The lipid raft-dwelling protein US9 can be manipulated to target APP compartmentalization, APP processing, and neurodegenerative disease pathogenesis

Abstract

The trafficking behavior of the lipid raft-dwelling US9 protein from Herpes Simplex Virus strikingly overlaps with that of the amyloid precursor protein (APP). Both US9 and APP processing machinery rely on their ability to shuttle between endosomes and plasma membranes, as well as on their lateral accumulation in lipid rafts. Therefore, repurposing US9 to track/modify these molecular events represents a valid approach to investigate pathological states including Alzheimer’s disease and HIV-associated neurocognitive disorders where APP misprocessing to amyloid beta formation has been observed. Accordingly, we investigated the cellular localization of US9-driven cargo in neurons and created a US9-driven functional assay based on the exogenous enzymatic activity of Tobacco Etch Virus Protease. Our results demonstrate that US9 can direct and control cleavage of recombinant proteins exposed on the luminal leaflet of transport vesicles. Furthermore, we confirmed that US9 is associated with lipid-rafts and can target functional enzymes to membrane microdomains where pathologic APP-processing is thought to occur. Overall, our results suggest strongly that US9 can serve as a molecular driver that targets functional cargos to the APP machinery and can be used as a tool to study the contribution of lipid rafts to neurodegenerative disease conditions where amyloidogenesis has been implicated.

The US9-Derived Protein gPTB9TM Modulates APP Processing Without Targeting Secretase Activities

“…Studies in cell cultures, including primary neurons, demonstrated that after reaching the plasma membrane, US9 is recycled to endosomes [ 53 ], closely overlapping APP trafficking behavior. We also demonstrated that US9-driven TEV protease (TEV: tobacco etch virus) can cleave an APP-driven TEV protease reporter substrate, demonstrating that US9 can locate a functional cargo in close proximity of APP [ 39 ]. Building on these observations, we explored the possibility to use US9 to modulate APP processing without targeting endogenous enzymes.…”

“…We recently discovered a remarkable overlap between the cellular trafficking of APP and US9 [39]. US9 is a protein necessary for α-herpesviruses anterograde transport in neurons [40][41][42][43].…”

“…To move inside and between neurons, HSV hijacks the cellular transport machinery, with the viral protein US9 required for its anterograde axonal trafficking. Our previous studies defined its intrinsic properties and established US9 from HSV as a driver of artificially loaded functional cargos [ 39 , 44 ]. This work has led us to envision US9 as a tool to alter APP processing toward the goal of neuroprotection.…”

The Role of a Pathological Interaction between β-amyloid and Mitochondria in the Occurrence and Development of Alzheimer’s Disease

“…Присутствие в МАМ пресенилинов и остатка C99 [68], который расщепляется γ-секретазой [69], может объяснить локализацию Aβ в митохондриях [50]. Кроме того, МАМ представляет собой липидный рафтподобный домен [70], а, как известно, расщепление АРР по амилоидогенному пути зависит от липидного рафтa [71,72]. Изменение активности γ-секретазы приводит к накоплению фрагмента C99 в МАМ, вызывая этерификацию холестерина и гидролиз сфинголипидов, а также митохондриальную дисфункцию [73].…”

“…The presence of presenilins and the C99 fragment, which is cleaved by γ-secretase [ 69 ], in MAM [ 68 ] may explain the mito chondrial localization of Aβ [ 50 ]. In addition, MAM is a lipid raft-like domain [ 70 ], while APP cleavage via the amyloidogenic pathway depends on the lipid raft [ 71 , 72 ]. A change in γ-secretase activity leads to the accumulation of the C99 fragment in MAM, inducing esterification of cholesterol, hydrolysis of sphingolipids, and mitochondrial dysfunction [ 73 ].…”