Robertson, C. D. | bioRxiv Science

bioRxiv2022

Phosphorylation Determines Whether Neuroligin-3 is at Excitatory or Inhibitory Synapses in Different Regions of the Brain

Neuroligin-3 is a postsynaptic adhesion molecule involved in development, function, and pathologies of synapses in the brain. It is a genetic cause of autism and a potent component of the tumor microenvironment in gliomas. There are four Neuroligins that operate at distinct synapse types, selectively interacting with presynaptic adhesion and postsynaptic scaffold proteins. We investigated the subcellular localization and scaffold specificities of synaptic Neuroligin-3 and demonstrate an unexpected pattern of localization to excitatory synapses in cortical areas, and inhibitory synapses in subcortical areas. Using phosphoproteomics, we identify Neuroligin-3-specific serine phosphorylation in cortex and hippocampus that obstructs a key binding site for inhibitory synapse scaffolds. Using in utero CRISPR/Cas9 knockout and replacement with phosphomimetic mutants, we demonstrate that phosphorylation at this site determines excitatory versus inhibitory synapse localization of Neuroligin-3 in vivo. Our data reveal a mechanism that differentially regulates the balance of Neuroligin-3 between excitatory and inhibitory synapses, adding to our emerging understanding of their role in the development of brain connectivity and associated pathologies.

neuroscience↗

bioRxiv2022

Brain Capillary Pericytes are Metabolic Sentinels that Control Blood Flow through KATP Channel Activity

Capillary pericytes and their processes cover [~]90% of the total length of the brains capillary bed. Despite their abundance, little is known of pericyte function, and their contributions to the control of brain hemodynamics remain unclear. Here, we report that deep capillary pericytes possess a mechanistic energy switch that, when activated by a decrease in glucose, elicits robust KATP channel activation to increase blood flow and protect energy substrate availability. We demonstrate that pharmacological activation of KATP channels profoundly hyperpolarizes capillary pericytes and leads to dilation of upstream penetrating arterioles and arteriole-proximate capillaries covered with contractile pericytes, leading to an increase in local capillary blood flow. Stimulation of a single capillary pericyte with a KATP channel agonist is sufficient to evoke this response, which is mediated via KIR channel-dependent retrograde propagation of hyperpolarizing electrical signals. Genetic inactivation of pericyte KATP channels via expression of a dominant-negative version of KIR6.1 eliminates these effects. Critically, we show that lowering extracellular glucose below 1 mM evokes dramatic KATP channel-mediated pericyte hyperpolarization. Inhibiting glucose uptake by blocking GLUT1 transporters in vivo also activates this energy switch to increase pericyte KATP channel activity, dilate arterioles and increase blood flow. Together, our findings recast capillary pericytes as metabolic sentinels that respond to local energy deficits by robustly increasing blood flow to protect metabolic substrate delivery to neurons and prevent energetic shortfalls.

neuroscience↗