BPS2026 - Rediscovering old friends: Exploiting ancient protein assembly for a novel KATP channelopathy gene therapy

ATP-sensitive potassium (K ATP) channels are octameric complexes of pore-forming Kir6 and regulatory SUR subunits which are key regulators of excitability in many tissues. SUR2 (encoded by ABCC9) is critically important for K ATP function in cardiac and skeletal muscle cells. Loss-of-function (LoF) variants of ABCC9 was recently associated with autosomal recessive ABCC9 -related intellectual disability and myopathy syndrome (AIMS). AIMS variants result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional K ATP channels. Affected individuals exhibit myopathy, a range of neurological abnormalities, and cardiac systolic dysfunction in older patients. No known therapy exists. Building upon recent developments in adeno-associated virus (AAV) mediated gene therapy for other myopathic diseases, we seek to develop a novel SUR2-replacement strategy. As the 4. 5 kb ABCC9 coding region is too large to package within AAV, we have tested whether SUR2 can be split into N- and C-terminal fragments which are able to co-assemble into functional channels. Extensive study of recombinant channels demonstrates that, when co-expressed with Kir6. 2, Split-SUR2 function is essentially identical to full length SUR2 with ATP, ADP, and pharmacological sensitivity retained. Administration of muscle targeted AAV9CK8ₑGFP virus in SUR2-null AIMS mice shows successful transduction of cardiac and skeletal muscle. Electrophysiological studies show that systemic co-administration of AAV9CK8C terminal-SUR2A and AAV9CK8N terminal-SUR2A can partially restore K ATP function in cardiomyocytes in SUR2-null AIMS mice. Ongoing studies seek to determine whether channel recovery can be achieved in skeletal muscle, and whether this Split-SUR2A approach can protect against myopathy. This strategy seeks to exploit the ancestral tendency for SUR2-related proteins to dimerize as a novel therapeutic approach for the orphan disease, AIMS