Dendritic and axonal localization of cytotoxic T-lymphocyte antigen-2 alpha protein in mouse brain

Cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2alpha) is a novel cysteine proteinase inhibitor protein originally discovered and expressed in mouse activated T-cells and mast cells. Expressed recombinant CTLA-2alpha is shown to exhibit selective inhibition of cathepsin L-like cysteine proteinases. We have recently reported the expression pattern of CTLA-2alpha mRNA in mouse brain by in situ hybridization, demonstrating that it is mainly enriched within neuronal populations. In this study we present the distribution profile of the protein by immunohistochemical analysis. Results showed that CTLA-2alpha protein is preferentially localized in dendritic and axonal compartments. In telencephalon, strong labeling was detected in dendrites in the cerebral cortices, stratum radiatum and stratum lacunosum moleculare and within axonal fibers of stratum lucidum where mossy fibers emanating from all parts of the granule cell layer of dentate gyrus terminate at pyramidal neurons and interneurons. In diencephalon, moderate staining was found in all thalamic nuclei but was strong in medial habenular nucleus and the hypothalamic nuclei including suprachiasmatic nucleus, optic chiasm, arcuate nucleus and median eminence. In mesencephalon, strong immunoreactivity was detected in superior colliculus, inferior colliculus and paramedian raphe nucleus. In the rhombencephalon, the pontine nucleus and transverse fibers of the pons revealed strong staining but were moderate in vestibular nuclei. Strong immunoreactivity was also observed in the internal white matter, granule cell layer and Purkinje cell layer within cerebellum. On Western blot analysis, a band of 14 kDa for CTLA-2alpha from protein extracts of the cerebrum, cerebellum, pons and medulla was detected. The distribution pattern and functional considerations of CTLA-2alpha in the brain are discussed.