Cell-specific alternative splicing of calcium-dependent secretion activator and coupling to voltage gated Ca V calcium channels

MUSTAFÁ, EMILIO ROMÁN; DAESCHNER, MELISSA; MOSLEY, QUIANA; LOPEZ SOTO, EDUARDO JAVIER

Washington

Congreso; Annual meeting Society for Neurosciences; 2023

Society for Neurosciences

Calcium signals at the nerve terminal are critical for the initiation of transmitter release. Voltage-gated calcium CaV channels are the main source of excitation-dependent calcium increase in nociceptors and CaV channels regulate vesicle exocytosis and release of glutamate and neuropeptides. Interactions of CaV channels and synaptic proteins including the soluble N-ethyl-maleimide-sensitive factor attachment protein receptor (SNAREs) complex have been shown toensure triggering of vesicle exocytosis and transmitter release at central synapses. With few exceptions, studies on the regulation of CaV channels by synapticproteins focus on the role of Syntaxin, Munc18 and SNAP-25, while overlooking the potential relevance of the calcium-dependent activator protein for secretion1, CAPS1. CAPS1 has been shown to regulate large dense core vesicle exocytosis and it is associated with calcium-dependent release of neuropeptides innociceptors. Here, we present evidence that CAPS1 regulates CaV channels. We used whole-cell patch clamp in voltage clamp mode with 1 mM Ca2+ or 5 mM Ba2+ as charge carrier. We recorded CaV macroscopic currents from tsA201 cells overexpressing CaVα1 subunits with required auxiliary subunits β3, α2δ1, andeGFP with or without CAPS1. The experimenter was blinded to conditions until post-analyses. We found that CaV2.2 and CaV3.2 currents, but not CaV1.2 currents,were ~66% and ~40% upregulated when CAPS1 was co-expressed, in comparison with control conditions without CAPS1. These findings suggest a role forCAPS1 in coupling with CaV channels to contribute to calcium-dependent vesicle exocytosis. We therefore characterized CAPS1 expression by performingtranscriptomic and western blot analysis of genetically identified sensory neurons from mice and we found cell-specific spliced CAPS1 isoforms in nociceptors.Spliced CAPS1 isoforms containing exon 16a are enriched in peptidergic nociceptors (50.75 ± 2.37%, p=0.0001) in comparison to non-peptidergic nociceptors(24.05 ± 0.64%) and low-threshold mechanoreceptors (1.62 ± 0.64%). Having established the precise spliced CAPS1 isoforms expressed in nociceptors, we areanalyzing CAPS isoform and CaV channel interactions to link these analyses directly to transmitter release. Given the impact of alternative splicing of synapticproteins in the brain, we argue that cell-specific spliced CAPS1 isoforms regulate cell-specific CaV channel function for neuropeptide release in nociceptors.