Tissue Inhibitor of Metalloproteinase-3 (TIMP-3) Regulates Hematopoiesis and Bone Formation In Vivo

Abstract

BackgroundTissue inhibitor of metalloproteinases-3 (TIMP-3) inhibits matrix metalloproteinases and membrane-bound sheddases. TIMP-3 is associated with the extracellular matrix and is expressed in highly remodeling tissues. TIMP-3 function in the hematopoietic system is unknown.Methodology/Principal FindingsWe now report that TIMP-3 is highly expressed in the endosteal region of the bone marrow (BM), particularly by osteoblasts, endothelial and multipotent mesenchymal stromal cells which are all important cellular components of hematopoietic stem cell (HSC) niches, whereas its expression is very low in mature leukocytes and hematopoietic stem and progenitor cells. A possible role of TIMP-3 as an important niche component was further suggested by its down-regulation during granulocyte colony-stimulating factor-induced mobilization. To further investigate TIMP-3 function, mouse HSC were retrovirally transduced with human TIMP-3 and transplanted into lethally irradiated recipients. TIMP-3 overexpression resulted in decreased frequency of B and T lymphocytes and increased frequency of myeloid cells in blood and BM, increased Lineage-negative Sca-1+KIT+ cell proliferation in vivo and in vitro and increased colony-forming cell trafficking to blood and spleen. Finally, over-expression of human TIMP-3 caused a late onset fatal osteosclerosis.Conclusions/SignificanceOur results suggest that TIMP-3 regulates HSC proliferation, differentiation and trafficking in vivo, as well as bone and bone turn-over, and that TIMP-3 is expressed by stromal cells forming HSC niches within the BM. Thus, TIMP-3 may be an important HSC niche component regulating both hematopoiesis and bone remodeling.

Tissue Inhibitor of Metalloproteinases–3 Moderates the Proinflammatory Status of Macrophages

“…In bone marrow, Timp3 is predominantly expressed by stromal cells, with much lower expression in hematopoietic stem cells (HSCs). However, TIMP-3 plays a role in regulating HSC proliferation and differentiation (36,37). TIMP-3, independent of its ability to inhibit metalloproteinases, promotes HSC proliferation, and the absence of TIMP-3 leads to impaired recovery from myelosuppression (37).…”

“…TIMP-3, independent of its ability to inhibit metalloproteinases, promotes HSC proliferation, and the absence of TIMP-3 leads to impaired recovery from myelosuppression (37). In addition, the overexpression of human TIMP-3 in mouse HSCs leads to increased myelopoiesis and subsequently increased CD11b 1 myeloid cells (36). Although we did not observe differences in the overall composition of white blood cell populations, our experiments provide support for these earlier findings, because we observed differences between unstimulated WT and Timp3 2/2 BMDMs at baseline (Figures 2 and 3).…”

Hematopoietic stem cell mobilizing agents G-CSF, cyclophosphamide or AMD3100 have distinct mechanisms of action on bone marrow HSC niches and bone formation

“…Cells and RNA from the central region of the BM and RNA from the endosteum were isolated from femurs as previously described. 27 For histomorphometric studies, tibias were fixed in ice cold PBS containing 4% paraformaldehyde, rotated overnight at 4 1C and transferred into 70% ethanol until embedding in methacrylate resin as described. 28 For immunohistology, tibias were fixed similarly for 24 h and then decalcified at 4 1C for 2 weeks with 14% EDTA before embedding in paraffin.…”

B-lymphopoiesis is stopped by mobilizing doses of G-CSF and is rescued by overexpression of the anti-apoptotic protein Bcl2

“…Cells and RNA from the central region of the BM, and RNA from the endosteum were isolated from femurs as previously described. 23 Inguinal and popliteal lymph nodes draining hind legs 24 were harvested and dissociated in PBS with 2% FCS similar to spleens.…”