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‐α‐induced NF‐κB activation. During skeletal muscle disuse, Hsp25/27 levels are decreased and NF‐κB activity increased, and this increase in NF‐κB 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‐κB activation. The 35% disuse muscle‐fiber atrophy observed in nontransfected fibers was attenuated by 50% in fibers transfected with Hsp27. Hsp27 also inhibited the disuseinduced increase in MuRF1 and atrogin‐1 transcription by 82 and 40%, respectively. Furthermore, disuse‐ and IKKβinduced NF‐κB transactivation were abolished by Hsp27. In contrast, Hsp27 had no effect on Foxo transactivation. In conclusion, Hsp27 is a negative regulator of NF‐κB in skeletal muscle, in vivo , and is sufficient to inhibit MuRF1 and atrogin‐1 and attenuate skeletal muscle disuse atrophy.—Dodd, S. L., Hain, B., Senf, S. M., Judge, A. R Hsp27 inhibits IKKβ‐induced NF‐κΕ activity and skeletal muscle atrophy. FASEB J . 23, 3415–3423 (2009). www.fasebj.org

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 10⁵ 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.

Clinical use of the chemotherapeutic doxorubicin (DOX) promotes skeletal muscle atrophy and weakness, adversely affecting patient mobility and strength. Although the mechanisms responsible for DOX-induced skeletal muscle dysfunction remain unclear, studies implicate the significant production of reactive oxygen species (ROS) in this pathology. Supraphysiological ROS levels can enhance protein degradation via autophagy, and it is established that DOX upregulates autophagic signaling in skeletal muscle. To determine the precise contribution of accelerated autophagy to DOX-induced skeletal muscle dysfunction, we inhibited autophagy in the soleus via transduction of a dominant negative mutation of the autophagy related 5 (ATG5) protein. Targeted inhibition of autophagy prevented soleus muscle atrophy and contractile dysfunction acutely following DOX administration, which was associated with a reduction in mitochondrial ROS and maintenance of mitochondrial respiratory capacity. These beneficial modifications were potentially the result of enhanced transcription of antioxidant response element-related genes and increased antioxidant capacity. Specifically, our results showed significant upregulation of peroxisome proliferator-activated receptor gamma co-activator 1-alpha, nuclear respiratory factor-1, nuclear factor erythroid-2-related factor-2, nicotinamide-adenine dinucleotide phosphate quinone dehydrogenase-1, and catalase in the soleus with DOX treatment when autophagy was inhibited. These findings establish a significant role of autophagy in the development of oxidative stress and skeletal muscle weakness following DOX administration.

Cancer cachexia is a debilitating and lethal consequence of many advanced cancers. REDD1, a negative regulator of mTORC1 activity, is an emerging target in cachexia. Our data show that skeletal muscle REDD1 expression is increased in LLC-induced cancer cachexia. Mice lacking REDD1 have attenuated skeletal muscle atrophy that is likely due to maintaining both protein synthesis and inhibiting protein degradation.