New Insights Into the Role of Ca2 Protein Family in Calcium Flux Deregulation in -KO Neurons.

Fragile X syndrome (FXS), the most common form of inherited intellectual disability (ID) and a leading cause of autism, results from the loss of expression of the gene which encodes the RNA-binding protein Fragile X Mental Retardation Protein (FMRP). Among the thousands mRNA targets of FMRP, numerous encode regulators of ion homeostasis. It has also been described that FMRP directly interacts with Ca channels modulating their activity. Collectively these findings suggest that FMRP plays critical roles in Ca homeostasis during nervous system development. We carried out a functional analysis of Ca regulation using a calcium imaging approach in -KO cultured neurons and we show that these cells display impaired steady state Ca concentration and an altered entry of Ca after KCl-triggered depolarization. Consistent with these data, we show that the protein product of the gene, the pore-forming subunit of the Ca2.1 channel, is less expressed at the plasma membrane of -KO neurons compared to wild-type (WT). Thus, our findings point out the critical role that Ca2.1 plays in the altered Ca flux in -KO neurons, impacting Ca homeostasis of these cells. Remarkably, we highlight a new phenotype of cultured -KO neurons that can be considered a novel cellular biomarker and is amenable to small molecule screening and identification of new drugs to treat FXS.