Cisplatin induces Sirt1 in association with histone deacetylation and increased Werner syndrome protein in the kidney

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.

Antagonistic Interaction between Histone Deacetylase Inhibitor: Cambinol and Cisplatin-An Isobolographic Analysis in Breast Cancer In Vitro Models

Breast cancer (BC) is the leading cause of death in women all over the world. Currently, combined chemotherapy with two or more agents is considered a promising anti-cancer tool to achieve better therapeutic response and to reduce therapy-related side effects. In our study, we demonstrated an antagonistic effect of cytostatic agent-cisplatin (CDDP) and histone deacetylase inhibitor: cambinol (CAM) for breast cancer cell lines with different phenotypes: estrogen receptor positive (MCF7, T47D) and triple negative (MDA-MB-231, MDA-MB-468). The type of pharmacological interaction was assessed by an isobolographic analysis. Our results showed that both agents used separately induced cell apoptosis; however, applying them in combination ameliorated antiproliferative effect for all BC cell lines indicating antagonistic interaction. Cell cycle analysis showed that CAM abolished cell cycle arrest in S phase, which was induced by CDDP. Additionally, CAM increased cell proliferation compared to CDDP used alone. Our data indicate that CAM and CDDP used in combination produce antagonistic interaction, which could inhibit anti-cancer treatment efficacy, showing importance of preclinical testing.

Epigenetic Mechanisms Involved in Cisplatin-Induced Nephrotoxicity: An Update

Cisplatin is an antineoplastic drug used for the treatment of many solid tumors. Among its various side effects, nephrotoxicity is the most detrimental. In recent years, epigenetic regulation has emerged as a modulatory mechanism of cisplatin-induced nephrotoxicity, involving non-coding RNAs, DNA methylation and histone modifications. These epigenetic marks alter different signaling pathways leading to damage and cell death. In this review, we describe how different epigenetic modifications alter different pathways leading to cell death by apoptosis, autophagy, necroptosis, among others. The study of epigenetic regulation is still under development, and much research remains to fully determine the epigenetic mechanisms underlying cell death, which will allow leading new strategies for the diagnosis and therapy of this disease.

The effect of energy restriction on development and progression of chronic kidney disease: review of the current evidence

Energy restriction (ER) has anti-ageing effects and probably protects from a range of chronic diseases including cancer, diabetes and chronic kidney disease (CKD). Specifically, ER has a positive impact on experimental kidney ageing, CKD (diabetic nephropathy, polycystic kidney disease) and acute kidney injury (nephrotoxic, ischaemia-reperfusion injury) through such mechanisms as increased autophagy, mitochondrial biogenesis and DNA repair, and decreased inflammation and oxidative stress. Key molecules contributing to ER-mediated kidney protection include adenosine monophosphate-activated protein kinase, sirtuin-1 and PPAR-γ coactivator 1α. However, CKD is a complex condition, and ER may potentially worsen CKD complications such as protein-energy wasting, bone-mineral disorders and impaired wound healing. ER mimetics are drugs, such as metformin and Na-glucose co-transporter-2 which mimic the action of ER. This review aims to provide comprehensive data regarding the effect of ER on CKD progression and outcomes.

Baicalin serves a protective role in diabetic nephropathy through preventing high glucose-induced podocyte apoptosis

Diabetic nephropathy (DN) is one of the late complications of diabetes, which seriously affects the lives of patients. Baicalin (BA) is a flavone glycoside that has been identified to improve renal function in patients with DN. The present study aimed to investigate the roles and mechanisms of BA in DN. For that purpose, podocytes were cultured for 48 h under conditions of high glucose (HG; 30 mM D-glucose) or normal glucose (NG; 5 mM D-glucose). Then, the cells were treated with different concentrations of BA (6.25, 12.5 and 25 µM) for 24 h. Cell viability and apoptosis were determined using an MTT assay and flow cytometry, respectively. Protein and mRNA expression levels were analyzed using western blotting and reverse transcription-quantitative PCR, respectively. BA treatment was identified to promote the viability of podocytes and suppress cell apoptosis in a dose-dependent manner. Compared with the results in the NG group, HG stimulation significantly decreased the viability of podocytes and increased the apoptotic rate, whereas BA treatment following HG stimulation increased the viability of podocytes and decreased the apoptotic rate. Moreover, the effect of BA was revealed to be associated with the sirtuin 1/NF-κB signaling pathway in DN. In conclusion, the results of the present study suggested that BA treatment may significantly decrease HG-induced podocyte apoptosis, which indicated that BA might be a promising agent for DN treatment.

Epigenetic Regulation in Kidney Toxicity: Insights From Cisplatin Nephrotoxicity

Nephrotoxicity, as a result of the exposure of kidney to endogenous and exogenous toxins, is an important factor for acute kidney injury and the development of progressive chronic kidney disease. Cisplatin is among the most widely studied kidney toxicants. In the past decade, epigenetic regulation has emerged as a notable pathogenic mechanism in cisplatin nephrotoxicity, including DNA methylation, histone modification, and noncoding RNAs. In this review, we use cisplatin nephrotoxicity as an example to highlight the epigenetic alteration, function, and underlying mechanism in kidney toxicity. The study of epigenetic regulation in kidney toxicity is still in its infancy, and further investigation will bring new insights for the development of novel diagnostic biomarkers and therapeutic interventions.

Epigenetic regulation in AKI and kidney repair: mechanisms and therapeutic implications

Acute kidney injury (AKI) is a major public health concern associated with high morbidity and mortality. Despite decades of research, the pathogenesis of AKI remains incompletely understood and effective therapies are lacking. An increasing body of evidence suggests a role for epigenetic regulation in the process of AKI and kidney repair, involving remarkable changes in histone modifications, DNA methylation and the expression of various non-coding RNAs. For instance, increases in levels of histone acetylation seem to protect kidneys from AKI and promote kidney repair. AKI is also associated with changes in genome-wide and gene-specific DNA methylation; however, the role and regulation of DNA methylation in kidney injury and repair remains largely elusive. MicroRNAs have been studied quite extensively in AKI, and a plethora of specific microRNAs have been implicated in the pathogenesis of AKI. Emerging research suggests potential for microRNAs as novel diagnostic biomarkers of AKI. Further investigation into these epigenetic mechanisms will not only generate novel insights into the mechanisms of AKI and kidney repair but also might lead to new strategies for the diagnosis and therapy of this disease.

Energy restriction in renal protection

Energy restriction (ER) has been widely studied as a novel intervention, and its ability to prolong life has been fully demonstrated. For example, ER can significantly extend the lifespans of model flies, worms, rodents and other mammals. The role of ER in renal protection has also been elucidated. In preclinical studies, adjusting total energy intake or consumption of specific nutrients has prophylactic or therapeutic effects on ageing-related kidney disease and acute and chronic kidney injury. Amino acid restriction has gradually attracted attention. ER mimetics have also been studied in depth. The protective mechanisms of ER and ER mimetics for renal injury include increasing AMP-activated protein kinase and sirtuin type 1 (Sirt1) levels and autophagy and reducing mammalian target of rapamycin, inflammation and oxidative stress. However, the renal protective effect of ER has mostly been investigated in rodent models, and the role of ER in patients cannot be determined due to the lack of large randomised controlled trials. To protect the kidney, the mechanism of ER must be thoroughly researched, and more accurate diet or drug interventions need to be identified.

Tangshen formula improves inflammation in renal tissue of diabetic nephropathy through SIRT1/NF-κB pathway

The present study investigated the mechanism underlying the anti-inflammatory effects of Tangshen formula (TS) in Sprague Dawley (SD) rats with diabetic nephropathy (DN). A rat model of DN was established by intraperitoneal injection of 1% (40 mg/kg) streptozotocin and administration of a high fat and glucose diet. Subsequently, SD rats were randomly divided into six groups (n=8): A DN group, a valsartan group, a high-dose TS group, a middle-dose TS group, a low-dose TS group and a control group with normal SD rats. Once rats received their allocated treatment for 12 weeks, body weight and kidney weight were recorded, and fasting blood glucose, ratio of urinary protein, β₂-MG and creatinine clearance rate were determined. Furthermore, hemodynamic indices, including plasma viscosity and whole blood reduction viscosity were detected. Immunohistochemistry was used to detect the infiltration of macrophages in the kidneys of rats. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to investigate the activation; mRNA and protein expression levels of monocyte chemoattractant protein-1 (MCP-1), macrophage migration inhibitory factor (MIF), nuclear factor-κB (NF-κB) and sirtuin-1 (SIRT1) in each group. In comparison with the DN group, each biochemical indicator of rats in the high-dose TS group was significantly decreased (P<0.05). Blood viscosity in each treatment group was significantly decreased when compared with the DN group (P<0.01). Hematoxylin and eosin staining indicated that the infiltration of macrophages was significantly decreased in the high-dose TS group when compared with the DN group (P<0.01). mRNA and protein expression levels of MCP-1 and MIF in the high-dose TS group were significantly decreased when compared with the DN group (P<0.05). In the treatment groups, SITR1 mRNA expression levels were significantly increased, whereas the mRNA expression levels of NF-κB were significantly decreased (P<0.01). Western blotting results indicated a significant decrease in the protein expression levels of acetylated NF-κB in the treatment groups when compared with the DN group (P<0.01) and the propensity of protein expression of the other inflammatory factors were consistent with the mRNA findings. The results of the high-dose TS group were similar to those of the valsartan group. The present study indicates that TS was able to activate SITR1, which lead to NF-κB deacetylation, thus reducing the release of inflammatory factors and decreasing the severity of diabetic nephropathy.

DNA methylation protects against cisplatin-induced kidney injury by regulating specific genes, including interferon regulatory factor 8

DNA methylation is an epigenetic mechanism that regulates gene transcription without changing primary nucleotide sequences. In mammals, DNA methylation involves the covalent addition of a methyl group to the 5-carbon position of cytosine by DNA methyltransferases (DNMTs). The change of DNA methylation and its pathological role in acute kidney injury (AKI) remain largely unknown. Here, we analyzed genome-wide DNA methylation during cisplatin-induced AKI by reduced representation bisulfite sequencing. This technique identified 215 differentially methylated regions between the kidneys of control and cisplatin-treated animals. While most of the differentially methylated regions were in the intergenic, intronic, and coding DNA sequences, some were located in the promoter or promoter-regulatory regions of 15 protein-coding genes. To determine the pathological role of DNA methylation, we initially examined the effects of the DNA methylation inhibitor 5-aza-2'-deoxycytidine and showed it increased cisplatin-induced apoptosis in a rat kidney proximal tubular cell line. We further established a kidney proximal tubule-specific DNMT1 (PT-DNMT1) knockout mouse model, which showed more severe AKI during cisplatin treatment than wild-type mice. Finally, interferon regulatory factor 8 (Irf8), a pro-apoptotic factor, was identified as a hypomethylated gene in cisplatin-induced AKI, and this hypomethylation was associated with a marked induction of Irf8. In the rat kidney proximal tubular cells, the knockdown of Irf8 suppressed cisplatin-induced apoptosis, supporting a pro-death role of Irf8 in renal tubular cells. Thus, DNA methylation plays a protective role in cisplatin-induced AKI by regulating specific genes, such as Irf8.

Interstrand Crosslink Repair as a Target for HDAC Inhibition

DNA interstrand crosslinks (ICLs) covalently connect complementary DNA strands. Consequently, DNA replication and transcription are hampered, DNA damage responses (DDR) are initiated, and cell death is triggered. Therefore, drugs inducing ICLs are effective against rapidly growing cancer cells. However, tumors engage a complicated enzymatic machinery to repair and survive ICLs. Several factors, including the post-translational acetylation/deacetylation of lysine residues within proteins, control this network. Histone deacetylases (HDACs) modulate the expression and functions of DNA repair proteins which remove ICLs and control the accessibility of chromatin. Accordingly, histone deacetylase inhibitors (HDACi) are small, pharmacologically and clinically relevant molecules that sensitize cancer cells to ICL inducers. We discuss the mechanism of ICL repair and targets of HDACi within this pathway.

Melatonin prevents acute kidney injury in severely burned rats via the activation of SIRT1

Acute kidney injury (AKI) is a common complication after severe burns. Melatonin has been reported to protect against multiple organ injuries by increasing the expression of SIRT1, a silent information regulator that regulates stress responses, inflammation, cellular senescence and apoptosis. This study aimed to investigate the protective effects of melatonin on renal tissues of burned rats and the role of SIRT1 involving the effects. Rat severely burned model was established, with or without the administration of melatonin and SIRT1 inhibitor. The renal function and histological manifestations were determined to evaluate the severity of kidney injury. The levels of acetylated-p53 (Ac-p53), acetylated-p65 (Ac-p65), NF-κB, acetylated-forkhead box O1 (Ac-FoxO1), Bcl-2 and Bax were analyzed to study the underlying mechanisms. Our results suggested that severe burns could induce acute kidney injury, which could be partially reversed by melatonin. Melatonin attenuated oxidative stress, inflammation and apoptosis accompanied by the increased expression of SIRT1. The protective effects of melatonin were abrogated by the inhibition of SIRT1. In conclusion, we demonstrate that melatonin improves severe burn-induced AKI via the activation of SIRT1 signaling.

Epigenetic changes in p21 expression in renal cells after exposure to bromate

This study tested the hypothesis that bromate (KBrO3)-induced renal cell death is mediated by epigenetic mechanisms. Global DNA methylation, as assessed by 5-methylcytosine staining, was not changed in normal rat kidney cells treated with acute cytotoxic doses of KBrO3 (100 and 200 ppm), as compared with controls. However, KBrO3 treatment did increase p38, p53 and histone 2AX (H2AX) phosphorylation, and p21 expression. Treatment of cells with inhibitors of DNA methyltransferase (5-azacytidine or 5-Aza) and histone deacetylase (trichostatin A or TSA) in addition to KBrO3 increased cytotoxicity, as compared with cells exposed to KBrO3 alone. 5-Aza and TSA co-treatment did not alter p38 or p53 phosphorylation, but slightly decreased H2AX phosphorylation and significantly decreased p21 expression. We also assessed epigenetic changes in cells treated under sub-chronic conditions with environmentally relevant concentrations of KBrO3. Under these conditions (0-10ppm KBrO3 for up to 18 days), we detected no increases in cell death or DNA damage. In contrast, slight alterations were detected in the phosphorylation of H2AX, p38, and p53. Sub-chronic low-dose KBrO3 treatment also induced a biphasic response in p21 expression, with lower concentrations increasing expression, but higher concentrations decreasing expression. Methylation-specific PCR demonstrated that sub-chronic KBrO3 treatment altered the methylation of cytosine bases in the p21 gene, as compared with controls, correlating to alterations in p21 protein expression. Collectively, these data show the novel finding that KBrO3-induced renal cell death is altered by inhibitors of epigenetic modifying enzymes and that KBrO3 itself induces epigenetic changes in the p21 gene.

Beneficial effects of short-term calorie restriction against cisplatin-induced acute renal injury in aged rats

BACKGROUND

The therapeutic use of the antineoplastic drug cisplatin (DDP) in the elderly is limited by its nephrotoxic effects. The aim of this study was to examine the effect of short-term calorie restriction (CR) on DDP-induced nephrotoxicity in aged rats.

METHODS

A group of 25-month-old male Sprague-Dawley rats were divided into two groups: ad libitum (AL) and CR, which were fed 60% of the food consumed by AL rats for 8 weeks. The two groups were each further randomly divided into two subgroups: OAL control, OAL+DDP, OCR control, and OCR+DDP. A single dose of DDP (6 mg/kg) was injected intraperitoneally. Functional and structural changes of the kidneys were evaluated quantitatively by biochemical, histopathological, and morphometric analyses.

RESULTS

At the end of the 8 weeks, rats in the OCR group lost 14.8% more body mass than rats in the OAL group. Pretreatment with CR had several effects: (1) it reduced the levels of blood urea nitrogen and serum creatinine, (2) it reduced the magnitude of the renal tubular epithelial damage, and (3) it significantly reduced the incidence of activated caspase-3 and TUNEL-positive cells in kidneys injured by DDP. However, SIRT1 had the opposite trend after DDP application between the two groups.

CONCLUSIONS

Short-term CR exhibits a renoprotective effect in experimental DDP-induced renal injury, the mechanism of which may involve CR antiapoptotic effects and promotion of SIRT1.

Renal protective effect of sirtuin 1

Silent information regulator 2 (Sir2) is a nicotinamide adenine dinucleotide- (NAD(+)-) dependent deacetylase. The homology of SIRT1 and Sir2 has been extensively studied. SIRT1 deacetylates target proteins using the coenzyme NAD(+) and is therefore linked to cellular energy metabolism and the redox state through multiple signalling and survival pathways. During the past decade, investigators have reported that SIRT1 activity is essential in cancer, neurodegenerative diseases, diabetes, cardiovascular disease, and other age-related diseases. In the kidneys, SIRT1 may inhibit renal cell apoptosis, inflammation, and fibrosis. Therefore its activation may also become a new therapeutic target in the patients with chronic kidney disease including diabetic nephropathy. In this paper, we would like to review the protective functions of sirtuins and the role of SIRT1 in the onset of kidney disease based on previous studies, including diabetic nephropathy, acute renal injury, chronic kidney disease as well as lupus nephritis.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Exogenous NAD(+) supplementation protects H9c2 cardiac myoblasts against hypoxia/reoxygenation injury via Sirt1-p53 pathway

Nicotinamide adenine dinucleotide (NAD(+) ) not only transfers electrons in mitochondrial respiration, but also acts as an indispensable cosubstrate for Sirt1, the class III histone/nonhistone deacetylase. However, NAD(+) is depleted in myocardial ischemia/reperfusion (IR) injury. The objective of this study was to investigate the role of exogenous NAD(+) supplementation in hypoxia/reoxygenation (HR)-stressed H9c2 cardiac myoblasts. Firstly, the effects of distinct treating time points and doses of NAD(+) supplementation on the viability of HR-stressed H9c2 cells were detected. Secondly, intracellular NAD(+) levels in HR-stressed H9c2 cells at various extracellular NAD(+) concentrations were determined. Thirdly, the role of NAD(+) supplementation in HR-induced cell apoptosis and its relevance to Sirtuin 1-p53 pathway were investigated. Exogenous NAD(+) supplementation elevated intracellular NAD(+) level and reduced HR-induced cell death in both time- and concentration-dependent manners. It appeared that NAD(+) supplementation exerted the greatest protection when extracellular concentration ranged from 500 to 1000 μm and when NAD(+) was added immediately after reoxygenation began. NAD(+) replenishment restored Sirt1 activity, reduced the acetylation level of p53 (Lys373 & 382), and attenuated cell apoptosis in HR-stressed H9c2 cells, whereas inhibition of Sirt1 activity alleviated the effects of NAD(+) replenishment. These results indicated that exogenous NAD(+) supplementation attenuated HR-induced cell apoptosis, which was at least partly mediated by restoring Sirt1 activity and subsequently inhibiting p53 activity via deacetylating p53 at lysine 373 and 382.

Telomerase-independent paths to immortality in predictable cancer subtypes

The vast majority of cancers commandeer the activity of telomerase - the remarkable enzyme responsible for prolonging cellular lifespan by maintaining the length of telomeres at the ends of chromosomes. Telomerase is only normally active in embryonic and highly proliferative somatic cells. Thus, targeting telomerase is an attractive anti-cancer therapeutic rationale currently under investigation in various phases of clinical development. However, previous reports suggest that an average of 10-15% of all cancers lose the functional activity of telomerase and most of these turn to an Alternative Lengthening of Telomeres pathway (ALT). ALT-positive tumours will therefore not respond to anti-telomerase therapies and there is a real possibility that such drugs would be toxic to normal telomerase-utilising cells and ultimately select for resistant cells that activate an ALT mechanism. ALT exploits certain DNA damage response (DDR) components to counteract telomere shortening and rapid trimming. ALT has been reported in many cancer subtypes including sarcoma, gastric carcinoma, central nervous system malignancies, subtypes of kidney (Wilm's Tumour) and bladder carcinoma, mesothelioma, malignant melanoma and germ cell testicular cancers to name but a few. A recent heroic study that analysed ALT in over six thousand tumour samples supports this historical spread, although only reporting an approximate 4% prevalence. This review highlights the various methods of ALT detection, unravels several molecular ALT models thought to promote telomere maintenance and elongation, spotlights the DDR components known to facilitate these and explores why certain tissues are more likely to subvert DDR away from its usually protective functions, resulting in a predictive pattern of prevalence in specific cancer subsets.