Abstract
BackgroundEmphysematous COPD is characterized by aberrant alveolar repair. Macrophage migration inhibitory factor (MIF) contributes to alveolar repair, but for its structural and functional homolog D-dopachrome tautomerase (DDT) this is unknown. MIF mediates its effects through CD74 and/or C-X-C chemokine receptors 2 (CXCR2), 4(CXCR4), and possibly 7 (ACKR3). DDT can also signal through CD74, but interactions with other receptors have not been described yet. We therefore aimed at investigating if and how DDT contributes to epithelial repair in COPD.MethodsWe studied effects of recombinant DDT on cell proliferation and survival by clonogenic assay and annexin V-PI staining respectively. DDT-induced signaling was investigated by Western blot. Effects on epithelial growth and differentiation was studied using lung organoid cultures with primary murine or human epithelial cells and incubating with DDT or an ACKR3-blocking nanobody. DDT-ACKR3 interactions were identified by ELISA and co-immunoprecipitation.FindingsWe found that DDT promoted proliferation of and prevented staurosporine-induced apoptosis in A549 lung epithelial cells. Importantly, DDT also stimulated growth of primary alveolar epithelial cells as DDT treatment resulted in significantly more and larger murine and human alveolar organoids compared to untreated controls. The anti-apoptotic effect of DDT and DDT-induced organoid growth were inhibited in the presence of an ACKR3-blocking nanobody. Furthermore, ELISA assay and co-immunoprecipitation suggested DDT complexes with ACKR3. DDT could activate the PI3K-Akt pathway and this activation was enhanced in ACKR3-overexpressing cells.InterpretationIn conclusion, DDT contributes to alveolar epithelial repair via ACKR3 and may thus augment lung epithelial repair in COPD.
Highlights
Chronic obstructive pulmonary disease (COPD) is one of leading causes of death worldwide and is characterized in many patients by emphysematous lung tissue destruction with impaired or insufficient alveolar epithelial repair [1]
We found D-dopachrome tautomerase (DDT) mainly expressed by epithelial cells, in particular by ATII cells in both mice (Fig. 1a) and human (Fig. 1b) lung tissue
The newly generated Lung Cell Atlas showed DDT mRNA was expressed by many cells in human lung tissue and most abundantly in ATII cells and macrophages (Fig. 1c, picture generated from the atlas), which was consistent with our protein staining data
Summary
Chronic obstructive pulmonary disease (COPD) is one of leading causes of death worldwide and is characterized in many patients by emphysematous lung tissue destruction with impaired or insufficient alveolar epithelial repair [1]. MIF is a pleiotropic cytokine found to stimulate type II alveolar epithelial cell proliferation through one of its receptors CD74. Macrophage migration inhibitory factor (MIF) contributes to alveolar repair, but for its structural and functional homolog D-dopachrome tautomerase (DDT) this is unknown. MIF mediates its effects through CD74 and/or C-X-C chemokine receptors 2 (CXCR2), 4(CXCR4), and possibly 7 (ACKR3). Effects on epithelial growth and differentiation was studied using lung organoid cultures with primary murine or human epithelial cells and incubating with DDT or an ACKR3-blocking nanobody. DDT stimulated growth of primary alveolar epithelial cells as DDT treatment resulted in significantly more and larger murine and human alveolar organoids compared to untreated controls. Interpretation: In conclusion, DDT contributes to alveolar epithelial repair via ACKR3 and may augment lung epithelial repair in COPD.
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