Intestinal steroidogenesis controls PPAR expression in the colon and is impaired during ulcerative colitis
Background and aims Immune tolerance breakdown during UC involves the peroxisome proliferator-activated receptor- (PPAR), a key factor in mucosal homoeostasis and the therapeutic target of 5-aminosalycilates, which expression is impaired during UC. Here we assess the impact of glucocorticoids (GCs) on PPAR expression, focusing especially on extra-adrenal cortisol production by colonic epithelial cells (CECs). Methods Activation of PPAR in the colon was evaluated using transgenic mice for the luciferase gene under PPAR control (peroxisome proliferator response element-luciferase mice). Protein and mRNA expression of PPAR were evaluated with colon fragments and purified CEC from mice. Cortisol production and steroidogenic factor expression were quantified in human CEC of patients with UC and those of controls. Gene expression knockdown by short hairpin RNA in Caco-2 cells was used for functional studies. Results GCs were able to raise luciferase activity in peroxisome proliferator response element-luciferase mice. In the mice colons and Caco-2 cells, PPAR expression was increased either with GCs or with an inducer of steroidogenesis and then decreased after treatment with a steroidogenesis inhibitor. Cortisol production and steroidogenic factor expression, such as liver receptor homologue-1 (LRH-1), were decreased in CEC isolated from patients with UC, directly correlating with PPAR impairment. Experiments on Caco-2 cells lacking LRH-1 expression confirmed that LRH-1 controls PPAR expression by regulating GC synthesis in CEC. Conclusions These results demonstrate cortisol control of PPAR expression in CEC, highlighting cortisol production deficiency in colonocytes as a key molecular event in the pathophysiology of UC.