IDH2 Deficiency Is Critical in Myogenesis and Fatty Acid Metabolism in Mice Skeletal Muscle

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) catalyzes the oxidative decarboxylation of isocitrate into α-ketoglutarate with concurrent reduction of NADP⁺ to NADPH. However, it is not fully understood how IDH2 is intertwined with muscle development and fatty acid metabolism. Here, we examined the effects of IDH2 knockout (KO) on skeletal muscle energy homeostasis. Calf skeletal muscle samples from 10-week-old male IDH2 KO and wild-type (WT; C57BL/6N) mice were harvested, and the ratio of skeletal muscle weight to body and the ratio of mitochondrial to nucleic DNA were measured. In addition, genes involved in myogenesis, mitochondria biogenesis, adipogenesis, and thermogenesis were compared. Results showed that the ratio of skeletal muscle weight to body weight was lower in IDH2 KO mice than those in WT mice. Of note, a noticeable shift in fiber size distribution was found in IDH2 KO mice. Additionally, there was a trend of a decrease in mitochondrial content in IDH2 KO mice than in WT mice (p = 0.09). Further, mRNA expressions for myogenesis and mitochondrial biogenesis were either decreased or showed a trend of decrease in IDH2 KO mice. Moreover, genes for adipogenesis pathway (Pparg, Znf423, and Fat1) were downregulated in IDH2 KO mice. Interestingly, mRNA and protein expression of uncoupling protein 1 (UCP1), a hallmark of thermogenesis, were remarkably increased in IDH2 KO mice. In line with the UCP1 expression, IDH2 KO mice showed higher rectal temperature than WT mice under cold stress. Taken together, IDH2 deficiency may affect myogenesis, possibly due to impairments of muscle generation and abnormal fatty acid oxidation as well as thermogenesis in muscle via upregulation of UCP1.

Muscle-Bone Crosstalk: Emerging Opportunities for Novel Therapeutic Approaches to Treat Musculoskeletal Pathologies

Osteoporosis and sarcopenia are age-related musculoskeletal pathologies that often develop in parallel. Osteoporosis is characterized by a reduced bone mass and an increased fracture risk. Sarcopenia describes muscle wasting with an increasing risk of injuries due to falls. The medical treatment of both diseases costs billions in health care per year. With the impact on public health and economy, and considering the increasing life expectancy of populations, more efficient treatment regimens are sought. The biomechanical interaction between both tissues with muscle acting on bone is well established. Recently, both tissues were also determined as secretory endocrine organs affecting the function of one another. New exciting discoveries on this front are made each year, with novel signaling molecules being discovered and potential controversies being described. While this review does not claim completeness, it will summarize the current knowledge on both the biomechanical and the biochemical link between muscle and bone. The review will highlight the known secreted molecules by both tissues affecting the other and finish with an outlook on novel therapeutics that could emerge from these discoveries.

Characterization of the zebrafish cx36.7 gene promoter: Its regulation of cardiac-specific expression and skeletal muscle-specific repression

Zebrafish connexin 36.7 (cx36.7/ecx) has been identified as a key molecule in the early stages of heart development in this species. A defect in cx36.7 causes severe heart malformation due to the downregulation of nkx2.5 expression, a result which resembles congenital heart disease in humans. It has been shown that cx36.7 is expressed specifically in early developing heart cardiomyocytes. However, the regulatory mechanism for the cardiac-restricted expression of cx36.7 remains to be elucidated. In this study we isolated the 5'-flanking promoter region of the cx36.7 gene and characterized its promoter activity in zebrafish embryos. Deletion analysis showed that a 316-bp upstream region is essential for cardiac-restricted expression. This region contains four GATA elements, the proximal two of which are responsible for promoter activation in the embryonic heart and serve as binding sites for gata4. When gata4, gata5 and gata6 were simultaneously knocked down, the promoter activity was significantly decreased. Moreover, the deletion of the region between -316 and -133bp led to EGFP expression in the embryonic trunk muscle. The distal two GATA and A/T-rich elements in this region act as repressors of promoter activity in skeletal muscle. These results suggest that cx36.7 expression is directed by cardiac promoter activation via the two proximal GATA elements as well as by skeletal muscle-specific promoter repression via the two distal GATA elements.

Neuronal control of bone and muscle

The functional interplay between bone and muscle that enables locomotion is a fundamental aspect of daily life. However, other interactions between bone and muscle continue to attract attention as our understanding of the breath and importance of this inter-relationship continues to expand. Of particular interest is the regulatory connection between bone and muscle, which adds a new insight to the coordination of the bone/muscle unit. We have appreciated the importance of neuronal signaling to the control of bone turnover and muscle contraction, but recent data indicate that neuronal inputs control a far wider range of bone and muscle physiology than previously appreciated. This review outlines the role of the sympathetic nervous system and neuronal/neuropeptide inputs upon the regulation of bone and muscle tissue, and the potential for co-regulatory actions, particularly involving the sympathetic nervous system. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Adverse effects from clenbuterol and ractopamine on nematode Caenorhabditis elegans and the underlying mechanism

In the present study, we used Caenorhabditis elegans assay system to investigate in vivo toxicity from clentuberol and ractopamine and the possible underlying mechanism. Both acute and prolonged exposures to clentuberol or ractopamine decreased brood size and locomotion behavior, and induced intestinal autofluorescence and reactive oxygen species (ROS) production. Although acute exposure to the examined concentrations of clentuberol or ractopamine did not induce lethality, prolonged exposure to 10 µg/L of clentuberol and ractopamine reduced lifespan. At relatively high concentrations, ractopamine exhibited more severe toxicity than clentuberol on nematodes. Overexpression of sod-2 gene encoding a Mn-SOD to prevent induction of oxidative stress effectively inhibited toxicity from clentuberol or ractopamine. Besides oxidative stress, we found that clentuberol might reduce lifespan through influencing insulin/IGF signaling pathway; however, ractopamine might reduce lifespan through affecting both insulin/IGF signaling pathway and TOR signaling pathway. Ractopamine more severely decreased expression levels of daf-16, sgk-1, skn-1, and aak-2 genes than clentuberol, and increased expression levels of daf-2 and age-1 genes at the examined concentration. Therefore, the C. elegans assay system may be useful for assessing the possible toxicity from weight loss agents, and clentuberol and ractopamine may induce toxicity through different molecular mechanisms.

Expression characterization and the promoter activity analysis of zebrafish hdac4

Histone deacetylase 4 (HDAC4) is an important modifier enzyme for chromatin remodeling and plays an essential role in regulating gene expression. Spatio-temporal expression spectrum revealed that zebrafish hdac4 mRNA, ubiquitously distributed in various tissues, were significantly higher at 36 hpf (hours post-fertilization) and 6 dpf (days post-fertilization) than other periods. Trichostatin A (TSA) inhibited the development of zebrafish embryos and transcription of hdac4 and mef2a (myocyte enhancer factor-2A). Moreover, five vectors containing different promoter regions of hdac4 were constructed in order to analyze promoter activity. The vector containing the region from -125 to +160 exhibited maximum luciferase activity that was approximately 30.3-fold and 58.9-fold higher than the control in two kinds of cells, respectively. By comparing the luciferase activities between the region from -302 to +30 and -698 to +30, it was suggested that the region between -698 and -302 might contain mild negative regulatory elements.

Position stand on androgen and human growth hormone use

Hoffman, JR, Kraemer, WJ, Bhasin, S, Storer, T, Ratamess, NA, Haff, GG, Willoughby, DS, and Rogol, AD. Position stand on Androgen and human growth hormone use. J Strength Cond Res 23(5): S1-S59, 2009-Perceived yet often misunderstood demands of a sport, overt benefits of anabolic drugs, and the inability to be offered any effective alternatives has fueled anabolic drug abuse despite any consequences. Motivational interactions with many situational demands including the desire for improved body image, sport performance, physical function, and body size influence and fuel such negative decisions. Positive countermeasures to deter the abuse of anabolic drugs are complex and yet unclear. Furthermore, anabolic drugs work and the optimized training and nutritional programs needed to cut into the magnitude of improvement mediated by drug abuse require more work, dedication, and preparation on the part of both athletes and coaches alike. Few shortcuts are available to the athlete who desires to train naturally. Historically, the NSCA has placed an emphasis on education to help athletes, coaches, and strength and conditioning professionals become more knowledgeable, highly skilled, and technically trained in their approach to exercise program design and implementation. Optimizing nutritional strategies are a vital interface to help cope with exercise and sport demands (). In addition, research-based supplements will also have to be acknowledged as a strategic set of tools (e.g., protein supplements before and after resistance exercise workout) that can be used in conjunction with optimized nutrition to allow more effective adaptation and recovery from exercise. Resistance exercise is the most effective anabolic form of exercise, and over the past 20 years, the research base for resistance exercise has just started to develop to a significant volume of work to help in the decision-making process in program design (). The interface with nutritional strategies has been less studied, yet may yield even greater benefits to the individual athlete in their attempt to train naturally. Nevertheless, these are the 2 domains that require the most attention when trying to optimize the physical adaptations to exercise training without drug use.Recent surveys indicate that the prevalence of androgen use among adolescents has decreased over the past 10-15 years (). The decrease in androgen use among these students may be attributed to several factors related to education and viable alternatives (i.e., sport supplements) to substitute for illegal drug use. Although success has been achieved in using peer pressure to educate high school athletes on behaviors designed to reduce the intent to use androgens (), it has not had the far-reaching effect desired. It would appear that using the people who have the greatest influence on adolescents (coaches and teachers) be the primary focus of the educational program. It becomes imperative that coaches provide realistic training goals for their athletes and understand the difference between normal physiological adaptation to training or that is pharmaceutically enhanced. Only through a stringent coaching certification program will academic institutions be ensured that coaches that they hire will have the minimal knowledge to provide support to their athletes in helping them make the correct choices regarding sport supplements and performance-enhancing drugs.The NSCA rejects the use of androgens and hGH or any performance-enhancing drugs on the basis of ethics, the ideals of fair play in competition, and concerns for the athlete's health. The NSCA has based this position stand on a critical analysis of the scientific literature evaluating the effects of androgens and human growth hormone on human physiology and performance. The use of anabolic drugs to enhance athletic performance has become a major concern for professional sport organizations, sport governing bodies, and the federal government. It is the belief of the NSCA that through education and research we can mitigate the abuse of androgens and hGH by athletes. Due to the diversity of testosterone-related drugs and molecules, the term androgens is believed to be a more appropriate term for anabolic steroids.

Effects of 28 days of resistance exercise and consuming a commercially available pre-workout supplement, NO-Shotgun(R), on body composition, muscle strength and mass, markers of satellite cell activation, and clinical safety markers in males

Purpose

This study determined the effects of 28 days of heavy resistance exercise combined with the nutritional supplement, NO-Shotgun^®, on body composition, muscle strength and mass, markers of satellite cell activation, and clinical safety markers.

Methods

Eighteen non-resistance-trained males participated in a resistance training program (3 × 10-RM) 4 times/wk for 28 days while also ingesting 27 g/day of placebo (PL) or NO-Shotgun^® (NO) 30 min prior to exercise. Data were analyzed with separate 2 × 2 ANOVA and t-tests (p < 0.05).

Results

Total body mass was increased in both groups (p = 0.001), but without any significant increases in total body water (p = 0.77). No significant changes occurred with fat mass (p = 0.62); however fat-free mass did increase with training (p = 0.001), and NO was significantly greater than PL (p = 0.001). Bench press strength for NO was significantly greater than PL (p = 0.003). Myofibrillar protein increased with training (p = 0.001), with NO being significantly greater than PL (p = 0.019). Serum IGF-1 (p = 0.046) and HGF (p = 0.06) were significantly increased with training and for NO HGF was greater than PL (p = 0.002). Muscle phosphorylated c-met was increased with training for both groups (p = 0.019). Total DNA was increased in both groups (p = 0.006), while NO was significantly greater than PL (p = 0.038). For DNA/protein, PL was decreased and NO was not changed (p = 0.014). All of the myogenic regulatory factors were increased with training; however, NO was shown to be significantly greater than PL for Myo-D (p = 0.008) and MRF-4 (p = 0.022). No significant differences were located for any of the whole blood and serum clinical chemistry markers (p > 0.05).

Conclusion

When combined with heavy resistance training for 28 days, NO-Shotgun^® is not associated with any negative side effects, nor does it abnormally impact any of the clinical chemistry markers. Rather, NO-Shotgun^® effectively increases muscle strength and mass, myofibrillar protein content, and increases the content of markers indicative of satellite cell activation.