Repairing of isoaspartyl residues by PCMT1 alleviates renal fibrosis through the repression of TGF-β1/TGFBR2/Smad signaling pathway

Protein L-isoaspartyl/D-aspartyl Methyltransferase (PCMT1) plays a pivotal role in repairing a spontaneous post-translational modification (PTM) of L-isoaspartyl residues resulted from asparagine deamidation or aspartate isomerization. This PTM is particularly important for extracellular matrix (ECM) proteins because their low turnover rate and are susceptible to factors that could accelerate such modification. Therefore, it becomes imperative to comprehensively investigate the impact of PCMT1 on ECM homeostasis and its associated pathological alterations. In this study, we revealed that secreted PCMT1 repairs the isoaspartyl residues of the TGFBR2 protein on the cell membrane to suppress TGF-β1/Smad pathway. Through this novel PTM regulation, PCMT1 played essential roles in combating renal fibrosis, as lack of PCMT1 worsened tubular injury, collagen deposition, myofibroblast activation, and macrophage infiltration in total kidney and tubular contexts in a mouse model of chronic kidney disease. Moreover, PCMT1 level decreased in fibrotic kidney tissues and inversely related to kidney function in mice and in humans. Our study highlights the important function of PCMT1 in modifying proteins in the extracellular space and identified a novel role of PCMT1 in regulating TGF-β1 pathway in renal fibrosis. This study holds the potential of innovative therapeutic avenue for the mitigation of renal fibrosis. To further elucidate the comprehensive transcriptome-wide transcriptional alterations resulting from PCMT1 deficiency, we conducted whole transcriptome sequencing in HK-2 WT and PCMT1-KO cells. Moreover, RNA sequencing was also carried out on kidney tissues from WT and Pcmt1-/- mice to achieve the same objective. We also conducted RNA sequencing on the kidney tissues from Pcmt1 fl/fl and Pcmt1 tKO mice after modeling of unilateral ureteral obstruction (UUO).