A?43-producing PS1 FAD mutants cause altered substrate interactions and respond to ?-secretase modulation
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ABSTRACT:
SUBMITTER: Dr. Harald Steiner
PROVIDER: S-SCDT-EMBOR-2019-47996V1 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:Microvascular pathology and ischemic lesions contribute substantially to neuronal dysfunction and loss that lead to Alzheimer disease (AD). To facilitate recovery, the brain stimulates neovascularization of damaged tissue via sprouting angiogenesis, a process regulated by endothelial cell (EC) sprouting and the EphB4/ephrinB2 system. Here, we show that in cultures of brain ECs, EphB4 stimulates the VE-cadherin/Rok-α angiogenic complexes known to mediate sprouting angiogenesis. Importantly, brain EC cultures expressing PS1 FAD mutants decrease the EphB4-stimulated γ-secretase cleavage of ephrinB2 and reduce production of the angiogenic peptide ephrinB2/CTF2, the VE-cadherin angiogenic complexes and EC sprouting and tube formation. These data suggest that FAD mutants may attenuate ischemia-induced brain angiogenesis. Supporting this hypothesis, ischemia-induced VE-cadherin angiogenic complexes, levels of neoangiogenesis marker Endoglin, vascular density, and cerebral blood flow recovery, are all decreased in brains of mouse models expressing PS1 FAD mutants. Ischemia-induced brain neuronal death and cognitive deficits also increase in these mice. Furthermore, a small peptide comprising the C-terminal sequence of peptide ephrinB2/CTF2 rescues angiogenic functions of brain ECs expressing PS1 FAD mutants. Together, our data show that PS1 FAD mutations impede the EphB4/ephrinB2-mediated angiogenic functions of ECs and impair brain neovascularization, neuronal survival and cognitive recovery following ischemia. Furthermore, our data reveal a novel brain angiogenic mechanism targeted by PS1 FAD mutants and a potential therapeutic target for ischemia-induced neurodegeneration. Importantly, FAD mutant effects occur in absence of neuropathological hallmarks of AD, supporting that such hallmarks may form downstream of mutant effects on neoangiogenesis and neuronal survival.
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Project description:BackgroundPresenilin 1(PS1) is the catalytic subunit of gamma-secretase, the enzyme responsible for the Abeta C-terminal cleavage site, which results in the production of Abeta peptides of various lengths. Production of longer forms of the Abeta peptide occur in patients with autosomal dominant Alzheimer disease (AD) due to mutations in presenilin. Many modulators of gamma-secretase function have been described. We hypothesize that these modulators act by a common mechanism by allosterically modifying the structure of presenilin.Methodology/principal findingsTo test this hypothesis we generated a genetically encoded GFP-PS1-RFP (G-PS1-R) FRET probe that allows monitoring of the conformation of the PS1 molecule in its native environment in live cells. We show that G-PS1-R can be incorporated into the gamma-secretase complex, reconstituting its activity in PS1/2 deficient cells. Using Förster resonance energy transfer (FRET)-based approaches we show that various pharmacological and genetic manipulations that target either gamma-secretase components (PS1, Pen2, Aph1) or gamma-secretase substrate (amyloid precursor protein, APP) and are known to change Abeta(42) production are associated with a consistent conformational change in PS1.Conclusions/significanceThese results strongly support the hypothesis that allosteric changes in PS1 conformation underlie changes in the Abeta(42/40) ratio. Direct measurement of physiological and pathological changes in the conformation of PS1/gamma-secretase may provide insight into molecular mechanism of Abeta(42) generation, which could be exploited therapeutically.
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