Biology subjects

Knutsen, C.

Publications and source records attributed to Knutsen, C..

5 recordsLinked to original sources

bioRxiv2025

Postnatal Abrogation of VEGFR2 Blocks Terminal Cap2 Differentiation by Preventing the Developmental Progression from a Capillary Intermediate Cell State

After birth, the alveolar capillary network expands to increase gas exchange surface area and endothelial-derived signals promote alveolarization. Lung capillaries are comprised of two distinct subsets, one with proliferative potential to facilitate growth and repair (Cap1), and the other serving a specialized role in gas exchange (Cap2). However, the molecular mechanisms directing capillary speciation, developmental plasticity, and fate transitions during development and repair are not well understood. Here, we show that Cap2 are absent in late embryonic life but rapidly appear and expand immediately after birth. We show that Cap1 progenitors first transition to a novel, intermediate cell state (CapINT), characterized by co-expression of Cap1 and Cap2 markers, and heightened proliferation. CapINT are present in both the developing mouse and human lung. Hyperoxia, an experimental model of bronchopulmonary dysplasia (BPD), a chronic lung disease marked by impaired alveolarization, increases CapINT abundance and persistence and expands Cap2 EC. CapINT EC are also increased in human infants dying with active BPD. Using genetic lineage tracing, single cell transcriptomics, ATAC-sequencing and a mouse model that permits inducible deletion of VEGFR2 in CapINT and Cap2 EC, we show that postnatal abrogation of VEGFR2 markedly increases CapINT EC abundance, blocks Cap2 terminal differentiation, impairs alveolarization, and activates alveolar fibroblasts. Finally, we identify ERG as a putative VEGFR2-downstream mechanism that promotes CapINT to Cap2 differentiation. Taken together, our data show that Cap1-Cap2 differentiation is a two-step process that only requires VEGFR2 for the second step. Elucidation of the physiologic and molecular pathways that control the initial transition of Cap1 to CapINT EC has the potential to reveal new therapeutic targets for lung diseases that disrupt the alveolar capillary formation and integrity.

developmental biology↗

bioRxiv2025

Single Cell RNA Sequencing Reveals Gene Expression Continuums Along the Spatial Hierarchy of the Pulmonary Circulation

BackgroundThe lung vasculature is comprised of a series of branching vessels extending from the main pulmonary artery to the alveolar capillaries, then back to the pulmonary veins. Lung endothelial cells (EC) exist along this continuum, exposed to gradients of shear stress, oxygen tension and pressure. Single cell RNA sequencing (scRNA-seq) has identified lung EC subsets, but many aspects of the vascular continuum, including vessel size and capillary polarity remain undefined from transcriptomic data. MethodsWe created an endothelial-enriched scRNA-seq dataset from the P3 mouse lung. Using diffusion pseudotime across all lung EC, we developed an analytical framework to delineate transcriptomic gradients and assign vessel-size scores to categorize individual endothelial cells (EC) along the vascular continuum. We confirmed size-related gene expression patterns with fluorescence in situ hybridization. ResultsWe categorized capillary 1, arterial and venous EC along two gradients: arterio-venous zonation and vessel size. This approach distinguished large arteries from arterioles, large veins from venules, and revealed arterio-venous polarity within the capillaries. Our data recapitulated previously established zonally defined cell signaling axes, such as high Cxcl12-Cxcr4 signaling in arterioles. We also identified unique cellular communication occurring in large versus small arteries and veins, and localized injury-induced venous EC proliferation to vessels of specific size. This analytical framework was successfully applied to several published mouse and human datasets across different stages of lung development. ConclusionsThese findings provide a comprehensive transcriptional map of EC across the pulmonary vascular tree, enabling assignment of each individual cell to vessels with defined size and position. This framework offers spatial inferences and novel mechanistic insights from scRNA-seq data sets that may elucidate therapeutic targets to treat pulmonary vascular diseases affecting specific vascular segments. We speculate that similar frameworks could be applied to tissues outside the lung.

cell biology↗

bioRxiv2025

Yes-associated Protein Induces Age-dependent Inflammatory Signaling in the Pulmonary Endothelium

Acute Lung Injury (ALI) causes the highly lethal Acute Respiratory Distress Syndrome (ARDS) in children and adults, for which therapy is lacking. Children with Pediatric ARDS (PARDS) have a mortality rate that is about half of adults with ARDS. Improved ALI measures can be reproduced in rodent models with juvenile animals, suggesting that physiologic differences may underlie these outcomes. Here, we show that pneumonia-induced ALI caused inflammatory signaling in the endothelium of adult mice which depended on Yes-associated protein (YAP). This signaling was not present in 21-day-old weanling mice. Transcriptomic analysis of lung endothelial responses revealed nuclear factor kappa-B (NF-{kappa}B) as significantly increased with ALI in adult versus weanling mice. Blockade of YAP signaling protected against inflammatory response, hypoxemia, and NF-{kappa}B nuclear translocation in response to Pseudomonas aeruginosa pneumonia in adult mice. Our results demonstrate an important signaling cascade in the lung endothelium of adult mice that is not present in weanlings. We suggest other pathways may also exhibit age-dependent signaling, which would have important implications for ARDS therapeutics in the adult and pediatric age groups.

physiology↗

bioRxiv2021

Progressive Increases in Mesenchymal Cell Diversity Modulate Lung Development and are Attenuated by Hyperoxia

Lung mesenchymal cells play an essential role in development and at birth, as the lung moves from a fluid-filled to an oxygen-rich environment with a stable gas-liquid interface. The molecular details and cellular changes accompanying this highly coordinated process remain incompletely understood. Therefore, we performed single cell transcriptomics and in-situ imaging of the developing lung in both health and disease to characterize the spectrum of mesenchymal cell states prior to the onset of air-breathing life through late alveolarization to gain insight into their role in orchestrating tissue maturation. We found that cell type diversity in the mesenchymal compartment increases rapidly during normal development but is delayed during neonatal exposure to 80% O2 hyperoxia, a model for bronchopulmonary dysplasia. This study identifies the molecular transitions between populations of mesenchymal cells at discrete developmental time points across fibroblast, smooth muscle, and mural compartments and elucidates the global and cell type-specific effects of neonatal hyperoxia, including the emergence of Acta1+ cells which are absent in normoxic neonatal lungs. These granular insights hold the promise of targeted treatment for neonatal lung disease, which remains a major cause of infant morbidity and mortality across the world.

developmental biology↗

bioRxiv2021

Phenotypic diversity and sensitivity to injury of the pulmonary endothelium during a period of rapid postnatal growth

At birth, the lung is still immature, heightening susceptibility to injury but enhancing regenerative capacity. Angiogenesis drives postnatal lung development. Therefore, we profiled the transcriptional ontogeny and sensitivity to injury of pulmonary endothelial cells (EC) during early postnatal life. Although subtype speciation was evident at birth, immature lung EC exhibited transcriptomes distinct from mature counterparts, which progressed dynamically over time. Gradual, temporal changes in aerocyte capillary EC (CAP2), contrasted with more marked alterations in general capillary EC (CAP1) phenotype, including distinct CAP1 present only in the early alveolar lung expressing Peg3, a paternally imprinted transcription factor. Hyperoxia, an injury which impairs angiogenesis, induced both common and unique endothelial gene signatures, dysregulated capillary EC cross-talk, and suppressed CAP1 proliferation while stimulating venous EC proliferation. These data highlight the diversity, transcriptomic evolution, and pleiotropic responses to injury of immature lung EC, possessing broad implications for lung development and injury across the lifespan.

developmental biology↗