CLIC4 Regulates Endothelial Barrier Control by Mediating PAR1 Signaling via RhoA.

BACKGROUND: Endothelial CLICs (chloride intracellular channel proteins) CLIC1 and CLIC4 are required for the GPCRs (G-protein-coupled receptors) S1PR1 (sphingosine-1-phosphate receptor 1) and S1PR3 to activate the small GTPases Rac1 (Ras-related C3 botulinum toxin substrate 1) and RhoA (Ras homolog family member A). To determine whether CLIC1 and CLIC4 function in additional endothelial GPCR pathways, we evaluated CLIC function in thrombin signaling via the thrombin-regulated PAR1 (protease-activated receptor 1) and downstream effector RhoA. METHODS: We assessed the ability of CLIC1 and CLIC4 to relocalize to cell membranes in response to thrombin in human umbilical vein endothelial cells (HUVEC). We examined CLIC1 and CLIC4 function in HUVEC by knocking down expression of each CLIC protein and compared thrombin-mediated RhoA or Rac1 activation, ERM (ezrin/radixin/moesin) phosphorylation, and endothelial barrier modulation in control and CLIC knockdown HUVEC. We generated a conditional murine allele of Clic4 and examined PAR1-mediated lung microvascular permeability and retinal angiogenesis in mice with endothelial-specific loss of Clic4. RESULTS: Thrombin promoted relocalization of CLIC4, but not CLIC1, to HUVEC membranes. Knockdown of CLIC4 in HUVEC reduced thrombin-mediated RhoA activation, ERM phosphorylation, and endothelial barrier disruption. Knockdown of CLIC1 did not reduce thrombin-mediated RhoA activity but prolonged the RhoA and endothelial barrier response to thrombin. Endothelial-specific deletion of Clic4 in mice reduced lung edema and microvascular permeability induced by PAR1 activating peptide. CONCLUSIONS: CLIC4 is a critical effector of endothelial PAR1 signaling and is required to regulate RhoA-mediated endothelial barrier disruption in cultured endothelial cells and murine lung endothelium. CLIC1 was not critical for thrombin-mediated barrier disruption but contributed to the barrier recovery phase after thrombin treatment.

Socioeconomic status impacts blood pressure response to positive airway pressure treatment.

STUDY OBJECTIVES: Positive airway pressure (PAP) treatment of obstructive sleep apnea reduces blood pressure (BP). Retrospective data suggest that African Americans (AA), a group at high-risk for hypertensive organ dysfunction, may have a greater BP response to PAP therapy than European Americans (EA). We examined the difference in 24-hour BP response to 3 months of PAP treatment between AA and EA. METHODS: Participants (n = 259, 161 AA and 98 EA) with apnea-hypopnea index ≥ 15 events/h from 2 prospective cohorts were included. t-Tests and multiple linear regression were used to examine BP outcomes in AA vs EA, adjusting for PAP adherence, socioeconomic status, and baseline characteristics. RESULTS: Participants were middle aged (mean ± SD, 53.8 ± 9.3 years), 86% (227) men, apnea-hypopnea index 35.6 ± 19.2 events/h, and PAP adherence of 3.36 ± 2.24 h/day. The reductions in 24-hour systolic and diastolic BP (mm Hg) were not different in AA vs EA (systolic = -1.13 ± 12.1 vs -0.61 ± 12.8, P = .80 and diastolic = -0.74 ± 7.9 vs -0.80 ± 7.4, P = .96), and race was not a predictor of 24-hour systolic or diastolic BP reduction (P = .75 and 0.54). Socioeconomic status and PAP adherence demonstrated a significant interaction; low socioeconomic status was associated with an increase in 24-hour systolic BP (ß = 19.3, P = .03) in the absence of PAP use but a greater reduction in 24-hour systolic BP with higher PAP adherence (ß = -3.96, P = .03). CONCLUSIONS: Twenty-four hour BP response to PAP treatment is similar in AA and EA. Adherence to PAP treatment is more effective in improving 24-hour systolic BP in those with low SES. CLINICAL TRIAL REGISTRATION: Registry: ClinicalTrials.gov; Name: Race and CPAP Effectiveness (RACE); URL: https://clinicaltrials.gov/ct2/show/NCT01960465; Identifier: NCT01960465 and Registry: ClinicalTrials.gov; Name: The Effects of Treating Obese and Lean Patients with Sleep Apnea (PISA); URL: https://clinicaltrials.gov/ct2/show/NCT01578031; Identifier: NCT01578031. CITATION: Imayama I, Gupta A, Yen PS, et al. Socioeconomic status impacts blood pressure response to positive airway pressure treatment. J Clin Sleep Med. 2022;18(5):1287-1295.

Racial Differences in Functional and Sleep Outcomes with Positive Airway Pressure Treatment.

It is unclear if the response to positive airway pressure (PAP) treatment is different between African American (AA) and European Americans (EA). We examined whether race modifies the effects of PAP on sleep and daytime function. We assessed Epworth Sleepiness Scale (ESS), Functional Outcomes of Sleep Questionnaire, Psychomotor Vigilance Task and actigraphy in 185 participants with moderate-to-severe obstructive sleep apnea before and 3-4 months after PAP treatment. The participants were middle-aged (mean, 55.1 years), 83.8% men and 60.5% AA. Linear regression models were used to examine the effect of race on outcomes. The AA had smaller reductions in ESS (mean change (95% confidence interval, CI) AA, -2.30 [-3.35, -1.25] vs. EA, -4.16 [-5.48, -2.84] and frequency of awakenings (AA, -0.73 [-4.92, 3.47] vs. EA, -9.35 [-15.20, -3.51]). A race × PAP usage interaction term was added to the model to examine if the change in outcomes per 1 h increase in PAP usage differed by race. AA exhibited greater improvement in wake after sleep onset (ß (95% CI) AA, -8.89 [-16.40, -1.37] vs. EA, 2.49 [-4.15, 9.12]) and frequency of awakening (ß (95% CI) AA, -2.59 [-4.44, -0.75] vs. EA, 1.71 [-1.08, 4.50]). The results indicate the importance of race in evaluating outcomes following PAP treatment.

The need for specificity in quantifying neurocirculatory vs. respiratory effects of eucapnic hypoxia and transient hyperoxia.

KEY POINTS: The carotid chemoreceptor mediates the ventilatory and muscle sympathetic nerve activity (MSNA) responses to hypoxia and contributes to tonic sympathetic and respiratory drives. It is often presumed that both excitatory and inhibitory tests of chemoreflex function show congruence in the end-organ responses. Ventilatory and neurocirculatory (MSNA, blood pressure and heart rate) responses to chemoreflex inhibition elicited by transient hyperoxia and to chemoreflex excitation produced by steady-state eucapnic hypoxia were measured in a cohort of 82 middle-aged individuals. Ventilatory and MSNA responsiveness to hyperoxia and hypoxia were not significantly correlated within individuals. It was concluded that ventilatory responses to hypoxia and hyperoxia do not predict MSNA responses and it is recommended that tests using the specific outcome of interest, i.e. MSNA or ventilation, are required. Transient hyperoxia is recommended as a sensitive and reliable means of quantifying tonic chemoreceptor-driven levels of sympathetic nervous system activity and respiratory drive. ABSTRACT: Hypersensitivity of the carotid chemoreceptor leading to sympathetic nervous system activation and ventilatory instability has been implicated in the pathogenesis and consequences of several common clinical conditions. A variety of treatment approaches aimed at lessening chemoreceptor-driven sympathetic overactivity are now under investigation; thus, the ability to quantify this outcome variable with specificity and precision is crucial. Accordingly, we measured ventilatory and neurocirculatory responses to chemoreflex inhibition elicited by transient hyperoxia and chemoreflex excitation produced by exposure to graded, steady-state eucapnic hypoxia in middle-aged men and women (n = 82) with continuous positive airway pressure-treated obstructive sleep apnoea. Progressive, eucapnic hypoxia produced robust and highly variable increases in ventilation (+83 ± 59%) and muscle sympathetic nerve activity (MSNA) burst frequency (+55 ± 31%), whereas transient hyperoxia caused marked reductions in these variables (-35 ± 14% and -42 ± 16%, respectively). Coefficients of variation for ventilatory and MSNA burst frequency responses, indicating test-retest reproducibility, were respectively 9% and 24% for hyperoxia and 35% and 28% for hypoxia. Based on statistical measures of rank correlation or even comparisons across quartiles of corresponding ventilatory and MSNA responses, we found that the magnitudes of ventilatory inhibition with hyperoxia or excitation with eucapnic hypoxia were not correlated with corresponding MSNA responses within individuals. We conclude that, in conscious, behaving humans, ventilatory sensitivities to progressive, steady-state, eucapnic hypoxia and transient hyperoxia do not predict MSNA responsiveness. Our findings also support the use of transient hyperoxia as a reliable, sensitive, measure of the carotid chemoreceptor contribution to tonic sympathetic nervous system activity and respiratory drive.