Center for Interdisciplinary Cardiovascular Sciences, Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Department of Medical Biochemistry, Kurume University School of Medicine, Kurume 830-0011, Japan.
Cardiovasc Res. 2021 Sep 28;117(11):2340-2353. doi: 10.1093/cvr/cvab034.
Proteostasis maintains protein homeostasis and participates in regulating critical cardiometabolic disease risk factors including proprotein convertase subtilisin/kexin type 9 (PCSK9). Endoplasmic reticulum (ER) remodeling through release and incorporation of trafficking vesicles mediates protein secretion and degradation. We hypothesized that ER remodeling that drives mitochondrial fission participates in cardiometabolic proteostasis.
We used in vitro and in vivo hepatocyte inhibition of a protein involved in mitochondrial fission, dynamin-related protein 1 (DRP1). Here, we show that DRP1 promotes remodeling of select ER microdomains by tethering vesicles at ER. A DRP1 inhibitor, mitochondrial division inhibitor 1 (mdivi-1) reduced ER localization of a DRP1 receptor, mitochondrial fission factor, suppressing ER remodeling-driven mitochondrial fission, autophagy, and increased mitochondrial calcium buffering and PCSK9 proteasomal degradation. DRP1 inhibition by CRISPR/Cas9 deletion or mdivi-1 alone or in combination with statin incubation in human hepatocytes and hepatocyte-specific Drp1-deficiency in mice reduced PCSK9 secretion (-78.5%). In HepG2 cells, mdivi-1 increased low-density lipoprotein receptor via c-Jun transcription and reduced PCSK9 mRNA levels via suppressed sterol regulatory binding protein-1c. Additionally, mdivi-1 reduced macrophage burden, oxidative stress, and advanced calcified atherosclerotic plaque in aortic roots of diabetic Apoe-deficient mice and inflammatory cytokine production in human macrophages.
We propose a novel tethering function of DRP1 beyond its established fission function, with DRP1-mediated ER remodeling likely contributing to ER constriction of mitochondria that drives mitochondrial fission. We report that DRP1-driven remodeling of select ER micro-domains may critically regulate hepatic proteostasis and identify mdivi-1 as a novel small molecule PCSK9 inhibitor.
蛋白质稳态维持蛋白质的内环境稳定，并参与调节包括前蛋白转化酶枯草溶菌素/柯萨奇蛋白酶 9（PCSK9）在内的关键代谢性心血管疾病风险因素。内质网（ER）通过释放和纳入转运小泡进行重塑，从而介导蛋白质的分泌和降解。我们假设，驱动线粒体裂变的 ER 重塑参与了代谢性心血管蛋白质稳态。
我们使用体外和体内肝细胞抑制一种参与线粒体裂变的蛋白质，即动力相关蛋白 1（DRP1）。在这里，我们表明 DRP1 通过将囊泡锚定在 ER 上，促进了特定 ER 微区的重塑。DRP1 抑制剂，线粒体分裂抑制剂 1（mdivi-1）减少了 ER 定位的 DRP1 受体，即线粒体裂变因子，从而抑制了 ER 重塑驱动的线粒体裂变、自噬，并增加了线粒体钙缓冲和 PCSK9 的蛋白酶体降解。人类肝细胞中 CRISPR/Cas9 缺失或 mdivi-1 单独或与他汀类药物孵育联合使用，以及小鼠肝细胞特异性 Drp1 缺陷，均可减少 PCSK9 的分泌（减少 78.5%）。在 HepG2 细胞中，mdivi-1 通过 c-Jun 转录增加了低密度脂蛋白受体，并通过抑制固醇调节结合蛋白-1c 降低了 PCSK9 mRNA 水平。此外，mdivi-1 减少了糖尿病 Apoe 缺陷小鼠主动脉根部的巨噬细胞负担、氧化应激和进展性钙化动脉粥样硬化斑块以及人巨噬细胞中炎症细胞因子的产生。
我们提出了 DRP1 的一种新的连接功能，超越了其已建立的裂变功能，DRP1 介导的 ER 重塑可能有助于驱动线粒体裂变的 ER 对线粒体的收缩。我们报告称，DRP1 驱动的特定 ER 微区的重塑可能对肝脏蛋白质稳态的调节至关重要，并确定 mdivi-1 是一种新的小分子 PCSK9 抑制剂。
