Abstract 544: Gja1-20k Uses the Actin Cytoskeleton to Promote Both Mitochondrial Fission and Fusion

Abstract

Connexin (Cx) 43 is encoded by the GJA1 gene and GJA1-20k has been identified as an N-terminal truncation of Cx43 generated endogenously by internal translation initiation in heart and other organs. We’ve previously identified that GJA1-20k, which increases with ischemic injury, can organize actin networks and also is strongly co-localized with mitochondria, utilizing the cytoskeleton to preserve mitochondrial distribution during stress. Mitochondrial distribution and morphology are associated with metabolic function, and thus we are interested in how GJA1-20k affects mitochondrial shape and connectivity. We transfected GFP-tagged GJA1-20k plasmids into HEK293T cells and assessed mitochondrial distribution and morphology by fluorescence microscopy. Mitochondria exposed to GJA1-20k are smaller, more circular, and more distributed than mitochondria exposed to a control plasmid. Quantitative image analysis indicates an increase in mitochondrial count but no increase in mitochondrial area, indicating greater mitochondrial fission in the presence of GJA1-20k. Paradoxically, acute disruption of actin with Latrunculin A decreased mitochondrial count, yet increased mitochondrial area, indicating acute fusion. Mitochondrial fusion was also observed by live cell imaging, and with high doses of GJA1-20k. Latrunculin A did not affect mitochondrial morphology in cells without GJA-20k. Together these data suggest that GJA1-20k, a mitochondrial and actin associated scaffold, has multiple effects on mitochondrial morphology. At baseline GJA1-20k promotes mitochondrial-actin association, promoting fission and cellular distribution. Yet, GJA1-20k also promotes mitochondrial membrane-membrane association that, in the presence of actin disruption, resulting in mitochondrial fusion. These data suggest GJA1-20k not only organizes mitochondria under physiologic conditions, but during ischemia, it promotes mitochondrial fusion, enhancing tissue survival during stress.