CaV1.3 Ca2+ channel in pancreatic ß-cell function and mass

Type 2 diabetes mellitus (T2DM) is caused by insufficient insulin secretion from pancreatic ß-cells or reduced insulin effects in the peripheral tissues. Glucose metabolism in pancreatic ß-cell leads to membrane depolarisation that activates the High Voltage-gated Calcium Channels (HVCCs). HVCC calcium influx increases electrical activity and intracellular calcium concentration triggering insulin release. Additionally, HVCCs are critical for the regulation of gene transcription that controls ß-cell differentiation and survival. ß-cells express several HVCC isoforms with CACNA1D gene encoding for CaV1.3-a1D being highly expressed in pancreatic islets of both mice and men. In humans CACNA1D polymorphisms resulting in channel loss-of-function (LOF) associate with increased susceptibility for Type 2 diabetes (T2DM) while CaV1.3 gain-of-function (GOF) mutations cause hyperinsulinemia and hypoglycaemia. Our unpublished data shows that CaV1.3 deletion in mice led to a 6-fold increase in DNA damage, a 3-fold decrease in proliferation markers, and ~20% reduced ß-cell mass. Functionally, CaV1.3 deletion caused a ~25% reduction in ß-cell calcium influx that resulted in delayed glucose- induced electrical activity with lower action potential frequency. However, the magnitude of the observed changes in calcium influx and electrical activity cannot explain how and why CaV1.3 deletion alters ß-cell mass. Therefore, we hypothesize that in pancreatic ß-cells CaV1.3 channel is coupled to gene transcription regulation. Using four different mouse models and state of the art methods including immunocytochemistry, electrophysiology, single cell RNAseq, and mass spectrometry we will test if either CaV1.3 calcium influx or channel complex is required for activity-dependent gene transcription, whether increasing Ca V1.3 activity alters ß-cell mass and function, and with which proteins CaV1.3 interacts. Identifying how Ca V1.3 LOF and GOF alter gene expression as well as identifying the Ca V1.3-interactome might give us critical clues on how to maintain ß-cell mass in T2DM. The in-depth characterization of the role of Ca V1.3 GOF on ß-cell function and mass will be crucial for understanding the disease aetiology in patients carrying GOF mutations. Additionally, our results will create testable hypotheses for neuroscience where Ca V1.3 GOF has been associated with neurodevelopmental and neurodegenerative disease.