Participation of Transthyretin in angiogenesis: biological and pathologic involvement

• Autor(a) principal: Saavedra, Joana do Amaral
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30434
• topic: Transthyretin; Alzheimer’s disease; Basement membrane; Angiogenesis; Neuroprotection; Tube formation assay; Chick chorioallantoic membrane assay; Collagen IV

Cerebral vascular dysfunction precedes other pathological hallmarks as the senile plaques (Aβ amyloid deposits) and neurofibrillary tangles in the brains of Alzheimer’s Disease (AD) patients. One of the reported structural vascular alterations in AD is the thickening of the basement membrane (BM) of brain microvessels, as well as alterations in the vessel density. Here we investigated the biological effects of transthyretin (TTR), an established neuroprotective protein in AD, in the vasculature. Using the in vitro tube formation assay we conclude that TTR leads to the formation of capillary like structures in a dose dependent manner and regulates angiogenic molecules such as interleukin (IL)- 6 and Angiopoietin (ANGPT)-2. Further in vivo investigation, using the chick chorioallantoic membrane (CAM) assay confirmed that TTR is a angiogenic molecule, and highlighted that the TTR neovessels are functional. Considering that ours CAM results also showed that Aβ is angiogenic, inducing the formation of functional vessels, we investigated if vascular remodeling, necessary to angiogenesis to occur, was dysregulated by the peptide. BM thickening observed in AD is often measured by quantification of the collagen IV, one of the main BM constituents. Here we show that brain endothelial cells incubated with Aβ oligomers expressed more collagen IV than control cells. This effect was counteracted by TTR, resulting in decreased expression of collagen IV. We also performed ex vivo assays to elucidate the involvement of TTR in the vascular pathology using our transgenic mouse model of AD, established in different TTR genetic backgrounds. We found that 7-months old transgenic AD mice with TTR genetic reduction, AD/TTR+/-, exhibit decreased vessel length as compared to AD/TTR+/+ animals, in the hippocampus. In this work we also compared the BM thickness in 3-months old mice, non -transgenic (NT) and AD with TTR genetic reduction, and concluded that AD/TTR +/- mice present an increased expression of collagen IV relatively to NT/TTR +/- littermates, in the hippocampus. Our results show the in vivo involvement of TTR in angiogenesis and in vascular remodeling, both physiologically and in the context of AD. In the long run, this project can contribute for an AD therapy with the potential to circumvent the amyloid hypothesis and the related failures, so far.