Influenza A virus activates Tropomyosin receptor kinase A (TrkA) signaling to promote viral replication and lung inflammation

Influenza A virus (IAV) infection causes acute respiratory disease with potential severe and deadly complications. Viral pathogenesis is not only due to the direct cytopathic effect of viral infections but also to the exacerbated host inflammatory responses. Influenza viral infection can activate various host signaling pathways that function to activate or inhibit viral replication. Our previous studies have shown that a receptor tyrosine kinase TrkA plays an important role in the replication of influenza viruses in vitro, but its biological roles and functional mechanisms in influenza viral infection have not been characterized. Here we show that IAV infection strongly activates TrkA in vitro and in vivo. Using a chemical-genetic approach to specifically control TrkA kinase activity through a small molecule compound 1NMPP1 in a TrkA knock-in (TrkA KI) mouse model, we show that 1NMPP1-mediated TrkA inhibition completely protected mice from a lethal IAV infection by significantly reducing viral loads and lung inflammation. Using primary lung cells isolated from the TrkA KI mice, we show that specific TrkA inhibition reduced viral RNA synthesis in airway epithelial cells (AECs) but not in alveolar macrophages (AMs). Transcriptomic analysis confirmed the cell-type-specific role of TrkA in viral RNA synthesis, and identified distinct gene expression patterns under the TrkA regulation in IAV-infected AECs and AMs. Among the TrkA-activated targets are various proinflammatory cytokines and chemokines such as IL6, IL-1?, IFNs, CCL-5, and CXCL9, supporting the role of TrkA in mediating lung inflammation. Indeed, TrkA inhibitor 1NMPP1 administered after the peak of IAV replication, though had no effect on viral load, was able to decrease lung inflammation and provide partial protection in mice. Taken together, our results have demonstrated for the first time an important biological role of TrkA signaling in IAV infection, identified its cell-type-specific contribution to viral replication, and revealed its functional mechanism in virus-induced lung inflammation. This study suggests TrkA as a novel host target for therapeutics against influenza viral disease. Overall design: To characterize the cell-type-specific role of the TrkA signaling in influenza A Virus (IAV) infection, we conducted transcriptomic analysis of virus-infected Alveolar epithelial cells (AECs) and alveolar macrophages (AMs) with or without the TrkA inhibition. Primary AECs and AMs seeded on 6-well plates were subjected to three treatments: mock infection, A/WSN infection (MOI=10), and A/WSN infection (MOI=10) in the presence of 1NMPP1 (10 µm), each in triplicates. Total RNAs at 10 hpi were stored in RNAlater and submitted to University of Minnesota Genomic Center (UMGC) for RNA extraction, mRNA enrichment, library construction, and RNA-sequencing.