β-Dystroglycan as a Target for MMP-9, in Response to Enhanced Neuronal Activity

Abstract

Matrix metalloproteinase-9 has recently emerged as an important molecule in control of extracellular proteolysis in the synaptic plasticity. However, no synaptic targets for its enzymatic activity had been identified before. In this report, we show that ␤-dystroglycan comprises such a neuronal activity-driven target for matrix metalloproteinase-9. This notion is based on the following observations. (i) Recombinant, autoactivating matrix metalloproteinase-9 produces limited proteolytic cleavage of ␤-dystroglycan. (ii) In neuronal cultures, ␤-dystroglycan proteolysis occurs in response to stimulation with either glutamate or bicuculline and is blocked by tissue inhibitor of metalloproteinases-1, a metalloproteinase inhibitor. (iii) ␤-Dystroglycan degradation is also observed in the hippocampus in vivo in response to seizures but not in the matrix metalloproteinase-9 knock-out mice. (iv) ␤-Dystroglycan cleavage correlates in time with increased matrix metalloproteinase-9 activity. (v) Finally, ␤-dystroglycan and matrix metalloproteinase-9 colocalize in postsynaptic elements in the hippocampus. In conclusion, our data identify the ␤-dystroglycan as a first matrix metalloproteinase-9 substrate digested in response to enhanced synaptic activity. This demonstration may help to understand the possible role of both proteins in neuronal functions, especially in synaptic plasticity, learning, and memory. Matrix metalloproteinases (MMPs)2 are a family of zinc-dependent endopeptidases acting outside the cells and therefore attributed with digesting extracellular matrix components. These enzymes are produced in a latent form, and after release to extracellular space, they are activated by cleavage off the propeptide (1, 2). MMPs are involved in a number of physiological and pathological conditions, including development, tissue remodeling, inflammation, and tumor metastasis (1-4). Specifically, multiple data show increased expression and activity of MMPs after brain injury and in certain diseases of the central nervous system (5). On the other hand, the physiological roles of MMPs in the adult brain have only recently been appreciated (4). In particular, MMP-9 (also known as gelatinase B) has been implicated in synaptic plasticity, learning, and memory (6, 7). Furthermore, a marked increase in MMP-9 mRNA protein and its enzymatic activity in the hippocampal dentate gyrus after kainate-evoked seizures has been shown (8). Kainate, a glutamate analog, produces excitotoxicity in the CA subfields of the hippocampus, sparing the granule neurons of the dentate gyrus that, however, undergo aberrant plastic changes (9).Despite data implicating MMP-9 in neuronal/synaptic plasticity, no synaptic targets for its enzymatic activity have as yet been identified in neurons. However, recent studies have suggested that this enzyme may digest the 43-kDa ␤-dystroglycan (␤-DG) to release a 30-kDa product from the full-length subunit. First, Yamada et al. (10) have shown that unidentified MMPs digest ␤-DG to reveal the 30-kDa product in the perip...

Enzymatic processing of β‐dystroglycan recombinant ectodomain by MMP‐9: Identification of the main cleavage site

“…However, its fairly low enzymatic efficiency under our conditions might indicate that this event is finely modulated by conformational changes of b-DG. The recent discovery of a b-DG processing carried out by MMP-9 in response to enhanced neuronal activity (23,24) would strengthen the hypothesis that MMP-9 cooperates with the DG complex in the signal transduction.…”

“…Interestingly, b-DG has been proposed to be the first substrate digested by MMP-9 in response to enhanced neuronal activity, playing a role in synaptic plasticity, learning and memory (23,24). These data suggest that modulating the a-DG/b-DG interaction may have a precise functional role and that MMP-9 may be involved in this physiological process.…”

Matrix Metalloproteinase-9 Contributes to Kindled Seizure Development in Pentylenetetrazole-Treated Mice by Converting Pro-BDNF to Mature BDNF in the Hippocampus

“…On the other hand, some of our findings are not consistent with previous reports. For instance, a prominent increase in MMP-9 mRNA levels was observed in rats 2 h after a single 50 mg/kg PTZ dose (Rylski et al, 2009), and MMP-9 activity increased as early as 5 min after bicuculline treatment in mouse cortical cultures (Michaluk et al, 2007). More detailed examination of temporal changes and species differences in MMP-9 expression after single and repeated PTZ injection may help explain these discrepant results.…”

“…Repeated PTZ treatment increased protein and mRNA levels of BDNF in the hippocampi of kindled mice as described below, whereas protein levels of other substrates for MMP, such as laminin (Gu et al, 2005), ␤-dystroglycan (Michaluk et al, 2007), and NCAM (Hübschmann et al, 2005), did not change (Table 1). In fully kindled …”

The extracellular protease matrix metalloproteinase-9 is activated by inhibitory avoidance learning and required for long-term memory

“…Generally, MMPs cleave a potentially large number of extracellular matrix proteins and other cell-surface or cell-adhesion molecules (Sternlicht and Werb 2001), many of which are expressed in hippocampus and are involved in synaptic plasticity and/or memory (Strekalova et al 2002;Dityatev and Schachner 2003). A recent study (Michaluk et al 2007) has identified ␤-dystroglycan (␤-dg) as an activity-dependent target of MMP-9 cleavage in cultured cortical neurons. ␤-dg is a transmembrane protein that links, via association with ␣-dystroglycan, proteins of the extracellular matrix with the actin cytoskeleton (Higginson and Winder 2005).…”