Homocysteine Triggers Inflammatory Responses in Macrophages through Inhibiting CSE-H2S Signaling via DNA Hypermethylation of CSE Promoter.

Jiao-Jiao Li,Xing-Shun Xu,Li-Fang Hu,Yong-Jun Cao,Ya-Li Wang,Fen Wang,Chun-Feng Liu,Jian Cheng,Shou-Jiang You,Qian Li,Hua-Ping Du

doi:10.3390/ijms160612560

Abstract

Hyperhomocysteinemia (HHcy) is an independent risk factor of atherosclerosis and other cardiovascular diseases. Unfortunately, Hcy-lowering strategies were found to have limited effects in reducing cardiovascular events. The underlying mechanisms remain unclear. Increasing evidence reveals a role of inflammation in the pathogenesis of HHcy. Homocysteine (Hcy) is a precursor of hydrogen sulfide (H2S), which is formed via the transsulfuration pathway catalyzed by cystathionine β-synthase and cystathionine γ-lyase (CSE) and serves as a novel modulator of inflammation. In the present study, we showed that methionine supplementation induced mild HHcy in mice, associated with the elevations of TNF-α and IL-1β in the plasma and reductions of plasma H2S level and CSE expression in the peritoneal macrophages. H2S-releasing compound GYY4137 attenuated the increases of TNF-α and IL-1β in the plasma of HHcy mice and Hcy-treated raw264.7 cells while CSE inhibitor PAG exacerbated it. Moreover, the in vitro study showed that Hcy inhibited CSE expression and H2S production in macrophages, accompanied by the increases of DNA methyltransferase (DNMT) expression and DNA hypermethylation in cse promoter region. DNMT inhibition or knockdown reversed the decrease of CSE transcription induced by Hcy in macrophages. In sum, our findings demonstrate that Hcy may trigger inflammation through inhibiting CSE-H2S signaling, associated with increased promoter DNA methylation and transcriptional repression of cse in macrophages.

Highlights

Homocysteine (Hcy) is a non-essential sulfhydryl-containing amino acid derived from methionine metabolism, and is dynamically regulated via two metabolic pathways: remethylation and transsulfuration pathway, respectively
Our findings revealed that Hcy repressed cystathionine γ-lyase (CSE) transcription in macrophages by inducing DNA hypermethylation in cse promoter, decreased H2S production and caused the elevations in pro-inflammatory cytokines generation in macrophages and in the plasma of mice with HHcy
Dietary supplementation with 2% methionine in drinking water resulted in significant elevations in plasma Hcy (15.56 ± 1.553 μM in methionine-treated group versus 6.3 ± 0.298 μM in control group) and pro-inflammatory cytokine (TNF-α, IL-1β) levels, accompanied by the reduction in plasma H2S

Summary

Introduction

Homocysteine (Hcy) is a non-essential sulfhydryl-containing amino acid derived from methionine metabolism, and is dynamically regulated via two metabolic pathways: remethylation and transsulfuration pathway, respectively. Elevation in plasma Hcy, called hyperhomocysteinemia (HHcy), commonly occurs due to high methionine diet, dietary deficiencies of folic acid/vitamin B, mutations in genes encoding Hcy-metabolizing enzymes, and impaired renal clearance as well [1]. Severe HHcy (>100 μM) is rare, mild (15–30 μM) to moderate (31–100 μM) HHcy occurs in. HHcy is an independent risk factor of cardiovascular disease, and associated with the onset of several neurologic disorders such as stroke, mild cognitive impairment and Alzheimer’s disease [2]. Chronic inflammation in vascular bed in particular, is implicated in the progression of HHcy-associated diseases

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