Microrna-155 protects against pulmonary fibrosis by targeting the transcription regulator LXR alpha

Kurowska-Stolarska, M. , Hasoo, M., Gilchrist, D. G., Ruzicska, E., Asquith, D., Welsh, D., Crawford, L., Hirani, N., McInnes, I. B. and McSharry, C. (2012) Microrna-155 protects against pulmonary fibrosis by targeting the transcription regulator LXR alpha. In: American College of Rheumatology & Association of Rheumatology Health Professionals, Annual Scientific Meeting, Washington DC, USA, 9-14 Nov 2012, S386. (doi:10.1002/art.37735)

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Abstract

Background/Purpose: MicroRNAs (miRs) are a novel class of posttranscriptional regulators. A single miR can have profound effects on cell activation due to its ability to modulate multiple pathways at once. We have previously shown that miR-155 is upregulated in rheumatoid arthritis (RA) synovial macrophages and promotes the development of autoimmunity and joint inflammation. Pre-clinical arthritis may be associated with lung changes e.g. bronchial wall thickening, thus the aim of this study was to investigate the contribution of miR-155 regulated pathways to lung homeostasis.

Methods: Normal human lung tissue was tested by in situ hybridisation with miR-155 and control probes. To model the fibrotic response, WT and miR-155 / mice were given bleomycin (0.06 unit/mouse) intranasally. Intervention included intraperitoneal injections of the Liver X Receptor (LXR) agonist (GW3965 daily; 40 mg/kg). End-points included bronchial lavage (BAL) cytology, lung tissue histology, evaluation of the expression of inflammatory and fibrotic genes by qPCR and concentrations of soluble mediators in serum and BAL fluid by multiplex assays. The validation of miR-155 binding to LXR, and the LXR response element in collagen gene promoters were performed with reporter assays.

Results: In situ hybridisation showed an abundant expression of miR-155 in the normal human lung suggesting that this miR may contribute to normal lung homeostasis. miR-155 / mice developed more severe bleomycininduced lung fibrosis compared to WT mice, as seen by increased collagen 1a/3a mRNA expression and protein deposition in the lungs, as well as accumulation of macrophages and lymphocytes in BAL. Gene expression analysis of lung extracts revealed an increase in the M2 pro-fibrotic macrophage markers Arginase 2, IL-13R and Ym1. In addition, the levels of pro-fibrotic cytokines such as VEGF and bFGF were significantly higher in BAL and serum of miR-155 / mice. Primary lung fibroblast lines derived from miR-155 / mice showed higher proliferation rates and motility compared to WT cells in wound healing assays. Computational analysis followed by functional luciferase assays revealed that the transcription activator LXR alpha is a direct target of miR-155 in the lungs. Expression of LXR alpha was significantly upregulated in the lungs of naive miR-155 / mice and was further increased in mice given bleomycin compared to similarly treated WT controls. Injection of the LXR agonist to WT mice increased LXR expression and mirrored the same phenotypic response to bleomycin as the miR-155 deficient mice; shown by increased collagen deposition and M2 macrophage and fibroblast activation. Promoter analysis revealed that LXRs could directly induce collagen production by binding to col1a and col3a promoters.

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Conclusion: miR-155 appears important for lung homeostasis, likely by fine tuning levels of LXR thereby protecting from excessive remodelling. Given this and the emerging contribution of miR-155 to development of autoimmunity, this miR may act as a master-switch determining the duration of inflammation and the initiation of remodelling, as well as the balance between the immune and auto-immune responses.

Item Type:Conference Proceedings
Additional Information:Supplement: Arthritis and Rheumatism, 64(10):S386
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:McInnes, Professor Iain and Asquith, Dr Darren and Gilchrist, Dr Derek and Ruzicska, Dr Eva and Kurowska-Stolarska, Dr Mariola and McSharry, Dr Charles
Authors: Kurowska-Stolarska, M., Hasoo, M., Gilchrist, D. G., Ruzicska, E., Asquith, D., Welsh, D., Crawford, L., Hirani, N., McInnes, I. B., and McSharry, C.
College/School:College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Journal Name:Arthritis and Rheumatism
Publisher:Wiley-Blackwell
ISSN:0004-3591
ISSN (Online):1529-0131

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