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

The impact of heat therapy on neuromuscular function and muscle atrophy in diabetic rats

Introduction: Diabetes Mellitus (DM) is the most common metabolic disease worldwide and is associated with many systemic complications. Muscle atrophy is one of the significant complications in DM patients, making routine tasks laborious as atrophy continues. It is known that heat stress stimulates heat shock proteins and other proteins that maintain muscle mass; however, it is not thoroughly studied in diabetic conditions. This study addressed whether heat therapy can attenuate muscle atrophy in STZ-induced diabetic rats and explored its mechanism of action on specific muscle proteins. Methods: Male Sprague Dawley rats were randomly divided into short-term (3 weeks) and long-term (6 weeks) experiments. In each experiment rats were divided into control, heat therapy, diabetic and diabetic + heat therapy groups. Rats in heat therapy groups were exposed to heat therapy for 30 min daily for three or six weeks in a temperature-controlled (42°C) chamber. Results: The attenuation of neuromuscular functions assessed by Rotarod, Kondziella's inverted screen, and extensor postural thrust tests showed that diabetic rats exposed to heat therapy performed significantly better than diabetic controls. Muscle cross sectional area data established that heat therapy reduced muscle atrophy by 34.3% within 3 weeks and 44.1% within 6 weeks in the diabetic groups. Further, heat therapy significantly decreased muscle atrophy markers (CD68, KLF, and MAFbx) and significantly elevated muscle hypertrophy markers (AKT, mTOR, and HSP70). Conclusions: This study shows the relevance and clinical significance of utilizing heat therapy as a viable treatment to attenuate muscle atrophy in diabetic patients.

Prevention of Doxorubicin-Induced Autophagy Attenuates Oxidative Stress and Skeletal Muscle Dysfunction

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.

Botulinum toxin A-induced muscle paralysis stimulates Hdac4 and differential miRNA expression

At sufficient dose, intramuscular injection of Botulinum toxin A causes muscle wasting that is physiologically consistent with surgical denervation and other types of neuromuscular dysfunction. The aim of this study was to clarify early molecular and micro-RNA alterations in skeletal muscle following Botulinum toxin A-induced muscle paralysis. Quadriceps were analyzed for changes in expression of micro- and messenger RNA and protein levels after a single injection of 0.4, 2 or 4U Botulinum toxin A (/100g body weight). After injection with 2.0U Botulinum toxin A, quadriceps exhibited significant reduction in muscle weight and increased levels of ubiquitin ligase proteins at 7, 14 and 28 days. Muscle miR-1 and miR-133a/b levels were decreased at these time points, whereas a dose-responsive increase in miR-206 expression at day 14 was observed. Expression of the miR-133a/b target genes RhoA, Tgfb1 and Ctfg, and the miR-1/206 target genes Igf-1 and Hdac4, were upregulated at 28 days after Botulinum toxin A injection. Increased levels of Hdac4 protein were observed after injection, consistent with anticipated expression changes in direct and indirect Hdac4 target genes, such as Myog. Our results suggest Botulinum toxin A-induced denervation of muscle shares molecular characteristics with surgical denervation and other types of neuromuscular dysfunction, and implicates miR-133/Tgf-β1/Ctfg and miR-1/Hdac4/Myog signaling during the resultant muscle atrophy.

Inhibition of the proteasome partially attenuates atrophy in botulinum neurotoxin treated skeletal muscle

Botulinum neurotoxin type A (BoNT/A) is used as a therapeutic tool to induce chemical denervation of spastically contracted muscles, yet the neurotoxin can also cause skeletal muscle atrophy. The underlying proteolytic mechanisms that induce this atrophy remain unclear. Our previous work has highlighted increased ubiquitin proteasome system (UPS) activity in soleus muscle of male Sprague Dawley rats following hind limb injection of BoNT/A, with the chymotrypsin-like activity of the 20s proteasome the most active. Thus, we chose to inhibit 20s proteasome activity in BoNT/A injected hind limb to determine the effect on soleus muscle atrophy. Epoxomicin is commonly used to inhibit the proteasome in vivo, binding specifically and irreversibly to the 20s proteasome catalytic subunits. Daily subcutaneous injections of epoxomicin abolished BoNT/A-induced elevations in 20s chymotrypsin-like activity both 3 days and 10 days post BoNT/A injection. Furthermore, BoNT/A-induced elevations in polyubiquitination remained elevated in BoNT/A + epoxomicin treated muscle, presumably due to epoxomicin's inhibition of the proteasome causing a back-up of polyubiquitinated proteins. Despite inhibition of the proteasome, epoxomicin was insufficient to significantly attenuate soleus muscle fiber atrophy 3 days following BoNT/A injection however, 10 days of daily epoxomicin injection was sufficient to spare ∼20% of muscle wasting. The mechanism of the remaining 80% of BoNT/A-induced atrophy presumably occurs via mechanisms outside of the 20s proteasome.

Evaluation of botulinum toxin type A effectiveness in preventing postoperative intraperitoneal adhesions

Purpose

Postoperative intraperitoneal adhesions (PIAs) are one of the most important problems surgeons have to face after laparotomies. In this study, we aimed to evaluate the effectiveness of local application of botulinum toxin type A (BoNT-A) in various dosages on the prevention of intra-abdominal adhesions in rats with experimental intra-abdominal adhesions.

Methods

Forty Wistar Albino female rats were randomly separated into 4 groups. The 4 groups were determined as follows: Control (group 1, n = 10); Sham (group 2, n = 10); 10-µg/kg low-dose BoNT-A (group 3, n = 10) and 30-µg/kg high-dose BoNT-A (group 4, n = 10). Subserosal injuries were created on the caecum of all rats. Laparotomy was performed on the fifth day. Adhesion scores, histopathological examination, and E-cadherin expression levels were evaluated.

Results

General adhesion scores for groups 1 and 2 were determined to be significantly high when compared to group 4 (P < 0.001). A significant difference was also determined between groups 3 and 4 in terms of general adhesion scores (P < 0.05). In pair comparisons, a significant decrease in high-dose BoNT-A group (group 4) when compared to groups 1 and 2 in terms of neovascularization, fibroblast density, collagen deposition and inflammatory cell count was determined (P < 0.05).

Conclusion

A significant decrease was observed only in postoperative PIAs in the high-dose BoNT-A group between all 4 rat-groups with experimentally created postoperative PIAs. In this study, high-dose BoNT-A is determined to be an effective agent in preventing postoperative PIAs.