Next generation calcium channel modulators

University Of Maryland Baltimore, Baltimore MD

Investigators

Linked publications, trials & patents

Abstract

Project Summary Timothy syndrome (TS) is a rare, multisystem disorder caused by a mutation within the CaV1.2 L-type Ca2+ channel. Despite considerable research, treatment for TS remains limited and often results in death in early childhood due to severe long-QT syndrome and cardiac arrythmia. Thus, there is a critical need for increased understanding of pathogenesis, and development of new treatment options for TS. While most TS mutations cause gain-of-function (GOF) effects on the channel, when broken down by channel property the mutations cause a spectrum of biophysical changes, differentially effecting channel activation, voltage-dependent inactivation (VDI) and Ca2+-dependent inactivation (CDI). By CRISPR-generating induced pluripotent stem cell (iPSC) lines harboring multiple distinct TS mutations, we will greatly expand the number and variety of iPSC models available to study pathogenesis and treatment. These models will enable new resolution of the role of CDI, VDI and activation in shaping the cardiac AP in physiological and pathological states, and in modulating drug efficacy, enabling informed decisions on the benefits and limitations of calcium channel blockers (CCBs) in the treatment of TS. Moreover, TS pathogenesis is exquisitely modulated by channel splice variation. In most patients, the mutation occurs within either mutually exclusive exon 8a (TS1) or 8 (TS2), resulting in distinct phenotypes dependent on the distribution and expression level of the affected variant. Splice variation is a critical and often overlooked contributor to pathogenesis, and we propose a complex interplay between channel splicing and TS pathogenesis. We hypothesize that expression of exons 8 and 8a are not uniform across the heart, and that variable expression of a mutant-containing exon leads to increased APD dispersion, and exacerbation of arrhythmogenesis in TS. Moreover, we propose that TS mutations perturb splice expression in the heart. Exploring the complex interplay between TS and splicing represents an important direction for understanding pathogenesis and may provide an opportunity for treatment. We propose that antisense oligonucleotide (ASO) mediated switching between exons 8 and 8a has the potential to significantly improve the cardiac function and life expectancy of TS patients harboring a mutation in either of the 2 alternative exons. By targeting channel splicing, ASOs are predicted to reduce the APD dispersion caused by non-homogeneous splicing, further reducing the arrhythmogenic potential of TS mutations. We will therefore utilize iPSC derived cardiomyocytes harboring TS mutations to reveal the capability of ASOs to overcome the arrhythmogenesis of TS in the context of APD dispersion. Further, we will utilize a newly developed TS2 mouse model to demonstrate the ability of ASOs to rescue the LQT phenotype in-vivo. As non-uniform splice variant distribution is likely to challenge the treatment of any channelopathy in which a mutation is expressed within a mutually exclusive exon, ASOs represent a powerful personalized medicine approach beyond TS.