Myostatin inhibits eEF2K-eEF2 by regulating AMPK to suppress protein synthesis

Carnosol suppresses cardiomyocyte hypertrophy via promoting the activation of AMPK pathway

Pathological cardiac hypertrophy is associated with adverse cardiovascular events and can gradually lead to heart failure, arrhythmia, and even sudden death. However, the current development of treatment strategies has been unsatisfactory. Therefore, it is of great significance to find new and effective drugs for the treatment of myocardial hypertrophy. We found that carnosol can inhibit myocardial hypertrophy induced by PE stimulation, and the effect is very significant at 5 μM. Moreover, we demonstrated that 50 mg/kg of carnosol protect against cardiac hypertrophy and fibrosis induced by TAC surgery in mice. Mechanically, we proved that the inhibitory effect of carnosol on cardiac hypertrophy depends on its regulation on the phosphorylation activation of AMPK. In conclusion, our study suggested that carnosol may be a novel drug component for the treatment of pathological cardiac hypertrophy.

Association between sarcopenia and osteoporosis: the cross-sectional study from NHANES 1999-2020 and a bi-directions Mendelian randomization study

Background

Osteoporosis (OP) and sarcopenia are prevalent musculoskeletal conditions among the elderly. Nevertheless, the causal relationship between sarcopenia and OP remains a subject of controversy and uncertainty. In this study, we employed cross-sectional analysis and Mendelian randomization (MR) to investigate the intricate relationship between sarcopenia and OP.

Methods

The cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) spanning 1999-2020, which involved in 116,876 participants. It assessed the correlation between sarcopenia, osteoporosis (OP), and bone mineral density (BMD) using Chi-square tests, T-tests, and a multiple logistic regression model. Additionally, we conducted Mendelian randomization (MR) analysis to investigate the causal effects of sarcopenia-related characteristics (ALM) on OP. We employed IVW, sensitivity analysis, heterogeneity testing, and other methods for MR. The ALM data was sourced from the UK Biobank (n=450,243), while the aggregated data on OP was obtained from GWAS statistics (n=53,236).

Results

In this cross-sectional analysis, we observed that in the multivariate logistic regression model, without adjusting for any variables, OP emerged as a risk factor for sarcopenia [OR 95% CI = 1.90 (1.13-3.18), P = 0.02]. Following adjustments for gender, age, BMI, and biochemical variables, OP retained its status as a risk factor for sarcopenia [OR 95% CI = 3.54 (1.91-6.54), P < 0.001]. Moreover, after accounting for all variables, OP emerged as an independent risk factor for sarcopenia [OR 95% CI = 4.57 (1.47-14.22), P = 0.01].In the MR analysis, we uncovered that femoral neck BMD (FN BMD), lumbar spine BMD (LS BMD), and forearm bone mineral density (FA BMD) exerted a direct causal influence on ALM [FA BMD: OR 95% CI = 1.028 (1.008, 1.049), p = 0.006; FN BMD: OR (95% CI) = 1.131 (1.092, 1.170), p = 3.18E-12; LS BMD: OR (95% CI) = 1.080 (1.062, 1.098), p = 2.86E-19].

Conclusion

Our study has revealed a positive correlation between OP and the prevalence of sarcopenia. It suggests a potentially robust causal relationship between OP and sarcopenia. Notably, OP appears to be associated with a higher likelihood of losing ALM, and a significant loss of ALM may contribute to a decline in LS BMD.

Roles of Myokines and Muscle-Derived Extracellular Vesicles in Musculoskeletal Deterioration under Disuse Conditions

Prolonged inactivity and disuse conditions, such as those experienced during spaceflight and prolonged bedrest, are frequently accompanied by detrimental effects on the motor system, including skeletal muscle atrophy and bone loss, which greatly increase the risk of osteoporosis and fractures. Moreover, the decrease in glucose and lipid utilization in skeletal muscles, a consequence of muscle atrophy, also contributes to the development of metabolic syndrome. Clarifying the mechanisms involved in disuse-induced musculoskeletal deterioration is important, providing therapeutic targets and a scientific foundation for the treatment of musculoskeletal disorders under disuse conditions. Skeletal muscle, as a powerful endocrine organ, participates in the regulation of physiological and biochemical functions of local or distal tissues and organs, including itself, in endocrine, autocrine, or paracrine manners. As a motor organ adjacent to muscle, bone tissue exhibits a relative lag in degenerative changes compared to skeletal muscle under disuse conditions. Based on this phenomenon, roles and mechanisms involved in the communication between skeletal muscle and bone, especially from muscle to bone, under disuse conditions have attracted widespread attention. In this review, we summarize the roles and regulatory mechanisms of muscle-derived myokines and extracellular vesicles (EVs) in the occurrence of muscle atrophy and bone loss under disuse conditions, as well as discuss future perspectives based on existing research.

Gelation of cytoplasmic expanded CAG RNA repeats suppresses global protein synthesis

RNA molecules with the expanded CAG repeat (eCAGr) may undergo sol-gel phase transitions, but the functional impact of RNA gelation is completely unknown. Here, we demonstrate that the eCAGr RNA may form cytoplasmic gel-like foci that are rapidly degraded by lysosomes. These RNA foci may significantly reduce the global protein synthesis rate, possibly by sequestering the translation elongation factor eEF2. Disrupting the eCAGr RNA gelation restored the global protein synthesis rate, whereas enhanced gelation exacerbated this phenotype. eEF2 puncta were significantly enhanced in brain slices from a knock-in mouse model and from patients with Huntington's disease, which is a CAG expansion disorder expressing eCAGr RNA. Finally, neuronal expression of the eCAGr RNA by adeno-associated virus injection caused significant behavioral deficits in mice. Our study demonstrates the existence of RNA gelation inside the cells and reveals its functional impact, providing insights into repeat expansion diseases and functional impacts of RNA phase transition.

Senescent adipocytes as potential effectors of muscle cells dysfunction: An in vitro model

Recently, there has been a growing body of evidence showing a negative effect of the white adipose tissue (WAT) dysfunction on the skeletal muscle function and quality. However, little is known about the effects of senescent adipocytes on muscle cells. Therefore, to explore potential mechanisms involved in age-related loss of muscle mass and function, we performed an in vitro experiment using conditioned medium obtained from cultures of mature and aged 3 T3-L1 adipocytes, as well as from cultures of dysfunctional adipocytes exposed to oxidative stress or high insulin doses, to treat C2C12 myocytes. The results from morphological measures indicated a significant decrease in diameter and fusion index of myotubes after treatment with medium of aged or stressed adipocytes. Aged and stressed adipocytes presented different morphological characteristics as well as a different gene expression profile of proinflammatory cytokines and ROS production. In myocytes treated with different adipocytes' conditioned media, we demonstrated a significant reduction of gene expression of myogenic differentiation markers as well as a significant increase of genes involved in atrophy. Finally, a significant reduction in protein synthesis as well as a significant increase of myostatin was found in muscle cells treated with medium of aged or stressed adipocytes compared to controls. In conclusion, these preliminary results suggest that aged adipocytes could influence negatively trophism, function and regenerative capacity of myocytes by a paracrine network of signaling.

eEF2 improves dense connective tissue repair and healing outcome by regulating cellular death, autophagy, apoptosis, proliferation and migration

Outcomes following human dense connective tissue (DCT) repair are often variable and suboptimal, resulting in compromised function and development of chronic painful degenerative diseases. Moreover, biomarkers and mechanisms that guide good clinical outcomes after DCT injuries are mostly unknown. Here, we characterize the proteomic landscape of DCT repair following human Achilles tendon rupture and its association with long-term patient-reported outcomes. Moreover, the potential regulatory mechanisms of relevant biomarkers were assessed partly by gene silencing experiments. A mass-spectrometry based proteomic approach quantified a large number (769) of proteins, including 51 differentially expressed proteins among 20 good versus 20 poor outcome patients. A novel biomarker, elongation factor-2 (eEF2) was identified as being strongly prognostic of the 1-year clinical outcome. Further bioinformatic and experimental investigation revealed that eEF2 positively regulated autophagy, cell proliferation and migration, as well as reduced cell death and apoptosis, leading to improved DCT repair and outcomes. Findings of eEF2 as novel prognostic biomarker could pave the way for new targeted treatments to improve healing outcomes after DCT injuries.Trial registration: NCT02318472 registered 17 December 2014 and NCT01317160 registered 17 March 2011, with URL http://clinicaltrials.gov/ct2/show/NCT02318472 and http://clinicaltrials.gov/ct2/show/study/NCT01317160 .

Novel Pro-myogenic Factor Neoruscogenin Induces Muscle Fiber Hypertrophy by Inhibiting MSTN Maturation and Activating the Akt/mTOR Pathway

Neoruscogenin is a plant-origin sapogenin that has the potential to modulate muscle growth among the small-molecule compounds that we previously predicted by artificial intelligence to target myostatin (MSTN). This study aimed to elucidate the biological role of neoruscogenin on muscle growth and its relationship with MSTN. Using molecular biological techniques, we found that neoruscogenin inhibited MSTN maturation, thereby repressing its signal transduction; further facilitated protein synthesis metabolism and reduced protein degradation metabolism, ultimately promoting the differentiation of myoblasts and hypertrophy of muscle fibers; and had the effect of repairing muscle injury. This study enriched the biological functions of neoruscogenin and provided a theoretical basis for the treatment of human myopathy and its application in the livestock industry.

AMPK: The key to ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) refers to a syndrome in which tissue damage is further aggravated and organ function further deteriorates when blood flow is restored after a period of tissue ischemia. Acute myocardial infarction, stress ulcer, pancreatitis, intestinal ischemia, intermittent claudication, acute tubular necrosis, postshock liver failure, and multisystem organ failure are all related to reperfusion injury. AMP-activated protein kinase (AMPK) has been identified in multiple catabolic and anabolic signaling pathways. The functions of AMPK during health and diseases are intriguing but still need further research. Except for its conventional roles as an intracellular energy switch, emerging evidence reveals the critical role of AMPK in IRI as an energy-sensing signal molecule by regulating metabolism, autophagy, oxidative stress, inflammation, and other progressions. At the same time, drugs based on AMPK for the treatment of IRI are constantly being researched and applied in clinics. In this review, we summarize the mechanisms underlying the effects of AMPK in IRI and describe the AMPK-targeting drugs in treatment, hoping to increase the understanding of AMPK in IRI and provide new insights into future clinical treatment.

Myostatin Deficiency Enhances Antioxidant Capacity of Bovine Muscle via the SMAD-AMPK-G6PD Pathway

During exercise, the body’s organs and skeletal muscles produce reactive oxygen species (ROS). Excessive ROS can destroy cellular lipids, sugars, proteins, and nucleotides and lead to cancer. The production of nicotinamide adenine dinucleotide phosphate (NADPH) by the pentose phosphate pathway (PPP) is an auxiliary process of the cellular antioxidant system that supplements the reducing power of glutathione (GSH) to eliminate ROS in the cell. Myostatin (MSTN) is mainly expressed in skeletal muscle and participates in the regulation of skeletal muscle growth and development. Loss of MSTN leads to muscular hypertrophy, and MSTN deficiency upregulates glycolysis. However, the effect of MSTN on the PPP has not been reported. This study investigated the effect of MSTN on muscle antioxidant capacity from a metabolic perspective. We found that reducing MSTN modulates AMP-activated protein kinase (AMPK), a key molecule in cellular energy metabolism that directly regulates glucose metabolism through phosphorylation. Downregulation of MSTN promotes tyrosine modification of glucose-6-phosphate-dehydrogenase (G6PD) by AMPK and is regulated by the Smad signaling pathway. The Smad2/3 complex acts as a transcription factor to inhibit the AMPK expression. These results suggest that reduced MSTN expression inhibits the Smad signaling pathway, promotes AMPK expression, enhances the activity of G6PD enzyme, and enhances the antioxidant capacity of nonenzymatic GSH.

Comparison of Microbial Community and Metabolites in Four Stomach Compartments of Myostatin-Gene-Edited and Non-edited Cattle

Myostatin (MSTN), a major negative regulator of skeletal muscle mass and an endocrine factor, can regulate the metabolism of various organisms. Inhibition of the MSTN gene can improve meat production from livestock. Rumen microorganisms are associated with production and health traits of cattle, but changes in the microbial composition and metabolome in the four stomach compartments of MSTN gene-edited cattle have not previously been studied. Our results indicated that microbial diversity and dominant bacteria in the four stomach compartments were very similar between MSTN gene-edited and wild-type (WT) cattle. The microbiota composition was significantly different between MSTN gene-edited and WT cattle. Our results show that the relative abundance of the phylum Proteobacteria in the reticulum of MSTN gene-edited cattle was lower than that of WT cattle, whereas the relative abundance of the genus Prevotella in the omasum of MSTN gene-edited cattle was significantly higher than that of WT cattle. Metabolomics analysis revealed that the intensity of L-proline and acetic acid was significantly different in the rumen, reticulum, and abomasum between the two types of cattle. Meanwhile, pathway topology analysis indicated that the differential metabolites were predominantly involved in arginine biosynthesis and glutamate metabolism in the rumen, reticulum, and omasum but were mainly involved in pyruvate metabolism and glycolysis/gluconeogenesis in the abomasum. Spearman correlation network analysis further demonstrated that there was a significant correlation between microflora composition and metabolic pathways. These findings provide clues for studying nutrient digestion and absorption ability of MSTN gene-edited cattle.

Pharmacological Manipulation of Translation as a Therapeutic Target for Chronic Pain

Dysfunction in regulation of mRNA translation is an increasingly recognized characteristic of many diseases and disorders, including cancer, diabetes, autoimmunity, neurodegeneration, and chronic pain. Approximately 50 million adults in the United States experience chronic pain. This economic burden is greater than annual costs associated with heart disease, cancer, and diabetes combined. Treatment options for chronic pain are inadequately efficacious and riddled with adverse side effects. There is thus an urgent unmet need for novel approaches to treating chronic pain. Sensitization of neurons along the nociceptive pathway causes chronic pain states driving symptoms that include spontaneous pain and mechanical and thermal hypersensitivity. More than a decade of preclinical research demonstrates that translational mechanisms regulate the changes in gene expression that are required for ongoing sensitization of nociceptive sensory neurons. This review will describe how key translation regulation signaling pathways, including the integrated stress response, mammalian target of rapamycin, AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase-interacting kinases, impact the translation of different subsets of mRNAs. We then place these mechanisms of translation regulation in the context of chronic pain states, evaluate currently available therapies, and examine the potential for developing novel drugs. Considering the large body of evidence now published in this area, we propose that pharmacologically manipulating specific aspects of the translational machinery may reverse key neuronal phenotypic changes causing different chronic pain conditions. Therapeutics targeting these pathways could eventually be first-line drugs used to treat chronic pain disorders. SIGNIFICANCE STATEMENT: Translational mechanisms regulating protein synthesis underlie phenotypic changes in the sensory nervous system that drive chronic pain states. This review highlights regulatory mechanisms that control translation initiation and how to exploit them in treating persistent pain conditions. We explore the role of mammalian/mechanistic target of rapamycin and mitogen-activated protein kinase-interacting kinase inhibitors and AMPK activators in alleviating pain hypersensitivity. Modulation of eukaryotic initiation factor 2α phosphorylation is also discussed as a potential therapy. Targeting specific translation regulation mechanisms may reverse changes in neuronal hyperexcitability associated with painful conditions.

The Failed Clinical Story of Myostatin Inhibitors against Duchenne Muscular Dystrophy: Exploring the Biology behind the Battle

Myostatin inhibition therapy has held much promise for the treatment of muscle wasting disorders. This is particularly true for the fatal myopathy, Duchenne Muscular Dystrophy (DMD). Following on from promising pre-clinical data in dystrophin-deficient mice and dogs, several clinical trials were initiated in DMD patients using different modality myostatin inhibition therapies. All failed to show modification of disease course as dictated by the primary and secondary outcome measures selected: the myostatin inhibition story, thus far, is a failed clinical story. These trials have recently been extensively reviewed and reasons why pre-clinical data collected in animal models have failed to translate into clinical benefit to patients have been purported. However, the biological mechanisms underlying translational failure need to be examined to ensure future myostatin inhibitor development endeavors do not meet with the same fate. Here, we explore the biology which could explain the failed translation of myostatin inhibitors in the treatment of DMD.

Bone and Muscle Crosstalk in Aging

Osteoporosis and sarcopenia are two age-related diseases that affect the quality of life in the elderly. Initially, they were thought to be two independent diseases; however, recently, increasing basic and clinical data suggest that skeletal muscle and bone are both spatially and metabolically connected. The term "osteosarcopenia" is used to define a condition of synergy of low bone mineral density with muscle atrophy and hypofunction. Bone and muscle cells secrete several factors, such as cytokines, myokines, and osteokines, into the circulation to influence the biological and pathological activities in local and distant organs and cells. Recent studies reveal that extracellular vesicles containing microRNAs derived from senescent skeletal muscle and bone cells can also be transported and aid in regulating bone-muscle crosstalk. In this review, we summarize the age-related changes in the secretome and extracellular vesicle-microRNAs secreted by the muscle and bone, and discuss their interactions between muscle and bone cells during aging.

Dysregulated Autophagy Mediates Sarcopenic Obesity and Its Complications via AMPK and PGC1α Signaling Pathways: Potential Involvement of Gut Dysbiosis as a Pathological Link

Sarcopenic obesity (SOB), which is closely related to being elderly as a feature of aging, is recently gaining attention because it is associated with many other age-related diseases that present as altered intercellular communication, dysregulated nutrient sensing, and mitochondrial dysfunction. Along with insulin resistance and inflammation as the core pathogenesis of SOB, autophagy has recently gained attention as a significant mechanism of muscle aging in SOB. Known as important cellular metabolic regulators, the AMP-activated protein kinase (AMPK) and the peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) signaling pathways play an important role in autophagy, inflammation, and insulin resistance, as well as mutual communication between skeletal muscle, adipose tissue, and the liver. Furthermore, AMPK and PGC-1α signaling pathways are implicated in the gut microbiome-muscle axis. In this review, we describe the pathological link between SOB and its associated complications such as metabolic, cardiovascular, and liver disease, falls and fractures, osteoarthritis, pulmonary disease, and mental health via dysregulated autophagy controlled by AMPK and/or PGC-1α signaling pathways. Here, we propose potential treatments for SOB by modulating autophagy activity and gut dysbiosis based on plausible pathological links.

Transcriptomic profile of semitendinosus muscle of bulls of different breed and performance

The aim of the study was to compare the transcriptomic profiles of fully differentiated skeletal muscle derived from bulls belonging to different breeds of varying performance. Microarray analyses were performed to determine the differences in the expression profiles of genes between semitendinosus muscles of 15-month-old beef-breed bulls (Limousin—LIM and Hereford—HER) and dairy-breed bulls (Holstein Friesian—HF). These analyses allowed for the identification of those genes the expression of which is similar and characteristic of fully differentiated muscle in beef breeds, but differs in skeletal muscle of a typical dairy breed. The analysis revealed 463 transcripts showing similar expression in the semitendinosus muscle of beef breeds (LIM/HER), in comparison with the dairy breed (HF). Among the identified genes, 227 were upregulated and 236 were downregulated in beef breeds. The ontological analyses revealed that the largest group of genes similarly expressed in LIM and HER was involved in the processes of protein metabolism and development of muscle organ. In beef breeds, some genes involved in protein synthesis and proteolysis showed an upregulation, including ctsd, ctsf, fhl2, fhl3, fst, sirt1, and trim63, whereas some were downregulated, including bmpr1a, bmpr2, mstn, smad2, hspa8, gsk3β, and tgfβ2. The expression of the chosen genes was confirmed by RT-qPCR technique. Thus, it can be assumed that the identified genes involved in the regulation of growth and development of muscle tissue and the processes of protein metabolism in the examined cattle breeds may be responsible for the greater gain of muscle mass in beef-breed bulls.

Generation of reporter cell lines for factors inducing muscle wasting in cancer cachexia

Rapidly identifying cachexia-inducing factors that directly induce muscle wasting is an existing challenge. We developed two reporter cell lines that allow swift detection of such factors in blood from patients. C2C12 myoblasts were used for the establishment of reporter cells. A luciferase reporter gene, driven by promoters of wasting genes, Muscle RING-finger protein-1 (MuRF1) and Muscle Atrophy F-Box Protein (MAFbx/Atrogin-1) were used for the construction of reporter constructs. Increased expression of these genes in muscle tissue under wasting conditions was shown in vivo and in vitro. We found these reporter cell lines could detect factors associated with cancer cachexia, such as myostatin (Mstn), activin A, and TNF-α. We further investigated the capacity to directly detect a cachectic state using plasma samples from cachectic mice and cancer patients. Activation of the reporter cell lines was observed by the addition of plasma from mice with cancer cachexia and serum samples from patients with pancreatic or colorectal cancer. These results indicate that the reporter cell lines are competent as a tool for screening cachexia-inducing factors and potentially distinguishing a cachectic state induced by cancer.

Circular RNA circ-ZEB1 acts as an oncogene in triple negative breast cancer via sponging miR-448

BACKGROUND

Circular RNAs (circRNAs) play an important role in tumor development. The miRNA sponge is a common role played by circRNAs in various tumors, including breast cancer.

OBJECTIVE

This study aimed to explore the role of circ-ZEB1 in the proliferation and apoptosis of triple negative breast cancer (TNBC) cells.

METHODS

The expressions of several circRNAs which were predicted to be bound with miR-448 were detected in 30 clinical TNBC tumor tissues and paired paracancer tissues. The cell counting kit-8 assay was performed to detect the TNBC cell proliferation. The TNBC cell apoptosis was detected using the TUNEL assay. The binding between circ-ZEB1 and miR-448, as well as between miR-448 and eukaryotic elongation factor 2 kinase (eEF2 K), was detected using the RNA pull-down assay and/or the luciferase reporter assay. The effect of circ-ZEB1 knockdown on TNBC tumor growth was detected using the mouse xenograft model.

RESULTS

Compared with normal tissues and breast epithelial cells, the expression of circ-ZEB1 was markedly higher in TNBC tumor tissues and tumor cell lines. The small hairpin RNA-mediated circ-ZEB1 knockdown inhibited TNBC cell proliferation and induced cell apoptosis. The RNA pull-down assay and the luciferase reporter assay confirmed the binding between circ-ZEB1 and miR-448, as well as between miR-448 and eEF2 K. The knockdown of circ-ZEB1 was proven to inhibit TNBC cell proliferation and tumor growth via releasing miR-448, and subsequently reducing the expression of the miR-448 target, eEF2 K.

CONCLUSION

In conclusion, our findings identified a new functional circ-ZEB1 in TNBC tumorigenesis, and revealed the important regulatory role of circ-ZEB1 via sponging miR-448, providing a novel insight for TNBC pathogenesis.

Myostatin Increases Smad2 Phosphorylation and Atrogin-1 Expression in Chick Embryonic Myotubes

Skeletal muscle mass is an important trait in poultry meat production. In mammals, myostatin, a negative regulator of skeletal muscle growth, activates Smad transcription factors and induces the expression of atrogin-1 by regulating the Akt/FOXO pathway. Although the amino acid sequence of chicken myostatin is known to be completely identical to its mammalian counterpart, previous studies in chicken skeletal muscles have implied that the physiological roles of chicken myostatin are different from those of mammals. Furthermore, it remains to be elucidated whether myostatin affects cellular signaling factors and atrogin-1 expression. In this study, using chick embryonic myotubes, we found that myostatin significantly increased the phosphorylation rate of Smad2 and mRNA levels of atrogin-1. No significant change was observed in the phosphorylation of Akt and FOXO1. These in vitro results suggest that the molecular mechanisms underlying myostatin-induced expression of atrogin-1 might be different between chickens and mammals.

Eukaryotic elongation factor 2 kinase inhibitor, A484954 inhibits noradrenaline-induced acute increase of blood pressure in rats

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) inhibits protein translation through the phosphorylation of its specific substrate, eEF2. We previously demonstrated that eEF2K expression increases in superior mesenteric artery from spontaneously hypertensive rats (SHR) and that eEF2K mediates development of hypertension in SHR. In addition, we recently revealed that A484954, a selective eEF2K inhibitor induced relaxation via opening smooth muscle inward rectifier K⁺ (K_ir) channel in rat isolated superior mesenteric artery. Here, we further examined the effects of A484954 on contractility and blood pressure (BP) in rats. Isometric contraction of rat isolated superior mesenteric artery was measured. BP was measured by a carotid cannulation method. A484954 (10 µM) inhibited noradrenaline (NA)-induced contraction in a biphasic manner (magnitude of inhibition higher at high dose NA). A484954 also inhibited an α₁-receptor agonist, phenylephrine-induced contraction, while it was not biphasic. Specifically, a β-receptor antagonist, propranolol (1 µM) prevented the A484954-mediated inhibition of NA (high-dose)-induced contraction. A484954 (10 µM) potentiated a β-receptor agonist, isoproterenol-induced relaxation, which was completely prevented by BaCl₂ (1 mM), a K_ir channel blocker. In vivo, A484954 (122 µg/kg) inhibited NA-induced increase of BP in rats. Another eEF2K inhibitor, NH125 (22 µg/kg) also inhibited the NA-induced BP increase in rats. In summary, it was concluded that A484954 lowers NA-induced BP rise perhaps through activation of β₂-receptor-K_ir channel and subsequent vasorelaxation via inhibiting eEF2K activity.

The Role of AMPK in the Regulation of Skeletal Muscle Size, Hypertrophy, and Regeneration

AMPK (5’-adenosine monophosphate-activated protein kinase) is heavily involved in skeletal muscle metabolic control through its regulation of many downstream targets. Because of their effects on anabolic and catabolic cellular processes, AMPK plays an important role in the control of skeletal muscle development and growth. In this review, the effects of AMPK signaling, and those of its upstream activator, liver kinase B1 (LKB1), on skeletal muscle growth and atrophy are reviewed. The effect of AMPK activity on satellite cell-mediated muscle growth and regeneration after injury is also reviewed. Together, the current data indicate that AMPK does play an important role in regulating muscle mass and regeneration, with AMPKα1 playing a prominent role in stimulating anabolism and in regulating satellite cell dynamics during regeneration, and AMPKα2 playing a potentially more important role in regulating muscle degradation during atrophy.