Endothelin-1 impairs skeletal muscle myogenesis and development via ETB receptors and p38 MAPK signaling pathway.

Myopenia is a condition marked by progressive decline of muscle mass and strength and is associated with aging or obesity. It poses the risk of falling, with potential bone fractures, thereby also increasing the burden on family and society. Skeletal muscle wasting is characterized by a reduced number of myoblasts, impaired muscle regeneration and increased muscle atrophy markers (Atrogin-1, MuRF-1). Endothelin-1 (ET-1) is a potent vasoconstrictor peptide. Increased circulating levels of ET-1 is noted with aging and is associated with muscular fibrosis and decline of strength. However, the regulatory mechanism controlling its effect on myogenesis and atrophy remains unknown. In the present study, the effects of ET-1 on myoblast proliferation, differentiation and development were investigated in C2C12 cells and in ET-1-infused mice. The results show that ET-1, acting via ETB receptors, reduced insulin-stimulated cell proliferation, and also reduced MyoD, MyoG and MyHC expression in the differentiation processes of C2C12 myoblasts. ET-1 inhibited myoblast differentiation through ETB receptors and the p38 mitogen-activated protein kinase (MAPK)-dependent pathway. Additionally, ET-1 decreased MyHC expression in differentiated myotubes. Inhibition of proteasome activity by MG132 ameliorated the ET-1-stimulated protein degradation in differentiated C2C12 myotubes. Furthermore, chronic ET-1 infusion caused skeletal muscle atrophy and impaired exercise performance in mice. In conclusion, ET-1 inhibits insulin-induced cell proliferation, impairs myogenesis and induces muscle atrophy via ETB receptors and the p38 MAPK-dependent pathway.

Cysteine-cysteine Chemokine Receptor Type 5 Plays a Critical Role in Exercise Performance by Regulating Mitochondrial Content in Skeletal Muscle.

Cysteine-cysteine chemokine receptor type 5 (CCR5) is thought to play an important role in the trafficking of lymphoid cells but has recently also been associated with AMPK signaling pathways that are implicated in energy metabolism in skeletal muscle. We hypothesized that genetic deletions of CCR5 would alter mitochondria content and exercise performance in mice. CCR5-/- and wild-type mice with the same genetic background were subjected to endurance exercise and grip strength tests. The soleus muscle was stained with immunofluorescence for myosin heavy chain 7 (MYH7) and succinate dehydrogenase (SDH) analysis as well as the expression of genes associated with muscle atrophy and mitochondrial oxidative phosphorylation were measured using qPCR. Although there were no differences in the weight of the soleus muscle between the CCR5-/- group and the wild-type mice, the CCR5-/- mice showed the following muscular dysfunctions: (i) decreased MYH7 percentage and cross-section area, (ii) higher myostatin and atrogin-1 mRNA levels, (iii) dropped expression of mitochondrial DNA-encoded electron respiratory chain genes (cytochrome B, cytochrome c oxidase subunit III, and ATP synthase subunit 6) as well as mitochondrial generation genes (PPARγ and PGC-1α), and (iv) lower SDH activity and exercise performance when compared with wild-type mice. In addition, genes associated with mitochondrial biogenesis (PGC-1α, PPARγ, and MFN2) and mitochondrial complex (ND4 and Cytb) were upregulated when the skeletal muscle cell line C2C12 was exposed to cysteine-cysteine chemokine ligand 4 (a ligand of CCR5) in vitro. These findings suggested that attenuation of endurance exercise performance is related to the loss of mitochondrial content and lower SDH activity of soleus muscle in CCR5 knockout mice. The present study provides evidence indicating that the chemokine receptor CCR5 might modulate the skeletal muscle metabolic energy system during exercise.

Nitric Oxide Mobilizes Intracellular Zn2+ via the GC/cGMP/PKG Signaling Pathway and Stimulates Adipocyte Differentiation.

Plasma and tissue zinc ion levels are associated with the development of obesity. Previous studies have suggested that zinc ions may regulate adipocyte metabolism and that nitric oxide (NO) plays a pivotal role in the regulation of adipocyte physiology. Our previous study showed that chronic NO deficiency causes a significant decrease in adipose tissue mass in rats. Studies also suggested that zinc ions play an important modulatory role in regulating NO function. This study aims to explore the role of zinc ions in NO-regulated adipocyte differentiation. We hypothesized that NO could increase intracellular Zn2+ level and then stimulate adipocyte differentiation. ZnCl2 and the NO donor, NONOate, were used to explore the effects of Zn2+ and NO on adipocyte differentiation. Regulatory mechanisms of NO on intracellular Zn2+ mobilization were determined by detection. Then, Zn2+-selective chelator TPEN was used to clarify the role of intracellular Zn2+ on NO-regulated adipocyte differentiation. Furthermore, the relationship between adipocyte size, Zn2+ level, and NOS expression in human subcutaneous fat tissue was elucidated. Results showed that both ZnCl2 and NO stimulated adipocyte differentiation in a dose-dependent manner. NO stimulated intracellular Zn2+ mobilization in adipocytes through the guanylate cyclase (GC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) pathway, and NO-stimulated adipocyte differentiation was Zn2+-dependent. In human subcutaneous adipose tissue, adipocyte size was negatively correlated with expression of eNOS. In conclusion, NO treatment stimulates intracellular Zn2+ mobilization through the GC/cGMP/PKG pathway, subsequently stimulating adipocyte differentiation.

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes.

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

[Expression Level and Clinical Value of PTEN Gene in Patients with Acute T Lymphocytic Leukemia].

OBJECTIVE: To study the PTEN gene expression level and its clinical significance in patients with acute T lymphoblastic leukemia. METHODS: One hundred and twenty-four patients with T-ALL treated in our hospital from January 2014 to May 2018 were selected, and 120 healthy people were selected as control group. The bone marrow of the patients were collected, and mononuclear cells were separated out. PTEN gene expression level was detected by RT-PCR, PTEN protein expression level was detected by Western blot, Kaplan-Meier was used to analyze the survival rate of patients with T-ALL, Cox multivariate regression analyzed was used to analyze the independent influencing factors of patients, and the correlation between PTEN level and clinical characteristics of patients with T-ALL and its prognostic value were analyzed. RESULTS: The relative level of PTEN gene in patients with T-ALL was 0.19±0.06, which was significantly lower than that in control groups (P<0.05). There was significantly positive correlation of the expression level of PTEN gene with white blood cell count （r=0.993）and peripheral blood immature cells （r=0.996） in patients with T-ALL. There was no correlation between PTEN gene expression level and sex, age, LDH level, Hb level, platelet count in patients with T-ALL. And it was found that expression levels PTEN protein in the middle-risk group, the standard-risk group and the high-risk group were significant lower than those in the control group (P<0.05), while those in the high-risk group were significantly lower than those in other groups (P<0.05). Kaplan-Meier survival analysis showed that OS and DFS in PTEN gene high expression group were higher than those in PTEN low expression group (P<0.05). Cox multivariate regression analysis showed that white blood cell count and PTEN gene were independent influencing factors of OS (P<0.05); platelet count and PTEN gene were independent influencing factors of DFS (P<0.05). CONCLUSION: PTEN gene level relates to the prognosis of patients with T-ALL. Patients with better prognosis show a higher PTEN gene level, which provides reference for clinical treatment of patients with T-ALL.

Effects of acute exposure to mild simulated hypoxia on hormonal responses to low-intensity resistance exercise in untrained men.

This study examined hormonal responses to low-intensity resistance exercise under mild simulated hypoxia. Ten resistance untrained men performed five sets of 15 repetitions of squat exercise at 30% of 1RM under normobaric hypoxia (FiO2 = 15%) and normoxia in a cross-over and counter-balanced design. Blood lactate (LAC), growth hormone (GH), total testosterone (T) and cortisol (C) were measured at pre-exercise, immediately post-exercise and 15 minutes post-exercise. LAC, GH and T significantly increased immediately after squat exercise in both trials (p < 0.05). While T returned to baseline, GH remained significantly greater at 15 minutes post-exercise. Cortisol significantly decreased immediately after and 15 minutes post-exercise in both trials (p < 0.05). No significant differences were observed between two trials in LAC, GH, T and C. It was concluded that low-intensity resistance exercise performed under mild simulated hypoxia does not induce greater anabolic hormonal responses in resistance untrained men.