Chop deficiency prevents UUO-induced renal fibrosis by attenuating fibrotic signals originated from Hmgb1/TLR4/NFκB/IL-1β signaling

Renal fibrosis, particularly tubulointerstitial fibrosis is considered to be the final manifestation of almost all chronic kidney diseases (CKDs). Herein we demonstrated evidence that CHOP-related ER stress is associated with the development of renal fibrosis in both CKD patients and unilateral ureteral obstruction (UUO)-induced animals, and specifically, mice deficient in Chop were protected from UUO-induced renal fibrosis. Mechanistic studies revealed that loss of Chop protected tubular cells from UUO-induced apoptosis and secondary necrosis along with attenuated Hmgb1 passive release and active secretion. As a result, Chop deficiency suppressed Hmgb1/TLR4/NF kappa B signaling, which then repressed UUO-induced IL-1 beta production. Consequently, the IL-1 beta downstream Erk1/2 activity and its related c-Jun transcriptional activity were reduced, leading to attenuated production of TGF-beta 1 following UUO insult. It was further noted that reduced IL-1 beta production also inhibited UUO-induced PI3K/AKT signaling, and both of which ultimately protected mice from UUO-induced renal fibrosis. Together, our data support that suppression of CHOP expression could be a viable therapeutic strategy to prevent renal fibrosis in patients with CKDs.