Expression of microRNA in Alveolar Macrophages Deficient in PPARy

Abstract

The nuclear transcription factor Peroxisome proliferator-activated receptor gamma (PPARgamma) is a negative regulator of macrophage activation and inflammatory mediators. Alveolar macrophages of healthy individuals constitutively express PPARgamma Decreased activity and expression of PPARgamma are observed in the alveolar macrophages from patients suffering from inflammatory conditions such as pulmonary alveolar proteinosis (PAP) and sarcoidosis. These finding suggest that PPAR<em>f</em>× activity may have an integral role in maintaining lung homeostasis. This study tested the hypothesis that microRNA expression would be dysregulated in murine alveolar macrophages deficient in PPARgamma. microRNA (miR) are small non-coding RNA molecules that post-transcriptionally regulate the expression of messenger RNA. Evaluation of microRNA in the murine model of PAP, the GM-CSF-KO mouse, demonstrates the elevation of miR-27a and miR-27b which target PPARgamma. The deficiency of PPARgamma and the lipid transporters ABCA1 and ABCG1 have been shown to contribute to the pathology of PAP. The microRNA miR-33-3p and miR-33-5p, which target these lipid transporters, were also elevated in GM-CSF-KO mice. Pulmonary granulomas comparable to those observed in pulmonary sarcoidosis are induced by instillation of multiwall carbon nanotubes (MWCNT) in C57Bl/6 mice. These animals have decreased PPARgamma activity and show elevated expression of miR-27a and miR-27b. It was also observed that the expression of the transporters ABCA1 and ABCG1 were decreased in MWCNT instilled mice. Expression of miR-33-3p and miR-33-5p was elevated in MWCNT instilled animals. The expression of microRNA that affects the activity of NF-£eB is also elevated in both murine models. We next investigated the use of PPARgamma agonist rosiglitazone on the expression of microRNA and messenger RNA. The use of rosiglitazone altered the expression of microRNA in both GM-CSF-KO and C57Bl/6+MWCNT mice. Rosiglitazone treatment altered the expression of the lipid transporter ABCA1and ABCG1 in C57Bl/6+MWCNT mice. The elevation of proinflammatory cytokines was also observed. Taken together, these observations support the hypothesis that PPARgamma activity effects the microRNA and gene expression in alveolar macrophages which is critical to overall lung homeostasis. Understanding the relationship between PPARgamma and microRNA in alveolar macrophage biology will provide insight into the regulation of the lung environment and possible therapeutic targets.