Perivascular cells function as mechano-structural sensors of vascular capillaries

A wide range of conditions, including chronic inflammatory diseases and cancer, are characterized by the fibrotic microarchitecture and increased stiffness of collagen type I extracellular matrix. These conditions are typically accompanied by altered vascular function, including vessel leakiness, abnormal capillary morphology and stability. The dynamic cell-matrix interactions that regulate vascular function in healthy tissues have been well documented. However, our understanding of how the gradual mechanical and structural alterations in collagen type I affect vascular homeostasis remains elusive, especially as a function of the interactions between endothelial and perivascular cell with the altered matrix. Here we hypothesized that perivascular cells might function as mechano-structural sensors of the microvasculature by mediating the interaction between endothelial cells and altered collagen type I. To test that, we utilized an organotypic model of perivascular cell-supported vascular capillaries in collagen scaffolds of controlled microarchitecture and mechanics. Our results demonstrate that capillaries cultured in soft reticular collagen exhibited consistent pericyte differentiation, endothelial cell-cell junctions, and barrier function. In contrast, capillaries embedded in stiff and bundled collagen fibrils to mimic a more fibrotic matrix induced abluminal migration of perivascular cells, increased leakage, and marked expression of vascular remodeling and inflammatory markers. These patterns, however, were only observed when endothelial capillaries were engineered with perivascular cells. Silencing of NOTCH3, a mediator of endothelial-perivascular cell communication, largely re-established normal vascular morphology and function. In summary, our findings point to a novel mechanism of perivascular regulation of vascular dysfunction in fibrotic tissues which may have important implications for anti-angiogenic and anti-fibrotic therapies in cancer, chronic inflammatory diseases and regenerative medicine.