Daily Respiratory Research Analysis
Three studies reshape core respiratory science and cardiopulmonary medicine. A structural biology study defines radial spoke 3 (RS3) as a metabolic-regulatory hub sustaining ATP for ciliary beating, informing ciliopathy mechanisms. Multi-omic human-mouse work maps regional microbiome function that sculpts airway metabolites, while an invasive physiology study links dynamic hyperinflation to higher exercise PCWP in HFpEF, reframing heart–lung interactions.
Summary
Three studies reshape core respiratory science and cardiopulmonary medicine. A structural biology study defines radial spoke 3 (RS3) as a metabolic-regulatory hub sustaining ATP for ciliary beating, informing ciliopathy mechanisms. Multi-omic human-mouse work maps regional microbiome function that sculpts airway metabolites, while an invasive physiology study links dynamic hyperinflation to higher exercise PCWP in HFpEF, reframing heart–lung interactions.
Research Themes
- Ciliary bioenergetics and motility regulation
- Airway microbiome-metabolome topography and host response
- Ventilatory mechanics influencing cardiac filling pressures in HFpEF
Selected Articles
1. Mouse radial spoke 3 is a metabolic and regulatory hub in cilia.
Using cryo-EM/tomography integrated with proteomics, the authors solved the 3D structure and atomic model of RS3 from mouse respiratory cilia and identified embedded regulatory/metabolic enzymes (PKA subunit, adenylate kinases, malate dehydrogenases). RS3 was absent in AK7-deficient mice with motility defects, positioning RS3 as a metabolic-regulatory hub that sustains ATP for ciliary beating and informing ciliopathy mechanisms.
Impact: This is the first comprehensive structural and proteomic delineation of RS3, revealing direct coupling of signaling and metabolism within a ciliary complex and linking RS3 integrity to motility phenotypes in vivo.
Clinical Implications: By defining RS3 as a metabolic hub, this work provides mechanistic targets for primary ciliary dyskinesia and related ciliopathies; modulators of ciliary ATP homeostasis or RS3 components could be explored for therapy.
Key Findings
- Determined the 3D structure and atomic model of full-length RS3 from mouse respiratory cilia.
- Identified RS3 components including a PKA subunit, adenylate kinases, and malate dehydrogenases, indicating integrated regulatory and metabolic functions.
- Confirmed RS3 loss in AK7-deficient mice that exhibit ciliary motility defects, linking RS3 integrity to function in vivo.
Methodological Strengths
- Integrated single-particle cryo-EM, cryo-ET, proteomics, and computational modeling for convergent structural and functional insight.
- In vivo validation via AK7-deficient mouse model linking structural findings to motility phenotypes.
Limitations
- Findings are in mouse respiratory cilia; translational relevance to human cilia requires direct confirmation.
- Functional perturbation of individual RS3 enzymatic components was not systematically tested for causality.
Future Directions: Dissect the causal roles of embedded enzymes within RS3 in human ciliated tissues, and evaluate therapeutic modulation of RS3-mediated ATP homeostasis in ciliopathies.
Cilia are microtubule-based organelles that have important roles in cell sensing, signaling and motility. Recent studies have revealed the atomic structures of many multicomponent ciliary complexes, elucidating their mechanisms of action. However, little is known about the structure, proteome and function of full-length radial spoke 3 (RS3), a conserved complex that transmits mechanochemical signals to coordinate ciliary motility. Here, we combined single-particle cryo-electron microscopy, cryo-electron tomography, proteomic analysis and computational modeling to determine the three-dimensional structure and atomic model of RS3 from mouse respiratory cilia. We reveal all RS3 components, including regulatory and metabolic enzymes such as a protein kinase A subunit, adenylate kinases (AKs) and malate dehydrogenases. Furthermore, we confirm RS3 loss in AK7-deficient mice, which exhibit motility defects. Our findings identify RS3 as an important regulatory and metabolic hub that maintains sufficient adenosine triphosphate for sustained ciliary beating, providing insights into the etiology of ciliopathies.
2. Microbial contribution to metabolic niche formation varies across the respiratory tract.
Integrated human respiratory metagenome/metatranscriptome with metabolomics revealed spatially varying microbial function across the airways, correlating with immunomodulatory metabolites (for example, glutamate, methionine). Oral commensals (Prevotella, Streptococcus, Veillonella) were more active in the lower airways; mouse inoculation increased region-specific metabolites and isotope labeling confirmed Prevotella melaninogenica’s metabolic contributions.
Impact: Defines a functional, topographical microbiome–metabolome map of the respiratory tract with causal support from isotope probing, informing mechanisms of airway inflammation and potential metabolic targets.
Clinical Implications: Findings motivate metabolite- or microbe-targeted interventions (for example, modulating Prevotella-driven pathways) and stratified sampling across airway regions for diagnostics in inflammatory lung diseases.
Key Findings
- Functional activity of airway taxa varies topographically and correlates with immunomodulatory metabolites such as glutamate and methionine.
- Oral commensals (Prevotella, Streptococcus, Veillonella) are more functionally active in the lower airways in humans.
- Mouse inoculation with these commensals elevates regional metabolites; isotope labeling validates Prevotella melaninogenica’s contribution.
Methodological Strengths
- Multi-omic integration (metagenome, metatranscriptome, metabolome) across airway regions.
- Causal triangulation using mouse inoculation and stable isotope probing to validate metabolic contributions.
Limitations
- Clinical endpoints were not assessed; translational impact on symptoms or lung function remains to be determined.
- Generalizability may be limited by cohort composition and sampling topography.
Future Directions: Test targeted modulation of microbe–metabolite axes in human trials and evaluate region-specific diagnostics/therapeutics for airway inflammatory diseases.
Variations in the airway microbiome are associated with inflammatory responses in the lung and pulmonary disease outcomes. Regional changes in microbiome composition could have spatial effects on the metabolic environment, contributing to differences in the host response. Here, we profiled the respiratory microbiome (metagenome/metatranscriptome) and metabolome of a patient cohort, uncovering topographical differences in microbial function, which were further delineated using isotope probing in mice. In humans, the functional activity of taxa varied across the respiratory tract and correlated with immunomodulatory metabolites such as glutamic acid/glutamate and methionine. Common oral commensals, such as Prevotella, Streptococcus, and Veillonella, were more functionally active in the lower airways. Inoculating mice with these commensals led to regional increases in several metabolites, notably methionine and tyrosine. Isotope labeling validated the contribution of Prevotella melaninogenica in generating specific metabolites. This functional characterization of microbial communities reveals topographical changes in the lung metabolome and potential impacts on host responses.
3. Heart-Lung Interactions in HFpEF: Dynamic Hyperinflation and Exercise PCWP.
In 55 HFpEF patients undergoing invasive exercise hemodynamics, those with dynamic hyperinflation had higher PCWP at submaximal and peak exercise, and the magnitude of hyperinflation correlated with PCWP. Findings implicate dysfunctional ventilatory mechanics and increased intrathoracic pressure, beyond ventricular stiffness, in driving exercise filling pressures.
Impact: Reframes elevated exercise PCWP in HFpEF as partially mechanistically driven by ventilatory mechanics, highlighting a modifiable, non-cardiac target for symptom relief and hemodynamic improvement.
Clinical Implications: Interventions that reduce dynamic hyperinflation (for example, bronchodilation, pulmonary rehabilitation, breathing strategies, external PEEP) may lower exercise PCWP and improve exertional dyspnea in HFpEF and warrant testing.
Key Findings
- HFpEF patients with dynamic hyperinflation had higher PCWP at 20-W and peak exercise versus those without hyperinflation.
- The degree of hyperinflation was significantly associated with higher exercise PCWP.
- Suggests increased intrathoracic pressure from ventilatory mechanics contributes to elevated PCWP beyond ventricular stiffness.
Methodological Strengths
- Direct invasive hemodynamic measurements during exercise with simultaneous ventilatory assessments.
- Standardized definition of dynamic hyperinflation using repeated inspiratory capacity maneuvers.
Limitations
- Single-center, relatively small sample size limits generalizability.
- Cross-sectional exercise assessment; interventional causality not established.
Future Directions: Randomized studies testing bronchodilation, ventilatory support, or rehabilitation to reduce dynamic hyperinflation and PCWP, with symptom and outcome endpoints.
BACKGROUND: Patients with heart failure with preserved ejection fraction (HFpEF) are characterized by an exaggerated rise in pulmonary capillary wedge pressure (PCWP) with exercise compared with healthy similar-aged adults. Due to the multisystemic effects of the disease, patients with HFpEF often experience expiratory flow limitation (EFL), thereby perpetuating dynamic hyperinflation (DH) and ventilation at a higher percentage of total lung volume. How lung mechanics and operational lung volume affect central hemodynamics in patients with HFpEF is not fully understood. OBJECTIVES: The authors sought to characterize the association and correlation of DH and EFL on PCWP in adults with HFpEF during exercise. METHODS: A total of 55 patients with HFpEF (71 ± 7 years of age, 70% female) were studied at rest and during 20-W and peak exercise on an upright semirecumbent cycle ergometer. Right atrial and mean pulmonary artery (mPAP) pressures as well as PCWP (via right heart catheterization), oxygen uptake (indirect calorimetry), cardiac output (direct Fick), and ventilation (flow-volume parameters) were measured at each timepoint. DH was defined as an increase in end-expiratory lung volume of ≥150 mL from rest as determined by repeated inspiratory capacity maneuvers. RESULTS: PCWP was greater in those with DH at 20-W exercise (DH 24 ± 6 mm Hg vs typical 18 ± 6; P = 0.033) and peak exercise (DH 44 ± 9 vs typical 31 ± 6 mm Hg; P = 0.002). The degree of dynamic inflation was modestly, but significantly associated with a greater PCWP at 20-W (r CONCLUSIONS: Patients with HFpEF that dynamically hyperinflate during exercise have greater PCWP as measured with reference to atmospheric pressure. The severity of hyperinflation scaled proportionally to higher exercise PCWP. Our findings suggest that the augmented exercise PCWP in patients with HFpEF may not be entirely attributed to ventricular stiffness, but also a consequence of increased intrathoracic pressure from dysfunctional ventilatory mechanics. (Mechanisms of Exercise Intolerance in Heart Failure With Preserved Ejection Fraction; NCT04068844).