Mutations of the α1A subunit of CaV 2.1 voltage gated calcium (VGCC) channels
are responsible for several inherited disorders affecting humans, including familial
hemiplegic migraine, episodic ataxia type and spinocerebellar ataxia type. The leaner
mouse also carries an autosomal recessive mutation in the α1A subunit of CaV 2.1 VGCCs,
which, in the homozygous condition, results in a severe cerebellar atrophy and ataxia.
The leaner mutation results in reduced calcium influx through CaV 2.1 VGCCs. To better
understand cerebellar neurodegeneration and cerebellar dysfunction we focused our
research on elucidating the relationship between mitochondrial function/dysfunction and
calcium channel mutations. The aims of this dissertation were: 1) to estimate the extent
of neuronal cell death, basal intracellular calcium and mitochondrial (dys)function in
cerebellar granule cells (CGC) of adult leaner mice; 2) to analyze the role of the leaner
calcium channel mutation on postnatal development of CGCs; and 3) to test whether
inducing increased calcium influx by exposing cultured granule cells to potassium
chloride can eliminate or reduce the CGC death. By using mechanism independent Fluoro-Jade staining and apoptosis specific
TUNEL staining, we demonstrated that leaner CGC death continues into adulthood and
the spatial pattern of granule cell death observed during postnatal development also
continues into adulthood. The present investigation showed a reduced resting
intracellular calcium in CGC from leaner mice as compared to age matched wild type
mice, and tottering mice. The tottering mouse is another mutant mouse that carries a
mutation in the α1A subunit of CaV 2.1 VGCCs like leaner mouse. However, these mice
do not show any neurodegeneration and therefore they were used as a second control.
Our results also showed that even though CGC of leaner mice have dysfunctional CaV2.1
channels, there is no change in depolarization induced Ca2+ influx, which suggests a
functional compensation for CaV2.1 calcium channels by other VGCCs. Our results
showed reduced mitochondrial membrane potential at the time of peak CGC death in
leaner mice as compared to wild type CGCs and tottering CGCs. The results of this
investigation suggest mitochondrial mediated but reactive oxygen species independent
cell death in CGCs of leaner mice
