Fig. 11

A model to explain how Def haploinsufficiency activates the p53-dependent inflammation-mediated TGFβ signalling and causes fibrotic scar formation in def^+/- after PH.

(A) Western blot of HMGB1 in the adult liver from wild-type, def^+/-, def^+/-Tg(fabp10:def)^+/- and def^+/-p53^M214K/M214K fish. Loading control: Bhmt. (B) Immunostaining of ColI and Bhmt in the wound epidermis in wild-type, def^+/- and def^+/-fish treated with 100 μM of glycyrrhizic acid ammonium 5 days after PH. lv, liver; we, wound epidermis. (C) In a wild-type liver, Def complexes with Capn3 to mediate p53 degradation in the nucleoli to mitigate the inflammatory response after acute injury. In def^+/- fish, the activity of the Def-Capn3 protein degradation pathway is compromised and p53 protein is thus stabilised, which in turn activates the p53 pathway. Constant activation of the p53 pathway up-regulates the expression of the pro-inflammatory factor HMGB1 that up-regulates the expression of cytokines (e.g., TNFα, IL-1β, IL-6 and IL-8) and other signalling pathways that lead to a prolonged inflammatory response in def^+/-. The prolonged inflammatory response activates TGFβ signalling and causes the over-production of fibrotic molecules (e.g., collagens, elastin and fibronectin) in the wound epidermis that finally forms a fibrotic scar at the amputation site in def^+/-. Fibrotic scar formation in def^+/- can be blocked by over-expressing Def specifically in the hepatocytes, by the loss of function of p53, and by treatment with Dex (anti-inflammatory drug), SB431542 (inhibitor of TGFβ signalling) or glycyrrhizic acid ammonium (inhibitor of HMGB1 function).