Roles and mechanisms of leptomeningeal collaterals in human distal MCA territory ischemia
Objective: Leptomeningeal collaterals (LMCs) provided hemodynamic support and reperfusion during acute ischemic stroke (AIS). Although regulation details have been deeply acquired from animal models, human cortex may share limited hemodynamic patterns due to larger physical scale that needs further investigation. Approach and Results: We performed 'sequential hierarchical blocking' during awake craniotomy on fourteen human subjects to mimic AIS in middle cerebral artery (MCA) M4 segment territory. Widefield microscope was applied to reveal microcirculation of LMCs. Relative flow rate (RFR) was measured to evaluate the impact of LMCs hierarchy on microcirculation maintenance. Single-cell sequencing and spatial transcriptomics were further performed to analyze the mechanism of different LMCs recruitment abilities. LMCs RFR decreased to 30.75% immediately (95% CI, 6.64 - 54.86%, P < 0.001), and about 80.25% RFR was finally recovered within 5 minutes (95% CI, 55.2 - 105.3%, P = 0.0034) during M4 occlusion. For M5 and pial branches occlusion, RFR decreased to 55.78% with no further recovery (95% CI, 22.50-89.05%, P = 0.014), and 4 in 11 subjects had no valid microcirculation. For subjects with better recruitment ability, the proportion of arteriole is much higher in leptomeninx (76 - 79% vs. 36 - 56%). There were more significant interaction pairs associated with key signaling pathways between arteriole and neuron/astrocyte (TGF-beta signaling pathway, ECM-receptor interaction). Conclusion: Abundant LMCs supported hemodynamic stability during AIS in human subjects. The proportion of arteriole is much higher in leptomeninx for subjects with better recruitment ability. The Active neuron/astrocyte - arteriole interaction may improve LMCs recruitment.