Inhibition of HSP90 attenuated muscle atrophy via disrupted HSP90-STAT3 interaction in C26 and LLC cachectic mice.
Next, we further investigated the protective effect of 17DMAG on cachectic skeletal muscle. H&E staining and morphometric analysis of the gastrocnemius revealed that C26 tumor-bearing mice exhibited an obvious decrease in muscle fiber size, which was markedly blocked by 17DMAG treatment (Figure 5a). The representative frequency distribution of the myofiber CSA showed a rightward shift in 17DMAG-treated mice (the most frequent value for the myofiber CSA was 1500-2000 ìm2) vs. C26 tumor-bearing mice (the most frequent value for the myofiber CSA was 1000-1500 ìm2) (Figure 5b). The mean CSA of the 17DMAG-treated mice was more than 40% higher than that of C26 tumor-bearing mice (Figure 5c).
We also observed that treatment with 17DMAG prevented the striking loss of MHC protein in C26 tumor-bearing mice compared with that in the vehicle control (Figure 5d, e). The significant decreases in STAT3 activation and myostatin, MuRF-1, and Atrogin-1 expression in cachectic muscles in C26 mice indicated that HSP90 blockade could alleviate muscle wasting (Figure 5d). Expression of MuRF1 and Atrogin1 was further confirmed at the transcriptional level (Figure 5f). In support of this data, the increased binding of HSP90 and STAT3 in the muscles of C26 (Figure S4a) and LLC (Figure S3f) cachectic mice was both disrupted byin vivo 17DMAG administration, indicating the HSP90-STAT3 interaction was a crucial event for the induction of cachectic muscle wasting in vivo . To further validate this data, we also repeat the experiments using another HSP90 inhibitor PU-H71, similar results were observed in PU-H71-treated mice or myotubes (Figure S2f).