ETP-Specific Knockout Mice Reveal Endotrophin as a Key Regulator of Kidney Fibrosis in Ischemia-Reperfusion Injury Models

Endotrophin (ETP), a cleavage product of the C5 domain of collagen VI 3 (COL6A3), plays a crucial role in extracellular matrix remodeling. Previously established Col6a3 knockout (KO) mouse models primarily reflect the consequences of COL6A3 loss rather than the specific effects of ETP depletion, making it challenging to directly assess ETPs function. These models either disrupt COL6A3 along with ETP production or express functionally defective COL6A3 while maintaining ETP production. To address this limitation, we developed and validated a novel ETP knockout (ETPKO) mouse model that selectively ablates ETP while preserving Col6a3 expression. To generate the ETPKO model, we introduced lox2272 sites and a fluorescent mCherry-CAAX reporter into the Col6a3 locus, ensuring that ETP expression is turned off and reporter expression is turned on upon Cre-mediated recombination. Crossing the Col6a3-Etp+mCherry-CAAX mouse line with CMV-Cre mice yielded ETPKO mice, in which successful ETP deletion was confirmed by genomic DNA sequencing and mCherry expression. Using this model, we investigated ETPs role in kidney fibrosis. ETPKO mice subjected to unilateral or bilateral renal ischemia-reperfusion injury (IRI) exhibited complete Etp mRNA ablation with only a partial reduction in Col6a3 mRNA. Notably, ETP depletion significantly attenuated fibrosis progression, demonstrating its critical role in the pathogenesis of kidney fibrosis. The ETPKO mouse model provides a targeted and specific approach for studying ETP function independently of Col6a3 expression. These findings establish ETP as a key driver of fibrosis and position ETPKO mice as a valuable tool for elucidating ETP-mediated mechanisms in preclinical disease models.