Fig. 4

β-arrestin 1 is required for β2AR-mediated fiber size hypertrophy. (a) Representative immunohistochemistry images of MHC isoforms were presented from EDL, soleus, and plantaris muscles from WT and βarr1KO mice treated by vehicle or clenbuterol (1 mg/kg/day) for four weeks. Multicolor immunohistochemistry was performed with primary antibodies against MHC I (BA-F8), MHC IIa (SC-71, 2F7), MHC IIb (BF-F3), and polyclonal dystrophin. Staining was visualized simultaneously using Alexa Fluor 488 anti-mouse IgG2a (BF-F3, MHC IIb, Green), Alexa Fluor 568 anti-mouse IgG1 (SC-71, MHC IIa, Red), Alexa Fluor 647 anti-mouse IgG2b (BA-F8, MHC I, Purple), and Alexa Fluor 405 anti-rabbit (dystrophin, Blue). Fiber size of MHC I, IIa, IIb, and IIx was measured and presented as a fold increase over vehicle stimulation for EDL (b), soleus (c), and plantaris (d). Data shown represent the means ± SEM from 6 to 8 mice per group. Statistical comparison was performed by using a two-way ANOVA with Tukey’s multiple comparison test (*, P < 0.05; **, p < 0.01; ***, P < 0.001)