C1orf21 DRIVES TRANSCRIPTIONAL REPROGRAMMING FOR TUBULAR REPAIR AFTER ACUTE KIDNEY INJURY

Chronic kidney disease (CKD) often develops after acute kidney injury (AKI) due to incomplete repair, yet effective therapies remain limited. Most studies have addressed maladaptive repair, whereas the mechanisms that initiate transcriptional reprogramming of repair after AKI remain poorly understood. We have demonstrated that mitochondrial Moxi deficiency accelerates tubular regeneration after AKI, providing a resource to identify regenerative factors. Given evidence that lysine lactylation (KLa) was implicated in repair gene transcription in tumor associated macrophages, we aimed to identify KLa(s) that initiate transcriptional reprogramming of repair genes after AKI and define their mechanisms. 

High-throughput mass spectrometry and bioinformatics were used to screen KLa in Moxi-deficient vs. wild-type kidneys after folic acid nephropathy. Functional validation employed wild-type and mutant mice, tubular C1orf21 knockout mice, and a lead KLa/C1orf21-enhancing compound in AKI–CKD models. Renal repair was assessed by histology and biochemical markers. Mechanistic studies included cell assays, CUT&Tag, EMSA, ChIP-qPCR, promoter activity, molecular simulation, and HDX-MS.

Deletion of Moxi accelerated recovery after FA-induced AKI, prompting identification of lactylated proteins involved in regeneration. Proteomic analysis highlighted Trap1K128 lactylation (Trap1KLa) as a candidate driver. In tubular epithelial cells, mimicking Trap1K128 lactylation enhanced proliferation, whereas blocking it suppressed proliferation. Transcriptome profiling confirmed that Trap1KLa activates cell cycle and DNA repair programs. A specific antibody showed that Trap1KLa rises early after injury, persists in Moxi KO kidneys with enhanced regeneration, and localizes to multiple subcellular compartments. In both mouse AKI and human CKD after AKI, proliferating tubular cells with high Trap1KLa expression correlated with better renal function.

Functionally, Trap1K128T mice (constitutive lactylation) exhibited accelerated repair, reduced tubular injury, lower DNA damage, higher proliferation, and attenuated fibrosis, while Trap1K128R mice (loss of lactylation) showed impaired repair and progressive fibrosis. Similar results in IRI and UUO confirmed a general role for Trap1KLa in tubular repair. Mechanistically, nuclear Trap1KLa bound an enhancer of C1orf21 (encoding the conserved micropeptide Cf21) and activated its transcription. Cf21 was essential for regeneration: overexpression promoted proliferation and preserved epithelial identity in vitro, while tubular deletion impaired repair and sustained DNA damage in vivo. CUT&Tag, EMSA, and promoter assays demonstrated that Cf21 functions as a transcription factor reprogramming repair-related gene transcription.

Trap1KLa is written by KAT7 and erased by SIRT5. Screening identified ET29, a small molecule binding an allosteric Trap1 pocket, which increased Trap1KLa, induced Cf21, and enhanced tubular regeneration. ET29 treatment improved renal function and reduced fibrosis and inflammation in FA and UUO models. Hydrogen–deuterium exchange mass spectrometry indicated that ET29 interacts with residues near Trap1’s putative allosteric site and/or induces conformational changes.

These findings establish Trap1KLa–Cf21 as a transcriptional axis that drives tubular repair after injury and highlight pharmacologic lactylation enhancement as a therapeutic strategy to prevent AKI-to-CKD progression.