The neuropeptide receptor subunit RAMP1 constrains the innate immune response during acute pancreatitis in mice

Objectives: The importance of the Calcitonin-gene-related-peptide-pathway (CGRP) as neuronal modulator of innate immune responses in mice has been previously demonstrated. The CGRP-receptor is composed of two subunits: the receptor-activity-modifying-protein-1 (RAMP1) and the calcitonin-receptor-like-receptor (CLR). CGRP can influence immune cells and their capacity of producing inflammatory cytokines. Using a RAMP1 knockout-mouse (RAMP1^−/−) we examined the role of the CGRP-receptor in the acute-phase of cerulein-induced pancreatitis. Methods: Hourly cerulein-injections for a period of 8 h in RAMP1^−/− and wild-type mice were performed. To compare severity and extent of inflammation in RAMP1^−/− and wild-type mice, histological analyses were done and cytokine levels were assessed using qRT-PCR 8 h, 24 h, 2 days, and 7 days post-cerulein-treatment. Furthermore, serum activities of LDH and lipase were determined. Results: After 8 h RAMP1^−/− mice showed a higher pancreas-to-body-weight-ratio, increased tissue edema and immune cell infiltration with higher amount of F4/80-positive cells as compared to wild-type mice. Overall infiltration of immune cells at 24 h was increased in RAMP1^−/− mice and composed predominantly of MPO-positive neutrophils. In addition, after 24 h RAMP1^−/− mice presented a higher pancreas-to-body-weight-ratio, higher expression of Ccl3, Il6, and Il1b and increased number of cleaved caspase 3 positive cells. Serum lipase correlated with the extent of tissue damage in RAMP1^−/− compared to wild-type mice 24 h post-cerulein treatment. Conclusion: Mice lacking RAMP1 showed increased inflammation, tissue edema, and pancreas injury particularly in the early phase of acute pancreatitis. This study highlights the essential role of CGRP for dampening the innate immune response in acute pancreatitis.