Alveolar macrophages strictly rely on GM-CSF from alveolar epithelial type 2 cells before and after birth

Abstract

Programs defining tissue-resident macrophage identity depend on local environmental cues. For alveolar macrophages (AMs), these signals are provided by immune and non-immune cells, and include GM-CSF (CSF2). However, evidence to functionally link components of this intercellular crosstalk remains scarce. We thus developed new transgenic mice to profile pulmonary GM-CSF expression, which we detected in both immune cells, including group 2 innate lymphoid cells and γδ T cells, as well as AT2s. AMs were unaffected by constitutive deletion of hematopoietic Csf2 and basophil depletion. Instead, AT2 lineage-specific constitutive and inducible Csf2 deletion revealed the non-redundant function of AT2-derived GM-CSF in instructing AM fate, establishing the postnatal AM compartment, and maintaining AMs in adult lungs. This AT2-AM relationship begins during embryogenesis, where nascent AT2s timely induce GM-CSF expression to support the proliferation and differentiation of fetal monocytes contemporaneously seeding the tissue, and persists into adulthood, when epithelial GM-CSF remains restricted to AT2s.

The transcription factor EGR2 is indispensable for tissue-specific imprinting of alveolar macrophages in health and tissue repair

“…However, despite having been reported to drive expression of EGR family members, including EGR2 (20) , in our hands, CSF-1 led to poor upregulation of EGR2 in maturing macrophages in vitro . Instead, we identified CSF-2 (GM-CSF) to be a potent inducer of EGR2 expression in maturing macrophages in vitro , a finding consistent with the almost unique dependence of alveolar macrophages on alveolar epithelial cell-derived CSF-2, and not CSF-1, for their development and survival (8–10) . However, TG-Fβ also induced EGR2 and we confirmed that TGF-β is indispensable for the development of alveolar macrophages (11) .…”

“…To determine if alterations in alveolar macrophage behaviour may contribute to this, we next tested the function of Egr2 -deficient alveolar macrophages. A major homeostatic function of alveolar macrophages is the regulation of pulmonary surfactant, and the absence of alveolar macrophages results in the development of pulmonary alveolar proteinosis (PAP) (8–10, 27, 28) . However, Egr2 deficiency did not lead to spontaneous PAP, as there were no differences in the levels of total protein in BAL fluid from Cre + and Cre − mice at either 4 or >9 months of age, a time at which PAP is detectable in Csf2rb −/− mice (28) ( Figure 4A ).…”

“…Alveolar macrophages are derived from erythromyeloid progenitors (EMPs) and foetal liver monocytes that seed the lung during embryonic development (6–8) . However, the characteristic phenotype and functional properties of alveolar macrophages do not develop until the first few days of postnatal life in parallel with alveolarisation of the lung and are controlled by CSF-2 (GM-CSF) (8–10) and the immunoregulatory cytokine TGF-β (11) . Together these cytokines induce expression of the transcription factor peroxisome proliferator-activated receptor gamma (PPAR-γ) to promote survival and tissue-specific specialisation, including upregulation of genes involved in lipid uptake and metabolism.…”

OTUB1 regulates lung development, adult lung tissue homeostasis, and respiratory control

“…E18.5 lungs were digested and the different cell types were profiled and analyzed for Ki67 staining using flow cytometry and three comprehensive marker panels for all major lung parenchymal and mesenchymal cell compartments as well as for cells of myeloid and lymphoid lineages. 38 In the CD45compartment, Ki67 positive cells were significantly increased in Otub1 −/− parenchymal epithelial cells (EpCAM + CD31 -) and endothelial cells (CD31 + EpCAM -) as well as in Otub1 −/− mesenchymal/ other non-hematopoietic cells (EpCAM -CD31 -) compared to corresponding Otub1 +/− and Wt cell populations (Figure 5). In the endothelial cell compartment, the percentage of Ki67-positive cells was already relatively high in Otub1 +/− and Wt lungs (average of 61.2% and 66.7% per parental population), but Otub1 KO still significantly increased the percentage of Ki67-positive endothelial cells (85.3% per parental population) by around 1.3-fold (Figure 5).…”

Pulmonary Eosinophils at the Center of the Allergic Space-Time Continuum

“…In the lower airways, alveolar macrophages (AMs) are the main immune cell type encountering airborne particles, the lungresident commensal microbiome and tasked with maintaining homeostasis (48). They actively patrol the alveoli in homeostasis and develop under the influence of epithelial-derived TGFb and GM-CSF (49)(50)(51). As such, it is not surprising that these cell types are found to behave distinctly different in the allergen- challenged lung (52).…”