Age-related epithelial defects limit thymic function and regeneration.

The thymus is essential for establishing adaptive immunity yet undergoes age-related involution that leads to compromised immune responsiveness. The thymus is also extremely sensitive to acute insult and although capable of regeneration, this capacity declines with age for unknown reasons. We applied single-cell and spatial transcriptomics, lineage-tracing and advanced imaging to define age-related changes in nonhematopoietic stromal cells and discovered the emergence of two atypical thymic epithelial cell (TEC) states. These age-associated TECs (aaTECs) formed high-density peri-medullary epithelial clusters that were devoid of thymocytes; an accretion of nonproductive thymic tissue that worsened with age, exhibited features of epithelial-to-mesenchymal transition and was associated with downregulation of FOXN1. Interaction analysis revealed that the emergence of aaTECs drew tonic signals from other functional TEC populations at baseline acting as a sink for TEC growth factors. Following acute injury, aaTECs expanded substantially, further perturbing trophic regeneration pathways and correlating with defective repair of the involuted thymus. These findings therefore define a unique feature of thymic involution linked to immune aging and could have implications for developing immune-boosting therapies in older individuals.

Exercise testing in patients with cystic fibrosis-importance of ventilatory parameters.

BACKGROUND: Ventilatory parameters obtained during exercise predict survival in several chronic diseases; however, long-term changes in exercise ventilatory parameters in patients with cystic fibrosis (CF) have yet to be examined and potential differences between sexes in CF are unknown. PURPOSE: We sought to examine the change in exercise ventilatory parameters over time in patients with CF and determine if the change is different between sexes. METHODS: Exercise capacity (VO2 peak) and exercise ventilatory parameters (VE/VO2 peak, VE/VCO2 peak, and VE/VCO2 slope) were determined from a maximal cardio-pulmonary test on a cycle ergometer on two visits separated by 39 ± 16 months in 20 patients with CF (10 female, 10 male). RESULTS: No differences between sexes were observed at visit 1 (all p > 0.05). Overall, exercise ventilatory parameters significantly (p < 0.05) deteriorated between visits, with no change (p > 0.05) in VO2 peak. Moreover, compared to males, female patients exhibited greater deteriorations in VE/VO2 peak (p = 0.001), VE/VCO2 peak (p = 0.002), and VE/VCO2 slope (p = 0.016) between visits. CONCLUSIONS: These data in patients with CF indicate that exercise ventilatory parameters decline over time despite no change in VO2 peak, and female patients exhibit a more rapid deterioration compared to males.

Sildenafil improves vascular endothelial function in patients with cystic fibrosis.

Cystic fibrosis (CF), characterized by defective CFTR function, is associated with multiple systemic complications, including vascular dysfunction. Sildenafil, a phosphodiesterase type 5 inhibitor, not only enhances nitric oxide (NO) metabolism but has been shown to improve CFTR functionality as well. Thus, sildenafil has been proposed as a therapy to improve vascular health in CF; however, its potential therapeutic role has yet to be determined. We sought to investigate the effect of sildenafil on endothelial function in patients with CF. Patients with CF completed a randomized, double-blind, placebo-controlled, crossover study with an acute dose of sildenafil (50 mg) or placebo followed by a 4-wk open-label extension with sildenafil (20 mg/day). Flow-mediated dilation (FMD) was used to evaluate endothelial function before and after treatments. In addition, phosphorylated endothelial NO synthase (pNOS3) and total NOS3 protein expression was determined from endothelial cells that were exposed to plasma from the patients before and after 4 wk of sildenafil treatment. No changes ( P ≥ 0.110) in endothelial function were observed after the acute dose of sildenafil. However, FMD significantly ( P = 0.029) increased after 4 wk of treatment (∆FMD: 1.5 ± 2.2%). Moreover, pNOS3 protein expression significantly ( P = 0.013) increased after 4 wk of treatment (∆pNOS3: 0.31 ± 0.39 arbitrary units) and was associated ( r = 0.593, P = 0.033) with the change in FMD. These data suggest that 4 wk of sildenafil treatment can improve vascular endothelial function in patients with CF, likely through an increase in NOS3 phosphorylation. NEW & NOTEWORTHY Findings from the present study demonstrate, for the first time, significant improvement of endothelial function in patients with cystic fibrosis treated with sildenafil that is associated with greater phosphorylation of endothelial nitric oxide synthase. These results support the use of sildenafil as a potential novel therapy for this patient population.

Assessment of endothelial function is reproducible in patients with cystic fibrosis.

BACKGROUND: New treatments have improved life-expectancy in patients with cystic fibrosis (CF); however, cardiovascular health remains an area of concern in this population. Flow-mediated dilation (FMD), a non-invasive assessment of vascular endothelial function that predicts future cardiovascular disease and events, is attenuated in patients with CF compared to controls. The reproducibility of FMD in CF; however, has yet to be evaluated. Thus, this study sought to examine the within-day, between-day, and between-month reproducibility of FMD in patients with CF. METHODS: Pulmonary function, baseline diameter (cm), peak diameter (cm), and FMD(%) were assessed 5 times (sessions A-E) over four visits in 13 patients with CF (six males, seven females, age range: 13-43 years old; mean forced expiratory volume in 1 s = 71% predicted). Sessions A and B (within-day), C (between-day), and D and E (between-month) were separated by 3 h, at least 10 days, and ~3 months, respectively. Reproducibility was assessed by: (1) paired t-tests, (2) coefficients of variation (CV), (3) CV prime, (4) Pearson's correlation (r), (5) intra-class correlation coefficient, and (6) Bland-Altman plots. Five acceptable parameters were required to determine reproducibility. RESULTS: Pulmonary function was stable throughout all visits. FMD(%) and baseline diameter (cm) satisfied all six reproducibility criteria for within-day, while peak diameter (cm) met five of six criteria. All six reproducibility criteria were met for all between-day and between-month assessments. CONCLUSION: The present study provides evidence that endothelial function assessed by FMD is reproducible in patients with CF not only within-day, but also between-day and between-month.

Tetrahydrobiopterin improves endothelial function in patients with cystic fibrosis.

Cystic fibrosis (CF) is a genetic disorder associated with vascular endothelial dysfunction. Nitric oxide (NO) plays a major role in maintaining vascular function, and tetrahydrobiopterin (BH4) is a critical determinant of NO bioavailability. Thus the purpose of this study was to investigate the effects of oral administration of BH4 on endothelial function in patients with CF. Twenty-nine patients with CF (18 ± 8 yr old) and 29 healthy matched controls were recruited. Patients with CF participated in a randomized trial where they received a 5 mg/kg dose of oral BH4 (BH4-5; n = 17) or a 20 mg/kg dose of oral BH4 (BH4-20; n = 12). On a separate visit, a subset of patients from each group was retested following a placebo (PLC; n = 9). Brachial artery flow-mediated dilation (FMD) was used to evaluate vascular endothelial function, and a plasma sample was obtained before and 3 h after treatment. Cultured endothelial cells were treated with plasma to assess NO bioavailability. Baseline FMD was lower in patients compared with controls (5.7 ± 3.4 vs. 8.4 ± 3.5%, respectively, P = 0.005). No change in FMD was observed following PLC or BH4-5 (∆FMD: -0.8 ± 1.9% and -0.5 ± 2.5%; P = 0.273 and 0.132, respectively). Treatment with BH4-20, however, resulted in significant improvements in FMD (∆FMD: 1.1 ± 1.4%) compared with BH4-5 ( P = 0.023) and PLC ( P = 0.017). Moreover, BH4-20 significantly decreased endothelial cell superoxide production and increased NO production. These data suggest that a single oral dose of BH4 at 20 mg/kg improves vascular endothelial function in patients with CF, likely via increased endothelial NO synthase coupling. These findings support the hypothesis that loss of BH4 bioactivity contributes, in part, to endothelial dysfunction in patients with CF. NEW & NOTEWORTHY For the first time, the present study documents that a single dose of oral BH4 can improve vascular endothelial function in patients with cystic fibrosis (CF), and our in vitro data suggest this is via decreasing uncoupled nitric oxide. These data provide insight into the important role of BH4 bioactivity in vascular dysfunction and provide the foundation for further investigation into the chronic effects of BH4 treatment in patients with CF.