The Studies of Cxcl12 on Mycobacterium Tuberculosis-Induced Fibrocyte Activation and Pulmonary Fibrosis

Pulmonary fibrosis is one of pathological characterized by Mycobacterium tuberculosis (M.tb) infection in the lungs, which in turns causes irreversible loss of pulmonary function and pulmonary failure. Fibrocyte is a bone marrow-derived progenitor cells which exist in circulating system. Recent study demonstrated that fibrocyte plays an important role in tissue repair and inflammation. Fibrocyte activation, proliferation and differentiation are considered to be a key factor of pulmonary fibrosis. Our previous studies indicated that transforming growth factor-P and endothelin-1 mediated circulating fibrocyte differentiation to myofibroblasts through connective tissue growth factor (CTGF) expression in chronic obstructive asthma (COA). C-X-C motif chemokine 12 (CXCL12) is a chemokine which is released by bone marrow stroma cells. Recent study showed that CXCL12 regulated bone marrow-derived cell migration, proliferation and tissue repair. CXCL12 had been reported to correlate with disease process of IPF. Inhibition of CXCR4 (CXCL12 receptor) decreased bleomycin-induced mice lung fibrosis. CXCL12 regulated astrocyte and myeloid progenitor cell proliferation. Our recent studies found that CXCL12 induced CTGF expression through Rac 1/ERK/JNK/AP-1 pathway, which in turns initiated a-smooth muscle actin (a-SMA) expression, then promoted fibroblast differentiation in human lung fibroblasts. However, whether CXCL12 is involved in fibrocyte proliferation and differentiation to myofibroblasts in Tuberculosis (TB), and the signal pathways of M.tb-induced CXCL12 expression in fibrocytes are still unknown. Our preliminary data found that CXCL12 antagonist (AMD3100) inhibited fibrocyte proliferation and differentiation to myofibroblasts in TB patients. The serum level of CXCL12 in TB patients was higher than in normal subjects. In addition, AMD3100 inhibited M.tb-induced human fibrocyte proliferation and differentiation. CXCL12 also induced fibrocyte proliferation and differentiation. Furthermore, we found that M.tb-induced CXCL12 expression was inhibited by HIF-1a inhibitor and transfection of C/EBPP siRNA in human fibrocytes. Therefore, the Central Hypothesis is that CXCL12 mediated fibrocyte proliferation and differentiation to myofibroblasts, which in turn caused pulmonary fibrosis in Tuberculosis. The overall objective of this project is to elucidate the role of CXCL12 in pulmonary fibrosis in patients with Tuberculosis so that effective interventions can be developed to prevent pulmonary fibrosis in Tuberculosis. The hypotheses and specific aims are described below: Specific Aim 1 (1st year): To study the role of CXCL12 in mediating fibrocyte proliferation and differentiation in patients with Tuberculosis. Hypothesis 1: CXCL12 mediated CTGF expression, proliferation and differentiation in circulating fibrocytes from patients with Tuberculosis. Specific Aim 2 (2nd year): To investigate the role of HIF-1a and C/EBPp in M.tb-induced CXCL12 release in human fibrocytes. Hypothesis 2: HIF-1a and C/EBPP are requiredfor M.tb-induced CXCL12 release in human fibroc^ytes. Specific Aim 3 (3rd year): To examine the role of CXCL12 in M.tb-induced fibrocyte activation and pulmonary fibrosis in CXCL12-conditional knockout mice Hypothesis 3: CXCL12 mediated fibrocyte proliferation and differentiation in M.tb-induced pulmonary fibrosis animal model