Matrix Metalloproteinase-9 Is a Predictive Factor for Systematic Hypertension and Heart Dysfunction in Patients with Obstructive Sleep Apnea Syndrome

Figure 4

Hypoxia upregulates MMP-9 secretion from vascular endothelial cells and enhances N-terminus cleavage of beta2-adrenergic receptor. The RNA level (a) and protein secretion (b) of MMP-9 were both increased in the rat aorta endothelial cells treated with hypoxia. Cells were cultured in different conditions, and the cell culturing medium was collected for gelatin zymography, which showed an elevated MMP-9 activity in the medium from hypoxia-treated cells (c, d); recombinant MMP-9 protein was used as positive control. The conditional cell culturing medium (from either normoxia or hypoxia conditions) was added to fresh vascular endothelial cells to determine its catalytic role on beta2-adrenergic receptor (β2AR); cells in positive control group were supplemented with recombinant MMP-9 protein. By using different antibody epitopes, we found that the N-terminus (extracellular domain) of β2AR was cleaved by hypoxia-conditioned medium, while no significant difference was observed on the C-terminus (intracellular domain) of β2AR (e, f). The result was consistent with the role of MMP-9 in cleaving extracellular domain of cell surface receptors. All statistical significance was acquired by comparing with normoxia group using Student’s t-test. compared with normoxia group.

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