Hypoxia rescues muscle degeneration after chronic or acute inactivation of Rb by inducing glycolysis via HIF-1α. (A) Immunostaining for MHC (green) in the indicated myoblasts induced to differentiate under normoxia or hypoxia treated or not with lonidamine. Note the shortened myotubes in the presence of lonidamine. (B) Representative immunoblot (left) and mean expression of myogenin and MCK normalized for MHC expression (right; n = 3). (C) Rb^f/f myoblasts transduced with Ad.GFP or Ad.Cre and immunoblotted for pRb. Tubulin was used as a loading control. (D) Rb^f/f myoblasts transduced with Ad.GFP or Ad.Cre and immunostained for pRb (red). (insets) DAPI staining for nuclei (blue). (E) Immunostaining for MHC in Rb^f/f myoblasts transduced with Ad.Cre and induced to differentiate in normoxia (top and middle) or hypoxia (bottom). (F, top) Brightfield images of Rb^f/f myoblasts transduced with Ad.EV or Ad.Cre and induced to differentiate under hypoxia. (bottom) Larger view of the boxed field. Arrowheads point to rescued Rb^−/− myotubes. This field is shown in Video 6. (G) Quantification of myotube formation in Rb^f/f myoblasts transduced with Ad.EV or Ad.Cre and induced to differentiate under hypoxia. Counts are mean of six representative fields (n = 3). *, P = 0.004. (H) Quantification of myotube formation in the indicated myoblasts induced to differentiate under the indicated conditions. Myotube counts are the mean of six fields (n = 4). (I) MHC staining (red) of the indicated myoblasts transduced with Ad.NF-κB/HIF-1α and induced to differentiate in normoxia. (J) Quantification of myotube formation in the indicated myoblasts transduced with Ad.EV or Ad.NF-κB/HIF-1α and induced to differentiate in normoxia. Myotube counts are the mean of six fields (n = 3). Error bars represent SD.