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Abstract

Evidence from a variety of sources suggests that pericytes have contractile properties and may therefore function in the regulation of capillary blood flow. However, it has been suggested that contractility is not a ubiquitous function of pericytes, and that pericytes surrounding true capillaries apparently lack the machinery for contraction. The present study used a variety of techniques to investigate the expression of contractile proteins in the pericytes of the CNS. The results of immunocytochemistry on cryosections of brain and retina, retinal whole-mounts and immunoblotting of isolated brain capillaries indicate strong expression of the smooth muscle isoform of actin (alpha-SM actin) in a significant number of mid-capillary pericytes. Immunogold labelling at the ultrastructural level showed that alpha-SM actin expression in capillaries was exclusive to pericytes, and endothelial cells were negative. Compared to alpha-SM actin, non-muscle myosin was present in lower concentrations. By contrast, smooth muscle myosin isoforms, were absent. Pericytes were strongly positive for the intermediate filament protein vimentin, but lacked desmin which was consistently found in vascular smooth muscle cells. These results add support for a contractile role in pericytes of the CNS microvasculature, similar to that of vascular smooth muscle cells.

Extracellular matrix and matrix receptors in blood–brain barrier formation and stroke

“…Pericytes provide a substantial but incomplete (approximately 30%) coverage of the endothelium (Mathiisen et al, 2010). They extend processes around capillaries and can contain contractile elements, such as alpha-smooth muscle actin (Allt and Lawrenson, 2001; Bandopadhyay et al, 2001; Peppiatt et al, 2006; Mathiisen et al, 2010). Despite a lot of controversy, pericytes appear to contract and modulate cerebral blood flow in capillaries (Allt and Lawrenson, 2001; Peppiatt et al, 2006).…”

Calcium Signalling in Pericytes

“…The presence of contractile proteins in capillary pericytes is quite controversial and seems to depend upon the vascular bed and their position within the capillary network. For example, smooth muscle myosin is found in capillary pericytes from the heart, diaphragm, pancreas and intestinal mucosa [30] but not in the brain and retina [40]. The contractile activity of the pericytes of midcapillaries is heterogenous and requires further investigation [21].…”

Emerging Roles of Pericytes in the Regulation of the Neurovascular Unit in Health and Disease

“…The primary agreed upon markers under normal conditions include PDGF receptor-β (PDGFR-β), α-smooth muscle actin (αSMA), chondroitin sulfate proteoglycan 4 (NG2), pericytic aminopeptidase N (pAPN), alanyl (membrane) aminopeptidase (CD13), desmin, and regulator of G protein signaling 5 (RGS5)(Bandopadhyay et al, 2001; Armulik et al, 2011a). Depending on the type of blood vessel, resident pericytes display variable expression of contractile proteins such as αSMA.…”

“…Levels of αSMA are elevated in pre-capillary regions as compared to post-capillary regions(Dore-Duffy, 2008; Krueger and Bechmann, 2010). Interestingly, not all populations of pericytes express αSMA, whereas neighboring cells such as vSMCs do express αSMA(Bandopadhyay et al, 2001). …”