http://stroke.ahajournals.org/content/early/2013/06/06/STROKEAHA.113.001320.abstract
Abstract
Background and Purpose—Loss-of-function
mutations of the lipoprotein receptor–related protein-6 (LRP6), a
coreceptor in the Wingless-related integration
site-β−catenin prosurvival pathway, have been
implicated in myocardial ischemia and neurodegeneration. However, it
remains
to be established whether LRP6 is also
involved in ischemic brain injury. We used LRP6+/− mice to examine the role of this receptor in the mechanisms of focal cerebral ischemia.
Methods—Focal
cerebral ischemia was induced by transient occlusion of the middle
cerebral artery. Motor deficits and infarct volume
were assessed 3 days later.
Glycogen-synthase-kinase-3β (GSK-3β) phosphorylation was examined by
Western blotting with phosphospecific
antibodies, and the mitochondrial membrane
potential changes induced by Ca2+ were also assessed.
Results—LRP6+/−
mice have larger stroke and more severe motor deficits, effects that
were independent of intraischemic cerebral blood flow,
vascular factors, or cytosolic β-catenin
levels. Rather, LRP6 haploinsufficiency increased the activating
phosphorylation
and decreased the inhibitory phosphorylation
of GSK-3β, a kinase involved in proinflammatory signaling and
mitochondrial dysfunction.
Accordingly, postischemic inflammatory gene
expression was enhanced in LRP6+/− mice. Furthermore, the association of mitochondria with activated GSK-3β was increased in LRP6+/− mice, resulting in a reduction in the Ca2+ handling ability of mitochondria. The mitochondrial dysfunction was reversed by pharmacological inhibition of GSK-3β.
Conclusions—LRP6
activates an endogenous neuroprotective pathway that acts independently
of β-catenin by controlling GSK-3β activity and
preventing its deleterious mitochondrial and
proinflammatory effects. The findings raise the possibility that
emerging treatment
strategies for diseases attributable to LRP6
loss-of-function mutations could also lead to new therapeutic avenues
for ischemic
stroke.
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