CC16 Deficiency in the Context of Early-Life Mycoplasma pneumoniae Infection Results in Augmented Airway Responses in Adult Mice

Abstract

Studies have shown that club cell secretory protein (CC16) plays important protective roles in the lungs, yet its complete biological functions are unclear. We devised a translational mouse model in order to investigate the impact of early life infections, in the context of CC16 deficiency, on lung function in adult mice. CC16 sufficient (WT) and deficient (CC16 -/- ) mice were infected with Mycoplasma pneumoniae (Mp) as weanlings and assessed as adults ( e arly l ife i nfection m odel; ELIM) and compared to adult mice infected for only three days ( a dult i nfection m odel; AIM). CC16 -/- Mp-infected mice had significantly increased airway hyperresponsiveness (AHR) in both models compared to WT mice. However, CC16 -/- mice infected in early life (ELIM) displayed significantly increased AHR compared to CC16 -/- mice infected in adulthood (AIM). In stark contrast, lung function in ELIM WT mice returned to levels similar to saline-treated controls. While WT mice cleared Mp infection in the ELIM, CC16 -/- mice remained colonized with Mp throughout the model, which likely contributed to increased airway remodeling and persistence of Muc5ac expression. When CC16 -/- mouse tracheal epithelial cells (MTECs) were infected with Mp, increased Mp colonization and collagen gene expression were also detected compared to WT cells, suggesting that CC16 plays a protective role during Mp infection, in part through epithelial-driven host defense mechanisms.

The Impact of CC16 on Pulmonary Epithelial-Driven Host Responses during Mycoplasma pneumoniae Infection in Mouse Tracheal Epithelial Cells

“…The proteins with the greatest fold change or significance for "Extracellular Matrix Structural Constituent Conferring Compression Resistance" are Versican (CSPG2) and PGBM (Figure 6E). The abundance of enrichment terms associated with extracellular matrix components for the CC16 −/− MTECs during Mp infection may represent increased airway remodeling, which aligns with previous findings [20].…”

“…We have also shown that CC16 protects against pulmonary leukocyte infiltration and inflammation during Mp infection by binding to the integrin complex Very Late Antigen-4 (VLA-4) on leukocytes [21]. Additionally, we found that CC16 −/− MTECs have increased Mp burden when infected in vitro compared to WT MTECs (CC16 sufficient), indicating an epithelial-driven impairment in host defense during infections [20]. Based on these supporting data, and since Mp targets the pulmonary epithelium during infection, we seek to define how CC16 −/− MTECs respond when challenged with Mp.…”

“…Our group has shown that in WT mice, CC16 plays a protective role during early life Mp infections in mice by limiting inflammation and lung remodeling. Moreover, mice lacking CC16 during early life Mp infection have severely augmented airway hyperresponsiveness and collagen deposition, which results in decreased lung function in adulthood [20]. We have also shown that CC16 protects against pulmonary leukocyte infiltration and inflammation during Mp infection by binding to the integrin complex Very Late Antigen-4 (VLA-4) on leukocytes [21].…”

“…Next, we compared proteins secreted by both WT and CC16 −/− MTECs during Mp infection to better understand how CC16 impacts pulmonary epithelial-driven responses during Mp infection. Based on our previous experiments showing that CC16 −/− mice infected with Mp have increased airway remodeling, compared to infected WT mice [20,21], we sought to determine if during Mp infection, CC16-sufficient (WT) MTECs would be protected from epithelial-driven airway remodeling responses compared to CC16 −/− MTECs. Additionally, based on prior publications, we expected that WT MTECs would have an increased expression of antioxidants during Mp infection, which may assist in attenuating the Mp pathogen burden, as previously observed [20].…”

“…Based on our previous experiments showing that CC16 −/− mice infected with Mp have increased airway remodeling, compared to infected WT mice [20,21], we sought to determine if during Mp infection, CC16-sufficient (WT) MTECs would be protected from epithelial-driven airway remodeling responses compared to CC16 −/− MTECs. Additionally, based on prior publications, we expected that WT MTECs would have an increased expression of antioxidants during Mp infection, which may assist in attenuating the Mp pathogen burden, as previously observed [20]. Apically secreted proteins from Mp-infected WT and CC16 −/− MTECs were identified and characterized using mass spectrometry and quantitative proteomics, respectively.…”