Introduction: The disruption of the blood-brain barrier (BBB) is a contributing factor for the deterioration of brain damages in ischemic stroke. Recent studies revealed that microvascular pericytes are involved in the maintenance of the BBB and in the repair process through platelet-derived growth factor receptor β (PDGFRβ), the expression of which is increased around the ischemic lesion. Here we focus on perlecan, the major heparan sulfate proteoglycan in the basement membrane (BM). It is expressed by endothelial cells in the brain and is implicated in many biological functions. In this report, we have studied the role of Perlecan in the BBB breakdown and in the subsequent repair process after ischemic stroke in a mouse model. We hypothesized that perlecan may play a protective role in the disruption of BBB through the interaction with pericytes after ischemic stroke.
Methods: To elucidate the role of perlecan in the brain vasculature, we induced a 60-minute transient middle cerebral artery occlusion (MCAO) in adult conditional perlecan-deficient (Perlecan-/--Tg) mice, which express the perlecan transgene only in the cartilage to rescue the perinatal lethality of perlecan-deficient mice.
Results: Although the BBB formation and function in the brain vasculature appeared to be unaffected in Perlecan-/--Tg mice under healthy condition, Perlecan-/--Tg mice demonstrated larger infarct volumes and more BBB leakage than control mice on post-surgery day (PSD) 2 after MCAO. Perlecan-/--Tg mice exhibited less PDGFRβ-positive pericytes around the ischemic lesion on PSD 3 to 7 than control mice, suggesting that the perlecan deficiency suppressed pericyte activation. At a mechanistic level, integrin α5, a potential receptor for perlecan, was detectable in both endothelial cells and pericytes in the ischemic lesion, suggesting that endothelial cell-derived perlecan may regulate pericyte activation in response to ischemia through integrin α5.
Conclusions: Our results suggest that perlecan is required for the activation of pericytes and thereby, contributing to the endothelial cell-pericyte integrity in the BBB maintenance after ischemic stroke.