Strategies targeting fusion machinery of bone marrow derived macrophage may ameliorate intestinal fibrosis after radiation

[[abstract]]Background: Bone marrow (BM) cells could repopulate damaged tissue and contribute to repair in non-hematopoietic tissues. Our previous observations demonstrated that the mitigating effect to intestine after acute radiation damage was achieved through paracrine mediators released by BM cells. Maximal appearance of BM cells, however, occurred long after intestine mucosa recovered from radiation damage. Recent studies revealed cell fusion between BM and somatic cells were enhanced by chronic inflammation. There was a significant role of BM cells in triggering fibrotic responses and contributing to liver and renal fibrosis.We would like to explore the association between cell fusion and intestine fibrosis after radiation. Material and Methods: Using gender-mismatched BMT and BMT from GFP mice donors, we quantified the fusion phenomenon within intestine of mice after irradiation. By using pravastatin, an HMG Co-A reductase inhibitor, to diminish intestine fibrosis after WBI, we evaluated the proliferation and fusion phenomenon as well as fusion signaling proteins (macrophage fusion receptor (MFR) and CD47) and fibrosis markers (CCN2, fibronectin, collagen). Using immunohistochemical study and isolated CD11b(+) BM cells for BMT, we evaluated the major BM derived cells contributing to the fusion phenomenon. Clodronate liposome was used to deplete macrophage/myelomonocytic cells in mice as BMT donors. Anti-cell fusion strategies including MMP9 inhibitor, Rac 1 inhibitor and MFR RNA silencing were used to suppress fibrotic protein expression of co-culture between intestine stromal and BM cells. Results: BM cells fused with intestine stromal cells after BMT to mice after WBI. The maximal fusion phenomenon occurred before significant level of fibrosis appeared within intestine of mice after WBI+BMT. Pravastatin suppressed intestine fibrosis and fusion phenomenon of mice. The cell fusion protein expression and the proliferation index within fused cells were also decreased by prvastatin. BM derived macrophage/myelomonocytic cells contributed majorly to the fusion phenomenon. Treatment with MMP9 inhibitor, Rac 1 inhibitor or MFRsiRNA during co-culture between BM and intestine stromal cells suppressed fibrosis protein expression. Intestine mucosa lysates from mice receiving clodronate liposome after WBI and BMT revealed decreased cell fusion and fibrosis in histology as well as in biochemical examination. Conclusions: Fusion between BM and intestine stromal cells is associated with chronic intestine fibrosis after radiation. The fusion phenomenon can be diminished by anti-fibrosis agent. Intestine fibrosis may be ameliorated by depleting macrophage/myelomonocytic cells as well as strategies against fusion machinery