MTMR3 risk allele enhances innate receptor-induced signaling and cytokines by decreasing autophagy and increasing caspase-1 activation

Abstract

Inflammatory bowel disease (IBD) is characterized by dysregulated host:microbial interactions and cytokine production. Host pattern recognition receptors (PRRs) are critical in regulating these interactions. Multiple genetic loci are associated with IBD, but altered functions for most, including in the rs713875 MTMR3/HORMAD2/LIF/OSM region, are unknown. We identified a previously undefined role for myotubularinrelated protein 3 (MTMR3) in amplifying PRR-induced cytokine secretion in human macrophages and defined MTMR3-initiated mechanisms contributing to this amplification. MTMR3 decreased PRR-induced phosphatidylinositol 3-phosphate (PtdIns3P) and autophagy levels, thereby increasing PRR-induced caspase-1 activation, autocrine IL-1β secretion, NFκB signaling, and, ultimately, overall cytokine secretion. This MTMR3-mediated regulation required the N-terminal pleckstrin homology-GRAM domain and Cys413 within the phosphatase domain of MTMR3. In MTMR3-deficient macrophages, reducing the enhanced autophagy or restoring NFκB signaling rescued PRRinduced cytokines. Macrophages from rs713875 CC IBD risk carriers demonstrated increased MTMR3 expression and, in turn, decreased PRR-induced PtdIns3P and autophagy and increased PRR-induced caspase-1 activation, signaling, and cytokine secretion. Thus, the rs713875 IBD risk polymorphism increases MTMR3 expression, which modulates PRR-induced outcomes, ultimately leading to enhanced PRR-induced cytokines.Crohn's disease | ulcerative colitis | NOD2 | genetics | Toll-like receptors I nflammatory bowel disease (IBD) is characterized by dysregulated intestinal immune homeostasis and cytokine production (1). Given the key role for host-microbe interactions in the intestine, proper regulation of pattern recognition receptor (PRR) signaling and cytokine secretion is critical. Although a number of loci have now been associated with IBD (2), altered functions for the majority of these loci are unknown. Defining these functions is essential to our understanding of IBD pathophysiology and to our ability to ultimately target these implicated pathways.Polymorphisms in the MTMR3/HORMAD2/LIF/OSM region on chromosome 22 are associated with Crohn's disease and ulcerative colitis (2, 3), the two IBD subtypes. The specific gene(s) mediating the association and the functional consequences of the polymorphisms are not yet reported, although leukemia inhibitory factor (LIF) and Oncostatin M (OSM) have been proposed as candidates (2). Myotubularin-related protein 3 (MTMR3) is a member of the myotubularin family. Mutations in certain myotubularin members can lead to neuro-muscular diseases (4). Active myotubularin members possess phosphoinositide 3-protein tyrosine phosphatase activity; the active phosphatase domain located in the MTMR3 N-terminal region dephosphorylates phosphatidylinositol 3-phosphate (PtdIns3P) and PtdIns(3,5)P 2 (4, 5). PtdIns3P is an important lipid mediator of membrane trafficking and signaling and participates in effector recruitment to autophagic membranes. Consistently, MTM...

The role of autophagy in colitis-associated colorectal cancer

“… 38 However, decreasing autophagy in macrophages can increase PRR-induced IL-1β secretion, nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) signaling, and ultimately, overall cytokine secretion. 39 Consistently, mice with myeloid cell-specific deletion of Atg7 were more susceptible to experimental colitis, accompanied by increased colonic cytokine expression and systemic bacterial invasion. 40 A lack of ATG16L1 in macrophages impairs mitophagy, which increases ROS production, reduces microbial killing, impairs processing of major histocompatibility complex (MHC) class II antigens, and alters intracellular trafficking to lysosomal compartments, leading to colitis development in mice.…”

New insights into the interplay between autophagy, gut microbiota and inflammatory responses in IBD

“…Another IBD-associated MTMR3 (myotubularin-related protein 3) risk allele was shown to amplify the PRR-induced innate immune response by decreasing autophagy [84]. Indeed, myeloid cells from healthy individuals carrying the IBDassociated polymorphism in the MTMR3 gene exhibit increased MTMR3 expression, leading to decreased PRRinduced autophagy by reducing cellular levels of phosphatidylinositol-3-phosphate, which are associated with autophagy initiation and maturation.…”

“…Indeed, myeloid cells from healthy individuals carrying the IBDassociated polymorphism in the MTMR3 gene exhibit increased MTMR3 expression, leading to decreased PRRinduced autophagy by reducing cellular levels of phosphatidylinositol-3-phosphate, which are associated with autophagy initiation and maturation. This consequently leads to increased PRR-induced CASP1 activation and cytokine secretion [84].…”

Mechanisms and function of autophagy in intestinal disease

“…For example, polymorphisms in MTMR3 (myotubularin related protein 3) lead to impaired autophagy, increased stimulation-dependent CASP1 activation, and increased IL1B release. 17 Additionally, a CD-associated polymorphism within PTPN2 (protein tyrosine phosphatase, non-receptor type 2) alters autophagosome formation and bacterial clearance resulting in increased inflammatory cytokine secretion in intestinal cells. 18,19 A number of genes within IBD susceptibility loci were recently found to function in antibacterial autophagy and bacterial clearance, including the E3 ligase SMURF1 and the peroxisomal protein PEX13 (Fig.…”