Alterations of the murine gut microbiome in allergic airway disease are independent of surfactant protein D

Lactobacillus rhamnosus probiotic prevents airway function deterioration and promotes gut microbiome resilience in a murine asthma model

Allergic asthma is a highly prevalent inflammatory disease of the lower airways, clinically characterized by airway hyperreactivity and deterioration of airway function. Immunomodulatory probiotic bacteria are increasingly being explored to prevent asthma development, alone or in combination with other treatments. In this study, wild-type and recombinant probiotic Lactobacillus rhamnosus GR-1 were tested as preventive treatment of experimental allergic asthma in mice. Recombinant L. rhamnosus GR-1 was designed to produce the major birch pollen allergen Bet v 1, to promote allergen-specific immunomodulation. Administration of wild-type and recombinant L. rhamnosus GR-1 prevented the development of airway hyperreactivity. Recombinant L. rhamnosus GR-1 also prevented elevation of airway total cell counts, lymphocyte counts and lung IL-1β levels, while wild-type L. rhamnosus GR-1 inhibited airway eosinophilia. Of note, a shift in gut microbiome composition was observed after asthma development, which correlated with the severity of airway inflammation and airway hyperreactivity. In the groups that received L. rhamnosus GR-1, this asthma-associated shift in gut microbiome composition was not observed, indicating microbiome-modulating effects of this probiotic. These data demonstrate that L. rhamnosus GR-1 can prevent airway function deterioration in allergic asthma. Bet v 1 expression by L. rhamnosus GR-1 further contributed to lower airway inflammation, although not solely through the expected reduction in T helper 2-associated responses, suggesting involvement of additional mechanisms. The beneficial effects of L. rhamnosus GR-1 correlate with increased gut microbiome resilience, which in turn is linked to protection of airway function, and thus further adds support to the existence of a gut-lung axis.

Perinatal maternal antibiotic exposure augments lung injury in offspring in experimental bronchopulmonary dysplasia

During the newborn period, intestinal commensal bacteria influence pulmonary mucosal immunology via the gut-lung axis. Epidemiological studies have linked perinatal antibiotic exposure in human newborns to an increased risk for bronchopulmonary dysplasia, but whether this effect is mediated by the gut-lung axis is unknown. To explore antibiotic disruption of the newborn gut-lung axis, we studied how perinatal maternal antibiotic exposure influenced lung injury in a hyperoxia-based mouse model of bronchopulmonary dysplasia. We report that disruption of intestinal commensal colonization during the perinatal period promotes a more severe bronchopulmonary dysplasia phenotype characterized by increased mortality and pulmonary fibrosis. Mechanistically, metagenomic shifts were associated with decreased IL-22 expression in bronchoalveolar lavage and were independent of hyperoxia-induced inflammasome activation. Collectively, these results demonstrate a previously unrecognized influence of the gut-lung axis during the development of neonatal lung injury, which could be leveraged to ameliorate the most severe and persistent pulmonary complication of preterm birth.

Colonic Epithelial Surfactant Protein D Expression Correlates with Inflammation in Clinical Colonic Inflammatory Bowel Disease

BACKGROUND

Inflammatory bowel diseases (IBD) are chronic disorders of the gastrointestinal tract. Surfactant protein D (SP-D) is expressed in the intestinal epithelium and is essential for innate host defense and regulation of inflammatory responses. Genetic variations of SP-D are associated with IBD, but the effects of SP-D in clinical disease development have not been clarified. We hypothesized that colonic epithelial SP-D expression is increased in parallel with intestinal inflammation with the capacity to dampen deleterious effects.

METHODS

Surgical specimens from IBD patients including Crohn's disease (n = 9) and ulcerative colitis (n = 18) were scored for expression of SP-D and inflammatory activity. Cohoused Sftpd+/+ and Sftpd-/- mouse littermates were subjected to dextran sodium sulfate (DSS) for 7 days to induce colitis. Colonic tissue was scored for histologic damage and analyzed for inflammatory markers and expression of SP-D.

RESULTS

Surgical specimens from IBD patients showed a strong positive correlation between immunoscore for SP-D and inflammatory activity (R2 = 0.78, P < 0.0001). In mice, colonic epithelial SP-D expression was very low, and DSS-induced colitis was unaffected by SP-D deficiency, although DSS induced transcription of colonic SP-D to a mild degree.

CONCLUSIONS

A strong positive correlation between inflammatory activity and epithelial expression of SP-D was observed in surgical specimens from IBD patients supporting a role for SP-D in clinical disease. The in vivo study was inconclusive due to very low intestinal SP-D expression in the mouse. Further studies are warranted to support that increased SP-D expression in the human colonic epithelium is protective against intestinal inflammation.

Surfactant Protein D in Respiratory and Non-Respiratory Diseases

Surfactant protein D (SP-D) is a multimeric collectin that is involved in innate immune defense and expressed in pulmonary, as well as non-pulmonary, epithelia. SP-D exerts antimicrobial effects and dampens inflammation through direct microbial interactions and modulation of host cell responses via a series of cellular receptors. However, low protein concentrations, genetic variation, biochemical modification, and proteolytic breakdown can induce decomposition of multimeric SP-D into low-molecular weight forms, which may induce pro-inflammatory SP-D signaling. Multimeric SP-D can decompose into trimeric SP-D, and this process, and total SP-D levels, are partly determined by variation within the SP-D gene, SFTPD. SP-D has been implicated in the development of respiratory diseases including respiratory distress syndrome, bronchopulmonary dysplasia, allergic asthma, and chronic obstructive pulmonary disease. Disease-induced breakdown or modifications of SP-D facilitate its systemic leakage from the lung, and circulatory SP-D is a promising biomarker for lung injury. Moreover, studies in preclinical animal models have demonstrated that local pulmonary treatment with recombinant SP-D is beneficial in these diseases. In recent years, SP-D has been shown to exert antimicrobial and anti-inflammatory effects in various non-pulmonary organs and to have effects on lipid metabolism and pro-inflammatory effects in vessel walls, which enhance the risk of atherosclerosis. A common SFTPD polymorphism is associated with atherosclerosis and diabetes, and SP-D has been associated with metabolic disorders because of its effects in the endothelium and adipocytes and its obesity-dampening properties. This review summarizes and discusses the reported genetic associations of SP-D with disease and the clinical utility of circulating SP-D for respiratory disease prognosis. Moreover, basic research on the mechanistic links between SP-D and respiratory, cardiovascular, and metabolic diseases is summarized. Perspectives on the development of SP-D therapy are addressed.