We examined reactive oxygen species as upstream activators of NF-κB and Foxo in skeletal muscle during disuse atrophy. Catalase, an enzyme that degrades H 2 O 2 , was overexpressed in soleus muscles via plasmid injection prior to seven days of hind limb immobilization. The increased catalase activity abolished immobilization-induced transactivation of both NF-κB and Foxo, and it attenuated the loss of muscle mass. Thus, H 2 O 2 may be an important initiator of these signaling pathways which lead to muscle atrophy.

Heat shock protein 25/27 (Hsp25/27) is a cytoprotective protein that is ubiquitously expressed in most cells, and is up-regulated in response to cellular stress. Previous work, in nonmuscle cells, has shown that Hsp27 inhibits TNF-alpha-induced NF-kappaB activation. During skeletal muscle disuse, Hsp25/27 levels are decreased and NF-kappaB activity increased, and this increase in NF-kappaB activity is required for disuse muscle atrophy. Therefore, the purpose of the current study was to determine whether electrotransfer of Hsp27 into the soleus muscle of rats, prior to skeletal muscle disuse, is sufficient to inhibit skeletal muscle disuse atrophy and NF-kappaB activation. The 35% disuse muscle-fiber atrophy observed in nontransfected fibers was attenuated by 50% in fibers transfected with Hsp27. Hsp27 also inhibited the disuse-induced increase in MuRF1 and atrogin-1 transcription by 82 and 40%, respectively. Furthermore, disuse- and IKKbeta-induced NF-kappaB transactivation were abolished by Hsp27. In contrast, Hsp27 had no effect on Foxo transactivation. In conclusion, Hsp27 is a negative regulator of NF-kappaB in skeletal muscle, in vivo, and is sufficient to inhibit MuRF1 and atrogin-1 and attenuate skeletal muscle disuse atrophy.

Background Chemotherapy used to treat malignancy can lead to loss of skeletal muscle mass and reduced force production, and can reduce bone volume in mice. We have shown that bone-muscle crosstalk is a key nexus in skeletal muscle function and bone homeostasis in osteolytic breast cancer bone metastases. Because chemotherapy has significant negative side effects on bone mass, and because bone loss can drive skeletal muscle weakness, we have examined the effects of chemotherapy on the musculoskeletal system in mice with breast cancer bone metastases. Methods and results Six-week-old Female athymic nude mice were inoculated with 10 5 MDA-MB231 human breast cancer cells into the left ventricle and bone metastases were confirmed by X-ray. Mice were injected with carboplatin at a dose of 60mg/kg once per week starting 4 days after tumor inoculation. Skeletal muscle was collected for biochemical analysis and extensor digitorum longus (EDL) whole muscle contractility was measured. The femur and tibia bone parameters were assessed by microCT and tumor burden in bone was determined by histology. Healthy mice treated with carboplatin lose whole body weight and have reduced individual muscle weights (gastrocnemius, tibialis anterior (TA), and EDL), reduced trabecular bone volume (BV/TV), and reduced EDL function. Mice with MDA-MB-231 bone metastases treated with carboplatin lose body weight, and have reduced EDL function as healthy mice treated with carboplatin. Mice with MDA-MB-231 bone metastases plus carboplatin do have reduced proximal tibia BV/TV compared to carboplatin alone, but carboplatin does reduce tumor burden in bone. Conclusions Our data shows that carboplatin treatment, aimed at reducing tumor burden, contributes to cachexia and trabecular bone loss. The muscle atrophy and weakness may occur through bone-muscle crosstalk and would lead to a feed-forward cycle of musculoskeletal degradation. Despite anti-tumor effects of chemotherapy, musculoskeletal impairment is still significant in mice with bone metastases.

Carboplatin is a chemotherapy drug used to treat solid tumors but also causes bone loss and muscle atrophy and weakness. Bone loss contributes to muscle weakness through bone-muscle crosstalk, which is prevented with the bisphosphonate zoledronic acid (ZA). We treated mice with carboplatin in the presence or absence of ZA to assess the impact of bone resorption on muscle. Carboplatin caused loss of body weight, muscle mass, and bone mass, and also led to muscle weakness as early as 7 days after treatment. Mice treated with carboplatin and ZA lost body weight and muscle mass but did not lose bone mass. In addition, muscle function in mice treated with ZA was similar to control animals. We also used the anti-TGFβ antibody (1D11) to prevent carboplatin-induced bone loss and showed similar results to ZA-treated mice. We found that atrogin-1 mRNA expression was increased in muscle from mice treated with carboplatin, which explained muscle atrophy. In mice treated with carboplatin for 1 or 3 days, we did not observe any bone or muscle loss, or muscle weakness. In addition, reduced caloric intake in the carboplatin treated mice did not cause loss of bone or muscle mass, or muscle weakness. Our results show that blocking carboplatin-induced bone resorption is sufficient to prevent skeletal muscle weakness and suggests another benefit to bone therapy beyond bone in patients receiving chemotherapy.n 368 HAIN ET AL. TissueMice were euthanized and the tibialis anterior (TA), soleus, and gastrocnemius were dissected. The extensor digitorum longus (EDL) muscle was dissected for muscle contractility. Muscles were either snap frozen in liquid nitrogen for biochemical analysis or embedded in optimum cutting temperature (O.C.T., Tissue Tek, Torrance, CA, USA) compound in cryomolds and frozen in liquid nitrogencooled 2-methylbutane (isopentane) for histological analysis. (38) Journal of Bone and Mineral Research ZA IMPROVES MUSCLE FUNCTION IN HEALTHY MICE TREATED WITH CHEMOTHERAPY 369 n 40. Wen Y, Murach KA, Vechetti IJ Jr, et al. MyoVision: software for automated high-content analysis of skeletal muscle immunohistochemistry. J Appl Physiol. 2018;124(1):40-51. 41. Edwards JR, Nyman JS, Lwin ST, et al. Inhibition of TGF-beta signaling by 1D11 antibody treatment increases bone mass and quality in vivo.