Original Contributions
Perfusion Enhances Functions of Bone Marrow Stromal Cells in Three-Dimensional Culture

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Abstract

Perfusion of medium through three-dimensional (3D) collagen sponges enhanced viability and function of cocultivated marrow stromal and hematopoietic cell lines. Cells of the murine bone marrow stromal cell line GPIa were cultured in novel 3D collagen sponges, made from pepsin-digested bovine skin. Static cultures of sponges were maintained in dishes with media changes every other day. Perfused sponges were contained in a glass column with medium flow set at 1.3 mL/min. In some sponges, the 32D cl3 c-fmsm (CRX-1) hematopoietic progenitor cell line was added 7 days after GPIa cells. At 7 and 16 days, light microscopic evaluation showed poor viability of cells in static sponge cultures. In perfused sponge cultures, there was greater cellularity throughout the sponge and abundant accumulation of metachromatic extracellular matrix surrounding GPIa cells. Chondroitin 6-sulfate and heparan sulfate were identified as components of the matrix by immunohistochemical methods. DNA synthesis was evaluated by 15-h exposure of cultures to bromodeoxyuridine (BrdU), with subsequent immunohistochemical localization with monoclonal anti-BrdU antibody. Cells positive for BrdU were identified at the outer surfaces of both static and perfused sponges; however, positive cells were also seen throughout the internal areas of the sponges that were perfused. These results suggest that better nutrient exchange occurred in perfused sponges. In static cocultures of GPIa and CRX-1 cells, there was no detectable viability of the IL-3–dependent CRX-1 cells; however, under perfused conditions, CRX-1 cells flourished within the sponges as documented by BrdU incorporation. Thus, medium perfusion enhanced GPIa stromal cell line viability and function in 3D collagen sponge cultures, as demonstrated by BrdU incorporation, matrix production, and support of CRX-1 cells. This novel culture system may be useful for examining the interactions of bone marrow stromal cells with extracellular matrix molecules, soluble and matrix-bound factors, and with other cell types.

Introduction

The anatomic and physiological relationships between self-renewing stem cell populations and stromal cells have been described for hematopoietic tissues, but detailed mechanisms of these interactions are not completely understood. Stromal cells of the bone marrow have the potential for differentiation to adipocytes and osteoblasts 28, 31. In addition, bone marrow stromal cells play a critical role in the support of self-renewal and differentiation of the dependent population of hematopoietic stem cells. Bone marrow stromal cells support hematopoietic cells through mediating cytokines that stimulate growth and/or differentiation of hematopoietic cells to multiple lineages, and through cell surface mediators such as matrix proteins, glycosaminoglycans, fibronectin, and other adhesion molecules.

There is recent evidence that bone marrow stromal cells contribute to osteoclast differentiation of hematopoietic cells through several mechanisms [14]. We demonstrated that bone marrow stromal cells mediate the modulation of osteoclast differentiation of hematopoietic cells by PTH, IL-1β, and 1,25-dihydroxyvitamin D3 18, 27. Those studies documented the importance of cell contact with osteoclast progenitors for stromal cell-mediated osteoclast differentiation.

Two-dimensional (2D) culture systems do not allow one to fully exploit the interaction between the cellular components of osteoclast differentiation (stem cells and stromal cells) because such cultures do not reproduce several critical aspects of the three-dimensional (3D) structure of the bone marrow microenvironment, including high cell density and microanatomical relationships between the cell types and the mineralized bone matrix. For these reasons, 3D culture systems provide an attractive model with which to examine normal and abnormal cellular interactions in the marrow. However, three-dimensional culture systems pose significant and unique problems in experimental design. Diffusion of oxygen and nutrients and removal of waste products in 3D culture systems require special attention particularly if cells are to be maintained at high density and reside several millimeters from the tissue culture medium. We have developed a novel 3D culture perfusion system to allow regulation of several physiological parameters of bone marrow stromal cells cocultivated with hematopoietic stem cells in the matrix of a collagen sponge.

In this report, we describe the beneficial effects of continuous liquid perfusion of novel 3D collagen sponges containing the GPIa murine bone marrow stromal cell line. These effects include improved viability, accumulation of stromal cell-synthesized extracellular matrix, increased stromal and hematopoietic cell DNA synthesis, and ability of stromal cells to support viability of the IL-3–dependent hematopoietic cell line, 32D cl3 c-fmsm (CRX-1) in the absence of added IL-3.

Section snippets

Fabrication of Collagen Sponge

Collagen sponges were constructed as previously reported 19, 20. Briefly, a solution of 0.5% pepsin-digested collagen from bovine skin (Cellagen™, ICN Biomedical, Costa Mesa, CA) was neutralized with HEPES and NaHCO3. Two-hundred-fifty microliters of this collagen solution was poured into a mold and frozen at −20°C. After lyophilization, both sides of the collagen sponge were irradiated by UV light for 3 h at a distance of 30 cm.

Cell Seeding and Culture

A cell-seeding chamber was used for seeding and for the initial 2

Morphology of GPIa Murine Stromal Cell Line Grown in Perfused and Static 3D Sponge Cultures

Light microscopic evaluation revealed distribution of GPIa cells on the surfaces and throughout the sponges. Cells deposited onto the sponges migrated into the collagen network. In static sponge cultures, there was a layer of elongated cells that formed a sheath around the sponge; however, the majority of the cells within the sponge was not viable, showing pycnotic nuclei and evidence of autolysis (Fig. 1a). In contrast, in perfused sponge cultures, there were many healthy elongated GPIa cells

Discussion

Although important information about mechanisms of cellular regulation within the bone marrow has been obtained from monolayer or flask culture techniques, 3D model systems are needed for more detailed investigations of cell/cell and cell/microenvironment interactions. Standard 2D techniques also limit the opportunity for examining processes dependent upon high cell density. Recently, we developed a collagen sponge device that allows cellular migration, viability, and function in vitro and

Acknowledgements

This work was supported by NIH Grant DE08798.

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