Gelatinase B/matrix metalloproteinase-9 is a phase-specific effector molecule, independent from Fas, in experimental autoimmune encephalomyelitis

Abstract

Gelatinase B/matrix metalloproteinase-9 (MMP-9) triggers multiple sclerosis (MS) and the animal model of experimental autoimmune encephalomyelitis (EAE) by the breakdown of the blood-brain barrier. Interestingly, MMP-9 is beneficial in systemic autoimmunity caused by Fas-deficiency. Fas-deficient (faslpr) and Fas-ligand-deficient mice are protected against EAE. We here investigated the interaction between Fas and MMP-9 in the setting of induction of EAE and compared short- and long-term effects. We provoked EAE with myelin oligodendrocyte glycoprotein (MOG) peptide and compared EAE development in four genotypes (wild-type (WT), single knockout mmp-9-/-, faslpr, and mmp-9-/-/faslpr) and monitored leukocytes, cytokines and chemokines as immunological parameters. As expected, faslpr mice were resistant against EAE induction, whereas MMP-9 single knockout mice were not. In the double mmp-9-/-/ faslpr mice the effects on disease scores pointed to independent rather than interrelated disease mechanisms. On a short term, after EAE induction leukocytes infiltrated into the brain and cytokine and chemokine levels were significantly higher in all the four genotypes studied, even in the faslpr and mmp-9-/-/faslpr, which did not develop clinical disease. The levels of MMP-9 but not of MMP-2 were increased in the brain and in the peripheral organs after EAE induction. After 40 days all the animals recovered and did not show signs of EAE. However, the absence of MMP-9 in the remission phase suggested a protective role of MMP-9 in the late phase of the disease, because single mmp-9-/- mice presented a delayed remission in comparison with WT animals suggesting a phase-dependent role of MMP-9 in the disease. Nevertheless, the levels of some cytokines and chemokines remained higher than in control animals even 100 days after EAE induction, attesting to a prolonged state of immune activation. We thus yielded new insights and useful markers to monitor this activated immune status. Furthermore, MMP-9 but not MMP-2 levels remained increased in the brains and, to a higher extend, in the spleens of the WT mice even during the remission phase, which is in line with the role of MMP-9 as a useful marker and a protective factor for EAE in the remission phase.

Remnant Epitopes Generating Autoimmunity: From Model to Useful Paradigm

“…This phenomenon aligns with the REGA paradigm: (i) in the absence of (intact) autoantigen, no remnant epitopes are generated; and (ii) autoantigens may be cleared by MMP-9, even when captured in immune complexes [75]. In this sense, the action of proteases in the mouse SLE model is phase-specific, as is the case with the EAE mouse model for MS in humans [76]. In these studies [75,76], it came as a surprise that IgM (900 kDa) and IgG (150 kDa) were not cleaved, whereas much smaller EAE or SLE autoantigens, such as MBP and actin, respectively (monomers are about 20 kDa), were efficiently cleaved by MMP-9 into remnant epitopes even when the latter were captured into immune complexes [75,76].…”

“…Providing Consequently, MMP-9 generates remnant epitopes of MBP in the initiation phase of EAE and thus contributes to the exacerbation of the disease. However, it plays a protective role in the remission phase by cleaving antigens out of the immune complexes [76]. Similar elements are essential in systemic lupus erythematosus (SLE), where MMP-9 is also involved in the clearance of immune complexes [75].…”

“…In this sense, the action of proteases in the mouse SLE model is phase-specific, as is the case with the EAE mouse model for MS in humans [76]. In these studies [75,76], it came as a surprise that IgM (900 kDa) and IgG (150 kDa) were not cleaved, whereas much smaller EAE or SLE autoantigens, such as MBP and actin, respectively (monomers are about 20 kDa), were efficiently cleaved by MMP-9 into remnant epitopes even when the latter were captured into immune complexes [75,76]. The presumed phase-dependent dual role of MMP-9 suggests that, in the onset of autoimmune stimulation, the protease network may be detrimental and needs to be 'shut off', whereas in the later phases, once immune complexes aggravate the pathology, proteolysis may be beneficial for their elimination.…”

Neutrophils: Underestimated Players in the Pathogenesis of Multiple Sclerosis (MS)

“…Indeed, proMMP-9 released from neutrophils and activated into MMP-9 by ROS (and other proteases) has the capacity to truncate human IL-8/CXCL8 into a ten-fold more active chemokine [104]. Many additional studies and roles of MMP-9 in mouse EAE are mentioned in a recent publication by Ugarte-Berzal et al [105]. MMP-2 and MMP-9 synergize in the attraction of neutrophils to the site of injury by enhancing the potency of human CXCL8 and mouse CXCL6 after cleavage.…”

“…It was shown in EAE that MBP epitopes are proteolytically generated by MMP-9 in the initiation phase and these MBP peptides activate T cells [136,137]. In addition, although MMP-9 does not cleave IgG, it is able to cleave MBP from circulating immune complexes, thereby degrading the antigen from immune complexes in the remission phase and thus playing a protective role in the remission phase by promoting clearance of the autoantigen [50,105]. Another example of a remnant epitope in MS is the autoantigen αB-crystallin, which is a heat shock protein found in active MS lesions for presentation to T cells, but its role in MS is still unclear [138,139].…”