Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Alam, MR.
Mitochondrial Ca2+ homeostasis and its contribution to metabolism-secretion coupling in pancreatic ß-cells
[ Dissertation ] Medical University of Graz; 2013. pp. 88
[OPEN ACCESS]
FullText
- Autor*innen der Med Uni Graz:
- Alam Muhammad Rizwan
- Betreuer*innen:
- Graier Wolfgang
- Malli Roland
- Altmetrics:
- Abstract:
- Mitochondria Ca2+ uptake is an important physiological process which contributes in many cellular functions. In addition to its involvement in the modulation of mitochondrial metabolism and cytosolic Ca2+ homeostasis, it has also emerged as a central hub in many cell survival/death pathways such as apoptosis, necrosis and autophagy. In pancreatic ß-cells, mitochondrial Ca2+ uptake promotes metabolism ¿ secretion coupling by activation of some rate limiting enzymes in the matrix. This accelerates the process of oxidative phosphorylation which generates ATP and other coupling factors necessary for glucose ¿ stimulated insulin secretion (GSIS). Thus transfer of Ca2+ signals from the cytosol to mitochondria plays a crucial role in boosting the oxidative metabolism and any interference with mitochondrial Ca2+ transport may disrupt the metabolism-secretion coupling and compromise GSIS. This study was designed to identify the contribution of recently identified MICU1 and, MCU, along with other putative candidates LETM1 and UCP2 in mitochondrial Ca2+ homeostasis, ATP production and GSIS in clonal pancreatic ß-cells. Using a combination of siRNA ¿ mediated silencing and Ca2+ measurement with FRET ¿ based genetic sensor, we found that MICU1 and MCU are involved in mitochondrial Ca2+ sequestration upon Ca2+ mobilization with both IP3 ¿ generating agonists and plasma membrane depolarization. In contrast, knockdown of UCP2 and LETM1 solely diminished mitochondrial Ca2+ uptake in response to either intracellular Ca2+ release or Ca2+ entry from extracellular side, respectively. Moreover, a simultaneous knockdown of both MICU1 and MCU did not yield any additional effect on mitochondrial Ca2+ response which ruled out the association of these proteins with other pathways of Ca2+ transport. Based on the involvement of MICU1 and MCU in both pathways of Ca2+ uptake, we further explored their role in mitochondrial metabolism and GSIS. Glucose, the major trigger for insulin secretion, induced cytosolic Ca2+ oscillations which were also transferred to mitochondria. However, the silencing of MICU1 and MCU hampered the relay of these Ca2+ transients into the mitochondria. Conversely this was not accompanied by an inhibition or increase of global cytosolic Ca2+ signals. Furthermore glucose ¿ triggered elevation of cytosolic ATP and insulin secretion was also diminished upon suppression of MICU1 and MCU. In summary this data provides convincing evidence about the role of MICU1 and MCU in the physiology of pancreatic ß-cells and makes them a compelling target for therapy to improve the GSIS by modulation of mitochondrial Ca2+ in patients with type 2 diabetes mellitus.