Department of Orthopaedic Surgery, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA.
Institute of Orthopaedics and Traumatology, the First Affiliated Hospital of Zhejiang Chinese Medical University, Hangzhou, China.
JCI Insight. 2019 Sep 19;4(18):128568. doi: 10.1172/jci.insight.128568.
Recently we demonstrated that ablation of the DNA methyltransferase enzyme, Dnmt3b, resulted in catabolism and progression of osteoarthritis (OA) in murine articular cartilage through a mechanism involving increased mitochondrial respiration. In this study, we identify 4-aminobutyrate aminotransferase (Abat) as a downstream target of Dnmt3b. Abat is an enzyme that metabolizes γ-aminobutyric acid to succinate, a key intermediate in the tricarboxylic acid cycle. We show that Dnmt3b binds to the Abat promoter, increases methylation of a conserved CpG sequence just upstream of the transcriptional start site, and inhibits Abat expression. Dnmt3b deletion in articular chondrocytes results in reduced methylation of the CpG sequence in the Abat promoter, which subsequently increases expression of Abat. Increased Abat expression in chondrocytes leads to enhanced mitochondrial respiration and elevated expression of catabolic genes. Overexpression of Abat in murine knee joints via lentiviral injection results in accelerated cartilage degradation following surgical induction of OA. In contrast, lentiviral-based knockdown of Abat attenuates the expression of IL-1β-induced catabolic genes in primary murine articular chondrocytes in vitro and also protects against murine articular cartilage degradation in vivo. Strikingly, treatment with the FDA-approved small-molecule Abat inhibitor, vigabatrin, significantly prevents the development of injury-induced OA in mice. In summary, these studies establish Abat as an important new target for therapies to prevent OA.
最近，我们证明通过一种涉及增加线粒体呼吸的机制，DNA 甲基转移酶酶 Dnmt3b 的消融导致了鼠类关节软骨中骨关节炎（OA）的分解代谢和进展。在这项研究中，我们确定 4-氨基丁酸转氨酶（Abat）是 Dnmt3b 的下游靶标。Abat 是一种将 γ-氨基丁酸代谢为琥珀酸的酶，琥珀酸是三羧酸循环中的关键中间产物。我们表明，Dnmt3b 结合到 Abat 启动子上，增加了转录起始位点上游的一个保守 CpG 序列的甲基化，并抑制了 Abat 的表达。关节软骨细胞中的 Dnmt3b 缺失导致 Abat 启动子中的 CpG 序列甲基化减少，从而导致 Abat 的表达增加。软骨细胞中 Abat 的表达增加导致线粒体呼吸增强和分解代谢基因的表达升高。通过慢病毒注射在鼠膝关节中过表达 Abat 会导致 OA 手术后软骨降解加速。相比之下，通过慢病毒的 Abat 敲低可在体外减弱 IL-1β诱导的原发性鼠类关节软骨细胞中分解代谢基因的表达，并在体内防止鼠类关节软骨降解。引人注目的是，FDA 批准的小分子 Abat 抑制剂 vigabatrin 的治疗显著预防了小鼠损伤诱导的 OA 的发展。总之，这些研究确立了 Abat 作为预防 OA 的治疗的一个重要新靶点。
