Functional characterisation of neurovascular components in physiological and pathological conditions

Abstract

Pericytes, which are embedded in the basement membrane of the capillary wall, play important roles in many processes in the brain including blood brain barrier maintenance and angiogenesis. However, there is considerable confusion about the role of pericytes in blood flow regulation due to the lack of a uniform pericyte definition. Increased knowledge of pericyte function will be critical for further understanding of their role in neurovascular coupling and diseases. The aim of this thesis was to identify signalling mechanisms of human brain pericytes since so far the majority of studies described pericytes from other organs and species. In addition, in vivo two-photon imaging of the mouse brain was to be established to study the cells in their native environment. Calcium imaging and patch-clamping were applied to functionally characterise the cells regarding Ca2+ dynamics and electrophysiological properties. The expression pattern of various cell-specific markers, G protein-coupled receptors (GPCRs) and ion channels was measured via RNA-sequencing. Finally, in vivo two-photon imaging was used to visualise pericytes in the mouse brain. The cells responded to GPCR agonists that are known to raise Ca2+ in pericytes with a variety of Ca2+ dynamics. Furthermore, we establish the expression and function of GPCR agonists that have not been linked to pericytes before. The patch-clamp experiments revealed the resting membrane potential, resistance and capacitance of human brain pericytes. The cells expressed a limited number of ion channels conducting small currents, but they seem to play a role in the intracellular Ca2+ signalling cascade. The lack of response to a number of well-established agonists made us sceptical about the identity of the human CNS pericytes. The transcriptomic analysis revealed their real identity and the expression of yet untested GPCRs and ion channels. Finally, different pericyte labelling techniques were established to investigate the location and morphology of pericytes in the mouse brain. Overall, this work contributes to our understanding of Ca2+ signalling dynamics and electrophysiological properties of human vascular cells. We provide evidence that the human CNS pericytes used in this thesis are likely a different vascular-associated cell type, which was recently found in the mouse brain. Lastly, the in vivo imaging technique builds the basis for future studies in the lab investigating the mouse brain microvasculature in health and disease.