Heat shock protein 70 overexpression does not attenuate atrophy in botulinum neurotoxin type A-treated skeletal muscle

• Published in: Journal of applied physiology (1985) Vol. 119; no. 1; pp. 83 - 92
• Main Authors: Houston, Fraser E, Hain, Brian A, Adams, Thomas J, Houston, Kati L, O'Keeffe, Roderic, Dodd, Stephen L
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.07.2015
• Subjects: Animals; Botulinum Toxins, Type A - toxicity; Cytotoxicity; Electroporation; Forkhead Transcription Factors - biosynthesis; Forkhead Transcription Factors - genetics; Gene Expression - drug effects; Heat shock proteins; Hindlimb - pathology; HSP70 Heat-Shock Proteins - biosynthesis; Male; Muscle Contraction - drug effects; Muscle, Skeletal - drug effects; Muscle, Skeletal - pathology; Muscular Atrophy - metabolism; Musculoskeletal system; Nerve Tissue Proteins - biosynthesis; Nerve Tissue Proteins - genetics; NF-kappa B - metabolism; Peptide Hydrolases - drug effects; Peptide Hydrolases - genetics; Peptide Hydrolases - metabolism; Plasmids - drug effects; Plasmids - genetics; Proteasome Endopeptidase Complex - metabolism; Protein expression; Protein folding; Rats; Rats, Sprague-Dawley; Rodents; Toxins; nuclear factor-κB; Foxo; NF-κB; chemical denervation; ubiquitin proteasome system; Forkhead box O; protein degradation
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00233.2015

Botulinum neurotoxin type A (BoNT/A) is used clinically to induce therapeutic chemical denervation of spastically contracted skeletal muscles. However, BoNT/A administration can also cause atrophy. We sought to determine whether a major proteolytic pathway contributing to atrophy in multiple models of muscle wasting, the ubiquitin proteasome system (UPS), is involved in BoNT/A-induced atrophy. Three and ten days following BoNT/A injection of rat hindlimb, soleus muscle fiber cross-sectional area was reduced 25 and 65%, respectively. The transcriptional activity of NF-κB and Foxo was significantly elevated at 3 days (2- to 4-fold) and 10 days (5- to 6-fold). Muscle RING-finger protein-1 (MuRF1) activity was elevated (2-fold) after 3 days but not 10 days, while atrogin-1 activity was not elevated at any time point. BoNT/A-induced polyubiquitination occurred after 3 days (3-fold increase) but was totally absent after 10 days. Proteasome activity was elevated (1.5- to 2-fold) after 3 and 10 days. We employed the use of heat shock protein 70 (Hsp70) to inhibit NF-κB and Foxo transcriptional activity. Electrotransfer of Hsp70 into rat soleus, before BoNT/A administration, was insufficient to attenuate atrophy. It was also insufficient to decrease BoNT/A-induced Foxo activity at 3 days, although NF-κB activity was abolished. By 10 days both NF-κB and Foxo activation were abolished by Hsp70. Hsp70-overexpression was unable to alter the levels of BoNT/A-induced effects on MuRF1/atrogin-1, polyubiquitination, or proteasome activity. In conclusion, Hsp70 overexpression is insufficient to attenuate BoNT/A-induced atrophy. It remains unclear what proteolytic mechanism/s are contributing to BoNT/A-induced atrophy, although a Foxo-MuRF1-ubiquitin-proteasome contribution may exist, at least in early BoNT/A-induced atrophy. Further clarification of UPS involvement in BoNT/A-induced atrophy is warranted.