Dysregulated phosphoinositide (PI) signaling has been implicated in human gastrointestinal (GI) malignancies and inflammatory states, underlining the need to study pathophysiological roles of PI in an in vivo genetic model. Here, we study the significance of PI in GI pathophysiology using the zebrafish mutant cdipthi559, which lacks PI synthesis, and unravel a critical role of PI in intestinal mucosal integrity and inflammation. The cdipthi559 mutants exhibit abnormal villous architecture and disorganized proliferation of intestinal epithelial cells (IECs), with pathologies reminiscent of inflammatory bowel disease (IBD), including apoptosis of goblet cells, abnormal mucosecretion, bacterial overgrowth, and leukocyte infiltration. The mutant IECs exhibit vacuolation, microvillus atrophy and impaired proliferation. The cdipthi559 gene expression profile shows enrichment of acute phase response signaling and the endoplasmic reticulum (ER) stress factors, hspa5 and xbp1, are robustly activated in the mutant GI tissue. Temporal electron micrographic analyses reveal that PI-deficient IECs undergo sequential ER-Golgi disruption, mitochondrial depletion, macroautophagy and cell death, consistent with chronic ER stress-mediated cytopathology. Furthermore, pharmacological induction of ER stress by inhibiting protein glycosylation or PI synthase inhibition in leukocyte-specific reporter lines replicates the cdipthi559 inflammatory phenotype, suggesting a fundamental role of PI metabolism and ER stress in mucosal inflammation. Antibiotics and anti-inflammatory drugs resolved the inflammation, but not the autophagic necroapoptosis of IECs, suggesting that bacterial overgrowth may exacerbate ER stress pathology, whereas persistent ER stress is sufficient to trigger inflammation. Interestingly, the intestinal phenotype was partially alleviated by chemical chaperones, suggesting their therapeutic potential. Using zebrafish genetic and pharmacological models, this study demonstrates a novel link between intracellular PI signaling and ER stress-mediated mucosal inflammation. The zebrafish Cdipt mutants provide a powerful tool to dissect the fundamental mechanisms of ER stress-mediated human GI diseases and a platform to develop molecularly targeted therapies.
- Received May 4, 2013.
- Accepted October 10, 2013.
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