Cardiac mitochondrial acetylome after chronic TBI

ABSTRACT
Epidemiological studies show that irradiation increases the risk of cardiovascular disease decades after the exposure. Alteration in cardiac energy metabolism has been suggested to contribute to radiation-induced heart pathology. A hallmark of this radiation-associated metabolic impairment is mitochondrial dysfunction and deactivation of the transcription factor PPAR alpha.
The goal of this study was to investigate the role of acetylation in heart mitochondria in the long-term response to chronic radiation. ApoE-deficient (ApoE-/-) C57Bl/6J mice were continuously exposed to low-dose-rate (20 mGy/day) gamma radiation for 300 days, resulting in a cumulative total body dose of 6.0 Gy. Heart mitochondria from irradiated and sham-irradiated control mice were analysed using label-free proteomics. Radiation-induced proteome and acetylome alterations were further validated using immunoblotting, activity assay and ELISA.
In total, 72 proteins showed a changed acetylation status, of which a great majority (96%) were hyperacetylated. These proteins were involved in the mitochondrial energy metabolism, and sirtuin pathway. The elevated acetylation was associated with reduced activity of mitochondrial sirtuins (Sirt3 and 4) and increased amount of Acetyl-CoA. Mitochondrial acetylation has an inhibitory effect on the PPAR alpha-PGC1 regulatory network of metabolism in irradiated hearts.
These data highlight for the first time the role of mitochondrial acetylation in the radiation-induced cardiac injury and suggest a novel mechanism for the late heart damage following irradiation.

摘要
流行病学研究表明，辐射暴露数十年后会增加心血管疾病的发病风险。有研究提示，心脏能量代谢异常可能参与辐射诱导的心脏病变，这类辐射相关代谢损伤的典型特征为线粒体功能障碍与转录因子PPARα（PPAR alpha）的失活。

本研究旨在探讨乙酰化修饰在心脏线粒体应对慢性辐射的长期应答过程中的作用。实验选用载脂蛋白E基因敲除（ApoE-/-）C57Bl/6J小鼠，以低剂量率（20 mGy/天）持续暴露于γ射线300天，累积全身辐射剂量达6.0 Gy。采用无标记蛋白质组学（label-free proteomics）技术，对辐射暴露组与假照射对照组小鼠的心脏线粒体进行分析；并通过免疫印迹（immunoblotting）、活性检测及酶联免疫吸附实验（ELISA），进一步验证辐射诱导的蛋白质组与乙酰化组学改变。

本研究共鉴定出72个乙酰化状态发生改变的蛋白质，其中绝大多数（96%）呈现高乙酰化修饰。这些蛋白质主要参与线粒体能量代谢与沉默信息调节因子（sirtuin）通路。乙酰化水平升高与线粒体沉默信息调节因子Sirt3、Sirt4的活性降低及乙酰辅酶A含量增加显著相关。在辐射暴露的心脏组织中，线粒体乙酰化修饰可抑制PPARα-PGC1代谢调控网络的功能。

本研究首次揭示了线粒体乙酰化修饰在辐射诱导心脏损伤中的作用，为阐明辐射暴露后心脏晚期损伤的潜在机制提供了全新的研究方向。