Epigenetic regulation of glucose-stimulated osteopontin (OPN) expression in diabetic kidney

Single-cell RNA sequencing in diabetic kidney disease: a literature review

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), and its pathogenesis has not been clarified. Current research suggests that DKD involves multiple cell types and extra-renal factors, and it is particularly important to clarify the pathogenesis and identify new therapeutic targets. Single-cell RNA sequencing (scRNA-seq) technology is high-throughput sequencing of the transcriptomes of individual cells at the single-cell level, which is an effective technology for exploring the development of diseases by comparing genetic information, reflecting the differences in genetic information between cells, and identifying different cell subpopulations. Accumulating evidence supports the role of scRNA-seq in revealing the pathogenesis of diabetes and strengthening our understanding of the molecular mechanisms of DKD. We reviewed the scRNA-seq data this time. Then, we analyzed and discussed the applications of scRNA-seq technology in DKD research, including annotation of cell types, identification of novel cell types (or subtypes), identification of intercellular communication, analysis of cell differentiation trajectories, gene expression detection, and analysis of gene regulatory networks, and lastly, we explored the future perspectives of scRNA-seq technology in DKD research.

Osteopontin/SPP1: a potential mediator between immune cells and vascular calcification

Vascular calcification (VC) is considered a common pathological process in various vascular diseases. Accumulating studies have confirmed that VC is involved in the inflammatory response in heart disease, and SPP1+ macrophages play an important role in this process. In VC, studies have focused on the physiological and pathological functions of macrophages, such as pro-inflammatory or anti-inflammatory cytokines and pro-fibrotic vesicles. Additionally, macrophages and activated lymphocytes highly express SPP1 in atherosclerotic plaques, which promote the formation of fatty streaks and plaque development, and SPP1 is also involved in the calcification process of atherosclerotic plaques that results in heart failure, but the crosstalk between SPP1-mediated immune cells and VC has not been adequately addressed. In this review, we summarize the regulatory effect of SPP1 on VC in T cells, macrophages, and dendritic cells in different organs' VC, which could be a potential therapeutic target for VC.

Mechanism of KDM5A-mediated H3K4me3 modification in the osteogenic differentiation of mesenchymal stem cells in steroid-induced osteonecrosis of the femoral head

OBJECTIVES

Steroid-induced osteonecrosis of the femoral head (SONFH) is characterized by impaired osteogenesis in bone marrow mesenchymal stem cells (BMSCs). This study investigates the role of lysine-specific demethylase 5A (KDM5A) in SONFH to identify potential therapeutic targets.

METHODS

Human BMSCs were isolated and characterized for cell surface markers and differentiation capacity. A SONFH cell model was established using dexamethasone treatment. BMSCs were transfected with KDM5A overexpression vectors or si-KDM5A, and the expression of KDM5A, miR-107, runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OPN) was assessed. Alizarin red staining was used to observe mineralization nodules, while alkaline phosphatase activity and cell viability were measured. The enrichment of KDM5A and histone 3 lysine 4 trimethylation (H3K4me3) on the promoters of RUNX2, OCN, and OPN was analyzed. The binding between miR-107 and KDM5A 3'UTR was validated, and the combined effect of miR-107 overexpression and KDM5A overexpression on BMSC osteogenic differentiation was evaluated.

RESULTS

KDM5A was upregulated in BMSCs from SONFH. Inhibition of KDM5A promoted osteogenic differentiation of BMSCs, associated with increased RUNX2, OCN, and OPN promoters. KDM5A bound to the promoters of RUNX2, OCN, and OPN, leading to reduced H3K4me3 levels and downregulation of their expression. Overexpression of miR-107 inhibited KDM5A and enhanced BMSC osteogenic differentiation.

CONCLUSION

KDM5A negatively regulates BMSC osteogenic differentiation by modulating H3K4me3 levels on the promoters of key osteogenic genes. miR-107 overexpression counteracts the inhibitory effect of KDM5A on osteogenic differentiation. These findings highlight the potential of targeting the KDM5A/miR-107 axis for SONFH therapy.

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

Tenascin-C promotes the proliferation and fibrosis of mesangial cells in diabetic nephropathy through the β-catenin pathway

OBJECTIVE

To mechanistically assess the involvement of tenascin-C (TNC) in diabetic nephropathy (DN).

METHODS

Renal specimens from DN patients were histopathologically examined, and their TNC expression patterns were evaluated via immunohistochemistry. Additionally, the hereditarily diabetic C57BL/KsJ db/db mice were induced to develop DN via adaptive feeding, and then their renal levels of TNC and β-catenin were assessed via western blotting and immunohistochemistry. Furthermore, the TNC and β-catenin levels in primary rat mesangial cells (RMCs) cultured with high glucose levels were assessed via western blotting. In parallel, RMCs cultured with TNC in the presence or absence of the β-catenin blocker ICG-001 were analyzed for their fibronectin and collagen I levels via immunostaining, and for their fibronectin, α-SMA, vimentin, PDGFR-β, PCNA, and β-catenin levels via western blotting.

RESULTS

The TNC levels in the specimens were associated with the pathological classification. In these DN specimens, TNC protein was highly detected in the MCs and slightly in the tubulointerstitium. Renal TNC (P < 0.05) and β-catenin (P < 0.001) were upregulated in db/db vs. db/m mice. High-glucose treatment upregulated TNC (P < 0.01) and β-catenin (P < 0.05) in RMCs. TNC treatment upregulated fibronectin (P < 0.05), α-SMA (P < 0.01), vimentin (P < 0.05), PCNA (P < 0.05), and β-catenin (P < 0.05) in RMCs, as assessed via western blotting. Immunohistochemical analysis confirmed the fibronectin upregulation and showed collagen I upregulation. Western-blot results also showed that levels of fibronectin (P < 0.001), α-SMA (P < 0.01), vimentin (P < 0.001), PCNA (P < 0.05), PDGFR-β (P < 0.05), and β-catenin (P < 0.01) were lower in RMCs co-treated with TNC and ICG-001 than in TNC-treated cells. Immunofluorescence analysis confirmed the decreased fibronectin level and showed that the collagen I level was also decreased by ICG-001.

CONCLUSION

TNC is upregulated in DN and induces MC proliferation and fibrosis through the β-catenin pathway.

Fetal Reprogramming of Nutrient Surplus Signaling, O-GlcNAcylation, and the Evolution of CKD

ABSTRACT

Fetal kidney development is characterized by increased uptake of glucose, ATP production by glycolysis, and upregulation of mammalian target of rapamycin (mTOR) and hypoxia-inducible factor-1 alpha (HIF-1 α ), which (acting in concert) promote nephrogenesis in a hypoxic low-tubular-workload environment. By contrast, the healthy adult kidney is characterized by upregulation of sirtuin-1 and adenosine monophosphate-activated protein kinase, which enhances ATP production through fatty acid oxidation to fulfill the needs of a normoxic high-tubular-workload environment. During stress or injury, the kidney reverts to a fetal signaling program, which is adaptive in the short term, but is deleterious if sustained for prolonged periods when both oxygen tension and tubular workload are heightened. Prolonged increases in glucose uptake in glomerular and proximal tubular cells lead to enhanced flux through the hexosamine biosynthesis pathway; its end product-uridine diphosphate N -acetylglucosamine-drives the rapid and reversible O-GlcNAcylation of thousands of intracellular proteins, typically those that are not membrane-bound or secreted. Both O-GlcNAcylation and phosphorylation act at serine/threonine residues, but whereas phosphorylation is regulated by hundreds of specific kinases and phosphatases, O-GlcNAcylation is regulated only by O-GlcNAc transferase and O-GlcNAcase, which adds or removes N-acetylglucosamine, respectively, from target proteins. Diabetic and nondiabetic CKD is characterized by fetal reprogramming (with upregulation of mTOR and HIF-1 α ) and increased O-GlcNAcylation, both experimentally and clinically. Augmentation of O-GlcNAcylation in the adult kidney enhances oxidative stress, cell cycle entry, apoptosis, and activation of proinflammatory and profibrotic pathways, and it inhibits megalin-mediated albumin endocytosis in glomerular mesangial and proximal tubular cells-effects that can be aggravated and attenuated by augmentation and muting of O-GlcNAcylation, respectively. In addition, drugs with known nephroprotective effects-angiotensin receptor blockers, mineralocorticoid receptor antagonists, and sodium-glucose cotransporter 2 inhibitors-are accompanied by diminished O-GlcNAcylation in the kidney, although the role of such suppression in mediating their benefits has not been explored. The available evidence supports further work on the role of uridine diphosphate N -acetylglucosamine as a critical nutrient surplus sensor (acting in concert with upregulated mTOR and HIF-1 α signaling) in the development of diabetic and nondiabetic CKD.

The Role of Histone Modifications in the Pathogenesis of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease. The pathogenesis of DKD is multifactorial, with several molecular pathways implicated. Recent data suggest that histone modification plays an important role in the development and progression of DKD. Histone modification appears to induce oxidative stress, inflammation and fibrosis in the diabetic kidney. In the present review, we summarize the current knowledge on the association between histone modification and DKD.

On the Relationship between Diabetes and Obstructive Sleep Apnea: Evolution and Epigenetics

This review offers an overview of the relationship between diabetes, obstructive sleep apnea (OSA), obesity, and heart disease. It then addresses evidence that the traditional understanding of this relationship is incomplete or misleading. In the process, there is a brief discussion of the evolutionary rationale for the development and retention of OSA in light of blood sugar dysregulation, as an adaptive mechanism in response to environmental stressors, followed by a brief overview of the general concepts of epigenetics. Finally, this paper presents the results of a literature search on the epigenetic marks and changes in gene expression found in OSA and diabetes. (While some of these marks will also correlate with obesity and heart disease, that is beyond the scope of this project). We conclude with an exploration of alternative explanations for the etiology of these interlinking diseases.

Recent Advances in Diabetic Kidney Diseases: From Kidney Injury to Kidney Fibrosis

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal disease. The natural history of DKD includes glomerular hyperfiltration, progressive albuminuria, declining estimated glomerular filtration rate, and, ultimately, kidney failure. It is known that DKD is associated with metabolic changes caused by hyperglycemia, resulting in glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial inflammation and fibrosis. Hyperglycemia is also known to cause programmed epigenetic modification. However, the detailed mechanisms involved in the onset and progression of DKD remain elusive. In this review, we discuss recent advances regarding the pathogenic mechanisms involved in DKD.

Osteopontin as a Regulator of Colorectal Cancer Progression and Its Clinical Applications

Simple Summary

The mortality of colorectal cancer is principally related to metastatic disease at the time of diagnosis or to the growth of initially undetectable micro-metastasis. Current therapeutic strategies are efficient in patients with locally advanced cancer, but are rarely able to cure patients with metastatic disease. Therapeutic failure is mainly associated with drug resistance and an aggressive phenotype. The identification of new biomarkers for micro-metastasis and tumor progression remains an unmet clinical need that should allow for improved patient stratification for optimal treatment and may lead to the identification of novel therapeutic targets. Osteopontin (OPN), a multifunctional protein, has emerged as a potentially valuable biomarker in several cancer types. This review principally describes the molecular mechanisms of OPN that are associated with colorectal cancer (CRC) progression and metastasis, as well as the use of OPN as a clinical biomarker. This review identifies a role for OPN as a biomarker ready for extended clinical application and discusses its use as a therapeutic target.

Abstract

A high expression of the phosphoprotein osteopontin (OPN) has been associated with cancer progression in several tumor types, including breast cancer, hepatocarcinoma, ovarian cancer, and colorectal cancer (CRC). Interestingly, OPN is overexpressed in CRC and is associated with a poor prognosis linked to invasion and metastasis. Here, we review the regulation and functions of OPN with an emphasis on CRC. We examine how epigenetic and genetic regulators interact with the key signaling pathways involved in this disease. Then, we describe the role of OPN in cancer progression, including proliferation, survival, migration, invasion, and angiogenesis. Furthermore, we outline the interest of using OPN as a clinical biomarker, and discuss if and how osteopontin can be implemented as a routine assay in clinical laboratories for monitoring CRC patients. Finally, we discuss the use of OPN an attractive, but challenging, therapeutic target.

Osteopontin in Cardiovascular Diseases

Unprecedented advances in secondary prevention have greatly improved the prognosis of cardiovascular diseases (CVDs); however, CVDs remain a leading cause of death globally. These findings suggest the need to reconsider cardiovascular risk and optimal medical therapy. Numerous studies have shown that inflammation, pro-thrombotic factors, and gene mutations are focused not only on cardiovascular residual risk but also as the next therapeutic target for CVDs. Furthermore, recent clinical trials, such as the Canakinumab Anti-inflammatory Thrombosis Outcomes Study trial, showed the possibility of anti-inflammatory therapy for patients with CVDs. Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions and is involved in a number of pathological states in CVDs. OPN has a two-faced phenotype that is dependent on the pathological state. Acute increases in OPN have protective roles, including wound healing, neovascularization, and amelioration of vascular calcification. By contrast, chronic increases in OPN predict poor prognosis of a major adverse cardiovascular event independent of conventional cardiovascular risk factors. Thus, OPN can be a therapeutic target for CVDs but is not clinically available. In this review, we discuss the role of OPN in the development of CVDs and its potential as a therapeutic target.

Osteopontin Serum Concentration and Metabolic Syndrome in Male Psoriatic Patients

Psoriasis (Ps) is an immune-mediated inflammatory skin disease that is widely associated with the clinical features of metabolic syndrome (MetS), including hypertension, abdominal obesity, insulin resistance, type 2 diabetes and dyslipidemia. Osteopontin (OPN), a multifunctional protein involved in the modulation of inflammatory processes, may contribute to the development of atherosclerosis and MetS. Therefore, the aim of the study was the assessment of the correlation between OPN concentration in the peripheral blood and the presence of MetS as well as its particular components in the Ps patients. The study comprised 107 male Ps patients (50 patients with MetS and 57 without MetS) and 38 healthy volunteers (HVs). The concentration of OPN in serum was determined using enzyme-linked immunosorbent assay (ELISA) method. Fasting blood glucose and lipid profile components: total cholesterol (total CHOL), high-density lipoprotein cholesterol (HDL-CHOL), low-density lipoprotein cholesterol (LDL-CHOL), triglycerides (TG) were examined. Ps patients with MetS had significantly higher obesity, systolic blood pressure, TG, CHOL/HDL, LDL/HDL and TG/HDL ratios than Ps patients without MetS. OPN serum concentration was significantly higher in the Ps patients than in the HVs (p = 0.022) but not significantly different between the Ps patients with and without MetS (p = 0.275). OPN serum concentration in Ps patients correlated negatively with total CHOL (p = 0.004) and TG (p = 0.009). OPN is increased in Ps patients and may serve as a biomarker of some lipid abnormalities in them.

Elevated glucose alters global gene expression and tenascin-C alternative splicing in mesangial cells

Mesangial cells are the major extracellular matrix (ECM)-producing cells in the kidney glomerulus and, when exposed to elevated glucose levels, they up-regulate assembly of fibronectin (FN) and other ECM proteins. Increases in glucose concentration are known to alter gene expression; here we investigated the connection between increased ECM production and changes in gene expression in mesangial cells. Comparison of mesangial cells grown in normal or high glucose conditions by RNA-sequencing showed significant expression changes in over 6000 genes and, when grouped by KEGG pathway analysis, identified the ECM-receptor interaction and focal adhesion pathways among the top 5 upregulated pathways. Of note was the significant increase in expression of tenascin-C (TN-C), a known regulator of FN matrix assembly. Mouse TN-C has multiple isoforms due to alternative splicing of 6 FNIII repeat exons. In addition to the transcriptional increase with high glucose, exon inclusion via alternative splicing was also changed resulting in production of higher molecular weight isoforms of TN-C. Mesangial cells grown in normal glucose secreted small isoforms with 1–2 variable repeats included whereas in high glucose large isoforms estimated to include 5 repeats were secreted. Unlike the smaller isoforms, the larger TN-C was not detected in the FN matrix. This change in TN-C isoforms may affect the regulation of FN matrix assembly and in this way may contribute to increased ECM accumulation under high glucose conditions.

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Elevated glucose alters gene expression in cultured mesangial cells.

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RNA-sequencing identifies increased expression of ECM proteins and receptors.

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High glucose changes tenascin-C isoform expression by alternative splicing.

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Differential ECM localization is detected for large vs small tenascin-C isoforms.

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Switch in tenascin-C may contribute to ECM accumulation in the diabetic glomerulus.

Epigenetic Histone Modifications in the Pathogenesis of Diabetic Kidney Disease

Diabetic kidney disease (DKD), as the main complication of diabetes mellitus, is the primary cause of the end-stage renal disease (ESRD) and the most common chronic kidney disease. Overall, 30-40% of patients with type 1 and type 2 diabetes eventually develop DKD. Although some diabetes patients have intensified glycemic control, they still develop diabetic kidney disease. Current treatment methods can alleviate but do not markedly halt disease development, resulting in renal failure and severe complications, even contributing to elevated morbidity and mortality rates. DKD is a disease with interactions of genes and the environment. Emerging evidence indicates that DKD-associated key genes are also regulated by the epigenetic mechanism. Recently, increasing researches involving cells and experimental animals demonstrated that histone post-translational modifications can mediate gene expression, which correlated with diabetic kidney disease. Novel therapeutic strategies for epigenetic events could be beneficial for the early detection and treatment of DKD to prevent it from developing into end-stage renal disease (ESRD). In this review, we discuss prior findings in the field of histone modifications in DKD, especially histone acetylation and histone methylation. We then focus on recent developments in histone acetylation and methylation involved in the pathogenesis of DKD.

The Potential Role of Osteopontin and Furin in Worsening Disease Outcomes in COVID-19 Patients with Pre-Existing Diabetes

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the ongoing coronavirus disease 2019 (COVID-19) pandemic, with more than 50 million cases reported globally. Findings have consistently identified an increased severity of SARS-CoV-2 infection in individuals with diabetes. Osteopontin, a cytokine-like matrix-associated phosphoglycoprotein, is elevated in diabetes and drives the expression of furin, a proprotein convertase implicated in the proteolytic processing and activation of several precursors, including chemokines, growth factors, hormones, adhesion molecules, and receptors. Elevated serum furin is a signature of diabetes mellitus progression and is associated with a dysmetabolic phenotype and increased risk of diabetes-linked premature mortality. Additionally, furin plays an important role in enhancing the infectivity of SARS-CoV-2 by promoting its entry and replication in the host cell. Here, we hypothesize that diabetes-induced osteopontin and furin protein upregulation results in worse outcomes in diabetic patients with SARS-CoV-2 infection owing to the roles of these protein in promoting viral infection and increasing metabolic dysfunction. Thus, targeting the osteopontin-furin axis may be a plausible strategy for reducing mortality in SARS-CoV-2 patients with diabetes.

Identification of hub genes in diabetic kidney disease via multiple-microarray analysis

Background

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease; however, the underlying molecular mechanisms remain unclear. Recently, bioinformatics analysis has provided a comprehensive insight toward the molecular mechanisms of DKD. Here, we re-analyzed three mRNA microarray datasets including a single-cell RNA sequencing (scRNA-seq) dataset, with the aim of identifying crucial genes correlated with DKD and contribute to a better understanding of DKD pathogenesis.

Methods

Three datasets including GSE131882, GSE30122, and GSE30529 were utilized to find differentially expressed genes (DEGs). The potential functions of DEGs were analyzed by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. A protein-protein interaction (PPI) network was constructed, and hub genes were selected with the top three molecular complex detection (MCODE) score. A correlation analysis between hub genes and clinical indicators was also performed.

Results

In total, 84 upregulated DEGs and 49 downregulated DEGs were identified. Enriched pathways of the upregulated DEGs included extracellular matrix (ECM) receptor interaction, focal adhesion, human papillomavirus infection, malaria, and cell adhesion molecules. The downregulated DEGs were mainly enriched in ascorbate and aldarate metabolism, arginine and proline metabolism, endocrine- and other factor-regulated calcium reabsorption, mineral absorption and longevity regulating pathway, and multiple species signaling pathway. Seventeen hub genes were identified, and correlation analysis between unexplored hub genes and clinical features of DKD suggested that EGF, KNG1, GADD45B, and CDH2 might have reno-protective roles in DKD. Meanwhile, ATF3, B2M, VCAM1, CLDN4, SPP1, SOX9, JAG1, C3, and CD24 might promote the progression of DKD. Finally, most hub genes were found present in the immune cells of diabetic kidneys, which suggest the important role of inflammation infiltration in DKD pathogenesis.

Conclusions

In this study, we found seventeen hub genes using a scRNA-seq contained multiple-microarray analysis, which enriched the present understanding of molecular mechanisms underlying the pathogenesis of DKD in cells' level and provided candidate targets for diagnosis and treatment of DKD.

Co-culture of human fibroblasts, smooth muscle and endothelial cells promotes osteopontin induction in hypoxia

Arteriovenous fistulas (AVFs) are the preferred vascular access for haemodialysis of patients suffering from end-stage renal disease, a worldwide public health problem. However, they are prone to a high rate of failure due to neointimal hyperplasia and stenosis. This study aimed to determine if osteopontin (OPN) was induced in hypoxia and if OPN could be responsible for driving AVF failure. Identification of new factors that participate in remodelling of AVFs is a challenge. Three cell lines representing the cells of the three layers of the walls of arteries and veins, fibroblasts, smooth muscle cells and endothelial cells, were tested in mono- and co-culture in vitro for OPN expression and secretion in normoxia compared to hypoxia after silencing the hypoxia-inducible factors (HIF-1α, HIF-2α and HIF-1/2α) with siRNA or after treatment with an inhibitor of NF-kB. None of the cells in mono-culture showed OPN induction in hypoxia, whereas cells in co-culture secreted OPN in hypoxia. The changes in oxygenation that occur during AVF maturation up-regulate secretion of OPN through cell-cell interactions between the different cell layers that form AVF, and in turn, these promote endothelial cell proliferation and could participate in neointimal hyperplasia.

Osteopontin in Vascular Disease

Inflammatory cytokines are necessary for an acute response to injury and the progressive healing process. However, when this acute response does not resolve and becomes chronic, the same proteins that once promoted healing then contribute to chronic inflammatory pathologies, such as atherosclerosis. OPN (Osteopontin) is a secreted matricellular cytokine that signals through integrin and CD44 receptors, is highly upregulated in acute and chronic inflammatory settings, and has been implicated in physiological and pathophysiologic processes. Evidence from the literature suggests that OPN may fit within the Goldilocks paradigm with respect to cardiovascular disease, where acute increases are protective, attenuate vascular calcification, and promote postischemic neovascularization. In contrast, chronic increases in OPN are clinically associated with an increased risk for a major adverse cardiovascular event, and OPN expression is a strong predictor of cardiovascular disease independent of traditional risk factors. With the recent finding that humans express multiple OPN isoforms as the result of alternative splicing and that these isoforms have distinct biologic functions, future studies are required to determine what OPN isoform(s) are expressed in the setting of vascular disease and what role each of these isoforms plays in vascular disease progression. This review aims to discuss our current understanding of the role(s) of OPN in vascular disease pathologies using evidence from in vitro, animal, and clinical studies. Where possible, we discuss what is known about OPN isoform expression and our understanding of OPN isoform contributions to cardiovascular disease pathologies.

Histone Methyltransferases as Therapeutic Targets for Kidney Diseases

Emerging evidence has demonstrated that epigenetic regulation plays a vital role in gene expression under normal and pathological conditions. Alterations in the expression and activation of histone methyltransferases (HMTs) have been reported in preclinical models of multiple kidney diseases, including acute kidney injury, chronic kidney disease, diabetic nephropathy, polycystic kidney disease, and renal cell carcinoma. Pharmacological inhibition of these enzymes has shown promise in preclinical models of those renal diseases. In this review, we summarize recent knowledge regarding expression and activation of various HMTs and their functional roles in some kidney diseases. The preclinical activity of currently available HMT inhibitors and the mechanisms of their actions are highlighted.

Genetic and Epigenetic Studies in Diabetic Kidney Disease

Chronic kidney disease is a worldwide health crisis, while diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease (ESRD). DKD is a microvascular complication and occurs in 30–40% of diabetes patients. Epidemiological investigations and clinical observations on the familial clustering and heritability in DKD have highlighted an underlying genetic susceptibility. Furthermore, DKD is a progressive and long-term diabetic complication, in which epigenetic effects and environmental factors interact with an individual’s genetic background. In recent years, researchers have undertaken genetic and epigenetic studies of DKD in order to better understand its molecular mechanisms. In this review, clinical material, research approaches and experimental designs that have been used for genetic and epigenetic studies of DKD are described. Current information from genetic and epigenetic studies of DKD and ESRD in patients with diabetes, including the approaches of genome-wide association study (GWAS) or epigenome-wide association study (EWAS) and candidate gene association analyses, are summarized. Further investigation of molecular defects in DKD with new approaches such as next generation sequencing analysis and phenome-wide association study (PheWAS) is also discussed.

Histone Deacetylase Inhibitors and Diabetic Kidney Disease

Despite recent clinical trial advances and improvements in clinical care, kidney disease due to diabetes remains the most common cause of chronic kidney failure worldwide. In the search for new treatments, recent attentions have turned to drug repurposing opportunities, including study of the histone deacetylase (HDAC) inhibitor class of agents. HDACs are a group of enzymes that remove functional acetyl groups from histone and non-histone proteins and they can affect cellular function through both epigenetic and non-epigenetic means. Over the past decade, several HDAC inhibitors have been adopted into clinical practice, primarily for the treatment of hematological malignancy, whereas other existing therapies (for instance valproate) have been found to have HDAC inhibitory effects. Here we review the current HDAC inhibitors in the clinic and under development; the literature evidence supporting the renoprotective effects of HDAC inhibitors in experimental diabetic kidney disease; and the adverse effect profiles that may prevent existing therapies from entering the clinic for this indication. Whereas recent research efforts have shed light on the fundamental actions of HDACs in the diabetic kidney, whether these efforts will translate into novel therapies for patients will require more specific and better-tolerated therapies.

The multiple functions and mechanisms of osteopontin

Osteopontin (OPN) is a highly phosphorylated glycophosphoprotein having acidic characteristics and rich in aspartic acid. OPN, a multifunctional protein, has important functions on cardiovascular diseases, cancer, diabetes and kidney stone diseases and in the process of inflammation, biomineralization, cell viability and wound healing. Osteopontin acts on organisms by playing a key role in secretion levels of interleukin-10 (IL-10), interleukin-12 (IL-12), interleukin-3 (IL-3), interferon-γ (IFN-γ), integrin αvB3, nuclear factor kappa B (NF-kB), macrophage and T cells, regulating the osteoclast function and affecting CD44 receptors. The aim of the present review is to address majority of different functions of OPN protein which are known, suspected or suggested through the data obtained about this protein yet.

Effect of TET2 on the pathogenesis of diabetic nephropathy through activation of transforming growth factor β1 expression via DNA demethylation

AIMS

Transforming growth factor β1 (TGFβ1) plays a pivotal role in the pathogenesis of diabetic nephropathy (DN). However, the mechanism of its expression and activation induced by high glucose (HG) is still unclear. We mainly explored the role of ten-eleven translocation enzyme-2 (TET2) in regulating TGFβ1 expression in the process of DN.

MAIN METHODS

Human mesangial cells (HMCs) and db/db mice were used to analyze the biological effects of hyperglycemia both in vivo and in vitro. Gene expression levels, cell proliferation, protein recruitment levels to TGFβ1 regulatory region, DNA methylation statues and pathological changes in kidney were tested in different groups. Short hairpin RNA(shRNA) and oral inhibitor were used to knock down or inhibit TET2 expression.

KEY FINDINGS

Our study demonstrated that TET2 expression was increased in the renal cortex of db/db mice and in HMCs inducing by HG. We also found that TET2 binding was increased while DNA methylation of CpG islands was reduced in the TGFβ1 regulation region in HG, resulting in the increased expression level of TGFβ1 and cell phenotype transformation. More importantly, clinical research revealed that gradually decreased DNA methylation in the TGFβ1 regulatory region was also present in patients with diabetes and DN.

SIGNIFICANCE

Our work suggests that TET2 plays an important role in the pathogenesis of DN by activating TGFβ1 expression through demethylation of CpG islands in the TGFβ1 regulatory region. This may provide a potential new therapeutic target for DN.

Role of osteopontin and its regulation in pancreatic islet

Osteopontin (OPN) is involved in various physiological processes and also implicated in multiple pathological states. It has been suggested that OPN may have a role in type 2 diabetes (T2D) by protecting pancreatic islets and interaction with incretins. However, the regulation and function of OPN in islets, especially in humans, remains largely unexplored. In this study, we performed our investigations on both diabetic mouse model SUR1-E1506K+/+ and islets from human donors. We demonstrated that OPN protein, secretion and gene expression was elevated in the diabetic SUR1-E1506K+/+ islets. We also showed that high glucose and incretins simultaneously stimulated islet OPN secretion. In islets from human cadaver donors, OPN gene expression was elevated in diabetic islets, and externally added OPN significantly increased glucose-stimulated insulin secretion (GSIS) from diabetic but not normal glycemic donors. The increase in GSIS by OPN in diabetic human islets was Ca²⁺ dependent, which was abolished by Ca²⁺-channel inhibitor isradipine. Furthermore, we also confirmed that OPN promoted cell metabolic activity when challenged by high glucose. These observations provided evidence on the protective role of OPN in pancreatic islets under diabetic condition, and may point to novel therapeutic targets for islet protection in T2D.

Personalized epigenetic management of diabetes

The novel genome-wide assays of epigenetic marks have resulted in a greater understanding of how genetics and the environment interact in the development and inheritance of diabetes. Chronic hyperglycemia induces epigenetic changes in multiple organs, contributing to diabetic complications. Specific epigenetic-modifying compounds have been developed to erase these modifications, possibly slowing down the onset of diabetes-related complications. The current review is an update of the previously published paper, describing the most recent advances in the epigenetics of diabetes.

Mechanisms of metabolic memory and renal hypoxia as a therapeutic target in diabetic kidney disease

Diabetic kidney disease (DKD) is a worldwide public health problem. The definition of DKD is under discussion. Although the term DKD was originally defined as ‘kidney disease specific to diabetes,’ DKD frequently means chronic kidney disease with diabetes mellitus and includes not only classical diabetic nephropathy, but also kidney dysfunction as a result of nephrosclerosis and other causes. Metabolic memory plays a crucial role in the progression of various complications of diabetes, including DKD. The mechanisms of metabolic memory in DKD are supposed to include advanced glycation end‐products, deoxyribonucleic acid methylation, histone modifications and non‐coding ribonucleic acid including micro ribonucleic acid. Regardless of the presence of diabetes mellitus, the final common pathway in chronic kidney disease is chronic kidney hypoxia, which influences epigenetic processes, including deoxyribonucleic acid methylation, histone modification, and conformational changes in micro ribonucleic acid and chromatin. Therefore, hypoxia and oxidative stress are appropriate targets of therapies against DKD. Prolyl hydroxylase domain inhibitor enhances the defensive mechanisms against hypoxia. Bardoxolone methyl protects against oxidative stress, and can even reverse impaired renal function; a phase 2 trial with considerable attention to heart complications is currently ongoing in Japan.

Elucidation of mechanism of blood-brain barrier damage for prevention and treatment of vascular dementia

It is well-known that the blood-brain barrier (BBB) plays significant roles in transporting intravascular substances into the brain. The BBB in cerebral capillaries essentially impedes the influx of intravascular compounds from the blood to the brain, while nutritive substances, such as glucose, can be selectively transported through several types of influx transporters in endothelial cells. In the choroid plexus, intravascular substances can invade the parenchyma as fenestrations exist in endothelial cells of capillaries. However, the substances cannot invade the ventricles easily as there are tight junctions between epithelial cells in the choroid plexus. This restricted movement of the substances across the cytoplasm of the epithelial cells constitutes a blood-cerebrospinal fluid barrier (BCSFB). In the brain, there are circumventricular organs, in which the barrier function is imperfect in capillaries. Accordingly, it is reasonable to consider that intravascular substances can move in and around the parenchyma of the organs. Actually, it was reported in mice that intravascular substances moved in the corpus callosum, medial portions of the hippocampus, and periventricular areas via the subfornical organs or the choroid plexus. Regarding pathways of intracerebral interstitial and cerebrospinal fluids to the outside of the brain, two representative drainage pathways, or perivascular drainage and glymphatic pathways, are being established. The first is the pathway in a retrograde direction to the blood flow through the basement membrane in walls of cerebral capillaries, the tunica media of arteries, and the vessels walls of the internal carotid artery. The second is in an anterograde direction to blood flow through the para-arterial routes, aquaporin 4-dependent transport through the astroglial cytoplasm, and para-venous routes, and then the fluids drain into the subarachnoid CSF. These fluids are finally considered to drain into the cervical lymph nodes or veins. These clearance pathways may play a role in maintenance of the barrier in the entire brain. Obstruction of the passage of fluids through the perivascular drainage and glymphatic pathways as well as damage of the BBB and BCSFB may induce several kinds of brain disorders, such as vascular dementia. In this review, we focus on the relationship between damage of the barriers and the pathogenesis of vascular dementia and introduce recent findings including our experimental data using animal models.

High Glucose-Induced Hypomethylation Promotes Binding of Sp-1 to Myo-Inositol Oxygenase: Implication in the Pathobiology of Diabetic Tubulopathy

The catabolic enzyme myo-inositol oxygenase (MIOX) is expressed in proximal tubules and up-regulated in the diabetic state. Previously, we reported its transcriptional and translation regulation by high glucose (HG), osmolytes, and fatty acids. However, its epigenetic regulation is unknown. Bisulfite sequencing revealed that both human and mouse MIOX promoters, enriched with CpG sites, are hypomethylated and unmethylated under HG ambience and hyperglycemic states associated with increased MIOX expression. Eletrophoretic mobility shift assays revealed increased binding of unmethylated oligos with nucleoproteins of cells maintained under HG. In addition, a strong binding of specificity protein (Sp)-1 transcription factor with MIOX promoter was observed under HG, especially with unmethylated Sp-1 oligo. Specificity of binding was established by supershift assays and treatment with the Sp-1 inhibitor mithramycin. Promoter analysis revealed an increase in luciferase activity under HG, which was reduced after mutation of the Sp-1-binding site. Sp1 siRNA treatment reduced mRNA and protein expression of Sp-1 and MIOX and generation of reactive oxygen species derived from NADPH oxidase (NOX)-4 and mitochondrial sources. In addition, there was reduced expression of hypoxia-inducible factor-1α relevant in the pathogenesis of diabetic nephropathy. Sp1 siRNA treatment reduced fibronectin expression, an extracellular matrix protein that is increased in diabetic nephropathy and tubulopathy. HG-induced MIOX expression was also reduced with the treatment of apelin-13, which deacetylates histones. Overall, these findings highlight the epigenetic regulation of MIOX in the pathogenesis of diabetic tubulopathy.

Diabetic nephropathy and endothelial dysfunction: Current and future therapies, and emerging of vascular imaging for preclinical renal-kinetic study

An explosion in global epidemic of type 2 diabetes mellitus poses major rise in cases with vascular endothelial dysfunction ranging from micro- (retinopathy, nephropathy and neuropathy) to macro-vascular (atherosclerosis and cardiomyopathy) conditions. Functional destruction of endothelium is regarded as an early event that lays the groundwork for the development of renal microangiopathy and subsequent clinical manifestation of nephropathic symptoms. Recent research has shed some light on the molecular mechanisms of type 2 diabetes-associated comorbidity of endothelial dysfunction and nephropathy. Stemming from currently proposed endothelium-centered therapeutic strategies for diabetic nephropathy, this review highlighted some most exploited pathways that involve the intricate coordination of vasodilators, vasoconstrictors and vaso-modulatory molecules in the pathogenesis of diabetic nephropathy. We also emphasized the emerging roles of oxidative and epigenetic modifications of microvasculature as our prospective therapeutics for diabetic renal diseases. Finally, this review in particular addressed the potential use of multispectral optoacoustic tomography in real-time, minimally-invasive vascular imaging of small experimental animals for preclinical renal-kinetic drug trials.