The Effect Of Skeletal Myotubes’ Secretome After Mechanical Loading On Breast Cancer Cells Viability And Apoptosis Regulation

Skeletal muscle secretome contains various bioactive molecules, such as myokines, growth factors, miRNAs and exosomes, which have been proposed to mediate the anti-oncogenic effects of exercise, restraining cancer onset and progression. PURPOSE: The present study investigated the effect of the conditioned media (secretome) of skeletal myotubes, with or without loading preconditioning, on breast cancer cells viability, in vitro. METHODS: C2C12 myoblasts were differentiated into myotubes, underwent mechanical stretching (15% elongation at 0.25 Hz for 12 hrs), and their secretome (stretch media, SM) was collected. The secretome of unstretched myotubes (non-stretch media, NSM) was also used as non-preconditioned media. Afterwards, breast cancer cells (MCF-7) were cultured with the SM or NSM conditioned secretome for 24 to 48 hours and their viability was assessed with the ΜΤΤ and LDH cytotoxicity assays, while the expression of apoptosis and cell survival-regulation factors was also examined using confocal fluorescence microscopy. RESULTS: The metabolic activity of MCF-7 decreased significantly in the NSM condition (p < 0.05), while a more pronounced decrease was observed in the cells cultured with the SM secretome (p < 0.001) compared with the cells cultured with typical media. The LDH activity was also reduced only in the SM-treated MCF-7 (p < 0.05). Moreover, the expression of apoptosis-executing Caspase-7 (p < 0.001) and Caspase-8 (p < 0.01) was increased, whereas cell survival-regulation factors VEGF (p < 0.01), IL-8 (p < 0.001) and SOD-2 (p < 0.05) were downregulated in the SM condition. CONCLUSIONS: These findings suggest that the secretome of mechanically-loaded myotubes can promote breast cancer cells apoptosis, implying the anti-carcinogenic properties of skeletal muscle secretome after load preconditioning.