Formyl peptide receptor 1 up-regulation and formyl peptide receptor 2/3 down-regulation of blood immune cells along with defective lipoxin A4/resolvin D1 production in obstructive sleep apnea patients

Abstract

Background: This study aims to investigate the role of FPR 1/2/3 expressions in patients with obstructive sleep apnea (OSA).

Method: We made cross-sectional comparisons of FPR1/2/3 expressions of blood neutrophil, M1/M2a monocyte, and natural killer (NK) cell between 16 healthy subjects (HS), 16 primary snoring (PS) subjects, 46 treatment-naive OSA patients, and 18 severe OSA patients under long-term continuous positive airway pressure treatment (severe OSA on CPAP).

Results: FPR1 expressions on neutrophil were increased in treatment-naive OSA and severe OSA on CPAP groups versus either HS or PS. FPR2 expressions on neutrophil were decreased in treatment-naive OSA versus HS, and returned to normal in severe OSA on CPAP group. FPR1/FPR2 expression ratio on neutrophil was increased in treatment-naive OSA versus either HS or PS. Serum lipoxin A4, resolvin D1 levels, and FPR3 expressions of M1, M2a and NK cells were all decreased in treatment-naive OSA versus HS. OSA patients with hypertension had decreased FPR2 expressions on neutrophil and FPR3 expressions of NK cell. FPR1 expression, FPR1/FPR2 expression ratio on neutrophil, and FPR3 expression of M1 cell were all reversed after > 6-month CPAP treatment in 9 selected patients. In vitro intermittent hypoxia with re-oxygenation treatment in THP-1 cells resulted in increased FPR1/FPR2 expression ratio of M1 cells, and increased FPR1/FPR3 expression ratio of M2a cells.

Conclusions: FPR1 over-expression and insufficiency of FPR2 and FPR3 in association with defective lipoxin A4 and resolving D1 production were associated with disease severity of OSA and its adverse consequences.

Fig 1. Flow diagram shows the process of the patients’ selection and enrollment.

Fig 2. Formyl peptide receptor (FPR) 1/2/3 expressions of blood innate immune cells in patients with sleep disordered breathing and healthy subject without snoring.

(A) Increased FPR1 expression on neutrophil in patients with treatment-naive obstructive sleep apnea (OSA), and severe OSA under long-term CPAP treatment groups as compared with that in subjects with primary snoring (PS) and healthy subjects (HS). (B) Decreased FPR2 expression on neutrophil in treatment-naïve OSA group as compared with that in HS, and severe OSA on CPAP groups. (C) Increased FPR1/FPR2 expression ratio in treatment-naïve OSA and severe OSA on CPAP groups as compared with that in HS group. (D) Decreased FPR3 expression of M1 monocyte in treatment-naïve OSA and severe OSA on CPAP groups as compared with that in HS group. (E) Decreased FPR3 expression of M2a monocyte in treatment-naïve OSA versus HS group. (F) Decreased FPR3 expression of NK cell in PS, and treatment-naïve OSA, groups as compared with that in HS group. The box plots show the 25th, 50th, 75th percentiles, maximum, and minimum. *P<0.05 for comparisons between HS and another groups by Kruskal-Wallis test followed by post-hoc corrections and linear regression adjustments #p<0.05 for comparisons between PS and another groups by Kruskal-Wallis test followed by post-hoc corrections and linear regression adjustments @p<0.05 for comparisons between treatment-naïve OSA and severe OSA on CPAP groups by Kruskal-Wallis test followed by post-hoc corrections and linear regression adjustments.

Fig 3. Correlations of FPR expressions of blood immune cells with sleep parameters.

(A) FPR1 expression on neutrophil was positively correlated with ODI. FPR1/FPR2 expression ratio was (B) negatively correlated with minimum SaO2, and positively correlated with (C) snoring index and (D) Epworth Sleepiness Scale. FPR3 expression of M1 monocyte was negatively correlated with (E) apnea hypopnea index, (F) percent time of SaO2<90%, and (G) Epworth Sleepiness Scale, and (H) positively correlated with mean SaO2.

Fig 4. FPR1/2/3 expression changes of blood immune cells after 6-month CPAP treatment.

(A) FPR1 (+) percentage on neutrophil was decreased after > 6-month CPAP treatment. (B) FPR2 expression on neutrophil was increased after >6-month CPAP treatment. (C) FPR1/FPR2 expression ratio on neutrophil was decreased after > 6-month CPAP treatment. (D) FPR3 expression of M1 cell was increased after > 6-month CPAP treatment. The box plots show the 25th, 50th, 75th percentiles, maximum, and minimum.

Fig 5. Serum lipoxin A4 (LXA4) and resolvin D1 (RvD1) deficiency in patients with sleep-disordered breathing.

(A) Serum RvD1 and (B) LXA4 levels were both decreased in patients with primary snoring (PS), treatment-naïve OSA, and severe OSA on CPAP treatment as compared with that in the healthy subjects (HS). (C) Serum LXA4 was negatively correlated with cell surface FPR1/FPR2 expression ratio on blood neutrophil. (D) Serum RvD1 levels were further reduced after > 6-month CPAP treatment in 9 selected OSA patients. The box plots show the 25th, 50th, 75th percentiles, maximum, and minimum. *P<0.05 for comparisons between HS and another groups by Kruskal-Wallis test followed by post-hoc corrections.

Fig 6. FPR1/2/3 expressions of human monocytic THP-1 cells exposed to normoxia (NOX), 2 days of persistent hypoxia (PH), or 2 days of intermittent hypoxia with re-oxygenation (IHR).

The box plots show the 25th, 50th, 75th percentiles, maximum, and minimum. IHR treatment resulted in increased (A) FPR1 and (B) FPR2 expressions on M2a cells. Both IHR and PH treatment resulted in decreased (C) FPR1, (D) FPR2, and (E) FPR3 expressions on CD14⁺CD209^-M1 cells. PH and IHR treatment resulted in decreased (F) FPR3 expression of CD14⁺Cd209⁺M2a cells. Both PH and IHR (G) increased FPR1/FPR2 expression ratio of M1 cell, and (H) increased FPR1/FPR3 expression ratio of M2a cell. (I) Cell viability was decreased in both PH and IHR versus NOX condition. *p<0.05 for comparisons between IHR and NOX conditions by U test #p<0.05 for comparisons between PH and NOX conditions by U test.