The novel PKC isoform, PKC-theta, is particularly enriched in T lymphocyte populations, serving a critical role in signal transduction after CD3/CD28 T cell receptor stimulation. PKC-theta is known to be involved in promoting T cell mediated immunity and has been implicated in other autoimmune diseases. We hypothesized that inhibition of this isoform would increase regulatory T cell phenotypes, promote an anti-inflammatory environment, and lead to delayed onset of type 1 diabetes in the NOD mouse model. A cell permeable pseudosubstrate peptide inhibitor was identified with potent suppression of IL-2 secretion at concentrations ≤15 μg in T cell enriched populations stimulated in vitro with CD3 and CD28 antibodies and a significant reduction in stimulated IL-2 secretion after 7 days of intraperitoneal treatment with 50 μg of pseudosubstrate inhibitor. Five-week-old prediabetic NOD mice were either treated daily with 50 μg of inhibitor or mock treated with saline for 4 weeks, then allowed to progress until 17 weeks of age. An 80% conversion to diabetes, based on IP glucose tolerance tests, was observed in saline mice compared to 30% conversion in inhibitor-treated mice, which correlated with a greater frequency of inflammation-free islets and islets with periinsulitis only in inhibitor-treated mice. Inhibitor-treated mice had increased frequencies of IL-10 secreting cells by ELISPOT, and increased Tregs in spleen at 17 weeks of age while reduced frequencies of IL-17+ CD4+ T cells. This study was repeated with a scrambled peptide control and later endpoint to determine if T1D would be prevented entirely. At 25 weeks of age a 66% conversion to diabetes was observed in scrambled peptide treated mice, while only 33% converted in the peptide treated. Our data demonstrate that PKC theta activation contributes to the progression of beta cell destruction in NOD mice, where inhibition of this isoform may confer an increase in protective regulatory T cell populations.
J.E. DiLisio: None. N. Mishkin: None. B. Podell: None.
National Institutes of Health (5K01OD016997 to B.P.); National Center for Advancing Translational Sciences (UL1TR001082 to B.P.)