Abstract 83: β1 Vs β2 Adrenergic Signaling Differentially Regulates Mitochondrial Dynamics Through Alterations In Calcineurin And Drp1

Signal transduction through β1 and β2-adrenergic receptors (ARs) is considered a primary mechanism for regulating cardiovascular function and remodeling. Upon β-AR activation (i.e., physical activity, cardiac pathology) inotropy and chonotropy increase and mitochondria must quickly meet increased energy demand. This suggests that βARs and mitochondria are coupled mechanistically to rapidly respond to the functional and energetic needs of the heart. To investigate the role of β1 vs. β2-AR signaling on mitochondrial dynamics, we compared β1-/- and β2-/- to WT controls. β2-/- had increased mitochondrial fragmentation (increased number and decreased size) by electron microscopy vs. both WT and β1-/-. β2-/- showed altered regulation of mitochondrial fission: increased Drp1 translocation to the mitochondria vs. WT, whereas β1-/- had lower Drp1 translocation. These data suggest differential regulation of fission by βAR signaling, β1 activating and β2 suppressing fission. Since Ca2+-dependent calcineurin is known to activate Drp1 and [Ca2+]i is differentially regulated by β-AR signaling, we examined calcineurin as the bridge between β-AR signaling and Drp1 activation. In β2-/-, both Ca2+ transients and calcineurin activity were increased, suggesting β1-AR/Ca2+/calcinurin-mediated fission. To quantify mitochondrial fragmentation and biogenesis, mitotimer-transfected C2C12 cells were treated with the non-specific β-AR agonist isoproterenol resulting in mitochondrial fragmentation that was inhibited by the β1-antagonist CGP 12177 but not by the ß2-antagonist ICI 118551. Taken together, our data indicate that β1 and β2-AR signaling differentially regulate mitochondrial dynamics in the heart through alterations in [Ca2+]i, leading to calcineurin-induced translocation of Drp1.