Attenuating endogenous Fgfr2b ligands during bleomycin-induced lung fibrosis does not compromise murine lung repair

Abstract

Fibroblast growth factors (Fgfs) mediate organ repair. Lung epithelial cell overexpression of Fgf10 postbleomycin injury is both protective and therapeutic, characterized by increased survival and attenuated fibrosis. Exogenous administration of FGF7 (palifermin) also showed prophylactic survival benefits in mice. The role of endogenous Fgfr2b ligands on bleomycin-induced lung fibrosis is still elusive. This study reports the expression of endogenous Fgfr2b ligands, receptors, and signaling targets in wild-type mice following bleomycin lung injury. In addition, the impact of attenuating endogenous Fgfr2b-ligands following bleomycin-induced fibrosis was tested by using a doxycycline (dox)-based inducible, soluble, dominant-negative form of the Fgfr2b receptor. Double-transgenic (DTG) Rosa26rtTA/+;tet(O)solFgfr2b mice were validated for the expression and activity of soluble Fgfr2b (failure to regenerate maxillary incisors, attenuated recombinant FGF7 signal in the lung). As previously reported, no defects in lung morphometry were detected in DTG (+dox) mice exposed from postnatal days (PN) 1 through PN105. Female single-transgenic (STG) and DTG mice were subjected to various levels of bleomycin injury (1.0, 2.0, and 3.0 U/kg). Fgfr2b ligands were attenuated either throughout injury ( days 0– 11; days 0– 28) or during later stages ( days 6– 28 and 14– 28). No significant changes in survival, weight, lung function, confluent areas of fibrosis, or hydroxyproline deposition were detected in DTG mice. These results indicate that endogenous Fgfr2b ligands do not significantly protect against bleomycin injury, nor do they expedite the resolution of bleomycin-induced lung injury in mice.

Fgf10 deficiency is causative for lethality in a mouse model of bronchopulmonary dysplasia

“…As no congenital mutation in the FGF10 gene in patients with BPD has been reported so far, it is likely that in BPD babies, the initial stages of lung development occur in the presence of normal levels of FGF10. To mimic this situation in a mouse model, we used a previously reported dominant negative soluble Fgfr2b expression approach [ Rosa26 rtTA/+ ;Tg(tet(O)sFgfr2b)/+ mice] to scavenge, in a ubiquitous and doxycycline‐inducible manner, all the Fgfr2b ligands, thereby turning off Fgfr2b signalling . Using this approach, we disrupted Fgfr2b signalling (mediated by Fgf1, −3, −7, and −10; see Figure A) in the postnatal lung during the saccular and the beginning of the alveolar stages, between P0 and P8 (Figure A–D).…”

“…Fgfr2b signalling [15][16][17][18][19]26]. Using this approach, we disrupted Fgfr2b signalling (mediated by Fgf1, −3, −7, and −10; see Figure 1A) in the postnatal lung during the saccular and the beginning of the alveolar stages, between P0 and P8 ( Figure 5A-D).…”

Pulmonary fibrosis requires cell-autonomous mesenchymal fibroblast growth factor (FGF) signaling

“…FGF9 and FGF18 are increased in IPF, stimulate fibroblast migration, and decrease fibroblast apoptosis (44,45). Inhibition of endogenous FGFR2b ligands (FGF7 and FGF10) does not alter bleomycin-induced pulmonary fibrosis (46), suggesting that these ligands are not essential for fibrosis. As the FGF ligand(s) critical for bleomycin-induced fibrosis remain unclear, further examination of the critical FGFRs are likely to provide insight to the ligands involved, as FGF-FGFR specificity is well described (22).…”

Therapeutic and pathological roles of fibroblast growth factors in pulmonary diseases

“…Moreover, alveolar epithelium‐specific deletion of tyrosine phosphatase Shp2 , a mediator of FGF‐mitogen‐activated protein kinase (MAPK) signaling, leads to spontaneous lung fibrosis (Zhang et al, ). Interestingly, our group has shown that attenuation of endogenous FGFR2b ligand activity does not compromise murine lung repair after bleomycin injury (MacKenzie et al, ). However, exogenous application of FGFR2b ligands clearly protects the lung from developing fibrosis.…”