Progressive Changes in Microglial Morphology in SCA1 and Calbindin-SCA1 Double Mutant Mice
Madison Elise Land, Asiah Clay, Maripar E. Lopez, Parminder J. S. Vig
Department of Neurology, The University of Mississippi Medical Center, Jackson, MS
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurological disorder caused by the expansion of a polyglutamine tract in the mutant protein ataxin-1. Progressive ataxia in SCA1 disease results in the loss of Purkinje cells (PCs) in the cerebellum. The mechanism of PC death in SCA1 is not known; however, our previous work indicates that targeted deprivation of PC specific calcium binding protein calbindin-D28k (CaB) exacerbates ataxin-1 mediated toxicity in SCA1 transgenic (Tg) mice. Microglia are resident immune cells of the Central Nervous System (CNS) and are acutely sensitive to homeostatic perturbations and actively participate in CNS disease processes and injury resolution. The objective of this study was to determine if the cerebellar microglia in SCA1 are early indicators of neuronal stress and exhibit altered morphology. Further, this study was to understand if these morphologic alterations are more pronounced in calbindin (CaB) knockout: SCA1 Tg double mutants than SCA1 mice. Paraffin embedded mouse cerebellar tissue from wild type (WT), SCA1, and CaB: SCA1 double mutant (DM) mice at postnatal week 2 and 4 were cut into 6 um sections. Sections were de-paraffinized, rehydrated and processed for immunohistochemistry using IBA1 antibody, a microglial marker. The immunostained sections were observed by Olympus Epi-fluorescence microscope and sections photographed by a high resolution digital camera. Changes in morphology were measured in the digitized images by Image J software and further subjected to statistical analysis. Results showed that the DM mice had a markedly larger microglial cell size than both SCA1 and WT at both ages. SCA1 and DM mice do not show behavior or immunohistochemical abnormalities at 2 weeks of age; however, in the present study, microglia showed early signs of activation in SCA1, the activated cells with enlarged cell bodies and processes were markedly higher in DMs, which increased with age. These data indicate that microglia may get sensitized to PC stress early on in SCA1 and could be used as markers in chronic neurodegenerative diseases.