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Consequences of SUR2[A478V] Mutation in Skeletal Muscle of Murine Model of Cantu Syndrome.

ABSTRACT: (1) Background: Cantu syndrome (CS) arises from gain-of-function (GOF) mutations in the ABCC9 and KCNJ8 genes, which encode ATP-sensitive K⁺ (KATP) channel subunits SUR2 and Kir6.1, respectively. Most CS patients have mutations in SUR2, the major component of skeletal muscle KATP, but the consequences of SUR2 GOF in skeletal muscle are unknown. (2) Methods: We performed in vivo and ex vivo characterization of skeletal muscle in heterozygous SUR2[A478V] (SUR2^wt/AV) and homozygous SUR2[A478V] (SUR2^AV/AV) CS mice. (3) Results: In SUR2^wt/AV and SUR2^AV/AV mice, forelimb strength and diaphragm amplitude movement were reduced; muscle echodensity was enhanced. KATP channel currents recorded in Flexor digitorum brevis fibers showed reduced MgATP-sensitivity in SUR2^wt/AV, dramatically so in SUR2^AV/AV mice; IC₅₀ for MgATP inhibition of KATP currents were 1.9 ± 0.5 × 10^-5 M in SUR2^wt/AV and 8.6 ± 0.4 × 10^-6 M in WT mice and was not measurable in SUR2^AV/AV. A slight rightward shift of sensitivity to inhibition by glibenclamide was detected in SUR2^AV/AV mice. Histopathological and qPCR analysis revealed atrophy of soleus and tibialis anterior muscles and up-regulation of atrogin-1 and MuRF1 mRNA in CS mice. (4) Conclusions: SUR2[A478V] "knock-in" mutation in mice impairs KATP channel modulation by MgATP, markedly so in SUR2^AV/AV, with atrophy and non-inflammatory edema in different skeletal muscle phenotypes.

SUBMITTER: Scala R

PROVIDER: S-EPMC8307364 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Cantu syndrome (CS) is characterized by multiple vascular and cardiac abnormalities including vascular dilation and tortuosity, systemic hypotension, and cardiomegaly. The disorder is caused by gain-of-function (GOF) mutations in genes encoding pore-forming (Kir6.1, KCNJ8) and accessory (SUR2, ABCC9) ATP-sensitive potassium (KATP) channel subunits. However, there is little understanding of the link between molecular dysfunction and the complex pathophysiology observed, and there is no known treatment, in large part due to the lack of appropriate preclinical disease models in which to test therapies. Notably, expression of Kir6.1 and SUR2 does not fully overlap, and the relative contribution of KATP GOF in various cardiovascular tissues remains to be elucidated. To investigate pathophysiologic mechanisms in CS we have used CRISPR/Cas9 engineering to introduce CS-associated SUR2[A478V] and Kir6.1[V65M] mutations to the equivalent endogenous loci in mice. Mirroring human CS, both of these animals exhibit low systemic blood pressure and dilated, compliant blood vessels, as well dramatic cardiac enlargement, the effects being more severe in V65M animals than in A478V animals. In both animals, whole-cell patch-clamp recordings reveal enhanced basal KATP conductance in vascular smooth muscle, explaining vasodilation and lower blood pressure, and demonstrating a cardinal role for smooth muscle KATP dysfunction in CS etiology. Echocardiography confirms in situ cardiac enlargement and increased cardiac output in both animals. Patch-clamp recordings reveal reduced ATP sensitivity of ventricular myocyte KATP channels in A478V, but normal ATP sensitivity in V65M, suggesting that cardiac remodeling occurs secondary to KATP overactivity outside of the heart. These SUR2[A478V] and Kir6.1[V65M] animals thus reiterate the key cardiovascular features seen in human CS. They establish the molecular basis of the pathophysiological consequences of reduced smooth muscle excitability resulting from SUR2/Kir6.1-dependent KATP GOF, and provide a validated animal model in which to examine potential therapeutic approaches to treating CS.

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Consequences of SUR2[A478V] Mutation in Skeletal Muscle of Murine Model of Cantu Syndrome.

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