Postsynaptic density-95 scaffolding of Shaker-type K⁺ channels in smooth muscle cells regulates the diameter of cerebral arteries.

Non-Technical Summary  Shaker-type potassium channels are found on the smooth muscle cells of blood vessels in the brain and are important in keeping the blood vessels open or dilated. We show that a protein called PSD95, previously found in nerve cells, interacts with these potassium channels. PSD95 may act as a scaffold to ensure that the potassium channels are expressed in adequate numbers and in the right location on the smooth muscle cells. When we reduced the number of PSD95 proteins, we saw that the potassium channels were also reduced and the blood vessels were not as dilated compared to blood vessels with normal amounts of PSD95. This research may help us understand how abnormal constriction of blood vessels in the brain occurs in diseases such as high blood pressure and stroke. Abstract  Postsynaptic density-95 (PSD95) is a 95 kDa scaffolding molecule in the brain that clusters postsynaptic proteins including ion channels, receptors, enzymes and other signalling partners required for normal cognition. The voltage-gated, Shaker-type K+ (KV1) channel is one key binding partner of PSD95 scaffolds in neurons. However, KV1 channels composed of α1.2 and α1.5 pore-forming subunits also are expressed in the vascular smooth muscle cells (cVSMCs) of the cerebral circulation, although the identity of their molecular scaffolds is unknown. Since α1.2 contains a binding motif for PSD95, we explored the possibility that cVSMCs express PSD95 as a scaffold to promote KV1 channel expression and cerebral vasodilatation. Cerebral arteries from Sprague–Dawley rats were isolated for analysis of PSD95 and KV1 channel proteins. PSD95 was detected in cVSMCs and it co-immunoprecipitated and co-localized with the pore-forming α1.2 subunit of the KV1 channel. Antisense-mediated knockdown of PSD95 profoundly reduced KV1 channel expression and suppressed KV1 current in patch-clamped cVSMCs. Loss of PSD95 also depolarized cVSMCs in pressurized cerebral arteries and induced a strong constriction associated with a loss of functional KV1 channels. Our findings provide initial evidence that PSD95 is expressed in cVSMCs, and the KV1 channel is one of its important binding partners. PSD95 appears to function as a critical ‘dilator’ scaffold in cerebral arteries by increasing the number of functional KV1 channels at the plasma membrane.