Figure 7. Autophagy-related changes in protein expression and cathepsin L activity during hindlimb unloading (HU) and reloading. Expression of the autophagy-related proteins phospho- and total Ulk1, p62, Atg7, Beclin, and LC3B-II was measured by Western blot and quantified after 14 days of HU and following 3, 7, and 14 days of reloading in the soleus (A) and tibialis anterior (TA) (B) muscles of adult (9 mo, open squares) and old (29 mo, filled squares) rats. Total protein, determined by stain-free imaging of the PVDF membrane, was used to normalize protein expression. Data are expressed as a percentage relative to the adult control group for each protein (n=4-6/group). Cathepsin L activity was measured by fluorometric assay after 14 days of HU and following 3, 7, and 14 days of reloading in the soleus (C) and TA (D) muscles of adult (open squares) and old (filled squares) rats. Data are expressed as a percentage relative to the activity of the adult control group (n=5-6/group). Values are mean ± SEM, *p<0.05 vs adult control, #p<0.05 vs old control, φp<0.05 vs adult at same time point.