Retinoic acid signaling balances adult distal lung epithelial progenitor cell growth and differentiation

Abstract

BackgroundDespite compelling data describing pro-regenerative effects of all-trans retinoic acid (ATRA) in pre-clinical models of chronic obstructive pulmonary disease (COPD), clinical trials using retinoids for emphysema patients have failed. Crucial information about the specific role of RA signaling in adult rodent and human lung epithelial progenitor cells is largely missing.MethodsAdult lung organoid cultures were generated from isolated primary mouse and human lung epithelial cells, and incubated with pharmacological pathway modulators and recombinant proteins. Organoid number and size were measured, and differentiation was assessed with quantitative immunofluorescence and gene expression analyses.FindingsWe unexpectedly found that ATRA decreased lung organoid size, whereas RA pathway inhibition increased mouse and human lung organoid size. RA pathway inhibition stimulated mouse lung epithelial proliferation via YAP pathway activation and epithelial-mesenchymal FGF signaling, while concomitantly suppressing alveolar and airway differentiation. HDAC inhibition rescued differentiation in growth-augmented lung organoids.InterpretationIn contrast to prevailing notions, our study suggests that regenerative pharmacology using transient RA pathway inhibition followed by HDAC inhibition might hold promise to promote lung epithelial regeneration in diseased adult lung tissue.FundThis project is funded by the Lung Foundation Netherlands (Longfonds) grant 6.1.14.009 (RG, MK, JS, PSH) and W2/W3 Professorship Award by the Helmholtz Association, Berlin, Germany (MK).

Evolution of Bioengineered Lung Models: Recent Advances and Challenges in Tissue Mimicry for Studying the Role of Mechanical Forces in Cell Biology

“…Notwithstanding even more advanced technologies are already pursued such as more complex 3D organ‐specific cell structures representing functional organ units (organoids) and the integration of organ‐specific chips/organoids into in vitro organism systems. Although these methods are still in an early stage, they hold the promise to overcome remaining shortcomings of current advanced in vitro models of the lung such as failure of fully mimicking the complexity of the 3D alveolar structure, the multicell interplay in the lung (≈60 different cell types) and inter‐organ connectedness via blood circulation …”

Fatty acid-binding protein 5 limits ILC2-mediated allergic lung inflammation in a murine asthma model

“…It was considered that this down-regulation of ST2 was attributed to the decrease in the expression of PPARγ by FABP5deficiency or knockdown, since PPARγ is involved in ST2 regulation 41 . Retinoic acid, a metabolite of vitamin A, is known to be involved in maintaining homeostasis of epithelial and mucosal tissues and regulating immune responses [42][43][44] . Although it has been reported that vitamin A supplementation induces aggravation of asthma in a mouse experimental model, the fact that RA suppresses allergic lung diseases, such as asthma is now widely accepted.…”

“…Retinoic acid, a metabolite of vitamin A, is known to be involved in maintaining homeostasis of epithelial and mucosal tissues and regulating immune responses 42 – 44 . Although it has been reported that vitamin A supplementation induces aggravation of asthma in a mouse experimental model, the fact that RA suppresses allergic lung diseases, such as asthma is now widely accepted.…”

Organoids as a Powerful Model for Respiratory Diseases

“…An obvious benefit of ex vivo organoid culture is that a capillary network usually develops over the spheroid structures, which is not seen in in vitro assays. Human distal EpCAM + epithelial cells, including AT2 cells, can be isolated from peripheral lung tissue specimens by magnetic bead sorting (MACS) [44]. Coculture of these EpCAM + cells with MRC5 human lung fibroblasts in Matrigel resulted in the formation of organoids that allows airway differentiation but not alveolar differentiation [44].…”

“…Human distal EpCAM + epithelial cells, including AT2 cells, can be isolated from peripheral lung tissue specimens by magnetic bead sorting (MACS) [44]. Coculture of these EpCAM + cells with MRC5 human lung fibroblasts in Matrigel resulted in the formation of organoids that allows airway differentiation but not alveolar differentiation [44]. Alveolar differentiation was promoted by inhibiting TGF-β receptor signaling in organoids derived from human distal airway ΔNp63 + TTF-1 + stem cells [40].…”