Abstract
The development of new blood vessels (capillaries) from existing ones, a process known as angiogenesis, is affected by circadian rhythms, but the role of the vasculature clock in Controlling vascular cells’ cross-communication is not yet known. Molecular clocks in vascular cells have been studied in vitro in the endothelium and in smooth muscle cells. Nevertheless, to date, limited evidence has been presented regarding pericytes, a perivascular cell population. Pericytes are a promising cell source for cell therapy and tissue engineering, being key players in angiogenesis by contributing to vessel maturation and homeostasis. In this thesis, it is presented that primary pericytes express circadian genes and proteins in a circadian manner, after synchronisation. On the contrary, cultured endothelial cells did not display circadian patterns. More crucially, endothelial cells’ circadian rhythms could be induced following contact mediated exposure to synchronised pericytes. A potential mechanism was suggested to be linked to the release/uptake of lactate, a glycolytic by-product known to be a mediator in endothelial cells and pericytes cell-cell interaction. Particularly, lactate patterns were altered in pericytes by the knockdown of the key circadian regulator BMAL1. Moreover, BMAL1 knockdown unduly affected pericytes’ viability, as compared to endothelial cells. In an in vitro angiogenesis assay, when both endothelial cells and pericytes’ clocks were disrupted, an impaired maturation of vessel-like structures was observed. Additionally, a synchronised clock supported a more structured organization of cells around the scaffold pores, and a maturation of vascular structures in a 3D scaffold.
The results presented in this thesis demonstrate that pericytes play a crucial role in regulating circadian rhythms in endothelial cells, and that silencing this system disproportionately affects their pro-angiogenic function. Especially, in perspective of the development of mature vascular structures for tissue engineering applications, the role of circadian rhythms may constitute a critical element for reparative outcomes.