Lack of CFTR in skeletal muscle predisposes to muscle wasting and diaphragm muscle pump failure in cystic fibrosis mice

Peripheral Muscle Function and Body Composition in People With Cystic Fibrosis on Elexacaftor/Tezacaftor/Ivacaftor: A Cross-Sectional Single-Centre Study

BACKGROUND

People with cystic fibrosis (pwCF) often have multifactorial peripheral muscle abnormalities attributed to, for example, malnutrition, steroid use, altered redox balance and, potentially, CF-specific intrinsic alterations. Malnutrition in CF now includes an increasing prevalence of overweight and obesity, particularly in those receiving CF transmembrane conductance regulator (CFTR) modulator therapy (CFTRm). We aimed to characterise peripheral muscle function and body composition in pwCF on Elexacaftor/Tezacaftor/Ivacaftor (ETI) CFTRm, compared to healthy controls.

METHODS

Fifteen pwCF on ETI, and 15 healthy age- and sex-matched controls (CON), underwent whole-body dual-energy X-ray absorptiometry scans, and a comprehensive evaluation of peripheral muscle function. Tests included quadriceps maximal isometric force measurement, an intermittent isometric quadriceps fatiguing protocol, handgrip strength dynamometry, squat jump height assessment, and 1-min sit-to-stand testing.

RESULTS

No significant differences in quadriceps maximal isometric force (CON: 181.60 ± 92.90 Nm vs. CF: 146.15 ± 52.48 Nm, p = 0.21, d = 0.47), handgrip strength (CON: 34 ± 15 kg vs. CF: 31 ± 11 kg, p = 0.62, d = 0.18), peripheral muscle endurance, fatigue, or power were observed between the groups. Moreover, no significant differences in whole-body, trunk or limb lean mass, fat-free mass, fat mass, or whole-body bone mineral density were evident.

CONCLUSION

Comparable peripheral muscle mass and function has been demonstrated in pwCF on ETI, albeit a group with good lung function. Research is needed to confirm these findings longitudinally in pwCF, including those with more severe lung disease, who are less physically active, and have less optimal nutrition and exercise support.

Defective Cystic Fibrosis Transmembrane Conductance Regulator Accelerates Skeletal Muscle Aging by Impairing Autophagy/Myogenesis

BACKGROUND

Regenerative capacity of skeletal muscles decreases with age. Deficiency in cystic fibrosis transmembrane conductance regulator (CFTR) is associated with skeletal muscle weakness as well as epithelial cell senescence. However, whether and how CFTR plays a role in skeletal muscle regeneration and aging were unclear.

METHODS

Vastus lateralis biopsy samples from male and female human subjects (n = 23) of 7- to 86-year-old and gastrocnemii tissues from mice of 4- to 29-month-old were examined for CFTR expression. Skeletal muscle tissues or cultured myoblasts from mice carrying CFTR mutation (DF508) at 4- to 18-month-old were used for assessment of muscle mass, contractile force and regenerative capacity as well as myogenic and autophagy signalling. Overexpression of LC3-β, an autophagy mediator, was conducted to reverse myogenic defects in DF508 myoblasts. Adenoviruses containing CFTR gene or pharmaceuticals that enhance CFTR (VX809) were locally injected into the gastrocnemius or femoris quadricep to rescue age-related skeletal muscle defects in mice.

RESULTS

mRNA levels of CFTR in human vastus lateralis exhibited significantly negative correlations with age (r = -0.87 in males and -0.62 in females, p < 0.05). Gastrocnemius mRNA level of CFTR decreased by 77.7 ± 4.6% in 29-month-old wild-type mice compared to the 4-month-old. At 18-month-old, DF508 mice showed significantly reduced lean mass (by 35.6%), lower specific twitch force of the gastrocnemius (by 46.2%), decrease in fast/slow-twitch muscle isoform ratio as well as downregulation of myogenic (e.g., MYOD and MYOG) or autophagy/mitophagy (e.g., LC3-β) genes, compared to age-matched wild-types. Post-injury gastrocnemius regeneration was found impaired in DF508 mice. Myoblast cultures from DF508 mice showed defective myogenic differentiation, which was reversed by overexpressing LC3-β. In aged (> 15-month-old) mice, overexpressing CFTR or VX809 restored the expression of autophagy or myogenic genes, increased mitochondrial LC3-β level and improved skeletal muscle mass and function.

CONCLUSION

Age-related reduction in skeletal muscle expression of CFTR impairs autophagy and myogenesis, exacerbating skeletal muscle aging. Enhancing CFTR might be a potential treatment strategy for age-related skeletal muscle disorders.

Longitudinal Evaluation of Physical Fitness in Adults with Cystic Fibrosis in the Era of CFTR-Modulating-Therapies

Purpose: Maintaining physical fitness plays an important role in the management of people with cystic fibrosis (pwCF). Longitudinal data on the course of physical fitness and the potential impact of the introduction of highly effective CFTR modulator therapy with elexacaftor/tezacaftor/ivacaftor (ETI) in adult pwCF are scarce. Methods: Health-related and skill-related components of physical fitness were assessed using an incremental cycle test (Wpeak), plus forward bend (FB), prone bent knee hip extension (HE), plank leg raise (PLR), standing long jump (SLJ), and standing on one leg (OLS). Relevant disease-specific clinical data (body mass index [BMI] and forced expiratory volume in 1 second [FEV1]) were recorded. Results: Twenty-eight adult pwCF (age 26.0 ± 7.8 years) were followed over 5.6 ± 0.9 years; 21 started ETI therapy during this period. Significant improvements from baseline were noted in BMI (p < 0.001) and health-related fitness components (HE, p = 0.002; PLR, p = < 0.001), whereas Wpeak and FB remained stable over time (all p > 0.05). Skill-related components (SLJ, OLS) showed no change (all p > 0.05). Subgroup analysis revealed significant improvements in BMI, FEV1, and health-related fitness measures of muscular strength and endurance (HE, p = 0.009; PLR, p < 0.001) only in pwCF using ETI. Conclusion: Despite the improvements, the impact of ETI on the individual parameters was small. Other factors than implementation of ETI alone need to be considered on the way to a high level of physical fitness in adult pwCF.

Skeletal muscle mitochondrial dysfunction mediated by Pseudomonas aeruginosa quorum-sensing transcription factor MvfR: reversing effects with anti-MvfR and mitochondrial-targeted compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum-sensing transcription factor MvfR (multiple virulence factor regulator) by interrogating, 5 days post-infection, its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs adenosine triphosphate generation, oxidative phosphorylation, and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR-mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

IMPORTANCE

Skeletal muscle, pivotal for many functions in the human body, including breathing and protecting internal organs, contains abundant mitochondria essential for maintaining cellular homeostasis during infection. The effect of Pseudomonas aeruginosa (PA) infections on skeletal muscle remains poorly understood. Our study delves into the role of a central quorum-sensing transcription factor, multiple virulence factor regulator (MvfR), that controls the expression of multiple acute and chronic virulence functions that contribute to the pathogenicity of PA. The significance of our study lies in the role of MvfR in the metabolic perturbances linked to mitochondrial functions in skeletal muscle and the effectiveness of the novel MvfR inhibitor and the mitochondrial-targeted peptide SS-31 in alleviating the mitochondrial disturbances caused by PA in skeletal muscle. Inhibiting MvfR or interfering with its effects can be a potential therapeutic strategy to curb PA virulence.

The long-term effect of elexacaftor/tezacaftor/ivacaftor on cardiorespiratory fitness in adolescent patients with cystic fibrosis: a pilot observational study

BACKGROUND

Physical activity is a crucial demand on cystic fibrosis treatment management. The highest value of oxygen uptake (VO2peak) is an appropriate tool to evaluate the physical activity in these patients. However, there are several other valuable CPET parameters describing exercise tolerance (Wpeak, VO2VT1, VO2VT2, VO2/HRpeak, etc.), and helping to better understand the effect of specific treatment (VE, VT, VD/VT etc.). Limited data showed ambiguous results of this improvement after CFTR modulator treatment. Elexacaftor/tezacaftor/ivacaftor medication improves pulmonary function and quality of life, whereas its effect on CPET has yet to be sufficiently demonstrated.

METHODS

We performed a single group prospective observational study of 10 adolescent patients with cystic fibrosis who completed two CPET measurements between January 2019 and February 2023. During this period, elexacaftor/tezacaftor/ivacaftor treatment was initiated in all of them. The first CPET at the baseline was followed by controlled CPET at least one year after medication commencement. We focused on interpreting the data on their influence by the novel therapy. We hypothesized improvements in cardiorespiratory fitness following treatment. We applied the Wilcoxon signed-rank test. The data were adjusted for age at the time of CPET to eliminate bias of aging in adolescent patients.

RESULTS

We observed significant improvement in peak workload, VO2 peak, VO2VT1, VO2VT2, VE/VCO2 slope, VE, VT, RQ, VO2/HR peak and RR peak. The mean change in VO2 peak was 5.7 mL/kg/min, or 15.9% of the reference value (SD ± 16.6; p= 0.014). VO2VT1 improved by 15% of the reference value (SD ± 0.1; p= 0.014), VO2VT2 improved by 0.5 (SD ± 0.4; p= 0.01). There were no differences in other parameters.

CONCLUSION

Exercise tolerance improved after elexacaftor/tezacaftor/ivacaftor treatment initiation. We suggest that the CFTR modulator alone is not enough for recovering physical decondition, but should be supplemented with physical activity and respiratory physiotherapy. Further studies are needed to examine the effect of CFTR modulators and physical therapy on cardiopulmonary exercise tolerance.

Skeletal Muscle Mitochondrial Dysfunction Mediated by Pseudomonas aeruginosa Quorum Sensing Transcription Factor MvfR: Reversing Effects with Anti-MvfR and Mitochondrial-Targeted Compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum sensing (QS) transcription factor MvfR by interrogating five days post-infection its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs ATP generation, oxidative phosphorylation (OXPHOS), and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR- mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

Extrapulmonary manifestations of pulmonary arterial hypertension

INTRODUCTION

Extrapulmonary manifestations of pulmonary arterial hypertension (PAH) may play a critical pathobiological role and a deeper understanding will advance insight into mechanisms and novel therapeutic targets. This manuscript reviews our understanding of extrapulmonary manifestations of PAH.

AREAS COVERED

A group of experts was assembled and a complimentary PubMed search performed (October 2023 - March 2024). Inflammation is observed throughout the central nervous system and attempts at manipulation are an encouraging step toward novel therapeutics. Retinal vascular imaging holds promise as a noninvasive method of detecting early disease and monitoring treatment responses. PAH patients have gut flora alterations and dysbiosis likely plays a role in systemic inflammation. Despite inconsistent observations, the roles of obesity, insulin resistance and dysregulated metabolism may be illuminated by deep phenotyping of body composition. Skeletal muscle dysfunction is perpetuated by metabolic dysfunction, inflammation, and hypoperfusion, but exercise training shows benefit. Renal, hepatic, and bone marrow abnormalities are observed in PAH and may represent both end-organ damage and disease modifiers.

EXPERT OPINION

Insights into systemic manifestations of PAH will illuminate disease mechanisms and novel therapeutic targets. Additional study is needed to understand whether extrapulmonary manifestations are a cause or effect of PAH and how manipulation may affect outcomes.

Effects of a remotely supervised resistance training program on muscle strength and body composition in adults with cystic fibrosis: Randomized controlled trial

INTRODUCTION

Among the limited studies on physical exercise interventions in adults with cystic fibrosis (CF), few have specifically addressed the improvement of peripheral muscle strength and body fat-free mass. The aim of this study was to examine the impacts of a remotely supervised, individualized 8-week resistance training program of moderate to high intensity on strength and body composition in these subjects.

METHODS

This was a randomized controlled trial performed in adults with CF. The exercise group (EX) performed three 1-h resistance training sessions per week over 8 weeks. The control group (CON) followed the physical activity recommendations of their physician. The main outcomes were muscle strength and body composition, with secondary measures including pulmonary function and quality of life. Two-way repeated measures analysis was used.

RESULTS

In 23 participants (age 32.13 ± 7.72 years), the intervention showed a significant beneficial effect on leg press strength, with a large effect size, both in absolute (p = 0.011;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.281) and relative (p = 0.007;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.310) terms. Large intervention effects were observed on total fat mass (p < 0.001;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.415), body adiposity index (p < 0.001;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.436), and fat mass index (p < 0.001;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.445), all showing reduction in the EX group. In addition, significant large size effects were detected on total fat-free mass (p = 0.046;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.177), trunk fat-free mass (p = 0.039;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.188), and fat-free mass index (p = 0.048;η p 2 $$ {\eta}_{\mathrm{p}}^2 $$  = 0.174), all favoring exercise. No significant effects were observed on pulmonary function and quality of life.

CONCLUSIONS

An 8-week remotely supervised resistance training program, with moderate to high intensity, effectively improved lower limb muscle strength and body composition.

Computed tomography reveals hypertrophic remodelling of the diaphragm in cystic fibrosis but not in COPD

Background

Computed tomography (CT) is increasingly used for assessing skeletal muscle characteristics. In cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), reduced limb muscle mass predicts poor clinical outcomes. However, the degree to which quantity or quality of respiratory and nonrespiratory muscles is affected by these diseases remains controversial.

Methods

Thoracic CT images of 29 CF, 21 COPD and 20 normal spirometry control subjects were analysed to measure indices of muscle quantity (volume or cross-sectional area) and quality (radiodensity) in respiratory (diaphragm, abdominal) and nonrespiratory (pectoralis, lumbar paraspinal) muscles. Multivariable linear regression assessed relationships of CT measurements with body mass index (BMI), forced expiratory volume in 1 s (FEV1) % pred, inflammation and infection biomarkers, nutritional status and CF genotype.

Results

Diaphragm volume in CF was significantly higher than in COPD (by 154%) or controls (by 140%). Abdominal muscle area in CF was also greater than in COPD (by 130%). Nonrespiratory muscles in COPD had more low radiodensity muscle (marker of lipid content) compared to CF and controls. In CF but not COPD, higher BMI and FEV1 % pred were independently associated with higher diaphragm and/or abdominal muscle quantity indices. Serum creatinine also predicted respiratory and nonrespiratory muscle quantity in CF, whereas other biomarkers including genotype correlated poorly with muscle CT parameters.

Conclusions

Our data suggest that the CF diaphragm undergoes hypertrophic remodelling, whereas in COPD the nonrespiratory muscles show altered muscle quality consistent with greater lipid content. Thoracic CT can thus identify distinctive respiratory and nonrespiratory muscle remodelling signatures associated with different chronic lung diseases.

Skeletal muscle contributions to reduced fitness in cystic fibrosis youth

Background

Increased maximal oxygen uptake (V̇O_2max) is beneficial in children with cystic fibrosis (CF) but remains lower compared to healthy peers. Intrinsic metabolic deficiencies within skeletal muscle (muscle "quality") and skeletal muscle size (muscle "quantity") are both proposed as potential causes for the lower V̇O_2max, although exact mechanisms remain unknown. This study utilises gold-standard methodologies to control for the residual effects of muscle size from V̇O_2max to address this "quality" vs. "quantity" debate.

Methods

Fourteen children (7 CF vs. 7 age- and sex-matched controls) were recruited. Parameters of muscle size - muscle cross-sectional area (mCSA) and thigh muscle volume (TMV) were derived from magnetic resonance imaging, and V̇O_2max obtained via cardiopulmonary exercise testing. Allometric scaling removed residual effects of muscle size, and independent samples t-tests and effect sizes (ES) identified differences between groups in V̇O_2max, once mCSA and TMV were controlled for.

Results

V̇O_2max was shown to be lower in the CF group, relative to controls, with large ES being identified when allometrically scaled to mCSA (ES = 1.76) and TMV (ES = 0.92). Reduced peak work rate was also identified in the CF group when allometrically controlled for mCSA (ES = 1.18) and TMV (ES = 0.45).

Conclusions

A lower V̇O_2max was still observed in children with CF after allometrically scaling for muscle size, suggesting reduced muscle "quality" in CF (as muscle "quantity" is fully controlled for). This observation likely reflects intrinsic metabolic defects within CF skeletal muscle.

Systematic review and meta-analysis: Associations of vitamin D with pulmonary function in children and young people with cystic fibrosis

BACKGROUND

Increasing evidence suggests that vitamin D is associated with pulmonary health, which may benefit children and young people diagnosed with Cystic Fibrosis (cypCF). Therefore, the aim of this systematic review was to evaluate primary research to establish associations between 25OHD and pulmonary health in cypCF.

METHODS

Electronic databases were searched with keywords related to CF, vitamin D, children/young people and pulmonary function. Included studies were cypCF (aged ≤21 years) treated in a paediatric setting. The primary outcome was lung function [forced expiratory volume in 1 s (FEV₁% predicted)] and secondary outcomes were rate of pulmonary exacerbations, 25OHD status and growth. Evidence was appraised for risk of bias using the CASP tool, and quality using the EPHPP tool. A Meta-analysis was performed.

RESULTS

Twenty-one studies were included with mixed quality ratings and heterogeneity of reported outcomes. The Meta-analysis including 5 studies showed a significantly higher FEV₁% predicted in the 25OHD sufficiency compared to the deficiency group [FEV₁% predicted mean difference (95% CI) was 7.71 (1.69-13.74) %; p = 0.01]. The mean ± SD FEV₁% predicted for the sufficient (≥75 nmol/L) vs. deficient (<50 nmol/L) group was 94.7 ± 31.9% vs. 86.9 ± 13.2%; I² = 0%; χ² = 0.5; df = 4). Five studies (5/21) found significantly higher rate of pulmonary exacerbations in those who were 25OHD deficient when compared to the sufficient group and negative associations between 25OHD and FEV% predicted. The effects of vitamin D supplementation dosages on 25OHD status (10/21) varied across studies and no study (12/21) showed associations between 25OHD concentration and growth.

CONCLUSION

This systematic review suggests that 25OHD concentration is positively associated with lung function and a concentration of >75 nmol/L is associated with reduced frequency of pulmonary exacerbations, which may slow lung function decline in cypCF. Future randomised clinical trials and mechanistic studies are warranted.

Brain motor and fear circuits regulate leukocytes during acute stress

The nervous and immune systems are intricately linked1. Although psychological stress is known to modulate immune function, mechanistic pathways linking stress networks in the brain to peripheral leukocytes remain poorly understood2. Here we show that distinct brain regions shape leukocyte distribution and function throughout the body during acute stress in mice. Using optogenetics and chemogenetics, we demonstrate that motor circuits induce rapid neutrophil mobilization from the bone marrow to peripheral tissues through skeletal-muscle-derived neutrophil-attracting chemokines. Conversely, the paraventricular hypothalamus controls monocyte and lymphocyte egress from secondary lymphoid organs and blood to the bone marrow through direct, cell-intrinsic glucocorticoid signalling. These stress-induced, counter-directional, population-wide leukocyte shifts are associated with altered disease susceptibility. On the one hand, acute stress changes innate immunity by reprogramming neutrophils and directing their recruitment to sites of injury. On the other hand, corticotropin-releasing hormone neuron-mediated leukocyte shifts protect against the acquisition of autoimmunity, but impair immunity to SARS-CoV-2 and influenza infection. Collectively, these data show that distinct brain regions differentially and rapidly tailor the leukocyte landscape during psychological stress, therefore calibrating the ability of the immune system to respond to physical threats.

Diaphragmatic plication among lung transplant patients: A single-center experience

BACKGROUND

There is lack of data reporting outcomes among patients needing diaphragmatic plication (DP) during or after lung transplantation (LT). We sought to assess the association of DP with post-transplant spirometry among other outcomes.

METHODS

We included all patients who underwent LT between 2012&2016 (n = 324, mean age 56.3±13.4 years; M:F 198:126). We compared early and late outcomes based on the need for DP.

RESULTS

The frequency of diaphragm dysfunction (DD)on pre-transplant fluoroscopy was 52.2%. A total of 38 DP procedures were performed among 37 patients (11.4% of LT patients). DP was done for anatomic (sizing or spacing issues) or functional indications (symptomatic DD). While patients with DP had significantly lower spirometry throughout the 3-year follow-up period, their slope of decline, functional assessments at the first annual visit, the risk of CLAD, and mortality were similar to patients without DP. A sub-group analysis limited to patients with restrictive lung diseases as the transplant indication had similar findings.

CONCLUSIONS

Pre-transplant DD is common among LT candidates although it did not predict the need for DP. DP may be performed for functional or anatomic indications especially for addressing the donor-recipient size mismatch. Despite the lack of favorable effect on post-transplant spirometry, patients undergoing DP have acceptable and comparable early and late outcomes. This article is protected by copyright. All rights reserved.

Characterization of skeletal muscle wasting pathways in diaphragm and limb muscles of cystic fibrosis mice

BACKGROUND

Cystic fibrosis (CF) patients often suffer from skeletal muscle atrophy, most often attributed to physical inactivity and nutritional factors. CF is also characterized by abnormally elevated systemic inflammation. However, it is unknown whether the lack of a functional CF transmembrane conductance regulator (CFTR) gene predisposes to exaggerated inflammation-induced muscle proteolysis.

METHODS

CF mice (CFTR-/-) and their wild-type (WT=CFTR+/+) littermate controls were systemically injected with Pseudomonas-derived lipopolysaccharide (LPS). After 24 hours, the diaphragm and limb muscles (fast-twitch tibialis anterior, slow-twitch soleus) were assessed for induction of inflammatory cytokines (TNFa, IL1b, IL6), oxidative stress, canonical muscle proteolysis pathways (Calpain, Ubiquitin-Proteasome, Autophagy), muscle fiber histology, and diaphragm contractile function.

RESULTS

At baseline, CF and WT muscles did not differ with respect to indices of inflammation, proteolysis, or contractile function. After LPS exposure, there was significantly greater induction of all proteolysis pathways (Calpain activity; Ubiquitin-Proteasome: MuRF1 and Atrogin1; Autophagy: LC3B, Gabarapl-1, BNIP3) in CF mice for the diaphragm and tibialis anterior, but not the soleus. Proteolysis pathway upregulation and correlations with inflammatory cytokine induction were most prominent in the tibialis anterior. Diaphragm force normalized to muscle cross-sectional area was reduced by LPS to an equivalent degree in CF and WT mice.

CONCLUSIONS

CF skeletal muscles containing a high proportion of fast-twitch fibers (diaphragm, tibialis anterior) exhibit abnormally exaggerated upregulation of multiple muscle wasting pathways after exposure to an acute inflammatory stimulus, but not under basal conditions.

Comparison of quadriceps muscle size and quality in adults with cystic fibrosis with different severities of cystic fibrosis transmembrane conductance regulator protein dysfunction

Background

Cystic fibrosis (CF) is characterized by CF transmembrane conductance regulator (CFTR) dysfunction. CFTR protein is expressed in human skeletal muscle; however, its impact on skeletal muscle is unknown. The objectives of this study were to compare quadriceps muscle size and quality between adults with various severities of CFTR protein dysfunction.

Methods

We conducted a prospective, cross-sectional study comparing 34 adults with severe versus 18 with mild CFTR protein dysfunction, recruited from a specialized CF centre. Ultrasound images of rectus femoris cross-sectional area (RF-CSA) and quadriceps layer thickness for muscle size, and rectus femoris echogenicity (RF-ECHO) (muscle quality) were obtained. Multivariable linear regression models were developed using purposeful selection technique.

Results

People with severe CFTR protein dysfunction had larger RF-CSA by 3.22 cm², 95% CI (1.03, 5.41) cm², p=.0049], after adjusting for oral corticosteroid use and Pseudomonas aeruginosa colonization. However, a sensitivity analysis indicated that the result was influenced by the specific confounders being adjusted for in the model. We did not find any significant differences in quadriceps layer thickness or RF-ECHO between the two groups.

Conclusion

We found no differential impact of the extent of diminished CFTR protein activity on quadriceps muscle size or quality in our study cohort. Based on these findings, CFTR mutation status cannot be used differentiate leg muscle size or quality in people with CF.

Exercise intolerance in cystic fibrosis-the role of CFTR modulator therapies

Exercise intolerance is common in people with CF (pwCF), but not universal among all individuals. While associated with disease prognosis, exercise intolerance is not simply a reflection of the degree of lung disease. In people with severe CF, respiratory limitations may contribute more significantly to impaired exercise capacity than in those with mild-moderate CF. At all levels of disease severity, there are peripheral factors e.g., abnormal macro- and micro-vascular function that impair blood flow and reduce oxygen extraction, and mitochondrial defects that diminish metabolic efficiency. We discuss advances in understanding the central and peripheral mechanisms underlying exercise intolerance in pwCF. Exploring both the central and peripheral factors that contribute to exercise intolerance in CF can help inform the development of new therapeutic targets, as well as help define prognostic criteria.

Health-Related and Motor Performance-Related Fitness and Physical Activity Among Youth With Cystic Fibrosis

Little is known about motor competence and the longitudinal development of motor performance among youth with cystic fibrosis (CF). In this study, we assessed aspects of motor performance in different age groups of young patients with CF and compared them with a healthy reference group of same aged children. We also examined the development of motor performance among different age groups of these children with CF, using The Deutscher Motorik Test (DMT) to assess attributes of health-related and motor performance-related fitness. We used an incremental ergometer cycle test to determine maximal exercise capacity (expressed as peak workload). We evaluated and recorded habitual physical activity (PA) as measured by the number of steps per day and the time spent in different PA intensities (expressed in metabolic equivalents). In total, 31 children and adolescents with CF agreed to participate (13 girls,18 boys) aged 6-17 years (M = 11.3, SD =3.3 years); they had a mean one second forced expiratory volume (expressed as a percentage of predicted value [% pred]) of 87.2% (SD = 22.3%). We found their values of health-related and motor performance-related fitness to be significantly lower (p < 0.05) than those of their healthy peer participants. In contrast to the reference group, participants with CF up to 14 years of age showed a linear improvement in these values and in their PA, followed by a plateau or even a nonsignificant decrease after age 14. These findings have important implications for the development and prescription of exercise programs for children with CF. Besides aerobic and strength exercises, we recommend that neuromuscular training be integrated into exercise programs to improve the coordinative abilities of youth with CF. More attention should be paid to vulnerable older adolescents to ensure their long-term motivation to maintain exercise participation.

Orthopedic Manifestations of Cystic Fibrosis

Cystic fibrosis (CF) is a relatively common disease seen in Whites of northern European descent. Classically, it was a lethal disease and uncommon for the orthopedic practitioner to interact with CF patients. Recent pharmaceutical breakthroughs targeting the CF transmembrane conductance regulator (CFTR) gene have significantly prolonged patient life expectancy. This makes it increasingly likely that orthopedic surgeons will encounter CF patients in their clinic. In this article, the authors discuss pertinent musculoskeletal manifestations of the CF population, including the increased risk of decreased bone mineral density and bone mineral content, muscle deconditioning, spinal kyphosis, fractures, and elevated systemic inflammation predisposing these individuals to CF-related arthralgia. The diagnoses are grouped into subspecialties (arthroplasty, pediatrics, spine, sports, and trauma) most likely to evaluate the patient. Additionally, the authors review treatment options for these conditions and discuss the need for these patients to be seen in the perioperative period by their CF care team for patient optimization due to their diminished pulmonary function. Interspersed with this literature review, the authors present 2 unique cases. The first case details a patient with pain over her spine due to multilevel spinous process bursitis caused by a high-frequency chest wall oscillation system, which masquerades as an infection. The second case is a non-contact midsubstance rectus femoris tear in an athlete. These cases highlight the need for increased vigilance for uncommon diagnoses in the CF patient population. [Orthopedics. 2021;44(3):e440-e445.].

Heart rate variability, exercise capacity and levels of daily physical activity in children and adolescents with mild-to-moderate cystic fibrosis

Background: Autonomic nervous system balance is altered in cystic fibrosis (CF), although its influence on physical fitness has been poorly explored.

Objective: This study aimed to evaluate the association of heart rate variability (HRV) with exercise capacity and levels of daily physical activity in children and adolescents with mild-to-moderate CF.

Methods: A cross-sectional study including individuals with CF aged 6–18 years, not under CFTR modulator therapy, was performed. Sociodemographic (age, sex) and clinical information (airway colonization, pancreatic insufficiency, and genotyping) were collected. In addition, exercise capacity (modified shuttle test — MST), lung function (spirometry), body composition (bioimpedance), levels of daily physical activity (5-day accelerometer), and HRV (both at rest and during the MST) were evaluated.

Results: 30 individuals (20 females) aged [Formula: see text] years, mean FEV[Formula: see text]%, were included. A sympathovagal balance (LF/HF) increase ([Formula: see text]) during the MST was shown, indicating a predominance of sympathetic modulation. The standard deviation of all RR intervals (SDNN) and the high frequency (HF) index during exercise correlated significantly with FEV1 ([Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text]; respectively). MST distance also correlated positively and significantly with SDNN ([Formula: see text], [Formula: see text]), square root of the mean of the sums of squares of frequencies between RR intervals greater than 50[Formula: see text]ms — RMSSD ([Formula: see text], [Formula: see text]), low frequency — LF ([Formula: see text], [Formula: see text]), HF ([Formula: see text], [Formula: see text]), dispersion of points perpendicular to the short-term identity line — SD1 ([Formula: see text], [Formula: see text]) and negatively with LF/HF ([Formula: see text], [Formula: see text]). Regarding daily physical activity, SDNN at rest ([Formula: see text], [Formula: see text]) and exercise ([Formula: see text], [Formula: see text]) showed positive correlations with time in moderate-to-vigorous activities. When normalizing the SDNN and classifying individuals as normal or altered, those presenting altered SDNN showed poorest FEV1 ([Formula: see text]) and lower exercise capacity ([Formula: see text]).

Conclusion: HRV correlates with lung function, exercise capacity and levels of daily physical activity in children and adolescents with CF. The study highlights the influence of CF on autonomic function and suggests HRV measurement as an easy tool to be used in clinical settings as an alternative marker to monitor CF individuals.

Peripheral muscle strength is associated with aerobic fitness and use of antibiotics in patients with cystic fibrosis

AIMS

Individuals with cystic fibrosis (CF) may develop muscle abnormalities, although little is known on its clinical and functional impact. This study aimed to evaluate the association of peripheral muscle strength with aerobic fitness, habitual physical activity, lung function and the use of antibiotics (ATB) in patients with CF.

METHODS

A cross-sectional study where individuals aged ≥6 years underwent peripheral muscle strength evaluation (biceps, quadriceps and hamstrings) and performed a cardiopulmonary exercise test. Demographic, anthropometric, genetic, lung function and total days of ATB use within 1 year of tests were also collected.

RESULTS

Correlation was found for biceps (r = .45; P = .002) strength with the peak oxygen consumption (VO₂ peak). Muscle strength (biceps and quadriceps) also correlated with the ventilatory equivalent for oxygen consumption (V_E /VO₂ ) at anaerobic threshold (AT) and with the ventilatory equivalent for carbon dioxide production (V_E /VCO₂ ) both at AT and peak exercise. Negative correlations were found for quadriceps (r = -.39) and hamstrings (r = -.42) with the total days of ATB use in the following year. Patients needing to use ATB presented lower biceps strength (P = .05) and individuals with VO₂ peak lower than 37 mL·kg^-1 ·min^-1 presented lower muscle strength for both biceps (P = .01) and quadriceps (P = .02).

CONCLUSIONS

The results have shown that peripheral muscle strength is associated with aerobic fitness and the use of antibiotics in patients with CF.

The impact of plasma 25-hydroxyvitamin D on pulmonary function and exercise physiology in cystic fibrosis: A multicentre retrospective study

BACKGROUND

A 25-hydroxyvitamin D (25OHD) may exert immunomodulatory effects on respiratory health, which may translate to improvements in exercise physiology. Thus, we aimed to investigate whether plasma 25OHD is associated with lung function and aerobic fitness in people with cystic fibrosis (pwCF).

METHODS

A multicentre retrospective review of pwCF (> 9 years old) attending the Royal Hospital for Sick Children (Edinburgh) or Wessex CF-Unit (Southampton) was performed between July 2017 and October 2019. Demographic and clinical data were collected. Plasma 25OHD measured closest in time to clinical cardiopulmonary exercise testing and/or spirometry [forced expiratory volume (FEV₁ )% predicted] was recorded. Pancreatic insufficiency was diagnosed based on faecal elastase of < 100 µg g^-1 . We performed multiple-regression analysis with aerobic fitness outcomes [peak oxygen uptake (VO_2 peak )] and FEV₁ % predicted as primary outcomes.

RESULTS

Ninety pwCF [mean ± SD age: 19.1 ± 8.6 years, 54 (60%) children, 48 (53%) males and 88 (98%) Caucasian] were included. 25OHD deficiency and insufficiency was 15 (17%) and 44 (49%), respectively. 25OHD deficiency and insufficiency was significantly associated with pancreatic insufficiency (χ²  = 4.8, p = 0.02). Plasma 25OHD was not significantly associated with FEV₁ % predicted (r²  = 0.06, p = 0.42, 95% CI = -0.09 to 0.19) or VO_2 peak (r²  = 0.04, p = 0.07, 95% CI = -011 to 0.005) in all pwCF. However, 25OHD was significantly associated with both FEV₁ % (r²  = 0.15, p = 0.02, 95% CI = 1.99-2.64) and VO_2 peak (r²  = 0.13, p = 0.05, 95% CI = -0.26 to -0.005) in the paediatric cohort.

CONCLUSIONS

We showed that 25OHD is associated with improved lung function and aerobic fitness in children and adolescents with CF. Mechanistic and high-quality prospective studies including both lung function and aerobic fitness as primary outcomes are now warranted.

Exercise Intolerance in Cystic Fibrosis: Importance of Skeletal Muscle

PURPOSE

Exercise intolerance, evaluated by O2 consumption, predicts mortality in cystic fibrosis (CF). People with CF exhibit skeletal muscle dysfunctions that may contribute to an imbalance between O2 delivery and utilization. Sildenafil, a phosphodiesterase type 5 inhibitor, increases blood flow and improves O2 consumption, although the exact mechanisms in CF have yet to be elucidated. Thus, we hypothesized that exercise intolerance in CF is limited primarily by an impaired skeletal muscle O2 utilization, and sildenafil improves exercise tolerance in CF by addressing this mismatch between O2 demand and extraction.

METHODS

Fifteen individuals with mild to moderate CF and 18 healthy controls completed an incremental exercise test and measurements of gaseous exchange, chronotropic response, hemodynamics, and O2 extraction and utilization. People with CF also completed a 4-wk treatment with sildenafil with a subsequent follow-up evaluation after treatment.

RESULTS

Skeletal muscle O2 extraction and utilization during exercise were reduced in people with CF when compared with controls. Exercise capacity in our CF population was minimally limited by hemodynamic or chronotopic responses, whereas peripheral O2 extraction was more closely associated with exercise capacity. The study also demonstrated that 4 wk of sildenafil improved skeletal muscle O2 utilization during exercise to similar values observed in healthy individuals.

CONCLUSIONS

Individuals with mild to moderate CF exhibit exercise intolerance secondary to a reduction in O2 utilization by the exercising skeletal muscle. The present study demonstrated that 4 wk of sildenafil treatment improves the capacity of the skeletal muscle to use O2 more efficiently during exercise. Findings from the present study highlight the importance of targeting skeletal muscle O2 utilization to improve exercise tolerance in CF.

Effects of a Short-Term Resistance-Training Program on Heart Rate Variability in Children With Cystic Fibrosis-A Randomized Controlled Trial

Background: Cystic fibrosis (CF) affects the autonomic nervous system (ANS) and exercise in healthy children modulates the interaction between sympathetic and parasympathetic activity. This study aimed to evaluate the effects of a short-term resistance exercise program on heart rate variability (HRV) in children and adolescents with CF.

Methods: A randomized controlled trial was carried out in children diagnosed with CF aged 6–18 years. Individuals were divided into two groups: control (CON) and resistance-training (EX). Individuals in the EX group completed an individualized guided resistance program (5-RM—60–80%) for 8 weeks (3 sessions of 60 min/week). Upper and lower limbs exercises (seated bench press, seated lateral row, and leg press) were used. HRV was measured using a Suunto watch with subjects in lying position.

Results: Nineteen subjects (13 boys) were included (CON = 11; and EX = 8). Mean age was 12.2 ± 3.3, FEV₁ (forced expiratory volume in the first second) z-score was 1.72 ± 1.54 and peak oxygen consumption (VO₂peak) 42.7 ± 7.4 mL.Kg^–1.min^–1. Exercise induced significant changes in the frequency-domain variables, including a decrease in LF power (p = 0.001, d = 0.98) and LF/HF ratio (p = 0.020, d = 0.92), and an increase in HF power (p = 0.001, d = −0.97), compared to the CON group. No significant changes were found for time-domain variables, although increases with a moderate effect size were seen for SDNN (p = 0.152, d = −0.41) and RMSSD (p = 0.059, d = −0.49) compared to the CON group.

Conclusion: A short-term resistance exercise-training program was able to modulate HRV in children and adolescents with CF presenting mild to moderate lung function impairment and good physical condition.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier NCT04293926.

Limb muscle size and contractile function in adults with cystic fibrosis: A systematic review and meta-analysis

BACKGROUND

There is conflicting evidence regarding the presence of limb muscle impairments in adults with cystic fibrosis (CF), and the factors associated with these muscle impairments. The objectives of this study were to compare limb muscle size and function between adults with CF and healthy controls; and to examine their associations with demographic and clinical variables in adults with CF.

METHODS

The systematic review was performed using PRISMA guidelines. Studies were included if they measured any aspect of limb muscle size or function in adults with CF. Meta-analyses were performed to compare muscle variables between CF and healthy controls; and to examine their associations with demographic and clinical variables.

RESULTS

Twenty-eight studies were included, with 747 adults with CF. The meta-analyses showed that adults with CF have smaller thigh muscles [standardized mean difference (SMD) = 0.57, p<.0011, I²=0%], and lower handgrip strength (SMD = 0.89, p=.0034, I²=74.03%), which was weakly correlated with forced expiratory volume in one second (FEV₁) (r=0.24, p=.035, I²=0%) and lower in females with CF (SMD = 2.05, p<.0001, I²=0%). There is no significant difference between adults with CF and controls in knee extensor strength (SMD = 0.25, p=.095, I²=42.79%).

CONCLUSIONS

Leg muscle atrophy and lower handgrip strength were noted. There may be a subgroup of adults with CF with knee extensor (quadriceps) weakness. Future studies are needed to better understand muscle impairments in people with CF; to explore the factors that can predict these muscle impairments; and to investigate their clinical significance in people with CF.

Physical exercise as a tool to minimize the consequences of the Covid-19 quarantine: An overview for cystic fibrosis

Coronavirus (SARS-CoV-2) outbreak leading to the coronavirus disease (Covid-19) has become a global pandemic. Patients with Cystic fibrosis are considered of major risk, as respiratory tract infections are more severe than in the general population, with a higher risk of complications and a negative impact on lung function. The performance of physical exercise is considered as key for its well-known general benefits and also as a complementary method to help airway clearance. Therefore, physical exercise is also considered as key in the therapeutic strategy during the quarantine period. However, the impossibility to perform exercise with appropriate prescription and monitoring is of considerable worry to health care professionals. Thus, alternative strategies, such as online measures to monitor this therapy and, consequently, to achieve a safe and effective dose are highly needed. Exercise regimens should include strength and endurance, as well as balance and flexibility exercises. Patients are highly encouraged to participate in exercise programs to maintain fitness and exercise should be continued during the quarantine period. This commentary provides a summary of the main effects and benefits of physical exercise, as well as the main recommendations for its adequate execution, including exercise modality, frequency, intensity, and volume.

Oxygen transport and utilisation during exercise in cystic fibrosis: contributors to exercise intolerance

NEW FINDINGS

What is the topic of this review? This review highlights the central and peripheral mechanisms that alter oxygen transport and utilisation and thereby contribute to exercise limitation in people with cystic fibrosis, considering also viable therapeutic targets for intervention. What advances does it highlight? Although traditionally considered a respiratory condition, pathological intramuscular and cardiovascular changes in people with cystic fibrosis appear to be key determinants of exercise intolerance up until the later stages of respiratory disease. Even young, habitually active patients with normal lung function experience multisystemic abnormalities, which play a role in exercise intolerance.

ABSTRACT

Cystic fibrosis (CF) is a complex condition, commonly associated with exercise limitation. The mechanisms responsible for this in CF are of interest, given that lower aerobic fitness is associated with an increased risk of being hospitalised with pulmonary exacerbation, a poorer quality of life and a poorer prognosis. Pathophysiological changes in lung function are considered central to CF, and may contribute to exercise limitation. However, it is now clear that the pathogenesis of exercise limitation in this population is multifactorial, with alterations in cardiovascular, muscle and pulmonary function contributing. Whilst some of these changes are attributable to respiratory disease per se, the CF transmembrane conductance regulator protein is also found in skeletal muscle and the vascular endothelium and can directly alter central and localised oxygen delivery, as well as the ability to effectively extract and utilise oxygen at the myocyte level. Since intense exercise poses considerable challenges to arterial oxygen content and/or blood flow and its supply to the working skeletal muscle, evaluating the exercise physiology of people with CF has helped us understand the mechanisms underlying exercise intolerance. Through several investigations over recent years, we have collectively demonstrated that people with CF exhibit reduced skeletal muscle oxygen extraction and utilisation during exercise, with a lesser contribution from haemodynamic or chronotropic mechanisms. Taken together, our findings highlight the importance of targeting mechanisms of skeletal muscle oxygen utilisation in CF to improve exercise tolerance and we offer potential therapeutic interventional strategies.

Tissue oxygenation in peripheral muscles and functional capacity in cystic fibrosis: a cross-sectional study

NEW FINDINGS

What is the central question of this study? How do peripheral muscle tissue oxygenation and physical conditioning levels of children and adolescents with cystic fibrosis compare to demographically matched controls? What is the main finding and its importance? Children and adolescents with cystic fibrosis consumed more oxygen, more quickly and exhibited slower recovery, demonstrating that there may have been deficiencies in oxygen supply related to both oxygen uptake and oxygen transport.

ABSTRACT

Cystic fibrosis affects skeletal muscle performance and functional capacity. However, it is currently unclear how peripheral muscle behaviour is affected, especially in children and adolescents. To examine this, we compared tissue oxygenation of children and adolescents with cystic fibrosis against healthy volunteers. We also evaluated the functional capacity of participants via the modified shuttle test (MST) and assessed for associations between performance and near-infrared spectroscopy. A total of 124 participants enrolled. Participants were divided into either the cystic fibrosis group (CFG) or the healthy group (HG). Statistical comparisons between groups were evaluated with the Mann-Whitney U test and associations with functional capacity were evaluated using Spearman's correlation coefficient. CFG volunteers scored lower on the MST compared to the HG. They walked shorter distances (P = 0.001) with less efficiency because they performed the tests with a less efficient walking economy (P = 0.001) and a greater deoxyhaemoglobin concentration (P = 0.001). Further, they experienced reduced tissue oxygen saturation (P = 0.037) faster than the HG. As a result, they presented lower respiratory (P = 0.001) and lower heart (P = 0.001) rate values at the end of the MST, with a longer post-test heart rate recovery time (P = 0.005). There was a significant association between deoxygenation time and functional capacity. The CFG consumed more oxygen, more quickly, with a slower recovery, reflecting impairments in the dynamics of muscle oxygen extraction. The results suggest differences in functional capacity and haemodynamic recovery in children and adolescents with cystic fibrosis.

Clinimetric evaluation of muscle function tests for individuals with cystic fibrosis: A systematic review

Accurate testing of muscle function is essential in individuals with cystic fibrosis (CF). A literature search was conducted in MEDLINE, CENTRAL, CINAHL, PEDro, ScienceDirect and Web of Science according to PRISMA and COSMIN guidelines from inception to September 2019 to investigate the clinimetric properties of muscle tests in individuals with CF. The search identified 37 studies (1310 individuals) and 34 different muscle tests. Maximal inspiratory pressure, inspiratory work capacity and quadriceps strength measured by computerised dynamometry were identified as reliable tests of muscle function. The one-minute sit-to-stand test was found to have high reliability but its validity to measure quadriceps strength is unknown. The clinimetric properties of other routinely used tests have not been reported in people with CF. Very different measurement procedures were identified. Inspiratory muscle and quadriceps testing can be considered as reliable but high-quality studies evaluating tests of other muscles function (e.g. muscle endurance) are lacking.

Re-imagining cystic fibrosis care: next generation thinking

Cystic fibrosis (CF) is a common multi-system genetically inherited condition, predominately found in individuals of Caucasian decent. Since the identification of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene in 1989, and the subsequent improvement in understanding of CF pathophysiology, significant increases in life-expectancy have followed. Initially this was related to improvements in the management and systems of care for treating the various affected organ systems. These cornerstone treatments are still essential for CF patients born today. However, over the last decade, the major advance has been in therapies that target the resultant genetic defect: the dysfunctional CFTR protein. Small molecule agents that target this dysfunctional protein via a variety of mechanisms have led to lung function improvements, reductions in pulmonary exacerbation rates and increases in weight and quality-of-life indices. As more patients receive these agents earlier and earlier in life, it is likely that general CF care will increasingly pivot around these specific therapies, although it is also likely that effects other than those identified in the initial trials will be discovered and need to be managed. Despite great excitement for modulator therapies, they are unlikely to be suitable or available for all; whether this is due to a lack of availability for specific CFTR mutations, drug-reactions or the health economic set-up in certain countries. Nevertheless, the CF community must be applauded for its ongoing focus on research and development for this life-limiting disease. With time, personalised individualised therapy would ideally be the mainstay of CF care.

Three-axis accelerometer system for comparison of gait parameters in children with cystic fibrosis and healthy peers

BACKGROUND

Cystic Fibrosis (CF), affecting functional exercise capacity generally measured by submaximal exercise test such as 6min walk test, is a progressive, autosomal recessive and metabolic disorder. Three-axis accelerometers, which are used during gait, are an easy way to assess gait parameters in patients and healthy individuals. Gait parameters were significantly associated with clinical outcomes of COPD. However, the association between gait parameters and clinical outcomes in children with CF is unclear.

RESEARCH QUESTION

Do clinical outcomes in CF have an important role in determining gait parameters?.

METHODS

Twenty-one CF and 21 healthy subjects participated in this case-control study. Body composition was evaluated using Tanita-BC 418. Respiratory and knee extension muscle strengths were assessed. Functional exercise capacity was evaluated using the 6-min walk test (6MWT). Spatiotemporal gait parameters were evaluated using a validated wireless inertial sensing device (G-Sensor, BTS Bioengineering S.p.A., Italy) during the 6MWT and 7-meter gait test.

RESULTS

MIP, the distance of 6MWT, and stride length were significantly lower in the CF group compare to healthy children (p<0.05). Gait speed and functional exercise capacity, cadence and functional exercise capacity, quadriceps muscle strength, FEV1, fat-free mass were found to be correlated in CF patients (p<0.05).

SIGNIFICANCE

The aerobic capacity and gait parameters were affected in CF patients with mild disease severity in our study. Clinical outcomes were associated with gait parameters in CF patients. This is the first study to use the 3-axis accelerometer to evaluate functional exercise capacity and gait parameters of CF and healthy children. A three-axis accelerometer can be used to assess functional exercise capacity and gait parameters in CF patients at the clinics.

Utility and validity of dynamic chest radiography in cystic fibrosis (dynamic CF): an observational, non-controlled, non-randomised, single-centre, prospective study

INTRODUCTION

Dynamic chest radiography (DCR) uses novel, low-dose radiographic technology to capture images of the thoracic cavity while in motion. Pulmonary function testing is important in cystic fibrosis (CF). The tolerability, rapid acquisition and lower radiation and cost compared with CT imaging may make DCR a useful adjunct to current standards of care.

METHODS AND ANALYSIS

This is an observational, non-controlled, non-randomised, single-centre, prospective study. This study is conducted at the Liverpool Heart and Chest Hospital (LHCH) adult CF unit. Participants are adults with CF. This study reviews DCR taken during routine CF Annual Review (n=150), validates DCR-derived lung volumes against whole body plethysmography (n=20) and examines DCR at the start and end of pulmonary exacerbations of CF (n=20). The primary objectives of this study are to examine if DCR provides lung function information that correlates with PFT, and lung volumes that correlate whole body plethysmography.

ETHICS AND DISSEMINATION

This study has received the following approvals: HRA REC (11 December 2019) and LHCH R&I (11 October 2019). Results are made available to people with CF, the funders and other researchers. Processed, anonymised data are available from the research team on request.

TRIAL REGISTRATION NUMBER

ISRCTN 64994816.

Size-adjusted muscle power and muscle metabolism in patients with cystic fibrosis are equal to healthy controls - a case control study

Background

Skeletal muscle function dysfunction has been reported in patients with cystic fibrosis (CF). Studies so far showed inconclusive data whether reduced exercise capacity is related to intrinsic muscle dysfunction in CF.

Methods

Twenty patients with CF and 23 age-matched controls completed an incremental cardiopulmonary cycling test. Further, a Wingate anaerobic test to assess muscle power was performed. In addition, all participants completed an incremental knee-extension test with ³¹P magnetic resonance spectroscopy to assess muscle metabolism (inorganic phosphate (Pi) and phosphocreatinine (PCr) as well as intracellular pH). In the MRI, muscle cross-sectional area of the M. quadriceps (qCSA) was also measured. A subgroup of 15 participants (5 CF, 10 control) additionally completed a continuous high-intensity, high-frequency knee-extension exercise task during ³¹P magnetic resonance spectroscopy to assess muscle metabolism.

Results

Patients with CF showed a reduced exercise capacity in the incremental cardiopulmonary cycling test (VO₂peak: CF 77.8 ± 16.2%predicted (36.5 ± 7.4 ml/qCSA/min), control 100.6 ± 18.8%predicted (49.1 ± 11.4 ml/qCSA/min); p < 0.001), and deficits in anaerobic capacity reflected by the Wingate test (peak power: CF 537 ± 180 W, control 727 ± 186 W; mean power: CF 378 ± 127 W, control 486 ± 126 W; power drop CF 12 ± 5 W, control 8 ± 4 W. all: p < 0.001). In the knee-extension task, patients with CF achieved a significantly lower workload (p < 0.05). However, in a linear model analysing maximal work load of the incremental knee-extension task and results of the Wingate test, respectively, only muscle size and height, but not disease status (CF or not) contributed to explaining variance. In line with this finding, no differences were found in muscle metabolism reflected by intracellular pH and the ratio of Pi/PCr at submaximal stages and peak exercise measured through MRI spectroscopy.

Conclusions

The lower absolute muscle power in patients with CF compared to controls is exclusively explained by the reduced muscle size in this study. No evidence was found for an intrinsic skeletal muscle dysfunction due to primary alterations of muscle metabolism.

Exercise Physiology Across the Lifespan in Cystic Fibrosis

Cystic fibrosis (CF), a severe life-limiting disease, is associated with multi-organ pathologies that contribute to a reduced exercise capacity. At present, the impact of, and interaction between, disease progression and other age-related physiological changes in CF on exercise capacity from child- to adult-hood is poorly understood. Indeed, the influences of disease progression and aging are inherently linked, leading to increasingly complex interactions. Thus, when interpreting age-related differences in exercise tolerance and devising exercise-based therapies for those with CF, it is critical to consider age-specific factors. Specifically, changes in lung function, chronic airway colonization by increasingly pathogenic and drug-resistant bacteria, the frequency and severity of pulmonary exacerbations, endocrine comorbidities, nutrition-related factors, and CFTR (cystic fibrosis transmembrane conductance regulator protein) modulator therapy, duration, and age of onset are important to consider. Accounting for how these factors ultimately influence the ability to exercise is central to understanding exercise impairments in individuals with CF, especially as the expected lifespan with CF continues to increase with advancements in therapies. Further studies are required that account for these factors and the changing landscape of CF in order to better understand how the evolution of CF disease impacts exercise (in)tolerance across the lifespan and thereby identify appropriate intervention targets and strategies.

Pseudomonas aeruginosa Quorum Sensing Molecule Alters Skeletal Muscle Protein Homeostasis by Perturbing the Antioxidant Defense System

Skeletal muscle function is compromised in many illnesses, including chronic infections. The Pseudomonas aeruginosa quorum sensing (QS) signal, 2-amino acetophenone (2-AA), is produced during acute and chronic infections and excreted in human tissues, including the lungs of cystic fibrosis patients. We have shown that 2-AA facilitates pathogen persistence, likely via its ability to promote the formation of bacterial persister cells, and that it acts as an interkingdom immunomodulatory signal that epigenetically reprograms innate immune functions. Moreover, 2-AA compromises muscle contractility and impacts the expression of genes involved in reactive oxygen species (ROS) homeostasis in skeletal muscle and in mitochondrial functions. Here, we elucidate the molecular mechanisms of 2-AA's impairment of skeletal muscle function and ROS homeostasis. Murine in vivo and differentiated C2C12 myotube cell studies showed that 2-AA promotes ROS generation in skeletal muscle via the modulation of xanthine oxidase (XO) activity, NAD(P)H oxidase2 (NOX2) protein level, and the activity of antioxidant enzymes. ROS accumulation triggers the activity of AMP-activated protein kinase (AMPK), likely upstream of the observed locations of induction of ubiquitin ligases Muscle RING Finger 1 (MuRF1) and Muscle Atrophy F-box (MAFbx), and induces autophagy-related proteins. The protein-level perturbation in skeletal muscle of silent mating type information regulation 2 homolog 1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), and uncoupling protein 3 (UCP3) is rescued by the antioxidant N-acetyl-l-cysteine (NAC). Together, these results unveil a novel form of action of a QS bacterial molecule and provide molecular insights into the 2-AA-mediated skeletal muscle dysfunction caused by P. aeruginosa IMPORTANCE Pseudomonas aeruginosa, a bacterium that is resistant to treatment, causes serious acute, persistent, and relapsing infections in humans. There is increasing evidence that bacterial excreted small molecules play a critical role during infection. We have shown that a quorum sensing (QS)-regulated excreted small molecule, 2-AA, which is abundantly produced by P. aeruginosa, promotes persistent infections, dampens host inflammation, and triggers mitochondrial dysfunction in skeletal muscle. QS is a cell-to-cell communication system utilized by bacteria to promote collective behaviors. The significance of our study in identifying a mechanism that leads to skeletal muscle dysfunction, via the action of a QS molecule, is that it may open new avenues in the control of muscle loss as a result of infection and sepsis. Given that QS is a common characteristic of prokaryotes, it is possible that 2-AA-like molecules promoting similar effects may exist in other pathogens.

Alterations of skeletal muscle bioenergetics in a mouse with F508del mutation leading to a cystic fibrosis-like condition

High energy expenditure is reported in cystic fibrosis (CF) animal models and patients. Alterations in skeletal muscle oxidative capacity, fuel utilization, and the creatine kinase-phosphocreatine system suggest mitochondrial dysfunction. Studies were performed on congenic C57BL/6J and F508del (Cftr^tm1kth) mice. Indirect calorimetry was used to measure gas exchange to evaluate aerobic capacity during treadmill exercise. The bioenergetic function of skeletal muscle subsarcolemmal (SSM) and interfibrillar mitochondria (IFM) was evaluated using an integrated approach combining measurement of the rate of oxidative phosphorylation by polarography and of electron transport chain activities by spectrophotometry. CF mice have reduced maximal aerobic capacity. In SSM of these mice, oxidative phosphorylation was impaired in the presence of complex I, II, III, and IV substrates except when glutamate was used as substrate. This impairment appeared to be caused by a defect in complex V activity, whereas the oxidative system of the electron transport chain was unchanged. In IFM, oxidative phosphorylation and electron transport chain activities were preserved, whereas complex V activity was reduced, in CF. Furthermore, creatine kinase activity was reduced in both SSM and IFM of CF skeletal muscle. The decreased complex V activity in SSM resulted in reduced oxidative phosphorylation, which could explain the reduced skeletal muscle response to exercise in CF mice. The decrease in mitochondrial creatine kinase activity also contributed to this poor exercise response.

Exercise as a therapeutic intervention for people with cystic fibrosis

INTRODUCTION

The complex multisystem nature of cystic fibrosis (CF) commonly results in reduced exercise tolerance, which is independently associated with poor clinical outcomes. Exercise is routinely recommended as part of the therapeutic regimen in CF to improve both respiratory and non-respiratory impairments. Areas covered: This article summarises the most recent evidence regarding the use of exercise as a therapeutic intervention in CF and discusses some of the practical considerations for exercise prescription in this setting. Clinical trials in progress and future research priorities are outlined. Expert opinion: On the balance of available evidence, exercise is likely to assist in improving physical fitness and health-related quality of life (HRQOL) and may be associated with a slower rate of decline in respiratory function in CF. Limitations to current studies include small sample sizes, study durations insufficient to achieve a training effect and difficulty distinguishing the effects of exercise training from that of other interventions implemented as part of a package of care. Larger, multi-centred trials are required to clarify the role of exercise in CF in improving physical fitness, respiratory function, HRQOL, as a substitute for traditional airway clearance techniques and in the management of common CF-related comorbidities.

Exercise capacity and muscle fatiguability alterations following a progressive maximal exercise of lower extremities in children with cystic fibrosis

Background

Impairment of peripheral skeletal muscle function is a common phenomenon in patients with cystic fibrosis (CF) in addition to great clinical connotations, such as lack of exercise tolerance and decrease of health-related quality of life. There is very limited data on the effects of maximal exercise on muscle fatiguability and exercise capacity in children with cystic fibrosis.

Objectives

The aim of this study was to evaluate the effect of progressive maximal exercise training of the lower extremities on exercise capacity and muscle fatiguability in children with cystic fibrosis.

Study design

Between June and September 2017, eighteen children aged 8–12 years were recruited in this study. This study had two groups of children; the CF group consisted of nine children (6 males and 3 females) with cystic fibrosis and the control group consisted of nine healthy age matched children (6 males and 3 females). The children underwent a progressive maximal cardiopulmonary exercise cycling test (CPET), muscle fatigue test, and magnetic resonance imaging (MRI) to measure a muscle cross-section area (CSA). Also, pulmonary functions were assessed.

Results

The findings of this study showed that the CF children had less pulmonary functions, had a less exercise capacity, and had a higher breathing reserve index and oxygen desaturation when compared with healthy children (p<0.05). On the other hand, there was a non-significant difference in muscle fatiguability, muscle cross-section area, and maximal voluntary contraction between the CF and healthy children (p>0.05).

Conclusion

This study indicates that progressive maximal exercise doesn't affect muscle fatiguability, muscle cross-section area, and maximal voluntary contraction in CF children with moderate respiratory diseases but includes lower exercise capacity. CF children and healthy age matched children have similar responses to maximal exercise in muscle fatiguability, muscle cross-section area, and maximal voluntary contractions but lower exercise capacity in the CF group.

Identification of an Anti-Inflammation Protein, Annexin A1, in Tendon Derived Stem Cells (TDSCs) of Cystic Fibrosis Mice: A Comparative Proteomic Analysis

PURPOSE

A previous study reported an elevated inflammation during tendon injury in mice with cystic fibrosis (CF), indicating the inadequate management of inflammation due to dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR). The objective of this study is to identify the targets of CFTR that contribute to the abnormal inflammation during tendon injury.

EXPERIMENTAL DESIGN

A 2D gel electrophoresis and mass-spectrometry-based comparative proteomics is performed to find the molecular targets of CFTR. And the targeted protein is further confirmed at both mRNA and protein levels.

RESULTS

It is identified that 14 proteins are differentially expressed, with annexin A1 being one of the most significantly downregulated protein. Further confirmation shows that annexin A1 is significantly decreased in TDSCs isolated from DF508 mice. As an essential anti-inflammation mediator, it is also downregulated in the injured tendon tissue of DF508 mice when compared with WT mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Decreased annexin A1 expression can contribute to the elevated inflammation in DF508 mice during tendon injury. Therefore, annexin A1 can be considered as a new potential biomarker or drug target for a possible therapeutic approach in clinical practice.

Respiratory Muscle Strength and Exercise Performance in Cystic Fibrosis-A Cross Sectional Study

Introduction: Decreased respiratory muscle strength in patients with cystic fibrosis (CF) may cause progressive exercise intolerance during cardiopulmonary exercise testing (CPET), and may contribute to the development of chronic respiratory insufficiency. The aim of this study is to evaluate exercise tolerance during CPET of children and adults with clinically stable CF who exhibit different respiratory muscle strength. Methods: Sixty-nine clinically stable CF subjects aged 8-33 years underwent spirometry, body plethysmography, CPET, and respiratory muscle strength measurement. Respiratory muscle strength was measured using maximal inspiratory pressures (Pi_max) and maximal expiratory pressures (Pe_max). Participants were stratified into three groups according to Pi_max values:below normal (≤80% predicted), normal (81-100% predicted), and above normal (>100% predicted). A similar stratification of participants was made according to Pe_max values. The oxygen consumption on peak load (VO_2peak) was expressed relative to BM (VO_2peak/kg), relative to BM raised by the exponent of 0.67 (VO_2peak/kg^0.67) and as log-linear adjustment of VO_2peak (VO_2peak/kg-alo). Results: Participants with low Pe_max values had a lower mean maximum load per kilogram/predicted (W_max; p = 0.001) VO_2peak/kg (p = 0.006), VO_2peak/kg^0.67 (p = 0.038) and VO_2peak/kg-alo (p = 0.001). There were no significant differences in exercise tolerance parameters with regard to Pi_max values. Stepwise multiple linear regressions confirmed that Pe_max (B = 24.88, β = 0.48, p < 0.001) was the most powerful predictor of W_max. There were no statistically significant differences in age, lung function parameters, exacerbation score, or respiratory muscle strength according to gender. Conclusions: In subjects with clinically stable CF, expiratory muscle strength is associated with a decrease in exercise performance during CPET and can predict exercise intolerance. Increase in expiratory muscle strength by patient specific rehabilitation protocols would result in improvement of exercise tolerance.

CFTR Genotype and Maximal Exercise Capacity in Cystic Fibrosis: A Cross-sectional Study

RATIONALE

Cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in human skeletal muscle cells. Variations of CFTR dysfunction among patients with cystic fibrosis may be an important determinant of maximal exercise capacity in cystic fibrosis. Previous studies on the relationship between CFTR genotype and maximal exercise capacity are scarce and contradictory.

OBJECTIVES

This study was designed to explore factors influencing maximal exercise capacity, expressed as peak oxygen uptake (V.O2peak), with a specific focus on CFTR genotype in children and adults with cystic fibrosis.

METHODS

In an international, multicenter, cross-sectional study, we collected data on CFTR genotype and cardiopulmonary exercise tests in patients with cystic fibrosis who were ages 8 years and older. CFTR mutations were classified into functional classes I–V.

RESULTS

The final analysis included 726 patients (45% females; age range, 8–61 yr; forced expiratory volume in 1 s, 16 to 123% predicted) from 17 cystic fibrosis centers in North America, Europe, Australia, and Asia, all of whom had both valid maximal cardiopulmonary exercise tests and complete CFTR genotype data. Overall, patients exhibited exercise intolerance (V.O2peak, 77.3 ± 19.1% predicted), but values were comparable among different CFTR classes. We did not detect an association between CFTR genotype functional classes I–III and either V.O2peak (percent predicted) (adjusted β = −0.95; 95% CI, −4.18 to 2.29; P = 0.57) or maximum work rate (Wattmax) (adjusted β = −1.38; 95% CI, −5.04 to 2.27; P = 0.46) compared with classes IV–V. Those with at least one copy of a F508del-CFTR mutation and one copy of a class V mutation had a significantly lower V.O2peak (β = −8.24%; 95% CI, −14.53 to −2.99; P = 0.003) and lower Wattmax (adjusted β = −7.59%; 95% CI, −14.21 to −0.95; P = 0.025) than those with two copies of a class II mutation. On the basis of linear regression analysis adjusted for relevant confounders, lung function and body mass index were associated with V.O2peak.

CONCLUSIONS

CFTR functional genotype class was not associated with maximal exercise capacity in patients with cystic fibrosis overall, but those with at least one copy of a F508del-CFTR mutation and a single class V mutation had lower maximal exercise capacity.

Pulmonary Pseudomonas aeruginosa infection induces autophagy and proteasome proteolytic pathways in skeletal muscles: effects of a pressurized whey protein-based diet in mice

Background: Pulmonary Pseudomonas aeruginosa infection in cystic fibrosis patients is associated with skeletal muscle atrophy. In this study, we investigated the effects of P. aeurginosa infection and a whey protein-rich diet on skeletal muscle proteolytic pathways.

Design: An agar bead model of pulmonary P. aeurginosa infection was established in adult C57/Bl6 mice. Protein ubiquitinaiton, lipidation of LC3B protein and expressions of autophagy-related genes and ubiquitin E3 ligases were quantified using immunoblotting and qPCR. The effects of pressure-treated whey protein diet on muscle proteolysis were also evaluated.

Results: Pulmonary P. aeurginosa infection reduced diaphragm, tibialis anterior, and soleus muscle weights and increased protein ubiquitination, LC3B protein lipidation, and the expressions of Lc3b, Gabarapl1, Bnip3, Parkin, Atrogin-1, and MuRF1 genes in each muscle. These changes were greater in the tibialis as compared to soleus and diaphragm. Proteolysis indicators increased within one day of infection but were not evident after seven days of infection. A pressurized whey diet attenuated LC3B protein lipidation, expressions of autophagy-related genes (BNIP3), pro-inflammatory cytokines, and protein ubiquitination.

Conclusions: We conclude that pulmonary P. aeruginosa infection activates the autophagy, and the proteasome pathways in skeletal muscles and that a pressurized whey protein diet attenuates muscle proteolysis in this model.

Cystic fibrosis transmembrane conductance regulator mediates tenogenic differentiation of tendon-derived stem cells and tendon repair: accelerating tendon injury healing by intervening in its downstream signaling

Tendons are a mechanosensitive tissue, which enables them to transmit to bone forces that are derived from muscle. Patients with tendon injuries, such as tendinopathy or tendon rupture, were often observed with matrix degeneration, and the healing of tendon injuries remains a challenge as a result of the limited understanding of tendon biology. Our study demonstrates that the stretch-mediated activation channel, cystic fibrosis transmembrane conductance regulator (CFTR), was up-regulated in tendon-derived stem cells (TDSCs) during tenogenic differentiation under mechanical stretching. Tendon tissues in CFTR-dysfunctional DF508 mice exhibited irregular cell arrangement, uneven fibril diameter distribution, weak mechanical properties, and less matrix formation in a tendon defect model. Moreover, both tendon tissues and TDSCs isolated from DF508 mice showed significantly decreased levels of tendon markers, such as scleraxis, tenomodulin, Col1A1 (collagen type I α 1 chain), and decorin Furthermore, by RNA sequencing analysis, we demonstrated that Wnt/β-catenin signaling was abnormally activated in TDSCs from DF508 mice, thereby further activating the pERK1/2 signaling pathway. Of most importance, we found that intervention in pERK1/2 signaling could promote tenogenic differentiation and tendon regeneration both in vitro and in vivo Taken together, our study demonstrates that CFTR plays an important role in tenogenic differentiation and tendon regeneration by inhibiting the β-catinin/pERK1/2 signaling pathway. The therapeutic strategy of intervening in the CFTR/β-catenin/pERK1/2 regulatory axis may be helpful for accelerating tendon injury healing, which has implications for tendon injury management.-Liu, Y., Xu, J., Xu, L., Wu, T., Sun, Y., Lee, Y.-W., Wang, B., Chan, H.-C., Jiang, X., Zhang, J., Li, G. Cystic fibrosis transmembrane conductance regulator mediates tenogenic differentiation of tendon-derived stem cells and tendon repair: accelerating tendon injury healing by intervening in its downstream signaling.