Pre-heating stress associated with acute oral leucine supplementation effects in rat gastrocnemius muscle: Implications for protein synthesis signaling pathways.

Skeletal muscle is a highly plastic tissue. The role of heat shock protein 72 (Hsp72) in heat stress-induced skeletal muscle hypertrophy has been well demonstrated; however, the precise mechanisms remain unclear. Essential amino acids, such as leucine, mainly mediate muscle protein synthesis. We investigated the effects of pre-heating and increased Hsp72 expression on the mechanistic target of rapamycin (mTOR) signaling and protein synthesis following leucine administration in rat gastrocnemius muscle. To ensure increased Hsp72 expression in both the red and white portions of the muscle, one leg of male Wistar rats (10-week-old, n = 23) was heat-stressed in 43 °C water for 30 min twice at a 48-h-interval (heat-stressed leg, HS leg). The contralateral leg served as a non-heated internal control (CT leg). After the recovery period (48 h), rats were divided into the pre-administration or oral leucine administration groups. We harvested the gastrocnemius muscle (red and white parts) prior to administration and 30 and 90 min after leucine treatment (n = 7-8 per group) and intramuscular signaling responses to leucine ingestion were determined using western blotting. Heat stress significantly upregulated the expression of Hsp72 and was not altered by leucine administration. Although the phosphorylation levels of mTOR/S6K1 and ERK were similar regardless of heating, 4E-BP1 was less phosphorylated in the HS legs than the CT legs after leucine administration in the red portion of the muscles (P < 0.05). Moreover, c-Myc expression differed significantly after leucine administration in both the red and white portions of the muscles. Our findings indicate that following oral leucine administration, pre-heating partially blunted the muscle protein synthesis signaling response in the rat gastrocnemius muscle.

Serum albumin levels as a predictive biomarker for low-load resistance training programs' effects on muscle thickness in the community-dwelling elderly Japanese population: interventional study result.

BACKGROUND: Resistance training has been recommended as an effective measure against age-related loss of muscle mass and muscle strength, called sarcopenia, even in older adults. However, despite subjecting each participant to the same training program, the training effect solely depended on the individual. This study aimed to evaluate whether certain blood parameters influenced the effect of a low-load resistance training program on muscle thickness in the community-dwelling elderly population. METHODS: Sixty-nine community-dwelling Japanese (49 women and 20 men) subjects aged 69.4 ± 6.5 years were included. Low-load resistance training was performed twice a week for 12 weeks. Muscle thickness at the anterior aspects of the thigh (AT) was measured using a B-mode ultrasound device, and 22 blood parameter levels were assessed before and after the program. We checked the first quartile value of each parameter to establish cutoff values, and participants were divided into low or normal groups for each parameter. RESULTS: A low-load resistance training program significantly increased muscle thickness at the AT. The interaction between time and groups was examined at low (< 4.1 g/dL) versus normal (≥ 4.1 g/dL) serum albumin (Alb) levels. Although there was no difference in muscle thickness at the AT before the training intervention, the hypertrophic effects were higher in the normal serum Alb level group than in the low serum Alb level group. The binomial logistic regression analysis showed that participants in the low serum Alb group had an odds ratio of 7.08 for decreased muscle thickness at the AT. The effect of a low-load resistance training program on lower limb muscle thickness appears to be limited in participants with low serum Alb levels before training interventions. CONCLUSIONS: Serum Alb level may act as a biomarker to predict the effects of low-load resistance training programs on muscle hypertrophy in elderly individuals. TRIAL REGISTRATION: This study was retrospectively registered in UMIN-Clinical Trial Registry (CTR), ID: UMIN000042759 (date of registration, 14 Dec 2020).

The 30-s chair stand test can be a useful tool for screening sarcopenia in elderly Japanese participants.

BACKGROUND: Low muscle strength has been focused on as an essential characteristic of sarcopenia, and the 30-s chair stand test (CS-30) could be a particularly useful test for assessing muscle strength. While it is speculated to be a beneficial tool for the assessment of sarcopenia, this remains to be verified. In this study, we examined the reliability and optimal diagnostic score of the CS-30 for assessing sarcopenia in elderly Japanese participants. METHODS: This cross-sectional study included 678 participants (443 females and 235 males) who underwent the test for sarcopenia as per the Asian Working Group for Sarcopenia (AWGS) 2019, the CS-30 test, and the isometric knee-extension muscle strength test. ROC analysis was used to estimate the optimal CS-30 scores at which sarcopenia was detected. RESULTS: CS-30 scores were positively associated with sarcopenia (OR: 0.88; 95% CI:0.82-0.93). The AUC of the CS-30 for sarcopenia definition were 0.84 (p < 0.001) for females and 0.80 (p < 0.001) for males. The optimal number of stands in the CS-30 that predicted sarcopenia was 15 for females (sensitivity, 76.4%; specificity, 76.8%) and 17 for males (sensitivity, 75.0%; specificity, 71.7%). CONCLUSIONS: The CS-30 was found to be a reliable test for sarcopenia screening in the elderly Japanese population.

Site-Specific Muscle Loss in the Abdomen and Anterior Thigh in Elderly Males with Locomotive Syndrome.

Although locomotive syndrome (LS) is a condition of reduced mobility, little information is available regarding the loss of site-specific skeletal muscle mass. The aim of the present study is to examine site-specific muscle loss in elderly males with LS. A total of 100 men ranging in age from 65 to 74 years were divided into two groups (LS and non-LS) using LS risk tests including the stand-up test, two-step test, and the 25-question geriatric locomotive function scale Muscle thickness (MTH) at eight sites-anterior and posterior thigh (AT and PT, respectively), anterior and posterior lower leg (AL and PL, respectively), rectus abdominis (RA), anterior and posterior upper arm (AU and PU, respectively), and anterior forearm (AF)-was evaluated using B-mode ultrasound. Furthermore, the 30-s chair stand test (CS-30), 10-m walking time, zig-zag walking time, and sit-up test were assessed as physical functions. There were no significant differences in age and body mass index between the LS and non-LS groups. The percentage of skeletal muscle was lower in the LS group than in the non-LS group. Although there were no differences in the MTH of AU, PU, AF, PT, Al and PL, site-specific muscle loss was observed at RA and AT in the LS group. CS-30, 10-m walking time, zig-zag walking time, and sit-up test in the LS group were all worse than those in the non-LS group. The MTHs of RA and AT were both correlated to those physical functions. In conclusion, the LS group had site-specific muscle loss and worse physical functions. This study suggests that site-specific changes may be associated with age-related physical functions. These results may suggest what the essential characteristics of LS are.

Zinc transporter ZIP13 suppresses beige adipocyte biogenesis and energy expenditure by regulating C/EBP-ß expression.

Given the relevance of beige adipocytes in adult humans, a better understanding of the molecular circuits involved in beige adipocyte biogenesis has provided new insight into human brown adipocyte biology. Genetic mutations in SLC39A13/ZIP13, a member of zinc transporter family, are known to reduce adipose tissue mass in humans; however, the underlying mechanisms remains unknown. Here, we demonstrate that the Zip13-deficient mouse shows enhanced beige adipocyte biogenesis and energy expenditure, and shows ameliorated diet-induced obesity and insulin resistance. Both gain- and loss-of-function studies showed that an accumulation of the CCAAT/enhancer binding protein-ß (C/EBP-ß) protein, which cooperates with dominant transcriptional co-regulator PR domain containing 16 (PRDM16) to determine brown/beige adipocyte lineage, is essential for the enhanced adipocyte browning caused by the loss of ZIP13. Furthermore, ZIP13-mediated zinc transport is a prerequisite for degrading the C/EBP-ß protein to inhibit adipocyte browning. Thus, our data reveal an unexpected association between zinc homeostasis and beige adipocyte biogenesis, which may contribute significantly to the development of new therapies for obesity and metabolic syndrome.

Muscle Size and Strength of the Lower Body in Supervised and in Combined Supervised and Unsupervised Low-Load Resistance Training.

This study aimed to clarify whether low-load resistance training at a low frequency (twice a week) using body weight and elastic band improves muscle size, muscle strength, and physical functions and to compare the training effects between supervised training and a combination of supervised and unsupervised training in untrained older adults. Fifty-one older adults (ages: 57-75 years) selected to either a supervised (S) training group (n = 34) or a combined supervised and unsupervised (SU) group (n = 17). Both groups performed low-load resistance training composed of nine exercises for 12 weeks. The S group participated in supervised exercise sessions twice a week, and the SU group performed a supervised exercise session once a week and an unsupervised exercise session at home also once a week. For muscle thicknesses in the anterior aspects of the forearm, upper arm, and thigh and the posterior aspect of the thigh, group × time interactions were observed (p < 0.05). The hypertrophic effects were higher in the S group. Isometric knee extension strength and physical functions increased similarly in both groups. Low-load resistance training using body weight and elastic band twice a week for 12 weeks induces muscle hypertrophy and increases muscle strength and physical functions in older adults. Although the muscle hypertrophic effects are greater in the S group than in the SU group, the other effects were similar between the groups.

Mitochondrial dysfunction induces muscle atrophy during prolonged inactivity: A review of the causes and effects.

Prolonged skeletal muscle inactivity (e.g. limb immobilization, bed rest, mechanical ventilation, spinal cord injury, etc.) results in muscle atrophy that manifests into a decreased quality of life and in select patient populations, a higher risk of morbidity and mortality. Thus, understanding the processes that contribute to muscle atrophy during prolonged periods of muscle disuse is an important area of research. In this regard, mitochondrial dysfunction has been directly linked to the muscle wasting that occurs during extended periods of skeletal muscle inactivity. While the concept that mitochondrial dysfunction contributes to disuse muscle atrophy has been contemplated for nearly 50 years, the mechanisms connecting mitochondrial signaling events to skeletal muscle atrophy remained largely unexplained until recently. Indeed, emerging evidence reveals that mitochondrial dysfunction and the associated mitochondrial signaling events are a requirement for several forms of inactivity-induced skeletal muscle atrophy. Specifically, inactivity-induced alterations in skeletal muscle mitochondria phenotype and increased ROS emission, impaired Ca2+ handling, and release of mitochondria-specific proteolytic activators are established occurrences that promote fiber atrophy during prolonged periods of muscle inactivity. This review highlights the evidence that directly connects mitochondrial dysfunction and aberrant mitochondrial signaling with skeletal muscle atrophy and discusses the mechanisms linking these interconnected phenomena.

Association between locomotive syndrome and blood parameters in Japanese middle-aged and elderly individuals: a cross-sectional study.

BACKGROUND: Locomotive syndrome (LS) is associated with weakness and loss of function in the musculoskeletal organs. We aimed to determine the association between LS components and blood parameters in middle-aged and elderly individuals. METHODS: We included 223 middle-aged and elderly individuals in this study (104 men and 119 women; age: 40-85 years). All participants were asked to fast for at least 3 h before the venous blood samples were obtained and the hemoglobin, total protein, glycated hemoglobin (HbA1c), growth hormone, albumin and lipid profile were measured. Three functional tests, the stand-up test, the two-step test, and the 25-question geriatric locomotive function scale (GLFS) were used to assess the risk of LS. Walking speed was assessed by the 10-m walking test. Maximal isometric muscle strengths of the knee extensors were examined, and the weight bearing index (knee extension strength/body weight) was calculated. To assess an independent association between blood parameters and LS, the area under the receiver operating characteristic curve analysis (area under the curve, sensitivity, and specificity) and a binary logistic regression analysis were performed with adjustment for age. RESULTS: Of the 223 subjects, 119 (53.3%) fulfilled the diagnostic criteria for LS (including a two-step test score < 1.3, difficulty with one-leg standing from 40 cm in the stand-up test, and a 25-question GLFS score ≥ 7). Increased levels of HbA1c were significant risk factors for LS with an OR of 2.62 (OR95%CI = 1.43-4.80), as determined by a logistic regression analysis. Additionally, dehydroepiandrosterone-sulfate (DHEA-S) levels were significant only in the male subjects (OR = 0.992 [OR95%CI = 0.986-0.998]), at a threshold of 88 (AUC; 0.70, sensitivity; 79.6%, specificity; 49.1%). Moreover, 101 of 223 participants (41 men, 60 women) were analyzed for serum albumin levels, with a prevalence of LS at 55.4%, indicating that low levels of albumin were significant risk factors for LS (OR = 0.148 [OR95%CI = 0.023-0.954], p = 0.0445). CONCLUSIONS: These results suggest that higher HbA1c and lower albumin are associated with the prevalence of LS in Japanese middle-aged and elderly individuals. Furthermore, low DHEA-S levels may be useful screening tools for LS in men.

Effects of Progressive Walking and Stair-Climbing Training Program on Muscle Size and Strength of the Lower Body in Untrained Older Adults.

The purpose of the present study was to investigate the effect of the progressive walking program on lower limb muscle size and strength and evaluated whether the stair-climbing exercise provided additional training effects when combined with the walking program. Fifteen elderly subjects (age 69 ± 1 years, height 1.63 ± 0.02 m, body weight 64.5 ± 2.0 kg) were randomly assigned to a walking group or a walking and stair-climbing group. The progressive walking program comprised continuous (week 1-8) and interval (week 9-17) exercises. The walking and stair-climbing group also performed stair climbing. Muscle thickness, strength, and walking performance were evaluated before and 8 and 17 weeks after the start of the program. The muscle thickness of the anterior and posterior parts of the thigh significantly (p < 0.05) increased in both groups. There was also a significant (p < 0.01) main effect of time in isometric maximal strength and the values expressed relative to body mass for both knee extension and flexion. However, no group × time interactions were noted. Furthermore, the percentage change of knee flexion strength after the training period was significantly (p < 0.01) correlated with the pre-intervention value. Seventeen weeks of the progressive walking program can increase thigh muscle size and strength for older adults; however, an added stair-climbing exercise may not provide additional training effects. Furthermore, the magnitude of improvement in knee flexion strength would depend on the pre-intervention value.

Effects of a progressive walking program on the risk of developing locomotive syndrome in elderly Japanese people: a single-arm trial.

[Purpose] This study aimed to identify the efficacy of a progressive walking program on the risk of developing locomotive syndrome among untrained elderly Japanese people. [Participants and Methods] Twenty-four untrained elderly individuals (68 ± 4 years) completed a 17-week progressive walking program. The stand-up, two-step tests and the 25-question geriatric locomotive function scale were used to assess the risk of locomotive syndrome at baseline, the 8-week midpoint (2 months), and the 17-week endpoint (4 months). Maximal isometric muscle strength of the knee extensors and flexors were measured using a dynamometer with the hip joint angle at 90° of flexion and physical function (the 30-s sit-to-stand, sit-up, 10-meter walk, and grip strength) were evaluated. [Results] The 4-month walking program significantly improved the two-step test and geriatric locomotive function scale scores. This may be attributable to the improvement in knee flexor strength and physical function. [Conclusion] A 4-month program of progressive walking effectively lowered the risk of developing locomotive syndrome in elderly Japanese people by improving knee flexor muscle strength and physical function.

Whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in human skeletal muscle.

PURPOSE: Protein ingestion after resistance exercise increases muscle protein synthesis (MPS) in a dose-dependent manner. However, the molecular mechanism(s) for the dose-dependency of MPS remains unclear. This study aimed to determine the dose response of mammalian target of rapamycin (mTOR) signaling in muscle with ingestion of protein after resistance exercise. METHODS: Fifteen male subjects performed four sets of six unilateral isokinetic concentric knee extensions. Immediately after exercise, eight subjects consumed water only. The other seven subjects, in a randomized-order crossover design, took either a 10 [3.6 g essential amino acids (EAA)] or 20 g (7.1 g EAA) solution of whey protein. Muscle biopsies from the vastus lateralis muscle were taken 30 min before and 1 h after resistance exercise. Phosphorylation of Akt (Ser473), mTOR (Ser2448), 4E-BP1 (Thr37/46), and S6K1 (Thr389) was measured by western blotting. RESULTS: Concentric knee extension exercise alone did not increase phosphorylation of Akt and mTOR 1 h after exercise, but ingesting protein after exercise significantly increased the phosphorylation of Akt and mTOR in a dose-dependent manner (P < 0.05). 4E-BP1 phosphorylation significantly decreased after resistance exercise (P < 0.05), but subjects who took 10 or 20 g of protein after exercise showed increased 4E-BP1 from post-exercise dephosphorylation (P < 0.05). S6K1 phosphorylation significantly increased after resistance exercise (P < 0.05), and 20 g of protein further increased S6K1 phosphorylation compared with ingestion of 10 g (P < 0.05). CONCLUSIONS: These findings suggest that whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in untrained men.

Effects of preconditioning with heat stress on acute exercise-induced intracellular signaling in male rat gastrocnemius muscle.

Heat stress (HS) induces Akt/mTOR phosphorylation and FoxO3a signaling; however, whether a prior increase in heat shock protein 72 (HSP72) expression affects intracellular signaling following eccentric exercise remains unclear. We analyzed the effects of HS pretreatment on intramuscular signaling in response to acute exercise in 10-week-old male Wistar rats (n = 24). One leg of each rat was exposed to HS and the other served as an internal control (CT). Post-HS, rats were either rested or subjected to downhill treadmill running. Intramuscular signaling responses in the red and white regions of the gastrocnemius muscle were analyzed before, immediately after, or 1 h after exercise (n = 8/group). HS significantly increased HSP72 levels in both deep red and superficial white regions. Although HS did not affect exercise-induced mTOR signaling (S6K1/ERK) responses in the red region, mTOR phosphorylation in the white region was significantly higher in CT legs than in HS legs after exercise. Thr308 phosphorylation of Akt showed region-specific alteration with a decrease in the red region and an increase in the white region immediately after downhill running. Overall, a prior increase in HSP72 expression elicits fiber type-specific changes in exercise-induced Akt and mTOR phosphorylation in rat gastrocnemius muscle.

Normobaric hypoxia accelerates high-intensity intermittent training-induced mitochondrial biogenesis (PGC-1α)- and dynamics (OPA1)-related protein expressions in rat gastrocnemius muscle.

High-intensity intermittent training (HIIT) in a normobaric hypoxic environment enhances exercise capacity, possibly by increasing the mitochondrial content in skeletal muscle; however, the molecular mechanisms underlying these adaptations are not well understood. Therefore, we investigated whether HIIT under normobaric hypoxia can enhance the expression of proteins involved in mitochondrial biogenesis and dynamics in rat gastrocnemius muscle. Five-week-old male Wistar rats (n = 24) were randomly assigned to the following four groups: (1) sedentary under normoxia (20.9% O2) (NS), (2) training under normoxia (NT), (3) sedentary under normobaric hypoxia (14.5% O2) (HS), and (4) training under normobaric hypoxia (HT). The training groups in both conditions were engaged in HIIT on a treadmill five to six days per week for nine weeks. From the fourth week of the training period, the group assigned to hypoxic conditions was exposed to normobaric hypoxia. Forty-eight hours after completing the final training session, gastrocnemius muscles were surgically removed, and mitochondrial enzyme activity and mitochondrial biogenesis and dynamics regulatory protein levels were determined. Citrate synthase (CS) activity and mitochondrial oxygen phosphorylation (OXPHOS) subunits in the gastrocnemius muscle in the HT significantly exceeded those in the other three groups. Moreover, the levels of a master regulator of mitochondrial biogenesis, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), and a mitochondrial fusion-related protein, optic atrophy 1 (OPA1), were significantly increased by HIIT under normobaric hypoxia. Our data indicates that HIIT and normobaric hypoxia increase the expression of mitochondrial biogenesis- and dynamics-related proteins in skeletal muscles.

Effects of hindlimb unloading on the mevalonate and mechanistic target of rapamycin complex 1 signaling pathways in a fast-twitch muscle in rats.

Fast-twitch muscles are less susceptible to disuse atrophy, activate the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway, and increase protein synthesis under prolonged muscle disuse conditions. However, the mechanism underlying prolonged muscle disuse-induced mTORC1 signaling activation remains unclear. The mevalonate pathway activates the mTORC1 signaling pathway via the prenylation and activation of Ras homolog enriched in brain (Rheb). Therefore, we investigated the effects of hindlimb unloading (HU) for 14 days on the mevalonate and mTORC1 signaling pathways in the plantaris muscle, a fast-twitch muscle, in adult male rats. Rats were divided into HU and control groups. The plantaris muscles of both groups were harvested after the treatment period, and the expression and phosphorylation levels of metabolic and intracellular signaling proteins were analyzed using Western blotting. We found that HU increased the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme of the mevalonate pathway, and activated the mTORC1 signaling pathway without activating AKT, an upstream activator of mTORC1. Furthermore, HU increased prenylated Rheb. Collectively, these findings suggest that the activated mevalonate pathway may be involved in the activation of the Rheb/mTORC1 signaling pathway without AKT activation in fast-twitch muscles under prolonged disuse conditions.

Cage restriction-induced physical inactivity promotes subsequent hepatic apoptosis during tail suspension in young male rats.

This study investigated the impact of long-term physical inactivity on hepatic cytoprotective- and inflammatory-related protein expressions in young rats and the subsequent apoptotic response during microgravity stress simulated by tail suspension. Four-week-old male Wistar rats were randomly assigned to the control (CT) and physical inactivity (IN) groups. The floor space of the cages provided to the IN group was reduced to half of that provided to the CT group. After 8 weeks, rats in both groups (n = 6-7) underwent tail suspension. Their livers were harvested immediately before (0 day) or 1, 3, and 7 days after tail suspension. Levels of hepatic heat shock protein 72 (HSP72), an anti-apoptotic protein, reduced over 7 days of tail suspension in the IN group than in the CT group (p < 0.01). Fragmented nucleosomes in the cytoplasmic fraction of the liver, an apoptotic index, were drastically increased by physical inactivity and tail suspension, and this change was significantly greater after 7 days of tail suspension in the IN group than in the CT group (p < 0.01). The apoptotic response was accompanied by the upregulation of pro-apoptotic proteins (cleaved caspase-3 and -7). Moreover, the levels of other pro-apoptotic proteins (tumor necrosis factor-1α and histone deacetylase 5) were also significantly higher in the IN than in the CT group (p < 0.05). Our results indicated that 8 weeks of physical inactivity decreased hepatic HSP72 levels and promoted hepatic apoptosis during the subsequent 7 days of tail suspension.

Correction: Ishihara et al. Association between Daily Physical Activity and Locomotive Syndrome in Community-Dwelling Japanese Older Adults: A Cross-Sectional Study. Int. J. Environ. Res. Public Health 2022, 19, 8164.

There was an error in the "d-value of the first paragraph in Section 3 (Results)" in the original publication (Page 5, Line 41) [...].

Fiber-type specific expression of α-actinin isoforms in rat skeletal muscle.

α-Actinins are actin-binding proteins, and two isoforms (α-actinin-2 and -3) are major structural components of the sarcomeric Z line in mammalian skeletal muscle. Based on human and knockout mice studies, α-actinin-3 is thought to be associated with muscle force output and high contraction velocities. However, fiber-type specific expression of α-actinin isoforms is not well understood and may vary among species. In this study, we investigated the expression of α-actinin isoforms and the difference between fiber types in rat skeletal muscle and compared it with those of humans and mice from previous reports. Soleus and plantaris muscles were analyzed immunohistochemically to identify muscle fiber types and α-actinin protein expression. α-Actinin-2 was stained in all muscle fibers in both the soleus and plantaris muscles; i.e., all α-actinin-3 co-expressed with α-actinin-2 in rat skeletal muscles. The proportions of α-actinin-3 expression, regardless of fiber type, were significantly higher in the plantaris (75.8 ± 0.6%) than the soleus (8.0 ± 1.7%). No α-actinin-3 expression was observed in type I fibers, whereas all type IIx+b fibers expressed α-actinin-3. α-Actinin-3 was also expressed in type IIa fibers; however, approximately 75% of type IIa fibers were not stained by α-actinin-3, and the proportion varied between muscles. The proportion of α-actinin-3 expression in type IIa fibers was significantly higher in the soleus muscle than the plantaris muscle. Our results showed that fiber-type specific expression of α-actinin isoforms in rats is more similar to that in humans compared to that of the mouse, whereas the proportion of α-actinin-3 protein varied between muscles.

Effect of losartan treatment on Smad signaling and recovery from hindlimb unloading-induced soleus muscle atrophy in female rats.

Losartan, an angiotensin II type 1 receptor blocker, exerts protective effect on soleus muscle atrophy in female rats. Thus, we aimed to examine the effect of losartan treatment on the recovery of atrophied soleus muscles. Female Wistar rats were subjected to hindlimb unloading for 7 d and then reloading for 7 d with either phosphate-buffered saline (PBS; n = 9) or losartan (40 mg/kg/day; n = 9). The soleus muscles were removed at rest (sedentary control [SED]; n = 9), after 7 d of hindlimb unloading (HU; n = 9), and after 7 d of reloading (HUR-PBS or HUR-LOS; n = 9 each). The absolute and relative weights, and fiber cross-sectional area (CSA) of the soleus muscles of rats in the HU group were significantly reduced as compared to those of the rats in the SED group at 7 d post-hindlimb unloading. Seven days of reloading significantly increased the muscle weights of rats in the HUR-PBS and HUR-LOS groups, with the recovery rate of the absolute muscle weight and type I fiber CSA being significantly higher in the HUR-LOS group (6.1% and 10.1%, respectively) than in the HUR-PBS group (4.7% and 5.2%, respectively) (p < 0.05). Moreover, the absolute and relative muscle weight in HUR-PBS were lower than SED; however, no significant difference was observed between the SED and HUR-LOS groups. CSAs of type I and IIa fiber were significantly higher in the HUR-LOS group than in the HU group. Losartan administration during reloading resulted in increased Smad1/5/8 and mTOR signaling and decreased Smad2/3 signaling and protein ubiquitination, facilitating the recovery of atrophied soleus muscle. Therefore, losartan administration-induced muscle recovery may partially be attributed to enhanced Smad1/5/8 and mTOR signaling activation, and reduced activation of canonical TGF-ß signaling (Smad2/3) in the soleus muscle.

Losartan treatment attenuates hindlimb unloading-induced atrophy in the soleus muscle of female rats via canonical TGF-ß signaling.

We investigated the protective effect of losartan, an angiotensin II type 1 receptor blocker, on soleus muscle atrophy. Age-matched male and female Wistar rats were subjected to hindlimb unloading, and the soleus muscle was removed on days 1 and 7 for analysis. Females showed greater reductions in relative weight and myofiber cross-sectional area of the soleus muscle than males on day 7 post-hindlimb unloading. Losartan partially protected females against muscle atrophy. Activation of the canonical TGF-ß signaling pathway, assessed via Smad2/3 phosphorylation, was lower in females following losartan treatment and associated with lower levels of protein ubiquitination after 1 (myofibril) and 7 (cytosol) days of unloading. However, no effect was observed in non-canonical TGF-ß signaling (p44/p42 and p38 MAPK phosphorylation) in males or females during unloading. Our results suggest that losartan provides partial protection against hindlimb unloading-induced soleus muscle atrophy in female rats, possibly associated with decreased canonical TGF-ß signaling.

Exercise training improves obesity-induced inflammatory signaling in rat brown adipose tissue.

Chronic inflammation is considered as an etiology of obesity and type 2 diabetes. Brown adipose tissue (BAT) of obese animals shows increased inflammation. Regular exercise has anti-inflammatory effects; however, the effects of exercise training on BAT inflammation in obese animals remain unclear. Thus, this study aimed to investigate the effects of exercise training on inflammation-related signaling in the BAT of obese and diabetic rats. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an obese/diabetic rodent model, were randomly divided into either sedentary (n = 11) or exercise training (n = 8) groups. Long-Evans Tokushima Otsuka (LETO; n = 9) rats were used as the nondiabetic sedentary controls. Exercise training using a treadmill was conducted 4 days per week for 20 weeks, starting at 5 weeks old. As a result, exercise training attenuated the phosphorylation levels of p65 and mitogen-activated protein kinases in the BAT of OLETF rats, concurrently with the improvement of obesity and systemic glucose tolerance. Moreover, exercise training decreased oxidative stress and increased the antioxidant and anti-inflammatory protein levels in the BAT. Conversely, exercise training did not alter the expression levels of uncoupling protein-1 and oxidative phosphorylation-related proteins in the BAT, which were lower in the OLETF rats than the LETO rats. In conclusion, our data suggest that exercise training prevents the activation of inflammatory signaling in the BAT of obese/diabetic rats.