We have shown in a variety of human wounds that collagenase-1 (MMP-1), a matrix metalloproteinase that cleaves fibrillar type I collagen, is invariably expressed by basal keratinocytes migrating across the dermal matrix. Furthermore, we have demonstrated that MMP-1 expression is induced in primary keratinocytes by contact with native type I collagen and not by basement membrane proteins or by other components of the dermal or provisional (wound) matrix. Based on these observations, we hypothesized that the catalytic activity of MMP-1 is necessary for keratinocyte migration on type I collagen. To test this idea, we assessed keratinocyte motility on type I collagen using colony dispersion and colloidal gold migration assays. In both assays, primary human keratinocytes migrated efficiently on collagen. The specificity of MMP-1 in promoting cell movement was demonstrated in four distinct experiments. One, keratinocyte migration was completely blocked by peptide hydroxymates, which are potent inhibitors of the catalytic activity of MMPs. Two, HaCaTs, a line of human keratinocytes that do not express MMP-1 in response to collagen, did not migrate on a type I collagen matrix but moved efficiently on denatured type I collagen (gelatin). EGF, which induces MMP-I production by HaCaT cells, resulted in the ability of these cells to migrate across a type I collagen matrix. Three, keratinocytes did not migrate on mutant type I collagen lacking the collagenase cleavage site, even though this substrate induced MMP-1 expression. Four, cell migration on collagen was completely blocked by recombinant tissue inhibitor of metalloproteinase-1 (TIMP-1) and by affinity-purified anti–MMP-1 antiserum. In addition, the collagen-mediated induction of collagenase-1 and migration of primary keratinocytes on collagen was blocked by antibodies against the α2 integrin subunit but not by antibodies against the α1 or α3 subunits. We propose that interaction of the α2β1 integrin with dermal collagen mediates induction of collagenase-1 in keratinocytes at the onset of healing and that the activity of collagenase-1 is needed to initiate cell movement. Furthermore, we propose that cleavage of dermal collagen provides keratinocytes with a mechanism to maintain their directionality during reepithelialization.
In injured skin, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is induced in migrating keratinocytes. This site-specific expression is regulated by binding of the ␣ 2  1 integrin with dermal type I collagen, and the catalytic activity of MMP-1 is required for keratinocyte migration. Because of this functional association among substrate/ligand, receptor, and proteinase, we assessed whether the integrin also directs the compartmentalization of MMP-1 to its matrix target. Indeed, pro-MMP-1 co-localized to sites of ␣ 2  1 contacts in migrating keratinocytes. Furthermore, pro-MMP-1 co-immunoprecipitated with ␣ 2  1 from keratinocytes, and ␣ 2  1 co-immunoprecipitated with pro-MMP-1. No other MMPs bound ␣ 2  1 , and no other integrins interacted with MMP-1. Pro-MMP-1 also provided a substrate for ␣ 2  1 -dependent adhesion of platelets. Complex formation on keratinocytes was most efficient on native type I collagen and reduced or ablated on denatured or cleaved collagen. Competition studies suggested that the ␣ 2 I domain interacts with the linker and hemopexin domains of pro-MMP-1, not with the pro-domain. These data indicate that the interaction of pro-MMP-1 with ␣ 2  1 confines this proteinase to points of cell contact with collagen and that the ternary complex of integrin, enzyme, and substrate function together to drive and regulate keratinocyte migration.Cells, either resting or activated, use a variety of surface receptors to sense the presence and location of specific molecules in the extracellular space. For example, integrin-ligand interactions tell cells which structural proteins they have encountered in the extracellular space, and in turn, these contacts activate signaling pathways involved in differentiation, proliferation, and gene expression, among other processes. During migration, cells need to proteolyze, to some extent, nearby extracellular matrix proteins, and hence, cell-matrix contacts can also instruct cells which proteinases are needed and where the enzyme should be targeted and released.An example of cell-matrix-mediated spatial regulation of proteolysis is seen with collagenase-1 (MMP-1), 1 a matrix metalloproteinase, in human cutaneous wounds. In response to injury, collagenase-1 is induced in basal epidermal cells (keratinocytes) as the cells move off of the basement membrane and contact native type I collagen in the underlying dermis (1), and this inductive response is specifically controlled by the collagen-binding integrin ␣ 2  1 (2). As we demonstrated in various experiments, the catalytic activity of collagenase-1 is required and sufficient for keratinocyte migration on complex matrices containing type I collagen. For example, keratinocytes plated on mutant, collagenase-resistant type I collagen do not migrate, even in the presence of fibronectin and vitronectin; yet they express MMP-1 at levels equivalent to those released by cells on wild-type collagen (2). Keratinocyte migration is also completely inhibited by anti-collagenase-1 antibodies, which block the catalytic a...
Background:Truly phosphospecific antibodies are difficult to generate and are poorly understood. Results: Avian single chain Fv library selections yielded fully phosphospecific anti-phospho-tau antibodies, enabling the generation of a 1.9 Å co-crystal structure. Conclusion: Phosphospecific antibodies were readily generated and can exhibit unique epitope recognition mechanisms. Significance: High-affinity antibody phosphoepitope recognition has been defined, at high resolution, for the first time.
Previous studies have established that ligation of keratinocyte ␣ 2  1 integrin by type I collagen induces expression of matrix metalloproteinase-1 (MMP-1) and that MMP-1 activity is required for the ␣ 2  1 integrin-dependent migration of primary keratinocytes across collagenous matrices. We now present evidence that MMP-1 binds the ␣ 2  1 integrin via the I domain of the ␣ 2 integrin subunit. Using an enzyme-linked immunosorbent assay with purified human MMP-1 and recombinant ␣ 2 integrin I domain, we showed that the ␣ 2 integrin I domain specifically bound in a divalent cation-dependent manner to both the pro and active forms of MMP-1, but not to MMP-3 or MMP-13. Although both the I domain and MMP-1 bind divalent cations, MMP-1 bound, in a divalent cation-dependent manner, to ␣ 2 integrin I domains containing metal ion-dependent adhesion sites motif mutations that prevent divalent cation binding to the I domain, demonstrating that the metal ion dependence is a function of MMP-1. Using a series of MMP-1-MMP-3 and MMP-1-MMP-13 chimeras, we determined that both the linker domain and the hemopexin-like domain of MMP-1 were required for optimal binding to the I domain. The ␣ 2 integrin/MMP-1 interaction described here extends an emerging paradigm in matrix biology involving anchoring of proteinases to the cell surface to regulate their biological activities.The extracellular matrix is not a static environment. Remodeling and degradation of the extracellular matrix is a vital component of physiological and pathophysiological processes, such as development and differentiation, cell migration, angiogenesis, wound healing, and metastasis. Matrix metalloproteinases (MMPs) 1 play a central role in the turnover of extracellular matrix components (1).MMPs constitute a large family of metal-dependent endoproteases with varying substrate specificities for many extracellular proteins. The structure of native triple helical type I collagen makes it resistant to proteolysis, and only six MMPs, MMP-1, MMP-8, MMP-13, MMP-14 (MT1-MMP), MMP-18, and MMP-2, exhibit an ability to cleave native fibrillar collagen within its triple helical domain (2-8). Similar to most MMPs, the collagenases (MMP-1, MMP-8, and MMP-13) have several structural features in common, including an N-terminal prodomain, a catalytic domain, and a short proline-rich linker connected to a hemopexin-like domain at the C terminus (9). The catalytic domain contains a Zn 2ϩ -binding site that is conserved in all MMPs and is required for catalytic activity (10, 11). The catalytic domain of the collagenases contains an additional structural Zn 2ϩ , as well as three structural Ca 2ϩ ions (12). The hemopexin-like domain contains a Ca 2ϩ and a Ca 2ϩ -Cl Ϫ ion pair (12).The three collagenases differ in patterns of tissue expression. In humans, MMP-1, which is expressed by epithelium, endothelium, fibroblasts, chondrocytes, and macrophages, seems to be the enzyme principally responsible for collagen turnover in most tissues (13-18). During cutaneous wound healing, human k...
The Amyloid Hypothesis states that the cascade of events associated with Alzheimer's disease (AD)—formation of amyloid plaques, neurofibrillary tangles, synaptic loss, neurodegeneration, and cognitive decline—are triggered by Aβ peptide dysregulation (Kakuda et al., 2006, Sato et al., 2003, Qi-Takahara et al., 2005). Since γ-secretase is critical for Aβ production, many in the biopharmaceutical community focused on γ-secretase as a target for therapeutic approaches for Alzheimer's disease. However, pharmacological approaches to control γ-secretase activity are challenging because the enzyme has multiple, physiologically critical protein substrates. To lower amyloidogenic Aβ peptides without affecting other γ-secretase substrates, the epsilon (ε) cleavage that is essential for the activity of many substrates must be preserved. Small molecule modulators of γ-secretase activity have been discovered that spare the ε cleavage of APP and other substrates while decreasing the production of Aβ 42. Multiple chemical classes of γ-secretase modulators have been identified which differ in the pattern of Aβ peptides produced. Ideally, modulators will allow the ε cleavage of all substrates while shifting APP cleavage from Aβ 42 and other highly amyloidogenic Aβ peptides to shorter and less neurotoxic forms of the peptides without altering the total Aβ pool. Here, we compare chemically distinct modulators for effects on APP processing and in vivo activity.
Adult rats were treated acutely with peripheral kainic acid (KA), and changes in brain-derived neurotrophic factor (BDNF) mRNA and protein were tracked over time across multiple brain regions. Despite robust elevation in both mRNA and protein in multiple brain regions, plasma BDNF was unchanged and cerebrospinal fluid (CSF) BDNF levels remained undetectable. Primary neurons were then treated with KA. BDNF was similarly elevated within neurons, but was undetectable in neuronal media. Thus, while deficits in BDNF signaling have been implicated in a number of diseases, these data suggest that extracellular concentrations of BDNF may not be a facile biomarker for changes in neurons.
IntroductionModulation of the gamma-secretase enzyme, which reduces the production of the amyloidogenic Aβ42 peptide while sparing the production of other Aβ species, is a promising therapeutic approach for the treatment of Alzheimer's disease. Satori has identified a unique class of small molecule gamma-secretase modulators (GSMs) capable of decreasing Aβ42 levels in cellular and rodent model systems. The compound class exhibits potency in the nM range in vitro and is selective for lowering Aβ42 and Aβ38 while sparing Aβ40 and total Aβ levels. In vivo, a compound from the series, SPI-1865, demonstrates similar pharmacology in wild-type CD1 mice, Tg2576 mice and Sprague Dawley rats.MethodsAnimals were orally administered either a single dose of SPI-1865 or dosed for multiple days. Aβ levels were measured using a sensitive plate-based ELISA system (MSD) and brain and plasma exposure of drug were assessed by LC/MS/MS.ResultsIn wild-type mice using either dosing regimen, brain Aβ42 and Aβ38 levels were decreased upon treatment with SPI-1865 and little to no statistically meaningful effect on Aβ40 was observed, reflecting the changes observed in vitro. In rats, brain Aβ levels were examined and similar to the mouse studies, brain Aβ42 and Aβ38 were lowered. Comparable changes were also observed in the Tg2576 mice, where Aβ levels were measured in brain as well as plasma and CSF.ConclusionsTaken together, these data indicate that SPI-1865 is orally bioavailable, brain penetrant, and effective at lowering Aβ42 in a dose responsive manner. With this unique profile, the class of compounds represented by SPI-1865 may be a promising new therapy for Alzheimer's disease.
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