Cellular Biochemistry Lab., Graduate School of Pharmaceutical Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601, Japan.
Sci Rep. 2018 May 9;8(1):7306. doi: 10.1038/s41598-018-25674-4.
Chronic kidney disease is characterized by prolonged decline in renal function, excessive accumulation of ECM, and progressive tissue fibrosis. Transglutaminase (TG) is a crosslinking enzyme that catalyzes the formation of covalent bonds between glutamine and lysine residues, and is involved in the induction of renal fibrosis via the stabilization of ECM and the activation of TGF-β1. Despite the accumulating evidences indicating that TG2 is a key enzyme in fibrosis, genetic knockout of TG2 reduced by only 50% the elevated protein crosslinking and fibrous protein in renal fibrosis model, whereas treatment with TG inhibitor almost completely reduced these levels. Here, we also clarified the distributions of TG isozymes and their in situ activities and identified the isozyme-specific crosslinked substrates for both TG1 and TG2 in fibrotic kidney. We found that TG1 activity was markedly enhanced in renal tubular epithelium and interstitial areas, whereas TG2 activity increased only in the extracellular space. In total, 47 and 67 possible candidates were identified as TG1 and TG2 substrates, respectively, only in fibrotic kidney. Among them, several possible substrates related to renal disease and fibrosis were identified. These findings provide novel insights into the mechanisms of renal fibrosis through the targeting of isozyme-specific TG substrates.
慢性肾脏病的特征是肾功能的长期下降，细胞外基质（ECM）的过度积累以及组织的进行性纤维化。转谷氨酰胺酶（TG）是一种交联酶，可催化谷氨酰胺和赖氨酸残基之间的共价键形成，并通过 ECM 的稳定和 TGF-β1 的激活参与诱导肾纤维化。尽管越来越多的证据表明 TG2 是纤维化的关键酶，但 TG2 的基因敲除仅使肾纤维化模型中升高的蛋白质交联和纤维蛋白减少了 50％，而 TG 抑制剂的治疗几乎完全降低了这些水平。在这里，我们还阐明了 TG 同工酶的分布及其原位活性，并鉴定了纤维化肾脏中 TG1 和 TG2 的同工酶特异性交联底物。我们发现，TG1 活性在肾小管上皮细胞和间质区域中明显增强，而 TG2 活性仅在细胞外空间中增加。总的来说，仅在纤维化的肾脏中，分别鉴定出 47 个和 67 个可能的 TG1 和 TG2 底物。其中，鉴定出了几种与肾脏疾病和纤维化有关的可能的底物。这些发现为通过靶向同工酶特异性 TG 底物来了解肾脏纤维化的机制提供了新的见解。
