ABSTRACT
<p><b>OBJECTIVE</b>This study investigated the role and mechanism of calcineurin (CaN)-nuclear factor of activated T cells (NFAT) pathway in the myoblast apoptosis induced by cyclic tensile strain.</p><p><b>METHODS</b>Myoblasts were cultured using an in vitro-mechanical stimulation model and imposed with tension for different hours with a multi-channel cell stress loading system. Cyclosporine (CsA) was used as CaN inhibitor to clarify the role of CaN in the apoptosis induced by cyclic stress. Hochest 33258 staining and flow cytometry detection were performed to detect the apoptotic cells. Real-time polymerase chain reaction was conducted to detect the mRNA expression of CaN and NFAT. Protein levels of NFAT3 were evaluated by Western blot.</p><p><b>RESULTS</b>The apoptosis rate increased with the extension of loading time. The mRNA expression of the CaN subunits, CnA and CnB, and the protein levels of NFAT3 also increased. When the myoblasts were incubated with CsA, the apoptosis rate decreased, the mRNA expression of CnA and NFAT3 significantly decreased, and the NFAT3 protein expression levels became significantly lower than those of the groups without CsA.</p><p><b>CONCLUSION</b>Continuous cyclic tensile stress can induce myoblast apoptosis. The CaN-NFAT signaling pathway may be involved in the cyclic stretch-induced apoptosis of myoblasts.</p>
Subject(s)
Apoptosis , Calcineurin , Genetics , Cyclosporine , Flow Cytometry , Myoblasts , Physiology , NFATC Transcription Factors , Metabolism , Real-Time Polymerase Chain Reaction , Signal Transduction , T-LymphocytesABSTRACT
BACKGROUND:The adaptive reconstruction of maxil ofacial muscles would happen when functional orthopedic treatment is done to cure micromaxil ary deformity. The myoblast is the main responder in the process of adaptive reconstruction, and cyclic stretch can induce apoptosis of myoblasts. Caspase-9 is an important factor in the mitochondrial apoptosis pathway. OBJECTIVE:To investigate the expression of Caspase-9 in different cyclic stretch. METHODS:Based on myoblasts cultured in vitro-mechanical stimulation model, the rat L6 myoblasts were loaded stretch for 1, 6, 12 and 24 hours through multi-channel cellstress loading system, while the control group received no stretch. The morphological change and growth of myoblasts were observed under inverted phase contrast microscope;the expression of the mRNA and protein of Caspase-9 were detected by RT-PCR and western blot analysis, respectively. RESULTS AND CONCLUSION:Under inverted phase contrast microscope, the rat L6 myoblasts at cyclic stretch maintained a good growth state and biological characteristics;there was no celldegeneration;and the loss rate was extremely low, which could demonstrate that myoblast in vitro-mechanical stimulation model was established successful y. The results of RT-PCR and western blot analysis showed that, the expression of Caspase-9 mRNA and Cleaved Caspase-9 protein was significantly increased as the loading time prolonged, and the expression of Procaspase-9 protein was significantly decreased as the time. We can conclude that Caspase-9 is involved in the mechanical signal transduction of cyclic stretch.
ABSTRACT
BACKGROUND:Endoplasmic reticulum stress participates in the occurrence and development of many diseases, such as atherosclerosis, diabetes, and Alzheimer’s disease. GRP78 is a marker of endoplasmic reticulum stress. The expression of GRP78 reflects the degree of endoplasmic reticulum stress. OBJECTIVE:To investigate the effect of cyclic stretch on GRP78 expression of L6 rat myoblasts, and to identify the relationship between cyclic stretch and endoplasmic reticulum stress. METHODS:In vitro culture-tensile stimulation models of myoblasts of L6 rats were established successful y. The expression of GRP78 of myoblasts exposed to cyclic stretch was determined by reverse transcription-PCR and western blot assay. Stretch groups were subjected to 15%surface elongation at a frequency of 10 cycles per minute, over a period of 1, 6, 12 and 24 hours. cells were simultaneously seeded on a plate in the control and experimental groups with no stimulation. RESULTS AND CONCLUSION:The expression of GRP78 mRNA was continuously elevated over time after stretched treatment, and significant differences were detected as compared with the control group (P<0.05). GRP78 protein expression began to increase at 1 hour after stretched treatment, was significantly increased at 6 hours, peaked at 24 hours, and significant differences were visible as compared with the control group (P<0.05). In conclusion, cyclic stretch induced the occurrence of endoplasmic reticulum stress, which was enhanced with prolonged time. However, prolonged stretch caused severe endoplasmic reticulum stress and leaded to apoptosis of myoblasts.