMT Control

Epithelial–mesenchymal transition (EMT), a physiological process during embryogenesis, can become pathological in the presence of different driving forces. Reduced oxygen tension or hypoxia is one of these forces, triggering a large number of molecular pathways with aberrant EMT induction, resulting in cancer and fibrosis onset. Both hypoxia-induced factors, HIF-1α and HIF-2α, act as master transcription factors implicated in EMT. On the other hand, hypoxia-dependent HIF-independent EMT has also been described. Recently, a new class of seven proteins with deacylase activity, called sirtuins, have been implicated in the control of both hypoxia responses, HIF-1α and HIF-2α activation, as well as EMT induction. Intriguingly, different sirtuins have different effects on hypoxia and EMT, acting as either activators or inhibitors, depending on the tissue and cell type. Interestingly, sirtuins and HIF can be activated or inhibited with natural or synthetic molecules. Moreover, recent studies have shown that these natural or synthetic molecules can be better conveyed using nanoparticles, representing a valid strategy for EMT modulation. The following review, by detailing the aspects listed above, summarizes the interplay between hypoxia, sirtuins, and EMT, as well as the possible strategies to modulate them by using a nanoparticle-based approach.

Signaling pathways of chronic kidney diseases, implications for therapeutics

Chronic kidney disease (CKD) is a chronic renal dysfunction syndrome that is characterized by nephron loss, inflammation, myofibroblasts activation, and extracellular matrix (ECM) deposition. Lipotoxicity and oxidative stress are the driving force for the loss of nephron including tubules, glomerulus, and endothelium. NLRP3 inflammasome signaling, MAPK signaling, PI3K/Akt signaling, and RAAS signaling involves in lipotoxicity. The upregulated Nox expression and the decreased Nrf2 expression result in oxidative stress directly. The injured renal resident cells release proinflammatory cytokines and chemokines to recruit immune cells such as macrophages from bone marrow. NF-κB signaling, NLRP3 inflammasome signaling, JAK-STAT signaling, Toll-like receptor signaling, and cGAS-STING signaling are major signaling pathways that mediate inflammation in inflammatory cells including immune cells and injured renal resident cells. The inflammatory cells produce and secret a great number of profibrotic cytokines such as TGF-β1, Wnt ligands, and angiotensin II. TGF-β signaling, Wnt signaling, RAAS signaling, and Notch signaling evoke the activation of myofibroblasts and promote the generation of ECM. The potential therapies targeted to these signaling pathways are also introduced here. In this review, we update the key signaling pathways of lipotoxicity, oxidative stress, inflammation, and myofibroblasts activation in kidneys with chronic injury, and the targeted drugs based on the latest studies. Unifying these pathways and the targeted therapies will be instrumental to advance further basic and clinical investigation in CKD.