Peroxisome Proliferator-Activated Receptor Gamma Deficiency Promotes a T Lymphocyte Response in a Murine Model of Chronic Pulmonary Sarcoidosis

Abstract

Sarcoidosis is a chronic granulomatous disease of unknown etiology. Previous studies from our lab have shown a deficiency of the nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPAR[gamma]) in the alveolar macrophages of sarcoidosis patients. We established a murine model of granuloma formation by instillation with multiwall carbon nanotubes (MWCNT), and the expression of PPAR[gamma] was also decreased in MWCNT instilled mice. There is evidence linking lymphocyte reactivity to mycobacterial antigens in sarcoidosis, so we hypothesized that addition of mycobacterial peptide early secretory antigenic target 6 (ESAT-6) to MWCNT might exacerbate the murine T effector cell response. MWCNT with or without ESAT-6 peptide 14 were instilled into macrophage-specific PPAR[gamma]-KO or wild-type mice. Controls received vehicle or ESAT-6 alone. Bronchoalveolar lavage (BAL) fluid was collected for analysis via qPCR, and lymph nodes were collected for histology, qPCR, in vitro studies, or flow cytometric analysis. PPAR[gamma]-KO mice receiving MWCNT+ESAT-6 displayed markedly increased granuloma formation and exhibited mediastinal lymphadenopathy. Additionally, PPAR[gamma]-KO mice treated with MWCNT+ESAT-6 exhibited exacerbated fibrotic severity at 20- and 60- days post-instillation. Similarly, lymphocyte frequency was elevated in the BAL of PPAR[gamma]-KO mice compared to controls at 20- and 60-days post-instillation with MWCNT+ESAT-6. Further, TH17 associated transcription factor ROR[gamma]t and immune regulatory marker PD1 were elevated in PPAR[gamma]-KO mice treated with MWCNT+ESAT-6 compared to sham mice at both time points, with elevation of multiple other TH17 associated genes at 60 days post instillation. Carbon nanotubes were observed in the mediastinal lymph nodes of PPAR[gamma]-KO and wild-type mice post-instillation with MWCNT and MWCNT+ESAT-6, and flow cytometric analyses revealed that CD4+ T cells were significantly elevated in PPAR[gamma]KO mice receiving MWCNT+ESAT-6. These findings suggest that instillation of PPAR[gamma]-KO mice with MWCNT+ESAT-6 elicits an exacerbated granulomatous and T lymphocyte mediated response.