Mitochondrial connexin40 regulates mitochondrial calcium uptake in coronary endothelial cells

Abstract

Connexins (Cxs) are a group of integral membrane proteins that can form gap junctions between adjacent cells. Recently, it was reported that Cx43 is expressed not only in the plasma membrane but also in the inner mitochondrial membrane and that it regulates mitochondrial functions. Cx40 is predominantly expressed in vascular endothelial cells (ECs) and plays an important role in the electrical propagation between ECs and endothelial/smooth muscle cells. However, it is unknown whether Cx40 is expressed in the mitochondria and what the role of mitochondrial Cx40 is in endothelial functions. We observed in coronary ECs that Cx40 protein was expressed in the mitochondria, as determined by Western blot and immunofluorescence studies. We found that mouse coronary ECs (MCECs) isolated from Cx40 knockout (Cx40 KO) mice exhibited significantly lower resting mitochondrial calcium concentration ([Ca]) than MCECs from wild-type (WT) mice. After increase in cytosolic Ca concentration ([Ca]) with cyclopiazonic acid, calcium uptake into the mitochondria was significantly attenuated in MCECs from Cx40 KO mice compared with WT MCECs. There was no difference in resting [Ca] and store-operated calcium entry in MCECs from WT and Cx40 KO mice. We also detected a significant decrease in the concentration of mitochondrial reactive oxygen species (ROS) in Cx40 KO MCECs. Cx40 overexpression in ECs significantly increased resting [Ca] level and calcium uptake by mitochondria in response to increased [Ca] and augmented mitochondrial ROS production. These data suggest that mitochondrial Cx40 contributes to the regulation of mitochondrial calcium homeostasis.

Biological Functions of Connexin43 Beyond Intercellular Communication

“…Subsequent to the early landmark discoveries around Cx43, other members of the connexin family have been found to regulate mitochondrial metabolism. For example, the closely related alpha-connexin Cx40 (GJA5) is expressed in mitochondria of coronary endothelial cells and its depletion leads to a decrease in mitochondrial Ca 2+ uptake and ROS concentration [54].…”

Vitamin C and Microvascular Dysfunction in Systemic Inflammation

“…Intriguingly, the stimulated ROS increase is Cx40-dependent, possibly involving a cross-talk between Cx40 and NADPH oxidase [ 74 ]. Thus, Cx40 may not function only as a structural protein in intercellular gap junctions [ 29 , 75 ], but also as a signaling molecule responsible for the H/R-stimulated ROS increase in endothelial cells. Given the reported aggravation by I/R in sepsis-induced inflammatory response [ 41 , 42 ], and the critical roles of NAPDH oxidase in impaired arteriolar vasoconstriction in sepsis and of Cx40 in impaired electrical coupling in endothelial cells exposed to LPS, H/R or LPS+H/R, the possible signaling function of Cx40 warrants further investigation.…”

Myocardial Adaptation in Pseudohypoxia: Signaling and Regulation of mPTP via Mitochondrial Connexin 43 and Cardiolipin

“…MtCx43 import to the IMM of SSM is mediated by the interaction between Cx43 with the heat shock protein 90 (HSP90) and translocase of the outer membrane 20 [109]. The physiological role of mtCx43 is not fully clarified, but some studies support its involvement in the regulation of K + fluxes [112], mitochondrial respiration [113], oxygen consumption [111,112], mitochondrial redox state [114], and in mitochondrial Ca 2+ homeostasis [115] (Figure 1). In this context, it is understandable that mtCx43 is attributed to cardioprotection.…”