Secretoglobin 3A2 attenuates lipopolysaccharide-induced inflammation through inhibition of ERK and JNK pathways in bronchial epithelial cells.

Secretoglobin (SCGB) 3A2, previously known as uteroglobin-related protein 1, is a secreted protein highly expressed in the epithelial cells of the airways. It has been demonstrated that SCGB3A2 is involved in allergic airway inflammation such as bronchial asthma. However, the role of SCGB3A2 in lipopolysaccharide (LPS)-induced airway inflammation has yet to be reported. The goal of this study was therefore to clarify the role of SCGB3A2 in LPS-induced airway inflammation. We stimulated BEAS-2B, human bronchial epithelial cells, with LPS and analyzed messenger RNA (mRNA) expression of tumor necrosis factor (TNF)-α and CXCL8 with or without pre-incubation of SCGB3A2. The mRNA expression of TNF-α and CXCL8 was clearly upregulated 3 h after LPS stimulation, and pre-incubation of SCGB3A2 significantly inhibited the upregulation of the mRNA expression. The pre-incubation of SCGB3A2 also inhibited LPS-induced phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), but not p38 mitogen-activated protein kinase in BEAS-2B cells. Furthermore, PD98059, a specific inhibitor for ERK, as well as SP600125, a specific inhibitor for JNK, inhibited LPS-induced mRNA upregulation of inflammatory mediators. These results demonstrate the novel biological activity of SCGB3A2, which is that it attenuates LPS-induced inflammation in bronchial epithelial cells through inhibition of ERK and JNK activation.

Secretoglobin 1A1 and 1A1A differentially regulate neutrophil reactive oxygen species production, phagocytosis and extracellular trap formation.

Secretoglobin family 1A member 1 (SCGB 1A1) is a small protein mainly secreted by mucosal epithelial cells of the lungs and uterus. SCGB 1A1, also known as club (Clara) cell secretory protein, represents a major constituent of airway surface fluid. The protein has anti-inflammatory properties, and its concentration is reduced in equine recurrent airway obstruction (RAO) and human asthma. RAO is characterized by reversible airway obstruction, bronchoconstriction and neutrophilic inflammation. Direct effects of SCGB 1A1 on neutrophil functions are unknown. We have recently identified that the SCGB1A1 gene is triplicated in equids and gives rise to two distinct proteins. In this study we produced the endogenously expressed forms of SCGBs (SCGB 1A1 and 1A1A) as recombinant proteins, and analyzed their effects on reactive oxygen species production, phagocytosis, chemotaxis and neutrophil extracellular trap (NET) formation ex vivo. We further evaluated whether NETs are present in vivo in control and inflamed lungs. Our data show that SCGB 1A1A but not SCGB 1A1 increase neutrophil oxidative burst and phagocytosis; and that both proteins markedly reduce neutrophil chemotaxis. SCGB 1A1A reduced chemotaxis significantly more than SCGB 1A1. NET formation was significantly reduced in a time- and concentration-dependent manner by SCGB 1A1 and 1A1A. SCGB mRNA in bronchial biopsies, and protein concentration in bronchoalveolar lavage fluid, was lower in horses with RAO. NETs were present in bronchoalveolar lavage fluid from horses with exacerbated RAO, but not in fluid from horses with RAO in remission or in challenged healthy horses. These findings indicate that SCGB 1A1 and 1A1A have overlapping and diverging functions. Considering disparities in the relative abundance of SCGB 1A1 and 1A1A in airway secretions of animals with RAO suggests that these functional differences may contribute to the pathogenesis of RAO and other neutrophilic inflammatory lung diseases.