Tissue-specific protein kinase C isoforms differentially mediate macrophage TNFα, and IL-1β production

Macrophage subpopulations are differentially activated during sepsis, shock, or trauma; however, it is unknown whether inherent mechanistic and phenotypic differences exist between macrophage subpopulations that may account for region-specific inflammation. We hypothesized that macrophage expression/function of protein kinase C (PKC) isoforms is tissue specific (alveolar versus peritoneal). Rat alveolar and peritoneal macrophages were each probed for the expression of PKC isoforms alpha, beta(1), beta(2), gamma, delta, epsilon, zeta, and theta by immunoblot. PKC isoforms alpha, beta(1), beta(2), delta, and zeta were detected in both populations; however, isoforms epsilon, gamma, and eta were found in alveolar macrophages only. To investigate the functional role of the Ca2+-dependent PKC (cPKC) versus Ca2+-independent PKC (nPKC) isoforms, pan-PKC isoform inhibition (cPKC and nPKC), or cPKC isoform selective inhibition (alpha, beta(1), beta(2), gamma) was performed before endotoxin (lipopolysaccharide, Salmonella minnesota, 100 ng/mL) stimulation in vitro. Pan-PKC isoform inhibition attenuated TNF alpha and IL-1 beta production by each population; however, selective cPKC (alpha, beta(1), beta(2), gamma) inhibition decreased peritoneal, but not alveolar, macrophage TNF alpha production. IL-1 beta production was not affected by cPKC inhibition in either population. Conclusions: 1) alveolar and peritoneal macrophages constitutively express different PKC isoforms; 2) alveolar macrophages uniquely express isoforms epsilon, gamma, eta; 3) TNF alpha production is regulated by cPKCs in peritoneal macrophages, but by nPKCs in alveolar macrophages; 4) nPKCs regulate IL-1 beta production in both populations. These results suggest that tissue-specific PKC isoforms differentially mediate macrophage function, which may have important regulatory implications in the compartmentalization of immune function. Further understanding may allow region-specific manipulation of inflammation.