Platelets isolated from an Alzheimer mouse damage healthy cortical vessels and cause inflammation in an organotypic ex vivo brain slice model

Abstract

Platelets are anuclear blood cells and play a major role in hemostasis and thrombosis. Platelets express amyloid-precursor protein (APP), release beta-amyloid (Aβ) and are stimulated (pre-activated) in Alzheimer’s disease (AD). We hypothesize that such stimulated platelets severely damage brain vessels which subsequently leads to cerebrovascular damage in AD. In order to study this issue we isolated platelets from AD mice (expressing APP with the Swedish-Dutch-Iowa mutations), labeled them with the red fluorescent dye PKH26 and transcardially infused these freshly isolated platelets into the brains of anesthetized healthy C57BL6 wildtype mice. Brains were immediately taken, 110 µm thick organotypic brain slices prepared and cultured for 1 or 14 days. We observed that red PKH26+ fluorescent platelets were localized in collagen IV and Lectin-649 counterstained cortical brain vessels and that platelets from AD mice severely damaged cortical brain vessels in wildtype mice and entered the brain parenchyma. Confocal microscopy showed immunoreactivity for matrix metalloproteinases (MMP-2 and MMP-9) and beta-amyloid around these platelets. The effect was completely inhibited with an MMP inhibitor. Furthermore, isolated AD platelets caused inflammation and activated microglia around the site where platelets damaged cortical brain vessels. We conclude that AD-derived platelets more aggressively damage healthy vessels which may consequently play a role in the progression of cerebral amyloid angiopathy in AD.

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signaling

“…Slices from adult APP_SweDI mice have been found to express L-type calcium channels and substance P around amyloid plaques, pointing to altered angiogenesis at this key pathological site (35). Another study demonstrated that platelets from an AD mouse model damage healthy cortical vessels and induced Aβ accumulation when infused into wildtype OBSC vessels (28). Here we report, for the first time, pathological sprouting angiogenesis in OBSCs from an AD mouse model that is dependent on BACE1 processing of APP.…”

“…Crucially, OBSCs provide a 3dimensional culture system that supports the formation of new blood vessels and are amenable to pharmacological manipulation, live imaging and repeated measurements (23)(24)(25)(26). We and others have previously shown that OBSCs are powerful tools for investigating the progression of AD-like alterations including Aβ accumulation (27), synaptic disruption (24) and cerebrovascular damage (28).…”

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signalling

“…This study took advantage of the OBSC system to explore mechanisms of pathological angiogenesis that are difficult to study in vivo. OBSCs are a potent, underused tool for exploring vascular phenotypes 23,36,37 with few prior studies seeking to explore this in combination with AD models 32,38 . Interestingly, the increased sprouting angiogenesis we observed in TgCRND8 OBSCs is more pronounced than we find in vivo at a similar age.…”

“…Crucially, OBSCs provide a three-dimensional culture system that supports the formation of new blood vessels and are amenable to pharmacological manipulation, live imaging and repeated measurements without interference from peripheral systems [26][27][28][29] . We and others have previously shown that OBSCs are powerful tools for investigating the progression of AD-like alterations including Aβ accumulation 30 , synaptic disruption 27,31 and cerebrovascular damage 32 .…”

Platelets in Amyloidogenic Mice Are Activated and Invade the Brain

“…In the context of brain aging and neurodegeneration, bloodderived elements with therapeutic potential are platelets. Platelets have repeatedly been hypothesized to play a role in AD pathology (Li et al, 1998;Evin et al, 2003), in particular, in cerebral amyloid angiopathy (CAA) (Gowert et al, 2014;Jarre et al, 2014;Donner et al, 2016;Kniewallner et al, 2016Kniewallner et al, , 2018. Platelets are small anuclear blood cells, which store a plethora of bioactive factors in specialized cytoplasmic compartments (Rumbaut and Thiagarajan, 2010).…”