Role of Macrophage Polarization and Apolipoprotein E in Granuloma Resolution

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

David R Ogburn (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Sarcoidosis is a chronic disease characterized by the development and accumulation of granulomas. Through multiwall carbon nanotube (MWCNT) instillation of C57 Bl/6 (wild-type) mice, we have established a murine model that induces granulomatous formations, histologically resembling the granulomas in human sarcoidosis. This model has proven to have a large number of commonly upregulated genes and pathways with human sarcoidosis. Matrix metalloproteinase-12 (MMP12), a protein elastase implicated in several chronic inflammatory diseases, was found to be the most upregulated gene expressed by alveolar macrophages of both human sarcoid patients and MWCNT-instilled wild-type mice. Previous studies have found that MMP12 levels are correlated to disease severity in human sarcoid patients. These findings led to the development of a MMP12 KO model of granulomatous formation via MWCNT-instillation. As in the wild-type model, granulomatous formations present at ten days post-instillation. Granulomas in wild-type MWCNT-instilled mice persist past 60D post-instillation, while granulomas in MMP12 KO mice are resolving at 60D. We observed a change in macrophage morphology between the MMP12 KO and wild-type bronchoalveolar lavage (BAL) cells. This led us to investigate the macrophage phenotypes M1 and M2. We stained for the presence of M2 macrophages via their unique surface protein mannose receptor 1 (CD206, MRC1). At 60D post-instillation, we found that CD206 was highly prevalent in the MMP12 KO strain and very low in the wild-type strain. In the MMP12 KO model we utilized dectin-1 and the receptor for advanced glycation end-products (RAGE) to stain for M2a and M2c macrophages, respectively. In sham-instilled MMP12 KO the predominant macrophage subtype is M2c, while in MWCNT-instilled MMP12 KO the predominant macrophage subtype is M2a. At 10D, both sham and MWCNT-instilled MMP12 KO had a high prevalence of M2c cells. The shift in the phenotype of the macrophage population from M2c to M2a and the subsequent release of IL-13 by M2a macrophages corresponds with the resolution of granulomas in the MMP12 KO model. Thus, M2a macrophages may be critical to granuloma resolution. The knock out of apolipoprotein E (ApoE) has been utilized to induce granulomatous formations in a murine model of sarcoidosis. Thus, we hypothesized that high levels of ApoE would be associated with granuloma resolution. At 10D in the MMP12 KO model, when granulomatous formations are present, ApoE intracellular protein levels were found to be low. However, ApoE gene and protein expression were increased at 60D in MWCNT-instilled MMP12 KO mice, compared to low levels in wild-type MWCNT-instilled mice. Thus, we observed that increased ApoE levels are associated with granuloma resolution. These observations suggest that ApoE may be playing a role in the resolution of granulomatous formations, potentially through enhanced phagocytosis of degraded collagen fragments.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

sarcoidosis;MMP12;APOE;granuloma formation;macrophage polarization

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