| P-glycoprotein (P-gp) is an ATP-binding transmembrane pump associated with substrate extrusion in cells of epithelial and hematopoietic lineage. Polymorphisms in multidrug resistance genes (MDR), which encode this protein, are associated with development of inflammatory bowel disease in patient subsets. Furthermore, FVB/N animals deficient in P-gp expression develop spontaneous colitis. Disease in FVB.mdr1a-/- animals is reported to be the result of P-gp deficiencies in intestinal epithelial cells. We developed a neonatal model of bone marrow reconstitution to accurately evaluate the contribution of P-gp deficiencies in either epithelial or immune cell populations. Our data indicate that deficiency of P-gp in epithelial tissue alone is not sufficient to initiate spontaneous colitis.;It has been theorized that P-gp extrudes bacterial ligands from the intracellular environment. To address this we conferred P-gp deficiency onto C67BL/6 mice, in hopes of studying colitic rescue in animals jointly expressing mutations to innate pattern recognition sensors. B6.mdr1a-/- mice were protected from developing colitis. Further analysis demonstrated these animals were resistant to colitis induction by bacterial inoculation with Helicobacter bilis, and by inhibition of prostaglandin synthesis with piroxicam. B6.mdr1a-/- animals demonstrated an increased susceptibility to colitis induction following epithelial disruption using dextran sodium sulfate, indicating a role for P-gp in epithelial maintenance and injury repair.;To evaluate the role of P-gp deficiency in injury repair, B6. mdr1a-/- and B6 mice were lethally irradiated with 12 Gy X-ray irradiation and crypt regeneration was assessed. B6.mdr1a -/- and B6 animals demonstrated cyclooxygenase dependent crypt regeneration following exposure to irradiation. LPS pretreatment is known to induce radioprotection when administered prior to irradiation. B6 and B6.mdr1a-/- animals demonstrated LPS induced radioprotection, however radioprotection was significantly more profound in B6 animals. Following LPS pretreatment and exposure to radiation, B6 animals expressed significantly more IL1alpha, and IL22 when compared to B6. mdr1a-/- animals.;We demonstrate that a lack of P-gp expression on lymphocytic populations plays a contributory role in the development of spontaneous colitis. We show that P-gp deficiency renders cells unable to properly respond to systemically applied bacterial stimuli. Additionally, we demonstrate P-gp deficiency may affect rates of epithelial apoptosis, and intestinal injury repair.;Keywords. P-glycoprotein, neonatal, epithelium, injury repair, gastrointestinal, colitis. |
