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

DNA methylation in promoter region of immune related genes STAT3 and VEGFA and biochemical parameters change in muscle of Japanese flounder under acute hypoxia

Acute hypoxic stress can lead to immune response in fish, but the molecular mechanism of muscle immunity in fish under acute hypoxia are still unclear. In this study, we carried out the effect of signal transducer and activator of transcription3(STAT3) and vascular endothelial growth factor A(VEGFA) on muscle immune responses of Japanese flounder (Paralichthys olivaceus) during acute hypoxic stimulation (1.65 ± 0.28mg/L O₂; 3h, 6h, 12h, 24h) and reoxygenation (7.30 ± 0.40mg/L O₂; R12h, R24h, R48h). In situ hybridization (ISH) showed that STAT3 and VEGFA RNA were co-located in the skeletal muscle of Japanese flounder. Japanese flounder was seriously affected by hypoxia for 3h and 6h. The expression of STAT3 and VEGFA increased significantly. The methylation levels of STAT3 5'UTR region and VEGFA promoter region were significantly lower than those in normoxia group, which was negatively correlated with the expression levels of STAT3 and VEGFA. The enzyme activities (LDH, ALT, AST, ALP) changed significantly. In addition, enzyme-linked immunosorbent assay (ELISA) detected a positive correlation between serum VEGFA concentration and muscle VEGFA mRNA. The current study have shown that Japanese flounder responded to acute hypoxic stress at multiple metabolic levels by changing DNA methylation status and activating transcription factors such as HIF-1α, Nrf2 and STAT3. It is significant for the scientific development of aquaculture through analyzing the effects of hypoxia on biological immunity.

Bench press performance during an intermittent hypoxic resistance training to muscle failure

BACKGROUND

Resistance training performed under hypoxia conditions has been shown to cause major metabolic and hormonal responses. However, the influence of hypoxia on an acute session has been barely studied. The aim of this study was to evaluate the acute effects of an intermittent hypoxic resistance training (IHRT) to muscle failure on bench press performance.

METHODS

A randomized crossover design was performed, and 25 untrained men performed a resistance training under two different conditions: normoxia (FIO2=21%) and high-level hypoxia (FIO2=13%). Resistance training consisted of 3 sets of 75% 1RM to muscle failure, with a 2-minute rest between sets. Physical performance was assessed by quantifying total repetitions, concentric velocity and power variable during all sets. Arterial oxygen saturation, heart rate, rating of perceived exertion (RPE), capillary blood lactate and muscle soreness were also assessed after training.

RESULTS

Physical performance during bench press did not differ under hypoxic conditions (P>0.05). However, there were significant increases (P<0.05) of RPE (from 7.5±0.8 to 7.9±0.8) and blood lactate concentrations (from 5.5±1.2 to 6.2±1.5 mmol/L) in the hypoxia group.

CONCLUSIONS

These findings suggest that hypoxic resistance exercise does not affect exercise performance during bench press exercise. However, influence to perceived exercise intensity and blood lactate concentrations, suggesting that hypoxic resistance training may add substantially to the training dose experienced.

Hypoxia and resistance exercise: a comparison of localized and systemic methods

It is generally believed that optimal hypertrophic and strength gains are induced through moderate- or high-intensity resistance training, equivalent to at least 60% of an individual's 1-repetition maximum (1RM). However, recent evidence suggests that similar adaptations are facilitated when low-intensity resistance exercise (~20-50% 1RM) is combined with blood flow restriction (BFR) to the working muscles. Although the mechanisms underpinning these responses are not yet firmly established, it appears that localized hypoxia created by BFR may provide an anabolic stimulus by enhancing the metabolic and endocrine response, and increase cellular swelling and signalling function following resistance exercise. Moreover, BFR has also been demonstrated to increase type II muscle fibre recruitment during exercise. However, inappropriate implementation of BFR can result in detrimental effects, including petechial haemorrhage and dizziness. Furthermore, as BFR is limited to the limbs, the muscles of the trunk are unable to be trained under localized hypoxia. More recently, the use of systemic hypoxia via hypoxic chambers and devices has been investigated as a novel way to stimulate similar physiological responses to resistance training as BFR techniques. While little evidence is available, reports indicate that beneficial adaptations, similar to those induced by BFR, are possible using these methods. The use of systemic hypoxia allows large groups to train concurrently within a hypoxic chamber using multi-joint exercises. However, further scientific research is required to fully understand the mechanisms that cause augmented muscular changes during resistance exercise with a localized or systemic hypoxic stimulus.

Non-uniform muscle oxygenation despite uniform neuromuscular activity within the vastus lateralis during fatiguing heavy resistance exercise

Previous studies have reported for the vastus lateralis (VL) that the extent of muscle hypertrophy in response to resistance training is greater in the distal than in the middle region, despite uniform muscle fibre composition within VL along its length. In the present study, to investigate mechanism(s) for such non-uniform muscle hypertrophy, we simultaneously measured neuromuscular activity and muscle oxygenation state at the middle and distal regions of VL during fatiguing heavy resistance exercise. Twelve males performed unilateral knee extension exercise which consisted of 4 sets of 8 repetitions at intensity of 80% of the individual one repetition maximum. During the resistance exercise, neuromuscular activities and muscle oxygenation status at the middle and distal regions (50% and 70% of the thigh length, respectively) of VL were measured by using electromyography and near-infrared spectroscopy, respectively. Neuromuscular activities were similar between the distal and middle regions of VL, whereas muscle tissue oxygenation saturation was significantly lower at the distal than at the middle region of VL. These results suggest a possibility that the regional difference in muscle oxygenation but not in neuromuscular activity during fatiguing heavy resistance exercise is responsible for the regional difference in hypertrophy within a muscle.

Ishemia-reperfusion enhances GAPDH nitration in aging skeletal muscle

Aging and skeletal muscle ischemia/reperfusion (I/R) injury leads to decreased contractile force generation that increases severely with age. Our studies show that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) protein expression is significantly decreased at 3 and 5 days reperfusion in the young mouse muscle and at 1, 3, 5, and 7 days in the aged muscle. Using PCR, we have shown that GAPDH mRNA levels in young and old muscle increase at 5 days reperfusion compared to control, suggesting that the protein deficit is not transcriptional. Furthermore, while total tyrosine nitration did not increase in the young muscle, GAPDH nitration increased significantly at 1 and 3 days reperfusion. In contrast, total tyrosine nitration in aged muscle increased significantly at 1, 3, and 5 days of reperfusion, with increases in GAPDH nitration at the same time points. We conclude that GAPDH protein levels decrease following I/R, that this is not transcriptionally mediated, that the aged muscle experiences greater oxidative stress, protein modification and GAPDH degradation, possibly contributing to decreased muscle function. We propose that tyrosine nitration enhances GAPDH degradation following I/R and that the persistent decrease of GAPDH in aged muscle is due to the prolonged increase in oxidative modification in this age group.

Effects of low-volume hemoglobin glutamer-200 versus normal saline and arginine vasopressin resuscitation on systemic and skeletal muscle blood flow and oxygenation in a canine hemorrhagic shock model

OBJECTIVE

To test the hypothesis that low-volume resuscitation with hemoglobin glutamer-200 improves hemodynamic function and tissue oxygenation, whereas arginine vasopressin resuscitation improves blood pressures more than low-volume saline or hemoglobin glutamer infusion but compromises systemic and muscle blood flow and oxygenation.

DESIGN

Randomized laboratory investigation.

SETTING

University research facility.

SUBJECTS

Nineteen dogs.

INTERVENTIONS

Dogs were instrumented to determine heart rate; arterial, central venous, pulmonary arterial, and pulmonary arterial occlusion pressures; cardiac output; and quadriceps muscle blood flow and oxygen tension (PMo2). Total and plasma hemoglobin, oxygen content, lactate, pH, standard base excess, and arginine vasopressin levels were determined, and systemic oxygen delivery (Do2I) and extraction ratio were calculated. Measurements were made before and 30 mins following hemorrhage. Dogs were resuscitated over 60 mins with saline (8.5 mL/kg), arginine vasopressin (0.4 IU/kg bolus plus 0.08 IU x kg x min), or 1:1 diluted hemoglobin glutamer-200. Recordings were then repeated. Subsequently, animals received 30 mL/kg shed blood (60 mL x kg x hr), and recordings were repeated immediately and 1 hr later.

MEASUREMENTS AND MAIN RESULTS

Hemorrhage ( approximately 52 mL/kg) caused characteristic changes in hemodynamic, hematologic, systemic PMo2, and acid-base variables. Saline resuscitation increased both Do2I and muscle perfusion by 42% and 51%, while arginine vasopressin treatment reduced heart rate by 31% and increased mean arterial pressure by 22% but not cardiac output, Do2I, or muscle blood flow, resulting in a further decrease of PMo2 by 68% and worse metabolic acidosis. Hemoglobin glutamer-200 infusion caused systemic and pulmonary vasoconstriction, however, without deterioration of cardiac output, Do2I, muscle blood flow, or PMo2 despite lack of oxygen content increase. Blood transfusion restored most variables.

CONCLUSIONS

Low-volume crystalloid or hemoglobin glutamer-200 resuscitation posthemorrhage may improve (but not restore) macro- and microvascular functions and tissue oxygenation, while arginine vasopressin infusion may only improve blood pressures and result in lower overall systemic perfusion compared with low-volume saline or hemoglobin glutamer-200 treatment and worsening of anaerobic conditions in skeletal muscle.

Periods of systemic partial hypoxia induces apoptosis and inflammation in rat skeletal muscle

Critical illness myopathy (CIM) causes significant morbidity. In this study, we investigated the effect of repeated mild hypoxia on the skeletal muscle inflammation. Sprague-Dawley rats anesthetized with 2% inhaled isoflurane were divided into two groups (n = 6 each), normoxia and hypoxia (12.5% for 12 min followed by 35% for 12 min, at which point the cycle was repeated for three times). We measured the tissue oxygen tension and perfusion (simultaneously) in hind limb skeletal muscle. Inflammation in skeletal muscle was assessed by light microcopy (Hematoxylin-Eosin staining) and apoptosis (Fluorescein-FragEL DNA fragmentation detection) and expressed as percent normoxia. Compared to the control group, hypoxia significantly (P < 0.001) altered histomorphometrics. Similarly, DNA fragmentation analysis revealed that hypoxia significantly (P < 0.001) induced apoptosis. We conclude that after a mild but repeated hypoxic insult there is marked histological alterations and induced apoptosis in skeletal muscle. We postulate that variable periods of hypoxia in the critically ill may be playing a role in the etiology of CIM.

The Belfast approach to managing complex lower limb vascular injuries

INTRODUCTION

Complex lower limb vascular injuries (CLVIs) in high-energy penetrating or blunt trauma are associated with an unacceptably high incidence of complications including amputation. Traumatic ischaemia and ischaemia-reperfusion injury (IRI) of skeletal muscle often lead to limb loss, the systemic inflammatory response syndrome (SIRS) which affects remote organs and even the potentially fatal multiple organ dysfunction syndrome (MODS). Surgical care of CLVIs everywhere, including Northern Ireland until 1978, was governed by an anxiety to restore arterial flow quickly often using expedient and flawed repair techniques while a damaged major vein was frequently ligated.

MATERIALS AND METHODS

A new policy centred on early intraluminal shunting of both artery and vein, restoring arterial inflow and venous outflow, respectively, was introduced at the Regional Vascular Surgery Unit of The Royal Victoria Hospital, Belfast in 1979. It imposed a disciplined one-stage comprehensive approach to treatment involving a sequence of operative manoeuvres in which all damaged anatomical elements receive meticulous and optimal attention unshackled by time constraints.

RESULTS

Comparisons drawn between the pre-shunt period of unplanned treatment (1969-1978) and the post-shunt period centred on the use of shunts (1979-2000) showed that early shunting of both artery and vein in both penetrating (P) and blunt (B) injuries significantly reduced the necessity for fasciotomy (P: p=0.016, B: p=0.02) and caused a significant fall in the incidence of contracture (P: p=0.018, B: p=0.02) and of amputation (P: p=0.009, P: p=0.012).

CONCLUSIONS

The policy of early shunting of artery and vein in CLVIs has proved to be of great benefit in terms of significantly improved outcomes, better operative discipline and harmonious collaboration among the specialists involved.

Up-regulation of cell cycle regulatory genes after renal ischemia/reperfusion: differential expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes depending on reperfusion time

The aim of this study was to evaluate the influence of renal ischemia, cold preservation and reperfusion on the degree of renal kidney senescence. An experimental model of ex vivo renal hemoperfusion was used. Expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes (CDKIGs) was studied immunohistochemically in kidney biopsy samples at baseline and different time points after reperfusion. All three markers were up-regulated in kidney tissue after the reperfusion; however, their activation in different renal cells varied according to the reperfusion time. Expression of p16 was significantly increased in tubular cells at 180 min of reperfusion when compared with the baseline. Activation of p27 was detected in glomerular cells at 15 min and was significantly higher at 60, 120 and 180 min of reperfusion. The marker started increasing in tubular cells at 15 min and was elevated at every time point afterwards. p21 was significantly over-expressed in all renal cells after the reperfusion. It has been shown by the results of the current study that renal ischemia/reperfusion is associated with over-expression of CDKIGs indicating on substantial DNA damage and/or accelerated tissue senescence. For the first time it has been shown that tissue expression of CDKIGs is positively related with the reperfusion time.

Comparative gene expression profile of mouse carotid body and adrenal medulla under physiological hypoxia

The carotid body (CB) is an arterial chemoreceptor, bearing specialized type I cells that respond to hypoxia by closing specific K+ channels and releasing neurotransmitters to activate sensory axons. Despite having detailed information on the electrical and neurochemical changes triggered by hypoxia in CB, the knowledge of the molecular components involved in the signalling cascade of the hypoxic response is fragmentary. This study analyses the mouse CB transcriptional changes in response to low PO2 by hybridization to oligonucleotide microarrays. The transcripts were obtained from whole CBs after mice were exposed to either normoxia (21% O2), or physiological hypoxia (10% O2) for 24 h. The CB transcriptional profiles obtained under these environmental conditions were subtracted from the profile of control non-chemoreceptor adrenal medulla extracted from the same animals. Given the common developmental origin of these two organs, they share many properties but differ specifically in their response to O2. Our analysis revealed 751 probe sets regulated specifically in CB under hypoxia (388 up-regulated and 363 down-regulated). These results were corroborated by assessing the transcriptional changes of selected genes under physiological hypoxia with quantitative RT-PCR. Our microarray experiments revealed a number of CB-expressed genes (e.g. TH, ferritin and triosephosphate isomerase) that were known to change their expression under hypoxia. However, we also found novel genes that consistently changed their expression under physiological hypoxia. Among them, a group of ion channels show specific regulation in CB: the potassium channels Kir6.1 and Kcnn4 are up-regulated, while the modulatory subunit Kcnab1 is down-regulated by low PO2 levels.