Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human induced pluripotent stem cells, neural stem cells and neurons

Abstract

The coupling of the endoplasmic reticulum (ER) with mitochondria modulates neuronal calcium signaling. Whether this link changes with neuronal development is unknown. The current study first determined whether ER calcium stores are similar during development of human neurons, and then tested if the ER/mitochondrial coupling varied with development. The release of ER calcium to the cytosol by the IP₃ agonist bradykinin was determined in human induced-pluripotent stem cells (iPSC), neural stem cells (NSC) and neurons. The concentration dependence for the release of ER calcium was similar at different stages of development. Metabolism changes dramatically with development. Glycolysis is the main energy source in iPSC and NSC whereas mitochondrial metabolism is more prominent in neurons. To test whether the coupling of mitochondria and ER changed with development, bombesin or bradykinin releasable calcium stores (BRCS) were monitored after inhibiting either of two key mitochondrial enzyme complexes: the alpha-ketoglutarate dehydrogenase complex (KGDHC) or the pyruvate dehydrogenase complex (PDHC). Inhibition of KGDHC did not alter BRCS in either iPSC or NSC. Inhibition of PDHC in neurons diminished BRCS whereas decreased KGDHC activity exaggerated BRCS. The latter finding may help understand the pathology of Alzheimer’s disease (AD). BRCS is exaggerated in cells from AD patients and KGDHC is reduced in brains of patients with AD. In summary, a prominent ER/mitochondrial link in neurons is associated with selective mitochondrial enzymes. The ER/mitochondrial link changes with human neuronal development and plausibly links ER calcium changes to AD.