BaxInactivation in Lurcher Mutants Rescues Cerebellar Granule Cells But Not Purkinje Cells or Inferior Olivary Neurons

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Abstract
Lurcher is a gain-of-function mutation in the δ2 glutamate receptor gene (Grid2) that turns the receptor into a leaky ion channel. The expression of the Lurcher gene in heterozygous (Grid2Lc/+ ) mutants induces the death of almost all Purkinje cells starting from the second postnatal week. Ninety percent of the granule cells and 60–75% of the inferior olivary neurons die because of the loss of their target neurons, the Purkinje cells. The apoptotic nature of the neurodegeneration has been demonstrated previously by the presence of activated caspase-3 and DNA fragmentation. Bax, a pro-apoptotic gene of the Bcl-2 family, has been shown to be involved in developmental neuronal death. To study the role of Bax inGrid2Lc/+ neurodegeneration, double mutants with Grid2Lc/ + mice and Baxknock-out mice (Bax−/−) were generated.Bax deletion had no effect on the death of Purkinje cells and inferior olivary neurons, although a temporary rescue of some Purkinje cells could be detected in P15Grid2Lc/ +;Bax−/− animals. From postnatal day 15 (P15) to P60, the number of granule cells inGrid2Lc/ +;Bax−/−mice did not significantly change and was significantly increased compared with the number found in Grid2Lc/ +;Bax+/+ mice. Granule cell number in P60 Grid2Lc/ +;Bax−/− mice corresponded to 70% of the number found in wild-type mice. Our results show that Bax inactivation inGrid2Lc/+ mice does not rescue intrinsic Purkinje cell death or the target-related cell death of olivary neurons, but Bax inactivation does inhibit persistently target-related cell death in cerebellar granule cells.