Difference of molecular response to ischemia-reperfusion of rat skeletal muscle as a function of ischemic time: study of the expression of p53, p21(WAF-1), Bax protein, and apoptosis

Adiponectin protects skeletal muscle from ischaemia-reperfusion injury in mice through miR-21/PI3K/Akt signalling pathway

Previous studies have confirmed that adiponectin (APN) plays a protective role in myocardial ischaemia-reperfusion (IR) injury, and the aim of this study was to investigate its effect on skeletal muscle. ELISA was used to detect the levels of Creatinine Kinase (CK), LDH, SOD and MDA in the plasma of the lower limbs of mice, and the levels of IL-6, IL-1β and TNF-α in the gastrocnemius. Quantitative PCR was used to detect the expression level of miR-21. TUNEL staining was used to detect the apoptosis of the gastrocnemius. The expression levels of apoptosis proteins, autophagy marker proteins and downstream target genes of miR-21 in gastrocnemius were detected by Western Blot. The results of this study revealed that APN levels were significantly reduced in gastrocnemius of IR mice. The oxidative stress, inflammatory response, apoptosis and autophagy induced by IR were significantly ameliorated by APN injection. The above effects of APN may be achieved through miR-21/PI3K signalling pathway, as found by interfering gene expression levels with miRNA antagomir and lentiviral injection. Taken together, our study revealed that APN protects skeletal muscle from IR injury through miR-21 /PI3K/Akt signalling pathway through inhibiting inflammatory response, apoptosis and autophagy.

Protective Effect of Unacylated Ghrelin on Compression-Induced Skeletal Muscle Injury Mediated by SIRT1-Signaling

Unacylated ghrelin, the predominant form of circulating ghrelin, protects myotubes from cell death, which is a known attribute of pressure ulcers. In this study, we investigated whether unacylated ghrelin protects skeletal muscle from pressure-induced deep tissue injury by abolishing necroptosis and apoptosis signaling and whether these effects were mediated by SIRT1 pathway. Fifteen adult Sprague Dawley rats were assigned to receive saline or unacylated ghrelin with or without EX527 (a SIRT1 inhibitor). Animals underwent two 6-h compression cycles with 100 mmHg static pressure applied over the mid-tibialis region of the right limb whereas the left uncompressed limb served as the intra-animal control. Muscle tissues underneath the compression region, and at the similar region of the opposite uncompressed limb, were collected for analysis. Unacylated ghrelin attenuated the compression-induced muscle pathohistological alterations including rounding contour of myofibers, extensive nucleus accumulation in the interstitial space, and increased interstitial space. Unacylated ghrelin abolished the increase in necroptosis proteins including RIP1 and RIP3 and attenuated the elevation of apoptotic proteins including p53, Bax, and AIF in the compressed muscle. Furthermore, unacylated ghrelin opposed the compression-induced phosphorylation and acetylation of p65 subunit of NF-kB. The anti-apoptotic effect of unacylated ghrelin was shown by a decrease in apoptotic DNA fragmentation and terminal dUTP nick-end labeling index in the compressed muscle. The protective effects of unacylated ghrelin vanished when co-treated with EX527. Our findings demonstrated that unacylated ghrelin protected skeletal muscle from compression-induced injury. The myoprotective effects of unacylated ghrelin on pressure-induced tissue injury were associated with SIRT1 signaling.

4‑Phenylbutyrate protects rat skin flaps against ischemia‑reperfusion injury and apoptosis by inhibiting endoplasmic reticulum stress

4-phenylbutyrate (4-PBA) is a low molecular weight fatty acid, which has been demonstrated to regulate endoplasmic reticulum (ER) stress. ER stress-induced cell apoptosis has an important role in skin flap ischemia; however, a pharmacological approach for treating ischemia-induced ER dysfunction has yet to be reported. In the present study, the effects of 4-PBA-induced ER stress inhibition on ischemia-reperfusion injury were investigated in the skin flap of rats, and transcriptional regulation was examined. 4-PBA attenuated ischemia-reperfusion injury and inhibited cell apoptosis in the skin flap. Furthermore, 4-PBA reversed the increased expression levels of two ER stress markers: CCAAT/enhancer-binding protein-homologous protein and glucose-regulated protein 78. These results suggested that 4-PBA was able to protect rat skin flaps against ischemia-reperfusion injury and apoptosis by inhibiting ER stress marker expression and ER stress-mediated apoptosis. The beneficial effects of 4-PBA may prove useful in the treatment of skin flap ischemia-reperfusion injury.

Hydrogen-rich saline attenuates ischemia-reperfusion injury in skeletal muscle

BACKGROUND

To investigate the potential beneficial effect of hydrogen-rich saline (HRS) in ischemia-reperfusion (IR) injury of skeletal muscle.

METHODS

Three experimental groups were established in male Sprague-Dawley rats: (1) sham group, (2) IR with normal saline group, (3) and IR with HRS group. A rat model of skeletal muscle IR injury was induced by 3-h tourniquet occlusion on its left hind limb and 4-h reperfusion. Normal saline and HRS (1.0 mL/100 g) were administered intraperitoneally at 10 min before reperfusion, respectively. Muscle and serum samples were analyzed for detecting the levels of myeloperoxidase (MPO), superoxide dismutase (SOD), malondialdehyde (MDA), and hydroxyl radical (•OH). Muscle samples were assessed by wet/dry rate, hematoxylin and eosin histologic assessment, Bcl2, Bax, cytochrome C, LC3B, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, and electron microscopy.

RESULTS

The wet/dry ratio increased significantly in the IR group (P < 0.01 compared with that in the sham group) and decreased significantly in IR with HRS groups (4.12 ± 0.14 versus 4.12 ± 0.14, P < 0.01 compared with that in the IR group). Muscle tissues and serum of the IR group had significantly increased levels of MPO, MDA, •OH content, and decreased SOD activities compared with the sham group (P < 0.01). The activity of SOD in the IR with HRS group was greatly elevated compared with that in the IR group (295.028 ± 9.288 versus 249.190 ± 5.450 in muscle tissues; 91.627 ± 2.604 versus 73.4045 ± 6.487 in serum; P < 0.01), whereas the levels of MPO, MDA, and •OH content were clearly reduced (MPO: 0.5649 ± 0.0724 versus 1.0984 ± 0.0824 in muscle tissues; 0.7257 ± 0.1232 versus 1.3147 ± 0.0531 in serum. MDA: 4.457 ± 0.650 versus 7.107 ± 0.597 in muscle tissues; 2.531 ± 0.434 versus 4.626 ± 0.237 in serum. •OH: 16.451 ± 0.806 versus 19.871 ± 0.594 in muscle tissues; 500.212 ± 7.387 versus 621.352 ± 7.591 in serum, P < 0.01). The integrated optical density of positive amethyst staining increased significantly in the IR group (P < 0.01 compared with that in the sham group) and decreased significantly in IR with HRS group (928.79 ± 234.537 versus 3005.972 ± 83.567, P < 0.01 compared with that in the IR group). Muscle tissues of the IR group had significantly increased levels of Bax, cytochrome C, LC3B content, and decreased Bcl2 activities compared with those in the sham group (P < 0.01). The activity of Bcl2 in the IR with HRS group was greatly elevated compared with that in the IR group (0.2635 ± 0.0704 versus 0.1242 ± 0.0662; P < 0.01), whereas the levels of Bax, cytochrome C, and LC3B content were clearly reduced (Bax: 0.3103 ± 0.0506 versus 0.5122 ± 0.0148; cytochrome C: 0.4194 ± 0.1116 versus 0.8127 ± 0.0166; LC3B: 0.5884 ± 0.0604 versus 1.3758 ± 0.0319; respectively, P < 0.01).

CONCLUSIONS

HRS seems to be effective in attenuating IR injury in skeletal muscle via its antioxidant, anti-apoptosis, and anti-autophagy effect.

A novel laser-Doppler flowmetry assisted murine model of acute hindlimb ischemia-reperfusion for free flap research

Suitable and reproducible experimental models of translational research in reconstructive surgery that allow in-vivo investigation of diverse molecular and cellular mechanisms are still limited. To this end we created a novel murine model of acute hindlimb ischemia-reperfusion to mimic a microsurgical free flap procedure. Thirty-six C57BL6 mice (n = 6/group) were assigned to one control and five experimental groups (subject to 6, 12, 96, 120 hours and 14 days of reperfusion, respectively) following 4 hours of complete hindlimb ischemia. Ischemia and reperfusion were monitored using Laser-Doppler Flowmetry. Hindlimb tissue components (skin and muscle) were investigated using histopathology, quantitative immunohistochemistry and immunofluorescence. Despite massive initial tissue damage induced by ischemia-reperfusion injury, the structure of the skin component was restored after 96 hours. During the same time, muscle cells were replaced by young myotubes. In addition, initial neuromuscular dysfunction, edema and swelling resolved by day 4. After two weeks, no functional or neuromuscular deficits were detectable. Furthermore, upregulation of VEGF and tissue infiltration with CD34-positive stem cells led to new capillary formation, which peaked with significantly higher values after two weeks. These data indicate that our model is suitable to investigate cellular and molecular tissue alterations from ischemia-reperfusion such as occur during free flap procedures.

Oxidative stress and DNA damage signalling in skeletal muscle in pressure-induced deep tissue injury

The molecular mechanisms that contribute to the pathogenesis of pressure-induced deep tissue injury are largely unknown. This study tested the hypothesis that oxidative stress and DNA damage signalling mechanism in skeletal muscle are involved in deep tissue injury. Adult Sprague Dawley rats were subject to an experimental protocol to induce deep tissue injury. Two compression cycles with a static pressure of 100 mmHg was applied to an area of 1.5 cm(2) over the mid-tibialis region of right limb of the rats. The left uncompressed limb served as intra-animal control. Muscle tissues underneath compression region were collected for examination. Our analyses indicated that pathohistological characteristics including rounding contour of myofibres and extensive nuclei accumulation were apparently shown in compressed muscles. The elevation of 8OHdG immunopositively stained nuclei indicated the presence of oxidative DNA damage. Increase in oxidative stress was revealed by showing significant elevation of 4HNE and decreases in mRNA abundance of SOD1, catalase and GPx, and protein content of SOD2 in compressed muscles relative to control muscles. Increase in nitrosative stress was demonstrated by significant elevation of nitrotyrosine and NOS2 mRNA content. The activation of tumor suppressor p53 signalling was indicated by the remarkable increases in protein contents of total p53 and serine-15 phosphorylated p53. The transcript expression of the DNA-repairing enzyme, Rad23A, was significantly suppressed in compressed muscles. Our time-course study indicated that increased oxidative/nitrosative stress and proapoptotic signalling were maintained in muscles receiving increasing amount of compression cycles and post-compression time. Furthermore, resveratrol was found to attenuate the histological damage, oxidative/nitrosative stress and proapoptotic signalling in response to prolonged moderate compression. In conclusion, our findings are consistent with the hypothesis that oxidative stress and DNA damage signalling in skeletal muscle are involved in the underlying mechanisms responsible for the pathogenesis of pressure-induced deep tissue injury.

Pretreatment with brain natriuretic peptide reduces skeletal muscle mitochondrial dysfunction and oxidative stress after ischemia-reperfusion

Brain natriuretic peptide (BNP) reduces the extent of myocardial infarction. We aimed to determine whether BNP may reduce skeletal muscle mitochondrial dysfunctions and oxidative stress through mitochondrial K(ATP) (mK(ATP)) channel opening after ischemia-reperfusion (IR). Wistar rats were assigned to four groups: sham, 3-h leg ischemia followed by 2-h reperfusion (IR), pretreatment with BNP, and pretreatment with 5-hydroxydecanoic acid, an mK(ATP) channel blocker, before BNP. Mitochondrial respiratory chain complex activities of gastrocnemius muscles were determined using glutamate-malate (V(max)), succinate (V(succ)), and N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride ascorbate (V(TMPD/asc)). Apoptosis (Bax-to-Bcl2 mRNA ratio and caspase-3 activity) and oxidative stress (dihydroethidium staining) were also assessed. Compared with the sham group, IR significantly decreased V(max), reflecting complex I, II, and IV activities (-36%, 3.7 ± 0.3 vs. 5.8 ± 0.2 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01), and V(TMPD/asc), reflecting complex IV activity (-37%, 8.6 ± 0.8 vs. 13.7 ± 0.9 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01). IR increased Bax-to-Bcl2 ratio (+57%, 1.1 ± 0.1 vs. 0.7 ± 0.1, P < 0.05) and oxidative stress (+45%, 9,067 ± 935 vs. 6,249 ± 723 pixels, P > 0.05). BNP pretreatment reduced the above alterations, increasing V(max) (+38%, P < 0.05) and reducing Bax-to-Bcl2 ratio (-55%, P < 0.01) and oxidative stress (-58%, P < 0.01). BNP protection against deleterious IR effects on skeletal muscles was abolished by 5-hydroxydecanoic acid. Caspase-3 activities did not change significantly. Conversely, BNP injected during ischemia failed to protect against muscle injury. In addition to maintaining the activity of mitochondrial respiratory chain complexes and possibly decreasing apoptosis, pretreatment with BNP protects skeletal muscle against IR-induced lesions, most likely by decreasing excessive production of radical oxygen species and opening mK(ATP) channels.

Skeletal muscle post-conditioning by diazoxide, anti-oxidative and anti-apoptotic mechanisms

Pretreatment with diazoxide, K(ATP) channel opener, increases tissue tolerance against ischemia reperfusion (IR) injury. In clinical settings pretreatment is rarely an option therefore we evaluated the effect of post-ischemic treatment with diazoxide on skeletal muscle IR injury. Rats were treated with either saline, diazoxide (K(ATP) opener; 40 mg/kg) or 5-hydroxydecanoate (5-HD; mitochondrial K(ATP) inhibitor; 40 mg/kg) after skeletal muscle ischemia (3 h) and reperfusion (6, 24 or 48 h). Tissue contents of malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) activities, Bax and Bcl-2 protein expression and muscle histology were determined. Apoptosis was examined (24 and 48 h) after ischemia. IR induced severe histological damage, increased MDA content and Bax expression (24 and 48 h; p < 0.01) and decreased CAT and SOD activities (6 and 24 h, p < 0.01 and 48 h, p < 0.05), with no significant effect on Bcl-2 expression. Diazoxide reversed IR effects on MDA (6 and 24 h; p < 0.05), SOD (6 and 24 h; p < 0.01) and CAT (6 and 48 h, p < 0.05 and 24 h p < 0.01) and tissue damage. Diazoxide also decreased Bax (24 and 48 h; p < 0.05) and increased Bcl-2 protein expression (24 and 48 h; p < 0.01). Post-ischemic treatment with 5-HD had no significant effect on IR injury. Number of apoptotic nuclei in IR and 5-HD treated groups significantly increased (p < 0.001) while diazoxide decreased apoptosis (p < 0.01). The results suggested that post-ischemic treatment with diazoxide decrease oxidative stress in acute phase which modulates expression of apoptotic proteins in the late phase of reperfusion injury. Involvement of KATP channels in this effect require further evaluations.

The effects of deformation, ischemia, and reperfusion on the development of muscle damage during prolonged loading

Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. In the present study, the contributions of deformation, ischemia, and reperfusion to skeletal muscle damage development were examined in a rat model during a 6-h period. Magnetic resonance imaging (MRI) was used to study perfusion (contrast-enhanced MRI) and tissue integrity (T2-weighted MRI). The levels of tissue deformation were estimated using finite element models. Complete ischemia caused a gradual homogeneous increase in T2 (∼20% during the 6-h period). The effect of reperfusion on T2 was highly variable, depending on the anatomical location. In experiments involving deformation, inevitably associated with partial ischemia, a variable T2 increase (17–66% during the 6-h period) was observed reflecting the significant variation in deformation (with two-dimensional strain energies of 0.60–1.51 J/mm) and ischemia (50.8–99.8% of the leg) between experiments. These results imply that deformation, ischemia, and reperfusion all contribute to the damage process during prolonged loading, although their importance varies with time. The critical deformation threshold and period of ischemia that cause muscle damage will certainly vary between individuals. These variations are related to intrinsic factors, such as pathological state, which partly explain the individual susceptibility to the development of DTI and highlight the need for regular assessments of individual subjects.

Protective effect of caspase inhibition on compression-induced muscle damage

There are currently no effective therapies for treating pressure-induced deep tissue injury. This study tested the efficacy of pharmacological inhibition of caspase in preventing muscle damage following sustained moderate compression. Adult Sprague-Dawley rats were subjected to prolonged moderate compression. Static pressure of 100 mm Hg compression was applied to an area of 1.5 cm2 in the tibialis region of the right limb of the rats for 6 h each day for two consecutive days. The left uncompressed limb served as intra-animal control. Rats were randomized to receive either vehicle (DMSO) as control treatment (n =8) or 6 mg kg⁻¹ of caspase inhibitor (z-VAD-fmk; n =8) prior to the 6 h compression on the two consecutive days.Muscle tissues directly underneath the compression region of the compressed limb and the same region of control limb were harvested after the compression procedure.Histological examination and biochemical/molecular measurement of apoptosis and autophagy were performed. Caspase inhibition was effective in alleviating the compression-induced pathohistology of muscle. The increases in caspase-3 protease activity, TUNEL index, apoptotic DNA fragmentation and pro-apoptotic factors (Bax, p53 and EndoG) and the decreases in anti-apoptotic factors (XIAP and HSP70) observed in compressed muscle of DMSO-treated animals were not found in animals treated with caspase inhibitor. The mRNA content of autophagic factors (Beclin-1, Atg5 and Atg12) and the protein content of LC3, FoxO3 and phospho-FoxO3 that were down-regulated in compressed muscle of DMSO-treated animals were all maintained at their basal level in the caspase inhibitor treated animals. Our data provide evidence that caspase inhibition attenuates compression-induced muscle apoptosis and maintains the basal autophagy level. These findings demonstrate that pharmacological inhibition of caspase/apoptosis is effective in alleviating muscle damage as induced by prolonged compression.

Biomechanics of Pressure Ulcer in Body Tissues Interacting with External Forces during Locomotion

Forces acting on the body via various external surfaces during locomotion are needed to support the body under gravity, control posture, and overcome inertia. Examples include the forces acting on the body via the seating surfaces during wheelchair propulsion, the forces acting on the plantar foot tissues via the insole during gait, and the forces acting on the residual-limb tissues via the prosthetic socket during various movement activities. Excessive exposure to unwarranted stresses at the body-support interfaces could lead to tissue breakdowns commonly known as pressure ulcers, often presented as deep-tissue injuries around bony prominences or as surface damage on the skin. In this article, we review the literature that describes how the involved tissues respond to epidermal loading, taking into account both experimental and computational findings from in vivo and in vitro studies. In particular, we discuss related literature about internal tissue deformation and stresses, microcirculatory responses, and histological, cellular, and molecular observations.

Ischaemia-reperfusion modulates inflammation and fibrosis of skeletal muscle after contusion injury

Regeneration of skeletal muscle following injury is dependent on numerous factors including age, the inflammatory response, revascularization, gene expression of myogenic and growth factors and the activation and proliferation of endogenous progenitor cells. It is our hypothesis that oxidative stress preceding a contusion injury to muscle modulates the inflammatory response to inhibit muscle regeneration and enhance fibrotic scar formation. Male F344/BN rats were assigned to one of four groups. Group 1: uinjured control; Group 2: ischaemic occlusion of femoral vessels for 2 h followed by reperfusion (I-R); Group 3: contusion injury of the tibialis anterior (TA); Group 4: I-R, then contusion injury. The acute inflammatory response (8 h, 3 days) was determined by expression of the chemokine CINC-1, TGF-beta1, IFN-gamma and markers of neutrophil (myeloperoxidase) and macrophage (CD68) activity and recruitment. Acute oxidative stress caused by I-R and/or contusion, was determined by measuring GP91(phox) and lipid peroxidation. Muscle recovery (21 days) was assessed by examining the fibrosis after I-R and contusion injuries to the TA with Sirius Red staining and quantification of collagen I expression. Consistent with our hypothesis, I-R preceding contusion increased all markers of the acute inflammatory response and oxidative stress after injury and elevated the expression of collagen. We conclude that ischaemia-induced oxidative stress exacerbated the inflammatory response and enhanced fibrotic scar tissue formation after injury. This response may be attributable to increased levels of TGF-beta1 and diminished expression of IFN-gamma in the ischaemic contused muscle.

Isorhamnetin protects rat ventricular myocytes from ischemia and reperfusion injury

Ischemia/reperfusion (I/R) has been known to cause damages to ventricular myocytes. Isorhamnetin, one member of flavonoid compounds, has cardioprotective effect, the effect that suggests a possible treatment for I/R damages. In the present investigation, we found that isorhamnetin could significantly promote the viability of neonatal rat ventricular myocytes that were exposed to ischemia/reperfusion (I/R) in vitro. Ventricular myocytes were obtained from neonatal SD rats, and then were divided randomly into three groups, namely I/R-/isor-, I/R+/isor- and I/R+/isor+ group. Before the whole experiment, the most appropriate concentration of isorhamnetin (4 μM) was determined by MTT assay. Our results showed that isorhamnetin could alleviate the damages of I/R to ventricular myocytes through inhibiting lactate dehydrogenase (LDH) activity, and repressing apoptosis. Compared with the counterpart of the I/R+/isor- group, LDH activity in the isorhamnetin-treated group weakened, halving from 24.1 ± 2.3 to 11.4 ± 1.2U/L. Additionally, flow cytometry showed the apparently increased apoptosis rate induced by I/R, the result that was further confirmed by transmission electron microscope. Administration of isorhamnetin, however, assuaged the apoptosis induced by I/R. Corresponding to the reduced apoptosis rate in the I/R+/isor+ group, western blotting assay showed increased amount of Bcl-2 and p53, decreased amount of Bax, and nuclear accumulation of NF-κB/p65.

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.

Ischemia/reperfusion-induced necrosis and apoptosis in the cells isolated from rat skeletal muscle

Necrosis was considered to be the solo mechanism for ischemia/reperfusion (I/R)-induced cell death. Recent evidence from I/R models of the heart, liver, kidney, and brain indicates that apoptosis is a major contributor to I/R-induced cell death. However, evidence of I/R-induced apoptosis in skeletal muscle is sparse and divided. The purpose for the present study was to investigate I/R-induced necrosis and apoptosis in the cells isolated from rat skeletal muscle. A rat gracilis muscle model was used. After surgical preparation, clamps were applied on the vascular pedicle to create 4 h of ischemia and released for 24 h of reperfusion (I/R, n = 10). Clamping was omitted in sham I/R rats (sham I/R, n = 10). The muscle samples were harvested after 24 h of reperfusion for the process of cell isolation. Cells were stained by Propidium Iodide (PI) or Annexin V-FITC or both. Twenty thousand cells from each muscle sample were scanned and analyzed by flow cytometry. The average percentage of live cells was 45 +/- 2% in the I/R group versus 65 +/- 3% in the sham I/R group (p < 0.01). The average percentage of necrotic cells was 18 +/- 1% in I/R versus 12 +/- 1% in sham I/R (p < 0.01). The average percentage of apoptotic cells was 40 +/- 3% in I/R versus 27 +/- 3% in sham I/R (p < 0.01). Our results clearly demonstrated that I/R not only causes necrosis, but also accelerates apoptosis in the cells isolated from rat skeletal muscle.

Exogenous acid fibroblast growth factor inhibits ischemia-reperfusion-induced damage in intestinal epithelium via regulating P53 and P21WAF-1 expression

AIM

To detect the effect of acid fibroblast growth factor (aFGF) on P53 and P21WAF-1 expression in rat intestine after ischemia-reperfusion (I-R) injury in order to explore the protective mechanisms of aFGF.

METHODS

Male rats were randomly divided into four groups, namely intestinal ischemia-reperfusion group (R), aFGF treatment group (A), intestinal ischemia group (I), and sham-operated control group (C). In group I, the animals were killed after 45 min of superior mesenteric artery (SMA) occlusion. In groups R and A, the rats sustained for 45 min of SMA occlusion and were treated with normal saline (0.15 mL) and aFGF (20 mug/kg, 0.15 mL), then sustained at various times for up to 48 h after reperfusion. In group C, SMA was separated, but without occlusion. Apoptosis in intestinal villi was determined with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling technique (TUNEL). Intestinal tissue samples were taken not only for RT-PCR to detect P53 and P21WAF-1 gene expression, but also for immunohistochemical analysis to detect P53 and P21WAF-1 protein expression and distribution.

RESULTS

In histopathological study, ameliorated intestinal structures were observed at 2, 6, and 12 h after reperfusion in A group compared to R group. The apoptotic rates were (41.17+/-3.49)%, (42.83+/-5.23)%, and (53.33+/-6.92)% at 2, 6, and 12 h after reperfusion, respectively in A group, which were apparently lower than those in R group at their matched time points (50.67+/-6.95)%, (54.17+/-7.86)%, and (64.33+/-6.47)%, respectively, (P<0.05)). The protein contents of P53 and P21WAF-1 were both significantly decreased in A group compared to R group (P<0.05) at 2-12 h after reperfusion, while the mRNA levels of P53 and P21WAF-1 in A group were obviously lower than those in R group at 6-12 h after reperfusion (P<0.05).

CONCLUSION

P53 and P21WAF-1 protein accumulations are associated with intestinal barrier injury induced by I-R insult, while intravenous aFGF can alleviate apoptosis of rat intestinal cells by inhibiting P53 and P21WAF-1 protein expression.

Hindlimb unloading increases muscle content of cytosolic but not nuclear Id2 and p53 proteins in young adult and aged rats

This study tested the hypothesis that inhibitor of differentiation-2 (Id2), p53, and heat shock proteins (HSP) are responsive to suspension-induced muscle atrophy. Fourteen days of hindlimb suspension were used to unload the hindlimbs and induce atrophy in gastrocnemius muscles of young adult and aged rats. Following suspension, medial gastrocnemius muscle wet weight was reduced by approximately 30%, and the muscle wet weight normalized to the animal body weight decreased by 11 and 15% in young adult and aged animals, respectively. mRNA abundances of Id2, p53, HSP70-2, and HSP27 did not change with suspension, whereas HSP70-1 mRNA content was lower in the suspended muscle compared with the control muscle in both young adult and aged animals. Our immunoblot analyses indicated that protein expressions of HSP70 and HSP60 were not different between suspended and control muscles in both ages, whereas HSP27 protein content was increased in suspended muscle relative to control muscle only in young adult animals. Id2 and p53 protein contents were elevated in the cytosolic fraction of suspended muscle compared with the control muscle in both young and aged animals, but these changes were not found in the nuclear protein fraction. Furthermore, compared with young adult, aged muscles had a lower HSP70-1 mRNA content but higher HSP70-2 mRNA content and protein contents of Id2, p53, HSP70, and HSP27. These findings are consistent with the hypothesis that Id2 and p53 are responsive to unloading-induced muscle atrophy. Moreover, our data indicate that aging is accompanied with altered abundances of HSP70-1 and HSP70-2 mRNA, in addition to Id2, p53, HSP70, and HSP27 protein in rat gastrocnemius muscle.

Acid fibroblast growth factor reduces rat intestinal mucosal damage caused by ischemia-reperfusion insult

AIM: To detect the effects of acid fibroblast growth factor (aFGF) on apoptosis and proliferation of intestinal epithelial cells in differentiation or proliferation status to explore the protective mechanisms of aFGF.

METHODS: Wistar rats were randomly divided into sham-operated control group (C, n = 6), intestinal ischemia group (I, n = 6), aFGF treatment group (A, n = 48) and intestinal ischemia-reperfusion group (R, n = 48). Apoptosis of intestinal mucosal cells was determined with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) technique. Proliferating cell nuclear antigen (PCNA) protein expression and distribution were detected with immunohistochemical method. Plasma levels of D-lactate were determined with modified Brandts method.

RESULTS: In A group, administration of exogenous aFGF could improve intestinal histological structure and decrease plasma D-lactate levels at 2-12 h after the reperfusion compared with R group. The apoptotic rates and PCNA protein expressions were not increased until 2 h after reperfusion and were maximal at 12 h. After reperfusion for 2-12 h, the apoptotic rates were gradually augmented along the length of jejunal crypt-villus units. Administration of aFGF could significantly reduce the apoptotic response at 2-12 h after reperfusion (P<0.05). Apoptosis rates in villus and crypt epithelial cells in A group at 12 h after reperfusion were (62.5±5.5)% and (73.2±18.6)% of those in R group, respectively. Treatment of aFGF could apparently induce protein expression of PCNA in intestinal mucosal cells of A group compared with R group during 2-12 h after reperfusion (P<0.05). There were approximately 1.3- and 1.5-times increments of PCNA expression levels in villus and crypt cells in A group at 12 h after reperfusion compared with R group, respectively.

CONCLUSION: Intestinal I/R insult could lead to histological structure change and apoptotic rate increment. The protective effects of aFGF against ischemia/reperfusion in rat intestinal mucosa might be partially due to its ability to inhibit ischemia/reperfusion-induced apoptosis and to promote cell proliferation of crypt cells and villus epithelial cells.

Intronic regulation of matrix metalloproteinase-2 revealed by in vivo transcriptional analysis in ischemia

Matrix metalloproteinase-2 (MMP-2) plays an essential role in angiogenesis and arteriogenesis, two processes critical to restoration of tissue perfusion after ischemia. MMP-2 expression is increased in tissue ischemia, but the responsible mechanisms remain unknown. We studied the transcriptional activation of the MMP-2 gene in a model of hindlimb ischemia by using various MMP-2-lacZ reporter mice and chromatin immunoprecipitation. MMP-2 activity and mRNA were increased after hindlimb ischemia. Mice with targeted deletion of MMP-2 had impaired restoration of perfusion and a high incidence of limb gangrene, indicating that MMP-2 plays a critical role in ischemia-induced revascularization. Ischemia induced the expression and binding of c-Fos, c-Jun, JunB, FosB, and Fra2 to a noncanonical activating protein-1 (AP-1) site present in the MMP-2 promoter and decreased binding of the transcriptional repressor JunD. Ischemia also activated the expression and binding of p53 to an adjacent enhancer site (RE-1) and increased expression and binding of nuclear factor of activated T-cells-c2 to consensus sequences within the first intron. Deletion of either the 5' AP-1/RE-1 region of the promoter or substitution of the first intron abolished ischemia-induced MMP-2 transcription in vivo. Thus, AP-1 transcription factors and intronic activation by nuclear factor of activated T-cells-c2 act in concert to drive ischemia-induced MMP-2 transcription. These findings define a critical role for MMP-2 in ischemia-induced revascularization and identify both previously uncharacterized regulatory elements within the MMP-2 gene and the cognate transcription factors required for MMP-2 activation in vivo after tissue ischemia.

Transcriptional responses of rat skeletal muscle following hypoxia-reoxygenation and near ischaemia-reperfusion

AIM

The effect of ischaemia/reperfusion or hypoxia/reoxygenation on gene expression has not been extensively studied. We hypothesized that in skeletal muscle, tissue hypoxia of similar magnitude but induced by different mechanisms would lead to different transcriptional responses.

METHODS

Muscle gene transcription was assessed using microarray analysis and reverse transcriptase polymerase chain reaction in 18 rats exposed to regional hind limb near ischaemia/reperfusion (n = 6), hypoxia/reoxygenation (n = 6) or sham operation (n = 6). Hypoxic burden was measured by the area under the PtO(2)-time curve.

RESULTS

PtO(2) was reduced in both the near ischaemia/reperfusion and hypoxia/reoxygenation groups. Although the hypoxic burden was similar, the genomic response was different for each condition. Near ischaemia/reperfusion had a greater effect on gene expression than hypoxia/reoxygenation. Using stringent criteria for changes in gene expression (i.e. more than or equal to twofold change vs. control) unique patterns of gene expression could be identified suggesting individualized transcriptional responses to each of these injuries. Several genes, including insulin-like growth factor 1 (IGF-1) and cyclin-dependent kinase inhibitor (p27(Kip1)) were induced by both injury types and these may have potential clinical application as markers of tissue damage. In contrast, no single gene was downregulated by both injury conditions.

CONCLUSIONS

The mechanism of skeletal muscle hypoxia has a profound effect on its subsequent transcriptional response. We identified several potential candidates as markers of skeletal muscle ischaemic damage.

Subcellular responses of p53 and Id2 in fast and slow skeletal muscle in response to stretch-induced overload

Tumor suppressor p53 and inhibitor of DNA-binding/differentiation Id2 were examined after 7 or 21 days of wing weighting in fast patagialis (PAT) and slow anterior latissimus dorsi (ALD) wing muscles of young adult and old Japanese quails. The contralateral wing served as the intra-animal control. Seven days of loading increased PAT and ALD muscle weight by 28 and 96%, respectively, in young birds. PAT and ALD muscle weight was 49 and 179% greater, respectively, than control muscles after 21 days of loading in young birds. In aged birds, no PAT or ALD hypertrophy was found after 7 days of loading; however, PAT and ALD muscle weight increased by 29 and 102%, respectively, after 21 days of loading. Id2 protein in the nuclear muscle fraction increased in both PAT and ALD muscles from young adult and old birds that were loaded for 7 days and in ALD muscles after 21 days of loading relative to contralateral control muscles. Nuclear p53 protein was greater in 7- or 21-day loaded PAT and ALD muscles relative to control muscles in both age groups. Cytosolic Id2 and p53 protein contents were not changed in loaded PAT or ALD muscles relative to control muscles at any time point. These data suggest that nuclear, but not cytosolic, Id2 and p53 are responsive to stretch-induced muscle overload. Moreover, the attenuated ability of the aged skeletal muscle to achieve hypertrophy does not appear to be explained by the subcellular changes in Id2 and p53 content with overload.

Intravenous acid fibroblast growth factor protects intestinal mucosal cells against ischemia-reperfusion injury via regulating Bcl-2/Bax expression

AIM: To detect the effect of acid fibroblast growth factor (aFGF) on apoptosis and gene expression of bax and bcl-2 gene in rat intestine after ischemia/reperfusion (I/R) injury, and to explore the protective mechanisms of aFGF.

METHODS: One hundred and eight Wistar rats were randomly divided into sham-operated control group (C) (n = 6), intestinal ischemia group (I) (n = 6), aFGF treatment group (A) (n = 48) and intestinal ischemia-reperfusion group (R) (n = 48). In group I, the animals were killed after 45 min of superior mesenteric artery (SMA) occlusion, while in groups R and A, the rats sustained 45 min of SMA occlusion and were then treated with normal saline and aFGF, respectively, sustained 15 min, 30 min, 1, 2, 6, 12, 24, or 48 h of reperfusion, respectively. In group C, SMA was separated, but without occlusion. Apoptosis in intestinal villus was determined with terminal deoxynucleotidyl transferase mediated dUTP-biotin nick-end labeling technique (TUNEL). Intestinal tissue samples were taken not only for detection of bax and bcl-2 gene expression by RT-PCR, but also for detection of bax and bcl-2 protein expression and distribution by immunohistochemical analysis.

RESULTS: The rat survival rates in aFGF treated group were higher than group R (P<0.05) and the improvement of intestinal histological structures was observed at 2, 6, and 12 h after the reperfusion in group A compared with group R. The apoptotic rates were (41.17±3.49)%, (42.83±5.23)% and (53.33±6.92)% at 2, 6 and 12 h after reperfusion, respectively in group A, apparently less than those of group R at matched time points (50.67±6.95, 54.17±7.86, 64.33±6.47, respectively) (P<0.05). The bax gene transcription and translation were significantly decreased in group A vs group R, while mRNA and protein contents of Bcl-2 in group A were obviously higher than those in group R during 2-12 h period after reperfusion.

CONCLUSION: The changes in histological structure and the increment of apoptotic rate indicated that the intestinal barrier was damaged after intestinal I/R injury, whilst intravenous aFGF could alleviate apoptosis induced by ischemia and reperfusion in rat intestinal tissues, in which genes of bax and bcl-2 might play important roles.

Id2 and p53 participate in apoptosis during unloading-induced muscle atrophy

Apoptotic signaling was examined in the patagialis (PAT) muscles of young adult and old quail. One wing was loaded for 14 days to induce hypertrophy and then unloaded for 7 or 14 days to induce muscle atrophy. Although the nuclear Id2 protein content was not different between unloaded and control muscles in either age group, cytoplasmic Id2 protein content of unloaded muscles was higher than that in contralateral control muscles after 7 days of unloading in young quails. Nuclear and cytoplasmic p53 contents and the p53 nuclear index of the unloaded muscles were higher than those in control muscles after 7 days of unloading in young quails, whereas in aged quails, the p53 and Id2 contents and p53 nuclear index of the unloaded muscles were not altered by unloading. Immunofluorescent staining indicated that myonuclei and activated satellite cell nuclei contributed to the increased number of p53-positive nuclei. Conversely, unloading in either young adult or aged PAT muscles did not alter c-Myc protein content. Although Cu-Zn-SOD content was not different in unloaded and control muscles, Mn-SOD content increased in PAT muscles after 7 days of unloading in young quails, suggesting that unloading induced an oxidative disturbance in these muscles. Moderate correlational relationships existed among Id2, p53, c-Myc, SOD, apoptosis-regulatory factors, and TdT-mediated dUTP nick end labeling index. These data indicate that Id2 and p53 are involved in the apoptotic responses during unloading-induced muscle atrophy after hypertrophy in young adult birds. Furthermore, our data suggest that there is an aging-dependent regulation of Id2 and p53 during unloading of previously hypertrophied muscles.

Effects of extrogenous aFGF on bax and bcl-2 expression in intestinal cells after ischemia/reperfusion

AIM: To detect the effects of acid fibroblast growth factor (aFGF) on apoptosis and Bax and bcl-2 expression in rat intestine after I/R injury, and to explore the protective mechanisms of aFGF on intestinal villus.

METHODS: One hundred and eight Wistar rats were randomly divided into 4 groups, namely intestinal ischemia/reperfusion group (R, n = 48), intestinal ischemia group (I, n = 6), aFGF treatment group (A, n = 48) and sham-operated group (C, n = 6). The rats sustained 45 min of arteria mesenterica (SMA) occlusion to establish the ischemia model. At the beginning of reperfusion, rats in group R and A were treated with normal saline (0.15 mL) and aFGF (20 μg/kg, 0.15 mL) respectively. Then each six rats as a sub-group were reperfused for a duration of 0.25, 0.5, 1, 2, 6, 12, 24, 48 h respectively. Cell apoptotic rates in intestinal villus were determined with terminal deoxynucl-eotidy transferase mediated dUTP-biotin nick-end-labeling technique (TUNEL). RT-PCR was used to detect the expressions of bax and bcl-2 gene in intestinal villus. Immunohistochemical methods were adopted to detect bax and bcl-2 protein expressions and distributions.

RESULTS: The improvement of intestinal histological structures was observed at 2 h, 6 h and 12 h after the reperfusion in group A, compared with group R. The apoptotic rates were (41.17±3.49 %), (42.83±5.23 %) and (53.33±6.92 %) at 2, 6, 12 h after reperfusion respectively in group A, and these rates were significantly lower than those in group R (P < 0.05). The expressions of bax gene and bax protein in intestinal villus were gradually increased after ischemia/reperfusion, while the transcription of bcl-2 gene and expression of bcl-2 protein were decreased. During the 2-12 h of reperfusion, the transcription of bcl-2 gene and expression of bcl-2 protein were significantly increased in group A compared with those in group R (P < 0.05). However, the expressions of bax gene and bax protein were significantly higher than those in group R (P < 0.05).

CONCLUSION: Intravenous aFGF could alleviate I/R-induced injury, in which its effects on the facilitation of bcl-2 transcription and inhibition of bax expression may play an important role.

p66 ShcA Modulates Tissue Response to Hindlimb Ischemia

Background— Oxidative stress plays a pivotal role in ischemia and ischemia/reperfusion injury. Because p66 ShcA -null (p66 ShcA −/−) mice exhibit both lower levels of intracellular reactive oxygen species and increased resistance to cell death induced by oxidative stress, we investigated whether tissue damage that follows acute ischemia or ischemia/reperfusion was altered in p66 ShcA −/− mice.

Methods and Results— Unilateral hindlimb ischemia was induced by femoral artery dissection, and ischemia/reperfusion was induced with an elastic tourniquet. Both procedures caused similar changes in blood perfusion in p66 ShcA wild-type (p66 ShcA wt) and p66 ShcA −/− mice. However, significant differences in tissue damage were found: p66 ShcA wt mice displayed marked capillary density decrease and muscle fiber necrosis. In contrast, in p66 ShcA −/− mice, minimal capillary density decrease and myofiber death were present. When apoptosis after ischemia was assayed, significantly lower levels of apoptotic endothelial cells and myofibers were found in p66 ShcA −/− mice. In agreement with these data, both satellite muscle cells and endothelial cells isolated from p66 ShcA −/− mice were resistant to apoptosis induced by simulated ischemia in vitro. Lower apoptosis levels after ischemia in p66 ShcA −/− cells correlated with decreased levels of oxidative stress both in vivo and in vitro.

Conclusions— p66 ShcA plays a crucial role in the cell death pathways activated by acute ischemia and ischemia/reperfusion, indicating p66 ShcA as a potential therapeutic target for prevention and treatment of ischemic tissue damage.

Vascular endothelial growth factor modulates skeletal myoblast function

Vascular endothelial growth factor (VEGF) expression is enhanced in ischemic skeletal muscle and is thought to play a key role in the angiogenic response to ischemia. However, it is still unknown whether, in addition to new blood vessel growth, VEGF modulates skeletal muscle cell function. In the present study immunohistochemical analysis showed that, in normoperfused mouse hindlimb, VEGF and its receptors Flk-1 and Flt-1 were expressed mostly in quiescent satellite cells. Unilateral hindlimb ischemia was induced by left femoral artery ligation. At day 3 and day 7 after the induction of ischemia, Flk-1 and Flt-1 were expressed in regenerating muscle fibers and VEGF expression by these fibers was markedly enhanced. Additional in vitro experiments showed that in growing medium both cultured satellite cells and myoblast cell line C2C12 expressed VEGF and its receptors. Under these conditions, Flk-1 receptor exhibited constitutive tyrosine phosphorylation that was increased by VEGF treatment. During myogenic differentiation Flk-1 and Flt-1 were down-regulated. In a modified Boyden Chamber assay, VEGF enhanced C2C12 myoblasts migration approximately fivefold. Moreover, VEGF administration to differentiating C2C12 myoblasts prevented apoptosis, while inhibition of VEGF signaling either with selective VEGF receptor inhibitors (SU1498 and CB676475) or a neutralizing Flk-1 antibody, enhanced cell death approximately 3.5-fold. Finally, adenovirus-mediated VEGF(165) gene transfer inhibited ischemia-induced apoptosis in skeletal muscle. These results support a role for VEGF in myoblast migration and survival, and suggest a novel autocrine role of VEGF in skeletal muscle repair during ischemia.