Plasmin-matrix metalloproteinase cascades in spinal response to an experimental disc lesion in pig

Abstract

Study design: Proteinases were immunohistochemically stained to analyze degenerated discs and paradiscal tissues in comparison to contiguous control tissues in an experimental porcine model of intervertebral disc degeneration.

Objective: The aim was to analyze plasmin and metalloproteinases known to participate in mutual activation cascades.

Summary of background data: Comparison of the degenerated discs and paradiscal structures with control tissues disclosed accumulation of plasmin and induction of matrix metalloproteinases (MMP), MMP-1 and MMP-2 in the discs, but some other MMPs in reactive and remodeling tissues.

Material and methods: In 6 domestic pigs, the cranial L4 endplate was perforated to penetrate the nucleus pulposus. Three months later, the animals were killed and the experimental and the contiguous control vertebrae, complete with their intervertebral discs, were excised and subjected to histologic and immunohistochemical examinations.

Results: Immunohistochemical analysis disclosed increased expression of MMP-1 and MMP-2 in the traumatized and degenerated intervertebral discs. Some MMPs were also induced in all paradiscal structures (bone marrow, vertebral bone, and spinal ligaments), or decreased in already scarred areas. The common denominator for all the anatomic sites studied was accumulation of plasmin.

Conclusion: Fibroblast collagenase (MMP-1) and gelatinase A (MMP-2), capable of degrading native and denatured collagen, were induced in degenerating intervertebral discs. Use of an experimental model enabled demonstration that biomechanical destabilization and degeneration of the disc also affects all other paradiscal structures, which are subjected to proteolysis and/or reparative fibrosis apparently representing remodeling of the spine subjected to pathologic stress. Profiling of various MMPs and plasmin, known to participate in mutual activation cascades, suggests that plasmin could activate pro-MMP-1, pro-MMP-2, pro-MMP-3, pro-MMP-7, pro-MMP-9, and pro-MMP-13 and alone or/and in cooperation with MMP-3 initiate at least 2 mutual MMPs activation cascades driven by activated MMP-3 and MMP-7.