Bee T. Teng

Muscle apoptosis is induced in pressure-induced deep tissue injury.

Pressure ulcer is a complex and significant health problem. Although the factors including pressure, shear, and ischemia have been identified in the etiology of pressure ulcer, the cellular and molecular mechanisms that contribute to the development of pressure ulcer are unclear. This study tested the hypothesis that the early-onset molecular regulation of pressure ulcer involves apoptosis in muscle tissue. Adult Sprague-Dawley rats were subjected to an in vivo protocol to mimic pressure-induced deep tissue injury. Static pressure was applied to the tibialis region of the right limb of the rats for 6 h each day on two consecutive days. The compression force was continuously monitored by a three-axial force transducer equipped in the compression indentor. The contralateral uncompressed limb served as intra-animal control. Tissues underneath the compressed region were collected for histological analysis, terminal dUTP nick-end labeling (TUNEL), cell death ELISA, immunocytochemical staining, and real-time RT-PCR gene expression analysis. The compressed muscle tissue generally demonstrated degenerative characteristics. TUNEL/dystrophin labeling showed a significant increase in the apoptotic muscle-related nuclei, and cell death ELISA demonstrated a threefold elevation of apoptotic DNA fragmentation in the compressed muscle tissue relative to control. Positive immunoreactivities of cleaved caspase-3, Bax, and Bcl-2 were evident in compressed muscle. The mRNA contents of Bax, caspase-3, caspase-8, and caspase-9 were found to be higher in the compressed muscle tissue than control. These results demonstrated that apoptosis is activated in muscle tissue following prolonged moderate compression. The data are consistent with the hypothesis that muscle apoptosis is involved in the underlying mechanism of pressure-induced deep tissue injury.

Habitual exercise increases resistance of lymphocytes to oxidant‐induced DNA damage by upregulating expression of antioxidant and DNA repairing enzymes

The underlying mechanisms of adaptation from staying physically active are not completely revealed. This study examined the effects of 8 and 20 weeks of habitual voluntary exercise on the susceptibility of lymphocytes to oxidant‐induced DNA damage, antioxidant enzyme activities in cardiac and skeletal muscles, and circulatory antioxidant profile. Forty young adult rats were randomly assigned to sedentary control and exercise groups for an experimental period of 8 or 20 weeks. Animals assigned to exercise groups were subjected to 24 h daily free access to an in‐cage running wheel with circumference of 1.19 m. A magnetic digital counter was attached to the running wheel to record daily exercise distance run by the animals. Control rats were housed in cages without a running wheel, located next to the exercised animals. Body weight and food intake were recorded weekly. After the experimental periods of 8 and 20 weeks, blood, left ventricle, soleus and plantaris muscles were collected for analysis. No significant difference was found in plasma total antioxidant capacity between exercised and control animals in the 8 and 20 week groups according to our ferric reducing/antioxidant power (FRAP) analysis. However, modified FRAP for ascorbic acid (FRASC) analysis indicated that plasma ascorbic acid content was significantly increased by 46 and 34% in 8 and 20 week exercise groups, respectively, when compared with the corresponding control groups. Superoxide dismutase (SOD) activity was significantly elevated by 39% in erythrocytes of animals exercised for 8 weeks relative to control animals. In the 20 week exercise group, Glutathione peroxidase (GPx) activity in ventricle and plantaris was significantly upregulated by 477 and 290%, respectively, relative to control values. As demonstrated by comet assay, the oxidant‐induced DNA damage was significantly reduced by 21 and 45% in lymphocytes of animals exercised for 8 and 20 weeks, respectively, when compared with the corresponding control lymphocytes. Our qRT‐PCR analysis showed that the transcript expression of SOD2 was significantly elevated by 939% in lymphocytes of animals exercised for 8 weeks relative to control animals. Increased expressions of SOD2 (by 19%), catalase (25%), APEX nuclease (multifunctional DNA repair enzyme) 1 (APEX1; 46%), Protein kinase, DNA‐activated, catalytic polypeptide (Prkdc; 9%) and O‐6‐methylguanine‐DNA methyltransferase (Mgmt; 26%) were found in lymphocytes of animals exercised for 20 weeks relative to control rats. These results demonstrate that habitual exercise confers increased resistance of lymphocytes to oxidant‐induced DNA damage, and this protective effect is possibly attributed to the regular exercise‐induced elevated expression of antioxidant and DNA repairing enzymes.

Protective effect of caspase inhibition on compression-induced muscle damage

Non‐technical summary  A pressure ulcer, also known as a pressure sore, bedsore or decubitus ulcer, results from localized ulcerated tissue breakdown caused by sustained, unrelieved mechanical pressure in the body–support interface such as with a bed, wheelchair and orthoses/prostheses. Pressure ulcers are common in the wheelchair bound or bedridden frail elderly patients with neuromuscular disorder and orthoses/prostheses clients. Pressure ulcers represent a significant health problem as they impose a heavy burden on sufferers, with negative psychological, physical, social and financial consequences. Most importantly, there are currently no effective therapies for preventing and treating pressure ulcers. In the present study, our data demonstrate that pharmacological inhibition of caspase is effective in alleviating muscle damage induced by prolonged moderate compression. These findings suggest that regimens targeting caspase/apoptosis inhibition might be of use to prevent or treat pressure ulcers.

Opposing responses of apoptosis and autophagy to moderate compression in skeletal muscle

Aim:  The molecular mechanism that contributes to the pathogenesis of deep pressure ulcer remains to be elucidated. This study tested the hypotheses that: (1) apoptosis and autophagy are activated in compression‐induced muscle pathology and (2) apoptotic and autophagic changes precede pathohistological changes in skeletal muscle in response to prolonged moderate compression.

Proteasome inhibition alleviates prolonged moderate compression-induced muscle pathology

BackgroundThe molecular mechanism initiating deep pressure ulcer remains to be elucidated. The present study tested the hypothesis that the ubiquitin proteasome system is involved in the signalling mechanism in pressure-induced deep tissue injury.MethodsAdult Sprague Dawley rats were subjected to an experimental compression model to induce deep tissue injury. The tibialis region of the right hind limb was subjected to 100 mmHg of static pressure for six hours on each of two consecutive days. The compression pressure was continuously monitored by a three-axial force transducer within the compression indentor. The left hind limb served as the intra-animal control. Muscle tissues underneath the compressed region were collected and used for analyses.ResultsOur results demonstrated that the activity of 20S proteasome and the protein abundance of ubiquitin and MAFbx/atrogin-1 were elevated in conjunction with pathohistological changes in the compressed muscle, as compared to control muscle. The administration of the proteasome inhibitor MG132 was found to be effective in ameliorating the development of pathological histology in compressed muscle. Furthermore, 20S proteasome activity and protein content of ubiquitin and MAFbx/atrogin-1 showed no apparent increase in the MG132-treated muscle following compression.ConclusionOur data suggest that the ubiquitin proteasome system may play a role in the pathogenesis of pressure-induced deep tissue injury.