Dissecting the Role of Ca2+ Channel Dysfunction in the Pathogenesis of Neurodevelopmental Disorders - Neurodevelopmental disorders (NDD) consist of a varied group of neurological conditions including autism spectrum disorder (ASD). In most cases, the underlying cause of NDD is unknown, making it difficult to dissect the fundamental pathogenic mechanisms. Yet, genome-sequencing studies have identified more than 100 rare protein coding variants which dramatically increase the risk of NDD. Many of these genes are directly involved in Ca2+ entry or encode synaptic components that regulate Ca2+ signaling. Thus, aberrant Ca2+ signaling has emerged as a potential mechanism underlying an important subset of NDD. Notably, 13 distinct components of voltage-gated Ca2+ channels are listed as high- or medium-confidence risk genes on the SFARI ASD Genes database, including the CaV1.2 L-type Ca2+ channel. CaV1.2 channels are critical elements in the brain required for proper electrical signaling, activation of downstream signaling pathways and gene transcription. As such, disruption of these channels has the potential to impair a myriad of neuronal functions. In fact, multiple studies have linked single point mutations in CaV1.2 to a severe, multisystem disorder known as Timothy syndrome (TS), in which patients exhibit neurological deficits including ASD and developmental delay. TS mutations largely increase channel opening, resulting in an increase in Ca2+ flux through the channel. However, the precise impact on channel gating differs between distinct mutations, potentially explaining the variability in symptoms among patients. Our lab has identified a hyperpolarizing shift in channel activation as a consistent feature of CaV1.2 mutations associated with NDD, pointing to a specific kinetic feature of Ca2+ dysregulation underlying NDD. We hypothesize that a left shift in CaV1.2 activation results in increased Ca2+ flux and excitation-transcription coupling, causing neuron-specific changes in membrane protein expression and function, and culminating in an overall increase in excitability. To evaluate this hypothesis, we will probe the impact of TS mutations on neuronal function using a combination of induced pluripotent stem cell (iPSC) derived neurons and transgenic mice. We will evaluate the effect of these mutations on neuronal excitability and consider the crosstalk between altered Ca2+ entry and other Ca2+-dependent proteins, including Ca2+ activated potassium channels. Utilizing patch clamp electrophysiology, quantitative Ca2+ imaging, single-cell RNA sequencing and in-vivo Ca2+ imaging we expect to gain traction on the functional implications of altered Ca2+ entry through the channel. As aberrant Ca2+ signaling may be a recurrent feature of multiple forms of NDD, studying rare mutations with large Ca2+ abnormalities, such as TS, may provide insight into the role of Ca2+ in the pathogenesis of an important subset of NDD.
