Sarcopenia, the age-related loss of skeletal muscle mass and function, is becoming more prevalent as the lifespan continues to increase in most populations. As sarcopenia is highly disabling, being associated with increased risk of dependence, falls, fractures, weakness, disability, and death, development of approaches to its prevention and treatment are required. Androgens are the main physiologic anabolic steroid hormones and normal testosterone levels are necessary for a range of developmental and biological processes, including maintenance of muscle mass. Testosterone concentrations decline as age increase, suggesting that low plasma testosterone levels can cause or accelerate muscle- and age-related diseases, as sarcopenia. Currently, there is increasing interest on the anabolic properties of testosterone for therapeutic use in muscle diseases including sarcopenia. However, the pathophysiological mechanisms underlying this muscle syndrome and its relationship with plasma level of androgens are not completely understood. This review discusses the recent findings regarding sarcopenia, the intrinsic, and extrinsic mechanisms involved in the onset and progression of this disease and the treatment approaches that have been developed based on testosterone deficiency and their implications.

Testosterone exerts important effects in the heart. Cardiomyocytes are target cells for androgens, and testosterone induces rapid effects via Ca(2+) release and protein kinase activation and long-term effects via cardiomyocyte differentiation and hypertrophy. Furthermore, it stimulates metabolic effects such as increasing glucose uptake in different tissues. Cardiomyocytes preferentially consume fatty acids for ATP production, but under particular circumstances, glucose uptake is increased to optimize energy production. We studied the effects of testosterone on glucose uptake in cardiomyocytes. We found that testosterone increased uptake of the fluorescent glucose analog 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-2-deoxyglucose and [(3) H]2-deoxyglucose, which was blocked by the glucose transporter 4 (GLUT4) inhibitor indinavir. Testosterone stimulation in the presence of cyproterone or albumin-bound testosterone-induced glucose uptake, which suggests an effect that is independent of the intracellular androgen receptor. To determine the degree of GLUT4 cell surface exposure, cardiomyocytes were transfected with the plasmid GLUT4myc-eGFP. Subsequently, testosterone increased GLUT4myc-GFP exposure at the plasma membrane. Inhibition of Akt by the Akt-inhibitor-VIII had no effect. However, inhibition of Ca(2+) /calmodulin protein kinase (CaMKII) (KN-93 and autocamtide-2 related inhibitory peptide II) and AMP-activated protein kinase (AMPK) (compound C and siRNA for AMPK) prevented glucose uptake induced by testosterone. Moreover, GLUT4myc-eGFP exposure at the cell surface caused by testosterone was also abolished after CaMKII and AMPK inhibition. These results suggest that testosterone increases GLUT4-dependent glucose uptake, which is mediated by CaMKII and AMPK in cultured cardiomyocytes. Glucose uptake could represent a mechanism by which testosterone increases energy production and protein synthesis in cardiomyocytes.

Introduction ESG is an effective treatment option for obesity. However, data comparing its efficacy to bariatric surgery is scarce. We aim to compare the effectiveness and safety of ESG to LSG and LGCP at 2-years. Methods We reviewed 353 patient records and identified 296 patients who underwent ESG (n=199), LSG (n=61), and LGCP (n=36) at 4-centers in Spain between 2014 to 2016. We compared their total body weight loss (%TBWL) and safety over 2-years. We used a linear mixed model (LMM) to analyse repeated measures of weight loss outcomes at 6, 12, 18, and 24-months for comparison between the three procedures. Results Among the 296 patients, 210 (ESG-135, LSG-43, LGCP-32) reached 1-year and 102 (ESG-46, LSG-34, LGCP-22) patients completed 2-years follow-up. The mean(SD) BMI was 39.6(4.8) kg/m2. There was no difference in the age, sex, and BMI between the groups. In LMM analysis, adjusting for age, sex, and initial BMI, we found ESG had a significantly lower TBWL, %TBWL, and BMI decline compared to LSG and LGCP at all time points (p=0.001). The adjusted mean %TBWL at 2-years with ESG, LSG, and LGCP was 18.5%, 28.3%, and 26.9%, respectively. However, ESG, as compared to LSG and LGCP, had a shorter inpatient stay (1 vs.3 vs. 3 days, p<0.001) and lower complication rate (0.5% vs.4.9% vs. 8.3%, p=0.006). Conclusion All three procedures induced significant weight loss in obese patients. Although the weight loss was lower with ESG compared to other techniques, it displayed a better safety profile and shorter hospital stay.

Testosterone induces cardiac hypertrophy through a mechanism that involves a concerted crosstalk between cytosolic and nuclear signaling pathways. Nuclear factor of activated T-cells (NFAT) is associated with the promotion of cardiac hypertrophy, glycogen synthase kinase-3β (GSK-3β) is considered to function as a negative regulator, mainly by modulating NFAT activity. However, the role played by calcineurin-NFAT and GSK-3β signaling in testosterone-induced cardiac hypertrophy has remained unknown. Here, we determined that testosterone stimulates cardiac myocyte hypertrophy through NFAT activation and GSK-3β inhibition. Testosterone increased the activity of NFAT-luciferase (NFAT-Luc) in a time- and dose-dependent manner, with the activity peaking after 24 h of stimulation with 100 nM testosterone. NFAT-Luc activity induced by testosterone was blocked by the calcineurin inhibitors FK506 and cyclosporine A and by 11R-VIVIT, a specific peptide inhibitor of NFAT. Conversely, testosterone inhibited GSK-3β activity as determined by increased GSK-3β phosphorylation at Ser9 and β-catenin protein accumulation, and also by reduction in β-catenin phosphorylation at residues Ser33, Ser37, and Thr41. GSK-3β inhibition with 1-azakenpaullone or a GSK-3β-targeting siRNA increased NFAT-Luc activity, whereas overexpression of a constitutively active GSK-3β mutant (GSK-3βS9A) inhibited NFAT-Luc activation mediated by testosterone. Testosterone-induced cardiac myocyte hypertrophy was established by increased cardiac myocyte size and [3H]-leucine incorporation (as a measurement of cellular protein synthesis). Calcineurin-NFAT inhibition abolished and GSK-3β inhibition promoted the hypertrophy stimulated by testosterone. GSK-3β activation by GSK-3βS9A blocked the increase of hypertrophic markers induced by testosterone. Moreover, inhibition of intracellular androgen receptor prevented testosterone-induced NFAT-Luc activation. Collectively, these results suggest that cardiac myocyte hypertrophy induced by testosterone involves a cooperative mechanism that links androgen signaling with the recruitment of NFAT through calcineurin activation and GSK-3β inhibition.

Growth differentiation factor 11 (GDF11), a member of the transforming growth factor-β family, has been shown to act as a negative regulator in cardiac hypertrophy. Ca2+ signaling modulates cardiomyocyte growth; however, the role of Ca2+-dependent mechanisms in mediating the effects of GDF11 remains elusive. Here, we found that GDF11 induced intracellular Ca2+ increases in neonatal rat cardiomyocytes and that this response was blocked by chelating the intracellular Ca2+ with BAPTA-AM or by pretreatment with inhibitors of the inositol 1,4,5-trisphosphate (IP3) pathway. Moreover, GDF11 increased the phosphorylation levels and luciferase activity of Smad2/3 in a concentration-dependent manner, and the inhibition of IP3-dependent Ca2+ release abolished GDF11-induced Smad2/3 activity. To assess whether GDF11 exerted antihypertrophic effects by modulating Ca2+ signaling, cardiomyocytes were exposed to hypertrophic agents (100 nM testosterone or 50 μM phenylephrine) for 24 h. Both treatments increased cardiomyocyte size and [3H]-leucine incorporation, and these responses were significantly blunted by pretreatment with GDF11 over 24 h. Moreover, downregulation of Smad2 and Smad3 with siRNA was accompanied by inhibition of the antihypertrophic effects of GDF11. These results suggest that GDF11 modulates Ca2+ signaling and the Smad2/3 pathway to prevent cardiomyocyte hypertrophy.

Testosterone is known to induce cardiac hypertrophy through androgen receptor (AR)-dependent and -independent pathways, but the molecular underpinnings of the androgen action remain poorly understood. Previous work has shown that Ca2+/calmodulin-dependent protein kinase II (CaMKII) and myocyte-enhancer factor 2 (MEF2) play key roles in promoting cardiac myocyte growth. In order to gain mechanistic insights into the action of androgens on the heart, we investigated how testosterone affects CaMKII and MEF2 in cardiac myocyte hypertrophy by performing studies on cultured rat cardiac myocytes and hearts obtained from adult male orchiectomized (ORX) rats. In cardiac myocytes, MEF2 activity was monitored using a luciferase reporter plasmid, and the effects of CaMKII and AR signaling pathways on MEF2C were examined by using siRNAs and pharmacological inhibitors targeting these two pathways. In the in vivo studies, ORX rats were randomly assigned to groups that were administered vehicle or testosterone (125 mg⋅kg-1⋅week-1) for 5 weeks, and plasma testosterone concentrations were determined using ELISA. Cardiac hypertrophy was evaluated by measuring well-characterized hypertrophy markers. Moreover, western blotting was used to assess CaMKII and phospholamban (PLN) phosphorylation, and MEF2C and AR protein levels in extracts of left-ventricle tissue from control and testosterone-treated ORX rats. Whereas testosterone treatment increased the phosphorylation levels of CaMKII (Thr286) and phospholambam (PLN) (Thr17) in cardiac myocytes in a time- and concentration-dependent manner, testosterone-induced MEF2 activity and cardiac myocyte hypertrophy were prevented upon inhibition of CaMKII, MEF2C, and AR signaling pathways. Notably, in the hypertrophied hearts obtained from testosterone-administered ORX rats, both CaMKII and PLN phosphorylation levels and AR and MEF2 protein levels were increased. Thus, this study presents the first evidence indicating that testosterone activates MEF2 through CaMKII and AR signaling. Our findings suggest that an orchestrated mechanism of action involving signal transduction and transcription pathways underlies testosterone-induced cardiac myocyte hypertrophy.

Background Testosterone regulates nutrient and energy balance to maintain protein synthesis and metabolism in cardiomyocytes, but supraphysiological concentrations induce cardiac hypertrophy. Previously, we determined that testosterone increased glucose uptake—via AMP-activated protein kinase (AMPK)—after acute treatment in cardiomyocytes. However, whether elevated glucose uptake is involved in long-term changes of glucose metabolism or is required during cardiomyocyte growth remained unknown. In this study, we hypothesized that glucose uptake and glycolysis increase in testosterone-treated cardiomyocytes through AMPK and androgen receptor (AR). Methods Cultured cardiomyocytes were stimulated with 100 nM testosterone for 24 h, and hypertrophy was verified by increased cell size and mRNA levels of β-myosin heavy chain (β-mhc). Glucose uptake was assessed by 2-NBDG. Glycolysis and glycolytic capacity were determined by measuring extracellular acidification rate (ECAR). Results Testosterone induced cardiomyocyte hypertrophy that was accompanied by increased glucose uptake, glycolysis enhancement and upregulated mRNA expression of hexokinase 2. In addition, testosterone increased AMPK phosphorylation (Thr172), while inhibition of both AMPK and AR blocked glycolysis and cardiomyocyte hypertrophy induced by testosterone. Moreover, testosterone supplementation in adult male rats by 5 weeks induced cardiac hypertrophy and upregulated β-mhc, Hk2 and Pfk2 mRNA levels. Conclusion These results indicate that testosterone stimulates glucose metabolism by activation of AMPK and AR signaling which are critical to induce cardiomyocyte hypertrophy.

RNA splicing has been recognized in recent years as a pivotal player in heart development and disease. The Ca2+/calmodulin dependent protein kinase II delta (CaMKIIδ) is a multifunctional Ser/Thr kinase family and generates at least 11 different splice variants through alternative splicing. This enzyme, which belongs to the CaMKII family, is the predominant family member in the heart and functions as a messenger toward adaptive or detrimental signaling in cardiomyocytes. Classically, the nuclear CaMKIIδB and cytoplasmic CaMKIIδC splice variants are described as mediators of arrhythmias, contractile function, Ca2+ handling, and gene transcription. Recent findings also put CaMKIIδA and CaMKIIδ9 as cardinal players in the global CaMKII response in the heart. In this review, we discuss and summarize the new insights into CaMKIIδ splice variants and their (proposed) functions, as well as CaMKII-engineered mouse phenotypes and cardiac dysfunction related to CaMKIIδ missplicing. We also discuss RNA splicing factors affecting CaMKII splicing. Finally, we discuss the translational perspective derived from these insights and future directions on CaMKIIδ splicing research in the healthy and diseased heart.