Calcium phosphate precipitation inhibits mitochondrial energy metabolism

Abstract

Early studies have shown that moderate levels of calcium overload can cause lower oxidative phosphorylation rates. However, the mechanistic interpretations of these findings were inadequate. And while the effect of excessive calcium overload on mitochondrial function is well appreciated, there has been little to no reports on the consequences of low to moderate calcium overload. To resolve this inadequacy, mitochondrial function from guinea pig hearts was quantified using several well-established methods including high-resolution respirometry and spectrofluorimetry and analyzed using mathematical modeling. We measured key mitochondrial variables such as respiration, mitochondrial membrane potential, buffer calcium, and substrate effects for a range of mitochondrial calcium loads from near zero to levels approaching mitochondrial permeability transition. In addition, we developed a computer model closely mimicking the experimental conditions and used this model to design experiments capable of eliminating many hypotheses generated from the data analysis. We subsequently performed those experiments and determined why mitochondrial ADP-stimulated respiration is significantly lowered during calcium overload. We found that when calcium phosphate levels, not matrix free calcium, reached sufficient levels, complex I activity is inhibited, and the rate of ATP synthesis is reduced. Our findings suggest that calcium phosphate granules form physical barriers that isolate complex I from NADH, disrupt complex I activity, or destabilize cristae and inhibit NADH-dependent respiration.

Cyclosporin A Increases Mitochondrial Buffering of Calcium: An Additional Mechanism in Delaying Mitochondrial Permeability Transition Pore Opening

“…Though P i plays an essential role in matrix Ca 2+ buffering, P i has also been suggested to induce mPTP opening [52]. A recent study associated Ca 2+ –P i precipitation with complex I inhibition and reduced ATP synthase rate during Ca 2+ overload [53]. Another report demonstrated that increasing [P i ] decreased the mitochondrial Ca 2+ loading capacity [14].…”

Computationally modeling mammalian succinate dehydrogenase kinetics identifies the origins and primary determinants of ROS production

“…Animal care and handling conformed to the National Institutes of Health's Guild for the Care and Use of Laboratory Animals and was approved by Michigan State University's Institutional Animal Care and Use Committee. Mitochondria from Hartley guinea pig ventricular myocytes were isolated based on protocol previously described (22,49,65) and will be briefly summarized here. Animals (4-6 weeks, 350-450 grams) were decapitated after being anesthetized with 5% isoflurane and tested to be unresponsive to noxious stimuli.…”

“…To test the model's ability to simulate ROS production from intact mitochondria, it was integrated into a recent model of oxidative phosphorylation (49). The integrated model was then used to simulate succinate-dependent leak-state and ADP-stimulated respiration and ROS emission reported in an earlier study (22).…”

“…A fully oxidized Q pool and pH 7 were used to calculate the percentages. The SDH ribbon diagram was generated from the crystal structure by Sun et al 3 using PyMOL 49 . *In addition to competing with succinate at the dicarboxylate binding site, oxaloacetate also causes the enzyme to resume an inactive conformation.…”

The Two-Way Relationship Between Calcium and Metabolism in Cancer

“…Most of the evidence to date has attributed this effect to inhibition of mitochondrial dehydrogenases, loss of purine nucleotides, and reduced m (Fagian et al, 1986;Lai et al, 1988;Fink et al, 2017). Moreover, a recent study suggested that inhibition of ETC complex I is the most likely cause of the decrease in OXPHOS through accumulation of mitochondrial Ca 2+ as phosphate precipitates (Malyala et al, 2019).…”