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Introduction: The blood-brain barrier (BBB) breakdown occurs when the integrity of BBB components is lost as a consequence of ischemic stroke. Perlecan, a major heparan sulfate proteoglycan of basement membranes, is expressed by endothelial cells (ECs) and is adjacent to pericytes (PCs), suggesting supportive functions in the BBB. Recent studies highlight the importance of PCs in the process of repairing BBB functions, which are triggered by the upregulation of platelet-derived growth factor receptor β (PDGFRβ). We hypothesized that perlecan may play a protective role in BBB maintenance through the interaction with PCs during the repair process of the BBB disruption. Methods: We induced a 60-minute middle cerebral artery occlusion (MCAO) in adult conditional perlecan -deficient ( Perlecan -/- -Tg) mice in a C57BL/6 background, which express the perlecan transgene only in cartilage to rescue the perinatal lethality of Perlecan -/- mice. Recombinant perlecan C-terminal domain V (DV) was used for in vitro assays. Results: Perlecan -/- -Tg mice exhibited larger infarct volumes and more BBB leakage than the control mice on post-surgery day (PSD) 2 after MCAO. While the control mice showed increased numbers of PDGFRβ-positive PCs around the ischemic lesion on PSD 3, such upregulation was not observed in Perlecan -/- -Tg mice, suggesting that perlecan may participate in PC activation against the BBB breakdown. In wild-type mice, the expression of integrin α5, a potential receptor for perlecan, was upregulated both in PCs and in ECs in the ischemic lesion. In culture, PCs showed attachment activity to DV through integrin α5β1. DV induced well-assembled actin stress fibers and focal adhesions in PCs and promoted the PC migration induced by PDGF-BB. At molecular level, DV enhanced the PDGF-BB-induced phosphorylation of PDGFRβ, in addition to that of SHP-2 and FAK, suggesting that DV enhanced both PDGFRβ and integrin signaling. Conclusions: These results revealed that perlecan regulates the activation of PCs through the cooperative function of PDGFRβ and integrin α5β1, contributing to the repair process of the BBB. Perlecan DV may provide a potential therapeutic effect, based on a new approach from extracellular matrix to the disrupted BBB in ischemic stroke.

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.