The LDL receptor-related protein (LRP) is a signaling receptor for LDL, linking the nature and levels of extracellular lipoprotein particles to intracellular signaling pathways, one of which is the Rho-dependent protein kinase (ROCK) pathway. We have recently discovered that ROCK inhibits activated nonamyloidogenic alpha-secretase processing (""""""""ectodomain shedding"""""""") of the Alzheimer amyloid precursor protein (APP). We hypothesize that each component of this lipoprotein signaling pathway (i.e., apoE isoforms, cholesterol, LRP, the receptor-associated protein [abbreviated RAP], ROCK) has a distinct impact on alpha-secretase activity and ectodomain shedding.
Aim 1 is to dissect the individual contribution of each component to the modulation of APP shedding. Based on the observation that alpha-secretase overexpression can abolish Abeta pathology in transgenic mice, we hypothesize that dissection of this regulatory pathway will reveal novel sites of pathogenesis and novel targets for anti-amyloid drugs. At the level of the effector molecules, ROCK signals act via the alpha-secretase proteolytic pathway, but the identities of the phospho-state-specific ROCK substrate(s) that regulate shedding are unknown. We and others have shown that at least one important phosphoprotein target resides between the trans-Golgi network (TGN) and the plasma membrane, and controls either (i) budding of APP-bearing vesicles; (ii) fusion of APP-bearing vesicles with alpha-secretase-bearing vesicles; or (iii) intra-plasma-membrane activation of alpha-secretase.
Aim 2 is to study the murine counterparts of selected SEC proteins (known as """"""""Munc"""""""" proteins) as candidate phospho-state-specific modulators of ectodomain shedding (PMES). """"""""Munc"""""""" proteins are the murine homologues of unc proteins (which, in turn, are the nematode homlogues of yeast SEC mutants). We hypothesize that discovery of one or more PMES molecules will reveal novel sites of pathogenesis and targets for anti-amyloid interventions.
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