Background The clinical success of stem cell (SC) therapy for myocardial infarction is compromised by poor cardiac homing following systemic delivery. As such therapy may depend on beneficial paracrine effects, it is a further hindrance that little is known about the inflammatory response dynamics within myocardial microcirculation in vivo.
Methods 3D-printed stabilisers were bonded to the beating heart of anaesthetised (ketamine/xylazine) mice to enable confocal intravital imaging of ventricular microcirculation. PE-anti-Gr-1 and APC-anti-CD41 antibodies were injected to label neutrophils and platelets respectively with FITC-BSA enabling blood flow visualisation. In some mice, haematopoietic SCs (HSCs; HPC-7s) were introduced intra-arterially. IR injury was induced by 45 min (reversible) ligation of the LAD artery.
Results Neutrophil adhesion and platelet accumulation were both significantly (p<0.001) and rapidly increased in injured microvessels with platelet accumulation increasing with time. No difference in number or velocity of free-flowing neutrophils was observed. A significant (p<0.05) decrease in functional capillary density was also observed in injured hearts. Although HSC adhesion was not significantly enhanced following injury, a time-dependent increase in adhesion was observed in sham and injured hearts. No significant change in number or velocity of free-flowing HSCs was observed following injury. Interestingly, despite reduced capillary perfusion, approximately 10–20 HSCs were observed trafficking though the heart at each time point throughout reperfusion.
Discussion Intravital microscopy has allowed successful visualisation of the microvascular inflammatory response and HSC homing events in the beating mouse heart post-reperfusion. Subsequent experiments will allow us to assess whether HSC administration can confer vasculoprotection.
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