Matrix metalloproteinase-19 is highly expressed in active multiple sclerosis lesions

Matrix metalloproteinases (MMPs) are proteases known for their capacity to degrade extracellular matrix (ECM) components. MMPs have been implicated in several central nervous system (CNS) diseases, including multiple sclerosis (MS). Microarray analysis has demonstrated significant increased mRNA levels of MMP-19 in chronic MS lesions, suggesting a role of MMP-19 in MS pathogenesis. Therefore, in this study, we investigated the expression pattern and cellular localization of MMP-19 protein in various well-characterized MS lesion stages. In normal control patient white matter, MMP-19 was constitutively expressed by microglia throughout the brain parenchyma, suggesting a physiological role for this MMP family member. Likewise, MMP-19 was expressed by microglia in (p)reactive MS lesions, albeit more intense. In highly active demyelinating MS lesions, parenchymal and perivascular myelin-laden macrophages were strongly immunoreactive for MMP-19, whereas reactive astrocytes were occasionally immunopositive. Astrocytes in chronic inactive lesions were weakly stained for MMP-19. In vitro, MMP-19 was expressed in cultures of primary human microglia, not in astrocyte cultures. As MMP-19 is able to degrade basement membrane constituents and other ECM proteins, it is conceivable that this relatively novel MMP family member contributes to MS pathology by remodelling the ECM of the CNS, thereby influencing leucocyte infiltration, axonal regeneration and astrogliosis.