Department of Geriatrics, Shenzhen People's Hospital (The Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Guangdong, China.
Guangdong Provincial Clinical Research Center for Geriatrics, Shenzhen Clinical Research Center for Geriatrics, Shenzhen People's Hospital (The Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Guangdong, China.
Elife. 2024 Nov 4;13:RP98524. doi: 10.7554/eLife.98524.
TGF-β stimulates CCN2 expression which in turn amplifies TGF-β signaling. This process promotes extracellular matrix production and accelerates the pathological progression of fibrotic diseases. Alternative splicing plays an important role in multiple disease development, while U2 small nuclear RNA auxiliary factor 2 (U2AF2) is an essential factor in the early steps of pre-mRNA splicing. However, the molecular mechanism underlying abnormal expression upon TGF-β stimulation remains unclear. This study elucidates that SIRT4 acts as a master regulator for CCN2 expression in response to TGF-β by modulating U2AF2-mediated alternative splicing. Analyses of renal biopsy specimens from patients with CKD and mouse fibrotic kidney tissues revealed marked nuclear accumulation of SIRT4. The tubulointerstitial fibrosis was alleviated by global deletion or tubular epithelial cell (TEC)-specific knockout of , and aggravated by adeno-associated virus-mediated SIRT4 overexpression in TECs. Furthermore, SIRT4 was found to translocate from the mitochondria to the cytoplasm through the BAX/BAK pore under TGF-β stimulation. In the cytoplasm, TGF-β activated the ERK pathway and induced the phosphorylation of SIRT4 at Ser36, which further promoted its interaction with importin α1 and subsequent nuclear translocation. In the nucleus, SIRT4 was found to deacetylate U2AF2 at K413, facilitating the splicing of CCN2 pre-mRNA to promote CCN2 protein expression. Importantly, exosomes containing anti-SIRT4 antibodies were found to effectively mitigate the UUO-induced kidney fibrosis in mice. Collectively, these findings indicated that SIRT4 plays a role in kidney fibrosis by regulating CCN2 expression via the pre-mRNA splicing.
TGF-β 刺激 CCN2 的表达，进而放大 TGF-β 信号。这个过程促进细胞外基质的产生，并加速纤维化疾病的病理进展。可变剪接在多种疾病的发展中起着重要作用，而 U2 小核 RNA 辅助因子 2（U2AF2）是前体 mRNA 剪接早期步骤中的一个必需因子。然而，TGF-β 刺激后异常表达的分子机制尚不清楚。本研究阐明 SIRT4 通过调节 U2AF2 介导的可变剪接，作为 TGF-β 刺激下 CCN2 表达的主要调节因子。对 CKD 患者的肾活检标本和小鼠纤维化肾组织的分析显示 SIRT4 有明显的核积累。通过全局缺失或肾小管上皮细胞（TEC）特异性敲除，以及在 TEC 中通过腺相关病毒介导的 SIRT4 过表达加重了 tubulointerstitial 纤维化。此外，研究发现 SIRT4 在 TGF-β 刺激下通过 BAX/BAK 孔从线粒体易位到细胞质。在细胞质中，TGF-β 激活 ERK 通路，并诱导 SIRT4 在 Ser36 处磷酸化，这进一步促进了其与 importin α1 的相互作用，并随后进行核易位。在核内，SIRT4 被发现去乙酰化 U2AF2 在 K413 处，促进 CCN2 前体 mRNA 的剪接，从而促进 CCN2 蛋白表达。重要的是，含有抗 SIRT4 抗体的外泌体被发现可有效减轻 UUO 诱导的小鼠肾脏纤维化。总之，这些发现表明 SIRT4 通过调节前体 mRNA 剪接来调节 CCN2 表达，从而在肾脏纤维化中发挥作用。
