Abstract 1704: Atrogin-1 Ubiquitin Ligase is Upregulated by Doxorubicin, Leading to Muscle Atrophy in Cardiac Myocytes
Background: Doxorubicin(DOX)is a highly effective anti-tumor agent, however its cardiotoxicity causes cardiomyopathy and limits its clinical usage. Recently, muscle atrophy has been demonstrated to be closely associated with the induction of atrogin-1, a striated muscle-specific unbiquitin ligase, in skeletal muscles. Similarly, it has also been proposed that atrogin-1 is a key regulator of the cell size in cardiac myocytes, though pathological significances of atrogin-1 remain to be fully elucidated in cardiovascular diseases. In the present study, we investigated the involvement of atrogin-1 in DOX-induced cardiotoxicity.
Methods and results: DOX (15 mg/kg) was peritoneally administered into 10 week-old male mice and total RNA was prepared from the various kinds of tissues 48 hours after injection. Northernblot analyses demonstrated that DOX-treatment increased atrogin-1 mRNA expression in hearts and skeletal muscles, by 3.6- and 7.0-fold, respectively, but not in brain, liver, and kidney. In cultured cardiomyocytes, DOX treatment (0.1 microM) induced atrigin-1 by 6.5 fold (p<0.05 vs control). Adenoviral transfer of constitutively-active Akt antagonized DOX-mediated induction of atrogin-1. However, DOX did not activate 3.6 kb atrogin-1 promoter that contains the binding sites of FOXO transcriptional factor, a well-known target downstream of Akt, suggesting that DOX induces atrogin-1 in a novel signaling pathway that is sensitive to Akt, but independent of FOXO. The overexpression of atrogin-1, using adenovirus vector, reduced the cell length of short axis by 49 % (p<0.05 vs adenovirus vector expressing beta-galactosidase, a control), without affecting the long axis, as is the case with DOX treatment. These morphological changes were significantly ameliorated by MG132, an inhibitor of ubiquitin proteosome.
Conclusion: These findings suggest that DOX activates ubiquitin proteosome system by inducing atrogin-1 in cardiac myocytes, leading to cardiomyocyte atrophy. These findings propose that atrogin-1 is a therapeutic target against DOX-induced cardiomyopathy.