Temporal, spatial, and phenotypical changes of PDGFRα expressing fibroblasts during late lung development

Abstract

Many studies have investigated the source and role of epithelial progenitors during lung development; such information is limited for fibroblast populations and their complex role in the developing lung. In this study, we characterized the spatial location, mRNA expression and Immunophenotyping of PDGFRα+ fibroblasts during sacculation and alveolarization. Confocal microscopy identified spatial association of PDGFRα expressing fibroblasts with proximal epithelial cells of the branching bronchioles and the dilating acinar tubules at E16.5; with distal terminal saccules at E18.5; and with alveolar epithelial cells at PN7 and PN28. Immunohistochemistry for alpha smooth muscle actin revealed that PDGFRα+ fibroblasts contribute to proximal peribronchiolar smooth muscle at E16.5 and to transient distal alveolar myofibroblasts at PN7. Time series RNA-Seq analyses of PDGFRα+ fibroblasts identified differentially expressed genes that, based on gene expression similarity were clustered into 7 major gene expression profile patterns. The presence of myofibroblast and smooth muscle precursors at E16.5 and PN7 was reflected by a two-peak gene expression profile on these days and gene ontology enrichment in muscle contraction. Additional molecular and functional differences between peribronchiolar smooth muscle cells at E16.5 and transient intraseptal myofibroblasts at PN7 were suggested by a single peak in gene expression at PN7 with functional enrichment in cell projection and muscle cell differentiation. Immunophenotyping of subsets of PDGFRα+ fibroblasts by flow cytometry confirmed the predicted increase in proliferation at E16.5 and PN7, and identified subsets of CD29+ myofibroblasts and CD34+ lipofibroblasts. These data can be further mined to develop novel hypotheses and valuable understanding of the molecular and cellular basis of alveolarization.

PDGF-A signaling is required for secondary alveolar septation and controls epithelial proliferation in the developing lung

“…4J). During alveogenesis, there is normally an increase in Pdgfra + cells (Branchfield et al, 2016;Endale et al, 2017;Gouveia et al, 2017) in the alveolar region, reflecting a necessity for Pdgfra + cells during this stage of development. At P7, Pdgfa fl/− ; Spc-cre; Pdgfra GFP/+ lungs sustained a significant decrease in the expression of Pdgfra GFP -positive cells, compared with control lungs (Fig.…”

“…They play important roles in development, homeostasis and disease, and downstream signaling from the PDGFRs is known to regulate cell differentiation, proliferation, migration, actin reorganization and apoptosis (reviewed by Andrae et al, 2008). In mice, PDGFRα and PDGF-A are expressed in the lung from embryonic time points to adulthood (Branchfield et al, 2016;Endale et al, 2017;Gouveia et al, 2017;Ntokou et al, 2015). Pioneering studies of global Pdgfa knockout (Pdgfa −/− ) mice demonstrated a role for PDGF-A in lung development.…”

Oligomeric amyloid beta prevents myelination in a clusterin-dependent manner

“…Mature oligodendrocytes comprise one cluster, having potentially differentiated following initial tamoxifen labeling of PDGFRα expressing progenitor cells. Also captured in the sequencing were three cell-types outside the oligolineage that are known to either express PDGFRα or come from PDGFRα expressing precursors, including fibroblasts, endothelial cells, and 2 populations of pericytes [29][30][31][32] . These clusters were identified by expression of known cell type markers such as Igfbp6 and Fn1 (fibroblasts), Tek, Pecam1, and Kdr (endothelial cells), as well as Rgs5, Pdgfrb, and Des (pericytes) [33][34][35][36] .…”

Can We Understand the Pathobiology of Bronchopulmonary Dysplasia?

“…How the ECM deposition is dysregulated in BPD is also a matter of much interest, and this idea is currently being extensively explored in the context of (myo)fibroblast subpopulations in the developing lung, where (myo)fibroblasts may be marked by platelet-derived growth factor receptor (PDGFR)α, or perilipin-2, or combinations thereof. Lineage tracing and other studies have highlighted the likely role of (myo)fibroblast subpopulation in normal and aberrant lung development 155, 156 , and these studies await causal analysis, for example, by in vivo depletion studies. The dysregulation of signaling by the elastogenic growth factor, transforming growth factor (TGF)-β 157 ; and the ability of TGF-β to regulate aberrant alveolarization and ECM production in a BPD animal model 158 underscores a key regulatory role for TGF-β in ECM production and remodeling in the developing lung.…”