Investigating TREM2-mediated vasculo-protection during chronic mild hypoxia in vivo

Abstract

Cerebrovascular dysfunction, leading to inadequate brain perfusion and oxygenation, is a major contributor to cognitive decline and dementia. Chronic hypoxia is a putative mechanism of vascular-mediated brain damage, particularly in relation to white matter lesions, as demonstrated by human neuroimaging and histopathology studies. Moreover, increasing evidence suggests that microglia, the primary immune cells of the brain parenchyma, may play a key role in modulating cerebrovascular disease outcomes. Indeed, unpublished work from our lab using a model of chronic cerebral hypoperfusion found greater vascular and white matter abnormalities concomitant with reduced microglial-vascular interactions in mice lacking the microglial immunoreceptor triggering receptor expressed on myeloid cells 2 (TREM2). However, the underlying mechanisms remain incompletely understood. Therefore, this project aims to further investigate whether microglial TREM2 signalling contributes to cerebrovascular resilience, and specifically vasculoprotection, focusing on the context of hypoxia. To address this, we are housing mice at 8%O2 to achieve chronic mild hypoxia (CMH). As corroborated by our studies, CMH induces cerebral microbleeds associated with parenchymal fibrinogen leakage in both grey and white matter regions (Figure 1), and is thus a reductionist approach well-suited for examining microglial mechanisms conferring vasculoprotection. Ongoing studies in young (5-6 months) and aged (15-18 months) cohorts are utilising histology and immunostaining to determine the impact of TREM2 deficiency and ageing on CMH-induced phenotypes, with particular focus on profiling microbleed burden, BBB integrity and interactions between microglia and other cell types within the neurovascular unit. Given that TREM2 is a key regulator of microglial metabolism and lipid processing, future work will utilise flow cytometry and spatial lipidomics to characterise microglia and brain lipid metabolism during CMH, thus providing insight into immunometabolic changes that may underpin microglial vasculoprotection in hypoxia. Findings from these studies will increase our understanding of microglia-vascular interactions, which can ultimately be exploited to promote resilience to cerebrovascular and other hypoxia- related pathologies.