Yoon S, et al. Chonnam Med J. 2016 Jan;52(1):1-11. http://dx.doi.org/10.4068/cmj.2016.52.1.1

Fibrosis is characterized by excessive deposition of the extracellular matrix and develops because of fibroblast differentiation during the process of inflammation. Various cytokines stimulate resident fibroblasts, which differentiate into myofibroblasts. Myofibroblasts actively synthesize an excessive amount of extracellular matrix, which indicates pathologic fibrosis. Although initial fibrosis is a physiologic response, the accumulated fibrous material causes failure of normal organ function. Cardiac fibrosis interferes with proper diastole, whereas pulmonary fibrosis results in chronic hypoxia; liver cirrhosis induces portal hypertension, and overgrowth of fibroblasts in the conjunctiva is a major cause of glaucoma surgical failure. Recently, several reports have clearly demonstrated the functional relevance of certain types of histone deacetylases (HDACs) in various kinds of fibrosis and the successful alleviation of the condition in animal models using HDAC inhibitors. In this review, we discuss the therapeutic potential of HDAC inhibitors in fibrosis-associated human diseases using results obtained from animal models.

Mesenchymal stem cells (MSCs) can suppress pathological inflammation. However, the mechanisms underlying the association between MSCs and inflammation remain unclear. Under coculture conditions with macrophages, MSCs highly expressed angiopoietin-like 4 (ANGPTL4) to blunt the polarization of macrophages toward the proinflammatory phenotype. ANGPTL4-deficient MSCs failed to inhibit the inflammatory macrophage phenotype. In inflammation-related animal models, the injection of coculture medium or ANGPTL4 protein increased the antiinflammatory macrophages in both peritonitis and myocardial infarction. In particular, cardiac function and pathology were markedly improved by ANGPTL4 treatment. We found that retinoic acid–related orphan receptor α (RORα) was increased by inflammatory mediators, such as IL-1β, and bound to ANGPTL4 promoter in MSCs. Collectively, RORα-mediated ANGPTL4 induction was shown to contribute to the antiinflammatory activity of MSCs against macrophages under pathological conditions. This study suggests that the capability of ANGPTL4 to induce tissue repair is a promising opportunity for safe stem cell–free regeneration therapy from a translational perspective.

The clinical importance of heart failure with preserved ejection fraction (HFpEF) has recently become apparent. HFpEF refers to heart failure (HF) symptoms with normal or near-normal cardiac function on echocardiography. Common clinical features of HFpEF include diastolic dysfunction, reduced compliance, and ventricular hypokinesia. HFpEF differs from the better-known HF with reduced ejection fraction (HFrEF). Despite having a “preserved ejection fraction,” patients with HFpEF have symptoms such as shortness of breath, excessive tiredness, and limited exercise capability. Furthermore, the mortality rate and cumulative survival rate are as severe in HFpEF as they are in HFrEF. While beta-blockers and renin-angiotensin-aldosterone system modulators can improve the survival rate in HFrEF, no known therapeutic agents show similar effectiveness in HFpEF. Researchers have examined molecular events in the development of HFpEF using small and middle-sized animal models. This review discusses HFpEF with regard to etiology and clinical features and introduces the use of mouse and other animal models of human HFpEF.

Background: Although the clinical importance of heart failure with preserved ejection fraction (HFpEF) has been extensively explored, most therapeutic regimens, including nitric oxide (NO) donors, lack therapeutic benefit. Although the clinical characteristics of HFpEF are somewhat heterogeneous, diastolic dysfunction (DD) is one of the most important features. Here we report that neuronal nitric oxide synthase (nNOS) induces DD by S-nitrosylation of histone deacetylase 2 (HDAC2). Methods: Two animal models of DD—SAUNA (SAlty drinking water/Unilateral Nephrectomy/Aldosterone) and mild transverse aortic constriction (mTAC) mice— as well as human heart samples from left ventricular hypertrophy (LVH) patients were used. Genetically modified mice that were either nNOS-ablated or HDAC2 S-nitrosylation-resistant were also challenged. N(ω)-propyl-L-arginine (NPLA), an nNOS selective inhibitor, and dimethyl fumarate (DMF), an NRF2 inducer, were used. Molecular events were further checked in human left ventricle specimens. Results: SAUNA or mTAC stress impaired diastolic function and exercise tolerance without overt systolic failure. Among the post-translational modifications tested, S-nitrosylation was most dramatically increased in both models. Utilizing heart samples from both mice and humans, we observed increases in nNOS expression and NO production. NPLA alleviated the development of DD in vivo. Similarly, nNOS knock out mice were resistant to SAUNA stress. nNOS-induced S-nitrosylation of HDAC2 was relayed by transnitrosylation of GAPDH. HDAC2 S-nitrosylation was confirmed in both DD mouse and human LVH. S-Nitrosylation of HDAC2 took place at C262 and C274. When DD was induced, HDAC2 S-nitrosylation was detected in wild type mouse, but not in HDAC2 knock-in mouse heart that expressed HDAC2 C262A/C274A. In addition, HDAC2 C262A/C274A mice maintained normal diastolic function under DD stimuli. Gene delivery with AAV9-NRF2, a putative denitrosylase of HDAC2, or pharmacologic intervention by DMF successfully induced HDAC2 denitrosylation and mitigated DD in vivo. Conclusions: Our observations are the first to demonstrate a new mechanism underlying DD pathophysiology. Our results provide theoretical and experimental evidence to explain the ineffectiveness of conventional NO-enhancement trials for improving DD with heart failure symptoms. More importantly, our results suggest that reduction of NO or denitrosylation of HDAC2 may provide a new therapeutic platform for the treatment of refractory HFpEF.

Proteins dynamically contribute towards maintaining cellular homeostasis. Posttranslational modification regulates the function of target proteins through their immediate activation, sudden inhibition, or permanent degradation. Among numerous protein modifications, protein nitrosation and its functional relevance have emerged. Nitrosation generally initiates nitric oxide (NO) production in association with NO synthase. NO is conjugated to free thiol in the cysteine side chain (S-nitrosylation) and is propagated via the transnitrosylation mechanism. S-nitrosylation is a signaling pathway frequently involved in physiologic regulation. NO forms peroxynitrite in excessive oxidation conditions and induces tyrosine nitration, which is quite stable and is considered irreversible. Two main reducing systems are attributed to denitrosylation: glutathione and thioredoxin (TRX). Glutathione captures NO from S-nitrosylated protein and forms S-nitrosoglutathione (GSNO). The intracellular reducing system catalyzes GSNO into GSH again. TRX can remove NO-like glutathione and break down the disulfide bridge. Although NO is usually beneficial in the basal context, cumulative stress from chronic inflammation or oxidative insult produces a large amount of NO, which induces atypical protein nitrosation. Herein, we (1) provide a brief introduction to the nitrosation and denitrosylation processes, (2) discuss nitrosation-associated human diseases, and (3) discuss a possible denitrosylation strategy and its therapeutic applications.