Pericytes in chronic lung disease.

Pericytes are mesenchymal cells embedded within the abluminal surface of the endothelium of microvessels such as capillaries, pre-capillary arterioles, post-capillary and collecting venules, where they maintain microvascular homeostasis and participate in angiogenesis. In addition to their roles in supporting the vasculature and facilitating leukocyte extravasation, pericytes have been recently investigated as a subpopulation of mesenchymal stem cells (MSCs) due to their capacity to differentiate into numerous cell types including the classic MSC triad, i.e. osteocytes, chondrocytes and adipocytes. Other studies in models of fibrotic inflammatory disease of the lung have demonstrated a vital role of pericytes in myofibroblast activation, collagen deposition and microvascular remodelling, which are hallmark features of chronic lung diseases such as asthma, chronic obstructive pulmonary disorder, pulmonary fibrosis and pulmonary hypertension. Further studies into the mechanisms of the pericyte-to-myofibroblast transition and migration to fibrotic foci will hopefully clarify the role of these cells in chronic lung disease and confirm the importance of pericytes in human fibrotic pulmonary disease.