Blockade of histone deacetylase 6 protects against cisplatin-induced acute kidney injury

Role of epigenetically regulated inflammation in renal diseases

In recent decades, renal disease research has witnessed remarkable advances. Experimental evidence in this field has highlighted the role of inflammation in kidney disease. Epigenetic dynamics and immunometabolic reprogramming underlie the alterations in cellular responses to intrinsic and extrinsic stimuli; these factors determine cell identity and cell fate decisions and represent current research hotspots. This review focuses on recent findings and emerging concepts in epigenetics and inflammatory regulation and their effect on renal diseases. This review aims to summarize the role and mechanisms of different epigenetic modifications in renal inflammation and injury and provide new avenues for future research on inflammation-related renal disease and drug development.

Hyperoside ameliorates cisplatin-induced acute kidney injury by regulating the expression and function of Oat1

Cisplatin is a widely used chemotherapeutic agent to treat solid tumours in clinics. However, cisplatin-induced acute kidney injury (AKI) limits its clinical application. This study investigated the effect of hyperoside (a flavonol glycoside compound) on regulating AKI.The model of cisplatin-induced AKI was established, and hyperoside was preadministered to investigate its effect on improving kidney injury.Hyperoside ameliorated renal pathological damage, reduced the accumulation of SCr, BUN, Kim-1 and indoxyl sulphate in vivo, increased the excretion of indoxyl sulphate into the urine, and upregulated the expression of renal organic anion transporter 1 (Oat1). Moreover, evaluation of rat kidney slices demonstrated that hyperoside promoted the uptake of PAH (p-aminohippurate, the Oat1 substrate), which was confirmed by transient over-expression of OAT1 in HEK-293T cells. Additionally, hyperoside upregulated the mRNA expression of Oat1 upstream regulators hepatocyte nuclear factor-1α (HNF-1α) and pregnane X receptor (PXR).These findings indicated hyperoside could protect against cisplatin-induced AKI by promoting indoxyl sulphate excretion through regulating the expression and function of Oat1, suggesting hyperoside may offer a potential tactic for cisplatin-induced AKI treatment.

Genetic and pharmacological inhibition of GRPR protects against acute kidney injury via attenuating renal inflammation and necroptosis

Gastrin-releasing peptide (GRP) binds to its receptor (GRP receptor [GRPR]) to regulate multiple biological processes, but the function of GRP/GRPR axis in acute kidney injury (AKI) remains unknown. In the present study, GRPR is highly expressed by tubular epithelial cells (TECs) in patients or mice with AKI, while histone deacetylase 8 may lead to the transcriptional activation of GRPR. Functionally, we uncovered that GRPR was pathogenic in AKI, as genetic deletion of GRPR was able to protect mice from cisplatin- and ischemia-induced AKI. This was further confirmed by specifically deleting the GRPR gene from TECs in GRPRFlox/Flox//KspCre mice. Mechanistically, we uncovered that GRPR was able to interact with Toll-like receptor 4 to activate STAT1 that bound the promoter of MLKL and CCL2 to induce TEC necroptosis, necroinflammation, and macrophages recruitment. This was further confirmed by overexpressing STAT1 to restore renal injury in GRPRFlox/Flox/KspCre mice. Concurrently, STAT1 induced GRP synthesis to enforce the GRP/GRPR/STAT1 positive feedback loop. Importantly, targeting GRPR by lentivirus-packaged small hairpin RNA or by treatment with a novel GRPR antagonist RH-1402 was able to inhibit cisplatin-induced AKI. In conclusion, GRPR is pathogenic in AKI and mediates AKI via the STAT1-dependent mechanism. Thus, targeting GRPR may be a novel therapeutic strategy for AKI.

Protective Role of Betulinic Acid against Cisplatin-Induced Nephrotoxicity and Its Antibacterial Potential toward Uropathogenic Bacteria

Acute kidney injury (AKI) is one of the major side effects of cisplatin, a remarkable anticancer agent. Therefore, there is a growing need to find an agent that could mitigate cisplatin-induced nephrotoxicity. Betulinic acid (BA) is a natural compound isolated from Silene succulenta Forssk for the first time, with miraculous biological activities and no reports of its effect on the nephrotoxicity induced by cisplatin. Mice received BA orally with doses of 30 and 50 mg/kg before the intraperitoneal injection of cisplatin. Betulinic acid was found to decrease serum levels of creatinine and tissue levels of NGAL and kidney injury molecule (KIM-1) and improve the histological changes in the kidney. In addition, BA decreased the oxidative stress marker malondialdehyde (MDA), increased superoxide dismutase (SOD) antioxidative activity and suppressed the intensity of IL-1B and NFкB immuno-staining. Interestingly, betulinic acid enhanced autophagy by increasing beclin 1, ATG5, and LC3II and decreasing p62 expressions. Thus, our findings suggest betulinic acid as a potential agent that may protect from acute kidney injury by targeting inflammation, oxidative stress, and autophagy processes. Novel drugs are needed to combat the spreading of multidrug resistance between pathogenic bacteria, especially uropathogenic isolates. So, we elucidated the antibacterial properties of BA on Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae. Betulinic acid had minimum inhibitory concentration values (128 to 512 µg/mL). In addition, it adversely affected the membrane integrity of the tested isolates. Accordingly, betulinic acid should be clinically investigated in the future for urinary tract diseases.

Autophagy and necroptosis in cisplatin-induced acute kidney injury: Recent advances regarding their role and therapeutic potential

Cisplatin (CP) is a broad-spectrum antineoplastic agent, used to treat many different types of malignancies due to its high efficacy and low cost. However, its use is largely limited by acute kidney injury (AKI), which, if left untreated, may progress to cause irreversible chronic renal dysfunction. Despite substantial research, the exact mechanisms of CP-induced AKI are still so far unclear and effective therapies are lacking and desperately needed. In recent years, necroptosis, a novel subtype of regulated necrosis, and autophagy, a form of homeostatic housekeeping mechanism have witnessed a burgeoning interest owing to their potential to regulate and alleviate CP-induced AKI. In this review, we elucidate in detail the molecular mechanisms and potential roles of both autophagy and necroptosis in CP-induced AKI. We also explore the potential of targeting these pathways to overcome CP-induced AKI according to recent advances.

Advances in the Mechanistic Study of the Control of Oxidative Stress Injury by Modulating HDAC6 Activity

Oxidative stress is defined as an injury resulting from a disturbance in the dynamic equilibrium of the redox environment due to the overproduction of active/radical oxygen exceeding the antioxidative ability of the body. This is a key step in the development of various diseases. Oxidative stress is modulated by different factors and events, including the modification of histones, which are the cores of nucleosomes. Histone modification includes acetylation and deacetylation of certain amino acid residues; this process is catalyzed by different enzymes. Histone deacetylase 6 (HDAC6) is a unique deacetylating protease that also catalyzes the deacetylation of different nonhistone substrates to regulate various physiologic processes. The intimate relationship between HDAC6 and oxidative stress has been demonstrated by different studies. The present paper aims to summarize the data obtained from a mechanistic study of HDAC6 and oxidative stress to guide further investigations on mechanistic characterization and drug development.

HDAC6 Inhibition Alleviates Ischemia- and Cisplatin-Induced Acute Kidney Injury by Promoting Autophagy

Histone deacetylase (HDAC) 6 exists exclusively in cytoplasm and deacetylates cytoplasmic proteins such as α-tubulin. HDAC6 dysfunction is associated with several pathological conditions in renal disorders, including UUO-induced fibrotic kidneys and rhabdomyolysis-induced nephropathy. However, the role of HDAC6 in ischemic acute kidney injury (AKI) and the mechanism by which HDAC6 inhibition protects tubular cells after AKI remain unclear. In the present study, we observed that HDAC6 was markedly activated in kidneys subjected to ischemia- and cisplatin (cis)-induced AKI treatment. Pharmacological inhibition of HDAC6 alleviated renal impairment and renal tubular damage after ischemia and cisplatin treatment. HDAC6 dysfunction was associated with decreased acetylation of α-tubulin at the residue of lysine 40 and autophagy. HDAC6 inhibition preserved acetyl-α-tubulin-enhanced autophagy flux in AKI and cultured tubular cells. Genetic ablation of the renal tubular (RT) Atg7 gene or pharmacological inhibition of autophagy suppressed the protective effects of HDAC6. Taken together, our study indicates that HDAC6 contributes to ischemia- and cisplatin-induced AKI by inhibiting autophagy and the acetylation of α-tubulin. These results suggest that HDAC6 could be a potential target for ischemic and nephrotoxic AKI.

Histone Deacetylases Cooperate with NF-κB to Support the Immediate Migratory Response after Zebrafish Pronephros Injury

Acute kidney injury (AKI) is commonly associated with severe human diseases, and often worsens the outcome in hospitalized patients. The mammalian kidney has the ability to recover spontaneously from AKI; however, little progress has been made in the development of supportive treatments. Increasing evidence suggest that histone deacetylases (HDAC) and NF-κB promote the pathogenesis of AKI, and inhibition of Hdac activity has a protective effect in murine models of AKI. However, the role of HDAC at the early stages of recovery is unknown. We used the zebrafish pronephros model to study the role of epigenetic modifiers in the immediate repair response after injury to the tubular epithelium. Using specific inhibitors, we found that the histone deacetylase Hdac2, Hdac6, and Hdac8 activities are required for the repair via collective cell migration. We found that hdac6, hdac8, and nfkbiaa expression levels were upregulated in the repairing epithelial cells shortly after injury. Depletion of hdac6, hdac8, or nfkbiaa with morpholino oligonucleotides impaired the repair process, whereas the combined depletion of all three genes synergistically suppressed the recovery process. Furthermore, time-lapse video microscopy revealed that the lamellipodia and filopodia formation in the flanking cells was strongly reduced in hdac6-depleted embryos. Our findings suggest that Hdac activity and NF-κB are synergistically required for the immediate repair response in the zebrafish pronephros model of AKI, and the timing of HDAC inhibition might be important in developing supportive protocols in the human disease.

Pharmacological inhibition of SMYD2 protects against cisplatin-induced acute kidney injury in mice

The histone methyltransferase SET and MYND domain protein 2 (SMYD2) has been implicated in tumorigenesis through methylating histone H3 at lysine36 (H3K36) and some non-histone substrates. Currently, the role of SMYD2 in acute kidney injury (AKI) remains unknown. Here, we investigated the effects of AZ505, a highly selective inhibitor of SMYD2, on the development of AKI and the mechanisms involved in a murine model of cisplatin-induced AKI. SMYD2 and trimethylated histone H3K36 (H3K36Me3) were highly expressed in the kidney following cisplatin treatment; administration of AZ505 remarkedly inhibited their expression, along with improving kidney function and ameliorating kidney damage. AZ505 also attenuated kidney tubular cell injury and apoptosis as evidenced by diminished the expression of neutrophil gelatinase associated lipocalin (NGAL) and kidney injury molecule (Kim-1), reduced the number of TUNEL positive cells, decreased the expression of cleaved caspase-3 and the BAX/BCL-2 ratio in injured kidneys. Moreover, AZ505 inhibited cisplatin-induced phosphorylation of p53, a key driver of kidney cell apoptosis and reduced expression of p21, a cell cycle inhibitor. Meanwhile, AZ505 promoted expression of proliferating cell nuclear antigen and cyclin D1, two markers of cell proliferation. Furthermore, AZ505 was effective in suppressing the phosphorylation of STAT3 and NF-κB, two transcriptional factors associated with kidney inflammation, attenuating the expression of monocyte chemoattractant protein-1 and intercellular cell adhesion molecule-1 and reducing infiltration of F4/80+ macrophages to the injured kidney. Finally, in cultured HK-2 cells, silencing of SMYD2 by specific siRNA inhibited cisplatin-induced apoptosis of kidney tubular epithelial cells. Collectively, these results suggests that SMYD2 is a key determinant of cisplatin nephrotoxicity and targeting SMYD2 protects against cisplatin-induced AKI by inhibiting apoptosis and inflammation and promoting cell proliferation.

Class IIa histone deacetylase inhibition ameliorates acute kidney injury by suppressing renal tubular cell apoptosis and enhancing autophagy and proliferation

Expression and function of histone deacetylases (HDACs) vary with cell types and pathological conditions. Our recent studies showed that pharmacological targeting class IIa HDACs attenuated renal fibrosis, but the effect of class IIa HDAC inhibition on acute kidney injury (AKI) remains unknown. In this study, we found that four class IIa HDACs (4, 5, 7, 9) were highly expressed in the kidney of folic acid (FA) and ischemia/reperfusion (I/R)-induced AKI in mice. Administration of TMP269, a potent and selective class IIa HDAC inhibitor, improved renal function and reduced tubular cell injury and apoptosis, with concomitant suppression of HDAC4 and elevation of acetyl-histone H3. Mechanistical studies showed that TMP269 treatment inhibited FA and I/R-induced caspase-3 cleavage, Bax expression and p53 phosphorylation. Conversely, TMP269 administration preserved expression of E-cadherin, BMP7, Klotho and Bcl-2 in injured kidneys. Moreover, TMP269 was effective in promoting cellular autophagy as indicated by increased expression of Atg7, beclin-1, and LC3II, and promoted renal tubular cell proliferation as shown by increased number of proliferating cell nuclear antigen-positive cells and expression of cyclin E. Finally, blocking class IIa HDACs inhibited FA-and I/R-induced phosphorylation of extracellular signal-regulated kinases 1 and 2, and p38, two signaling pathways associated with the pathogenesis of AKI. Collectively, these results suggest that pharmacological inhibition of class IIa HDACs protects against AKI through ameliorating apoptosis, enhancing autophagy and promoting proliferation of renal tubular cells by targeting multiple signaling pathways.

Epigenetic regulation of Toll-like receptors 2 and 4 in kidney disease

Kidney disease affects more than 10% of the worldwide population and causes significant morbidity and mortality. Epigenetic mechanisms such as DNA methylation, histone modifications, and non-coding RNAs (ncRNAs) play a pivotal role in the progression of kidney disease. These epigenetic mechanisms are reversible and majorly involved in regulating gene expression of inflammatory, fibrotic, and apoptotic proteins. Emerging data suggest that the Toll-like receptor 2 and Toll-like receptor 4 (TLR2 and TLR4) are expressed by almost all types of kidney cells and known for promoting inflammation by recognizing damage-associated molecular proteins (DAMPs). Epigenetic mechanisms regulate TLR2 and TLR4 signaling in various forms of kidney disease where different histone modifications promote the transcription of the TLR2 and TLR4 gene and its ligand high mobility group box protein 1 (HMGB1). Moreover, numerous long non-coding RNAs (LncRNAs) and microRNAs (miRNAs) modulate TLR2 and TLR4 signaling in kidney disease. However, the precise mechanisms behind this regulation are still enigmatic. Studying the epigenetic mechanisms involved in the regulation of TLR2 and TLR4 signaling in the development of kidney disease may help in understanding and finding novel therapeutic strategies. This review discusses the intricate relationship of epigenetic mechanisms with TLR2 and TLR4 in different forms of kidney diseases. In addition, we discuss the different lncRNAs and miRNAs that regulate TLR2 and TLR4 as potential therapeutic targets in kidney disease.

Nephrotoxicity in cancer treatment: An update

It has been estimated that nearly 80% of anticancer drug-treated patients receive potentially nephrotoxic drugs, while the kidneys play a central role in the excretion of anticancer drugs. Nephrotoxicity has long been a serious complication that hampers the effectiveness of cancer treatment and continues to influence both mortality and length of hospitalization among cancer patients exposed to either conventional cytotoxic agents or targeted therapies. Kidney injury arising from anticancer drugs tends to be associated with preexisting comorbidities, advanced cancer stage, and the use of concomitant non-chemotherapeutic nephrotoxic drugs. Despite the prevalence and impact of kidney injury on therapeutic outcomes, the field is sorely lacking in an understanding of the mechanisms driving cancer drug-induced renal pathophysiology, resulting in quite limited and largely ineffective management of anticancer drug-induced nephrotoxicity. Consequently, there is a clear imperative for understanding the basis for nephrotoxic manifestations of anticancer agents for the successful management of kidney injury by these drugs. This article provides an overview of current preclinical research on the nephrotoxicity of cancer treatments and highlights prospective approaches to mitigate cancer therapy-related renal toxicity.

Tissue Culture Models of AKI: From Tubule Cells to Human Kidney Organoids

AKI affects approximately 13.3 million people around the world each year, causing CKD and/or mortality. The mammalian kidney cannot generate new nephrons after postnatal renal damage and regenerative therapies for AKI are not available. Human kidney tissue culture systems can complement animal models of AKI and/or address some of their limitations. Donor-derived somatic cells, such as renal tubule epithelial cells or cell lines (RPTEC/hTERT, ciPTEC, HK-2, Nki-2, and CIHP-1), have been used for decades to permit drug toxicity screening and studies into potential AKI mechanisms. However, tubule cell lines do not fully recapitulate tubular epithelial cell properties in situ when grown under classic tissue culture conditions. Improving tissue culture models of AKI would increase our understanding of the mechanisms, leading to new therapeutics. Human pluripotent stem cells (hPSCs) can be differentiated into kidney organoids and various renal cell types. Injury to human kidney organoids results in renal cell-type crosstalk and upregulation of kidney injury biomarkers that are difficult to induce in primary tubule cell cultures. However, current protocols produce kidney organoids that are not mature and contain off-target cell types. Promising bioengineering techniques, such as bioprinting and "kidney-on-a-chip" methods, as applied to kidney nephrotoxicity modeling advantages and limitations are discussed. This review explores the mechanisms and detection of AKI in tissue culture, with an emphasis on bioengineered approaches such as human kidney organoid models.

Novel PHD2/HDACs hybrid inhibitors protect against cisplatin-induced acute kidney injury

Acute kidney injury (AKI) is associated with high morbidity and mortality. Cisplatin is a common chemotherapeutic, but its nephrotoxicity-driven AKI limits its clinical application. Currently, there are no specific and satisfactory therapies in the clinic for AKI. Inhibitors of hypoxia-inducible factor prolyl hydroxylase 2 (HIF-PHD2) or histone deacetylase (HDACs) had shown renoprotective effects against AKI in preclinical studies. This study aimed to develop a novel therapeutic to prevent AKI progression by targeting PHD2 and HDACs simultaneously. We designed and synthesized a series of PHD2/HDACs hybrid inhibitors. The initial drug activity screening identified a candidate compound 31c, which exhibited potent inhibitory activities against PHD2 and HDAC1/2/6. Cellular analyses further showed that 31c did not affect cisplatin's antitumor activity in cancer cells but strongly protected cisplatin-induced toxicity on HK-2 cells. In vivo studies with the cisplatin-induced AKI mouse model demonstrated that 31c remarkably alleviated kidney dysfunction with suppressed plasma BUN/SCr and increased EPO levels. The potent renoprotective effects of 31c on AKI were confirmed by significant improvements in pathological kidney conditions in the mouse model. These results suggest that the novel PHD2/HDACs hybrid inhibitor, 31c, has a clinical potential as the renoprotective agent for the treatment/prevention of cisplatin-induced AKI for various cancers.

Autophagy in Cisplatin Nephrotoxicity during Cancer Therapy

Simple Summary

Cisplatin is a broadly used chemotherapy drug, but its use and efficacy are limited by its nephrotoxicity. Autophagy protects against kidney injury during cisplatin exposure but may reduce the efficacy of chemotherapy by protecting cancer cells. In this review, we describe the role and regulation of autophagy in cisplatin-induced nephrotoxicity and discuss the therapeutic advances and challenges of targeting autophagy in chemotherapy.

Abstract

Cisplatin is a widely used chemotherapeutic agent but its clinical use is often limited by nephrotoxicity. Autophagy is a lysosomal degradation pathway that removes protein aggregates and damaged or dysfunctional cellular organelles for maintaining cell homeostasis. Upon cisplatin exposure, autophagy is rapidly activated in renal tubule cells to protect against acute cisplatin nephrotoxicity. Mechanistically, the protective effect is mainly related to the clearance of damaged mitochondria via mitophagy. The role and regulation of autophagy in chronic kidney problems after cisplatin treatment are currently unclear, despite the significance of research in this area. In cancers, autophagy may prevent tumorigenesis, but autophagy may reduce the efficacy of chemotherapy by protecting cancer cells. Future research should focus on developing drugs that enhance the anti-tumor effects of cisplatin while protecting kidneys during cisplatin chemotherapy.

The Role and Mechanism of Histone Deacetylases in Acute Kidney Injury

Acute kidney injury (AKI) is a common clinical complication with an incidence of up to 8-18% in hospitalized patients. AKI is also a complication of COVID-19 patients and is associated with an increased risk of death. In recent years, numerous studies have suggested that epigenetic regulation is critically involved in the pathophysiological process and prognosis of AKI. Histone acetylation, one of the epigenetic regulations, is negatively regulated by histone deacetylases (HDACs). Increasing evidence indicates that HDACs play an important role in the pathophysiological development of AKI by regulation of apoptosis, inflammation, oxidative stress, fibrosis, cell survival, autophagy, ATP production, and mitochondrial biogenesis (MB). In this review, we summarize and discuss the role and mechanism of HDACs in the pathogenesis of AKI.

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.

Epigenetic Remodeling in Obesity-Related Vascular Disease

Significance: The prevalence of obesity and cardiometabolic phenotypes is alarmingly increasing across the globe and is associated with atherosclerotic vascular complications and high mortality. In spite of multifactorial interventions, vascular residual risk remains high in this patient population, suggesting the need for breakthrough therapies. The mechanisms underpinning obesity-related vascular disease remain elusive and represent an intense area of investigation. Recent Advances: Epigenetic modifications-defined as environmentally induced chemical changes of DNA and histones that do not affect DNA sequence-are emerging as a potent modulator of gene transcription in the vasculature and might significantly contribute to the development of obesity-induced endothelial dysfunction. DNA methylation and histone post-translational modifications cooperate to build complex epigenetic signals, altering transcriptional networks that are implicated in redox homeostasis, mitochondrial function, vascular inflammation, and perivascular fat homeostasis in patients with cardiometabolic disturbances. Critical Issues: Deciphering the epigenetic landscape in the vasculature is extremely challenging due to the complexity of epigenetic signals and their function in regulating transcription. An overview of the most important epigenetic pathways is required to identify potential molecular targets to treat or prevent obesity-related endothelial dysfunction and atherosclerotic disease. This would enable the employment of precision medicine approaches in this setting. Future Directions: Current and future research efforts in this field entail a better definition of the vascular epigenome in obese patients as well as the unveiling of novel, cell-specific chromatin-modifying drugs that are able to erase specific epigenetic signals that are responsible for maladaptive transcriptional alterations and vascular dysfunction in obese patients. Antioxid. Redox Signal. 34, 1165-1199.

Histone Deacetylases in Kidney Physiology and Acute Kidney Injury

Histone deacetylases (HDACs) are part of the epigenetic machinery that regulates transcriptional processes. The current paradigm is that HDACs silence gene expression via regulation of histone protein lysine deacetylation, or by forming corepressor complexes with transcription factors. However, HDACs are more than just nuclear proteins, and they can interact and deacetylate a growing number of nonhistone proteins to regulate cellular function. Cancer-field studies have shown that deranged HDAC activity results in uncontrolled proliferation, inflammation, and fibrosis; all pathologies that also may occur in kidney disease. Over the past decade, studies have emerged suggesting that HDAC inhibitors may prevent and potentially treat various models of acute kidney injury. This review focuses on the physiology of kidney HDACs and highlights the recent advances using HDAC inhibitors to potentially treat kidney disease patients.

Correlation analysis between expression of histone deacetylase 6 and clinical parameters in IgA nephropathy patients

Background

It has been demonstrated that histone deacetylase 6 (HDAC6) is involved in various kidney diseases in experimental study. However, correlation between HDAC6 and clinical parameters in IgA nephropathy (IgAN) patients is still unknown.

Methods

A total of 46 human kidney biopsy specimens with IgAN were selected as observation group, specimens of normal renal cortex tissue that was not affected by the tumor from patients with renal carcinoma (n = 7) served as control. We investigated the relationship between HDAC6 and clinical parameters in IgAN.

Results

HDAC6 was highly expressed in human kidney biopsy specimens with IgAN compared with control group, while the number of acetyl histone H3 positive cells were significantly decreased. There was a statistical difference in the indexes of albumin, estimated glomerular filtration rate (eGFR), serum urea, serum creatinine, serum uric acid, β2-microglobulin, cystatin C, cholesterol, high-density lipoprotein, low-density lipoprotein, and HDAC6 positive area among the different Oxford Classification (p < 0.05). The expression of HDAC6 was different in various eGFR levels, the expression of HDAC6 increased with the decreasing of eGFR level, the expression of acetyl histone H3 decreased with the decreasing of eGFR level. In addition, the expression of HDAC6 positively correlated with Masson trichrome positive area, serum urea, serum creatinine, β2 macroglobulin, and cystatin C, while negatively correlated with eGFR and acetyl histone H3. Multivariate linear regression analysis demonstrated that eGFR and cystatin C were independently associated with HDAC6, respectively (p < 0.05).

Conclusions

These results suggested that high level of HDAC6 expression in IgAN is correlated with renal dysfunction.

A Review of Progress in Histone Deacetylase 6 Inhibitors Research: Structural Specificity and Functional Diversity

Histone deacetylases (HDACs) are essential for maintaining homeostasis by catalyzing histone deacetylation. Aberrant expression of HDACs is associated with various human diseases. Although HDAC inhibitors are used as effective chemotherapeutic agents in clinical practice, their applications remain limited due to associated side effects induced by weak isoform selectivity. HDAC6 displays unique structure and cellular localization as well as diverse substrates and exhibits a wider range of biological functions than other isoforms. HDAC6 inhibitors have been effectively used to treat cancers, neurodegenerative diseases, and autoimmune disorders without exerting significant toxic effects. Progress has been made in defining the crystal structures of HDAC6 catalytic domains which has influenced the structure-based drug design of HDAC6 inhibitors. This review summarizes recent literature on HDAC6 inhibitors with particular reference to structural specificity and functional diversity. It may provide up-to-date guidance for the development of HDAC6 inhibitors and perspectives for optimization of therapeutic applications.

2-Methylquinazoline derivative 23BB as a highly selective histone deacetylase 6 inhibitor alleviated cisplatin-induced acute kidney injury

Histone deacetylases 6 (HDAC6) has been reported to be involved in the pathogenesis of cisplatin-induced acute kidney injury (AKI). Selective inhibition of HDAC6 might be a potential treatment for AKI. In our previous study, a highly selective HDAC6 inhibitor (HDAC6i) 23BB effectively protected against rhabdomyolysis-induced AKI with good safety. However, whether 23BB possessed favorable renoprotection against cisplatin-induced AKI and the involved mechanisms remained unknown. In the study, cisplatin-injected mice developed severe AKI symptom as indicated by acute kidney dysfunction and pathological changes, companied by the overexpression of HDAC6 in tubular epithelial cells. Pharmacological inhibition of HDAC6 by the treatment of 23BB significantly attenuated sCr, BUN and renal tubular damage. Mechanistically, 23BB enhanced the acetylation of histone H3 to reduce the HDAC6 activity. Cisplatin-induced AKI triggered multiple signal mediators of endoplasmic reticulum (ER) stress including PERK, ATF6 and IRE1 pathway, as well as CHOP, GRP78, p-JNK and caspase 12 proteins. Oral administration of our HDAC6i 23BB at a dose of 40 mg/kg/d for 3 days notably improved above-mentioned responses in the injured kidney tissues. HDAC6 inhibition also reduced the number of TUNEL-positive tubular cells and regulated apoptosis-related protein expression. Overall, these data highlighted that HDAC6 inhibitor 23BB modulated apoptosis via the inhibition of ER stress in the tubular epithelial cells of cisplatin-induced AKI.

Wnt/β-catenin agonist BIO alleviates cisplatin-induced nephrotoxicity without compromising its efficacy of anti-proliferation in ovarian cancer

AIMS

Cisplatin is an anticancer agent marred by nephrotoxicity. Limiting this adverse effect may allow the use of higher doses to improve its efficacy. The Wnt/β-catenin signaling pathway plays a critical role in nephrogenesis and repair of renal diseases. BIO, a small molecule agonist of this pathway, exerted a protective effect in adriamycin nephropathy and promoted nephrogenesis. The aim of this study, therefore, was to investigate whether Wnt/β-catenin agonist BIO could protect against cisplatin-induced nephrotoxicity in vivo and in vitro, as well as its possible mechanism.

MAIN METHODS

Male mice and human renal proximal tubular cells (HK-2) were subjected to cisplatin to study reno-protective effect of BIO. Renal function, cell viability, tubular apoptosis, production of reactive oxygen species (ROS) and proliferative level were analyzed respectively. Additionally, xenograft model was induced to investigate if BIO would impair the antitumor effect of cisplatin.

KEY FINDINGS

Cisplatin increased serum creatinine levels and promoted histological renal injury as well as oxidative stress levels. Besides, renal apoptotic level and the expression of pro-apoptotic proteins, Bax/bcl-2 and cleaved-caspase3 included, in the kidney were increased. All these features were decreased by BIO, which also activated Wnt/β-catenin pathway in cisplatin-induced nephrotoxicity. Similarly, accompanied by the motivation of Wnt/β-catenin pathway, BIO exerted a positively protective effect on HK-2 challenged cisplatin. Last, the chemotherapeutic effects of cisplatin in xenograft mice of ovary tumor models and in lung cancer cells weren't compromised by BIO.

SIGNIFICANCE

Wnt/β-catenin agonist BIO has the potential to prevent cisplatin nephrotoxicity without compromising its anti-proliferation efficacy.

Histone deacetylase 6 inhibition mitigates renal fibrosis by suppressing TGF-β and EGFR signaling pathways in obstructive nephropathy

We have recently shown that histone deacetylase 6 (HDAC6) is critically involved in the pathogenesis of acute kidney injury. Its role in renal fibrosis, however, remains unclear. In this study, we examined the effect of ricolinostat (ACY-1215), a selective inhibitor of HDAC6, on the development of renal fibrosis in a murine model induced by unilateral ureteral obstruction (UUO). HDAC6 was highly expressed in the kidney following UUO injury, which was coincident with deposition of collagen fibrils and expression of α-smooth muscle actin, fibronectin, and collagen type III. Administration of ACY-1215 reduced these fibrotic changes and inhibited UUO-induced expression of transforming growth factor-β1 and phosphorylation of Smad3 while increasing expression of Smad7. ACY-1215 treatment also suppressed phosphorylation of epidermal growth factor receptor (EGFR) and several signaling molecules associated with renal fibrogenesis, including AKT, STAT3, and NF-κB in the injured kidney. Furthermore, ACY-1215 was effective in inhibiting dedifferentiation of renal fibroblasts to myofibroblasts and the fibrotic change of renal tubular epithelial cells in culture. Collectively, these results indicate that HDAC6 inhibition can attenuate development of renal fibrosis by suppression of transforming growth factor-β1 and EGFR signaling and suggest that HDAC6 would be a potential therapeutic target for the treatment of renal fibrosis.

Class IIa HDAC inhibitor TMP195 alleviates lipopolysaccharide-induced acute kidney injury

Sepsis-associated acute kidney injury (SA-AKI) is associated with high mortality rates, but clinicians lack effective treatments except supportive care or renal replacement therapies. Recently, histone deacetylase (HDAC) inhibitors have been recognized as potential treatments for acute kidney injury and sepsis in animal models; however, the adverse effect generated by the use of pan inhibitors of HDACs may limit their application in people. In the present study, we explored the possible renoprotective effect of a selective class IIa HDAC inhibitor, TMP195, in a murine model of SA-AKI induced by lipopolysaccharide (LPS). Administration of TMP195 significantly reduced increased serum creatinine and blood urea nitrogen levels and renal damage induced by LPS; this was coincident with reduced expression of HDAC4, a major isoform of class IIa HDACs, and elevated histone H3 acetylation. TMP195 treatment following LPS exposure also reduced renal tubular cell apoptosis and attenuated renal expression of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1, two biomarkers of tubular injury. Moreover, LPS exposure resulted in increased expression of BAX and cleaved caspase-3 and decreased expression of Bcl-2 and bone morphogenetic protein-7 in vivo and in vitro; TMP195 treatment reversed these responses. Finally, TMP195 inhibited LPS-induced upregulation of multiple proinflammatory cytokines/chemokines, including intercellular adhesion molecule-1, monocyte chemoattractant protein-1, tumor necrosis factor-α, and interleukin-1β, and accumulation of inflammatory cells in the injured kidney. Collectively, these data indicate that TMP195 has a powerful renoprotective effect in SA-AKI by mitigating renal tubular cell apoptosis and inflammation and suggest that targeting class IIa HDACs might be a novel therapeutic strategy for the treatment of SA-AKI that avoids the unintended adverse effects of a pan-HDAC inhibitor.

Activation of TFEB-mediated autophagy by trehalose attenuates mitochondrial dysfunction in cisplatin-induced acute kidney injury

Aims: Cisplatin, an anticancer drug, always leads to nephrotoxicity by causing mitochondrial dysfunction. As a major mechanism for cellular self-degradation, autophagy has been proven to protect against cisplatin-induced acute kidney injury (AKI). Based on the activation of autophagy induced by trehalose, we aimed to investigate the nephroprotective effects of trehalose on cisplatin-induced AKI and its underlying mechanisms.

Results: Due to the activation of autophagy, mitochondrial dysfunction (mitochondrial fragmentation, depolarization, reactive oxygen species (ROS), and reduced ATP generation) and apoptosis induced by cisplatin were markedly inhibited in trehalose-treated HK2 cells in vitro. Based on the transcriptional regulation role of transcription factor EB (TFEB) in autophagy and lysosome, we characterized trehalose-induced nuclear translocation of TFEB. Furthermore, consistent with trehalose treatment, overexpression of TFEB inhibited cell injury induced by cisplatin. However, the protective effects of trehalose were largely abrogated in tfeb-knockdown cells. In vivo, cisplatin injection resulted in severe kidney dysfunction and histological damage in mice. Trehalose administration activated TFEB-mediated autophagy, alleviated mitochondrial dysfunction and kidney injury in AKI mice.

Innovation and conclusion: Our data suggest that trehalose treatment preserves mitochondria function via activation of TFEB-mediated autophagy and attenuates cisplatin-induced kidney injury.

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.

The Predictive Role of the Biomarker Kidney Molecule-1 (KIM-1) in Acute Kidney Injury (AKI) Cisplatin-Induced Nephrotoxicity

Acute kidney injury (AKI) following platinum-based chemotherapeutics is a frequently reported serious side-effect. However, there are no approved biomarkers that can properly identify proximal tubular injury while routine assessments such as serum creatinine lack sensitivity. Kidney-injury-molecule 1 (KIM-1) is showing promise in identifying cisplatin-induced renal injury both in vitro and in vivo studies. In this review, we focus on describing the mechanisms of renal tubular cells cisplatin-induced apoptosis, the associated inflammatory response and oxidative stress and the role of KIM-1 as a possible biomarker used to predict cisplatin associated AKI.

2-methylquinazoline derivative F7 as a potent and selective HDAC6 inhibitor protected against rhabdomyolysis-induced acute kidney injury

Histone deacetylases 6 (HDAC6) has been reported to be involved in the pathogenesis of rhabdomyolysis-induced acute kidney injury (AKI). Selective inhibition of HDAC6 activity might be a potential treatment for AKI. In our lab, N-hydroxy-6-(4-(methyl(2-methylquinazolin-4-yl)amino)phenoxy)nicotinamide (F7) has been synthesized and inhibited HDAC6 activity with the IC₅₀ of 5.8 nM. However, whether F7 possessed favorable renoprotection against rhabdomyolysis-induced AKI and the involved mechanisms remained unclear. In the study, glycerol-injected mice developed severe AKI symptoms as indicated by acute renal dysfunction and pathological changes, accompanied by the overexpression of HDAC6 in tubular epithelial cells. Pretreatment with F7 at a dose of 40 mg/kg/d for 3 days significantly attenuated serum creatinine, serum urea, renal tubular damage and suppressed renal inflammatory responses. Mechanistically, F7 enhanced the acetylation of histone H3 and α-tubulin to reduce HDAC6 activity. Glycerol-induced AKI triggered multiple signal mediators of NF-κB pathway as well as the elevation of ERK1/2 protein and p38 phosphorylation. Glycerol also induced the high expression of proinflammatory cytokine IL-1β and IL-6 in kidney and human renal proximal tubule HK-2 cells. Treatment of F7 notably improved above-mentioned inflammatory responses in the injured kidney tissue and HK-2 cell. Overall, these data highlighted that 2-methylquinazoline derivative F7 inhibited renal HDAC6 activity and inflammatory responses to protect against rhabdomyolysis-induced AKI.

Inhibition of Histone Deacetylase 6 Protects Hippocampal Cells Against Mitochondria-mediated Apoptosis in a Model of Severe Oxygen-glucose Deprivation

Background:

Histone deacetylase (HDAC) 6 inhibitors have demonstrated significant protective effects in traumatic injuries. However, their roles in neuroprotection and underlying mechanisms are poorly understood. This study sought to investigate the neuroprotective effects of Tubastatin A (Tub-A), an HDAC6 inhibitor, during oxygenglucose deprivation (OGD) in HT22 hippocampal cells.

Methods:

HT22 hippocampal cells were exposed to OGD. Cell viability and cytotoxicity were assessed by cell counting kit-8 (CCK-8) and lactate dehydrogenase (LDH) release assay. Cellular apoptosis was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Mitochondria membrane potential was detected using JC-1 dye. Expressions of acetylated α-tubulin, α-tubulin, cytochrome c, VDAC, Bax, Bcl- 2, cleaved caspase 3, phosphorylated Akt, Akt, phosphorylated GSK3β and GSK3β were analyzed by Western blot analysis.

Results:

Tub-A induced acetylation of α-tubulin, demonstrating appropriate efficacy. Tub-A significantly increased cell viability and attenuated LDH release after exposure to OGD. Furthermore, Tub-A treatment blunted the increase in TUNEL-positive cells following OGD and preserved the mitochondrial membrane potential. Tub-A also attenuated the release of cytochrome c from the mitochondria into the cytoplasm and suppressed the ratio of Bax/Bcl-2 and cleaved caspase 3. This was mediated, in part, by the increased phosphorylation of Akt and GSK3β signaling pathways.

Conclusion:

HDAC 6 inhibition, using Tub-A, protects against OGD-induced injury in HT22 cells by modulating Akt/GSK3β signaling and inhibiting mitochondria-mediated apoptosis.

Pharmacological and genetic inhibition of fatty acid-binding protein 4 alleviated cisplatin-induced acute kidney injury

Fatty acid-binding protein 4 (FABP4) has been confirmed to be involved in the pathogenesis of ischaemia/reperfusion- and rhabdomyolysis-induced acute kidney injury (AKI), and targeting inhibition of FABP4 might be a potential strategy for AKI. Cisplatin as a commonly used cancer chemotherapeutic drug possessed a dose-limited side effect of nephrotoxicity. However, whether FABP4 inhibition exerted a favourable renoprotection against cisplatin-induced AKI and the involved mechanisms remained unknown. In the study, cisplatin-injected mice developed severe AKI symptom as indicated by renal dysfunction and pathological changes, companied by the high expression of FABP4 in tubular epithelial cells. Selective inhibition of FABP4 by BMS309403 at 40 mg/kg/d for 3 days and genetic knockout of FABP4 significantly attenuated the serum creatinine, blood urea nitrogen level and renal tubular damage. Mechanistically, cisplatin injection induced the increased apoptosis and regulated the corresponding protein expression of BCL-2, BCL-XL, BAX, cleaved caspase 3 and caspase 12 in the injured kidney tissues. Cisplatin also triggered multiple signal mediators of endoplasmic reticulum (ER) stress including double-stranded RNA-activated protein kinase-like ER kinase, activating transcription factor-6 and inositol-requiring enzyme-1 pathway, as well as CHOP, GRP78 and p-JNK proteins in the kidneys. Oral administration of BMS309403 significantly reduced the number of renal TUNEL-positive apoptotic cells. Knockout of FABP4 and BMS309403 notably improved ER stress-related apoptotic responses. In summary, pharmacological and genetic inhibition of FABP4 modulated apoptosis via the inactivation of ER stress in the tubular epithelial cells of cisplatin-induced AKI.

RIPK1 inhibitor Cpd-71 attenuates renal dysfunction in cisplatin-treated mice via attenuating necroptosis, inflammation and oxidative stress

Acute kidney injury (AKI) is a destructive clinical condition induced by multiple insults including ischemic reperfusion, nephrotoxic drugs and sepsis. It is characterized by a sudden decline in renal function, in addition to excessive inflammation, oxidative stress and programmed cell death of renal tubular epithelial cells. RIPK1-mediated necroptosis plays an important role in AKI. In the present study, we evaluated the treatment effects of Compound-71 (Cpd-71), a novel RIPK1 inhibitor, by comparing with Necrostatin-1 (Nec-1), a classic RIPK1 inhibitor, which has several drawbacks like the narrow structure–activity relationship (SAR) profile, moderate potency and non-ideal pharmacokinetic properties, in vivo and in vitro. Our results showed that pretreatment of Cpd-71 attenuated cisplatin-induced renal injury, restored renal function and suppressed renal inflammation, oxidative stress and cell necroptosis. In addition, Cpd-71 inhibited renal damage while reducing the up-regulated serum creatinine (Cr) and blood urea nitrogen (BUN) levels in established AKI mice model. Consistently, we confirmed that Cpd-71 exhibited more effectively suppressive effect on cisplatin-induced renal tubular cell necroptosis than Nec-1, by physically binding to the allosteric type III ligand binding site of RIPK1, thereby reduced RIPK1 kinase activity, RIPK1/RIPK3 complex formation and phosphor-MLKL membrane translocation by molecular docking, Western blot, co-immunoprecipitation and cellular thermal shift assay (CETSA). Taken together, we currently showed that targeting RIPK1 with Cpd-71 may serve as a promising clinical candidate for AKI treatment.

Inhibition of HDAC6 attenuates LPS-induced inflammation in macrophages by regulating oxidative stress and suppressing the TLR4-MAPK/NF-κB pathways

BACKGROUND

Histone deacetylase 6 (HDAC6) has been considered as an important regulator in the development of inflammatory diseases. However, the mechanism of HDAC6 in regulating inflammatory responses has not been fully determined. In the present study, we aim to investigate the role and mechanisms of HDAC6 in regulating inflammation in lipopolysaccharide (LPS)-activated macrophages.

METHODS

Flow cytometry was used to determine a suitable treatment dosage of ACY-1215 on lipopolysaccharide (LPS)-activated macrophages for the present study. The RAW264.7 macrophages were divided into normal, LPS-treated, and ACY-1215 treated groups, respectively. For the ACY-1215 group, ACY-1215 (10 μM) was added to the medium 2 h prior to treatment with LPS (1 μg/ml) for 24 h. In this study, ROS, inflammatory cytokines, the ultrastructure of mitochondria, mitochondrial membrane potential, RNA and protein expression assay were detected respectively. Subsequently, the effect of HDAC6 knockdown on inflammatory response in LPS-activated RAW264.7 macrophages was also detected.

RESULTS

Inhibition of HDAC6 inhibited the overproduction of ROS and suppressed the expression of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 in LPS-activated RAW264.7 cells. Pretreatment with ACY-1215 could normalize the ultrastructure of mitochondria and mitochondrial membrane potential in LPS-activated macrophages. Moreover, the protein expression of TLR4, Nrf2, HO-1 and the activation of MAPK and NF-κB signaling pathways were normalized by the inhibition of HDAC6.

CONCLUSIONS

Inhibition of HDAC6 exhibited protective role against LPS-induced inflammation in RAW264.7 cells by regulating oxidative stress and suppressing the activation of TLR4- MAPK/NF-κB signaling pathway.

Recent Advances in Models, Mechanisms, Biomarkers, and Interventions in Cisplatin-Induced Acute Kidney Injury

Cisplatin is a widely used chemotherapeutic agent used to treat solid tumours, such as ovarian, head and neck, and testicular germ cell. A known complication of cisplatin administration is acute kidney injury (AKI). The development of effective tumour interventions with reduced nephrotoxicity relies heavily on understanding the molecular pathophysiology of cisplatin-induced AKI. Rodent models have provided mechanistic insight into the pathophysiology of cisplatin-induced AKI. In the subsequent review, we provide a detailed discussion of recent advances in the cisplatin-induced AKI phenotype, principal mechanistic findings of injury and therapy, and pre-clinical use of AKI rodent models. Cisplatin-induced AKI murine models faithfully develop gross manifestations of clinical AKI such as decreased kidney function, increased expression of tubular injury biomarkers, and tubular injury evident by histology. Pathways involved in AKI include apoptosis, necrosis, inflammation, and increased oxidative stress, ultimately providing a translational platform for testing the therapeutic efficacy of potential interventions. This review provides a discussion of the foundation laid by cisplatin-induced AKI rodent models for our current understanding of AKI molecular pathophysiology.

Quantitative Proteomic Analysis Reveals the Sites Related to Acetylation and Mechanism of ACY-1215 in Acute Liver Failure Mice

Background: ACY-1215 is a well-known selective histone deacetylase 6 (HDAC6) inhibitor, and it has been considered as a potential therapeutic drug in inflammatory diseases, including acute liver failure (ALF). However, little is known about the impact of ACY-1215 treatment on histone lysine acetylation and proteome in ALF. In this study, we aim to investigate whether ACY-1215 has inhibitory effects and mechanism on the necrosis of hepatocytes; moreover, the impact of ACY-1215 treatment on histone lysine acetylation still needs further elucidation.

Methods: Male C57/BL6 mice were divided into normal, model, and ACY-1215 groups. ACY-1215 (25 mg/kg) and same amounts of saline were injected intraperitoneally to the mice before the establishment of ALF model induced by lipopolysaccharide (LPS) (100 µg/kg) combined with D-gal (400 mg/kg). All animals were sacrificed after 24 h. In this study, detection programs, including quantitative proteomic analysis, transmission electron microscopy (TEM) micrographs, pathological staining, protein expression, the detection of reactive oxygen species (ROS) as well as glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) measurement.

Results: The function of liver and the necrosis of hepatocytes in ALF mice were significantly normalized by ACY-1215 pretreatment. The quantitative proteomic analysis revealed that ACY-1215-restrained oxidative phosphorylation normalized the function respiratory electron-transport chain in the mitochondria. Moreover, pretreatment of ACY-1215 not only normalized the structure of mitochondria but also inhibited the generation of reactive oxygen species (ROS).

Conclusions: ACY-1215 was able to inhibit necrosis of hepatocytes in ALF mice through regulating the mitochondrial-mediated oxidative stress, and we identified the common sites related to acetylation level.

Autophagy and senescence: A new insight in selected human diseases

Senescence and autophagy play important roles in homeostasis. Cellular senescence and autophagy commonly cause several degenerative processes, including oxidative stress, DNA damage, telomere shortening, and oncogenic stress; hence, both events are known to be interrelated. Autophagy is well known for its disruptive effect on human diseases, and it is currently proposed to have a direct effect on triggering senescence and quiescence. However, it is yet to be proven whether autophagy has a positive or negative impact on senescence. It is known that elevated levels of autophagy induce cell death, whereas inadequate autophagy can trigger cellular senescence. Both have important roles in human diseases such as aging, renal degeneration, neurodegenerative disorders, and cancer. Therefore, this review aims to highlight the relevance of senescence and autophagy in selected human ailments through a summary of recent findings on the connection and effects of autophagy and senescence in these diseases.

Dynamic changes in histone deacetylases following kidney ischemia-reperfusion injury are critical for promoting proximal tubule proliferation

Deranged histone deacetylase (HDAC) activity causes uncontrolled proliferation, inflammation, fibrosis, and organ damage. It is unclear whether deranged HDAC activity results in acute kidney injury in the renal hypoperfusion model of bilateral ischemia-reperfusion injury (IRI) and whether in vivo inhibition is an appropriate therapeutic approach to limit injury. Male mice were implanted with intraperitoneal osmotic minipumps containing vehicle, the class I HDAC inhibitor, MS275, or the pan-HDAC inhibitor, trichostatin A (TSA), 3 days before sham/bilateral IRI surgery. Kidney cortical samples were analyzed using histological, immunohistochemical, and Western blotting techniques. HDAC-dependent proliferation rate was measured in immortalized rat epithelial cells and primary mouse or human proximal tubule (PT) cells. There were dynamic changes in cortical HDAC localization and abundance following IRI including a fourfold increase in HDAC4 in the PT. HDAC inhibition resulted in a significantly higher plasma creatinine, increased kidney damage, but reduced interstitial fibrosis compared with vehicle-treated IRI mice. HDAC-inhibited mice had reduced interstitial α-smooth muscle actin, fibronectin expression, and Sirius red-positive area, suggesting that IRI activates HDAC-mediated fibrotic pathways. In vivo proliferation of the kidney epithelium was significantly reduced in TSA-treated, but not MS275-treated, IRI mice, suggesting class II HDACs mediate proliferation. Furthermore, HDAC4 activation increased proliferation of human and mouse PTs. Kidney HDACs are activated during IRI with isoform-specific expression patterns. Our data point to mechanisms whereby IRI activates HDACs resulting in fibrotic pathways but also activation of PT proliferation and repair pathways. This study demonstrates the need to develop isoform-selective HDAC inhibitors for the treatment of renal hypoperfusion-induced injury.

Clinicopathological correlation of ARID1A status with HDAC6 and its related factors in ovarian clear cell carcinoma

Ovarian clear cell carcinoma (OCCC) is associated with a frequent loss in ARID1A function. ARID1A reportedly suppresses histone deacetylase (HDAC)6 in OCCC directly. Here, we evaluated the clinical significance of HDAC6 expression and its related factors in terms of ARID1A status. Immunohistochemical expression of HDAC6, hypoxia inducible factors-1α (HIF-1α), programmed death-1 ligand (PD-L1), CD44 (cancer stem cell marker), and ARID1A was analysed for 106 OCCC patients. High nuclear HDAC6 expression correlated with patient death (p = 0.038). In the multivariate analysis of overall survival, surgical status (complete or incomplete resection) (hazard ratio (HR) = 17.5; p = <0.001), HDAC6 nuclear expression (HR = 1.68; p = 0.034), and PD-L1 expression (HR = 1.95; p = 0.022) were the independent prognostic factors. HDAC6 upregulation and ARID1A loss did not necessarily occur simultaneously. High HDAC6 expression was associated with poor prognosis in OCCC with ARID1A loss; this was not observed without ARID1A loss. HDAC6 expression showed a significant positive correlation with HIF-1α, PD-L1, and CD44. In OCCC, HDAC6 involvement in prognosis depended on ARID1A status. HDAC6 also led to immuno- and hypoxia- tolerance and cancer stem cell phenotype. HDAC6 is a promising therapeutic target for OCCC with loss of ARID1A.

Blockade of ERK1/2 by U0126 alleviates uric acid-induced EMT and tubular cell injury in rats with hyperuricemic nephropathy

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) are serine/threonine kinases and function as regulators of cellular proliferation and differentiation. Recently, we demonstrated that inhibition of ERK1/2 alleviates the development and progression of hyperuricemia nephropathy (HN). However, its potential roles in uric acid-induced tubular epithelial-mesenchymal transition (EMT) and tubular epithelial cell injury are unknown. In this study, we showed that hyperuricemic injury induced EMT as characterized by downregulation of E-cadherin and upregulation of vimentin and Snail1 in a rat model of HN. This was coincident with epithelial cells arrested at the G₂/M phase of cell cycle, activation of Notch1/Jagged-1 and Wnt/β-catenin signaling pathways, and upregulation of matrix metalloproteinase-2 (MMP-2) and MMP-9. Administration of U0126, a selective inhibitor of ERK1/2, blocked all these responses. U0126 was also effective in inhibiting renal tubular cell injury, as shown by decreased expression of lipocalin-2 and kidney injury molecule-1 and active forms of caspase-3. U0126 or ERK1/2 siRNA can inhibit tubular cell EMT and cell apoptosis as characterized with decreased expression of cleaved caspase-3. Moreover, ERK1/2 inhibition suppressed hyperuricemic injury-induced oxidative stress as indicated by decreased malondialdehyde and increased superoxide dismutase. Collectively, ERK1/2 inhibition-elicited renal protection is associated with inhibition of EMT through inactivation of multiple signaling pathways and matrix metalloproteinases, as well as attenuation of renal tubule injury by enhancing cellular resistance to oxidative stress.

Epigenetic targeting for acute kidney injury

In recent years, epigenetics has emerged as important mechanisms for the regulation of pathogenesis in many diseases, including acute kidney injury (AKI). Numerous studies have demonstrated that AKI is associated with the changes in epigenetics, including histone modifications, DNA methylation and the expression of various non-coding RNAs. Through utilizing histone deacetylase (HDAC) inhibitors, studies have demonstrated that increase of histone acetylation either protects kidney from injury or potentiates this process, depending on which HDAC (s) isform is suppressed, whereas inhibition of histone methyltransferase, generally provides a protective effect in AKI. Although AKI is also associated with changes in DNA methylation, the role of DNA methylation in kidney injury remains unclear. In this article, we discuss the role and mechanism of histone acetylation and methylation in the pathogenesis of AKI.

Fragmentation of kidney epithelial cell primary cilia occurs by cisplatin and these cilia fragments are excreted into the urine

The primary cilium, which protrudes from the cell surface, is associated with the pathogenesis of various diseases, including acute kidney injury (AKI). Primary cilium length dynamically changes during the progression of diseases. However, its relevance in disease and the underlying mechanism are largely unknown. In this study, we investigated the role of primary cilia in AKI induced by cisplatin, an effective anticancer drug, and the underlying mechanisms. In addition, we evaluated the usefulness of length alteration and deciliation of primary cilia into the urine for the diagnosis of AKI. Cisplatin induced shortening, elongation, and normalization of the primary cilia in kidney epithelial cells over time. During shortening, primary cilia fragments and ciliary proteins were excreted into the urine. During deciliation, cell proliferation and the expression of cyclin-dependent kinase inhibitor and proliferating cell nuclear antigen were not significantly changed. Shortening and deciliation of primary cilia were observed before significant increases in plasma creatinine and blood urea nitrogen concentration occurred. Pretreatment with Mito-Tempo, a mitochondria-targeted antioxidant, prevented cisplatin-induced primary cilium shortening and inhibited the increases in superoxide formation, lipid peroxidation, blood urea nitrogen, and tissue damage. In contrast, isocitrate dehydrogenase 2 (Idh2) gene deletion, which results in defect of the NADPH-associated mitochondrial antioxidant system, exacerbated cisplatin-induced changes in mice. Taken together, our findings demonstrate that cisplatin induces deciliation into the urine and antioxidant treatment prevents this deciliation, renal dysfunction, and tissue damage after cisplatin injection. These results suggest that cisplatin-induced AKI is associated with primary cilia and urine primary cilia proteins might be a non-invasive biomarker of kidney injury.

Epigenetic Regulation of Autophagy: A Path to the Control of Autoimmunity

Autoimmune diseases are a significant cause of debilitation and mortality globally and are in need of cost-effective therapeutics. Autophagy is a cellular pathway that facilitates immune modulation involved in both pathogen control and autoimmunity. Regulation is multifactorial and includes a number of epigenetic pathways which can involve modification of DNA-binding histones to induce autophagy-related mRNA synthesis or microRNA and decapping-associated mRNA degradation which results in autophagy suppression. Appreciation of epigenetic-based pathways involved in autophagy and autoimmunity may facilitate application of a burgeoning group of epigenetic pharmaceuticals to these important diseases.

Inhibition of HDAC6 activity in kidney diseases: a new perspective

Histone deacetylase 6 (HDAC6), a cytoplasmic enzyme that plays important roles in many biological processes, is one isoform of a family of HDAC enzymes that catalyse the removal of functional acetyl groups from proteins. HDAC6 stands out from the other members of this family because it almost exclusively deacetylates cytoplasmic proteins and exerts deacetylation-independent effects, which has led to the successful development of relatively isoform-specific inhibitors of its enzymatic action. Numerous studies have recently demonstrated that HDAC6 expression and activity are increased in kidney disease, such as autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, and acute kidney injury (AKI), among others. Moreover, HDAC6 inhibitors have been investigated for use in treating these diseases. In fact, HDAC6 inhibitors effectively limit the progression of kidney diseases, suggesting that targeting HDAC6 may provide a novel treatment approach. However, the primary challenge in developing HDAC6-targeted therapies is understanding how the renoprotective effect of NDAC6 inhibitors can be selectively harnessed. Here, we discuss the unique function of HDAC6 and recapitulate the alluring potential of its inhibitors in kidney diseases.