Integrin α4 Overexpression on Rat Mesenchymal Stem Cells Enhances Transmigration and Reduces Cerebral Embolism After Intracarotid Injection.

BACKGROUND AND PURPOSE: Very late antigen-4 (integrin α4ß1)/vascular cell adhesion molecule-1 mediates leukocyte trafficking and transendothelial migration after stroke. Mesenchymal stem cells (MSCs) typically express integrin ß1 but insufficient ITGA4 (integrin α4), which limits their homing after intravascular transplantation. We tested whether ITGA4 overexpression on MSCs increases cerebral homing after intracarotid transplantation and reduces MSC-borne cerebral embolism. METHODS: Rat MSCs were lentivirally transduced to overexpress ITGA4. In vitro transendothelial migration was assessed using a Boyden chamber assay. Male Wistar rats intracarotidly received 0.5×106 control or modified MSCs 24 hours after sham or stroke surgery. In vivo behavior of MSCs in the cerebral vasculature was observed by intravital microscopy and single-photon emission computed tomography for up to 72 hours. RESULTS: Transendothelial migration of ITGA4-overexpressing MSCs was increased in vitro. MSCs were passively entrapped in microvessels in vivo and occasionally formed large cell aggregates causing local blood flow interruptions. MSCs were rarely found in perivascular niches or parenchyma at 72 hours post-transplantation, but ITGA4 overexpression significantly decreased cell aggregation and ameliorated the evoked cerebral embolism in stroke rats. CONCLUSIONS: ITGA4 overexpression on MSCs enhances transendothelial migration in vitro, but not in vivo, although it improves safety after intracarotid transplantation into stroke rats.

Opposite reactivity of meningeal versus cortical microvessels to the nitric oxide donor glyceryl trinitrate evaluated in vivo with two-photon imaging.

Vascular changes underlying headache in migraine patients induced by Glyceryl trinitrate (GTN) were previously studied with various imaging techniques. Despite the long history of medical and experimental use of GTN, its effects on the brain vasculature are still poorly understood presumably due to low spatial resolution of the imaging modalities used so far. We took advantage of the micrometer-scale vertical resolution of two-photon microscopy to differentiate between the vasodynamic effects of GTN on meningeal versus cortical vessels imaged simultaneously in anesthetized rats through either thinned skull or glass-sealed cranial window. Intermediate and small calibre vessels were visualized in vivo by imaging intravascular fluorescent dextran, and detection of blood flow direction allowed identification of individual arterioles and venules. We found that i.p.-injected GTN induced a transient constriction of meningeal arterioles, while their cortical counterparts were, in contrast, dilated. These opposing effects of GTN were restricted to arterioles, whereas the effects on venules were insignificant. Interestingly, the NO synthase inhibitor L-NAME did not affect the diameter of meningeal vessels but induced a constriction of cortical vessels. The different cellular environment in cortex versus meninges as well as distinct vessel wall anatomical features probably play crucial role in the observed phenomena. These findings highlight differential region- and vessel-type-specific effects of GTN on cranial vessels, and may implicate new vascular mechanisms of NO-mediated primary headaches.