Insulin Promotes Neuronal Survival via the Alternatively Spliced Protein Kinase CδII Isoform

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (12), p.9299-9310
• Main Authors: Apostolatos, André, Song, Shijie, Acosta, Sandra, Peart, Mishka, Watson, James E., Bickford, Paula, Cooper, Denise R., Patel, Niketa A.
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Animals; Apoptosis; bcl-X Protein - genetics; bcl-X Protein - metabolism; Bcl2; Cell Line; Cell Survival; Gene Expression Regulation; Gene Regulation; Insulin; Insulin - metabolism; Male; Mice; Mice, Inbred C57BL; Neuroendocrinology; Neurons - cytology; Neurons - enzymology; Neurons - metabolism; PKCδ; Protein kinase C (PKC); Protein Kinase C-delta - genetics; Protein Kinase C-delta - metabolism; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2; RNA splicing; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.313080

Insulin signaling pathways in the brain regulate food uptake and memory and learning. Insulin and protein kinase C (PKC) pathways are integrated and function closely together. PKC activation in the brain is essential for learning and neuronal repair. Intranasal delivery of insulin to the central nervous system (CNS) has been shown to improve memory, reduce cerebral atrophy, and reverse neurodegeneration. However, the neuronal molecular mechanisms of these effects have not been studied in depth. PKCδ plays a central role in cell survival. Its splice variants, PKCδI and PKCδII, are switches that determine cell survival and fate. PKCδI promotes apoptosis, whereas PKCδII promotes survival. Here, we demonstrate that insulin promotes alternative splicing of PKCδII isoform in HT22 cells. The expression of PKCδI splice variant remains unchanged. Insulin increases PKCδII alternative splicing via the PI3K pathway. We further demonstrate that Akt kinase mediates phosphorylation of the splicing factor SC35 to promote PKCδII alternative splicing. Using overexpression and knockdown assays, we demonstrate that insulin increases expression of Bcl2 and bcl-xL via PKCδII. We demonstrate increased cell proliferation and increased BrdU incorporation in insulin-treated cells as well as in HT22 cells overexpressing PKCδII. Finally, we demonstrate in vivo that intranasal insulin promotes cognitive function in mice with concomitant increases in PKCδII expression in the hippocampus. This is the first report of insulin, generally considered a growth or metabolic hormone, regulating the alternative isoform expression of a key signaling kinase in neuronal cells such that it results in increased neuronal survival. Alternatively spliced PKCδII is a pro-survival protein. Insulin regulates alternative splicing of PKCδII pre-mRNA, which promotes Bcl2 and bcl-xL expression. PKCδII is a key regulator of insulin-mediated neuronal survival. Elucidation of the molecular mechanisms by which insulin promotes survival in neuronal cells is necessary to understand how intranasal insulin improves cognition.