IBD-associated G protein-coupled receptor 65 variant compromises signalling and impairs key functions involved in inflammation

BACKGROUND AND AIMS

Inflammatory bowel diseases (IBD) result in chronic inflammation of the gastrointestinal tract. Genetic studies have shown that the GPR65 gene, as well as its missense coding variant, GPR65*Ile231Leu, is associated with IBD. We aimed to define the signalling and biological pathways downstream of GPR65 activation and evaluate the impact of GPR65*231Leu on these.

METHODS

We used HEK 293 cells stably expressing GPR65 and deficient for either Gα_s, Gα_q/11 or Gα_12/13, to define GPR65 signalling pathways, IBD patient biopsies and a panel of human tissues, primary immune cells and cell lines to determine biologic context, and genetic modulation of human THP-1-derived macrophages to examine the impact of GPR65 in bacterial phagocytosis and NLRP3 inflammasome activation.

RESULTS

We confirmed that GPR65 signals via the Gα_s pathway, leading to cAMP accumulation. GPR65 can also signal via the Gα_12/13 pathway leading to formation of stress fibers, actin remodeling and RhoA activation; all impaired by the IBD-associated GPR65*231Leu allele. Gene expression profiling revealed greater expression of GPR65 in biopsies from inflamed compared to non-inflamed tissues from IBD patients or control individuals, potentially explained by infiltration of inflammatory immune cells. Decreased GPR65 expression in THP-1-derived macrophages leads to impaired bacterial phagocytosis, increased NLRP3 inflammasome activation and IL-1β secretion in response to an inflammatory stimulus.

CONCLUSIONS

We demonstrate that GPR65 exerts its effects through Gα_s- and Gα_12/13-mediated pathways, that the IBD-associated GPR65*231Leu allele has compromised interactions with Gα_12/13 and that KD of GPR65 leads to impaired bacterial phagocytosis and increased inflammatory signalling via the NLRP3 inflammasome. This work identifies a target for development of small molecule therapies.

Proliferation and differentiation of circulating haemocytes of Ruditapes philippinarum as a response to bacterial challenge

Ultrastructural investigation confirmed the presence of four cell types (granulocytes, hyalinocytes, serous cells, and haemoblasts) in the haemolymph of the Manila clam, Ruditapes philippinarum. Granulocytes were characterised by numerous electron-dense granules, whereas hyalinocytes had a considerable number of small clear vesicles. Serous cells exhibited large vacuoles, which filled the cytoplasm, and haemoblasts (the undifferentiated cells) were small roundish cells characterised by a high nucleus/cytoplasm ratio. The presence of circulating haemoblasts was observed at various phases of mitosis. Updated data concerning the proliferation and differentiation of circulating haemocytes were obtained after both in vitro and in vivo bacterial challenge. The results demonstrated that cell proliferation occurred within 15 h of exposure, and most haemocyte types responded to the stimuli. The number of granulocytes significantly decreased after massive phagocytosis and ultrastructural observations confirmed that they were active phagocytic cells against both Gram-positive and Gram-negative bacteria, which were rapidly engulfed into large phagosomes. Granulocyte lysis may represent a protection response against bacterial proliferation inside phagosomes. The number of serous cells significantly increased, suggesting a previously unreported pivotal immune role during bacterial infection. A panel of lectins was used as probes to further characterise haemocytes and their relationships. Only hyalinocytes were not positive for the lectins assayed, whereas all lectins labelled serous cells, suggesting that these cells have a variety of specific carbohydrates, which are shared with certain haemoblasts. The hypothesis of the existence of a prospective haemoblast for serous cell origin is discussed.