The Oxysterol Synthesising Enzyme CH25H Contributes to the Development of Intestinal Fibrosis.

Intestinal fibrosis and stenosis are common complications of Crohn's disease [CD], frequently requiring surgery. Anti-inflammatory strategies can only partially prevent fibrosis; hence, anti-fibrotic therapies remain an unmet clinical need. Oxysterols are oxidised cholesterol derivatives with important roles in various biological processes. The enzyme cholesterol 25-hydroxylase [CH25H] converts cholesterol to 25-hydroxycholesterol [25-HC], which modulates immune responses and oxidative stress. In human intestinal samples from CD patients, we found a strong correlation of CH25H mRNA expression with the expression of fibrosis markers. We demonstrate reduced intestinal fibrosis in mice deficient for the CH25H enzyme, using the sodium dextran sulphate [DSS]-induced chronic colitis model. Additionally, using a heterotopic transplantation model of intestinal fibrosis, we demonstrate reduced collagen deposition and lower concentrations of hydroxyproline in CH25H knockouts. In the heterotopic transplant model, CH25H was expressed in fibroblasts. Taken together, our findings indicate an involvement of oxysterol synthesis in the pathogenesis of intestinal fibrosis.

Oxysterols regulate encephalitogenic CD4(+) T cell trafficking during central nervous system autoimmunity.

Perturbation of steroids pathways is linked to inflammation and chronic diseases, however the underlying mechanism remains unclear. Oxysterols, oxidized forms of cholesterol, are not only essential for bile synthesis and sterol transportation but have recently been shown to contribute to the immune response. In addition, serum oxysterols levels have been proposed as suitable candidate biomarkers for neurological diseases such as multiple sclerosis (MS). However how oxysterols modulate adaptive immunity is unknown and their functions in autoimmunity have not been investigated. The enzyme cholesterol 25 hydroxylase (Ch25h) is the rate limiting step to synthesize the oxysterol 7α,25-dihydroxycholesterol (7α,25-OHC) from cholesterol. We here report, using the MS murine model experimental autoimmune encephalomyelitis (EAE), that Ch25h deletion significantly attenuated EAE disease course by limiting trafficking of pathogenic CD4(+) T lymphocytes to the central nervous system (CNS). Mechanistically, we show a critical involvement for oxysterols in recruiting leukocytes into inflamed tissues and propose that 7α,25-OHC preferentially promotes the migration of activated CD44(+)CD4(+) T cells by binding the G protein-coupled receptor called Epstein-Barr virus induced gene 2 (EBI2). Collectively, our results support a pro-inflammatory role for oxysterols during EAE and identify oxysterols as a potential therapeutic target to treat autoimmune diseases.

Identification and characterization of a second melanin-concentrating hormone receptor, MCH-2R.

Melanin-concentrating hormone (MCH) is a 19-aa cyclic neuropeptide originally isolated from chum salmon pituitaries. Besides its effects on the aggregation of melanophores in fish several lines of evidence suggest that in mammals MCH functions as a regulator of energy homeostasis. Recently, several groups reported the identification of an orphan G protein-coupled receptor as a receptor for MCH (MCH-1R). We hereby report the identification of a second human MCH receptor termed MCH-2R, which shares about 38% amino acid identity with MCH-1R. MCH-2R displayed high-affinity MCH binding, resulting in inositol phosphate turnover and release of intracellular calcium in mammalian cells. In contrast to MCH-1R, MCH-2R signaling is not sensitive to pertussis toxin and MCH-2R cannot reduce forskolin-stimulated cAMP production, suggesting an exclusive G(alpha)q coupling of the MCH-2R in cell-based systems. Northern blot and in situ hybridization analysis of human and monkey tissue shows that expression of MCH-2R mRNA is restricted to several regions of the brain, including the arcuate nucleus and the ventral medial hypothalamus, areas implicated in regulation of body weight. In addition, the human MCH-2R gene was mapped to the long arm of chromosome 6 at band 6q16.2-16.3, a region reported to be associated with cytogenetic abnormalities of obese patients. The characterization of a second mammalian G protein-coupled receptor for MCH potentially indicates that the control of energy homeostasis in mammals by the MCH neuropeptide system may be more complex than initially anticipated.