Temporal lobe epilepsy (TLE) is a devastating disease in which aberrant synaptic plasticity plays a major role. We identify matrix metalloproteinase (MMP) 9 as a novel synaptic enzyme and a key pathogenic factor in two animal models of TLE: kainate-evoked epilepsy and pentylenetetrazole (PTZ) kindling–induced epilepsy. Notably, we show that the sensitivity to PTZ epileptogenesis is decreased in MMP-9 knockout mice but is increased in a novel line of transgenic rats overexpressing MMP-9. Immunoelectron microscopy reveals that MMP-9 associates with hippocampal dendritic spines bearing asymmetrical (excitatory) synapses, where both the MMP-9 protein levels and enzymatic activity become strongly increased upon seizures. Further, we find that MMP-9 deficiency diminishes seizure-evoked pruning of dendritic spines and decreases aberrant synaptogenesis after mossy fiber sprouting. The latter observation provides a possible mechanistic basis for the effect of MMP-9 on epileptogenesis. Our work suggests that a synaptic pool of MMP-9 is critical for the sequence of events that underlie the development of seizures in animal models of TLE.

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...

The acronym ICER (inducible cAMP early repressor) refers to a group of four proteins produced from the CREM/ICER gene due to use of an internal promoter (P2) placed in an intron of the CREM (cAMP responsive element modulator) gene. The ICER proteins contain DNA binding/leucine zipper domains that make them endogenous inhibitors of transcription driven by CREB (cAMP responsive element binding protein) and its cognates, CREM and ATF-1 (activating transcription factor-1). ICER expression is inducible in the brain and in neuronal culture by a variety of stimuli. As a CREB antagonist, ICER appears to be of pivotal importance in neuronal plasticity and programmed cell death.

Active CREB (cAMP responsive element-binding protein) transcription factor is crucial for neuronal survival. Several members of the CREM/ICER (cAMP responsive element modulator/inducible cAMP early repressor) protein family may act as endogenous CREB antagonists. However, their involvement in a process of programmed cell death remains unexplored. Here we report that ICER may play such a role in neuronal apoptosis because it is upregulated in apoptotic neurons in vitro, and overexpression of ICER, delivered in adenoviral vector, evokes programmed cell death of three different kinds of cultured neurons, namely those derived from hippocampal dentate gyrus, cerebral cortex, and superior cervical ganglion. Reporter gene assay with a promoter containing a CREB-responsive sequence revealed a decrease in both basal and induced CRE-dependent gene expression in neurons overexpressing ICER. Finally, the level of expression of the anti-apoptotic protein Bcl-2, a well known CREB target, was markedly diminished in ICER-treated neurons. We suggest that the naturally occurring CREB functional antagonist ICER may have a specific function in programmed cell death of neurons, probably by silencing the expression of anti-apoptotic genes.

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Membrane depolarization controls long lasting adaptive neuronal changes in brain physiology and pathology. Such responses are believed to be gene expression-dependent. Notably, however, only a couple of gene repressors active in nondepolarized neurons have been described. In this study, we show that in the unstimulated rat hippocampus in vivo, as well as in the nondepolarized brain neurons in primary culture, the transcriptional regulator Yin Yang 1 (YY1) is bound to the proximal Mmp-9 promoter and strongly represses Mmp-9 transcription. Furthermore, we demonstrate that monoubiquitinated and CtBP1 (C-terminal binding protein 1)-bound YY1 regulates Mmp-9 mRNA synthesis in rat brain neurons controlling its transcription apparently via HDAC3-dependent histone deacetylation. In conclusion, our data suggest that YY1 exerts, via epigenetic mechanisms, a control over neuronal expression of MMP-9. Because MMP-9 has recently been shown to play a pivotal role in physiological and pathological neuronal plasticity, YY1 may be implicated in these phenomena as well.Neuronal depolarization is important not only for a transmission of information throughout the nervous system but also for an initiation of adaptive neuronal responses to incoming stimuli. Examples of the adaptive changes are long term potentiation and kindling-evoked epileptogenesis believed to underlie physiological (such as learning and memory) and pathological neuronal plasticity, respectively. These long lasting adaptive changes have been linked to an activation of gene expression. Indeed, a number of depolarization-driven gene responses were described over the last 20 years, and in almost all cases inducible transcription factors, like cAMP-response element-binding protein, Elk-1, AP-1, Egrs, etc. (for review see Ref. 1), were found to be responsible for the increased gene expression. However, it is also conceivable to consider a repression of transcription, in addition to its activation, as a means to drive depolarization-evoked gene expression. So far only a very limited number of such repressive molecules has been discovered (2-4).In this study we set out to search for these transcriptional repressors. We focused on a regulation of Mmp-9 that codes for an extracellular matrix protease involved in physiological and pathological extracellular matrix remodeling. Aberrant, and usually excessive, Mmp-9 expression has been linked to numerous disorders of the central nervous system (5-7) as well as other devastating diseases such as tumors (8, 9). Hence, detailed knowledge of its transcriptional repression is of great importance for an understanding of those pathologies and for a potential development of novel therapeutic approaches.Our previous reports have shown that in the nondepolarized rat brain MMP-9 3 is predominantly expressed in neurons (10 -12). However, its expression levels in those cells are very low, which points toward a presence of an efficient mechanism(s) repressing its transcription in unstimulated neurons (10).Molecular mechanisms directly con...

Here, we show that differentiation of SVF cells to endothelial cells or adipocyte-like cells depended on the medium used. Our work provides a clear model for analysing the differentiation capacity of SVF cells.

Programmed cell death involving gene regulation and de novo protein synthesis is a major component of both normal development and a number of disease conditions. Hence, knowledge of its mechanisms, especially transcription factors, that regulate expression of the genes involved in neurodegenerative disorders is of great importance. cAMP-responsive element-binding protein (CREB) has repeatedly been implicated in the neuronal survival. In the present study we showed that inducible cAMP early repressor (ICER), an endogenous CREB antagonist, is expressed during both excitotoxic and spontaneous neuronal cell death in organotypic hippocampal slice cultures in vitro. Furthermore, overexpression of ICER via an adenoviral vector evoked neuronal cell loss in such cultures. The time course of ICER-dependent cell death was hippocampal subdivision specific, with dentate gyrus neurons dying mostly 3-7 days after the adenovector infection, followed by CA3, where neuronal death peaked after 7 days, and then CA1, where most neuronal death occurred after 7-14 days. These results underscore the usefulness of the organotypic cultures for studies of neurodegeneration and point to neuronal loss having a multifaceted nature in a complex cellular environment.