OP02 The role of PTPN2 SNP in the pathogenesis of fibrosis in Crohn’s disease
C. Li*1, J. Kuemmerle1
1Virginia Commonwealth University, Internal Medicine, Richmond, VA, USA
We identified altered IL-6-induced Jak1-dependent STAT3 phosphorylation in human ileal subepithelial myofibroblasts (SEMF) of patients with stricturing Crohn’s disease. This resulted in co-localisation of pSTAT3(Y705) to Rab5+ signalling endosomes along with pIGF-I receptors that jointly mediated excess collagen I production and proliferation in SEMF of strictures. PTPN2 gene variants occur in patients with Crohn’s disease with rs7234029 associated with apparent ‘loss-of-function’ and with stricturing disease. In other cells, PTPN2 targets Jak and STAT3. However, whether expression of rs7234029 in fibrostenotic Crohn’s disease is associated with altered phosphatase activity, increased STAT3 phosphorylation, and excess extracellular matrix deposition has not been studied yet.
Primary cultures of SEMF isolated from ileum of patients with Montreal B2 Crohn’s disease were naïve, transfected with wtPTPN2, or were used for CRISPR/Cas9-mediated PTPN2 gene deletion. Rs7234029 haplotype was determined in each subject by genotyping assay.
Increased basal pSTAT3, pErk1/2, collagen I production and proliferation in SEMF of strictured ileum were normalised by inhibition of STAT3 phosphorylation or expression of dominant negative STAT3 (Y705F). Despite a 3-fold increase in PTPN2 protein in strictured SEMF in these cells, levels of STAT3 phosphorylation were also increased suggesting a loss-of-phosphatase function had occurred. Phosphatase function was restored by expression of wtPTPN2 and resulted in lowered levels of pSTAT3 (Y705). This notion regarding PTPN2 was also confirmed in normal SEMF where CRISP/Cas9 mediated PTPN2 gene deletion resulted in a 4-fold increase in pSTAT3 (Y705) levels. The haplotype rs7234029 was significantly detected in Montreal B2 Crohn’s disease compared with other phenotypes.
A loss of PTPN2 function associated with rs7234029 in SEMF of patients with fibrostenotic Crohn’s disease leads to increased phosphorylation of pSTAT3 (Y705), and results in the excess collagen I production and proliferation that occur in these patients’ strictures.