SDF-1α/CXCR4: A Mechanism for Hepatic Oval Cell Activation and Bone Marrow Stem Cell Recruitment to the Injured Liver of Rats

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Abstract
Stromal derived factor-1 alpha (SDF-1α) and its receptor CXCR4 have been shown to play a role in the systematic movement of hematopoietic stem cells (HSC) in the fetal and adult stages of hematopoiesis. Under certain physiological conditions liver oval cells can participate in the regeneration of the liver. We have shown that a percentage of oval cells are of hematopoietic origin. Others have shown that bone marrow derived stem cells can participate in liver regeneration as well. In this study we examined the role of SDF-1α and its receptor CXCR4 as a possible mechanism for oval cell activation in oval cell aided liver regeneration. In massive liver injury models where oval cell repair is involved hepatocytes up-regulate the expression of SDF-1α, a potent chemoattractant for hematopoietic cells. However, when moderate liver injury occurs, proliferation of resident hepatocytes repairs the injury. Under these conditions SDF-1α expression is not up-regulated and oval cells are not activated in the liver. In addition, we show that oval cells express CXCR4, the only known receptor for SDF-1α. Lastly, in vitro chemotaxis assays demonstrated that oval cells migrate along a SDF-1α gradient which suggests that the SDF-1α/CXCR4 interaction is a mechanism by which the oval cell compartment could be activated and possibly recruit a second wave of bone marrow stem cells to the injured liver. In conclusion, these experiments begin to shed light on a possible mechanism, which may someday lead to a better understanding of the hepatic and hematopoietic interaction in oval cell aided liver regeneration.