DNA methyltransferase 1 may be a therapy target for attenuating diabetic nephropathy and podocyte injury

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 kidney 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.

Transcription factor specificity protein (SP) family in renal physiology and diseases

Dysregulated specificity proteins (SPs), members of the C2H2 zinc-finger family, are crucial transcription factors (TFs) with implications for renal physiology and diseases. This comprehensive review focuses on the role of SP family members, particularly SP1 and SP3, in renal physiology and pathology. A detailed analysis of their expression and cellular localization in the healthy human kidney is presented, highlighting their involvement in fatty acid metabolism, electrolyte regulation, and the synthesis of important molecules. The review also delves into the diverse roles of SPs in various renal diseases, including renal ischemia/reperfusion injury, diabetic nephropathy, renal interstitial fibrosis, and lupus nephritis, elucidating their molecular mechanisms and potential as therapeutic targets. The review further discusses pharmacological modulation of SPs and its implications for treatment. Our findings provide a comprehensive understanding of SPs in renal health and disease, offering new avenues for targeted therapeutic interventions and precision medicine in nephrology.

Diosgenin Improves Lipid Metabolism in Diabetic Nephropathy via Regulation of miR-148b-3p/DNMT1/FOXO1 Axis

BACKGROUND

The progression of diabetic nephropathy (DN) is closely associated with lipid accumulation. Diosgenin (Dio) plays a beneficial role in the lipid metabolism associated with multiple diseases. Thus, the mechanism underlying Dio's function in DN associated with aberrant lipid accumulation warrants further investigation.

METHODS

To model DN in vitro, HK-2 cells were treated with high glucose (HG) and palmitic acid. Cell viability was evaluated using MTT assay. The triglyceride (TG) content in HK-2 cells was measured using a commercial assay kit. The formation of lipid droplets in HK-2 cells was observed using Oil Red O staining. The expression levels of mRNA and protein were detected using RT-qPCR and Western blot, respectively. The DNA methylation of FOXO1 was assessed using MSP. The interaction between DNMT1 and the FOXO1 promoter was confirmed by ChIP assay.

RESULTS

Dio treatment reduced TG levels and lipid droplet formation in HK-2 cells co-treated with HG and palmitic acid. Simultaneously, the levels of miR-148b-3p and FOXO1 were increased by Dio, while Dio decreased the expression levels of DNMT1 and SREBP-2. Meanwhile, miR-148b-3p can bind to DNMT1, which in turn inhibits the expression of FOXO1 by mediating the DNA methylation of FOXO1. In addition, FOXO1 negatively regulates the expression of SREBP-2 by interacting with the SREBP-2 promoter. MiR-148b-3p inhibition or silencing of FOXO1 abolished the inhibitory effect of Dio on TG production and lipid droplet formation. This effect was further exacerbated by the downregulation of DNMT1. FOXO1 overexpression may counteract the promotive effects of miR-148b-3p inhibitor on lipid accumulation.

CONCLUSIONS

Dio treatment reduced TG production and lipid droplet formation in HK-2 cells during the progression of DN by modulating the miR-148b-3p/DNMT1/FOXO1/SREBP-2 axis. This finding provides new evidence supporting the therapeutic potential of Dio for DN.

DNA damage-induced AIM2 pyroptosis in high glucose-induced proximal tubular epithelial cell

Pyroptosis is one of the ways to cause proximal tubular epithelial cell death in diabetic nephropathy (DN), but the exact mechanism remains unclear. Absent in melanoma 2 (AIM2), a sensor for double-stranded DNA, creates an inflammasome that triggers the cleavage of gasdermin D (GSDMD), leading to a type of inflammatory cell death called pyroptosis. This study investigated the role of AIM2 in pyroptosis within proximal tubular epithelial cells in DN. We observed significantly elevated AIM2 expression in renal tubules from DN patients and db/db mice, as well as in high glucose (HG)-induced Human Kidney-2 (HK2) cells. Besides, increased AIM2 expression was accompanied by activation of the pyroptosis pathway (cleaved-caspase-1, GSDMD-FL, GSDMD-NT) in the renal cortex of db/db mice and HG-induced HK2 cells in vitro. Knocking down GSDMD can reduce HG-induced HK2 cell death, indicating that HG triggers pyroptosis in HK2 cells. Furthermore, HG-induced pyroptosis was mitigated in HK2 cells with AIM2 knockdown using siRNA. Additionally, reducing ROS levels using NAC was able to attenuate HG-induced HK2 cells DNA damage, AIM2 activation, and pyroptosis. Notably, AIM2 upregulation was observed in renal biopsies from DN patients, with expression levels positively correlating with serum creatinine and inversely with estimated glomerular filtration rate (eGFR). Collectively, DNA damage caused by HG could result in the activation of the AIM2 inflammasome, leading to the pyroptosis of proximal tubular epithelial cells, indicating that targeting AIM2 could be a potential novel approach for treating DN.

Inhibition of SGLT2 protects podocytes in diabetic kidney disease by rebalancing mitochondria-associated endoplasmic reticulum membranes

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have changed the therapeutic landscape for diabetic kidney disease (DKD) patients, but their underlying mechanisms are complicated and not fully understood. Mitochondria-associated endoplasmic reticulum membranes (MAMs), the dynamic contact sites between mitochondria and the endoplasmic reticulum (ER), serve as intracellular platforms important for regulating cellular fate and function. This study explored the roles and mechanisms of SGLT2 inhibitors in regulating MAMs formation in diabetic podocytes.

METHODS

We assessed MAMs formation in podocytes from DKD patients' renal biopsy samples and induced an increase in MAMs formation in cultured human podocytes by transfecting OMM-ER linker plasmid to investigate the effects of MAMs imbalance on podocyte injury. Empagliflozin-treated diabetic mice and podocyte-specific SGLT2 knockout diabetic mice (diabetic states were induced by streptozotocin and a high-fat diet), empagliflozin-treated podocytes, SGLT2-downregulated podocytes, and SGLT2-overexpressing podocytes were used to investigate the effects and mechanisms of SGLT2 inhibitors on MAMs formation in diabetic podocytes.

RESULTS

MAMs were increased in podocytes and were associated with renal dysfunction in DKD patients. Increased MAMs aggravated HG-induced podocyte injury. The expression of SGLT2 was increased in diabetic podocytes. In addition, empagliflozin-treatment and podocyte-specific SGLT2 knockout attenuated MAMs formation and podocyte injury in diabetic mice. Empagliflozin treatment and SGLT2 knockdown decreased podocyte MAMs formation by activating the AMP-activated protein kinase (AMPK) pathway, while SGLT2 overexpression had the opposite effect.

CONCLUSIONS

Inhibition of SGLT2 attenuates MAMs imbalance in diabetic podocytes by activating the AMPK pathway. This study expands our knowledge of the roles of SGLT2 inhibitors in improving DKD podocyte injury and provides new insights into DKD treatment.

Epigenetic DNA Methylation and Protein Homocysteinylation: Key Players in Hypertensive Renovascular Damage

Hypertension has been a threat to the health of people, the mechanism of which, however, remains poorly understood. It is clinically related to loss of nephron function, glomerular sclerosis, or necrosis, resulting in renal functional declines. The mechanisms underlying hypertension's development and progression to organ damage, including hypertensive renal damage, remain to be fully elucidated. As a developing approach, epigenetics has been postulated to elucidate the phenomena that otherwise cannot be explained by genetic studies. The main epigenetic hallmarks, such as DNA methylation, histone acetylation, deacetylation, noncoding RNAs, and protein N-homocysteinylation have been linked with hypertension. In addition to contributing to endothelial dysfunction and oxidative stress, biologically active gases, including NO, CO, and H2S, are crucial regulators contributing to vascular remodeling since their complex interplay conducts homeostatic functions in the renovascular system. Importantly, epigenetic modifications also directly contribute to the pathogenesis of kidney damage via protein N-homocysteinylation. Hence, epigenetic modulation to intervene in renovascular damage is a potential therapeutic approach to treat renal disease and dysfunction. This review illustrates some of the epigenetic hallmarks and their mediators, which have the ability to diminish the injury triggered by hypertension and renal disease. In the end, we provide potential therapeutic possibilities to treat renovascular diseases in hypertension.

Magnolol Inhibits High Fructose-Induced Podocyte Inflammation via Downregulation of TKFC/Sp1/HDAC4/Notch1 Activation

BACKGROUND/OBJECTIVES

High fructose has been implicated as an important trigger of kidney inflammation in patients and experimental models. Magnolol, isolated from Magnolia officinalis, has an anti-inflammatory effect, but its protective role in podocytes remains underexplored. This study explored the protective effects and underlying mechanism of magnolol against high fructose-induced podocyte inflammation.

METHODS

The effects of magnolol on high fructose-induced podocyte inflammation were assessed in male Sprague Dawley rats administered 10% (w/v) fructose water for 12 weeks and heat-sensitive human podocyte cell lines (HPCs) exposed to 5 mM fructose. Podocyte foot processes were examined using transmission electron microscopy. The expression levels of nephrin, podocin, tumor necrosis factor-α (TNF-α), Notch1 intracellular domain (NICD1), triokinase/FMN cyclase (TKFC), specificity protein 1 (Sp1) and histone deacetylase 4 (HDAC4) were determined by Western blot, immunofluorescence and real-time quantitative polymerase chain reaction (qRT-PCR). The chromatin immunoprecipitation (ChIP) assay was performed to evaluate the interaction between Sp1 and the promoter region of HDAC4.

RESULTS

Magnolol mitigated the impairment of glomerular filtration function in high fructose-fed rats. Besides, it significantly alleviated the inflammatory responses in glomeruli and HPCs, evidenced by decreased protein levels of TNF-α and NICD1. Increased protein levels of TKFC, Sp1 and HDAC4 were observed in high fructose-stimulated HPCs and rat glomeruli. TMP195, an HDAC4 inhibitor, reduced TNF-α and NICD1 protein levels in high fructose-exposed HPCs. The increased Sp1 was shown to associate with the promoter region of HDAC4, promoting HDAC4 protein expression in high fructose-exposed HPCs. The knockdown of TKFC in HPCs by TKFC siRNA decreased Sp1, HDAC4 and NICD1 protein levels, alleviating podocyte inflammatory response. Furthermore, magnolol inhibited TKFC/Sp1/HDAC4/Notch1 activation in vivo and in vitro.

CONCLUSIONS

Magnolol attenuated high fructose-induced podocyte inflammation possibly through the suppression of TKFC/Sp1/HDAC4/Notch1 activation, providing new evidence for its potential role in podocyte protection.

Molecular mechanisms of diabetic nephropathy: A narrative review

Diabetic nephropathy (DN) is the predominant secondary nephropathy resulting in global end-stage renal disease. It is attracting significant attention in both domestic and international research due to its widespread occurrence, fast advancement, and limited choices for prevention and treatment. The pathophysiology of this condition is intricate and involves multiple molecular and cellular pathways at various levels. This article provides a concise overview of the molecular processes involved in the development of DN. It discusses various factors, such as signaling pathways, cytokines, inflammatory responses, oxidative stress, cellular damage, autophagy, and epigenetics. The aim is to offer clinicians a valuable reference for DN's diagnosis, treatment, and intervention.

DNMT1-Mediated the Downregulation of FOXF1 Promotes High Glucose-induced Podocyte Damage by Regulating the miR-342-3p/E2F1 Axis

Podocyte damage plays a crucial role in the occurrence and development of diabetic nephropathy (DN). Accumulating evidence suggests that dysregulation of transcription factors plays a crucial role in podocyte damage in DN. However, the biological functions and underlying mechanisms of most transcription factors in hyperglycemia-induced podocytes damage remain largely unknown. Through integrated analysis of data mining, bioinformatics, and RT-qPCR validation, we identified a critical transcription factor forkhead box F1 (FOXF1) implicated in DN progression. Moreover, we discovered that FOXF1 was extensively down-regulated in renal tissue and serum from DN patients as well as in high glucose (HG)-induced podocyte damage. Meanwhile, our findings showed that FOXF1 might be a viable diagnostic marker for DN patients. Functional experiments demonstrated that overexpression of FOXF1 strikingly enhanced proliferation, outstandingly suppressed apoptosis, and dramatically reduced inflammation and fibrosis in HG-induced podocytes damage. Mechanistically, we found that the downregulation of FOXF1 in HG-induced podocyte damage was caused by DNMT1 directly binding to FOXF1 promoter and mediating DNA hypermethylation to block FOXF1 transcriptional activity. Furthermore, we found that FOXF1 inhibited the transcriptional expression of miR-342-3p by binding to the promoter of miR-342, resulting in reduced sponge adsorption of miR-342-3p to E2F1, promoting the expression of E2F1, and thereby inhibiting HG-induced podocytes damage. In conclusion, our findings showed that blocking the FOXF1/miR-342-3p/E2F1 axis greatly alleviated HG-induced podocyte damage, which provided a fresh perspective on the pathogenesis and therapeutic strategies for DN patients.

Hypermethylation leads to the loss of HOXA5, resulting in JAG1 expression and NOTCH signaling contributing to kidney fibrosis

Epigenetic regulations, including DNA methylation, are critical to the development and progression of kidney fibrosis, but the underlying mechanisms remain elusive. Here, we show that fibrosis of the mouse kidney was associated with the induction of DNA methyltransferases and increases in global DNA methylation and was alleviated by the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-Aza). Genome-wide analysis demonstrated the hypermethylation of 94 genes in mouse unilateral ureteral obstruction kidneys, which was markedly reduced by 5-Aza. Among these genes, Hoxa5 was hypermethylated at its gene promoter, and this hypermethylation was associated with reduced HOXA5 expression in fibrotic mouse kidneys after ureteral obstruction or unilateral ischemia-reperfusion injury. 5-Aza prevented Hoxa5 hypermethylation, restored HOXA5 expression, and suppressed kidney fibrosis. Downregulation of HOXA5 was verified in human kidney biopsies from patients with chronic kidney disease and correlated with the increased kidney fibrosis and DNA methylation. Kidney fibrosis was aggravated by conditional knockout of Hoxa5 and alleviated by conditional knockin of Hoxa5 in kidney proximal tubules of mice. Mechanistically, we found that HOXA5 repressed Jag1 transcription by directly binding to its gene promoter, resulting in the suppression of JAG1-NOTCH signaling during kidney fibrosis. Thus, our results indicate that loss of HOXA5 via DNA methylation contributes to fibrogenesis in kidney diseases by inducing JAG1 and consequent activation of the NOTCH signaling pathway.

Epigallocatechin-3-gallate attenuates arsenic-induced fibrogenic changes in human kidney epithelial cells through reversal of epigenetic aberrations and antioxidant activities

Renal fibrosis is a pathogenic intermediate stage of chronic kidney disease (CKD). Nephrotoxicants including arsenic can cause kidney fibrosis through induction of oxidative stress and epigenetic aberrations. Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, is known to have antioxidant and epigenetic modulation properties. Whether EGCG, through its antioxidant and epigenetic modulating activities, can attenuate fibrogenesis is not known. Therefore, the objective of this study was to determine whether EGCG can attenuate arsenic-induced acute injury and long-term exposure associated fibrogenicity in kidney epithelial cells. To address this question, two human kidney epithelial cell lines Caki-1 and HK-2 exposed to arsenic for both acute and long-term durations were treated with EGCG. The protective effect of EGCG on arsenic-induced cytotoxicity and fibrogenicity were evaluated by measuring the cell growth, reactive oxygen species (ROS) production, genes expression, and epigenetic changes in histone marks. Results revealed that EGCG has a protective effect in arsenic-induced acute cytotoxicity in these cells. EGCG scavenges the increased levels of ROS in arsenic exposed cells. Aberrant expression of fibrogenic genes in arsenic exposed cells were restored by EGCG. Abrogation of arsenic-induced fibrogenic changes was also associated with EGCG-mediated restoration of arsenic-induced aberrant expression of epigenetic regulatory proteins and histone marks. Novel findings of this study suggest that EGCG, through its antioxidant and epigenetic modulation capacities, has protective effects against arsenic-induced cytotoxicity and fibrogenic changes in kidney epithelial cells.

Nucleic acid and protein methylation modification in renal diseases

Although great efforts have been made to elucidate the pathological mechanisms of renal diseases and potential prevention and treatment targets that would allow us to retard kidney disease progression, we still lack specific and effective management methods. Epigenetic mechanisms are able to alter gene expression without requiring DNA mutations. Accumulating evidence suggests the critical roles of epigenetic events and processes in a variety of renal diseases, involving functionally relevant alterations in DNA methylation, histone methylation, RNA methylation, and expression of various non-coding RNAs. In this review, we highlight recent advances in the impact of methylation events (especially RNA m6A methylation, DNA methylation, and histone methylation) on renal disease progression, and their impact on treatments of renal diseases. We believe that a better understanding of methylation modification changes in kidneys may contribute to the development of novel strategies for the prevention and management of renal diseases.

Long non-coding RNAs as emerging regulators of miRNAs and epigenetics in diabetes-related chronic kidney disease

Diabetes is one of the major cause of chronic kidney disease (CKD), including "diabetic nephropathy," and is an increasingly prevalent accelerator of the progression of non-diabetic forms of CKD. The long non-coding RNAs (lncRNAs) have come into the limelight in the past few years as one of the emerging weapons against CKD in diabetes. Available data over the past few years demonstrate the interaction of lncRNAs with miRNAs and epigenetic machinery. Interestingly, the evolving data suggest that lncRNAs play a vital role in diabetes-associated CKD by regulation of epigenetic enzymes such as DNA methyltransferase, histone deacetylases, and histone methyltransferases. LncRNAs are also engaged in the regulation of several miRNAs in diabetic nephropathy. Hence this review will elaborate on the association between lncRNAs and their interaction with epigenetic regulators involved in different aspects and thus the progression of CKD in diabetes.

DNA hypomethylation of Syk induces oxidative stress and apoptosis via the PKCβ/P66shc signaling pathway in diabetic kidney disease

Epigenetic alterations, especially DNA methylation, have been shown to play a role in the pathogenesis of diabetes mellitus (DM) and its complications, including diabetic kidney disease (DKD). Spleen tyrosine kinase (Syk) is known to be involved in immune and inflammatory disorders. We, therefore, investigated the possible involvement of Syk promoter methylation in DKD, and the mechanisms underlying this process. Kidney tissues were obtained from renal biopsies of patients with early and advanced DKD. A diabetic mouse model (ApoE-/- DM) was generated from ApoE knockout (ApoE-/-) mice using a high-fat and high-glucose diet combined with low-dose streptozocin intraperitoneal injection. We also established an in vitro model using HK2 cells. A marked elevation in the expression levels of Syk, PKCβ, and P66shc in renal tubules was observed in patients with DKD. In ApoE-/- DM mice, Syk expression and the binding of Sp1 to the Syk gene promoter were both increased in the kidney. In addition, the promoter region of the Syk gene exhibited hypomethylation. Syk inhibitor (R788) intervention improved renal function and alleviated pathologic changes in ApoE-/- DM mice. Moreover, R788 intervention alleviated oxidative stress and apoptosis and downregulated the expression of PKCβ/P66shc signaling pathway proteins. In HK2 cells, oxLDL combined with high-glucose stimulation upregulated Sp1 expression in the nucleus (compared with control and oxLDL groups), and this was accompanied by an increase in the binding of Sp1 to the Syk gene promoter. SP1 silencing downregulated the expression of Syk and inhibited the production of reactive oxygen species and cell apoptosis. Finally, PKC agonist intervention reversed the oxidative stress and apoptosis induced by Syk inhibitor (R406). In DKD, hypomethylation at the Syk gene promoter was accompanied by an increase in Sp1 binding at the promoter. As a consequence of this enhanced Sp1 binding, Syk gene expression was upregulated. Syk inhibitors could attenuate DKD-associated oxidative stress and apoptosis via downregulation of PKCβ/P66shc signaling pathway proteins. Together, our results identify Syk as a promising target for intervention in DKD.

Hepatitis B virus-targeting sodium taurocholate cotransporting polypeptide mediates HBV infection and damage in human renal podocytes

Hepatitis B virus (HBV) may directly infect human podocytes (HPCs). However, the mechanism of direct infection is unclear. We found that HPCs express sodium taurocholate cotransporting polypeptide (NTCP), a specific receptor for HBV entry into hepatocytes. Thus, we investigated whether NTCP mediates HBV infection and damage in HPCs and further clarified the specific mechanism. We constructed shRNA-NTCP1,2, shRNA-NC, WT-NTCP, and MUT-NTCP and transfected them into HPCs. HPCs were infected with HBV, and HBV infection markers were detected by enzyme-linked immunosorbent assay (ELISA) and real-time quantitative PCR (RT-qPCR). The functional changes in HPCs were detected by Transwell migration and scratch assays, apoptosis was evaluated by flow cytometry (FCM), and podocytoskeletal proteins (nephrin, CD2AP, and synaptopodin) were determined by western blotting (WB). Compared with the control HPCs, HPCs infected with HBV showed increased levels of HBV infection markers and apoptosis along with decreased podocytoskeletal protein expressions, cell vitality, proliferation, and migration. Compared with the HPCs infected with HBV, the HPCs transfected with HBV + shRNA-NTCP, and HBV + MUT-NTCP showed decreased levels of HBV infection markers and apoptosis along with increased podocytoskeletal protein expressions, cell vitality, proliferation, and migration; the opposite effects were observed in the HPCs transfected with HBV + WT-NTCP. Overall, the changes to NTCP affected the susceptibility of HPCs to HBV and modulated HPC damage and repair. NTCP can mediate direct HBV infection and damage human podocytes, and the NTCP 157-165 locus is the main site of HBV entry. The findings provide a new target and theoretical basis for HBV-associated glomerulonephritis.

IMPORTANCE

This study identified for the first time that sodium taurocholate cotransporting polypeptide (NTCP) can mediate HBV direct infection and damage to human podocytes, and the NTCP157-165 locus is the main HBV entry site. The findings provide theoretical support for the pathogenesis of direct infection of HBV with kidney tissue. The findings provide a new target and theoretical basis for the treatment of HBV-related glomerulonephritis (HBV-GN). Blocking NTCP is a new target for the treatment of HBV-GN. We found that tacrolimus, a calcineurin inhibitor that blocks NTCP, can effectively treat HBV-GN. This study also provides a theoretical basis for the effective and safe treatment of immunosuppressant tacrolimus for HBV-GN.

Metabolic memory: mechanisms and diseases

Metabolic diseases and their complications impose health and economic burdens worldwide. Evidence from past experimental studies and clinical trials suggests our body may have the ability to remember the past metabolic environment, such as hyperglycemia or hyperlipidemia, thus leading to chronic inflammatory disorders and other diseases even after the elimination of these metabolic environments. The long-term effects of that aberrant metabolism on the body have been summarized as metabolic memory and are found to assume a crucial role in states of health and disease. Multiple molecular mechanisms collectively participate in metabolic memory management, resulting in different cellular alterations as well as tissue and organ dysfunctions, culminating in disease progression and even affecting offspring. The elucidation and expansion of the concept of metabolic memory provides more comprehensive insight into pathogenic mechanisms underlying metabolic diseases and complications and promises to be a new target in disease detection and management. Here, we retrace the history of relevant research on metabolic memory and summarize its salient characteristics. We provide a detailed discussion of the mechanisms by which metabolic memory may be involved in disease development at molecular, cellular, and organ levels, with emphasis on the impact of epigenetic modulations. Finally, we present some of the pivotal findings arguing in favor of targeting metabolic memory to develop therapeutic strategies for metabolic diseases and provide the latest reflections on the consequences of metabolic memory as well as their implications for human health and diseases.

Methylation of eNOS in the rat penile corpus cavernosum under different pathological states and its relationship with erectile function

BACKGROUND

It has been shown that methylation in the promoter region of eNOS can downregulate eNOS expression resulting in the endothelial dysfunction. However, it is unclear whether low androgen levels and type 1 diabetes cause ED by methylating the promoter region of eNOS in the penile corpus cavernosum.

OBJECTIVE

To clarify the effects of type 1 diabetes and hypo-androgen status on the methylation level of the promoter region of the eNOS gene in penile cavernous tissue and their relationship with the erectile function.

METHODS

Fifty-eight eight-week-old male Sprague-Dawley rats were randomly divided into six groups (n = 6): sham operation group, castration group, castration+testosterone (cast+T) group, normoglycemia group, diabetic group, and diabetic+methyltransferase inhibitor (5-aza-dc, 1.5 mg/kg) group. The ICPmax/MAP, serum T, the concentration of nitric oxide (NO), the expression of DNMT1, DNMT3a, DNMT3b, and eNOS, and the methylation level of the eNOS promoter region in penile corpus cavernosum of rat were examined 4 weeks after surgery in the sham-operated group, the castration group, and the castration + testosterone replacement group. Those tests were examined after 6 weeks using of methylation inhibitors in the normoglycemic group, the diabetic group, and the diabetic + methylation inhibitor group.

RESULTS

ICPmax/MAP, DNMT1, DNMT3a, DNMT3b, eNOS, and NO levels were significantly lower in castrated rats than in sham and cast+T rats (P < 0.05). ICPmax/MAP, eNOS, and NO levels were lower, and DNMT1, DNMT3a, and DNMT3b expression levels were significantly increased in the diabetic group compared with the normoglycemic and diabetic+methyltransferase inhibitor groups (P < 0.05). There was no significant difference in the methylation level of the promoter region of eNOS in penile cavernous tissue of castrated rats compared with the sham group or the testosterone replacement group. The methylation level of the promoter region of eNOS in penile cavernous tissue was significantly higher in the diabetic group than in the normoglycemic group and diabetic+methyltransferase inhibitor group (P < 0.05).

CONCLUSION

Although low androgen status inhibited the level of methyltransferase in rat penile cavernous tissue, did not affect the level of methylation in the promoter region of eNOS. Hyperglycemia inhibits the NO level in the penile cavernous tissue and the erectile function of rats by upregulating the methyltransferase level in the penile cavernous tissue and the methylation level in the promoter region of eNOS. Methylation inhibitors can partly improve the erectile function in type 1 diabetic rats.

Role of Epigenetic Changes in the Pathophysiology of Diabetic Kidney Disease

Background

Diabetic kidney disease (DKD) is a global health issue. Epigenetic changes play an important role in the pathogenesis of this disease.

Summary

DKD is currently the leading cause of kidney failure worldwide. Although much is known about the pathophysiology of DKD, the research field of epigenetics is relatively new. Several recent studies have demonstrated that diabetes-induced dysregulation of epigenetic mechanisms alters the expression of pathological genes in kidney cells. If these changes persist for a long time, the so-called "metabolic memory" could be established. In this review, we highlight diabetes-induced epigenetic modifications associated with DKD. While there is a substantial amount of literature on epigenetic changes, only a few studies describe the underlying molecular mechanisms. Detailed analyses have shown that epigenetic changes play an important role in known pathological features of DKD, such as podocyte injury, fibrosis, accumulation of extracellular matrix, or oxidative injury, all of which contribute to the pathophysiology of disease. The transforming growth factor-β plays a key role as it is involved in all-mentioned epigenetic types of regulation.

Key Messages

Epigenetic is crucial for the development and progression of DKD, but the detailed molecular mechanisms have to be further analyzed more in detail.

Targeting DNA methylation in diabetic kidney disease: A new perspective

Diabetic kidney disease (DKD) is a leading diabetic complication causing significant mortality among people around the globe. People with poor glycemic control accompanied by hyperinsulinemia, dyslipidemia, hypertension, and obesity develop diabetic complications. These diabetic patients develop epigenetic changes and suffer from diabetic kidney complications even after subsequent glucose control, the phenomenon that is recognized as metabolic memory. DNA methylation is an essential epigenetic modification that contributes to the development and progression of several diabetic complications, including DKD. The aberrant DNA methylation pattern at CpGs sites within several genes, such as mTOR, RPTOR, IRS2, GRK5, SLC27A3, LCAT, and SLC1A5, associated with the accompanying risk factors exacerbate the DKD progression. Although drugs such as azacytidine and decitabine have been approved to target DNA methylation for diseases such as hematological malignancies, none have been approved for the treatment of DKD. More importantly, no DNA hypomethylation-targeting drugs have been approved for any disease conditions. Understanding the alteration in DNA methylation and its association with the disease risk factors is essential to target DKD effectively. This review has discussed the abnormal DNA methylation pattern and the kidney tissue-specific expression of critical genes involved in DKD onset and progression. Moreover, we also discuss the new possible therapeutic approach that can be exploited for treating DNA methylation aberrancy in a site-specific manner against DKD.

MiR-29b modulates DNA methylation in promoter region of miR-130b in mouse model of Diabetic nephropathy

Epigenetic modifications play a role in Diabetic Nephropathy (DN). Downregulation of miR-29b leads to modulation of DNA methylation via DNA methyl transferases (DNMTs) and hence exaggerated renal fibrosis in DN. Therefore, the main aim of the study was to evaluate effect of miR-29b expression in vivo on DNMTs, renal fibrosis, glomerular and tubular damage as well as renal morphology in DN. In order to explore the role of miR-29b in DNA methylation of other miRNAs, methylation profiling study was performed. It revealed that miR-29b was involved in methylation on of miR-130b on the cytosine guanine dinucleotides rich DNA (CpG) island 1 located on promoter region. In conclusion, miR-29b expression was found to modulate DNA methylation via DNMTs and regulate methylation of miR-130b. The result of this study provides a future direction to unveil role of miRNA expression in DNA methylation and its consequent effect on other miRNAs in DN.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01208-2.

Sex-specific epigenetic programming in renal fibrosis and inflammation

The growing prevalence of hypertension, heart disease, diabetes, and obesity along with an aging population is leading to a higher incidence of renal diseases in society. Chronic kidney disease (CKD) is characterized mainly by persistent inflammation, fibrosis, and gradual loss of renal function leading to renal failure. Sex is a known contributor to the differences in incidence and progression of CKD. Epigenetic programming is an essential regulator of renal physiology and is critically involved in the pathophysiology of renal injury and fibrosis. Epigenetic signaling integrates intrinsic and extrinsic signals onto the genome, and various environmental and hormonal stimuli, including sex hormones, which regulate gene expression and downstream cellular responses. The most extensively studied epigenetic alterations that play a critical role in renal damage include histone modifications and DNA methylation. Notably, these epigenetic alterations are reversible, making them candidates for potential therapeutic targets for the treatment of renal diseases. Here, we will summarize the current knowledge on sex differences in epigenetic modulation of renal fibrosis and inflammation and highlight some possible epigenetic therapeutic strategies for CKD treatment.

Dietary flavonoids prevent diabetes through epigenetic regulation: advance and challenge

The pathophysiology of diabetes has been studied extensively in various countries, but effective prevention and treatment methods are still insufficient. In recent years, epigenetics has received increasing attention from researchers in exploring the etiology and treatment of diabetes. DNA methylation, histone modifications, and non-coding RNAs play critical roles in the occurrence, maintenance, and progression of diabetes and its complications. Therefore, preventing or reversing the epigenetic alterations that occur during the development of diabetes may reduce the individual and societal burden of the disease. Dietary flavonoids serve as natural epigenetic modulators for the discovery of biomarkers for diabetes prevention and the development of alternative therapies. However, there is limited knowledge about the potential beneficial effects of flavonoids on the epigenetics of diabetes. In this review, the multidimensional epigenetic effects of different flavonoid subtypes in diabetes were summarized. Furthermore, it was discussed that parental flavonoid diets might reduce diabetes incidence in offspring, which represent a promising opportunity to prevent diabetes in the future. Future work will depend on exploring anti-diabetic effects of different flavonoids with different epigenetic regulation mechanisms and clinical trials.Highlights• "Epigenetic therapy" could reduce the burden of diabetic patients• "Epigenetic diet" ameliorates diabetes• Targeting epigenetic regulations by dietary flavonoids in the diabetes prevention• Dietary flavonoids prevent diabetes via transgenerational epigenetic inheritance.

Role of TFEB in regulation of the podocyte actin cytoskeleton

Podocyte injury is linked to the pathogenesis and progression of renal disease. The Transcription Factor EB (TFEB), a master regulator of the autophagy and lysosomal pathways, has been found to exert cell- and tissue-specific biological function. To explore TFEB function and underlying mechanisms in podocytes, a total of 4645 differentially expressed genes (DEGs) were detected in TFEB-knockdown mouse podocytes by transcriptome sequencing. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Ingenuity Pathway Analysis showed that, apart from the enrichment in autophagy and lysosomal pathways, DEGs were enriched in cytoskeleton structure (Actin Cytoskeleton, Focal Adhesion, and Adherens Junction), as well as cytoskeleton regulatory molecular signaling (Hippo and Rho GTPase Signaling). In vitro, TFEB knockdown resulted in podocyte cytoskeletal rearrangement, which was disorganized with cortical distribution of actin filaments. Further, TFEB knockdown decreased mRNA and protein levels of Synaptopodin and led to the rearrangement of Synaptopodin. Inhibition of TFEB decreased mRNA levels for proteins involved in actin cytoskeleton dynamics. Moreover, apoptosis was increased by TFEB knockdown in podocyte. In summary, this study initiated a comprehensive analysis of the role of TFEB in podocyte function and the potential underlying mechanisms, and identified a novel role for TFEB in regulation of the podocyte actin cytoskeleton.

Targeting DNA Methylation in Podocytes to Overcome Chronic Kidney Disease

The number of patients with chronic kidney disease (CKD) is on the rise worldwide, and there is urgent need for the development of effective plans against the increasing incidence of CKD. Podocytes, glomerular epithelial cells, are an integral part of the primary filtration unit of the kidney and form a slit membrane as a barrier to prevent proteinuria. The role of podocytes in the pathogenesis and progression of CKD is now recognized. Podocyte function depends on a specialized morphology with the arranged foot processes, which is directly related to their function. Epigenetic changes responsible for the regulation of gene expression related to podocyte morphology have been shown to be important in the pathogenesis of CKD. Although epigenetic mechanisms include DNA methylation, histone modifications, and RNA-based regulation, we have focused on DNA methylation changes because they are more stable than other epigenetic modifications. This review summarizes recent literature about the role of altered DNA methylation in the kidney, especially in glomerular podocytes, focusing on transcription factors and DNA damage responses that are closely associated with the formation of DNA methylation changes.

Differential Methylation of Telomere-Related Genes Is Associated with Kidney Disease in Individuals with Type 1 Diabetes

Diabetic kidney disease (DKD) represents a major global health problem. Accelerated ageing is a key feature of DKD and, therefore, characteristics of accelerated ageing may provide useful biomarkers or therapeutic targets. Harnessing multi-omics, features affecting telomere biology and any associated methylome dysregulation in DKD were explored. Genotype data for nuclear genome polymorphisms in telomere-related genes were extracted from genome-wide case-control association data (n = 823 DKD/903 controls; n = 247 end-stage kidney disease (ESKD)/1479 controls). Telomere length was established using quantitative polymerase chain reaction. Quantitative methylation values for 1091 CpG sites in telomere-related genes were extracted from epigenome-wide case-control association data (n = 150 DKD/100 controls). Telomere length was significantly shorter in older age groups (p = 7.6 × 10^-6). Telomere length was also significantly reduced (p = 6.6 × 10^-5) in DKD versus control individuals, with significance remaining after covariate adjustment (p = 0.028). DKD and ESKD were nominally associated with telomere-related genetic variation, with Mendelian randomisation highlighting no significant association between genetically predicted telomere length and kidney disease. A total of 496 CpG sites in 212 genes reached epigenome-wide significance (p ≤ 10^-8) for DKD association, and 412 CpG sites in 193 genes for ESKD. Functional prediction revealed differentially methylated genes were enriched for Wnt signalling involvement. Harnessing previously published RNA-sequencing datasets, potential targets where epigenetic dysregulation may result in altered gene expression were revealed, useful as potential diagnostic and therapeutic targets for intervention.

DNA-damaged podocyte-CD8 T cell crosstalk exacerbates kidney injury by altering DNA methylation

Recent epigenome-wide studies suggest an association between blood DNA methylation and kidney function. However, the pathological importance remains unclear. Here, we show that the homing endonuclease I-PpoI-induced DNA double-strand breaks in kidney glomerular podocytes cause proteinuria, glomerulosclerosis, and tubulointerstitial fibrosis with DNA methylation changes in blood cells as well as in podocytes. Single-cell RNA-sequencing analysis reveals an increase in cytotoxic CD8+ T cells with the activating/costimulatory receptor NKG2D in the kidneys, which exhibit a memory precursor effector cell phenotype, and the CD44high memory CD8+ T cells are also increased in the peripheral circulation. NKG2D blockade attenuates the renal phenotype caused by podocyte DNA damage. Blood methylome shows increased DNA methylation in binding sites for STAT1, a transcription factor contributing to CD8+ T cell homeostasis. Collectively, podocyte DNA damage alters the blood methylome, leading to changes in CD8+ T cells, which contribute to sustained renal injury in chronic kidney disease.

DNA methylation enzymes in the kidneys of male and female BTBR ob/ob mice

Diabetic kidney disease (DKD) is the leading cause of the end-stage renal disease. Recent studies have shown that epigenetic modifications contribute to alterations in gene expression and the development of DKD. This study aimed to show an expression profile of key DNA (de)methylation enzymes (DNMT, TET proteins) and their differences between sexes under obesity and diabetic condition. Male and female black and tan brachyury (BTBR) ob/ob mice and their corresponding wild-type littermates (BTBR WT) were studied until 16 weeks of age. Metabolic parameters, kidney morphophysiology and the expression of fibrotic markers and epigenetic enzymes were studied in whole kidney tissue or specifically in the glomerulus. The results showed sexual dimorphism in the development of metabolic disease and in kidney morphophysiology. Female mice have a different profile of DNMTs expression in both WT and obese/diabetic condition. Furthermore, metabolic condition negatively modulated the glomerular expression of TET1 and TET3 only in females. To our knowledge, this is the first study that shows a kidney profile of the expression of key (de)methylation enzymes, DNMTs and TETs, in the BTBR ob/ob experimental model of DKD and its association with sex. The knowledge of this epigenetic profile may help future research to understand the pathophysiology of DKD in males and females.

Harnessing Genomic Analysis to Explore the Role of Telomeres in the Pathogenesis and Progression of Diabetic Kidney Disease

The prevalence of diabetes is increasing globally, and this trend is predicted to continue for future decades. Research is needed to uncover new ways to manage diabetes and its co-morbidities. A significant secondary complication of diabetes is kidney disease, which can ultimately result in the need for renal replacement therapy, via dialysis or transplantation. Diabetic kidney disease presents a substantial burden to patients, their families and global healthcare services. This review highlights studies that have harnessed genomic, epigenomic and functional prediction tools to uncover novel genes and pathways associated with DKD that are useful for the identification of therapeutic targets or novel biomarkers for risk stratification. Telomere length regulation is a specific pathway gaining attention recently because of its association with DKD. Researchers are employing both observational and genetics-based studies to identify telomere-related genes associated with kidney function decline in diabetes. Studies have also uncovered novel functions for telomere-related genes beyond the immediate regulation of telomere length, such as transcriptional regulation and inflammation. This review summarises studies that have revealed the potential to harness therapeutics that modulate telomere length, or the associated epigenetic modifications, for the treatment of DKD, to potentially slow renal function decline and reduce the global burden of this disease.

Molecular pathways that drive diabetic kidney disease

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

Linc279227 contributes to mitochondrial dysfunction in high glucose-treated mouse renal tubular epithelial cells

BACKGROUND

The aberrant expression of long noncoding RNAs (lncRNAs) has been associated with diabetic nephropathy (DN), a major complication of diabetes mellitus (DM). This study investigated the differential expression of lncRNAs in DM without renal damage and DM with renal damage, known as DN, and elucidated the functions of a pathogenic lncRNA.

METHODS

High-throughput sequencing was performed on the kidneys of male db/db mice with kidney injury, db/db mice without kidney involvement and db/m control littermates. Linc279227 expression was confirmed by RT‒qPCR and fluorescence in situ hybridization. The effects of linc279227 on high glucose (HG)-treated renal tubular epithelial cells (RTECs) were evaluated by autophagy flux monitoring, Western blot determination and mitochondrial morphological detection.

RESULTS

With high-throughput sequencing, we identified a 1024 nt long intergenic noncoding RNA, TCONS_00279227 (linc279227), whose expression was markedly increased in the kidneys of db/db mice with kidney injury compared to db/db mice without kidney injury and db/m control littermates. Fluorescence in situ hybridization confirmed that linc279227 was mainly located in the renal tubules of mice with DN. In vitro, linc279227 expression was found to be significantly increased in RTECs treated with high glucose (HG) for 48 h. Silencing linc279227 markedly restored the levels of autophagy-/mitophagy-associated proteins in HG-stimulated RTECs. Furthermore, silencing linc279227 reduced phosphorylated Drp1 expression and increased Mfn2 expression in RTECs exposed to HG.

CONCLUSION

Our data suggest that linc279227 plays an important role in mitochondrial dysfunction in HG-treated RTECs and that silencing linc279227 rescues RTECs exposed to HG.

Targeting epigenetics in diabetic cardiomyopathy: Therapeutic potential of flavonoids

The pathophysiological mechanisms of diabetic cardiomyopathy have been extensively studied, but there is still a lack of effective prevention and treatment methods. The ability of flavonoids to protect the heart from diabetic cardiomyopathy has been extensively described. In recent years, epigenetics has received increasing attention from scholars in exploring the etiology and treatment of diabetes and its complications. DNA methylation, histone modifications and non-coding RNAs play key functions in the development, maintenance and progression of diabetic cardiomyopathy. Hence, prevention or reversal of the epigenetic alterations that have occurred during the development of diabetic cardiomyopathy may alleviate the personal and social burden of the disease. Flavonoids can be used as natural epigenetic modulators in alternative therapies for diabetic cardiomyopathy. In this review, we discuss the epigenetic effects of different flavonoid subtypes in diabetic cardiomyopathy and summarize the evidence from preclinical and clinical studies that already exist. However, limited research is available on the potential beneficial effects of flavonoids on the epigenetics of diabetic cardiomyopathy. In the future, clinical trials in which different flavonoids exert their antidiabetic and cardioprotective effects through various epigenetic mechanisms should be further explored.

DNA methyltransferase 1 knockdown reverses PTEN and VDR by mediating demethylation of promoter and protects against renal injuries in hepatitis B virus-associated glomerulonephritis

Background

Aberrant DNA methylation patterns, including hypermethylation of key genes that inhibit fibrosis and inflammation, have been described in human kidney diseases. However, the role of DNA methyltransferase 1 (DNMT1) in hepatitis B virus-associated glomerulonephritis (HBV-GN) remains unclear.

Methods

We explored the underlying mechanism by establishing HBV X protein (HBx) overexpressing renal tubular epithelial (HK-2) cells and human podocytes with DNMT1 knockdown. Using RNA-sequencing to determine the downstream targets of DNMT1 and evaluate its levels of promoter methylation. HBV transgenic mice were used to examine the effects of DNMT1 inhibitor on renal in vivo.

Results

DNMT1 was significantly upregulated in the renal tissue of HBV-GN patients, accompanied by injuries of HK-2 cells and podocytes. HBx markedly upregulated DNMT1 and induced epithelial-mesenchymal transition (EMT) and inflammation in HK-2 cells and human podocytes. This increased DNMT1 expression was attenuated after DNMT1 knockdown, accompanied by restored HK-2 cells and podocyte injuries resulting from the activation of PI3K/Akt/mTOR and nuclear factor-kappa B (NF-κB) pathways. Hypermethylation of the phosphatase and tensin homolog (PTEN) promoter and vitamin D receptor (VDR) was induced in HBx-overexpressing HK-2 cells and podocytes, respectively, whereas DNMT1 knockdown effectively corrected these alterations. Furthermore, PTEN and VDR ablation resulted in marked EMT and inflammation induction in HBx-overexpressing HK-2 cells and human podocytes even with DNMT1 knockdown. Downregulation of the PI3K/Akt/mTOR-related pathway attenuated HBx-induced EMT and inflammation in HK-2 cells. Luciferase reporter assay revealed VDR as a direct target of the Snail family transcriptional repressor 1 (SNAI1) in HBx-overexpressing podocytes. DNA methylation inhibitor 5-azacytidine alleviated urinary protein and renal inflammation in HBV transgenic mice via PTEN-PI3K/Akt signaling and VDR signaling axis.

Conclusions

Our study clarifies the potential epigenetic mechanisms underlying HBx-induced renal injuries in HBV-GN and the renoprotective effects of inhibiting DNMT1, which can provide important insights into the development of treatments for HBV-GN.

The Protective Effect of Zebularine, an Inhibitor of DNA Methyltransferase, on Renal Tubulointerstitial Inflammation and Fibrosis

Renal fibrosis, the final pathway of chronic kidney disease, is caused by genetic and epigenetic mechanisms. Although DNA methylation has drawn attention as a developing mechanism of renal fibrosis, its contribution to renal fibrosis has not been clarified. To address this issue, the effect of zebularine, a DNA methyltransferase inhibitor, on renal inflammation and fibrosis in the murine unilateral ureteral obstruction (UUO) model was analyzed. Zebularine significantly attenuated renal tubulointerstitial fibrosis and inflammation. Zebularine decreased trichrome, α-smooth muscle actin, collagen IV, and transforming growth factor-β1 staining by 56.2%. 21.3%, 30.3%, and 29.9%, respectively, at 3 days, and by 54.6%, 41.9%, 45.9%, and 61.7%, respectively, at 7 days after UUO. Zebularine downregulated mRNA expression levels of matrix metalloproteinase (MMP)-2, MMP-9, fibronectin, and Snail1 by 48.6%. 71.4%, 31.8%, and 42.4%, respectively, at 7 days after UUO. Zebularine also suppressed the activation of nuclear factor-κB (NF-κB) and the expression of pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, by 69.8%, 74.9%, and 69.6%, respectively, in obstructed kidneys. Furthermore, inhibiting DNA methyltransferase buttressed the nuclear expression of nuclear factor (erythroid-derived 2)-like factor 2, which upregulated downstream effectors such as catalase (1.838-fold increase at 7 days, p < 0.01), superoxide dismutase 1 (1.494-fold increase at 7 days, p < 0.05), and NAD(P)H: quinone oxidoreduate-1 (1.376-fold increase at 7 days, p < 0.05) in obstructed kidneys. Collectively, these findings suggest that inhibiting DNA methylation restores the disrupted balance between pro-inflammatory and anti-inflammatory pathways to alleviate renal inflammation and fibrosis. Therefore, these results highlight the possibility of DNA methyltransferases as therapeutic targets for treating renal inflammation and fibrosis.

Low-dose 5-aza-2'-deoxycytidine protects against early renal injury by increasing klotho expression

Aim: To explore the effect of the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (Aza) on early renal injury. Materials & methods: Cell damage and inflammation are features of early renal injury. The apoptosis and inflammation in hypoxia/reoxygenation (H/R)-induced human proximal tubular epithelial cells (HK-2) and ischemia-reperfusion kidney were studied, and expression of the protein klotho was investigated. Results: Aza induced HK-2 apoptosis in a dose-dependent manner, but low-dose Aza attenuated the apoptosis and inflammation in H/R-induced HK-2 cells and ischemia-reperfusion kidney. Low-dose Aza ameliorated renal function in mice with renal ischemia-reperfusion injury. Meanwhile, low-dose Aza upregulated klotho expression in H/R-induced HK-2 cells and ischemia-reperfusion kidney. Klotho knockdown abrogated the effects of low-dose Aza on apoptosis and inflammation. Conclusion: Low-dose Aza protects against renal early injury by increasing klotho expression.

Dihydroartemisinin suppresses renal fibrosis in mice by inhibiting DNA-methyltransferase 1 and increasing Klotho

Renal fibrosis is an unavoidable end result of all forms of progressive chronic kidney diseases (CKD). Discovery of efficacious drugs against renal fibrosis is in crucial need. In a preliminary study we found that a derivative of artemisinin, dihydroartemisinin (DHA), exerted strong renoprotection, and reversed renal fibrosis in adenine-induced CKD mouse model. In this study we investigated the anti-fibrotic mechanisms of DHA, particularly its specific target in renal cells. Renal fibrosis was induced in mice by unilateral ureteral obstruction (UUO) or oral administration of adenine (80 mg · kg-1), the mice received DHA (30 mg · kg-1 · d-1, i.g.) for 14 or 21 days, respectively. We showed that DHA administration markedly attenuated the inflammation and fibrotic responses in the kidneys and significantly improved the renal function in both the renal fibrosis mouse models. In adenine-treated mice, DHA was more effective than 5-azacytidine against renal fibrosis. The anti-fibrotic effects of DHA were also observed in TGF-β1-treated HK-2 cells. In order to determine the target protein of DHA, we conducted pull-down technology coupled with shotgun proteomics using a small-molecule probe based on the structure of DHA (biotin-DHA). As a results, DNA methyltransferase 1 (DNMT1) was identified as the anti-fibrotic target of DHA in 3 different types of renal cell lines (HK-2, HEK293 and 3T3). We demonstrated that DHA directly bound to Asn 1529 and Thr 1528 of DNMT1 with a Kd value of 8.18 μM. In primary mouse renal tubular cells, we showed that DHA (10 μM) promoted DNMT1 degradation via the ubiquitin-proteasome pathway. DHA-reduced DNMT1 expression effectively reversed Klotho promoter hypermethylation, which led to the reversal of Klotho protein loss in the kidney of UUO mice. This subsequently resulted in inhibition of the Wnt/β-catenin and TGF-β/Smad signaling pathways and consequently conferred renoprotection in the animals. Knockdown of Klotho abolished the renoprotective effect of DHA in UUO mice. Our study reveals a novel pharmacological activity for DHA, i.e., renoprotection. DHA exhibits this effect by targeting DNMT1 to reverse Klotho repression. This study provides an evidence for the possible clinical application of DHA in the treatment of renal fibrosis.

Hydrogen Sulfide Improves Angiogenesis by Regulating the Transcription of pri-miR-126 in Diabetic Endothelial Cells

Introduction: Diabetes mellitus results in high rates of cardiovascular disease, such as microcirculation disorder of the lower limbs, with angiogenesis impairment being the main factor. The endothelium functions as a barrier between blood and the vessel wall. Vascular endothelial cell dysfunction caused by hyperglycemia is the main factor leading to angiogenesis impairment. Hydrogen sulfide (H₂S) and miR-126-3p are known for their pro-angiogenesis effects; however, little is known about how H₂S regulates miR-126-3p to promote angiogenesis under high-glucose conditions. Objectives: The main objective of this research was to explore how H₂S regulates the miR-126-3p levels under high-glucose conditions. Methods: We evaluated the pro-angiogenesis effects of H₂S in the diabetic hindlimb of an ischemia mice model and in vivo Matrigel plugs. Two microRNA datasets were used to screen microRNAs regulated by both diabetes and H₂S. The mRNA and protein levels were detected through real-time PCR and Western blot, respectively. Immunofluorescent staining was also used to assess the capillary density and to evaluate the protein levels in vascular endothelial cells. Human umbilical vein endothelial cells (HUVECs) were used in in vitro experiments. A scratch wound-healing assay was applied to detect the migration ability of endothelial cells. Methylated DNA immunoprecipitation combined with real-time PCR was chosen to identify the DNA methylation level in the HUVECs. Results: Exogenous H₂S improved angiogenesis in diabetic mice. miR-126-3p was regulated by both diabetes and H₂S. Exogenous H₂S up-regulated the miR-126-3p level and recovered the migration rate of endothelial cells via down-regulating the DNMT1 protein level, which was increased by high glucose. Furthermore, DNMT1 upregulation in the HUVECs increased the methylation levels of the gene sequences upstream of miR-126-3p and then inhibited the transcription of primary-miR-126, thus decreasing the miR-126-3p level. CSE overexpression in the HUVECs rescued the miR-126-3p level, by decreasing the methylation level to improve migration. Conclusion: H₂S increases the miR-126-3p level through down-regulating the methylation level, by decreasing the DNMT1 protein level induced by high glucose, thus improving the angiogenesis originally impaired by high glucose.

Phloretin ameliorates diabetic nephropathy by inhibiting nephrin and podocin reduction through a non-hypoglycemic effect

Phloretin is a dihydrochalcone flavonoid from natural plants, which has protective activities against oxidative stress and inflammation. To date, its effect on diabetic nephropathy (DN) has not been investigated. In this study, we examined the potential role of phloretin in diabetes-induced renal damage and associated mechanisms in a type 2 diabetes mellitus (T2DM) model induced by streptozotocin (STZ) and high-fat diet (HFD) in Apolipoprotein E knockout (ApoE^-/-) mice. We found that daily treatment with a low dose (20 mg kg^-1) of phloretin, as a dietary supplement, significantly alleviated polyuria, proteinuria, and glomerular histopathological changes in the T2DM mice, indicating a protective effect of phloretin on diabetic renal dysfunction. In the phloretin-treated T2DM mice, major metabolic parameters, including blood glucose levels, were not altered significantly, suggesting that the observed beneficial effects of phloretin may be due to a mechanism independent of blood glucose control. Further experiments revealed that phloretin had a protective effect on glomerular podocytes as indicated by ameliorated glomerular basement membrane (GBM) thickening and podocyte foot process effacement. Moreover, phloretin treatment restored levels of nephrin and podocin, two podocyte slit diaphragm proteins that were decreased in T2DM mice. Our results indicate that low-dose phloretin treatment has a protective effect on podocytes in DN via a non-hypoglycemic mechanism in preserving nephrin and podocin expression levels. These data suggest that phloretin may be exploited as a novel therapeutic agent for DN.

CCL5 Suppresses Klotho Expression via p-STAT3/DNA Methyltransferase1-Mediated Promoter Hypermethylation

Background

Enhanced inflammation and reduced Klotho are common features in chronic kidney disease (CKD). Inflammation induces DNA hypermethylation. This study assessed the performance of inflammatory marker C-C motif chemokine 5 (CCL5) in epigenetic regulation of Klotho expression.

Methods

Fifty CKD patients and 25 matched controls were enrolled, and serum CCL5 level, sKlotho level, and DNA methylation were evaluated in these subjects. A renal interstitial fibrosis (RIF) model with CKD was induced in mice via unilateral ureteral obstruction (UUO) in vivo and human proximal tubular epithelial (HK-2) cells treated with CCL5 in vitro. 5-aza-2′-deoxycytidine (5-Aza), a DNA methyltransferase inhibitor was given to UUO mice. Hematoxylin and eosin (HE) and Masson trichrome staining were adopted to evaluate renal pathological changes. Methylation-specific PCR was performed to assess DNA methylation of Klotho promoter in the peripheral blood leucocytes (PBLs) from CKD patients and obstructive kidney from UUO mice. CCL5, Klotho, and DNA methyltransferases (DNMTs) were determined by ELISAs, immunofluorescence, or western blotting. HK-2 cells were exposed to CCL5 with or without 5-Aza and stattic, a p-signal transducer and activator of transcription 3 (STAT3) inhibitor, and expressions of p-STAT3, DNMT1, and Klotho were determined by western blotting.

Results

CCL5 upregulation concomitant with Klotho downregulation in serum and global DNA methylation in PBLs were observed in CKD samples. UUO contributed to severe renal interstitial fibrosis and enhanced expressions of fibrotic markers. Moreover, UUO increased the CCL5 level, induced Klotho promoter methylation, suppressed Klotho level, activated p-STAT3 signaling, and upregulated DNMT1 level. A similar observation was made in HK-2 cells treated with CCL5. More importantly, 5-Aza inhibited UUO-induced Klotho hypermethylation, reversed Klotho, downregulated p-STAT3 expressions, and ameliorated RIF in vivo. The consistent findings in vitro were also obtained in HK-2 cells exposed to 5-Aza and stattic.

Conclusion

The CCL5/p-STAT3/DNMT1 axis is implicated in epigenetic regulation of Klotho expression in CKD. This study provides novel therapeutic possibilities for reversal of Klotho suppression by CKD.

High glucose-mediated VPS26a downregulation dysregulates neuronal amyloid precursor protein processing and tau phosphorylation

BACKGROUND AND PURPOSE

The relationship between hyperglycaemia-induced retromer dysfunction impairing intracellular trafficking and AD remains unclear, although Diabetes mellitus (DM) is considered a risk factor for Alzheimer's disease (AD). Here, we investigated the effects of high glucose on the retromer, and defined the dysregulation of mechanisms of amyloid precursor protein (APP) processing and tau phosphorylation.

EXPERIMENTAL APPROACH

We used human induced-pluripotent stem cell-derived neuronal differentiated cells and SH-SY5Ys exposed to high glucose to identify the underlying mechanisms. Streptozotocin-induced diabetic mice were used to elucidate whether the retromer contributes to the AD-like pathology.

KEY RESULTS

We found that vacuolar protein sorting-associated protein 26a (VPS26a) was decreased in the hippocampus of diabetic mice and high glucose-treated human neuronal cells. High glucose downregulated VPS26a through ROS/NF-κB/DNA methyltransferase1-mediated promoter hypermethylation. VPS26a recovery blocked retention of APP and cation-independent mannose-6-phosphate receptor in endosomes and promoted transport to the trans-Golgi, which decreased Aβ levels, and improved Cathepsin D activity, reducing p-tau levels, respectively. Retromer enhancement ameliorated synaptic deficits, astrocyte over-activation, and cognitive impairment in diabetic mice.

CONCLUSION AND IMPLICATIONS

In conclusion, VPS26a is a promising candidate for the inhibition of DM-associated AD pathogenesis by modulating APP processing and tau phosphorylation.

The Dynamics and Plasticity of Epigenetics in Diabetic Kidney Disease: Therapeutic Applications Vis-à-Vis

Chronic kidney disease (CKD) refers to the phenomenon of progressive decline in the glomerular filtration rate accompanied by adverse consequences, including fluid retention, electrolyte imbalance, and an increased cardiovascular risk compared to those with normal renal function. The triggers for the irreversible renal function deterioration are multifactorial, and diabetes mellitus serves as a major contributor to the development of CKD, namely diabetic kidney disease (DKD). Recently, epigenetic dysregulation emerged as a pivotal player steering the progression of DKD, partly resulting from hyperglycemia-associated metabolic disturbances, rising oxidative stress, and/or uncontrolled inflammation. In this review, we describe the major epigenetic molecular mechanisms, followed by summarizing current understandings of the epigenetic alterations pertaining to DKD. We highlight the epigenetic regulatory processes involved in several crucial renal cell types: Mesangial cells, podocytes, tubular epithelia, and glomerular endothelial cells. Finally, we highlight epigenetic biomarkers and related therapeutic candidates that hold promising potential for the early detection of DKD and the amelioration of its progression.

Altered DNA methylation in kidney disease: useful markers and therapeutic targets

Recent studies have demonstrated the association of altered epigenomes with lifestyle-related diseases. Epigenetic regulation promotes biological plasticity in response to environmental changes, and such plasticity may cause a ‘memory effect’, a sustained effect of transient treatment or an insult in the course of lifestyle-related diseases. We investigated the significance of epigenetic changes in several genes required for renal integrity, including the nephrin gene in podocytes, and the sustained anti-proteinuric effect, focusing on the transcription factor Krüppel-like factor 4 (KLF4). We further reported the role of the DNA repair factor lysine-acetyl transferase 5 (KAT5), which acts coordinately with KLF4, in podocyte injury caused by a hyperglycemic state through the acceleration of DNA damage and epigenetic alteration. In contrast, KAT5 in proximal tubular cells prevents acute kidney injury via glomerular filtration regulation by an epigenetic mechanism as well as promotion of DNA repair, indicating the cell type-specific action and roles of DNA repair factors. This review summarizes epigenetic alterations in kidney diseases, especially DNA methylation, and their utility as markers and potential therapeutic targets. Focusing on transcription factors or DNA damage repair factors associated with epigenetic changes may be meaningful due to their cell-specific expression or action. We believe that a better understanding of epigenetic alterations in the kidney will lead to the development of a novel strategy for chronic kidney disease (CKD) treatment.

Etoposide-induced protein 2.4 ameliorates high glucose-induced epithelial-mesenchymal transition by activating adenosine monophosphate-activated protein kinase pathway in renal tubular cells

Epithelial-mesenchymal transition (EMT), known as the transition of tubular epithelial cells into fibroblasts, is one of the potential mechanisms of renal fibrosis, which promotes the development of diabetic kidney disease (DKD). Etoposide-induced protein 2.4 (EI24) is known as an endoplasmic reticulum (ER)-localized Bcl-2-binding transmembrane protein with various functions that can affect autophagy, apoptosis and differentiation. However, whether EI24 is involved in EMT of renal tubular epithelial cells and the exact mechanism is still not known. In this study, we first reported that EI24 expression was significantly downregulated in the kidneys of diabetic mice and in high glucose-stimulated HK2 cells. Knockdown of EI24 led to EMT of HK2 cells, as indicated by decreased E-cadherin and increased α-smooth muscle actin (α-SMA). Meanwhile, overexpression of EI24 ameliorated high glucose-induced EMT of HK2 cells via activation of the adenosine monophosphate-activated protein kinase (AMPK) pathway. Then, DNA methyltransferase (DNMT) inhibitor 5-Aza-2'-deoxycytidine (5-Aza) treatment enhanced EI24 expression and alleviated EMT in high glucose-treated HK2 cells and the kidneys of diabetic mice. Furthermore, DNMT1 and DNMT3a upregulation were found to be involved in the decrease of EI24 in high glucose-stimulated HK2 cells. Silencing of DNMT1 and DNMT3a effectively reversed high glucose-induced downregulation of EI24 and aggravation of EMT. Our findings demonstrate that the DNA methyltransferase-regulated EI24 affects EMT of renal tubular cells via AMPK signaling pathway. It is suggested that EI24 may be a potential therapeutic target for diabetic renal injury.

Epigenetics in the pathogenesis of diabetic nephropathy

Diabetic nephropathy (DN), which is a common microvascular complication with a high incidence in diabetic patients, greatly increases the mortality of patients. With further study on DN, it is found that epigenetics plays a crucial role in the pathophysiological process of DN. Epigenetics has an important impact on the development of DN through a variety of mechanisms, and promotes the generation and maintenance of metabolic memory, thus ultimately leading to a poor prognosis. In this review we discuss the methylation of DNA, modification of histone, and regulation of non-coding RNA involved in the progress of cell dysfunction, inflammation and fibrosis in the kidney, which ultimately lead to the deterioration of DN.

Transmembrane signaling molecules play a key role in the pathogenesis of IgA nephropathy: a weighted gene co-expression network analysis study

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is one of the most common primary glomerulonephritis and a serious health concern worldwide; though still the underlying molecular mechanisms of IgAN are yet to be known and there is no efficient treatment for this disease. The main goal of this study was to explore the IgAN underlying pathogenic pathways, plus identifying the disease correlated modules and genes using the weighted gene co-expression network analysis (WGCNA) algorithm.

RESULTS

GSE104948 dataset (the expression data from glomerular tissue of IgAN patients) was analyzed and the identified differentially expressed genes (DEGs) were introduced to the WGCNA algorithm for building co-expression modules. Genes were classified into six co-expression modules. Genes of the disease's most correlated module were mainly enriched in the immune system, cell-cell communication and transmembrane cell signaling pathways. The PPI network was constructed by genes in all the modules and after hub-gene identification and validation steps, 11 genes, mostly transmembrane proteins (CD44, TLR1, TLR2, GNG11, CSF1R, TYROBP, ITGB2, PECAM1), as well as DNMT1, CYBB and PSMB9 were identified as potentially key players in the pathogenesis of IgAN. In the constructed regulatory network, hsa-miR-129-2-3p, hsa-miR-34a-5p and hsa-miR-27a-3p, as well as STAT3 were spotted as top molecules orchestrating the regulation of the hub genes.

CONCLUSIONS

The excavated hub genes from the hearts of co-expressed modules and the PPI network were mostly transmembrane signaling molecules. These genes and their upstream regulators could deepen our understanding of IgAN and be considered as potential targets for hindering its progression.

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.

Sanziguben polysaccharides inhibit diabetic nephropathy through NF-κB-mediated anti-inflammation

Background

Sanziguben polysaccharides (SZP) are large amounts of classical Chinese medicines from Sanziguben (SZGB). Moreover, SZGB is a widely applied compound prescription for diabetic nephropathy (DN) treatment, but the role is still unclear. This study initially explores the mechanism of SZP in the treatment of DN.

Methods

The high-fat diet plus streptozotocin injections were used to replicate the DN models in male C57BL/6 mice. DN mice were divided into five groups: DN mice, DN mice treated with SZP(1.01 or 2.02 g/kg), DN mice treated with SZGB decoction(4.7 g/kg), and DN mice treated with metformin (300 mg/kg). HG and LPS plus TNFα stimulated human tubule epithelial (HK-2) cells to establish an in vitro model and treated with SZP (100 or 200 μg/mL).

Results

SZP was found to comprise sugar, protein, and uronic acid. Furthermore, SZP alleviated the progression of inflammation in vivo and in vitro by inhibiting the expression of NF-κB.

Conclusions

NF-κB plays a critical role in the development of DN induced by STZ and HG. Furthermore, SZP can attenuate the NF-κB‐mediated progression of diabetic nephropathy, improve DN through anti-inflammation.

Epigenetics in kidney diseases

Epigenetics examines heritable changes in DNA and its associated proteins except mutations in gene sequence. Epigenetic regulation plays fundamental roles in kidney cell biology through the action of DNA methylation, chromatin modification via epigenetic regulators and non-coding RNA species. Kidney diseases, including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis are multistep processes associated with numerous molecular alterations even in individual kidney cells. Epigenetic alterations, including anomalous DNA methylation, aberrant histone alterations and changes of microRNA expression all contribute to kidney pathogenesis. These changes alter the genome-wide epigenetic signatures and disrupt essential pathways that protect renal cells from uncontrolled growth, apoptosis and development of other renal associated syndromes. Molecular changes impact cellular function within kidney cells and its microenvironment to drive and maintain disease phenotype. In this chapter, we briefly summarize epigenetic mechanisms in four kidney diseases including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis. We primarily focus on current knowledge about the genome-wide profiling of DNA methylation and histone modification, and epigenetic regulation on specific gene(s) in the pathophysiology of these diseases and the translational potential of identifying new biomarkers and treatment for prevention and therapy. Incorporating epigenomic testing into clinical research is essential to elucidate novel epigenetic biomarkers and develop precision medicine using emerging therapies.

Sirt6-mediated Nrf2/HO-1 activation alleviates angiotensin II-induced DNA DSBs and apoptosis in podocytes

Recent studies suggested that DNA double-strand breaks (DSBs) were associated with the pathogenesis of chronic kidney disease (CKD). The purpose of this investigation was to determine the role of Sirtuin6 (Sirt6), a histone deacetylase related to DNA damage repair, in angiotensin (Ang) II-induced DNA DSBs and the cell injury of podocytes and explore the possible mechanism. Here we showed that an increase of DNA DSBs was accompanied by a reduction in Sirt6 expression in the glomeruli of patients with hypertensive nephropathy (HN). Similar results were found in rat kidneys infused with Ang II and in cultured podocytes stimulated with Ang II. Sirt6 overexpression inhibited Ang II-induced ROS generation and DNA DSBs, and thus served as a protection against Ang II-induced apoptosis in podocytes. Moreover, Sirt6 activation enhanced Nrf2 and HO-1 gene expressions in podocytes after Ang II treatment. Furthermore, Nrf2 knockdown could partly reverse the cytoprotective effects of Sirt6 activation. In conclusion, our observations demonstrated that the Sirt6-Nrf2-HO-1 pathway played a vital role in relieving Ang II-mediated oxidative DNA damage and podocyte injury.

Receptor activator of NF-κB mediates podocyte injury in diabetic nephropathy

Receptor activator of NF-κB (RANK) expression is increased in podocytes of patients with diabetic nephropathy. However, the relevance of RANK to diabetic nephropathy pathobiology remains unclear. Here, to evaluate the role of podocyte RANK in the development of diabetic nephropathy, we generated a mouse model of podocyte-specific RANK depletion (RANK^-/-Cre T), and a model of podocyte-specific RANK overexpression (RANK TG), and induced diabetes in these mice with streptozotocin. We found that podocyte RANK depletion alleviated albuminuria, mesangial matrix expansion, and basement membrane thickening, while RANK overexpression aggravated these indices in streptozotocin-treated mice. Moreover, streptozotocin-triggered oxidative stress was increased in RANK overexpression but decreased in the RANK depleted mice. Particularly, the expression of NADPH oxidase 4, and its obligate partner, P22phox, were enhanced in RANK overexpression, but reduced in RANK depleted mice. In parallel, the transcription factor p65 was increased in the podocyte nuclei of RANK overexpressing mice but decreased in the RANK depleted mice. The relevant findings were largely replicated with high glucose-treated podocytes in vitro. Mechanistically, p65 could bind to the promoter regions of NADPH oxidase 4 and P22phox, and increased their respective gene promoter activity in podocytes, dependent on the levels of RANK. Taken together, these findings suggested that high glucose induced RANK in podocytes and caused the increase of NADPH oxidase 4 and P22phox via p65, possibly together with the cytokines TNF- α, MAC-2 and IL-1 β, resulting in podocyte injury. Thus, we found that podocyte RANK was induced in the diabetic milieu and RANK mediated the development of diabetic nephropathy, likely by promoting glomerular oxidative stress and proinflammatory cytokine production.