Targeted histone H4 acetylation via phosphoinositide 3-kinase- and p70s6-kinase-dependent pathways inhibits iNOS induction in mesangial cells

Butyrate inhibits IL-1β-induced inflammatory gene expression by suppression of NF-κB activity in pancreatic beta cells

Cytokine-induced beta cell dysfunction is a hallmark of type 2 diabetes (T2D). Chronic exposure of beta cells to inflammatory cytokines affects gene expression and impairs insulin secretion. Thus, identification of anti-inflammatory factors that preserve beta cell function represents an opportunity to prevent or treat T2D. Butyrate is a gut microbial metabolite with anti-inflammatory properties for which we recently showed a role in preventing interleukin-1β (IL-1β)-induced beta cell dysfunction, but how prevention is accomplished is unclear. Here, we investigated the mechanisms by which butyrate exerts anti-inflammatory activity in beta cells. We exposed mouse islets and INS-1E cells to a low dose of IL-1β and/or butyrate and measured expression of inflammatory genes and nitric oxide (NO) production. Additionally, we explored the molecular mechanisms underlying butyrate activity by dissecting the activation of the nuclear factor-κB (NF-κB) pathway. We found that butyrate suppressed IL-1β-induced expression of inflammatory genes, such as Nos2, Cxcl1, and Ptgs2, and reduced NO production. Butyrate did not inhibit IκBα degradation nor NF-κB p65 nuclear translocation. Furthermore, butyrate did not affect binding of NF-κB p65 to target sequences in synthetic DNA but inhibited NF-κB p65 binding and RNA polymerase II recruitment to inflammatory gene promoters in the context of native DNA. We found this was concurrent with increased acetylation of NF-κB p65 and histone H4, suggesting butyrate affects NF-κB activity via inhibition of histone deacetylases. Together, our results show butyrate inhibits IL-1β-induced inflammatory gene expression and NO production through suppression of NF-κB activation and thereby possibly preserves beta cell function.

Filtrated Adipose Tissue-Derived Mesenchymal Stem Cell Lysate Ameliorates Experimental Acute Colitis in Mice

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic, persistent, and intractable enteritis; however, an effective treatment strategy is yet to be established. Mesenchymal stem cells (MSCs) and their paracrine factors exhibit anti-inflammatory actions and have been proposed as a new therapeutic candidate for IBD treatment, although the efficacy of MSC lysate on enteritis is unclear.

AIMS

Here, we examined the efficacy and appropriate regimen of filtrated murine adipose-derived mesenchymal stem cell lysate (FADSTL) in an acute colitis mouse model as a novel cell-free MSC therapy.

METHODS

To confirm the clinical effects of FADSTL, survival rate, body weight, and disease activity index (DAI) were investigated in the DSS-induced colitis mouse model. Further, differences in efficacy with dosing frequency were assessed to optimize the proper regimen. Colon length, histological findings, gene expression of inflammatory mediators and tight junction proteins in colon tissues, and anti-apoptotic effects were also compared in 3-day continuous FADSTL administration and PBS groups.

RESULTS

Three-day continuous FADSTL administration significantly improved weight loss and DAI score compared to those in the PBS-treated group, whereas the effect was not observed with single administration. Additionally, colon shortening and histological inflammation were suppressed in the FADSTL-treated group. Further, this treatment decreased gene expression of inflammatory mediators, maintained expression of tight junction proteins in the colon, and showed anti-apoptotic effects.

CONCLUSIONS

FADSTL effects were dependent on its administration frequency, suggesting the requirement of continuous FADSTL administration. FADSTL improved colitis by maintaining the intestinal barrier function through its anti-inflammatory and anti-apoptotic actions.

7-Hydroxycoumarin Attenuates Colistin-Induced Kidney Injury in Mice Through the Decreased Level of Histone Deacetylase 1 and the Activation of Nrf2 Signaling Pathway

Colistin has been considered as the last line of defense against Gram-negative bacterial infections, however, the potential nephrotoxicity limited its clinical use. 7-Hydroxycoumarin (7-HC) possesses many beneficial pharmacological activities. This study aimed to investigate the nephroprotective effects of 7-HC against colistin-induced kidney injury. In vivo experiments showed that 7-HC alleviated kidney injury induced by colistin, as indicated by lower levels of serum neutrophil gelatinase-associated lipocalin, blood urea nitrogen and creatinine levels. Both in vivo and in vitro results demonstrated that 7-HC alleviated oxidative stress and apoptosis induced by colistin, as shown by decreased malondialdehyde levels, decreased caspase-3 and caspase-9 activities, and increased superoxide dismutase and catalase activities. We also found that colistin significantly induced histone deacetylase (HDAC) 1 expression that deacetylated histone 3 at Lys27 acetylation (H3K27AC) of Nrf2 promoter region and hence inhibiting Nrf2 signaling. 7-HC treatment restored histone acetylation at the Nrf2 promoter region and hence promoted Nrf2 expression. These results suggested that 7-HC alleviates colistin-induced renal injury and this effect was achieved by enhancement of renal antioxidant capacity with the decreased level of HDAC1 and the activation of Nrf2 signaling pathway.

Type I interferons exert anti-tumor effect via reversing immunosuppression mediated by mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are strongly immunosuppressive via producing nitric oxide (NO) and known to migrate into tumor sites to promote tumor growth, but the underlying mechanisms remain largely elusive. Here, we found that interferon alpha (IFNα)-secreting MSCs showed more dramatic inhibition effect on tumor progression than that of IFNα alone. Interestingly, IFNα-primed MSCs could also effectively suppress tumor growth. Mechanistically, we demonstrated that both IFNα and IFNβ (type I IFNs) reversed the immunosuppressive effect of MSCs on splenocyte proliferation. This effect of type I IFNs was exerted through inhibiting inducible NO synthase (iNOS) expression in IFNγ and TNFα-stimulated MSCs. Notably, only NO production was inhibited by IFNα production of other cytokines or chemokines tested was not suppressed. Furthermore, IFNα promoted the switch from signal transducer and activator of transcription 1 (Stat1) homodimers to Stat1-Stat2 heterodimers. Studies using the luciferase reporter system and chromatin immunoprecipitation assay revealed that IFNα suppressed iNOS transcription through inhibiting the binding of Stat1 to iNOS promoter. Therefore, the synergistic anti-tumor effects of type I IFNs and MSCs were achieved by inhibiting NO production. This study provides essential information for understanding the mechanisms of MSC-mediated immunosuppression and for the development of better clinical strategies using IFNs and MSCs for cancer immunotherapy.

Impairment of hepatic nuclear factor-4α binding to the Stim1 promoter contributes to high glucose-induced upregulation of STIM1 expression in glomerular mesangial cells

The present study was carried out to investigate if hepatic nuclear factor (HNF)4α contributed to the high glucose-induced increase in stromal interacting molecule (STIM)1 protein abundance in glomerular mesangial cells (MCs). Western blot and immunofluorescence experiments showed HNF4α expression in MCs. Knockdown of HNF4α using a small interfering RNA approach significantly increased mRNA expression levels of both STIM1 and Orai1 and protein expression levels of STIM1 in cultured human MCs. Consistently, overexpression of HNF4α reduced expressed STIM1 protein expression in human embryonic kidney-293 cells. Furthermore, high glucose treatment did not significantly change the abundance of HNF4α protein in MCs but significantly attenuated HNF4α binding activity to the Stim1 promoter. Moreover, knockdown of HNF4α significantly augmented store-operated Ca(2+) entry, which is known to be gated by STIM1 and has recently been found to be antifibrotic in MCs. In agreement with those results, knockdown of HNF4α significantly attenuated the fibrotic response of high glucose. These results suggest that HNF4α negatively regulates STIM1 transcription in MCs. High glucose increases STIM1 expression levels by impairing HNF4α binding activity to the Stim1 promoter, which subsequently releases Stim1 transcription from HNF4α repression. Since the STIM1-gated store-operated Ca(2+) entry pathway in MCs has an antifibrotic effect, inhibition of HNF4α in MCs might be a potential therapeutic option for diabetic kidney disease.

Veratric acid inhibits iNOS expression through the regulation of PI3K activation and histone acetylation in LPS-stimulated RAW264.7 cells

In the present study, we investigated regulatory effects of veratric acid on the production of nitric oxide (NO) in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. NO production was significantly decreased by veratric acid in the LPS-stimulated RAW264.7 cells in a dose-dependent manner. The reduction in nitric oxide production was induced by the downregulation of inducible NO synthase (iNOS) expression. Veratric acid suppressed the LPS-induced effects on the regulatory and catalytic subunits of phosphoinositide 3-kinase (PI3K), comprised of p85, p110α, p110β and Akt. The acetylation of p300 and the phosphorylation of activating transcription factor 2 (ATF-2) induced by LPS were downregulated following treatment with veratric acid; similar effects were observed following treatment with LY294002, a specific inhibitor of PI3K/Akt. The LPS-induced expression of histone deacetylase (HDAC)3 decreased to basal levels following treatment with veratric acid, and its expression was also downregulated by LY294002. In the measurement of histone acetylation levels, the LPS-stimulated acetylation of histone H4 was significantly attenuated by veratric acid, and was also reduced following the inhibition of PI3K/Akt with LY294002. From our data, it can be concluded that veratric acid exerts a regulatory effect on LPS-induced iNOS expression. Our results suggest that veratric acid impedes the PI3K/Akt-mediated histone acetyl-transferase (HAT) activation and HDAC expression induced by LPS, thereby abrogating iNOS expression.

Sodium butyrate, a HDAC inhibitor ameliorates eNOS, iNOS and TGF-β1-induced fibrogenesis, apoptosis and DNA damage in the kidney of juvenile diabetic rats

Recent reports highlighted the role of histone deacetylases (HDACs) in the pathogenesis of diabetic nephropathy (DN), but the exact molecular mechanisms by which HDAC inhibitors ameliorate DN still remain unclear. The present study was aimed to investigate the renoprotective effects of sodium butyrate (NaB) in diabetes-induced renal damages, apoptosis and fibrosis in juvenile rats. Diabetes was induced by single injection of STZ (60mg/kg), whereas NaB (500mg/kg/day) was administrated for 21days by i.p. route in a pre- and post-treatment schedule. End-points of evaluation included biochemical estimation, histology, protein expression as well as apoptosis and DNA damage examinations. Post-treatment with NaB significantly decreased plasma glucose, creatinine, urea, histological alterations including the fibrosis and collagen deposition as well as decreased the HDACs activity, expression of eNOS, iNOS, α-SMA, collagen I, fibronectin, TGFβ-1, NFκB, apoptosis and DNA damage in the diabetic kidney. These results showed that NaB treatment improved the renal function and ameliorated the histological alterations, fibrosis, apoptosis and DNA damage in the kidney of juvenile rats.

Comparison of trichostatin A and valproic acid treatment regimens in a mouse model of kidney fibrosis

Histone deacetylase (HDAC) inhibitors are promising new compounds for the therapy of fibrotic diseases. In this study we compared the effect of two HDAC inhibitors, trichostatin A and valproic acid, in an experimental model of kidney fibrosis. In mice, doxorubicin (adriamycin) can cause nephropathy characterized by chronic proteinuria, glomerular damage and interstitial inflammation and fibrosis, as seen in human focal segmental glomerulosclerosis. Two treatment regimens were applied, treatment was either started prior to the doxorubicin insult or delayed until a significant degree of proteinuria and fibrosis was present. Pre-treatment of trichostatin A significantly hampered glomerulosclerosis and tubulointerstitial fibrosis, as did the pre-treatment with valproic acid. In contrast, the development of proteinuria was only completely inhibited in the pre-treated valproic acid group, and not in the pre-treated trichostatin A animals. In the postponed treatment with valproic acid, a complete resolution of established doxorubicin-induced proteinuria was achieved within three days, whereas trichostatin A could not correct proteinuria in such a treatment regimen. However, both postponed regimens have comparable efficacy in maintaining the kidney fibrosis to the level reached at the start of the treatments. Moreover, not only the process of fibrosis, but also renal inflammation was attenuated by both HDAC inhibitors. Our data confirm a role for HDACs in renal fibrogenesis and point towards a therapeutic potential for HDAC inhibitors. The effect on renal disease progression and manifestation can however be different for individual HDAC inhibitors.

Nuclear factor κB mediates suppression of canonical transient receptor potential 6 expression by reactive oxygen species and protein kinase C in kidney cells

This study was carried out to explore the molecular mechanism for down-regulation of TRPC6 expression in the reactive oxygen species (ROS)/PKC signaling in kidney cells. In cultured human mesangial cells, H2O2 and TNF-α inhibited TRPC6 mRNA expression in a time-dependent manner. Inhibition of NF-κB reversed both H2O2- and phorbol 12-myristate 13-acetate (PMA)-induced decrease in TRPC6 protein expression. Activation of NF-κB by knocking down IκBα using siRNA could mimic the suppressive effect of ROS/PKC on TRPC6. a Ca(2+) imaging study showed that activation and inhibition of NF-κB significantly decreased and increased the TRPC6-mediated Ca(2+) entry, respectively. Further experiments showed that PMA, but not its inactive analog 4α-phorbol 12, 13-didecanoate (4α-PDD), caused phosphorylation of IκBα and stimulated the nuclear translocation of NF-κB p50 and p65 subunits. The PMA-dependent IκBα phosphorylation was significantly inhibited by Gö6976. Electrophoretic mobility shift assay revealed that PMA stimulated DNA binding activity of NF-κB. Furthermore, specific knockdown of p65, but not p50, prevented an H2O2 inhibitory effect on TRPC6 protein expression, suggesting p65 as a predominant NF-κB subunit repressing TRPC6. In agreement with a major role of p65, chromatin immunoprecipitation assays showed that PMA treatment induced p65 binding to the TRPC6 promoter. Moreover, PMA treatment increased the association of p65 with histone deacetylase (HDAC) and decreased histone acetylation at the TRPC6 promoter. Consistently, knockdown of HDAC2 by siRNA or inhibition of HDAC with trichostatin A prevented a H2O2-induced decrease in TRPC6 mRNA and protein expressions, respectively. Taken together, our findings imply an important role of NF-κB in a negative regulation of TRPC6 expression at the gene transcription level in kidney cells.

HDAC inhibitors in experimental liver and kidney fibrosis

Histone deacetylase (HDAC) inhibitors have been extensively studied in experimental models of cancer, where their inhibition of deacetylation has been proven to regulate cell survival, proliferation, differentiation and apoptosis. This in turn has led to the use of a variety of HDAC inhibitors in clinical trials. In recent years the applicability of HDAC inhibitors in other areas of disease has been explored, including the treatment of fibrotic disorders. Impaired wound healing involves the continuous deposition and cross-linking of extracellular matrix governed by myofibroblasts leading to diseases such as liver and kidney fibrosis; both diseases have high unmet medical needs which are a burden on health budgets worldwide. We provide an overview of the potential use of HDAC inhibitors against liver and kidney fibrosis using the current understanding of these inhibitors in experimental animal models and in vitro models of fibrosis.

Epigenetic imprinting by commensal probiotics inhibits the IL-23/IL-17 axis in an in vitro model of the intestinal mucosal immune system

The pathophysiology of IBD is characterized by a complex interaction between genes and the environment. Genetic and environmental differences are attributed to the heterogeneity of the disease pathway and to the epigenetic modifications that lead to altered gene expression in the diseased tissues. The epigenetic machinery consists of short interfering RNA, histone modifications, and DNA methylation. We evaluated the effects of Bifidobacterium breve (DSMZ 20213) and LGG (ATCC 53103), as representatives of commensal probiotics on the expression of IL-17 and IL-23, which play an important role in IBD, and on the epigenetic machinery in a 3D coculture model composed of human intestinal HT-29/B6 or T84 cells and PBMCs. The cells were treated with LPS in the presence or absence of bacteria for 48 h, and the expression of IL-17, IL-23, and CD40 at the mRNA and protein levels was assessed using TaqMan qRT-PCR and ELISA, respectively. Western blotting was used to assess the expression of the MyD88, the degradation of IRAK-1 and IκBα, the expression of the NF-κB p50/p65 subunits, the p-p38 MAPK and p-MEK1, as well as histone modifications. NF-κB activity was assessed by NF-κB-dependent luciferase reporter gene assays. The accumulation of Ac-H4 and DNA methylation was quantitatively assessed using colorimetric assays. B. breve and LGG diminished the LPS-induced expression of IL-17, IL-23, CD40, and histone acetylation, while slightly enhancing DNA methylation. These effects were paralleled by a decrease in the nuclear translocation of NF-κB, as demonstrated by a decrease in the expression of MyD88, degradation of IRAK-1 and IκBα expression of the nuclear NF-κB p50/p65 subunits, p-p38 MAPK and p-MEK1, and NF-κB-dependent luciferase reporter gene activity in LPS-stimulated cells. B. breve and LGG may exert their anti-inflammatory effects in the gut by down-regulating the expression of the IBD-causing factors (IL-23/IL-17/CD40) associated with epigenetic processes involving the inhibition of histone acetylation and the optimal enhancement of DNA methylation, reflected in the limited access of NF-κB to gene promoters and reduced NF-κB-mediated transcriptional activation. We describe a new regulatory mechanism in which commensal probiotics inhibit the NF-κB-mediated transcriptional activation of IBD-causing factors (IL-23/IL-17/CD40), thereby simultaneously reducing histone acetylation and enhancing DNA methylation.

A novel histone deacetylase inhibitor prevents IL-1beta induced metabolic dysfunction in pancreatic beta-cells

The histone deacetylase (HDAC) inhibitor trichostatin A (TSA) has recently been shown to inhibit deleterious effects of cytokines on beta-cells, but it is unable to protect beta-cells from death due to its own cytotoxicity. Herein, we investigated novel HDAC inhibitors for their cytoprotective effects against IL-1beta-induced damage to isolated beta-cells. We report that three novel compounds (THS-73-44, THS-72-5 and THS-78-5) significantly inhibited HDAC activity and increased the acetylation of histone H4 in isolated beta-cells. Further, these compounds exerted no toxic effects on metabolic cell viability in these cells. However, among the three compounds tested, only THS-78-5 protected against IL-1beta-mediated loss in beta-cell viability. THS-78-5 was also able to attenuate IL-1beta-induced inducible nitric oxide synthase expression and subsequent NO release. Our data also indicate that the cytoprotective properties of THS-78-5 against IL-1beta-mediated effects may, in part, be due to inhibition of IL-1beta-induced transactivation of nuclear factor kappaB (NF-kappaB) in these cells. Together, we provide evidence for a novel HDAC inhibitor with a significant potential to prevent IL-1beta-mediated effects on isolated beta-cells. Potential implications of these findings in the development of novel therapeutics to prevent deleterious effects of cytokines and the onset of autoimmune diabetes are discussed.

A novel histone deacetylase inhibitor prevents IL-1beta induced metabolic dysfunction in pancreatic beta-cells

The histone deacetylase (HDAC) inhibitor trichostatin A (TSA) has recently been shown to inhibit deleterious effects of cytokines on beta-cells, but it is unable to protect beta-cells from death due to its own cytotoxicity. Herein, we investigated novel HDAC inhibitors for their cytoprotective effects against IL-1beta-induced damage to isolated beta-cells. We report that three novel compounds (THS-73-44, THS-72-5 and THS-78-5) significantly inhibited HDAC activity and increased the acetylation of histone H4 in isolated beta-cells. Further, these compounds exerted no toxic effects on metabolic cell viability in these cells. However, among the three compounds tested, only THS-78-5 protected against IL-1beta-mediated loss in beta-cell viability. THS-78-5 was also able to attenuate IL-1beta-induced inducible nitric oxide synthase expression and subsequent NO release. Our data also indicate that the cytoprotective properties of THS-78-5 against IL-1beta-mediated effects may, in part, be due to inhibition of IL-1beta-induced transactivation of nuclear factor kappaB (NF-kappaB) in these cells. Together, we provide evidence for a novel HDAC inhibitor with a significant potential to prevent IL-1beta-mediated effects on isolated beta-cells. Potential implications of these findings in the development of novel therapeutics to prevent deleterious effects of cytokines and the onset of autoimmune diabetes are discussed.

The essential role of Oct-2 in LPS-induced expression of iNOS in RAW 264.7 macrophages and its regulation by trichostatin A

This article reports on a study of the effect of trichostatin A (TSA), an inhibitor of histone deacetylase, on lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase (iNOS) in RAW 264.7 macrophages and its underlying mechanisms. TSA pretreatment potently diminishes LPS-stimulated nitric oxide (NO) release and both mRNA and protein levels of iNOS in macrophages. The effects of TSA and LPS on transcription factors binding to two LPS-responsive elements within the iNOS promoter, one binding the NF-κB site and the other the octamer element, were investigated. Results show that TSA did not alter the LPS-activated NF-κB activity demonstrated by the nuclear translocation of p50 and p65 and by a NF-κB-driven reporter gene expression system. In addition, neither TSA nor LPS changed the expression of Oct-1, a ubiquitously expressed octamer binding protein. However, TSA suppressed the LPS-induced expression of Oct-2, another octamer binding protein, at both mRNA and protein levels. Chromatin immunoprecipitation assays revealed that binding of Oct-2 to the iNOS promoter was enhanced by LPS treatment; however, pretreatment with TSA resulted in loss of this binding. Moreover, forced expression of Oct-2 by transfection of pCG-Oct-2 plasmid restored the TSA-suppressed iNOS expression elevated by LPS stimulation, further indicating that Oct-2 activation is a crucial step for transcriptional activation of the iNOS gene in response to LPS stimulation in macrophages. This study demonstrates that TSA diminishes iNOS expression in LPS-treated macrophages by inhibiting Oct-2 expression and thus reducing the production of NO.

Regulatory roles for histone deacetylation in IL-1beta-induced nitric oxide release in pancreatic beta-cells

Histone (de)acetylases control gene transcription via modification of the chromatin structure. Herein, we investigated potential roles for histone deacetylation (or hypoacetylation) in interleukin-1β (IL-1β)-mediated inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release in insulin-secreting INS 832/13 (INS) cells. Western blot analysis suggested localization of members of Class 1 and Class 2 families of histone deacetylases (HDACs) in these cells. Trichostatin A (TSA), a known inhibitor of HDACs, markedly reduced IL-1β-mediated iNOS expression and NO release from these cells in a concentration-dependent manner. TSA also promoted hyperacetylation of histone H4 under conditions in which it inhibited IL-1β-mediated effects on isolated β cells. Rottlerin, a known inhibitor of protein kinase Cδ, also increased histone H4 acetylation, and inhibited IL-1β-induced iNOS expression and NO release in these cells. It appears that the putative mechanism underlying the stimulatory effects of rottlerin on acetylation status of histone H4 are distinct from the HDAC inhibitory property of TSA, since rottlerin failed to inhibit HDAC activity in nuclear extracts isolated from INS cells. These data are suggestive of potential regulatory effects of rottlerin at the level of increasing the histone acetyltransferase activity in these cells. Together our studies present the first evidence to suggest a PKCδ-mediated signalling step, which promotes hypoacetylation of candidate histones culminating in IL-1β-induced metabolic dysfunction of the isolated β cell.

Inhibition of histone deacetylases prevents cytokine-induced toxicity in beta cells

AIMS/HYPOTHESIS

The immune-mediated elimination of pancreatic beta cells in type 1 diabetes involves release of cytotoxic cytokines such as IL-1beta and IFNgamma, which induce beta cell death in vitro by mechanisms that are both dependent and independent of nitric oxide (NO). Nuclear factor kappa B (NFkappaB) is a critical signalling molecule in inflammation and is required for expression of the gene encoding inducible NO synthase (iNOS) and of pro-apoptotic genes. NFkappaB has recently been shown to associate with chromatin-modifying enzymes histone acetyltransferases and histone deacetylases (HDAC), and positive effects of HDAC inhibition have been obtained in several inflammatory diseases. Thus, the aim of this study was to investigate whether HDAC inhibition protects beta cells against cytokine-induced toxicity.

MATERIALS AND METHODS

The beta cell line, INS-1, or intact rat islets were precultured with HDAC inhibitors suberoylanilide hydroxamic acid or trichostatin A in the absence or presence of IL-1beta and IFNgamma. Effects on insulin secretion and NO formation were measured by ELISA and Griess reagent, respectively. iNOS levels and NFkappaB activity were measured by immunoblotting and by immunoblotting combined with electrophoretic mobility shift assay, respectively. Viability was analysed by 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and apoptosis by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and histone-DNA complex ELISA.

RESULTS

HDAC inhibition reduced cytokine-mediated decrease in insulin secretion and increase in iNOS levels, NO formation and apoptosis. IL-1beta induced a bi-phasic phosphorylation of inhibitor protein kappa Balpha (IkappaBalpha) with the 2nd peak being sensitive to HDAC inhibition. No effect was seen on IkappaBalpha degradation and NFkappaB DNA binding.

CONCLUSIONS/INTERPRETATION

HDAC inhibition prevents cytokine-induced beta cell apoptosis and impaired beta cell function associated with a downregulation of NFkappaB transactivating activity.

Nitric Oxide-dependent Negative Feedback of PARP-1 trans-Activation of the Inducible Nitric-oxide Synthase Gene

Nitric oxide (NO) participates in a variety of physiologic and pathophysiologic processes in diverse tissues, including the kidney. Although mechanisms for cytokine induction of inducible nitric-oxide synthase (iNOS) have been increasingly clarified, the controls for termination of NO production remain unclear. Because excessive NO production can be cytotoxic to host cells, feedback inhibition of iNOS transcription would represent a means of cytoprotection. Many of the cGMP-independent functions of NO are mediated by S-nitrosylation of cysteine thiols of target proteins. We hypothesized that NO-mediated S-nitrosylation of transcription factors might serve to feedback inhibit their trans-activation potential and deactivate iNOS gene transcription. Transient transfection of murine mesangial cells with iNOS promoter deletion-luciferase constructs revealed the region -915 to -849 to be NO sensitive with respect to IL-1beta-induced promoter activity. In vitro DNase I footprinting identified a footprint at -865/-842 in the absence of NO, but not in the presence of endogenous or exogenously delivered NO. Southwestern blotting using this probe coupled with partial peptide sequencing of the protein bands revealed that poly(ADP-ribose) polymerase isoform 1 (PARP-1) bound the probe in a sequence-specific manner. Gel shift/supershift experiments and chromatin immunoprecipitation assay analysis confirmed this binding in vitro and in vivo. Functionally, mutation of the -859/-850 site to prevent PARP-1 binding or PARP-1 knockdown by RNA interference relieved the inhibitory effects of NO on iNOS promoter activity. Biotin-switch assays and co-immunoprecipitation with an anti-nitrocysteine antibody indicated that PARP-1 was S-nitrosylated. We conclude that NO feedback inhibits iNOS gene transcription by S-nitrosylating the trans-activator PARP-1 and decreasing its binding and/or action at the iNOS promoter.