Center for Molecular and Translational Medicine, Georgia State University, Atlanta, Georgia.
Center for Molecular and Translational Medicine, Georgia State University, Atlanta, Georgia; Division of Vascular Surgery, The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China.
Cell Mol Gastroenterol Hepatol. 2022;14(2):375-403. doi: 10.1016/j.jcmgh.2022.05.006. Epub 2022 May 25.
BACKGROUND & AIMS: The expression and role of methyltransferase SET and MYND domain-containing protein 5 (SMYD5) in inflammatory bowel disease (IBD) is completely unknown. Here, we investigated the role and underlying mechanism of epithelial SMYD5 in IBD pathogenesis and progression.
The expression levels of SMYD5 and the mitochondrial transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) were examined by Western blot, immunofluorescence staining, and immunohistochemistry in intestinal epithelial cells (IECs) and in colon tissues from human IBD patients and colitic mice. Mice with Smyd5 conditional knockout in IECs and littermate controls were subjected to dextran sulfate sodium-induced colitis and the disease severity was assessed. SMYD5-regulated mitochondrial biogenesis was examined by quantitative reverse-transcription polymerase chain reaction and transmission electron microscopy, and the mitochondrial oxygen consumption rate was measured in a Seahorse Analyzer system (Agilent, Santa Clara, CA). SMYD5 and PGC-1α interaction was determined by co-immunoprecipitation assay. PGC-1α degradation and turnover (half-life) were analyzed by cycloheximide chase assay. SMYD5-mediated PGC-1α methylation was assessed via in vitro methylation assay followed by mass spectrometry for identification of methylated lysine residues.
Up-regulated SMYD5 and down-regulated PGC-1α were observed in intestinal epithelia from IBD patients and colitic mice. Smyd5 depletion in IECs protected mice from dextran sulfate sodium-induced colitis. SMYD5 was critically involved in regulating mitochondrial biology such as mitochondrial biogenesis, respiration, and apoptosis. Mechanistically, SMYD5 regulates mitochondrial functions in a PGC-1α-dependent manner. Furthermore, SMYD5 mediates lysine methylation of PGC-1α and subsequently facilitates its ubiquitination and degradation.
SMYD5 attenuates mitochondrial functions in IECs and promotes IBD progression by enhancing PGC-1α degradation in a methylation-dependent manner. Strategies to decrease SMYD5 expression and/or increase PGC-1α expression in IECs might be a promising therapeutic approach to treat IBD patients.
甲基转移酶 SET 和 MYND 结构域蛋白 5（SMYD5）在炎症性肠病（IBD）中的表达和作用尚不清楚。在这里，我们研究了上皮细胞 SMYD5 在 IBD 发病机制和进展中的作用和潜在机制。
通过 Western blot、免疫荧光染色和免疫组织化学染色检测肠上皮细胞（IEC）和人类 IBD 患者和结肠炎小鼠结肠组织中 SMYD5 和过氧化物酶体增殖物激活受体γ共激活因子 1α（PGC-1α）的表达水平。用葡聚糖硫酸钠诱导 SMYD5 条件性敲除的 IEC 小鼠及其同窝对照小鼠建立结肠炎模型，并评估疾病严重程度。通过定量逆转录聚合酶链反应和透射电子显微镜检测 SMYD5 调节的线粒体生物发生，并通过安捷伦 Seahorse 分析仪系统（加利福尼亚州圣克拉拉）测量线粒体耗氧量。通过免疫共沉淀测定 SMYD5 和 PGC-1α 的相互作用。通过环己酰亚胺追踪实验分析 PGC-1α 的降解和周转率（半衰期）。通过体外甲基化实验评估 SMYD5 介导的 PGC-1α 甲基化，然后通过质谱鉴定甲基化赖氨酸残基。
在 IBD 患者和结肠炎小鼠的肠道上皮中观察到上调的 SMYD5 和下调的 PGC-1α。IEC 中 Smyd5 的缺失可保护小鼠免受葡聚糖硫酸钠诱导的结肠炎。SMYD5 对于调节线粒体生物学（如线粒体生物发生、呼吸和凋亡）至关重要。从机制上讲，SMYD5 以 PGC-1α 依赖的方式调节线粒体功能。此外，SMYD5 介导 PGC-1α 的赖氨酸甲基化，随后促进其泛素化和降解。
SMYD5 通过依赖甲基化的方式增强 PGC-1α 的降解，从而减弱 IEC 中的线粒体功能并促进 IBD 的进展。降低 IEC 中 SMYD5 表达和/或增加 PGC-1α 表达的策略可能是治疗 IBD 患者的一种有前途的治疗方法。
