Activation of cannabinoid receptor 2 reduces inflammation in acute experimental pancreatitis via intra-acinar activation of p38 and MK2-dependent mechanisms

Michler T, Storr M, Kramer J, Ochs S, Malo A, Reu S, Goke B, Schafer C. Activation of cannabinoid receptor 2 reduces inflammation in acute experimental pancreatitis via intra-acinar activation of p38 and MK2-dependent mechanisms. Am J Physiol Gastrointest Liver Physiol 304: G181-G192, 2013. First published November 8, 2012; doi:10.1152/ajpgi.00133.2012.-The endocannabinoid system has been shown to mediate beneficial effects on gastrointestinal inflammation via cannabinoid receptors 1 (CB1) and 2 (CB2). These receptors have also been reported to activate the MAP kinases p38 and c-Jun NH2-terminal kinase (JNK), which are involved in early acinar events leading to acute pancreatitis and induction of proinflammatory cytokines. Our aim was to examine the role of cannabinoid receptor activation in an experimental model of acute pancreatitis and the potential involvement of MAP kinases. Cerulein pancreatitis was induced in wild-type, CB1-/-, and MK2-/- mice pretreated with selective cannabinoid receptor agonists or antagonists. Severity of pancreatitis was determined by serum amylase and IL-6 levels, intracellular activation of pancreatic trypsinogen, lung myeloperoxidase activity, pancreatic edema, and histological examinations. Pancreatic lysates were investigated by Western blotting using phospho-specific antibodies against p38 and JNK. Quantitative PCR data, Western blotting experiments, and immunohistochemistry clearly show that CB1 and CB2 are expressed in mouse pancreatic acini. During acute pancreatitis, an upregulation especially of CB2 on apoptotic cells occurred. The unselective CB1/CB2 agonist HU210 ameliorated pancreatitis in wild-type and CB1-/- mice, indicating that this effect is mediated by CB2. Furthermore, blockade of CB2, not CB1, with selective antagonists engraved pathology. Stimulation with a selective CB2 agonist attenuated acute pancreatitis and an increased activation of p38 was observed in the acini. With use of MK2-/- mice, it could be demonstrated that this attenuation is dependent on MK2. Hence, using the MK2-/- mouse model we reveal a novel CB2-activated and MAP kinase-dependent pathway that modulates cytokine expression and reduces pancreatic injury and affiliated complications.