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).