To determine the involvement of
cathepsins G and L in the mechanism of spontaneous resorption of herniated intervertebral discs, localization of these
cathepsins in this process was examined immunohistochemically using a rat model of
autologous transplantation of coccygeal discs. Rat coccygeal discs were resected and autotransplanted into the subcutaneous space of the skin of the back.
Paraffin-embedded sections of intervertebral disc tissue, harvested at various post-transplantational periods, were immunohistochemically stained with
antibodies for
cathepsin G,
cathepsin L, MMP-1, MMP-3 and ED-2. The number of positive cells was counted in each part of the transplanted discs. Immunolocalization of
cathepsins G and L in various types of disc cells was first observed early in the post-
transplantation period. From two days after the operation, histology showed invasion by granulation tissue, with many macrophages, in all sections. Subsequently, the number of macrophages in granulation tissue was observed to increase, along with a gradual increase in the percentage of cells positive for MMP-1 and MMP-3. In addition to the ability of
cathepsins G and L to degrade major extracellular matrix components of intervertebral discs,
cathepsin G is capable of activating latent pro-
MMPs. The up-regulation of
cathepsins G and L in the intervertebral disc tissue in this spontaneous resorption model suggests that these
proteinases may be involved in degradation of extracellular matrix, leading to the natural resorption of
herniated discs.