Physiologic Mechanical Stress Directly Induces Bone Formation by Activating Glucose Transporter 1 (Glut 1) in Osteoblasts, Inducing Signaling via NAD+-Dependent Deacetylase (Sirtuin 1) and Runt-Related Transcription Factor 2 (Runx2).

Mechanical stress is an important factor affecting bone tissue homeostasis. We focused on the interactions among mechanical stress, glucose uptake via glucose transporter 1 (Glut1), and the cellular energy sensor sirtuin 1 (SIRT1) in osteoblast energy metabolism, since it has been recognized that SIRT1, an NAD+-dependent deacetylase, may function as a master regulator of the mechanical stress response as well as of cellular energy metabolism (glucose metabolism). In addition, it has already been demonstrated that SIRT1 regulates the activity of the osteogenic transcription factor runt-related transcription factor 2 (Runx2). The effects of mechanical loading on cellular activities and the expressions of Glut1, SIRT1, and Runx2 were evaluated in osteoblasts and chondrocytes in a 3D cell-collagen sponge construct. Compressive mechanical loading increased osteoblast activity. Mechanical loading also significantly increased the expression of Glut1, significantly decreased the expression of SIRT1, and significantly increased the expression of Runx2 in osteoblasts in comparison with non-loaded osteoblasts. Incubation with a Glut1 inhibitor blocked mechanical stress-induced changes in SIRT1 and Runx2 in osteoblasts. In contrast with osteoblasts, the expressions of Glut1, SIRT1, and Runx2 in chondrocytes were not affected by loading. Our present study indicated that mechanical stress induced the upregulation of Glut1 following the downregulation of SIRT1 and the upregulation of Runx2 in osteoblasts but not in chondrocytes. Since SIRT1 is known to negatively regulate Runx2 activity, a mechanical stress-induced downregulation of SIRT1 may lead to the upregulation of Runx2, resulting in osteoblast differentiation. Incubation with a Glut1 inhibitor the blocked mechanical stress-induced downregulation of SIRT1 following the upregulation of Runx2, suggesting that Glut1 is necessary to mediate the responses of SIRT1 and Runx2 to mechanical loading in osteoblasts.

Age-related decrease in muscle satellite cells is accompanied with diminished expression of early growth response 3 in mice.

Skeletal muscle regeneration is mostly dependent on muscle satellite cells. Proper muscle regeneration requires enough number of satellite cells. Recent studies have suggested that the number of satellite cells in skeletal muscle declines as we age, leading to the impairment of muscle regeneration in older population. Our earlier study demonstrated that zinc finger transcription factor early growth response 3 (Egr3) plays an important role for maintaining the number of myoblasts, suggesting that age-related decrease in muscle satellite cell should be associated with the expression levels of Egr3. The aim of this study was to investigate whether aging would alter the Egr3 expression in satellite cells. A couple groups of male C57BL/6J mice were examined in this study: young (3 Mo) and old (17 Mo). Immunohistochemical staining showed that the satellite cell number decreased in normal and injured muscles of old mice. In fluorescence-activated cell sorting-isolated muscle satellite cells from normal and injured muscles, the mRNA expression of Egr3 was significantly decreased with age regardless of injury. In harmony with these results, Pax7 mRNA levels also decreased in the satellite cells from old mice. Alternatively, inhibition of Egr3 expression by shRNA decreased Pax7 protein expression in cultured myoblasts. These results suggest that Egr3 is associated with the age-related decline of muscle satellite cells in older population. Also, Egr3 might be implicated in the regulation of Pax7. Therefore, the loss of Egr3 expression may elucidate attenuated MSCs function and muscle regeneration in older age.

Long Term Changes in Muscles around the Knee Joint after ACL Resection in Rats: Comparisons of ACL-Resected, Contralateral and Normal Limb.

The purpose of this study was to investigate the long-term effects of anterior cruciate ligament (ACL) resection on the morphological and contractile characteristics of rectus femoris (RF) and semimembranosus (SM) muscles in both injured and contralateral hindlimbs in rats. Wistar male rats (8-week old) were used. Rats were divided into two groups; ACL-resected and (sham-operated) control groups. Furthermore, right and left limbs of rats in the ACL-resected group were assigned as ACL-resected and contralateral groups, respectively, at 1 day, 1, 4, and 48 weeks after ACL resection. No ACL-resection-associated changes in the mass of both muscles were observed 1 week after ACL resection. On the other hand, ACL-resection-associated reduction on mean fiber cross-sectional area (fiber CSA) in RF muscle lasted 48 weeks after ACL resection. Furthermore, ACL-resection associated increase in fiber composition of type I fiber in RF muscle in contralateral limbs. In addition, long-term effects of ACL resection were observed in both ACL-resected and contralateral limbs. Evidences from this study suggested that ACL resection may cause to change in the morphological (fiber CSA) and contractile (distribution of fiber types) properties of skeletal muscles around the knee joint in not only injured but also contralateral limb. Rehabilitation for quantitative and qualitative muscle changes by ACL resection may be required a special care for a long-term period.

The NAD-Dependent Deacetylase Sirtuin-1 Regulates the Expression of Osteogenic Transcriptional Activator Runt-Related Transcription Factor 2 (Runx2) and Production of Matrix Metalloproteinase (MMP)-13 in Chondrocytes in Osteoarthritis.

Aging is one of the major pathologic factors associated with osteoarthritis (OA). Recently, numerous reports have demonstrated the impact of sirtuin-1 (Sirt1), which is the NAD-dependent deacetylase, on human aging. It has been demonstrated that Sirt1 induces osteogenic and chondrogenic differentiation of mesenchymal stem cells. However, the role of Sirt1 in the OA chondrocytes still remains unknown. We postulated that Sirt1 regulates a hypertrophic chondrocyte lineage and degeneration of articular cartilage through the activation of osteogenic transcriptional activator Runx2 and matrix metalloproteinase (MMP)-13 in OA chondrocytes. To verify whether sirtuin-1 (Sirt1) regulates chondrocyte activity in OA, we studied expressions of Sirt1, Runx2 and production of MMP-13, and their associations in human OA chondrocytes. The expression of Sirt1 was ubiquitously observed in osteoarthritic chondrocytes; in contrast, Runx2 expressed in the osteophyte region in patients with OA and OA model mice. OA relating catabolic factor IL-1ßincreased the expression of Runx2 in OA chondrocytes. OA chondrocytes, which were pretreated with Sirt1 inhibitor, inhibited the IL-1ß-induced expression of Runx2 compared to the control. Since the Runx2 is a promotor of MMP-13 expression, Sirt1 inactivation may inhibit the Runx2 expression and the resultant down-regulation of MMP-13 production in chondrocytes. Our findings suggest thatSirt1 may regulate the expression of Runx2, which is the osteogenic transcription factor, and the production of MMP-13 from chondrocytes in OA. Since Sirt1 activity is known to be affected by several stresses, including inflammation and oxidative stress, as well as aging, SIRT may be involved in the development of OA.

Long-term outcome of joint-preserving surgery by combination metatarsal osteotomies for shortening for forefoot deformity in patients with rheumatoid arthritis.

OBJECTIVES: We report the long-term outcome of joint-preserving surgery by combining metatarsal osteotomies for shortening for forefoot deformity in patients with rheumatoid arthritis (RA). METHODS: Forty-three patients (57 feet) aged 41.7-70.8 years (mean, 57.7 years) underwent a combination of first tarsometatarsal fusion and distal realignment (modified Lapidus procedure), shortening oblique osteotomies of the bases of metatarsals 2-4, and fifth ray osteotomy (modified Coughlin procedure). Patients were followed up for 64-108 months (mean, 76.6 months). RESULTS: Average postoperative Foot Function Index scores for pain, disability, and activity were 10.3, 19.9, and 16.2, respectively. Average Japanese Society for Surgery of the Foot RA foot and ankle score improved significantly from 52.1 points preoperatively to 90.3 points postoperatively. Postoperatively, 41% of patients reported some forefoot stiffness, but showed no disability. Residual deformity and callosity were absent in all patients. Average hallux valgus and intermetatarsal angles decreased postoperatively from 48.5° to 8.6° and from 15.2° to 4.6°, respectively. Nonunion in two metatarsals, hardware breakage in three, and mild infection in one were identified during follow-up. CONCLUSIONS: With good perioperative medical management of RA, surgical repositioning of the metatarsophalangeal joints by proximal metatarsal shortening and consequent relaxing of the surrounding soft tissue shows successful long-term results.

Microcurrent electrical neuromuscular stimulation facilitates regeneration of injured skeletal muscle in mice.

Conservative therapies, mainly resting care for the damaged muscle, are generally used as a treatment for skeletal muscle injuries (such as muscle fragmentation). Several past studies reported that microcurrent electrical neuromuscular stimulation (MENS) facilitates a repair of injured soft tissues and shortens the recovery period. However, the effects of MENS on the regeneration in injured skeletal muscle are still unclear. The purpose of this study was to investigate the effect of MENS on the regenerative process of injured skeletal muscle and to elucidate whether satellite cells in injured skeletal muscle are activated by MENS by using animal models. Male C57BL/6J mice, aged 7 weeks old, were used (n = 30). Mice were randomly divided into two groups: (1) cardiotoxin (CTX)-injected (CX, n = 15) and (2) CTX-injected with MENS treatment (MX, n=15) groups. CTX was injected into tibialis anterior muscle (TA) of mice in CX and MX groups to initiate the necrosis-regeneration cycle of the muscle. TA was dissected 1, 2, and 3 weeks after the injection. Muscle weight, muscle protein content, the mean cross-sectional areas of muscle fibers, the relative percentage of fibers having central nuclei, and the number of muscle satellite cells were evaluated. MENS facilitated the recovery of the muscle dry weight and protein content relative to body weight, and the mean cross-sectional areas of muscle fibers in CTX-induced injured TA muscle. The number of Pax7-positive muscle satellite cells was increased by MENS during the regenerating period. Decrease in the percentages of fibers with central nuclei after CTX-injection was facilitated by MENS. MENS may facilitate the regeneration of injured skeletal muscles by activating the regenerative potential of skeletal muscles. Key pointsMicrocurrent electrical neuromuscular stimulation (MENS) facilitated the recovery of the relative muscle dry weight, the relative muscle protein content, and the mean cross-sectional areas of muscle fibers of injured TA muscle in mice.The number of satellite cells was increased by MENS during the regenerating phase of injured skeletal muscle.Decrease in the percentages of fibers with central nuclei was facilitated by MENS.MENS may facilitate the regeneration of injured skeletal muscles.

The DNA repair enzyme apurinic/apyrimidinic endonuclease (Apex nuclease) 2 has the potential to protect against down-regulation of chondrocyte activity in osteoarthritis.

Apurinic/apyrimidinic endonuclease 2 (Apex 2) plays a critical role in DNA repair caused by oxidative damage in a variety of human somatic cells. We speculated that chondrocyte Apex 2 may protect against the catabolic process of articular cartilage in osteoarthritis (OA). Higher levels of Apex 2 expression were histologically observed in severely compared with mildly degenerated OA cartilage from STR/OrtCrlj mice, an experimental model which spontaneously develops OA. The immunopositivity of Apex 2 was significantly correlated with the degree of cartilage degeneration. Moreover, the OA-related catabolic factor interleukin-1ß induced the expression of Apex 2 in chondrocytes, while Apex 2 silencing using small interfering RNA reduced chondrocyte activity in vitro. The expression of Apex 2 in chondrocytes therefore appears to be associated with the degeneration of articular cartilage and could be induced by an OA-related catabolic factor to protect against the catabolic process of articular cartilage. Our findings suggest that Apex 2 may have the potential to prevent the catabolic stress-mediated down-regulation of chondrocyte activity in OA.

Recovery Process for Sports-Related Concussion Assessed with Precise Ocular Motility.

Ocular motility has been linked to Sports Concussion Assessment Tool 5 scores. However, the link between ocular motility changes and assessment result changes remains unclear. Hence, we investigated that potential link in patients with sports-related concussions. We retrospectively included participants aged≥18 years who were diagnosed with a sports-related concussion. They underwent smooth pursuit eye movement assessment for allocation to the good improvement (rate of fundamental frequency≥15%) or minor improvement (<15%) groups. Sports Concussion Assessment Tool 5 scores were determined at baseline and two weeks later, and score changes were compared between the groups. Thirteen men (mean±standard deviation age: 20.6±5.0 years) were included: eight (19.0±4.5 years) in the good improvement group and five (20.6±5.7 years) in the minor improvement group. Symptom number (median=2.0 vs. 0.0), symptom severity (median=22.0 vs. 3.0), single-leg stance (median=4.0 vs. 0.5), tandem stance (median=1.0 vs. 0.0), and total errors (median=5.0 vs. 0.5) were worse (all p<0.05) in the minor improvement group. Smooth pursuit eye movement improvements measured using eye-tracking technology was linked to symptom recovery in patients with sports-related concussions. Therefore, ocular motility may be an objective indicator of sports-related concussions. Future studies with more patients are needed to confirm these findings.

Microcurrent electrical nerve stimulation facilitates regrowth of mouse soleus muscle.

Microcurrent electrical nerve stimulation (MENS) has been used to facilitate recovery from skeletal muscle injury. However, the effects of MENS on unloading-associated atrophied skeletal muscle remain unclear. Effects of MENS on the regrowing process of unloading-associated atrophied skeletal muscle were investigated. Male C57BL/6J mice (10-week old) were randomly assigned to untreated normal recovery (C) and MENS-treated (M) groups. Mice of both groups are subjected to continuous hindlimb suspension (HS) for 2 weeks followed by 7 days of ambulation recovery. Mice in M group were treated with MENS for 60 min 1, 3, and 5 days following HS, respectively, under anesthesia. The intensity, the frequency, and the pulse width of MENS were set at 10 µA, 0.3 Hz, and 250 msec, respectively. Soleus muscles were dissected before and immediately after, 1, 3 and 7 days after HS. Soleus muscle wet weight and protein content were decreased by HS. The regrowth of atrophied soleus muscle in M group was faster than that in C group. Decrease in the reloading-induced necrosis of atrophied soleus was facilitated by MENS. Significant increases in phosphorylated levels of p70 S6 kinase and protein kinase B (Akt) in M group were observed, compared with C group. These observations are consistent with that MENS facilitated regrowth of atrophied soleus muscle. MENS may be a potential extracellular stimulus to activate the intracellular signals involved in protein synthesis.

Medical care provision at the venue of the weightlifting event of the Tokyo 2020 Olympic Games.

Purpose: This study aimed to investigate the medical care provided at the venue of the weightlifting event of the Tokyo 2020 Olympic Games. Methods: We retrospectively evaluated athletes who availed of medical services at the venue during the weightlifting event of the Tokyo 2020 Olympic Games. In total, 194 athletes participated in the weightlifting competition.Injuries and illnesses were classified into cases handled without physician or cases requiring medical examination by a physician. These were tabulated for each examination location (athlete medical station, field of play [FOP], first-aid station of training floor or warm-up area). Results: Throughout the event, a cumulative total of 132 people used the venue medical services. Nine athletes required medical attention at the athlete medical stations. Of these nine cases, six occurred on the training floor. In the FOP, nine athletes were examined. Two experienced light-headedness, two had knee pain, and the rest had other symptoms. No athletes wanted to undergo medical examination at the athlete medical station. 89 medical procedures were performed in the first-aid station on the training floor, including 52 tapings and 37 ice compressions, and the most frequent body part which needed treatment was the knee, followed by the fingers. At the first-aid station on the match floor, 25 medical procedures were performed, including 17 ice compressions, 5 haemostasis, and 4 tapings. The body parts that most frequently needed treatment were the fingers, knees, and lower legs. Conclusion: Several athletes needed treatment; however, only a few required medical care from a physician.

Responses of muscle mass, strength and gene transcripts to long-term heat stress in healthy human subjects.

The present study was performed to investigate the effects of long-term heat stress on mass, strength and gene expression profile of human skeletal muscles without exercise training. Eight healthy men were subjected to 10-week application of heat stress, which was performed for the quadriceps muscles for 8 h/day and 4 days/week by using a heat- and steam-generating sheet. Maximum isometric force during knee extension of the heated leg significantly increased after heat stress (~5.8%, P < 0.05). Mean cross-sectional areas (CSAs) of vastus lateralis (VL, ~2.7%) and rectus femoris (~6.1%) muscles, as well as fiber CSA (8.3%) in VL, in the heated leg were also significantly increased (P < 0.05). Statistical analysis of microarrays (SAM) revealed that 10 weeks of heat stress increased the transcript level of 925 genes and decreased that of 1,300 genes, and gene function clustering analysis (Database for Annotation, Visualization and Integrated Discovery: DAVID) showed that these regulated transcripts stemmed from diverse functional categories. Transcript level of ubiquinol-cytochrome c reductase binding protein (UQCRB) was significantly increased by 10 weeks of heat stress (~3.0 folds). UQCRB is classified as one of the oxidative phosphorylation-associated genes, suggesting that heat stress can stimulate ATP synthesis. These results suggested that long-term application of heat stress could be effective in increasing the muscle strength associated with hypertrophy without exercise training.

Effects of Different Exercise Conditions on Antioxidant Potential and Mental Assessment.

Exercise increases oxidative stress, leading the body to strengthen its antioxidant defenses, thus reducing the incidence of major diseases. As these associations are relatively unclear for ordinary levels of exercise for reduced stress, this study evaluated the effects of different exercise conditions on diacron-reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), and subjective mood. Forty-nine students (22.4 ± 2.6 years) were assessed using the Profile of Mood States (POMS) before and after exercising for 60 min. Participants were divided into two groups: Group A engaged in compulsory sports and Group B in freely chosen sports. d-ROMs and BAP were measured, and their modified ratio was calculated as an index of antioxidant potential. Physiological evaluation showed significant improvements in BAP and the BAP/d-ROMs ratio, irrespective of exercise condition (p < 0.001, p < 0.01). Comparison between the exercise conditions revealed a significant difference in the modified ratio (p < 0.02). In mood assessment, scores on emotion-related scales without vigor improved significantly under both exercise conditions (p < 0.001). Mental changes were evident after exercise, and potential antioxidant capacity was higher in freely chosen sports (p < 0.03). Assessment of antioxidant status before and after exercise may provide an objective index of mental and physical conditioning.

Incidence of injury among adolescent soccer players: a comparative study of artificial and natural grass turfs.

OBJECTIVE: To investigate the incidence of acute injuries and soccer-related chronic pain from long-term training and during matches in adolescent players using natural grass turfs (NT) and artificial turfs (AT). DESIGN: Case-controlled prospective study. SETTING: Institutional-level Fédération Internationale de Football Association Medical Centre of Excellence. PARTICIPANTS: Youth soccer players (12-17 years of age) from 6 teams, with a predominant tendency to train on either NT or AT, were included. Of 332 players enrolled in this study, 301 remained to completion. INTERVENTIONS: Medically diagnosed acute injuries and chronic pain were recorded daily by team health care staff throughout 2005, and reports were provided monthly to the authors. ASSESSMENT OF RISK FACTORS: Noninvasive prospective study. INDEPENDENT VARIABLES: Age and turf type. MAIN OUTCOME MEASURES: Acute injuries per 1000 player hours on each surface and chronic complaints per 1000 player hours were evaluated according to frequency of surface used > or = 80% of the time. Incidence rate ratio (IRR) of acute injuries and chronic complaints during play on NT and AT was calculated. RESULTS: There was no significant difference in the incidence of acute injuries between the 2 surfaces during training and competition. However, the AT group showed a significantly higher incidence of low back pain during training (IRR, 1.62; 95% confidence interval, 1.06-2.48). Early adolescence and prolonged training hours were factors associated with an increased incidence of chronic pain in the AT group. CONCLUSION: Adolescent players routinely training on AT for prolonged periods should be carefully monitored, even on AT conforming to new standards.

A novel, self-assembled artificial cartilage-hydroxyapatite conjugate for combined articular cartilage and subchondral bone repair: histopathological analysis of cartilage tissue engineering in rat knee joints.

PURPOSE: We previously created a self-assembled cartilage-like complex in vitro from only three cartilage components, hyaluronic acid (HA), aggrecan (AG) and type II collagen, without other materials such as cross-linking agents. Based on this self-organized AG/HA/collagen complex, we have created three novel types of biphasic cartilage and bone-like scaffolds combined with hydroxyapatite (HAP) for osteochondral tissue engineering. These scaffolds have been developed from self-assembled cartilage component molecules and HAP at the nanometer scale by manipulating the intermolecular relations. PATIENTS AND METHODS: The surface structure of each self-organized biphasic cartilage and bone-like scaffold was evaluated by scanning electron microscopy, whereas the viscoelasticity was also analyzed in vitro. Three types of artificial cartilage-HAP conjugates were implanted into an osteochondral defect in rat knee joints, and bone and cartilage tissues of the implanted site were examined 4 and 8 weeks after implantation. The tissues were examined histopathologically to evaluate the effects of the implantation on the articular cartilage and subchondral bone tissues. RESULTS: Our in vitro and in vivo data reveal that the self-organized biphasic cartilage and bone-like scaffold conjugated with HAP are superior to the scaffold with no HAP in both cartilage regeneration and subchondral bone regeneration. CONCLUSION: Our present study indicates that the self-organized biphasic cartilage and bone-like scaffold, which is conjugated with an HAP layer, may have potential not only to repair articular cartilage defects but also to ameliorate the degeneration of subchondral bone in the diseases with osteochondral defect.

Peroneal spastic flatfoot in adolescents with accessory talar facet impingement: a preliminary report.

This study analyzed imaging, arthroscopic findings, and treatment responses for peroneal spastic flatfoot (PSFF) caused by talocalcaneal impingement at the accessory anterolateral talar facet (AALTF) (accessory talar facet impingement) in 13 adolescents without histories of trauma and tarsal coalition. The AALTF was determined with computed tomography and MRI. Focal abutting bone marrow edema (FABME) on MRI around the AALTF was confirmed. In seven patients who underwent AALTF resection, subtalar arthroscopy was performed. All experienced alleviation PSFF after treatment; reduction in FABME was observed. AALTF resection alone is beneficial for PSFF caused by accessory talar facet impingement when peroneal spasms are restored by an injection of local anesthesia.

Effect of muscle loads and torque applied to the tibia on the strain behavior of the anterior cruciate ligament: an in vitro investigation.

BACKGROUND: Very little is known about the effects of applied torque about the long axis of the tibia in combination with muscle loads on anterior cruciate ligament biomechanics. The purpose of this study was to determine the effect of muscle contraction and tibial torques applied about the long axis of the tibia on anterior cruciate ligament strain behavior. METHODS: Six cadaver knee specimens were used to measure the strain behavior of the anterior cruciate ligament. Internal and external axial torques were applied to the tibia when the knee was between 30° and 120° of flexion in combination with the conditions of no muscle load, isolated quadriceps load, and simultaneous quadriceps and hamstring loading. FINDINGS: The highest anterior cruciate ligament strain values were measured when the muscles were not loaded, when the knee was at 120° of flexion, and when internal tibial torques were applied to the knee. During muscle loading the highest anterior cruciate ligament strain values were measured at 30° of flexion and then the strain values gradually decreased with increase in knee flexion. During co-contraction of the quadriceps and hamstring muscles the anterior cruciate ligament was unstrained or minimally strained at 60°, 90° and 120° of knee flexion. INTERPRETATION: This study suggests that quadriceps and hamstring muscle co-contraction has a potential role in reducing the anterior cruciate ligament strain values when the knee is in deep flexion. These results can be used to gain insight into anterior cruciate ligament injury mechanisms and to design rehabilitation regimens.

Functional overloading facilitates the regeneration of injured soleus muscles in mice.

The effect of functional overloading on the regenerating process of injured skeletal muscle was investigated in 10-week-old male mice (C57BL/6J). Functional overloading on soleus of both hindlimbs was performed by cutting the distal tendons of plantaris and gastrocnemius muscles for 2 weeks before cardiotoxin (CTX) injection as the preconditioning and also during 10 weeks of recovery. To activate the necrosis-regeneration cycle, 0.1 ml of 10-microM CTX was injected into soleus muscle. The mean values of absolute muscle weight and the percentage of Pax7-positive nuclei in soleus were increased by the preconditioning. These values, as well as total muscle protein content, in the group with CTX injection plus overloading were larger than in the group with CTX injection alone. Fibers with central nucleus were noted in the group with CTX injection with or without overloading. The rate of disappearance of fibers having central nucleus during recovery was stimulated by overloading. Histological analyses revealed that the regeneration of injured soleus muscle with overloading proceeded more rapidly than the muscle without overloading. These results, in combination with previous lines of evidence, strongly suggest that functional overloading may facilitate the regeneration of injured skeletal muscles.

Geranylgeranylaceton induces heat shock protein 72 in skeletal muscle cells.

Effects of an antiulcer drug, geranylgeranylaceton (GGA), and/or heat-stress on 72 kDa heat shock protein (HSP72) expression and protein content in cultured skeletal muscle cells were studied. Mouse skeletal muscle cells (C(2)C(12)) were subjected to either 1) control (cultured at 37 degrees C without GGA), 2) GGA administration (10(-11) - 10(-8) M), 3) heat-stress at 41 degrees C for 60 min, or 4) GGA administration combined with heat-stress. Expression of HSP72 was up-regulated by GGA administration. Heat-stress further enhanced the GGA-related up-regulation of HSP72. Administration of GGA caused an increase of muscular protein content as a dose-dependent manner. Protein synthesis was also stimulated by heat-stress alone in myotubes. It was suggested that GGA stimulates the differentiation of myoblasts and protein synthesis. These observations may also suggest that the administration of GGA could be one of the useful tools to gain muscular mass not only in athletes, but also in patients during rehabilitation.

Heat stress facilitates the regeneration of injured skeletal muscle in rats.

BACKGROUND: Skeletal muscle stem cells, so-called muscle satellite cells, are responsible for the repair and the regeneration of adult skeletal muscle tissues. Heat stress can facilitate the proliferation and the differentiation of myoblasts in vitro and can enhance their proliferative potential, which may stimulate the regrowth of atrophied skeletal muscle. The purpose of this study was to investigate the effect of heat stress on the regeneration of skeletal muscle injury induced by cardiotoxin. METHODS: Male Wistar rats, aged 7 weeks, were randomly divided into six groups: a nonheated control group that received a physiological saline injection, a group heat stressed before physiological saline injection, a group heat stressed after physiological saline injection, a group injected with cardiotoxin without heat stress, a group heat stressed before cardiotoxin injection, and a group heat stressed after cardiotoxin injection (25 in each group). To initiate muscle injury and regeneration, 0.5 ml of 10 microM cardiotoxin was injected into the left tibialis anterior muscle. Conscious rats in some groups were exposed to environmental heat stress (41 degrees C for 60 min) in a heat chamber 24 h before or immediately after cardiotoxin or physiological saline injection. The heating protocol in the present study causes an increase in the colonic temperature to 41 degrees C. The left tibialis anterior muscles were dissected 1, 3, 7, 14, and 28 days after injection of cardiotoxin or physiological saline. RESULTS: The wet weight and water content of muscles increased 1 day after cardiotoxin injection regardless of the application of heat stress, but normalized after 7-14 days. The muscle protein content in control rats had increased 7 days after heat stress. Although the muscle protein content decreased on cardiotoxin injection, heat stress caused a significant recovery in protein level. Expression of heat shock protein 72 (HSP72) and the number of Pax7-positive nuclei decreased after cardiotoxin injection but increased on the application of heat stress in both normal control and cardiotoxin-injected groups. CONCLUSIONS: Heat stress stimulated not only the proliferation of satellite cells but also protein synthesis during the regeneration of injured skeletal muscle. It is thus strongly suggested that the heating of injured skeletal muscle may facilitate recovery. There was no direct relationship between the level of HSP72 expression and muscle protein content, suggesting that HSP72 expression may not be the key signal for protein synthesis in the necrosis-regeneration process.

Expression of heat shock protein 72 in rat quadriceps muscles following anterior cruciate ligament resection.

This study investigated the expression of heat shock protein 72 (HSP 72) in quadriceps femoris muscle following anterior cruciate ligament (ACL) resection and running training in rats. A group of 15 Wistar strain male rats (10 weeks old) were divided into three groups: sham-operated (S), ACL resection (A), and running training following ACL resection (R). In the A and R groups, the ACL of the right knee was resected using microsurgical techniques. Rats in the R group were subjected to running training for 9 weeks on a motor-driven treadmill for rodents 1 week after ACL resection. At 10 weeks after ACL resection, glycerinated single fibers were prepared from vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), and semimembranosus (SM) muscles. To determine the levels of HSP72 (HSP-inducible) in each muscle, we used the Western blotting technique. HSP72 expression in VL and VM increased following ACL resection ( P < 0.05) but not in RF or SM. Exercise training caused an elevation in HSP72 expression in VL and VM. There were no significant changes in HSP72 expression in RF or SM following exercise training. These results suggest that some stress would be generated by ACL resection in VM and VL and might cause atrophy in VM and VL.