Combined repetitive inhalant endotoxin and collagen-induced arthritis drives inflammatory lung disease and arthritis severity in a testosterone-dependent manner.

Respiratory-related diseases are a leading cause of death in rheumatoid arthritis (RA) and are disproportionately higher in men, which may be attributable to environmental risk factors. Animal studies have demonstrated potentiated autoimmunity, arthritis, and profibrotic/inflammatory lung disease with combination of airborne exposures and collagen-induced arthritis (CIA). This study aimed to determine whether hormone-dependent differences explained these observations. Arthritis prone male intact and castrated DBA/1J mice received intranasal inhalation of lipopolysaccharide (LPS) daily for 5 weeks and CIA induction. Arthritis scores and serum pentraxin-2 levels were increased in castrated vs. intact mice. In contrast, airway cell influx, lung tissue infiltrates, and lung levels of pro-inflammatory and pro-fibrotic markers (C5a, IL-33, and matrix metalloproteinases) were reduced in castrated vs. intact mice. CIA+LPS-induced lung histopathology changes and the expression of lung autoantigens including malondialdehyde acetaldehyde (MAA)- and citrulline (CIT)-modified proteins and vimentin were reduced in castrated animals. There were no differences for serum anti-MAA or anti-CIT protein antibody (ACPA) levels or serum pentraxin levels between groups. Testosterone replacement led to reversal of several lung inflammatory/profibrotic endpoints noted above in castrated male CIA+LPS-treated mice with testosterone supplementation promoting neutrophil influx, MAA expression, and TNF-⍺, IL-6, and MMP-9. These findings imply that testosterone contributes to lung and arthritis inflammatory responses following CIA+LPS co-exposure, but not to systemic autoantibody responses. The CIA+LPS model provides a paradigm for investigations focused on the mechanistic underpinnings for epidemiologic and phenotypic sex differences in RA-related lung disease.