What is a pericyte?

Abstract

Pericytes, spatially isolated contractile cells on capillaries, have been reported to control cerebral blood flow physiologically, and to limit blood flow after ischaemia by constricting capillaries and then dying. Paradoxically, a recent paper dismisses the idea of pericytes controlling cerebral blood flow, despite confirming earlier data showing a role for pericytes. We show that these discrepancies are apparent rather than real, and depend on the new paper defining pericytes differently from previous reports. An objective definition of different sub-classes of pericyte along the capillary bed is needed to develop novel therapeutic approaches for stroke and disorders caused by pericyte malfunction.

Keywords: Pericyte; blood–brain barrier; capillary; cerebral blood flow; stroke.

Figure 1.

Schematic (reproduced from Hartmann et al. with permission) showing the diversity of pericyte forms, based on imaging of the brain microvasculature in mice expressing fluorescent proteins under control of the NG2 and PDGFRβ promoters.

Figure 2.

(a) NG2-expressing cells on arteriole (smooth muscle cells) and venule from Hill et al. (b) NG2-expressing cells on the microvasculature from Hill et al: arteriole end of the capillary bed is at the left; venule end is at the right. Arrows denote pericytes. Arrow heads denote cells which Hill et al. defines to be smooth muscle cells similar to those in panel a, but which we (and Zimmermann) would define to be pericytes, like the cells labelled with arrows. (Both panels reproduced from Hill et al. with permission; green channel enhanced for clarity).