SIRT3 Deacetylates and Activates OPA1 To Regulate Mitochondrial Dynamics during Stress

Abstract

f Mitochondrial morphology is regulated by the balance between two counteracting mitochondrial processes of fusion and fission. There is significant evidence suggesting a stringent association between morphology and bioenergetics of mitochondria. Morphological alterations in mitochondria are linked to several pathological disorders, including cardiovascular diseases. The consequences of stress-induced acetylation of mitochondrial proteins on the organelle morphology remain largely unexplored. Here we report that OPA1, a mitochondrial fusion protein, was hyperacetylated in hearts under pathological stress and this posttranslational modification reduced the GTPase activity of the protein. The mitochondrial deacetylase SIRT3 was capable of deacetylating OPA1 and elevating its GTPase activity. Mass spectrometry and mutagenesis analyses indicated that in SIRT3-deficient cells OPA1 was acetylated at lysine 926 and 931 residues. Overexpression of a deacetylation-mimetic version of OPA1 recovered the mitochondrial functions of OPA1-null cells, thus demonstrating the functional significance of K926/931 acetylation in regulating OPA1 activity. Moreover, SIRT3-dependent activation of OPA1 contributed to the preservation of mitochondrial networking and protection of cardiomyocytes from doxorubicin-mediated cell death. In summary, these data indicated that SIRT3 promotes mitochondrial function not only by regulating activity of metabolic enzymes, as previously reported, but also by regulating mitochondrial dynamics by targeting OPA1.

Sirtuin-3 (SIRT3) Protein Attenuates Doxorubicin-induced Oxidative Stress and Improves Mitochondrial Respiration in H9c2 Cardiomyocytes

“…Importantly, these results suggest that the up-regulation of mitochondrial antioxidant defenses by SIRT3 contributed to the attenuation of DOX-induced ROS formation. DOX also increased the acetylation of OPA1 and disrupted mitochondrial integrity in the cardiomyocyte (25), which could also contribute to ROS production. Although SIRT3 expression maintained mitochondrial integrity in the presence of DOX, increasing SIRT3 expression did not appreciably affect DOXinduced OPA1 acetylation (25), suggesting that alternate mechanisms such as effects on SOD2 also contribute to the protective effect of SIRT3.…”

“…that DOX inhibited SIRT3 expression and that SIRT3 overexpression maintained mitochondrial integrity and prevented DOX-mediated cardiomyocyte death (25,35). The present study confirmed these findings and extended them to show that DOX treatment suppressed cardiac SIRT3 expression in association with increased levels of protein acetylation in the FIGURE 5.…”

“…Although SIRT3-deficient mice are permissive for cardiac hypertrophy (28), which is a risk factor for the development of heart failure, much remains to be learned with respect to the function of SIRT3 in the heart. It was recently reported that overexpression of SIRT3 protected cardiomyocytes from doxorubicin-induced cell death through the activation of OPA1 and the preservation of mitochondrial morphology (25). However, it was not determined whether DOX influences SIRT3 expression or how SIRT3 deficiency influenced DOX-induced ROS production.…”

“…SIRT3 is activated by NAD, which connects mitochondrial protein deacetylation with cellular energy status. SIRT3 also regulates mitochondrial dynamics through the deacetylation and activation of optic atrophy 1 (OPA1) proteins (25). In addition, SIRT3 regulates mitochondrial ROS production as SIRT3-deficient cells have high levels of ROS (26).…”

Mitochondrial Sirtuins and Their Relationships with Metabolic Disease and Cancer

“…Optic atrophy protein 1 (OPA1), a dynamin-related GTPase, mediates the fusion of inner mitochondrial membranes (126). A recent study found that activity of OPA1 is regulated by SIRT3-mediated deacetylation (135). Stress conditions induce OPA1 hyperacetylation, leading to a reduction in its GTPase activity.…”