Along these lines, another in vivo study reported
increased extrasynaptic NMDA receptor expression as well as
associated reductions in nuclear CREB activation in striatum of HD
mouse. These changes correlated with mutation severity, were
dependent on the cleavage of mHtt by caspase-6, and resulted in
manifestation of the disease (Milnerwood et al., 2010). The exact
link between Htt, caspase cleavage, and caspase activation patterns
in the pathogenesis of HD is poorly understood, however, the
activation of caspase-6, but not caspase-3, occurs before onset of
mobility abnormalities in human and murine HD brain.
Inositol hexakisphosphate kinases (InsP(6)Ks) has been proposed
as another apoptosis triggering factor, at least in a cellular
models of AD. InsP(6)Ks promote apoptosis in a caspaseindependent
manner. Under stress conditions, an isoform of
InsP6Ks, Inositol hexakisphosphate kinase type 2 (InsP(6)K2),
mediates apoptotic cell death via its translocation from the nucleus
to the cytoplasm. While InsP(6)K2 is localized in the nucleus of
normal lymphoblasts, this enzyme is observed mainly in the
cytoplasm of HD lymphoblast cells. This finding may suggests a
role for InsP6K2 activation in the pathogenesis of HD (Nagata et al.,
2010).