The Anti-Fibrotic Drug Nintedanib Promotes Expansion of Lung Macrophages with a Distinct Transcriptional Repair Program in Bleomycin-Exposed Mice

Idiopathic pulmonary fibrosis (IPF) is a progressing chronic and fibrotic lung response with poor prognosis. The current standard-of-care for IPF is the kinase inhibitor nintedanib, which has a broad target range. The mechanism of nintedanib’s action remains unclear as it inhibits diverse kinases expressed in lung epithelia, endothelia and putatively the immune populations distributed throughout the lung. Given the proposed role of multiple pulmonary macrophage populations in mediating both protective and pathogenic roles in lung fibrosis, we sought to identify repair-associated macrophage populations in mice influenced by nintedanib after bleomycin challenge for 7 and 14 days using single cell RNA sequencing. Bleomycin exposure triggered expansion of inflammatory MHCIIhigh macrophage populations, which was partially reversed after nintedanib treatment. Concurrently, nintedanib promoted the expansion of MHCIIlow macrophages, which were linked to attenuation of lung fibrosis. Concomitantly, nintedanib promoted an increased expression of mRNA for canonical macrophage repair markers in MHCIIlow macrophages. Finally, exposure of inflammatory macrophages to nintedanib in vitro resulted in attenuation of expression of transcripts for MCHII. In conclusion, a component of nintedanib’s protective mode of action in lung fibrosis relies on expanding distinct MHCIIlow macrophage populations and redirecting them toward a reparative phenotype. This study provides a rationale for further refinement of therapeutic kinase inhibition in fibrotic diseases. 6 conditions were evaluated in mouse: Mouse + Bleomycin, sacrificed 7 and 14 days after exposure, mouse + Bleomycin + Nintedanib, sacrificed 7 and 14 days after exposure, and control mouse + NaCl, sacrificed 7 & 14 days after exposure. Nintedanid was given from day 0 to day 6 for mice sacrificed on day 7 and from day 7 to day 13 on mice sacrificed on day 14. Each treatment had three replicates for a total of 18 single celll RNA samples. Each replicate was composed of three mice pooled together.