Fig. 2

Expression of sarcomeric and autophagy-related proteins in wildtype and Hom soleus muscle. a Western blotting revealed no differences in expression of the M-band component myomesin, the Z-disc component α-actinin2, intermediate filaments (desmin), the thick filament component MHC IIa, the muscle damage marker Xin and the molecular chaperone regulator BAG3, whereas the small heat-shock protein HSPB7 showed a striking reduction in Hom mice. GAPDH was used as loading control. b Quantification of the results shown in panel A revealed no significant differences in the expression levels of all analyzed proteins, except for the almost complete absence of HSPB7 in Hom mice (n = 4; p = 0.0286; Mann-Whitney U-test). c Proteomic analysis of laser dissected sarcoplasma of soleus muscle fibers from Hom and WT mice confirmed that the proportion of FLNc in Hom mice was reduced to 46 and 40% in type I and type II fibers, respectively, whereas FLNa and FLNb were not detectable. Investigation of other proteins tested by western blotting, revealed a slight underrepresentation of α-actinin2, whereas myomesin, desmin and Xin levels were not changed. Note that MHC IIa is not yet represented in the UniProt KB database [76], and could therefore not be detected in the mass spectrometric analyses. The autophagy related protein HSPB7 was hardly detectable in both fiber types of Hom mice, whereas other small heat shock proteins such as HSPB1 and HSPB5 are significantly upregulated in type II fibers. Notably, other autophagy-related proteins, such as synaptopodin-2, VPS11, STK11 and RAB-33B also show a significantly increased expression in type II fibers of our Hom mice (Student’s t-test)