Metabolic profiling of heat or anoxic stress in mouse C2C12 myotubes using multinuclear magnetic resonance spectroscopy

Lactate increases myotube diameter via activation of MEK/ERK pathway in C2C12 cells

AIM

Lactate is produced in and released from skeletal muscle cells. Lactate receptor, G-protein-coupled receptor 81 (GPR81), is expressed in skeletal muscle cells. However, a physiological role of extracellular lactate on skeletal muscle is not fully clarified. The purpose of this study was to investigate extracellular lactate-associated morphological changes and intracellular signals in C2C12 skeletal muscle cells.

METHODS

Mouse myoblast C2C12 cells were differentiated for 5 days to form myotubes. Sodium lactate (lactate) or GPR81 agonist, 3,5-dihydroxybenzoic acid (3,5-DHBA), was administered to the differentiation medium.

RESULTS

Lactate administration increased the diameter of C2C12 myotubes in a dose-dependent manner. Administration of 3,5-DHBA also increased myotube diameter. Not only lactate but also 3,5-DHBA upregulated the phosphorylation level of mitogen-activated protein kinase kinase 1/2 (MEK1/2), p42/44 extracellular signal-regulated kinase-1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK). MEK inhibitor U0126 depressed the phosphorylation of ERK-p90RSK and increase in myotube diameter induced by lactate. On the other hand, both lactate and 3,5-DHBA failed to induce significant responses in the phosphorylation level of Akt, mammalian target of rapamycin, p70 S6 kinase and protein degradation-related signals.

CONCLUSION

These observations suggest that lactate-associated increase in the diameter of C2C12 myotubes is induced via activation of GRP81-mediated MEK/ERK pathway. Extracellular lactate might have a positive effect on skeletal muscle size.

Recurrent heat shock impairs the proliferation and differentiation of C2C12 myoblasts

Heat-related illness and injury are becoming a growing safety concern for the farmers, construction workers, miners, firefighters, manufacturing workers, and other outdoor workforces who are exposed to heat stress in their routine lives. A primary response by a cell to an acute heat shock (HS) exposure is the induction of heat-shock proteins (HSPs), which chaperone and facilitate cellular protein folding and remodeling processes. While acute HS is well studied, the effect of repeated bouts of hyperthermia and the sustained production of HSPs in the myoblast-myotube model system of C2C12 cells are poorly characterized. In C2C12 myoblasts, we found that robust HS (43 °C, dose/time) significantly decreased the proliferation by 50% as early as on day 1 and maintained at the same level on days 2 and 3 of HS. This was accompanied by an accumulation of cells at G2 phase with reduced cell number in G1 phase indicating cell cycle arrest. FACS analysis indicates that there was no apparent change in apoptosis (markers) and cell death upon repeated HS. Immunoblot analysis and qPCR demonstrated a significant increase in the baseline expression of HSP25, 70, and 90 (among others) in cells after a single HS (43 °C) for 60 min as a typical HS response. Importantly, the repeated HS for 60 min each on days 2 and 3 maintained the elevated levels of HSPs compared to the control cells. Further, the continuous HS exposure resulted in significant inhibition of the differentiation of C2C12 myocytes to myotubes and only 1/10th of the cells underwent differentiation in HS relative to control. This was associated with significantly higher levels of HSPs and reduced expression of myogenin and Myh2 (P < 0.05), the genes involved in the differentiation process. Finally, the cell migration (scratch) assay indicated that the wound closure was significantly delayed in HS cells relative to the control cells. Overall, these results suggest that a repeated HS may perturb the active process of proliferation, motility, and differentiation processes in an in vitro murine myoblast-myotube model.

The Progress of Metabolomics Study in Traditional Chinese Medicine Research

Traditional Chinese medicine (TCM) has played important roles in health protection and disease treatment for thousands of years in China and has gained the gradual acceptance of the international community. However, many intricate issues, which cannot be explained by traditional methods, still remain, thus, new ideas and technologies are needed. As an emerging system biology technology, the holistic view adopted by metabolomics is similar to that of TCM, which allows us to investigate TCM with complicated conditions and multiple factors in depth. In this paper, we tried to give a timely and comprehensive update about the methodology progression of metabolomics, as well as its applications, in different fields of TCM studies including quality control, processing, safety and efficacy evaluation. The herbs investigated by metabolomics were selected for detailed examination, including Anemarrhena asphodeloides Bunge, Atractylodes macrocephala Kidd, Pinellia ternate, etc.; furthermore, some valuable results have been obtained and summarized. In conclusion, although the study of metabolomics is at the early phase and requires further scrutiny and validation, it still provides bright prospects to dissect the synergistic action of multiple components from TCM. Overall, with the further development of analytical techniques, especially multi-analysis techniques, we expect that metabolomics will greatly promote TCM research and the establishment of international standards, which is beneficial to TCM modernization.

Oxidative stress-induced metabolic changes in mouse C2C12 myotubes studied with high-resolution 13C, 1H, and 31P NMR spectroscopy

In this study, stress in relation to slaughter was investigated in a model system by the use of (13)C, (1)H, and (31)P nuclear magnetic resonance (NMR) spectroscopy for elucidating changes in the metabolites in C2C12 myotubes exposed to H(2)O(2)-induced stress. Oxidative stress resulted in lower levels of several metabolites, mainly amino acids; however, higher levels of alanine were apparent in the (13)C spectra after incubation with [(13)C(1)]glucose. In the (13)C spectra [(13)C(3)]lactate tended to increase after exposure to increasing concentrations of H(2)O(2); conversely, a tendency to lower levels of the unlabeled ((12)C) lactate were identified in the (1)H spectra after stress exposure. These data indicate an increase in de novo synthesis of alanine, concomitant with a release of lactate from the myotubes to the medium at oxidative stress conditions. The changes in the metabolite levels could possibly be useful as markers for meat quality traits.