The contribution of chronic intermittent hypoxia to OSAHS: from the perspective of serum extracellular microvesicle proteins

Abstract

Objective: Obstructive sleep apnea hypopnea syndrome (OSAHS) is an independent risk factor for many clinical complications. However, how OSAHS cause multiple organ injury and initiate inter-organ communication remains unclear. Moreover, despite it is well-recognized that chronic intermittent hypoxia (CIH) is a main feature of OSAHS, specific contribution of CIH to overall OSAHS-initiated pathological complications remains unclear. This study aimed to use an unbiased proteomic approach to determine whether OSAHS alters protein profiles of serum extracellular microvesicles (SEMVs) and how CIH contributes to such alterations. Methods: Tandem mass tag (TMT)-labeled quantitative proteomics assay was used to compare the differentially expressed proteins (DEPs) in SEMVs of OSAHS patients and non-OSAHS subjects. To evaluate the contribution of CIH to OSAHS, CIH rodent model was constructed and the same comparative proteomics study was performed in SEMVs from CIH and normoxia rats. The similarity and disparity of DEPs and DEPs-related functions predicted by bioinformatics tools were compared in above-mentioned two models, and several DEPs were selected and further verified by ELISA or Western blotting. Results: TMT-labeled quantitative proteomics assay unravels 32 DEPs in OSAHS patient SEMVs from a total of 560 human SEMV proteins identified. Four DEPs, namely C-reactive protein (CRP), Haptoglobin (HP),Fibronectin (FN1) and Platelet factor 4 (PF4), were further verified by ELISA and three of them (CRP, FN1 and Hp) showed significant difference in expression level between OSAHS and non-OSAHS groups. In SEMVs of rat CIH model, 121 DEPs out of 723 proteins were identified. By comparing the DEPs identified from the two models, 3 proteins (CRP and FN1 and F13a1) were found identical with the same alteration pattern (CRP was upregulated, FN1 and F13a1 were downregulated) in SEMVs from OSAHS patients and CIH rats, which were further verified by Western blotting. Computational functional analysis further revealed the common and distinct DEP-involved pathways under OSAHS or CIH status. Conclusions: This study provides the first evidence that OSAHS causes significant alteration in SEMV protein composition, which may contribute to OSAHS-triggered multiple organ injury and organ-to-organ communication. Moreover, we have demonstrated that CIH is the primary contributor for increased inflammatory protein expression in SEMV. As CRP is being increasingly recognized not only as a marker but also a mediator of inflammatory response to tissue injury, increased SEMV CRP in CIH/OSAHS may play an important role in OSAHS-induced tissue injury, suggesting SEMV CRP might be a therapeutic target against OSAHS-related complications.