Ryr2-Mediated Calcium Signals Specifically Promote Glucose Oxidation via Pyruvate Dehydrogenase.

J Biol Chem. 2016 Nov 4;291(45):23490-23505. Epub 2016 Sep 12.
Bround MJ, Wambolt R, Cen H, Asghari P, Albu RF, Han J, McAfee D, Pourrier M, Scott NE, Bohunek L, Kulpa JE, Chen SW, Fedida D, Brownsey RW, Borchers CH, Foster LJ, Mayor T, Moore ED, Allard MF, Johnson JD.

Cardiac ryanodine receptor (Ryr2) Ca2+ release channels and cellular metabolism are both disrupted in heart disease. Recently, we demonstrated that total loss of Ryr2 leads to cardiomyocyte contractile dysfunction, arrhythmia, and reduced heart rate. Acute total Ryr2 ablation also impaired metabolism, but it was not clear whether this was a cause or consequence of heart failure in this model. Previous in vitro studies have revealed that Ca2+ flux into the mitochondrial can help pace oxidative metabolism, but there is limited in vivo evidence supporting this model. Here, we studied heart specific, inducible Ryr2 haploinsufficiency (cRyr2Δ50) mice with a stable 50% reduction in Ryr2 protein. This manipulation decreased the amplitude and frequency of cytosolic and mitochondrial Ca2+ signals in isolated cardiomyocytes, without changes in cardiomyocyte contraction. Remarkably, in the context of well-preserved contractile function in perfused hearts, we observed decreased glucose oxidation, but not fat oxidation, with increased glycolysis. cRyr2Δ50 hearts exhibited hyper-phosphorylation and inhibition of pyruvate dehydrogenase, the key Ca2+-sensitive gatekeeper to glucose oxidation. Metabolomic, proteomic, and transcriptomic analyses revealed additional functional networks associated with altered metabolism in this model. These results demonstrate that Ryr2 controls mitochondrial Ca2+ dynamics and plays a specific, critical role in promoting glucose oxidation in cardiomyocytes. Our findings indicate partial RYR2 loss is sufficient to cause metabolic abnormalities seen in heart disease.