Matrix metalloproteinase-2 (MMP-2) regulates astrocyte motility in connection with the actin cytoskeleton and integrins.

Matrix Metalloproteinases (MMPs) play a role in migration of many cell types outside the central nervous system (CNS). Among neural cells, astrocytes are one of the main sources of MMPs in physiological and postlesional conditions. However, no data are available on the possible role of MMPs in astrocyte motility. Using an in vitro model of 2D migration and broad spectrum and selective MMP inhibitors, the authors demonstrated that MMP-2, but not MMP-9, is a key enzyme for astrocyte migration. In support of these data, the authors found constitutive expression of MMP-2 in astrocytes, while MMP-9 was nearly undetectable by gel zymography and immunocytochemical methods. The inhibition of migration by MMP inhibitors correlated with changes in cell morphology and in the organization of the actin cytoskeleton. In parallel, the characteristic focalized distribution of MMP-2 at the migration front observed in control cells became more diffuse and internalized by treatments that inhibited migration. The disruption of actin by cytochalasin D caused the partial recruitment of MMP-2 and gelatinolytic activity into actin aggregates, indicating a connection between the proteinase and the actin cytoskeleton. Finally, the authors found a co-localization of beta1-integrin with MMP-2 at the leading edge of migrating astrocytes. Altogether, these data provide the first evidence for the implication of MMP-2 in astrocyte motility, probably through the interaction of the proteinase with beta1-integrin that could act as a linker between pericellular proteolysis and the actin cytoskeleton.

Astrocyte reactivity to Fas activation is attenuated in TIMP-1 deficient mice, an in vitro study.

BACKGROUND: Tissue inhibitor of metalloproteinases-1 (TIMP-1) is a multifunctional secreted protein with pleiotropic actions, including the inhibition of matrix metalloproteinases (MMPs), cell death/survival and growth promoting activities. After inflammatory challenge, the levels of TIMP-1 are highly and selectively upregulated in astrocytes among glial cells, but little is know about its role in these neural cells. We investigated the influence of TIMP-1 null mutation in the reactivity of cultured astrocytes to pro-inflammatory stimuli with TNF-alpha and anti-Fas antibody. RESULTS: When compared to WT, mutant astrocytes displayed an overall increased constitutive gelatinase expression and were less responsive to Fas-mediated upregulation of MMP-9, of monocyte chemoattractant protein-1 (MCP-1) and of intercellular cell adhesion molecule-1 (ICAM-1), all markers of astrocyte inflammatory response. In contrast, TNF-alpha treatment induced all these factors similarly regardless of the astrocyte genotype. The incorporation of 3H-thymidin, a marker of cell proliferation, increased in wild-type (WT) astrocytes after treatment with anti-Fas antibody or recombinant TIMP-1 but not in mutant astrocytes. Finally, lymphocyte chemotaxis was differentially regulated by TNF-alpha in WT and TIMP-1 deficient astrocytes. CONCLUSION: We provide evidence that the alteration of the MMP/TIMP balance in astrocytes influences their reactivity to pro-inflammatory stimuli and that Fas activation modulates the expression of members of the MMP/TIMP axis. We hypothesise that the Fas/FasL transduction pathway and the MMP/TIMP system interact in astrocytes to modulate their inflammatory response to environmental stimuli.

[The MMP/TIMP system in the nervous system]. / Le système MMP/TIMP dans le système nerveux.

The matrix metalloproteinases (MMP) belong to a growing family of secreted or membrane-bound (MT-MMP) enzymes that cleave protein components of the extracellular matrix and bioactive factors involved in intercellular signaling. MMP activity is counterbalanced by their four physiological inhibitors, the tissue inhibitors of MMP (TIMPs). Together, MMP and TIMP control cell-cell and cell-matrix interactions associated with physiological processes. However, the breakdown of the protease-inhibitor balance may lead to the loss of tissue homeostasis and the development of degenerative and tumorigenic processes in various tissues. The emerging idea is that the MMP/TIMP system also plays a major role in the pathology and physiology of the nervous system and that mastering MMP activity will set the basis for new and more efficient therapeutic strategies against nervous system disorders.

[Matrix metalloproteinases and their inhibitors, modulators of neuro-immune interactions and of pathophysiological processes in the nervous system]. / Les Métalloprotéases de la matrice et leurs inhibiteurs, des modulateurs des interactions neuro-immunes et des processus physiopathologiques dans le système nerveux.

The matrix metalloproteinases (MMPs) belong to a growing family of Zn2+-dependent endopeptidases, secreted or membrane-bound (MT-MMP), that regulate or degrade by proteolytic cleavage protein components of the extracellular matrix, cytokines, chemokines, cell adhesion molecules and a variety of membrane receptors. MMP activity is counterbalanced by their physiological inhibitors, the tissue inhibitors of MMPs (TIMPs), a family of 4 secreted multifunctional proteins that have growth promoting activities. In physiological conditions MMP activity is tightly regulated and altered MMP regulation is associated with pathological processes including inflammation, cell proliferation, cell death and tissue remodeling. The MMP/TIMP system is involved in the development and function of cells of the immune system by promoting their differentiation, activation, migration across basement membranes and tissues. In the last years, data has accumulated indicating that the MMP/TIMP system is expressed in the nervous system where it regulates neuro-immune interactions and plays a major role in pathophysiological processes. In this review, we present recent in vivo and in vitro studies that highlight the contribution of the MMP/TIMP system to various diseases of the nervous system, involving blood brain barrier breakdown, neuroinflammation, glial reactivity, neuronal death, reactive plasticity, and to developmental and physiological processes including cell migration, axonal sprouting and neuronal plasticity. This review also alludes to the beneficial effects of synthetic MMP inhibitors in different animal models of neuropathology. In all, a further understanding of the role of MMPs and TIMPs in the nervous system should contribute to unravel mechanisms of neuronal plasticity and pathology and set the basis of new therapeutic strategies in nervous system disorders based on the development of synthetic MMP inhibitors.

Gelatinase B and TIMP-1 are regulated in a cell- and time-dependent manner in association with neuronal death and glial reactivity after global forebrain ischemia.

Matrix metalloproteinases (MMPs) belong to a large family of endopeptidases that regulate the pericellular environment through the cleavage of protein components of the extracellular matrix, membrane receptors and cytokines. MMP activity is controlled by the multifunctional tissue inhibitors of metalloproteinases (TIMPs). Proteases and their inhibitors are critically involved in developmental and pathological processes in numerous organs, including the brain. Global transient cerebral ischemia induces selective delayed neuronal death and neuroinflammation. We compared, in discrete vulnerable and resistant areas of the ischemic rat hippocampus, the kinetics and cellular distribution of gelatinase B and its principal inhibitor TIMP-1 and we assessed by in situ zymography, the net gelatinolytic activity at the cellular level. We show that gelatinases are expressed and active in neurons, suggesting that MMPs play a role in maintaining neural homeostasis. In the ischemic rat brain, expression and activity of gelatinase B, and expression of TIMP-1 are altered in a time-, region- and cell-dependent manner. Gelatinase B is induced first in reactive microglia and subsequently in reactive astrocytes. In situ, increases in gelatinase activity accompanied the progression of neuronal death and glial reactivity. Our results suggest that MMPs and TIMPs are involved in cell viability and tissue remodelling in the ischemic brain, and reinforces the idea that the MMP/TIMP system contributes both to neuronal demise and tissue repair in the context of glial reactivity.