Bone marrow stromal cells stimulate neurite outgrowth over neural proteoglycans (CSPG), myelin associated glycoprotein and Nogo-A

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Abstract

In animal models, transplantation of bone marrow stromal cells (MSC) into the spinal cord following injury enhances axonal regeneration and promotes functional recovery. How these improvements come about is currently unclear. We have examined the interaction of MSC with neurons, using an established in vitro model of nerve growth, in the presence of substrate-bound extracellular molecules that are thought to inhibit axonal regeneration, i.e., neural proteoglycans (CSPG), myelin associated glycoprotein (MAG) and Nogo-A. Each of these molecules repelled neurite outgrowth from dorsal root ganglia (DRG) in a concentration-dependent manner. However, these nerve-inhibitory effects were much reduced in MSC/DRG co-cultures. Video microscopy demonstrated that MSC acted as “cellular bridges” and also “towed” neurites over the nerve-inhibitory substrates. Whereas conditioned medium from MSC cultures stimulated DRG neurite outgrowth over type I collagen, it did not promote outgrowth over CSPG, MAG or Nogo-A. These findings suggest that MSC transplantation may promote axonal regeneration both by stimulating nerve growth via secreted factors and also by reducing the nerve-inhibitory effects of the extracellular molecules present.

Section snippets

Materials and methods

Primary bone marrow stromal cell (MSC) culture. Following local research ethical committee approval and informed consent, bone marrow aspirates were harvested from the iliac crest of individuals with a complete long-term SCI (n = 8; 3+ months post injury, ages 23–66) or from non SCI-patients undergoing spinal fusion in the treatment of low back pain (n = 4; ages 32–54). Mononuclear cells isolated by density gradient centrifugation (Lymphoprep, Fresenius Kabi Norge, AS) were plated out in Dulbecco’s

MSC promote DRG neurite outgrowth and extension over CSPG

In the absence of MSC, DRG neurites were repelled by CSPG in a concentration-dependent manner, as has been reported previously [34], [35], [41]. Thus, at relatively high CSPG concentrations (10–100 μg/ml), DRG neurites either stopped elongating at the collagen: CSPG boundary or they turned and subsequently elongated along the boundary, whilst at lower concentrations (0.1–1 μg/ml), DRG neurites continued to extend and cross over the CSPG. In marked contrast, in MSC/DRG co-cultures DRG neurites

Discussion

Human MSC transplantation has been shown to promote axonal regeneration and functional recovery in animal models of CNS damage, particularly following injury to the spinal cord [9], [10], [12], [14], [15]. Few experiments, however, have addressed how MSC are involved in this process. To investigate potential mechanisms, we have examined how human MSC and neurons interact in the absence and presence of extracellular molecules that are considered to be potent inhibitors of axonal regeneration. We

Acknowledgments

We are grateful to all participants in this study. This study was funded in part by the Institute of Orthopaedics, Robert Jones and Agnes Hunt Orthopaedic Hospital, Oswestry, UK.

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