Nitric oxide deficiency determines global chromatin changes in Duchenne muscular dystrophy

Nε-lysine acetylation determines dissociation from GAP junctions and lateralization of connexin 43 in normal and dystrophic heart

Wanting to explore the epigenetic basis of Duchenne cardiomyopathy, we found that global histone acetylase activity was abnormally elevated and the acetylase P300/CBP-associated factor (PCAF) coimmunoprecipitated with connexin 43 (Cx43), which was N(ε)-lysine acetylated and lateralized in mdx heart. This observation was paralleled by Cx43 dissociation from N-cadherin and zonula occludens 1, whereas pp60-c-Src association was unaltered. In vivo treatment of mdx with the pan-histone acetylase inhibitor anacardic acid significantly reduced Cx43 N(ε)-lysine acetylation and restored its association to GAP junctions (GJs) at intercalated discs. Noteworthy, in normal as well as mdx mice, the class IIa histone deacetylases 4 and 5 constitutively colocalized with Cx43 either at GJs or in the lateralized compartments. The class I histone deacetylase 3 was also part of the complex. Treatment of normal controls with the histone deacetylase pan-inhibitor suberoylanilide hydroxamic acid (MC1568) or the class IIa-selective inhibitor 3-{4-[3-(3-fluorophenyl)-3-oxo-1-propen-1-yl]-1-methyl-1H-pyrrol-2-yl}-N-hydroxy-2-propenamide (MC1568) determined Cx43 hyperacetylation, dissociation from GJs, and distribution along the long axis of ventricular cardiomyocytes. Consistently, the histone acetylase activator pentadecylidenemalonate 1b (SPV106) hyperacetylated cardiac proteins, including Cx43, which assumed a lateralized position that partly reproduced the dystrophic phenotype. In the presence of suberoylanilide hydroxamic acid, cell to cell permeability was significantly diminished, which is in agreement with a Cx43 close conformation in the consequence of hyperacetylation. Additional experiments, performed with Cx43 acetylation mutants, revealed, for the acetylated form of the molecule, a significant reduction in plasma membrane localization and a tendency to nuclear accumulation. These results suggest that Cx43 N(ε)-lysine acetylation may have physiopathological consequences for cell to cell coupling and cardiac function.

Nitrosative stress elicited by nNOSµ delocalization inhibits muscle force in dystrophin-null mice

The mechanism of force reduction is not completely understood in Duchenne muscular dystrophy (DMD), a dystrophin-deficient lethal disease. Nitric oxide regulates muscle force. Interestingly, neuronal nitric oxide synthase µ (nNOSµ), a major source of muscle nitric oxide, is lost from the sarcolemma in DMD muscle. We hypothesize that nNOSµ delocalization contributes to force reduction in DMD. To test this hypothesis, we generated dystrophin/nNOSµ double knockout mice. Genetic elimination of nNOSµ significantly enhanced force in dystrophin-null mice. Pharmacological inhibition of nNOS yielded similar results. To further test our hypothesis, we studied δ-sarcoglycan-null mice, a model of limb-girdle muscular dystrophy. These mice had minimal sarcolemmal nNOSµ delocalization and muscle force was less compromised. Annihilation of nNOSµ did not improve their force either. To determine whether nNOSµ delocalization itself inhibited force, we corrected muscle disease in dystrophin-null mice with micro-dystrophins that either restored or did not restore sarcolemmal nNOSµ. Similar muscle force was obtained irrespective of nNOSµ localization. Additional studies suggest that nNOSµ delocalization selectively inhibits muscle force in dystrophin-null mice via nitrosative stress. In summary, we have demonstrated for the first time that nitrosative stress elicited by nNOSµ delocalization is an important mechanism underlying force loss in DMD.

MicroRNAs involved in molecular circuitries relevant for the Duchenne muscular dystrophy pathogenesis are controlled by the dystrophin/nNOS pathway

In Duchenne muscular dystrophy (DMD) the absence of dystrophin at the sarcolemma delocalizes and downregulates nitric oxide synthase (nNOS); this alters S-nitrosylation of HDAC2 and its chromatin association. We show that the differential HDAC2 nitrosylation state in Duchenne versus wild-type conditions deregulates the expression of a specific subset of microRNA genes. Several circuitries controlled by the identified microRNAs, such as the one linking miR-1 to the G6PD enzyme and the redox state of cell, or miR-29 to extracellular proteins and the fibrotic process, explain some of the DMD pathogenetic traits. We also show that, at variance with other myomiRs, miR-206 escapes from the dystrophin-nNOS control being produced in activated satellite cells before dystrophin expression; in these cells, it contributes to muscle regeneration through repression of the satellite specific factor, Pax7. We conclude that the pathway activated by dystrophin/nNOS controls several important circuitries increasing the robustness of the muscle differentiation program.

Nitric oxide determines mesodermic differentiation of mouse embryonic stem cells by activating class IIa histone deacetylases: potential therapeutic implications in a mouse model of hindlimb ischemia

In human endothelial cells, nitric oxide (NO) results in class IIa histone deacetylases (HDACs) activation and marked histone deacetylation. It is unknown whether similar epigenetic events occur in embryonic stem cells (ESC) exposed to NO and how this treatment could influence ESC therapeutic potential during tissue regeneration.This study reports that the NO-dependent class IIa HDACs subcellular localization and activity decreases the global acetylation level of H3 histones in ESC and that this phenomenon is associated with the inhibition of Oct4, Nanog, and KLF4 expression. Further, a NO-induced formation of macromolecular complexes including HDAC3, 4, 7, and protein phosphatase 2A (PP2A) have been detected. These processes correlated with the expression of the mesodermal-specific protein brachyury (Bry) and the appearance of several vascular and skeletal muscle differentiation markers. These events were abolished by the class IIa-specific inhibitor MC1568 and by HDAC4 or HDAC7 short interfering RNA (siRNA). The ability of NO to induce mesodermic/cardiovascular gene expression prompted us to evaluate the regenerative potential of these cells in a mouse model of hindlimb ischemia. We found that NO-treated ESCs injected into the cardiac left ventricle selectively localized in the ischemic hindlimb and contributed to the regeneration of muscular and vascular structures. These findings establish a key role for NO and class IIa HDACs modulation in ESC mesodermal commitment and enhanced regenerative potential in vivo.

Histone deacetylase inhibitors: keeping momentum for neuromuscular and cardiovascular diseases treatment

Histone deacetylases (HDACs) are enzymes with a pleiotropic range of intracellular localizations and actions. They are principally involved in the withdrawal of acetyl-groups from a large number of nuclear and cytoplasmic proteins including nuclear core histones as well as cytoskeletal proteins and metabolically relevant enzymes. Initial findings indicated that HDAC inhibitors (DIs) could be successfully applied in a variety of cancer treatment protocols as a consequence of their anti-proliferative and pro-apoptotic properties. Recent observations, however, enlightened the important therapeutic effects of DIs in experimental animal models for arthritis, neurodegenerative and neuromuscular disorders, heart ischemia, cardiac hypertrophy, heart failure and arrhythmias. A small number of clinical trials are now open or planned for the near future to verify the therapeutic properties of DIs in non-cancer-related diseases. This review summarizes some of the most important observations and concepts aroused by the most recent experimental application of DIs to neuromuscular and cardiac diseases.

Identification of small molecule and genetic modulators of AON-induced dystrophin exon skipping by high-throughput screening

One therapeutic approach to Duchenne Muscular Dystrophy (DMD) recently entering clinical trials aims to convert DMD phenotypes to that of a milder disease variant, Becker Muscular Dystrophy (BMD), by employing antisense oligonucleotides (AONs) targeting splice sites, to induce exon skipping and restore partial dystrophin function. In order to search for small molecule and genetic modulators of AON-dependent and independent exon skipping, we screened ∼10,000 known small molecule drugs, >17,000 cDNA clones, and >2,000 kinase- targeted siRNAs against a 5.6 kb luciferase minigene construct, encompassing exon 71 to exon 73 of human dystrophin. As a result, we identified several enhancers of exon skipping, acting on both the reporter construct as well as endogenous dystrophin in mdx cells. Multiple mechanisms of action were identified, including histone deacetylase inhibition, tubulin modulation and pre-mRNA processing. Among others, the nucleolar protein NOL8 and staufen RNA binding protein homolog 2 (Stau2) were found to induce endogenous exon skipping in mdx cells in an AON-dependent fashion. An unexpected but recurrent theme observed in our screening efforts was the apparent link between the inhibition of cell cycle progression and the induction of exon skipping.

Proteomic profile of differentially expressed plasma proteins from dystrophic mice and following suberoylanilide hydroxamic acid treatment

PURPOSE

Histone Deacetylase Inhibitors (DI) ameliorates dystrophic muscle regeneration restoring muscular strength in the mdx mouse model of Duchenne muscular dystrophy (DMD). The further development of these compounds as drugs for DMD treatment is currently hampered by the lack of knowledge about DIs effect in large dystrophic animal models and that of suitable biomarkers to monitor their efficacy.

EXPERIMENTAL DESIGN

In this study we applied proteomic analysis to identify differentially expressed proteins present in plasma samples from mdx mice treated with the Suberoylanilide hydroxamic acid (SAHA) and relative normal controls (WT).

RESULTS

Several differentially expressed proteins were identified between untreated wild type and mdx mice. Among these, fibrinogen, epidermal growth factor 2 receptor, major urinary protein and glutathione peroxidase 3 (GPX3) were constitutively up-regulated in mdx, while complement C3, complement C6, gelsolin, leukaemia inhibitory factor receptor (LIFr), and alpha 2 macroglobulin were down-regulated compared to WT mice. SAHA determined the normalization of LIFr and GPX3 protein level while apoliprotein E was de novo up-regulated in comparison to vehicle-treated mdx mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Collectively, these data unravel potential serological disease biomarkers of mdx that could be useful to monitor muscular dystrophy response to DI treatment.

Homeodomain interacting protein kinase 2 activation compromises endothelial cell response to laminar flow: protective role of p21(waf1,cip1,sdi1)

BACKGROUND

In the cardiovascular system, laminar shear stress (SS) is one of the most important source of endothelial protecting signals. Physical and chemical agents, however, including ionising radiations and anticancer drugs, may injure endothelial cells determining an increase in oxidative stress and genotoxic damage. Whether the SS protective function remains intact in the presence of strong oxidants or DNA damage is currently unclear.

METHODS AND RESULTS

To investigate this aspect a series of experiments were performed in which HUVEC were exposed to sub-lethal doses of the radio-mimetic compound Bleomycin (Bleo; 10 microg/ml) which generated free radicals (ROS) without significantly compromising cell survival. Remarkably, the application of a SS of 12 dyne/cm(2) did not protect endothelial cells but markedly accelerated apoptosis compared to controls kept in static culture and in the presence of Bleo. Experiments with the inducible nitric oxide synthase (iNOS) inhibitor GW274150 significantly reduced the SS-dependent apoptosis indicating that the production of NO was relevant for this effect. At molecular level, the ataxia-telangectasia-mutated (ATM) kinase, the homeodomain-interacting protein kinase-2 (HIPK2) and p53 were found activated along a pro-apoptotic signalling pathway while p21(waf1,cip1,sdi1) was prevented from its protective action. RNA interference experiments revealed that HIPK2 and p53 were both important for this process, however, only the forced expression p21(waf1,cip1,sdi1) fully restored the SS-dependent pro-survival function.

CONCLUSIONS

This study provides the first evidence that, in the presence of genotoxic damage, laminar flow contributes to endothelial toxicity and death and identifies molecular targets potentially relevant in endothelial dysfunction and cardiovascular disease pathogenesis.

NO sparks off chromatin: tales of a multifaceted epigenetic regulator

The discovery of nitric oxide (NO) revealed its ambiguous nature, which is related to its pleiotropic activities that control the homeostasis of every organism from bacteria to mammals in several physiological and pathological situations. The wide range of action of NO basically depends on two features: 1) the variety of chemical reactions depending on NO, and 2) the differential cellular responses elicited by distinct NO concentrations. Despite the increasing body of knowledge regarding its chemistry, biology and NO-dependent signaling pathways, little information is available on the nuclear actions of NO in terms of gene expression regulation. Indeed, studies of a putative role for this diatomic compound in regulating chromatin remodeling are still in their infancy. Only recently has the role of NO in epigenetics emerged, and some of its putative epigenetic properties are still only hypothetical. In the present review, we discuss the current evidence for NO-related mechanisms of epigenetic gene expression regulation. We link some of the well known NO chemical reactions and metabolic processes (e.g., S-nitrosylation of thiols, tyrosine nitration, cGMP production) to chromatin modification and address the most recent, striking hypothesis about NO and the control of chromosomes structure.