Sequential dynamics of monocyte chemotactic protein-1 expression in herniated nucleus pulposus resorption

We previously demonstrated that the granulation tissues of herniated nucleus pulposus are composed of a marked infiltration of macrophages that strongly express monocyte chemotactic protein-1. Monocyte chemotactic protein-1 is a chemotactic cytokine that contributes to the activation and recruitment of macrophages. Relatively little is known about its role in the resorption process of herniated nucleus pulposus. To clarify the sequential dynamics of expression of monocyte chemotactic protein-1 in the granulation tissues of herniated nucleus pulposus, we introduced a rat autologous transplantation model of nuclear materials onto its lumbar dura mater and performed immunohistological analysis and competitive polymerase chain reaction assay using the grafted samples. Immunohistological analysis demonstrated that the majority of infiltrating mononuclear cells expressed monocyte chemotactic protein-1. Monocyte chemotactic protein-1 mRNA was expressed in the first 3 weeks after the procedure and was significantly and maximally upregulated at 1 week. To determine whether human recombinant monocyte chemotactic protein-1 facilitates the resorption process of herniated nucleus pulposus, we introduced another model of autologous transplantation, wherein the nuclear materials were grafted to the abdominal subcutaneous tissues and recombinant monocyte chemotactic protein-1 was subsequently applied to these materials. When monocyte chemotactic protein-1 was injected into the murine nucleus pulposus tissues, they reduced in size more rapidly than in the control group. These findings suggest that monocyte chemotactic protein-1 plays an important role in the recruitment of macrophages in the early phase of the resorption process of herniated nucleus pulposus and that its application may physiologically facilitate the resorption process of the nucleus pulposus.