BACKGROUND: Previous studies have demonstrated that sustained hypoxia in people with obstructive sleep apnea (OSA) impairs upper airway muscle activity, but the underlying mechanism remains poorly understood. As autophagy acts as an important regulator under hypoxia stress, we performed an in vitro investigation of the effects of sustained hypoxia on autophagy of genioglossus muscle-derived stem cells (GG MDSC), an important component of the upper airway muscle.
MATERIAL AND METHODS: Genioglossus MDSCs were obtained from Sprague-Dawley (SD) rats and identified by using immunofluorescence staining for CD34, Sca-1, and desmin. GG MDSCs were incubated under normoxic or sustained hypoxic conditions for different periods of time. Western blotting was used to detect LC3 and Beclin 1, which are 2 important proteins in autophagy flux, and autophagolysosomes accumulation was observed by transmission electron microscopy (TEM). The mRNA and protein levels of HIF-1α and BNIP3 were evaluated by RT-PCR and Western blot analysis, respectively.
RESULTS: Our study shows that sustained hypoxia promotes the expression of LC3BII and Beclin 1 in GG MDSCs in a time-dependent manner. TEM showed an increased number of autophagolysosomes in GG MDSCs under sustained hypoxia for 12 and 24 h. In addition, hypoxia activated the HIF-1α/BNIP3 signal pathway both at protein levels (shown by Western blot) and at mRNA levels (shown by RT-PCR).
CONCLUSIONS: Our study shows that sustained hypoxia promotes autophagy in GG MDSCs, and the HIF-1a/BNIP3 signal pathway was involved in this process.

Keywords: Autophagy, Cell Hypoxia, Hypoxia-Inducible Factor 1, alpha Subunit, Sleep apnea, obstructive