Islet

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islet calcium

 

 Molecular Endocrinology Group.

Researchers:

- Stefanie Geisler

- Noelia Jacobo Piqueras

- Tamara Theiner

- Petronel Tuluc

Internal Collaborators:

Jörg Striessnig

Alexandra Koschak

-CavX

Group picture

 

 

AIM

In many excitable cells plasma membrane depolarization leads to the activation of High Voltage-gated Calcium Channels (HVCC) increasing the cytosolic calcium concentration. Depending on the cell type, the higher intracellular calcium levels are translated into an effector function like muscle contraction, synaptic transmission, or hormone release. HVCCs are transmembrane protein complexes formed by the pore-forming α1 subunit and the auxiliary intracellular β, extracellular/transmembrane α2δ and, in certain cell types the transmembrane g subunits. Based on their unique biophysical properties and pharmacological profile the HVCC α1 subunits are classified in L-type (CaV1.1, CaV1.2, CaV1.3, CaV1.4), P/Q- (CaV2.1), N-(CaV2.2) and R-type (CaV2.3). While certain cell types like skeletal and cardiac muscle or retina express exclusively only one isoform, the endocrine cells like pancreatic β-cells or chromaffin cells of the adrenal medulla express at least 4 different isoforms each.

The Tuluc lab is interested in functional properties and physiological role of high voltage-gated calcium channels (HVCC) isoforms in endocrine cells where they play a key role in hormone synthesis and release.

 

 

Methods

The lab utilizes a combination of electrophysiological, molecular, biochemical and immunofluorescent methods. To understand the HVCC structure-function properties we express the channels in heterologous systems where the properties of the channel can be studied under defined and simplified conditions. The physiological role of the channel in hormone release is investigated in native micro organs (pancreatic islets) or isolated primary cells (pancreatic β-cells or adrenal medulla chromaffin cells) obtained from either wild-type mice or genetically modified mouse models.

 

Currently, our lab focuses on three research topics:

  1. Role of CaV1.3 L-type calcium channel in β-cell survival and function.
  2. Sex differences in pancreatic β-cell function.
  3. Role of auxiliary subunits in chromaffin cells.

 

  1. Role of CaV1.3 L-type calcium channel in β-cell survival and function (Tamara).

Mouse pancreatic β-cells express several high voltage activated (HVCC) calcium channels. Based on their pharmacological properties, the β-cells HVCC channels can be separated in: ~50% LTCC, ~25% CaV2.3, and ~10-15% CaV2.1. Many studies indicated that the pancreatic β-cells express two LTCC - CaV1.2 and CaV1.3 α1 subunits. Due to the high CaV1.3 mRNA copy number present in pancreatic β-cells initially it was thought that the main molecular entity responsible for the β-cell L-type calcium currents is CaV1.3. Nevertheless, several independent studies using different knock-out mouse models seem to contradict this conclusion. However, genetic polymorphisms in CACNA1D gene encoding for CaV1.3 channels have been associated with increased susceptibility for type 2 diabetes in humans. Despite that, the physiological role of CaV1.3 in β-cell function and development remains poorly understood. In this project we aim to investigate the effect of CaV1.3 deletion on postnatal survival and proliferation of β-cells and . 

 

  1. Sex differences in pancreatic β-cell function (Noelia).

The etiology of type 2 diabetes mellitus (T2DM) involves the deregulation and un-synchronization of insulin secretion from pancreatic β-cells and insulin sensitivity in the peripheral tissues. The incidence of T2DM in humans has a clear sexual dimorphism with diabetes and impaired fasting glycaemia being more common in men than in women. Recently we demonstrated that genetic deletion of α2δ-1 HVCC subunit in mice leads to diabetes in a sex-specific manner (Mastrolia et al. 2017, Diabetes). Although the insulin sensitivity was similar in males and females, the higher insulin release in females partially alleviated the diabetes phenotype in α2δ-1 KO mice. In the current project we aim to identify the molecular mechanisms responsible for the higher insulin release in females compared to males.

 

  1. Role of auxiliary subunits in chromaffin cells (Steffi).

Chromaffin cells (CCs) of the adrenal medulla are neuroendocrine cells that secrete catecholamines into the general circulation in response to stress. The release of adrenaline from CCs is controlled by the sympathetic nervous system. Acetylcholine released from the splanchnic nerve terminals close to CCs activates the nicotinic receptor depolarizing the membrane and triggering the opening of the voltage gated calcium channels. Mammalian CCs express all types of high voltage gated calcium channels (HVCC) (L-, N-, P/Q-, R- and T-type) with CaV1.2, CaV2.1 and CaV2.3 being dominant. Similar to pancreatic β-cells, HVCC activation also shapes the electrical activity of mouse chromaffin cells (MCCs) and controls catecholamine release. In this project we analyze how HVCC subunits modulate calcium influx and therefore cathecholamines release.

 

Selected publications:

  1. Calorio, C., D. Gavello, L. Guarina, C. Salio, M. Sassoe-Pognetto, C. Riganti, F. T. Bianchi, N. T. Hofer, P. Tuluc, G. J. Obermair, P. Defilippi, F. Balzac, E. Turco, G. C. Bett, R. L. Rasmusson, and E. Carbone. 2019. Impaired chromaffin cell excitability and exocytosis in autistic Timothy syndrome TS2-neo mouse rescued by L-type calcium channel blockers. The Journal of physiology 597:1705-1733.
  2. Pinggera, A., G. Negro, P. Tuluc, M. J. Brown, A. Lieb, and J. Striessnig. 2018. Gating defects of disease-causing de novo mutations in Cav1.3 Ca(2+) channels. Channels (Austin) 12:388-402.
  3. Monteleone, S., A. Lieb, A. Pinggera, G. Negro, J. E. Fuchs, F. Hofer, J. Striessnig, P. Tuluc, and K. R. Liedl. 2017. Mechanisms Responsible for omega-Pore Currents in Cav Calcium Channel Voltage-Sensing Domains. Biophysical journal 113:1485-1495.
  4. Mastrolia, V., S. M. Flucher, G. J. Obermair, M. Drach, H. Hofer, E. Renstrom, A. Schwartz, J. Striessnig, B. E. Flucher, and P. Tuluc. 2017. Loss of alpha2delta-1 Calcium Channel Subunit Function Increases the Susceptibility for Diabetes. Diabetes 66:897-907.
  5. Tuluc, P., V. Yarov-Yarovoy, B. Benedetti, and B. E. Flucher. 2016. Molecular Interactions in the Voltage Sensor Controlling Gating Properties of CaV Calcium Channels. Structure 24:261-271.
  6. Tuluc, P., B. Benedetti, P. Coste de Bagneaux, M. Grabner, and B. E. Flucher. 2016. Two distinct voltage-sensing domains control voltage sensitivity and kinetics of current activation in CaV1.1 calcium channels. The Journal of general physiology 147:437-449.
  7. Pinggera, A., A. Lieb, B. Benedetti, M. Lampert, S. Monteleone, K. R. Liedl, P. Tuluc, and J. Striessnig. 2015. CACNA1D de novo mutations in autism spectrum disorders activate Cav1.3 L-type calcium channels. Biol Psychiatry 77:816-822.
  8. Azizan, E. A., H. Poulsen, P. Tuluc, J. Zhou, M. V. Clausen, A. Lieb, C. Maniero, S. Garg, E. G. Bochukova, W. Zhao, L. H. Shaikh, C. A. Brighton, A. E. Teo, A. P. Davenport, T. Dekkers, B. Tops, B. Kusters, J. Ceral, G. S. Yeo, S. G. Neogi, I. McFarlane, N. Rosenfeld, F. Marass, J. Hadfield, W. Margas, K. Chaggar, M. Solar, J. Deinum, A. C. Dolphin, I. S. Farooqi, J. Striessnig, P. Nissen, and M. J. Brown. 2013. Somatic mutations in ATP1A1 and CACNA1D underlie a common subtype of adrenal hypertension. Nat Genet 45:1055-1060.
  9. Tuluc, P., N. Molenda, B. Schlick, G. J. Obermair, B. E. Flucher, and K. Jurkat-Rott. 2009. A CaV1.1 Ca2+ channel splice variant with high conductance and voltage-sensitivity alters EC coupling in developing skeletal muscle. Biophysical journal 96:35-44.
  10. Tuluc, P., G. Kern, G. J. Obermair, and B. E. Flucher. 2007. Computer modeling of siRNA knockdown effects indicates an essential role of the Ca2+ channel alpha2delta-1 subunit in cardiac excitation-contraction coupling. Proceedings of the National Academy of Sciences of the United States of America 104:11091-11096.

 

Full publication list (Pubmed search)

 

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