Is Drp1 a link between mitochondrial dysfunction and inflammation in Alzheimer's disease?

Recent advances highlight that inflammation is critical to Alzheimer Disease (AD) pathogenesis. Indeed, several diseases characterized by inflammation are considered risk factors for AD, such as type 2 diabetes, obesity, hypertension, and traumatic brain injury. Moreover, allelic variations in genes involved in the inflammatory cascade are risk factors for AD. AD is also characterized by mitochondrial dysfunction, which affects the energy homeostasis of the brain. The role of mitochondrial dysfunction has been characterized mostly in neuronal cells. However, recent data are demonstrating that mitochondrial dysfunction occurs also in inflammatory cells, promoting inflammation and the secretion of pro-inflammatory cytokines, which in turn induce neurodegeneration. In this review, we summarize the recent finding supporting the hypothesis of the inflammatory-amyloid cascade in AD. Moreover, we describe the recent data that demonstrate the link between altered mitochondrial dysfunction and the inflammatory cascade. We focus in summarizing the role of Drp1, which is involved in mitochondrial fission, showing that altered Drp1 activation affects the mitochondrial homeostasis and leads to the activation of the NLRP3 inflammasome, promoting the inflammatory cascade, which in turn aggravates Amyloid beta (Ab) deposition and tau-induced neurodegeneration, showing the relevance of this pro-inflammatory pathway as an early event in AD.

AGE-TXNIP axis drives inflammation in Alzheimer's by targeting Aß to mitochondria in microglia.

Alzheimer's disease (AD) is the most common form of dementia characterized by progressive memory loss and cognitive decline. Although neuroinflammation and oxidative stress are well-recognized features of AD, their correlations with the early molecular events characterizing the pathology are not yet well clarified. Here, we characterize the role of RAGE-TXNIP axis in neuroinflammation in relation to amyloid-beta (Aß) burden in both in vivo and in vitro models. In the hippocampus of 5xFAD mice microglial activation, cytokine secretion, and glial fibrillary acidic protein-enhanced expression are paralleled with increased TXNIP expression. TXNIP silencing or its pharmacological inhibition prevents neuroinflammation in those mice. TXNIP is also associated with RAGE and Aß. In particular, RAGE-TXNIP axis is required for targeting Aß in mitochondria, leading to mitochondrial dysfunction and oxidative stress. Silencing of TXNIP or inhibition of RAGE activation reduces Aß transport from the cellular surface to mitochondria, restores mitochondrial functionality, and mitigates Aß toxicity. Furthermore, Aß shuttling into mitochondria promotes Drp1 activation and exacerbates mitochondrial dysfunction, which induces NLRP3 inflammasome activation, leading to secretion of IL-1ß and activation of the pyroptosis-associated protein Gasdermin D (GSDMD). Downregulation of RAGE-TXNIP axis inhibits Aß-induced mitochondria dysfunction, inflammation, and induction of GSDMD. Herein we unveil a new pathway driven by TXNIP that links the mitochondrial transport of Aß to the activation of Drp1 and the NLRP3 inflammasome, promoting the secretion of IL-1ß and the pyroptosis pathway associated with GSDMD cleavage. Altogether these data shed new light on a novel mechanism of action of RAGE-TXNIP axis in microglia, which is intertwined with Aß and ultimately causes mitochondria dysfunction and NLRP3 inflammasome cascade activation, suggesting TXNIP as a druggable target to be better deepened for AD.

The actin binding protein α-actinin-2 expression is associated with dendritic spine plasticity and migrating granule cells in the rat dentate gyrus following pilocarpine-induced seizures.

α-actinin-2 (α-actn-2) is an F-actin-crosslinking protein, localized in dendritic spines. In vitro studies suggested that it is involved in spinogenesis, morphogenesis, actin organization, cell migration and anchoring of the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptors in dendritic spines. However, little is known regarding its function in vivo. We examined the levels of α-actn-2 expression within the dentate gyrus (DG) during the development of chronic limbic seizures (epileptogenesis) induced by pilocarpine in rats. In this model, plasticity of the DG glutamatergic granule cells including spine loss, spinogenesis, morphogenesis, neo-synaptogenesis, aberrant migration, and alterations of NMDA receptors have been well characterized. We showed that α-actn-2 immunolabeling was reduced in the inner molecular layer at 1-2 weeks post-status epilepticus (SE), when granule cell spinogenesis and morphogenesis occur. This low level persisted at the chronic stage when new functional synapses are established. This decreased of α-actn-2 protein is concomitant with the recovery of drebrin A (DA), another actin-binding protein, at the chronic stage. Indeed, we demonstrated in cultured cells that in contrast to DA, α-actn-2 did not protect F-actin destabilization and DA inhibited α-actn-2 binding to F-actin. Such alteration could affect the anchoring of NR1 in dendritic spines. Furthermore, we showed that the expression of α-actn-2 and NR1 are co-down-regulated in membrane fractions of pilocarpine animals at chronic stage. Last, we showed that α-actn-2 is expressed in migrating newly born granule cells observed within the hilus of pilocarpine-treated rats. Altogether, our results suggest that α-actn-2 is not critical for the structural integrity and stabilization of granule cell dendritic spines. Instead, its expression is regulated when spinogenesis and morphogenesis occur and within migrating granule cells. Our data also suggest that the balance between α-actn-2 and DA expression levels may modulate NR1 anchoring within dendritic spines.

Biased signaling through G-protein-coupled PROKR2 receptors harboring missense mutations.

Various missense mutations in the gene coding for prokineticin receptor 2 (PROKR2), a G-protein-coupled receptor, have been identified in patients with Kallmann syndrome. However, the functional consequences of these mutations on the different signaling pathways of this receptor have not been studied. We first showed that the wild-type PROKR2 can activate different G-protein subtypes (Gq, Gs, and Gi/o) and recruit ß-arrestins in transfected HEK-293 cells. We then examined, for each of these signaling pathways, the effects of 9 mutations that did not significantly impair cell surface targeting or ligand binding of the receptor. Four mutant receptors showing defective Gq signaling (R85C, R85H, R164Q, and V331M) could still recruit ß-arrestins on ligand activation, which may cause biased signaling in vivo. Conversely, the R80C receptor could activate the 3 types of G proteins but could not recruit ß-arrestins. Finally, the R268C receptor could recruit ß-arrestins and activate the Gq and Gs signaling pathways but could not activate the Gi/o signaling pathway. Our results validate the concept that mutations in the genes encoding membrane receptors can bias downstream signaling in various ways, possibly leading to pathogenic and, perhaps in some cases, protective (e.g., R268C) effects.

Variations in PROKR2, but not PROK2, are associated with hypopituitarism and septo-optic dysplasia.

CONTEXT: Loss-of-function mutations in PROK2 and PROKR2 have been implicated in Kallmann syndrome (KS), characterized by hypogonadotropic hypogonadism and anosmia. Recent data suggest overlapping phenotypes/genotypes between KS and congenital hypopituitarism (CH), including septo-optic dysplasia (SOD). OBJECTIVE: We screened a cohort of patients with complex forms of CH (n = 422) for mutations in PROK2 and PROKR2. RESULTS: We detected 5 PROKR2 variants in 11 patients with SOD/CH: novel p.G371R and previously reported p.A51T, p.R85L, p.L173R, and p.R268C-the latter 3 being known functionally deleterious variants. Surprisingly, 1 patient with SOD was heterozygous for the p.L173R variant, whereas his phenotypically unaffected mother was homozygous for the variant. We sought to clarify the role of PROKR2 in hypothalamopituitary development through analysis of Prokr2(-/-) mice. Interestingly, these revealed predominantly normal hypothalamopituitary development and terminal cell differentiation, with the exception of reduced LH; this was inconsistent with patient phenotypes and more analogous to the healthy mother, although she did not have KS, unlike the Prokr2(-/-) mice. CONCLUSIONS: The role of PROKR2 in the etiology of CH, SOD, and KS is uncertain, as demonstrated by no clear phenotype-genotype correlation; loss-of-function variants in heterozygosity or homozygosity can be associated with these disorders. However, we report a phenotypically normal parent, homozygous for p.L173R. Our data suggest that the variants identified herein are unlikely to be implicated in isolation in these disorders; other genetic or environmental modifiers may also impact on the etiology. Given the phenotypic variability, genetic counseling may presently be inappropriate.

TWEAK/Fn14 pathway modulates properties of a human microvascular endothelial cell model of blood brain barrier.

BACKGROUND: The TNF ligand family member TWEAK exists as membrane and soluble forms and is involved in the regulation of various human inflammatory pathologies, through binding to its main receptor, Fn14. We have shown that the soluble form of TWEAK has a pro-neuroinflammatory effect in an animal model of multiple sclerosis and we further demonstrated that blocking TWEAK activity during the recruitment phase of immune cells across the blood brain barrier (BBB) was protective in this model. It is now well established that endothelial cells in the periphery and astrocytes in the central nervous system (CNS) are targets of TWEAK. Moreover, it has been shown by others that, when injected into mice brains, TWEAK disrupts the architecture of the BBB and induces expression of matrix metalloproteinase-9 (MMP-9) in the brain. Nevertheless, the mechanisms involved in such conditions are complex and remain to be explored, especially because there is a lack of data concerning the TWEAK/Fn14 pathway in microvascular cerebral endothelial cells. METHODS: In this study, we used human cerebral microvascular endothelial cell (HCMEC) cultures as an in vitro model of the BBB to study the effects of soluble TWEAK on the properties and the integrity of the BBB model. RESULTS: We showed that soluble TWEAK induces an inflammatory profile on HCMECs, especially by promoting secretion of cytokines, by modulating production and activation of MMP-9, and by expression of cell adhesion molecules. We also demonstrated that these effects of TWEAK are associated with increased permeability of the HCMEC monolayer in the in vitro BBB model. CONCLUSIONS: Taken together, the data suggest a role for soluble TWEAK in BBB inflammation and in the promotion of BBB interactions with immune cells. These results support the contention that the TWEAK/Fn14 pathway could contribute at least to the endothelial steps of neuroinflammation.

Role of matrix metalloproteinases in migration and neurotrophic properties of nasal olfactory stem and ensheathing cells.

Adult olfactory ectomesenchymal stem cells (OE-MSCs) and olfactory ensheathing cells (OECs), both from the nasal olfactory lamina propria, display robust regenerative properties when transplanted into the nervous system, but the mechanisms supporting such therapeutic effects remain unknown. Matrix metalloproteinases (MMPs) are an important family of proteinases contributing to cell motility and axonal outgrowth across the extracellular matrix (ECM) in physiological and pathological conditions. In this study, we have characterized for the first time in nasal human OE-MSCs the expression profile of some MMPs currently associated with cell migration and invasiveness. We demonstrate different patterns of expression for MMP-1, MMP-2, MMP-9, and MT1-MMP upon cell migration when compared with nonmigrating cells. Our results establish a correspondence between the localization of these proteinases in the migration front with the ability of cells to migrate. Using various modulators of MMP activity, we also show that at least MMP-2, MMP-9, and MT1-MMP contribute to OE-MSC migration in an in vitro 3D test. Furthermore, we demonstrate under the same conditions of culture used for in vivo transplantation that OE-MSCs and OECs secrete neurotrophic factors that promote neurite outgrowth of cortical and dorsal root ganglia (DRG) neurons, as well as axo-dendritic differentiation of cortical neurons. These effects were abolished by the depletion of MMP-2 and MMP-9 from the culture conditioned media. Altogether, our results provide the first evidence that MMPs may contribute to the therapeutic features of OE-MSCs and OECs through the control of their motility and/or their neurotrophic properties. Our data provide new insight into the mechanisms of neuroregeneration and will contribute to optimization of cell therapy strategies.

The Complexity of Sporadic Alzheimer's Disease Pathogenesis: The Role of RAGE as Therapeutic Target to Promote Neuroprotection by Inhibiting Neurovascular Dysfunction.

Alzheimer's disease (AD) is the most common cause of dementia. Amyloid plaques and neurofibrillary tangles are prominent pathological features of AD. Aging and age-dependent oxidative stress are the major nongenetic risk factors for AD. The beta-amyloid peptide (Aß), the major component of plaques, and advanced glycation end products (AGEs) are key activators of plaque-associated cellular dysfunction. Aß and AGEs bind to the receptor for AGEs (RAGE), which transmits the signal from RAGE via redox-sensitive pathways to nuclear factor kappa-B (NF-κB). RAGE-mediated signaling is an important contributor to neurodegeneration in AD. We will summarize the current knowledge and ongoing studies on RAGE function in AD. We will also present evidence for a novel pathway induced by RAGE in AD, which leads to the expression of thioredoxin interacting protein (TXNIP), providing further evidence that pharmacological inhibition of RAGE will promote neuroprotection by blocking neurovascular dysfunction in AD.

Drebrin A expression is altered after pilocarpine-induced seizures: time course of changes is consistent for a role in the integrity and stability of dendritic spines of hippocampal granule cells.

We used a pathophysiological model of temporal lobe epilepsy induced by pilocarpine in adult rats in order to assess the in vivo role of drebrin A (DA), one of the major regulators of F-actin. This model displays a dynamic reorganization of the glutamatergic network including neo-spinogenesis, morphogenesis, and neo-synaptogenesis associated with an aberrant sprouting of granule cell axons in the dentate gyrus (DG). This reactive plasticity contributes in dentate granule-cell hyperexcitability that could lead to the emergence of recurrent spontaneous seizures. We investigated the hippocampal DA expression changes in pilocarpine animals using immunohistochemical, Western blot, and in situ hybridization analyses. We showed that DA immunoreactivity was decreased in the inner molecular layer (IML) and in the hilus (H) of the DG, at latent stage, when spinogenesis and morphogenesis occur. Western blot analysis confirmed these overall hippocampal decreases of DA protein expression. At chronic stage, when newly formed glutamatergic synapses are being established, the levels of immunolabeling for DA in the H and the IML were similar to control rats. This recovery is likely due to the increase of DA mRNA in perikarya of hilar and granule cells. Interestingly, our data showed that the changes pattern of labeling for Bassoon, a specific marker for presynaptic active zone, in the IML of pilocarpine-treated animals paralleled those found for DA at all time points examined. Furthermore, our double and triple immunofluorescence studies showed that the recovery in DA levels in the IML occurred within the dendritic spines involved in glutamatergic active synapses of presumed granule cells. Altogether, our results indicate that in vivo DA is not critical for spinogenesis and morphogenesis but instead is consistent with an involvement in synaptic structural integrity, stabilization, and function. Thus, DA appears as a novel modulator of reactive synaptic plasticity associated with epilepsy.

Trafficking and secretion of matrix metalloproteinase-2 in olfactory ensheathing glial cells: A role in cell migration?

Olfactory ensheathing cells (OECs) are unique glia found only in the olfactory system. They retain exceptional plasticity and support olfactory neurogenesis and retargeting across the PNS:CNS boundary in the olfactory system. OECs have been shown to improve functional outcome when transplanted into rodents with spinal cord injury. The growth-promoting properties of implanted OECs encompass their ability to migrate through the scar tissue and render it more permissive for axonal outgrowth, but the underlying molecular mechanisms remain poorly understood. OECs appear to regulate molecules of the extracellular matrix (ECM) that inhibit axonal growth. Among the proteins that have the potential to promote cell migration, axonal regeneration and remodeling of the ECM are matrix metalloproteinases (MMPs), a family of endopeptidases that cleave matrix, soluble, and membrane-bound proteins and that are regulated by their endogenous inhibitors, the tissue inhibitors of MMPs (TIMPs). Little is known about MMP/TIMP trafficking, secretion, and role in OECs. Using a combination of cell biology, biochemistry, pharmacology, and imaging techniques, we show that MMP-2 and MMP-9 are expressed and proteolytically active in the olfactory epithelium and in particular in the OECs of the lamina propria. These proteinases and regulatory proteins such as MT1-MMP and TIMP-2 are expressed in cultured OECs. MMPs exhibit nuclear localization and vesicular trafficking and secretion, with distribution along microtubules and microfilaments and co-localization with the molecular motor protein kinesin. Finally, we show that MMPs are involved in migration of OECs in vitro on different ECM substrates.

Olfactory stem cells, a new cellular model for studying molecular mechanisms underlying familial dysautonomia.

BACKGROUND: Familial dysautonomia (FD) is a hereditary neuropathy caused by mutations in the IKBKAP gene, the most common of which results in variable tissue-specific mRNA splicing with skipping of exon 20. Defective splicing is especially severe in nervous tissue, leading to incomplete development and progressive degeneration of sensory and autonomic neurons. The specificity of neuron loss in FD is poorly understood due to the lack of an appropriate model system. To better understand and modelize the molecular mechanisms of IKBKAP mRNA splicing, we collected human olfactory ecto-mesenchymal stem cells (hOE-MSC) from FD patients. hOE-MSCs have a pluripotent ability to differentiate into various cell lineages, including neurons and glial cells. METHODOLOGY/PRINCIPAL FINDINGS: We confirmed IKBKAP mRNA alternative splicing in FD hOE-MSCs and identified 2 novel spliced isoforms also present in control cells. We observed a significant lower expression of both IKBKAP transcript and IKAP/hELP1 protein in FD cells resulting from the degradation of the transcript isoform skipping exon 20. We localized IKAP/hELP1 in different cell compartments, including the nucleus, which supports multiple roles for that protein. We also investigated cellular pathways altered in FD, at the genome-wide level, and confirmed that cell migration and cytoskeleton reorganization were among the processes altered in FD. Indeed, FD hOE-MSCs exhibit impaired migration compared to control cells. Moreover, we showed that kinetin improved exon 20 inclusion and restores a normal level of IKAP/hELP1 in FD hOE-MSCs. Furthermore, we were able to modify the IKBKAP splicing ratio in FD hOE-MSCs, increasing or reducing the WT (exon 20 inclusion):MU (exon 20 skipping) ratio respectively, either by producing free-floating spheres, or by inducing cells into neural differentiation. CONCLUSIONS/SIGNIFICANCE: hOE-MSCs isolated from FD patients represent a new approach for modeling FD to better understand genetic expression and possible therapeutic approaches. This model could also be applied to other neurological genetic diseases.

RAGE-TXNIP axis is required for S100B-promoted Schwann cell migration, fibronectin expression and cytokine secretion.

During peripheral nerve injury, Schwann cells (SCs) adopt a migratory phenotype and remodel the extracellular matrix and provide a supportive activity for neuron regeneration. SCs synthesize neurotrophic factors and cytokines that are crucial for the repair of the injured nerve. The receptor for advanced glycation end products (RAGE) and its ligand S100B, which are secreted by SCs, are required for the repair of the injured peripheral nerve in vivo. However, the precise intracellular pathways involved have not been completely elucidated. Here, we show that RAGE-induced S100B secretion involves the recruitment of S100B in lipid rafts and caveolae. Moreover, we demonstrate for the first time that RAGE induces the expression of thioredoxin interacting protein (TXNIP) in SCs and the injured sciatic nerve in vivo. TXNIP is involved in the activation of p38 MAPK, CREB and NFκB in SCs. TXNIP silencing partially inhibits RAGE-induced SC migration and completely abolishes RAGE-induced fibronectin and IL-1ß expression. Our results support a model in which TXNIP mediates in part RAGE-induced SC migration and is required for the expression of provisional ECM and pro-inflammatory IL-1ß. We provide new insight on the role of the SC RAGE-TXNIP axis in the repair of injured peripheral nerves.

Ligation induced matrix-metalloproteinase-9 activity in peripheral frog nervous system.

Matrix metalloproteinases (MMPs) are endopeptidases that cleave matrix, soluble and membrane-bound proteins and are regulated by their endogenous inhibitors the tissue inhibitors of MMPs (TIMPs). MMP-2 and MMP-9 are two of the MMPs which are essential to contribute to inflammatory and degenerative processes in injured nerves. The aim of the present study was to examine expression and activities of MMP-2 and MMP-9 in the injured and control groups frog sciatic nerves using gelatin zymography. Our investigation demonstrated for the first time as far as we know the expression of MMP-2 and MMP-9 in frog sciatic nerve. The expression and activity of MMP-9 were increased two fold on average following ligation. By contrast, MMP-2 activities remained unchanged. These findings suggest that we can consider MMP-9 as a marker for degenerative changes that follow nerve ligation in frog nerve.

Differential vesicular distribution and trafficking of MMP-2, MMP-9, and their inhibitors in astrocytes.

Astrocytes play an active role in the central nervous system and are critically involved in astrogliosis, a homotypic response of these cells to disease, injury, and associated neuroinflammation. Among the numerous molecules involved in these processes are the matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases, secreted or membrane-bound, that regulate by proteolytic cleavage the extracellular matrix, cytokines, chemokines, cell adhesion molecules, and plasma membrane receptors. MMP activity is tightly regulated by the tissue inhibitors of MMPs (TIMPs), a family of secreted multifunctional proteins. Astrogliosis in vivo and astrocyte reactivity induced in vitro by proinflammatory cues are associated with modulation of expression and/or activity of members of the MMP/TIMP system. However, nothing is known concerning the intracellular distribution and secretory pathways of MMPs and TIMPs in astrocytes. Using a combination of cell biology, biochemistry, fluorescence and electron microscopy approaches, we investigated in cultured reactive astrocytes the intracellular distribution, transport, and secretion of MMP-2, MMP-9, TIMP-1, and TIMP-2. MMP-2 and MMP-9 demonstrate nuclear localization, differential intracellular vesicular distribution relative to the myosin V and kinesin molecular motors, and LAMP-2-labeled lysosomal compartment, and we show vesicular secretion for MMP-2, MMP-9, and their inhibitors. Our results suggest that these proteinases and their inhibitors use different pathways for trafficking and secretion for distinct astrocytic functions.

A new role for TIMP-1 in modulating neurite outgrowth and morphology of cortical neurons.

BACKGROUND: Tissue inhibitor of metalloproteinases-1 (TIMP-1) displays pleiotropic activities, both dependent and independent of its inhibitory activity on matrix metalloproteinases (MMPs). In the central nervous system (CNS), TIMP-1 is strongly upregulated in reactive astrocytes and cortical neurons following excitotoxic/inflammatory stimuli, but no information exists on its effects on growth and morphology of cortical neurons. PRINCIPAL FINDINGS: We found that 24 h incubation with recombinant TIMP-1 induced a 35% reduction in neurite length and significantly increased growth cones size and the number of F-actin rich microprocesses. TIMP-1 mediated reduction in neurite length affected both dendrites and axons after 48 h treatment. The effects on neurite length and morphology were not elicited by a mutated form of TIMP-1 inactive against MMP-1, -2 and -3, and still inhibitory for MMP-9, but were mimicked by a broad spectrum MMP inhibitor. MMP-9 was poorly expressed in developing cortical neurons, unlike MMP-2 which was present in growth cones and whose selective inhibition caused neurite length reductions similar to those induced by TIMP-1. Moreover, TIMP-1 mediated changes in cytoskeleton reorganisation were not accompanied by modifications in the expression levels of actin, betaIII-tubulin, or microtubule assembly regulatory protein MAP2c. Transfection-mediated overexpression of TIMP-1 dramatically reduced neuritic arbour extension in the absence of detectable levels of released extracellular TIMP-1. CONCLUSIONS: Altogether, TIMP-1 emerges as a modulator of neuronal outgrowth and morphology in a paracrine and autrocrine manner through the inhibition, at least in part, of MMP-2 and not MMP-9. These findings may help us understand the role of the MMP/TIMP system in post-lesion pre-scarring conditions.

Vesicular trafficking and secretion of matrix metalloproteinases-2, -9 and tissue inhibitor of metalloproteinases-1 in neuronal cells.

Matrix metalloproteinases (MMPs) are endopeptidases that cleave matrix, soluble and membrane-bound proteins and are regulated by their endogenous inhibitors the tissue inhibitors of MMPs (TIMPs). Nothing is known about MMP/TIMP trafficking and secretion in neuronal cells. We focussed our attention on the gelatinases MMP-2 and MMP-9, and their inhibitor TIMP-1. MMPs and TIMP-1 fused to GFP were expressed in N2a neuroblastoma and primary neuronal cells to study trafficking and secretion using real time video-microscopy, imaging, electron microscopy and biochemical approaches. We show that MMPs and TIMP-1 are secreted in 160-200 nm vesicles in a Golgi-dependent pathway. These vesicles distribute along microtubules and microfilaments, co-localise differentially with the molecular motors kinesin and myosin Va and undergo both anterograde and retrograde trafficking. MMP-9 retrograde transport involves the dynein/dynactin molecular motor. In hippocampal neurons, MMP-2 and MMP-9 vesicles are preferentially distributed in the somato-dendritic compartment and are found in dendritic spines. Non-transfected hippocampal neurons also demonstrate vesicular secretion of MMP-2 in both its pro- and active forms and gelatinolytic activity localised within dendritic spines. Our results show differential trafficking of MMP and TIMP-1-containing vesicles in neuronal cells and suggest that these vesicles could play a role in neuronal and synaptic plasticity.