title: Heat shock protein 70 overexpression does not attenuate atrophy in botulinum neurotoxin type A-treated skeletal muscle.
abstract: 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.
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Fraser E
authors.initials: FE
authors.lastname: Houston
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hain
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Adams
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Kati L
authors.initials: KL
authors.lastname: Houston
authors.affiliation: Ipsen Pharmaceuticals, Slough, Berkshire, United Kingdom.
authors.forename: Roderic
authors.initials: R
authors.lastname: O'Keeffe
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and sdodd@hhp.ufl.edu.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Dodd
mesh_terms: D000818:Animals; D019274:Botulinum Toxins, Type A / Q000633:toxicity*; D018274:Electroporation; D051858:Forkhead Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects*; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis*; D006614:Hindlimb / Q000473:pathology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000473:pathology*; D009133:Muscular Atrophy / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics; D010447:Peptide Hydrolases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000187:drug effects / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071161:Forkhead Box Protein O1
chemical_list: D019274:Botulinum Toxins, Type A; D051858:Forkhead Transcription Factors; D018840:HSP70 Heat-Shock Proteins; D016328:NF-kappa B; D009419:Nerve Tissue Proteins; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1
keywords: Forkhead box O; Foxo; NF-κB; chemical denervation; nuclear factor-κB; protein degradation; ubiquitin proteasome system