MBD2 Deficiency Protects Mice Against Bleomycin-induced Pulmonary Fibrosis By Attenuating M2 Macrophage Production

Rationale: Idiopathic pulmonary fibrosis(IPF) is a serious and progressive chronic lung disease that is characterized by altered cellular composition and homoeostasis in the peripheral lung, leading to excessive accumulation of extracellular matrix(ECM) and, ultimately, loss of lung function. Although genetic determinants, environmental exposures have been identified as risk factors for this disorder, its etiology and pathogenesis still remain largely unknown. Epigenetics is defined as the study of heritable changes in gene function by factors other than an individual's DNA sequence. DNA methylation is an important epigenetic mechanism, which often occurs in response to environmental stimuli and is crucial in regulating gene expression. Alterations in DNA methylome are read by a conserved family of methyl?Cp G–binding domain(MBD) proteins, such as MBD2, which has the highest binding affinity to methylated DNA.Objectives: To identity the function and role of MBD2 in pulmonary fibrosis.Methods: While co-immunostaining was used to examine MBD2 levels in bronchoalveolar lavage fluid(BALF) from patients with IPF and healthy subjects, mice were treated with bleomycin(BLM) via intratracheal instillation to induce pulmonary fibrosis. WT and MBD2-/- mice were divided into four groups: WT + Saline, WT + BLM, MBD2-/- + Saline, MBD2-/- + BLM. Lung injury and pulmonary fibrosis of mice were assessed by H&E, Sirius red and Masson's trichrome staining. Western Blot and q PCR were performed to detect the expression of collagen I, fibronectin, TGF-?1, FIZZ1, CD206, Arg-1, SOCS1 and SOCS3. Additionally, peritoneal macrophages were generated from WT and MBD2-/- mice and then exposed to IL-4 or PBS for 24 hours. Levels of FIZZ1, CCL17, SOCS1 and SOCS3 are shown by q PCR analysis.Results: MBD2 was predominantly overexpressed by the infiltrated macrophages in patients with IPF and highly expressed in the mouse model of pulmonary fibrosis. Histological analysis displayed dramatically attenuated lung injury and pulmonary fibrosis in MBD2-/- mice. Compared with WT mice, collagen I, fibronectin, TGF-?1, FIZZ1, CD206 and Arg-1 were expressed at lower levels in MBD2-/- mice, whereas SOCS1 and SOCS3 were enhanced in lung homogenates. Reduced expression of FIZZ1 and CCL17 were detected in peritoneal macrophages of MBD2-/- mice, although SOCS1 and SOCS3 were increased, compared to WT mice. Moreover, there was no significant difference in controls.Conclusions: These results suggest that MBD2 may be involved in the pathogenesis of IPF through attenuated polarization of M2 macrophage, which mitigates BLM-induced pulmonary fibrosis in mice.