OBJECTIVEThis 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.

METHODSMyoblasts 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.

RESULTSThe 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.

CONCLUSIONContinuous cyclic tensile stress can induce myoblast apoptosis. The CaN-NFAT signaling pathway may be involved in the cyclic stretch-induced apoptosis of myoblasts.

Apoptosis ; Calcineurin ; genetics ; Cyclosporine ; Flow Cytometry ; Myoblasts ; physiology ; NFATC Transcription Factors ; metabolism ; Real-Time Polymerase Chain Reaction ; Signal Transduction ; T-Lymphocytes

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.

Rhinovirus(RV)is the most common respiratory virus that can cause infectious diseases of the upper and lower respiratory tract, such as the common cold and bronchiolitis.Among them, bronchiolitis is the main cause of wheezing attacks in infants under 2 years old, and the prevalence is increasing year by year.Early research believed that the main etiology was respiratory syncytial virus(RSV), but in recent years, more and more bronchiolitis has been found that caused by rhinovirus infection.This article takes rhinovirus-infected bronchiolitis as the entry point, and reviews its epidemiological characteristics, pathogenesis, clinical manifestations, auxiliary examination, treatment and prevention.