Endothelial Arf6 sustains capillary electrical signaling and cerebral blood flow through PIP2 regeneration and activation of Kir2.1 channels.

Abstract

Brain capillaries sense neural activity and direct blood flow to active regions--a process termed neurovascular coupling that underlies activity-dependent increases in local perfusion (functional hyperemia). A key contributor to functional hyperemic responses is the capillary endothelial cell (cEC) inward rectifier K+ (Kir2.1) channel, which is activated by neuronal activity-derived extracellular K+ and initiates vasodilatory electrical signals that propagate through the vascular network. Kir2.1 channel function requires continual production of its lipid cofactor, phosphatidylinositol-4,5-bisphosphate (PIP2), and is compromised in mouse models of cerebral small vessel (cSVD). Although decreased PIP2 availability is a common feature of cSVD, mechanisms underlying PIP2 synthesis remain poorly understood. We hypothesized that Arf6, a small GTPase expressed in cECs that stimulates PIP2 production, is critical for this process. Using patch-clamp electrophysiology, we demonstrate that inhibiting Arf6 activity progressively decreased cEC Kir2.1 channel activity. This deficit corresponded to loss of capillary-to-arteriole electrical signaling in isolated vessels and diminished functional hyperemia in vivo. Exogenously provided PIP2 restored Kir2.1 currents and functional hyperemia after Arf6 inhibition or genetic knockdown. Collectively, our data indicate that cEC Arf6 sustains Kir2.1 activity by maintaining PIP2 levels and demonstrate that diminished PIP2 synthesis is sufficient to impair functional hyperemia. Furthermore, we identify Arf6 as a mechanistic link between PIP2 production and endothelial electrical signaling, highlighting Arf6 as a potential therapeutic target for restoring functional hyperemia. Significance StatementActive brain regions send electrical signals through capillaries to dilate upstream arterioles and increase blood flow. The resulting activity-dependent increase in local blood flow (functional hyperemia) is mediated through inward-rectifier potassium (Kir2.1) channels. These channels-- and hence functional hyperemia--require continuous regeneration of the lipid cofactor PIP2 (phosphatidylinositol-4,5-bisphosphate). If PIP2 is deficient, electrical signaling fails--a defect characteristic of models of cerebral small vessel disease and Alzheimers disease. We identify the small GTPase Arf6 as a key to maintaining PIP2 and thus preserving capillary Kir2.1 activity and functional hyperemia. Our findings reveal an important pathway for PIP2 homeostasis and position Arf6 as a cornerstone upholding functional hyperemic responses, highlighting Arf6 as a target for restoring cerebral blood flow in disease.