Mitochondrial Matrix Ca²⁺ Accumulation Regulates Cytosolic NAD⁺/NADH Metabolism, Protein Acetylation, and Sirtuin Expression

Abstract

Mitochondrial calcium uptake stimulates bioenergetics and drives energy production in metabolic tissue. It is unknown how a calcium-mediated acceleration in matrix bioenergetics would influence cellular metabolism in glycolytic cells that do not require mitochondria for ATP production. Using primary human endothelial cells (ECs), we discovered that repetitive cytosolic calcium signals (oscillations) chronically loaded into the mitochondrial matrix. Mitochondrial calcium loading in turn stimulated bioenergetics and a persistent elevation in NADH. Rather than serving as an impetus for mitochondrial ATP generation, matrix NADH rapidly transmitted to the cytosol to influence the activity and expression of cytosolic sirtuins, resulting in global changes in protein acetylation. In endothelial cells, the mitochondrion-driven reduction in both the cytosolic and mitochondrial NAD ؉ / NADH ratio stimulated a compensatory increase in SIRT1 protein levels that had an anti-inflammatory effect. Our studies reveal the physiologic importance of mitochondrial bioenergetics in the metabolic regulation of sirtuins and cytosolic signaling cascades.

Mitochondrial-epigenetic crosstalk in environmental toxicology

“…Cytosolic calcium uptake into the mitochondria communicates cytosolic energy needs to the mitochondria, which stimulates nuclear gene expression responses to drive energy production [65]. Cells respond to environmental cues that trigger calcium mobilization to the cytosol from endoplasmic reticular stores [65].…”

Investigating the Sensitivity of NAD+-dependent Sirtuin Deacylation Activities to NADH

“…Because of this unique enzymatic requirement, sirtuin activity has been linked to the energetic status of the cell, and the mammalian sirtuins have been described as sensors of the NAD ϩ / NADH ratio (43)(44)(45)(46)(47). However, the sensitivity of the latest list of reported mammalian sirtuin deacylation reactions to NADH has not been formally tested.…”

Sirtuin 1 suppresses mitochondrial dysfunction of ischemic mouse livers in a mitofusin 2-dependent manner

“…[4][5][6] Sirtuin1 (SIRT1) deacetylates Lys residues of both histone and nonhistone targets, and is activated in response to fasting and calorie restriction in the liver, a condition inducing autophagy. 7,8 Despite its extramitochondrial localization, SIRT1 appears to affect mitochondrial biogenesis 9 and bioenergetics, 10 but its mechanisms remain elusive. Using isolated hepatocytes, mouse livers, SIRT1-null mice, and human livers, we here demonstrate that I/R depletes livers of SIRT1 and that specific overexpression of SIRT1 mitigates defective autophagy, onset of the MPT, and subsequent hepatocyte death after both in vitro and in vivo I/R.…”