Elevated MicroRNA-33 in Sarcoidosis and a Carbon Nanotube Model of Chronic Granulomatous Disease

Abstract

We established a murine model of multiwall carbon nanotube (MWCNT)-induced chronic granulomatous disease, which resembles human sarcoidosis pathology. At 60 days after oropharyngeal MWCNT instillation, bronchoalveolar lavage (BAL) cells from wild-type mice exhibit an M1 phenotype with elevated proinflammatory cytokines and reduced peroxisome proliferator-activated receptor γ (PPARγ)-characteristics also present in human sarcoidosis. Based upon MWCNT-associated PPARγ deficiency, we hypothesized that the PPARγ target gene, ATP-binding cassette (ABC) G1, a lipid transporter with antiinflammatory properties, might also be repressed. Results after MWCNT instillation indicated significantly repressed ABCG1, but, surprisingly, lipid transporter ABCA1 was also repressed, suggesting a possible second pathway. Exploration of potential regulators revealed that microRNA (miR)-33, a lipid transporter regulator, was strikingly elevated (13.9 fold) in BAL cells from MWCNT-instilled mice but not sham control mice. Elevated miR-33 was also detected in murine granulomatous lung tissue. In vitro studies confirmed that lentivirus-miR-33 overexpression repressed both ABCA1 and ABCG1 (but not PPARγ) in cultured murine alveolar macrophages. BAL cells of patients with sarcoidosis also displayed elevated miR-33 together with reduced ABCA1 and ABCG1 messenger RNA and protein compared with healthy control subjects. Moreover, miR-33 was elevated within sarcoidosis granulomatous tissue. The findings suggest that alveolar macrophage miR-33 is up-regulated by proinflammatory cytokines and may perpetuate chronic inflammatory granulomatous disease by repressing antiinflammatory functions of ABCA1 and ABCG1 lipid transporters. The results also suggest two possible pathways for transporter dysregulation in granulomatous disease-one associated with intrinsic PPARγ status and the other with miR-33 up-regulation triggered by environmental challenges, such as MWCNT.

PPAR-gamma pathways attenuate pulmonary granuloma formation in a carbon nanotube induced murine model of sarcoidosis

“…Our previous studies have shown deficiency of PPARγ, ABCA1 and ABCG1 in alveolar macrophages from both sarcoidosis patients and the 60 day MWCNT model [13,19,30]. The inflammatory mediators, chemokine (C-C motif) ligand-2 (CCL2) and osteopontin, were elevated in sarcoidosis granulomatous tissue and in the 60 day MWCNT model [13,34–36].…”

“…Our recent studies in alveolar macrophages from sarcoidosis patients and MWCNT-instilled mice observed decreased expression of both ABCG1 and ABCA1 [30]. The deficiency of these lipid transporters correlates with increased alveolar macrophage lipid accumulation in MWCNT-instilled animals [30]. These observations suggest that downregulation of ABCG1 and ABCA1 may contribute to MWCNT-induced inflammation.…”

“…The inability to properly efflux cholesterol leads to increased sensitivity to extracellular inflammatory signaling in ABCA1/ABCG1 deficient macrophages [29]. Our recent studies in alveolar macrophages from sarcoidosis patients and MWCNT-instilled mice observed decreased expression of both ABCG1 and ABCA1 [30]. The deficiency of these lipid transporters correlates with increased alveolar macrophage lipid accumulation in MWCNT-instilled animals [30].…”

Thrombospondin‐1 and microRNA‐1 expression in response to multiwalled carbon nanotubes in alveolar epithelial cells

“…In nematode Caenorhabditis elegans (C. elegans), MWCNT differentially regulated 55 miRNAs, of which 5 miRNAs had a protective role and 7 miRNAs played a role in MWCNT toxicity . In bronchoalveolar lavage cells and lung granulomas, MWCNT increased miRNA‐33 expression …”

“…26 In bronchoalveolar lavage cells and lung granulomas, MWCNT increased miRNA-33 expression. 27 Our previous study showed that MWCNT activate alveolar epithelial A549 cells to express fibrosis markers TGFb and Col 3A1. MWCNT induced TGFb by 2.62-, and Co3A1 by 2.34-fold change versus control.…”