Endothelial Adgrl2 Expression and Alternative Splicing Controls the Cerebrovasculature.

Central nervous system development requires parallel but interrelated processes of neural circuit assembly and vascularization. Intersecting between these two processes is the cell-adhesion G-protein coupled receptor Adgrl2. In select neuronal populations, Adgrl2 is localized and control the assembly of specific synaptic sites. In non-neuronal brain cells, Adgrl2 is restricted in expression to endothelial cells. Testing for Adgrl2 function in these cells in mice (of either sex), here we find that endothelial cell-specific Adgrl2 deletion results in an impairment in cerebrovascular integrity. To understand how it might be possible for Adgrl2 to function independently in neuronal and endothelial contexts, we surveyed Adgrl2 transcripts within these cell classes. By analyzing single-cell RNA sequencing datasets, we find that Adgrl2 mRNA is subject to robust cell type-specific alternative splicing that results in distinct isoforms being produced in neurons compared with endothelial cells. To probe the functional significance of this alternative splicing, we forced expression of the neuronal isoform of Adgrl2 in endothelial cells. This resulted in altered cerebrovascular properties including the formation of ectopic glutamatergic synaptic contacts onto endothelial cells, indicating alterations in the cell-cell recognition process. Functionally, in direct contrast to endothelial Adgrl2 deletion, this genetic expression switch instead enhances blood-brain barrier integrity. This overly restrictive cerebrovascular function results in dysregulation of blood to cerebrospinal fluid homeostasis, enlargement of brain ventricles, and a higher risk of hydrocephalus. Thus, alternative splicing serves as a cell type-specific mechanism that provides isoform-specific Adgrl2 for discerning functions controlling neural circuit assembly and cerebrovascular homeostasis.