Ninjurin1 Plays a Crucial Role in Pulmonary Fibrosis by Promoting Interaction between Macrophages and Alveolar Epithelial Cells

Abstract

The transmembrane nerve injury-induced protein 1 (Ninjurin1 or Ninj1) is involved in progressing inflammatory diseases. In this study, we aimed to investigate a novel function of Ninj1 in pulmonary fibrosis. We found that the expression of Ninj1 in a patient cohort was upregulated in the lung specimens of idiopathic pulmonary fibrosis patients as well as mice with bleomycin-induced pulmonary fibrosis. In addition, the BLM-injected Ninj1 KO mice exhibited a mild fibrotic phenotype, as compared to WT mice. Therefore, we hypothesized that Ninj1 would play an important role in the development of pulmonary fibrosis. We discovered that Ninj1 expression increased in BLM-treated macrophages and alveolar epithelial cells (AECs). Interestingly, macrophages bound to BLM-treated AECs were activated. However, when Ninj1 expression was suppressed in either of AECs or macrophages, contact-dependent activation of macrophages with AECs was diminished. In addition, introduction of recombinant mouse Ninj11–50 to macrophages triggered an inflammatory response, but did not stimulate Ninj1-deficient macrophages. In conclusion, we propose that Ninj1 may contribute to activation of macrophages by enhancing interaction with AECs having elevated Ninj1 expression due to injury-inducing stimuli. Consequently, Ninj1 may be involved in the development of pulmonary fibrosis by enhancing inflammatory response of macrophages.

Detrimental Role of Nerve Injury-Induced Protein 1 in Myeloid Cells under Intestinal Inflammatory Conditions

“…Macrophage infiltration is shown to be crucial for regulating the progression of lung fibrosis [6,7]. However, in the study of lung fibrosis and Ninj1, we demonstrated similar numbers of infiltrating macrophages in bronchoalveolar lavage fluids of bleomycin-treated WT and Ninj1 KO mice for lung fibrosis, indicating that macrophage infiltration does not determine the phenotypic difference between bleomycin-treated WT and Ninj1 KO mice [5].…”

“…Thus, it was surprising that during colitis development, Ninj1 did not alter the migration capacity of macrophages, which is seen only in lung fibrosis. Upon bleomycin treatment, Ninj1 KO mice ameliorated lung fibrosis; however, the number of infiltrating macrophages from both KO and WT mice were not different [5]. During development of colitis and lung fibrosis, the Ninj1 pathway controlled activation of the macrophages, resulting in the triggering an inflammatory response.…”

“…Ninj1 KO C57BL/6 mice were generated as previously described [5]. To generate myeloid-specific Ninj1-deficient mice, Ninj1 fl/fl mice were bred with heterozygous Lyz2-cre+/− mice.…”

“…Raw264.7 cells were cultured in DMEM supplemented with 10% FBS (Welgene, Daegu, Korea). Using CRISPR Cas9, Ninj1-deficient cells were generated as previously described [5]. In the current study, Ninj1-expressing cells are denoted as WT cells, while Cas9-treated Ninj1 KO cells are referred to as Ninj1 KO cells.…”

“…Ninj1 inhibition reduces susceptibility to systemic inflammation, liver damage, and pulmonary inflammation in septic mice [4]. In addition, we have previously reported that Ninj1-deficient mice display a mild lung pulmonary fibrosis phenotype associated with the interaction between macrophages and alveolar epithelial cells [5]. Macrophage infiltration is shown to be crucial for regulating the progression of lung fibrosis [6,7].…”