Calpastatin modulates APP processing in the brains of β-amyloid depositing but not wild-type mice

Abstract

We report that neuronal overexpression of the endogenous inhibitor of calpains, calpastatin (CAST), in a mouse model of human Alzheimer’s disease (AD) β-amyloidosis, the APP23 mouse, reduces β-amyloid pathology and Aβ levels when comparing aged, double transgenic (tg) APP23/CAST with APP23 mice. Concurrent with Aβ plaque deposition, aged APP23/CAST mice show a decrease in the steady-state brain levels of the amyloid precursor protein (APP) and APP C-terminal fragments when compared to APP23 mice. This CAST-dependent decrease in APP metabolite levels was not observed in single tg CAST mice expressing endogenous APP or in younger, Aβ plaque predepositing APP23/CAST mice. We also determined that the CAST-mediated inhibition of calpain activity in the brain is greater in the CAST mice with β-amyloid pathology than in non-APP tg mice, as demonstrated by a decrease in calpain-mediated cytoskeleton protein cleavage. Moreover, aged APP23/CAST mice have reduced ERK1/2 activity and tau phosphorylation when compared to APP23 mice. In summary, in vivo calpain inhibition mediated by CAST transgene expression reduces Aβ pathology in APP23 mice, with our findings further suggesting that APP metabolism is modified by CAST overexpression as the mice develop β-amyloid pathology. Our results indicate that the calpain system in neurons is more responsive to CAST inhibition under conditions of β-amyloid pathology, suggesting that in the disease state neurons may be more sensitive to the therapeutic use of calpain inhibitors.

Hypoxia‐Triggered m‐Calpain Activation Evokes Endoplasmic Reticulum Stress and Neuropathogenesis in a Transgenic Mouse Model of Alzheimer's Disease

“…Calpain activation plays an important role in APP processing and plaque formation in APP/PS1 mice . Calpain system in neurons is more responsive to calpain inhibition under conditions of Aβ pathology . We postulated that calpain may play an important role in the hypoxia‐induced alterations of AD pathogenesis.…”

Dynamin‐like protein 1 cleavage by calpain in Alzheimer’s disease

“…The pathophysiological relevance of calpain‐dependent cleavage of DLP1 is further corroborated by the evidence from cortical neurons of CRND8 APP transgenic mice and brain tissues from AD patients. Calpain activation has been closely linked with AD as it has been shown to cleave: APP that regulates Aβ production (Morales‐Corraliza et al, ), tau leading to production of neurotoxic fragments (Ferreira & Bigio, ), synaptic proteins like dynamin‐1 (Kelly et al, ), and NMDA receptor subunit NR2B important for synaptic health (Simpkins et al, ). Our results thus added reduced DLP1 as a victim of enhanced calpain activation in AD which affect mitochondrial dynamics and contribute to mitochondrial dysfunction during AD pathogenesis.…”

Aβ Extraction from Murine Brain Homogenates

“…Our lab usually dilutes DEA and FA fractions for Aβ ELISAs at least five-fold to fall within our in-house ELISA detection limits. For western blots of Aβ and modified APP fragments, we recommend 10 to 50 micrograms protein per well, and for more details about Western blotting using the DEA-soluble extraction, please see Morales-Corraliza et al (2012).…”