UBC Theses and Dissertations
SHIP deficiency is associated with the Crohn’s disease susceptibility variant in ATG16L1 and leads to increased interleukin-1beta transcription and intestinal autoinflammation Ngoh, Eyler Ndumeya
Crohn`s disease (CD) is a polygenic immune-mediated disease of the gastrointestinal tract characterized by chronic inflammation. The SH2-domain-containing inositol polyphosphate 5΄phosphatase (SHIP) is a hematopoietic-specific negative regulator of inflammatory cytokine production and plays an important role in regulating immune homeostasis. Using the SHIP deficient mouse model of intestinal inflammation, we found that IL-1β is increased in SHIP-/- mouse macrophages due to increased class I PI3K p110α activity. Macrophage depletion or treatment with an IL-1 receptor antagonist reduced development of intestinal inflammation in SHIP-/- mice. To interrogate if SHIP is dysregulated in people with ileal CD, we demonstrate that subjects with ileal CD have reduced SHIP mRNA expression and enzymatic activity at sites of inflammation and in PBMCs, compared to control subjects. A single nucleotide polymorphism (SNP) in the gene encoding ATG16L1 (T300A) causes an autophagy defect and is associated with increased IL-1β production and susceptibility to CD. In all tissues from our patient cohort and in PBMCs from a second healthy control cohort, subjects, who were homozygous for the CD-associated ATG16L1 T300A encoding gene variant, had reduced SHIP mRNA expression and enzymatic activity, which correlated with increased IL-1β production. In addition, starvation-induced autophagy increased SHIP protein levels, which were reduced in the presence of the ATG16L1 CD-associated risk allele. Examining the effects of additional autophagy and CD-related gene variants, which may affect SHIP mRNA expression and enzymatic activity, on IL-1β production in PBMCs from a cohort of healthy control subjects, we found that the NOD2 rs2066844 and the XBP-1 rs35873774 gene variants were associated with increased IL-1β production in response to specific PAMPs. Collectively, these data identify SHIP up-regulation as a novel mechanism by which autophagy regulates IL-1β production and intestinal autoinflammation. Our findings also identify a subgroup of CD patients that could be amenable to treatment with therapy that targets IL-1β.
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