Genome-edited zebrafish model of ABCC8 loss-of-function disease

ATP-sensitive potassium channel (

Zebrafish Models of KATP Channelopathies

Much work has been carried out to understand the composition, structure, and function of ATP-sensitive potassium (KATP) channels in mammalian tissues, as well as the molecular basis of the channelopathies that result from loss-of-function or gain-of-function mutations in these channels. These studies have also highlighted that the available pharmacology to treat such diseases is limited. To overcome such limitations, a better understanding of the tissue specificity of expression, the exact mechanisms linking the molecular dysfunction to the development of complex pathophysiology, the potential for reducing cross-reactivity of drugs, and ultimately more specific therapies are needed. The work described in this thesis initially considers zebrafish as a model organism to further understand KATP channel physiology, pathology, and pharmacology. Detailed methods are described to isolate cardiac and vascular myocytes for patch-clamp studies. Using these methods, the molecular make-up and properties of zebrafish atrial, ventricular and vascular smooth muscle KATP channels are described, showing that the subunit expression is the same as in equivalent mammalian tissues, validating zebrafish as relevant models of human Cantu Syndrome. Additional studies reveal previously unrecognized secondary consequences of genetic manipulation of KATP channels – including decreased KATP channel expression in the case of a gain-of-function neonatal diabetes mutation and the up-regulation of an unknown large-conductance ATP-insensitive K+ channel accompanying KATP down-regulation in pancreatic β-cells – providing novel hypotheses that may help to explain associated KATP channelopathies

ABCC9-related intellectual disability Myopathy Syndrome is a KATP channelopathy with loss-of-function mutations in ABCC9

Mutations in genes encoding KATP channel subunits have been reported for pancreatic disorders and Cantú syndrome. Here, we report a syndrome in six patients from two families with a consistent phenotype of mild intellectual disability, similar facies, myopathy, and cerebral white matter hyperintensities, with cardiac systolic dysfunction present in the two oldest patients. Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels. This mutation results in an in-frame deletion of exon 8, which results in non-functional KATP channels in recombinant assays. SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish. We term this channelopathy resulting from loss-of-function of SUR2-containing KATP channels ABCC9-related Intellectual disability Myopathy Syndrome (AIMS). The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of KATP loss- versus gain-of-function