論文

Accumulation of DNA double-strand breaks (DSBs) is linked to aging and age-related diseases. We recently reported the possible association of DNA DSBs with altered DNA methylation in murine models of kidney disease. However, DSBs and DNA methylation in human kidneys was not adequately investigated. This study was a cross-sectional observational study to evaluate the glomerular DNA DSB marker γH2AX and phosphorylated Ataxia Telangiectasia Mutated (pATM), and the DNA methylation marker 5-methyl cytosine (5mC) by immunostaining, and investigated the association with pathological features and clinical parameters in 29 patients with IgA nephropathy. To evaluate podocyte DSBs, quantitative long-distance PCR of the nephrin gene using laser-microdissected glomerular samples and immunofluorescent double-staining with WT1 and γH2AX were performed. Glomerular γH2AX level was associated with glomerular DNA methylation level in IgA nephropathy. Podocytopathic features were associated with increased number of WT1(+)γH2AX(+) cells and reduced amount of PCR product of the nephrin gene, which indicate podocyte DNA DSBs. Glomerular γH2AX and 5mC levels were significantly associated with the slope of eGFR decline over one year in IgA nephropathy patients using multiple regression analysis adjusted for age, baseline eGFR, amount of proteinuria at biopsy and immunosuppressive therapy after biopsy. Glomerular γH2AX level was associated with DNA methylation level, both of which may be a good predictor of renal outcome in IgA nephropathy.

Recently it has been shown that epigenetic mechanisms are involved in initiation and progression of caridiovascular and metabolic diseases, including diabetes, obesity, atherosclerosis, heart failure, hypertension and kidney diseases. In these chronic diseases, various exogenous and endogenous stresses cause DNA damage, followed by DNA repair process. Accumulation of DNA damages and impaired repair process can lead to epigenetic changes, which may contribute to onset and progression of diseases. Recently we have shown that therapeutic effect of transcription factor KLF4 (Kruppel-like factor 4) in kidney glomerular epithelial cells (podocytes) on proteinuric kidney diseases through epigenetic mechanisms. Our result suggests the possibility of transcription factors as a target of selective epigenetic therapy. Moreover, we have reported that renin-angiotensin system (RAS) blockers, which are widely prescribed for the treatment of cardiovascular diseases, can restore epigenetic changes through KLF4 in part. These results suggest that activation of RAS causes epigenetic changes in disease states, and elucidation of the precise mechanism may lead to establishment of novel therapeutic target of kidney diseases. In this review we focus on DNA damage repair system and epigenetic modulators in disease states, and speculate a candidate for epigenetic therapy of kidney diseases.

Diabetes and hypertension have become the primary causes of chronic kidney disease worldwide. However, there are no established markers for early diagnosis or predicting renal prognosis. Here, we investigated the expression profiles of DNA repair and DNA methylation factors in human urine-derived cells as a possible diagnostic or renal prognosis-predicting marker. A total of 75 subjects, aged 63.3 ± 1.9 years old, were included in this study. DNA and RNA were extracted from 50 mL of urine samples. We evaluated DNA double-strand breaks (DSBs) by the quantitative long distance-PCR method and performed real-time RT-PCR analysis to analyze the expression of renal cell-specific markers, DNA DSB repair factor KAT5, DNA methyltransferases DNMTs, and demethylation enzymes TETs. In patients with hypertension and diabetes, DNA DSBs of the nephrin gene increased with decreased urine KAT5/nephrin expression, consistent with our previous study (Cell Rep 2019). In patients with hypertension, DNA DSBs of the AQP1 gene were increased with elevated urine DNMTs/AQP1 and TETs/AQP1 expression. Moreover, urine DNMTs/AQP1 expression was significantly correlated with the annual eGFR decline rate after adjustment for age, baseline eGFR, the presence of diabetes and the amount of albuminuria, suggesting a possible role as a renal prognosis predictor.

The "preconditioning effect" in AKI is a phenomenon in which an episode of ischemia-reperfusion results in tolerance to subsequent ischemia-reperfusion injury. However, its relationship between DNA damage repair has not been elucidated. Here, we show the role of KAT5 in the preconditioning effect. Preconditioning attenuated DNA damage in proximal tubular cells with elevated KAT5 expression. Ischemia-reperfusion (IR) injuries were exacerbated, and preconditioning effect vanished in proximal tubular-cell-specific KAT5 knockout mice. Investigation of tubuloglomerular feedback (TGF) by MALDI-IMS and urinary adenosine revealed that preconditioning caused attenuated TGF at least in part via KAT5. In addition, K-Cl cotransporter 3 (KCC3) expression decreased in damaged proximal tubular cells, which may be involved in accelerated TGF following IR. Furthermore, KAT5 induced KCC3 expression by maintaining chromatin accessibility and binding to the KCC3 promoter. These results suggest a novel mechanism of the preconditioning effect mediated by the promotion of DNA repair and attenuation of TGF through KAT5.

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.

The growing number of patients with chronic kidney disease (CKD) is recognized as an emerging problem worldwide. Recent studies have indicated that deregulation of transcription factors is associated with the onset or progression of kidney disease. Several clinical trials indicated that regression of CKD may be feasible via activation of the transcription factor nuclear factor erythroid-2 related factor 2 (Nrf2), which suggests that transcription factors may be potential drug targets for CKD. Agents stabilizing hypoxia-inducible factor (HIF), which may be beneficial for renal anemia and renal protection, are also now under clinical trial. Recently, we have reported that the transcription factor Kruppel-like factor 4 (KLF4) regulates the glomerular podocyte epigenome, and that the antiproteinuric effect of the renin–angiotensin system blockade may be partially mediated by KLF4. KLF4 is one of the Yamanaka factors that induces iPS cells and is reported to be involved in epigenetic remodeling. In this article, we summarize the transcription factors associated with CKD and particularly focus on the possibility of transcription factors being novel drug targets for CKD through epigenetic modulation.

Effective treatment of diabetic kidney disease (DKD) remains a large unmet medical need. Within the disease's complicated pathogenic mechanism, activation of the advanced glycation end products (AGEs)-receptor for AGE (RAGE) axis plays a pivotal role in the development and progression of DKD. To provide a new therapeutic strategy against DKD progression, we developed a vaccine against RAGE. Three rounds of immunization of mice with the RAGE vaccine successfully induced antigen-specific serum IgG antibody titers and elevated antibody titers were sustained for at least 38 weeks. In addition, RAGE vaccination significantly attenuated the increase in urinary albumin excretion in streptozotocin-induced diabetic mice (type 1 diabetes model) and leptin-receptor-deficient db/db mice (type 2 diabetes model). In microscopic analyses, RAGE vaccination suppressed glomerular hypertrophy and mesangial expansion in both diabetic models and significantly reduced glomerular basement membrane thickness in streptozotocin-induced diabetic mice. Results of an in vitro study indicated that the serum IgG antibody elicited by RAGE vaccination suppressed the expression of AGE-induced vascular cell adhesion molecule 1 and intracellular adhesion molecule 1 in endothelial cells. Thus, our newly developed RAGE vaccine attenuated the progression of DKD in mice and is a promising potential therapeutic strategy for patients with DKD.