Patients with obstructive sleep apnea syndrome (OSAS) showed higher prevalence in cardiovascular diseases due to aberrant hypoxia and oxidative stress. However, not all OSAS patients end up with cardiovascular disorders, and identification of novel biomarker will be invaluable for differentiating patients at risk. Here we tested the serum matrix metalloproteinase-9 (MMP-9) levels in 47 untreated OSAS patients and found that the MMP-9 level was positively correlated with severity of OSAS, which was consistent with hypoxia degree and duration. Besides, the MMP-9 level was higher in patients complicated with systematic hypertension (P < 0.001). Furthermore, we selected those OSAS patients without any cardiovascular dysfunction (n=35) and followed up for up to five years. By the end of follow-up, 12 patients had hypertension onset and 3 patients had left ventricular hypertrophy. By analyzing the clinical outcomes with MMP-9 expression, we demonstrated that high serum MMP-9 in OSAS patients was a risk factor for occurrence of cardiovascular diseases. In addition, we cultured the vascular endothelial cells (VEC) from rat aorta in hypoxia condition to investigate whether MMP-9 was elevated due to hypoxia in OSAS patients. Cellular results revealed that the expression, secretion, and activity of MMP-9 were all upregulated by hypoxia and can cleave the beta2-adrenergic receptor (β2AR) on VEC surface. Our results not only determined MMP-9 as a risk factor for cardiovascular diseases in OSAS patients, but also showed the possible involvement of hypoxia-MMP-9-β2AR signaling axis.
Serum matrix metalloproteinase-9 activity in obstructive sleep apnea
