Expression of Fusion Proteins in Different Subpopulations of Cardiac Mitochondria

Background Mitochondrial dynamics including fission and fusion, along with mitophagy, play a vital role in the maintenance of the structural and functional integrity and number of mitochondria in the cell. These processes work to sustain the mitochondrial quality in the cell, in order to ensure optimal functioning of the cell. Mitochondrial fission and fusion are mediated by several proteins; including dynamin‐related 1 and fission protein 1 for fission and, optic atrophy type 1 (OPA1) and mitofusins 1 (Mfn1) and 2 (Mfn2) for fusion. Fusion proteins (OPA1, Mfn1 and Mfn2) promote fusion of two mitochondria into one, thereby eliminating dysfunctional mitochondria and thus, maintaining their normal morphology, content, and function, as well as the quality of the mitochondria in different subcellular compartments. The mitochondria in cardiomyocytes can be categorized in subpopulations based on their structural and physiological differences: subsarcolemmal mitochondria (SSM), which are found underneath the sarcolemma; interfibrillar mitochondria (IFM), localized between the myofibrils; and perinuclear mitochondria, which reside near the nuclear poles. Connexin‐43, a transmembrane protein responsible for the formation of gap junctions, can be used to differentiate between the SSM and IFM. In this project, we aim to study the role of mitochondrial fusion proteins between these two populations of mitochondria. Hypothesis Expression of fusion proteins are different between the SSM and IFM in intact rat hearts. Methods Mitochondria were isolated from Sprague‐Dawley male rat hearts (n=6). Mitochondrial proteins were visualized by SDS‐PAGE followed by western blot analysis using antibodies against OPA1, Mfn1, and Mfn2. Results The level of connexin‐43 was 95% ( P <0.001) lower in IFM compared to SSM. Analysis of fusion proteins revealed that IFM contained 10% ( P <0.47), 88% ( P <0.001) and 24% ( P <0.31) less OPA‐1, Mfn1 and Mfn2, respectively, when compared to SSM. Short and long isoforms of OPA‐1 were 70% ( P < 0.002) and 32% ( P <0.05) lower in IFM compared to SSM. Conclusion Lower expression of fusion proteins in IFM can explain differences in functional parameters between two mitochondrial subpopulations in the heart. Support or Funding Information Supported by the NHLBI NIH grants SC1HL118669 (S.J.) and 1 R25 HL115473‐01 (R.G‐H.). This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .