Calcium pyrophosphate dihydrate crystal associated induction of neutrophil activation and repression of TNF-alpha-induced apoptosis is mediated by the p38 MAP kinase

The role of p38 mitogen-activated protein (MAP) kinase in the activation of human neutrophils and repression of TNF-alpha-induced apoptosis in response to plasma opsonized crystals of calcium pyrophosphate dihydrate (CPPD) was investigated. We monitored the endogenous phosphotransferase activity of p38 kinase in neutrophils stimulated with CPPD crystals (25 mg/ml) alone or in the presence of TNF-alpha (10 ng/ml), and with TNF-alpha alone. CPPD crystals induced a 2-fold activation of p38 kinase activity over the basal activity that was observed in untreated neutrophils. Furthermore, CPPD crystals repressed the TNF-alpha associated 6-fold induction of p38 kinase phosphotransferase activity to levels associated with CPPD crystal incubation alone in a PD98059 (20 ng/ml) and Wortmannin (100 nM) sensitive manner. Inhibition of CPPD crystal-induced activation of the neutrophil inflammatory response as measured by chemiluminescence, superoxide anion generation and degranulation as determined by myeloperoxidase and lysozyme release was observed in the presence of the specific p38 MAP kinase inhibitor SB203580 (5 microM). CPPD crystal associated repression of TNF-alpha-induced activation of neutrophil apoptosis as determined by DNA fragmentation correlated with the CPPD crystal mediated inhibition of p38 kinase activity, probably through crystal inhibition of caspase 3. Together, our results indicate that the CPPD crystal associated inflammatory response is regulated through the activation of p38 kinase to sub-apoptotic levels, and that the repression of the TNF-alpha-induced apoptosis program in neutrophils is mediated via the repression of caspase 3 mediated apoptosis-associated p38 kinase activity.