Distribution and localization of phosphatidylinositol 5-phosphate, 4-kinase alpha and beta in the brain

Abstract

Phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) is critical for synaptic vesicle docking and fusion and generation of the second messengers, diacylglycerol and inositol-1,4,5-trisphosphate. PI-4,5-P2 can be generated by two families of kinases: type 1 phosphatidylinositol-4-phosphate 5-kinases, encoded by PIP5K1A, PIP5K1B and PIP5K1C, and type 2 phosphatidylinositol-5-phosphate 4-kinases, encoded by PIP4K2A, PIP4K2B, and PIP4K2C. While the roles of the type 1 enzymes in brain function have been extensively studied, the roles of the type 2 enzymes are poorly understood. Using selective antibodies validated by genetic deletion of pip4k2a or pip4k2b in mouse brain, we characterized the location of the enzymes, PI5P4K and PI5P4K{beta}, encoded by these genes. In mice, we demonstrate that PI5P4K is expressed in adulthood, whereas PI5P4K{beta} is expressed early in development. PI5P4K localizes to white matter tracts, especially the corpus callosum, and at a low level in neurons, while PI5P4K{beta} is expressed in neuronal populations, especially hippocampus and cortex. Dual labeling studies demonstrate that PI5P4K co-localizes with the oligodendrocyte marker, Olig2, whereas PI5P4K{beta} co-localizes with the neuronal marker, NeuN. Immunohistochemical subcellular distribution studies demonstrate that PI5P4K and PI5P4K{beta} are expressed in the early endosome system. Ultrastructural analysis demonstrates that both kinases are contained in axon terminals and dendritic spines adjacent to the synaptic membrane, which support a potential role in synaptic transmission. Immunohistochemical analysis of macaque and human brain tissue demonstrate a conserved pattern for PI5P4K and PI5P4K{beta}. These results highlight the diverse cell-autonomous expression of PI5P4K and PI5P4K{beta} and support further exploration into their role in synaptic function in the brain.