Glutamate 73 Promotes Anti-arrhythmic Effects of Voltage-Dependent Anion Channel Through Regulation of Mitochondrial Ca2+ Uptake

Abstract

Mitochondria critically regulate a range of cellular processes including bioenergetics, cellular metabolism, apoptosis, and cellular Ca2+ signaling. The voltage-dependent anion channel (VDAC) functions as a passageway for the exchange of ions, including Ca2+, across the outer mitochondrial membrane. In cardiomyocytes, genetic or pharmacological activation of isoform 2 of VDAC (VDAC2) effectively potentiates mitochondrial Ca2+ uptake and suppresses Ca2+ overload-induced arrhythmogenic events. However, molecular mechanisms by which VDAC2 controls mitochondrial Ca2+ transport and thereby influences cardiac rhythmicity remain elusive. Vertebrates express three highly homologous VDAC isoforms. Here, we used the zebrafish tremblor/ncx1h mutant to dissect the isoform-specific roles of VDAC proteins in Ca2+ handling. We found that overexpression of VDAC1 or VDAC2, but not VDAC3, suppresses the fibrillation-like phenotype in zebrafish tremblor/ncx1h mutants. A chimeric approach showed that moieties in the N-terminal half of VDAC are responsible for their divergent functions in cardiac biology. Phylogenetic analysis further revealed that a glutamate at position 73, which was previously described to be an important regulator of VDAC function, is sevolutionarily conserved in VDAC1 and VDAC2, whereas a glutamine occupies position 73 (Q73) of VDAC3. To investigate whether E73/Q73 determines VDAC isoform-specific anti-arrhythmic effect, we mutated E73 to Q in VDAC2 (VDAC2E73Q) and Q73 to E in VDAC3 (VDAC3Q73E). Interestingly, VDAC2E73Q failed to restore rhythmic cardiac contractions in ncx1 deficient hearts, while the Q73E conversion induced a gain of function in VDAC3. In HL-1 cardiomyocytes, VDAC2 knockdown diminished the transfer of Ca2+ from the SR into mitochondria and overexpression of VDAC2 or VDAC3Q73E restored SR-mitochondrial Ca2+ transfer in VDAC2 deficient HL-1 cells, whereas this rescue effect was absent for VDAC3 and drastically compromised for VDAC2E73Q. Collectively, our findings demonstrate a critical role for the evolutionary conserved E73 in determining the anti-arrhythmic effect of VDAC isoforms through modulating Ca2+ cross-talk between the SR and mitochondria in cardiomyocytes.

Changes of urinary proteome in rats after intragastric administration of calcium gluconate

“…VDAC1 expression is up-regulated by elevated calcium ion levels [26] . VDAC1 and VDAC2 are differential proteins, and the voltage-dependent anion channel (VDAC) acts as a channel for the exchange of ions (including Ca2+) across the outer mitochondrial membrane [49] . The FC for VDAC2 was 6.2 with a P value of 0.037.…”

STING Suppresses Mitochondrial VDAC2 to Govern RCC Growth Independent of Innate Immunity

“…Furthermore, in STING and VDAC2 double‐depleted A498 cells, compared with WT‐VDAC2/WT‐STING, reconstitution with WT‐VDAC2/CACA‐STING (Figure S4N , Supporting Information) showed an increased mitochondrial calcium level due to the inability of CACA‐STING in binding and suppressing VDAC2 (Figure S4O , Supporting Information). On the other hand, E84Q‐VDAC2 was reported to be deficient in transporting calcium into mitochondria [ 47 ] and WT‐STING/E84Q‐VDAC2 reconstitution showed WT‐STING failed to bind and suppress E84Q‐VDAC2 induced reduction in mitochondrial calcium levels (Figure S4O , Supporting Information). These data further support the importance of STING/VDAC2 interactions in governing mitochondrial calcium homeostasis.…”

Mitochondrial Ion Channels

“…These studies revealed a transmembrane pore region composed of a 19-stranded β-barrel with an N-terminal α-helix lining the pore. The main differences among the three isoforms consist of (a) the absence of glutamate 73, recently linked to the ability of VDAC2 to control calcium flux across the OMM (201), in VDAC3, and (b) the presence of six cysteines in VDAC3 (54), proposed to confer an oxidative stress sensor function to this isoform (180,266). Thus, although the isoforms are structurally quite similar, subtle primary sequence differences may facilitate isoform-specific roles (e.g., 140,182).…”