REGULATION OF HEMATOPOIESIS.
Hematopoiesis in the adult vertebrate happens in the bone marrow space in the context of the marrow microenvironment (ME). The ME is defined by function as the cells and factors they secrete that regulate the hematopoietic stem cell (HSC) and its progeny that differentiate to different lineages. Our laboratory is interested in dissecting the role of interactions between the different cellular components of the ME ( in particular, macrophages and stromal cells) and how that may affect hematopoiesis. These studies are carried out in both in vitro (human) and in vivo (mouse) models.
1. Role of Monocyte/Macrophages in regulation of the microenvironment (ME).
Cloned stromal cell lines and peripheral blood monocytes (CD14 isolated) are used in human in-vitro work. A novel transgenic tetracycline inducible mouse utilizing a macrophage promoter (CD68 promoter) and a new generation reverse tetracycline activator (rtTA-M2) was generated and characterized, this will allow for the expression of various transgenes of interest at- will in a reversible fashion. This model will be extended to the study of macrophages in the hematopoietic ME as well as tumor associated macrophages (TAMs) in appropriate mouse models of cancer (lung, breast). By defining the nature of macrophage factors involved in diverse tissue MEs, it is hoped that the more effective therapeutic strategies can be devised in clinical scenarios where macrophage dysfunction is thought to contribute to the pathogenesis itself or its progression.
2. Regulation of stem-cell niche defining genes by microRNAs (miRNAs). We have identified novel microRNAs that regulate the expression of SDF1 (CXCL12) in niche-defining stromal cells. Currently we are pursuing the regulation of other niche-defining genes such as Jagged-1 and Angiopoietin-1 by microRNAs.
3. Role of macrophages in MSC (marrow stromal cells) mediated tissue repair. MSCs have been proposed as an exciting cellular therapy that may regenerate a variety of damaged tissues from heart to liver. Little is known about the underlying cellular and molecular mechanisms that may result in such regenerative properties. Since infused MSCs are not incorporated themselves into the damaged tissues, we hypothesized that intermediary cells are likely responsible for the effect. Using the murine model, we are exploring the role of monocytes and macrophages in regeneration of radiation-damaged hematopoietic cells after MSC infusion.
4. Role of dysregulated marrow microenvironment (ME) in the pathogenesis and progression of myelodysplastic syndrome (MDS). Although the stromal cells are genetically normal and do not belong to the malignant clone in MDS, our studies suggest that the ME is functionally dysregulated. Ongoing studies look at the role of clonally derived macrophages and their interactions with stromal cells in contributing to this dysregulation.
SELECTED PUBLICATIONS
Pillai MM, Yang X, Balakrishnan I, Bemis L and Torok-Storb B Mir-886-3p down regulates SDF1 (CXCL12) expression in marrow stromal cells. Manuscript submitted
Pillai MM and Torok-Storb B. “Inducible transgenes under the control of the hCD68 promoter identifies mouse macrophages distinct from the F4/80 and CSF-1R expressing populations”.
Exp Hematol. 2009 Dec;37(12):1387-92
Pillai MM, Kosak S, Venkataraman GK and Torok-Storb B “Integration site analysis in transgenic mice by TAIL (Thermal Asymmetric Amplification) PCR: Use for segregating multiple founder lines and determining zygosity.” Transgenic Research; 2008 Aug;17(4):749-54.
Iwata M, Pillai M, Ramakrishnan A, Hackman RC, Deeg HJ, Opdenakker GM,
Torok-Storb B. “Reduced expression of inducible gelatinase B/matrix metalloproteinase-9 in monocytes from patients with myelodysplastic syndrome: Correlation of inducible levels with the percentage of cytogenetically-marked cells and with marrow cellularity.” Blood. 2007 Jan 1;109(1):85-92
Pillai MM, Iwata M, Awaya N, Lynn Graf and Torok-Storb B. “Monocyte derived CXCL7 peptides in the marrow-microenvironment.” Blood, 1 May 2006, Vol. 107, No. 9, pp. 3520-3526.
Pillai M, Torok-Storb B, Iwata M.“Expression and Function of IL-7 Receptors in Marrow Stromal Cells. “ Leukemia & Lymphoma. 2004 Dec; 45(12): 2403-8
Funding
NIH/NIDDK K08 DK073701 03/2006 to 02/2011
Monocyte derived CXCL7 in the marrow microenvironment
NIH/NIDDK R03 DK082757 08/2009 to 07/2011
Role of macrophages in MSC-mediated recovery of hematopoiesis after irradiation