Enzymatic proteolysis of cell surface proteins and extracellular matrix (ECM) is critical for tissue homeostasis and cell signaling. These proteolytic activities are mediated predominantly by a ...family of proteases termed matrix metalloproteinases (MMPs). The growing evidence in recent years that ECM and non-ECM bioactive molecules (e.g., growth factors, cytokines, chemokines, on top of matrikines and matricryptins) have versatile functions redefines our view on the roles matrix remodeling enzymes play in many physiological and pathological processes, and underscores the notion that ECM proteolytic reaction mechanisms represent master switches in the regulation of critical biological processes and govern cell behavior. Accordingly, MMPs are not only responsible for direct degradation of ECM molecules but are also key modulators of cardinal bioactive factors. Many attempts were made to manipulate ECM degradation by targeting MMPs using small peptidic and organic inhibitors. However, due to the high structural homology shared by these enzymes, the majority of the developed compounds are broad-spectrum inhibitors affecting the proteolytic activity of various MMPs and other zinc-related proteases. These inhibitors, in many cases, failed as therapeutic agents, mainly due to the bilateral role of MMPs in pathological conditions such as cancer, in which MMPs have both pro- and anti-tumorigenic effects. Despite the important role of MMPs in many human diseases, none of the broad-range synthetic MMP inhibitors that were designed have successfully passed clinical trials. It appears that, designing highly selective MMP inhibitors that are also effective in vivo, is not trivial. The challenges related to designing selective and effective metalloprotease inhibitors, are associated in part with the aforesaid high structural homology and the dynamic nature of their protein scaffolds. Great progress was achieved in the last decade in understanding the biochemistry and biology of MMPs activity. This knowledge, combined with lessons from the past has drawn new “boundaries” for the development of the next-generation MMP inhibitors. These novel agents are currently designed to be highly specific, capable to discriminate between the homologous MMPs and ideally administered as a short-term topical treatment. In this review we discuss the latest progress in the fields of MMP inhibitors in terms of structure, function and their specific activity. The development of novel highly specific inhibitors targeting MMPs paves the path to study complex biological processes associated with ECM proteolysis in health and disease. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.
•MMPs are structurally homologous enzymes, involved in homeostasis and pathology.•Specifically targeting individual MMPs in vivo is challenging.•Protein engineering is utilized to produce highly selective and specific MMPIs.•Latest biochemical and structural data reveals new inhibitory hotspots in MMPs.•Next-generation engineered MMPIs specifically and selectively target these hotspots.
The extracellular matrix (ECM) is a key noncellular component in all organs and tissues. It is composed of a large number of proteins including collagens, glycoproteins (GP), and ECM‐associated ...proteins, which show diversity of biochemical and biophysical functions. The ECM is dynamic both in normal physiology of tissues and under pathological conditions. One cellular phenomenon associated with changes in both ECM components expression and in ECM remodeling enzymes secretion is cellular senescence. It represents a stable state form of cell cycle arrest induced in proliferating cells by various forms of stress. Short‐term induction of senescence is essential for tumor suppression and tissue repair. However, long‐term presence of senescent cells in tissues may have a detrimental role in promoting tissue damage and aging. Up to date, there is insufficient knowledge about the interplay between the ECM and senescence cells. Since changes in the ECM occur in many physiological and pathological conditions in which senescent cells are present, a better understanding of ECM‐senescence interactions is necessary. Here, we will review the functions of the different ECM components and will discuss the current knowledge about their regulation in senescent cells and their influence on the senescence state.
One cellular phenomena associated with changes in the extracellular matrix (ECM) is cellular senescence. The interplay between the ECM and senescent cells is complex and requires further investigation. Changes in the ECM occur in many physiological and pathological conditions in which senescent cells are present and secrete components of senescence associated secretory phenotype that interact with ECM. Here, we review current knowledge about the different ECM components and their regulation in senescence state.
Phagocytes, such as tumor‐associated macrophages (TAMs) and tumor‐associated neutrophils (TANs), are abundant in the stroma of experimental and human tumors and are locally educated to mediate ...important biological functions that profoundly affect tumor initiation, growth, and dissemination. Of considerable importance is the noncellular component of the tumor microenvironment, namely—the extracellular matrix (ECM). This milieu is often overlooked due to its complexity and vast heterogeneity. Biophysical and biomechanical cues provided by the dynamically evolving tumorigenic ECM fundamentally modulate every behavioral facet of the cancer cells and of associated stromal cells. In this review, we discuss the intricate interplay between phagocytes and ECM that are lined up to support tumor progression. TAMs and TANs shape the tumorigenic ECM by providing key matrix‐remodeling enzymes and structural proteins and in turn, the altered tumor ECM modulates their migration and function. A better mechanistic comprehension of this reciprocal dependence has exciting implications for the development of new therapeutic options for cancer.
Dysregulated deposition of extracellular matrix (ECM) is a hallmark of many tumors and fosters tumor progression and dissemination. Phagocytic immune cells actively participate in ECM organization by providing ECM‐remodeling enzymes and core molecules. In turn, the altered tumor ECM modulates their migration and function. Here, we discuss this intricate tumorigenic interplay, which has exciting implications for new therapeutic treatments.
Tumor-associated macrophages (TAMs) promote tumor development, invasion, and dissemination by various mechanisms. In this study, using an orthotopic colorectal cancer (CRC) model, we found that ...monocyte-derived TAMs advance tumor development by the remodeling of its extracellular matrix (ECM) composition and structure. Unbiased transcriptomic and proteomic analyses of (a) TAM-abundant and -deficient tumor tissues and (b) sorted tumor-associated and -resident colonic macrophage subpopulations defined a distinct TAM-induced ECM molecular signature composed of an ensemble of matricellular proteins and remodeling enzymes they provide to the tumor microenvironment. Remarkably, many of these ECM proteins are specifically increased in human CRC versus healthy colon. Specifically, we demonstrate that although differentiating into TAMs, monocytes up-regulate matrix-remodeling programs associated with the synthesis and assembly of collagenous ECM, specifically collagen types I, VI, and XIV. This finding was further established by advanced imaging showing that TAMs instruct the deposition, cross-linking, and linearization of collagen fibers during tumor development, especially at areas of tumor invasiveness. Finally, we show that cancer-associated fibroblasts are significantly outnumbered by TAMs in this model and that their expression of collagen XIV and I is reduced by TAM deficiency. Here, we outline a novel TAM protumoral function associated with building of the collagenous ECM niche.
The adult mammalian heart is non-regenerative owing to the post-mitotic nature of cardiomyocytes. The neonatal mouse heart can regenerate, but only during the first week of life. Here we show that ...changes in the composition of the extracellular matrix during this week can affect cardiomyocyte growth and differentiation in mice. We identify agrin, a component of neonatal extracellular matrix, as required for the full regenerative capacity of neonatal mouse hearts. In vitro, recombinant agrin promotes the division of cardiomyocytes that are derived from mouse and human induced pluripotent stem cells through a mechanism that involves the disassembly of the dystrophin-glycoprotein complex, and Yap- and ERK-mediated signalling. In vivo, a single administration of agrin promotes cardiac regeneration in adult mice after myocardial infarction, although the degree of cardiomyocyte proliferation observed in this model suggests that there are additional therapeutic mechanisms. Together, our results uncover a new inducer of mammalian heart regeneration and highlight fundamental roles of the extracellular matrix in cardiac repair.
Metal ions play essential roles in many aspects of biological chemistry. Detecting their presence and location in proteins and cells is important for understanding biological function. Conventional ...structural methods such as X-ray crystallography and cryo-transmission electron microscopy can identify metal atoms on protein only if the protein structure is solved to atomic resolution. We demonstrate here the detection of isolated atoms of Zn and Fe on ferritin, using cryogenic annular dark-field scanning transmission electron microscopy (cryo-STEM) coupled with single-particle 3D reconstructions. Zn atoms are found in a pattern that matches precisely their location at the ferroxidase sites determined earlier by X-ray crystallography. By contrast, the Fe distribution is smeared along an arc corresponding to the proposed path from the ferroxidase sites to the mineral nucleation sites along the twofold axes. In this case the single-particle reconstruction is interpreted as a probability distribution function based on the average of individual locations. These results establish conditions for detection of isolated metal atoms in the broader context of electron cryo-microscopy and tomography.
Progressive loss of organ function in most organs is associated with fibrosis, a tissue state associated with abnormal matrix buildup. If highly progressive, the fibrotic process eventually leads to ...organ failure and death. Fibrosis is a basic connective tissue lesion defined by the increase in the amount of fibrillar extracellular matrix (ECM) components in a tissue or organ. In addition, intrinsic changes in important structural cells can induce the fibrotic response by regulating the differentiation, recruitment, proliferation and activation of extracellular matrix-producing myofibroblasts. ECM enzymes belonging to the family of matrix metalloproteinases (MMPs) and lysyl oxidases (LOXs) play a crucial role in ECM remodeling and regeneration. MMPs have a catalytic role in degradation of ECM, whereas LOX/LOXLs mediate ECM, especially collagen, cross-linking and stiffening. Importantly, enzymes from both families are elevated during the fibrotic response to tissue injury and its resolution. Yet, the apparent molecular competition or antagonistic activities of these enzyme families during the various stages of fibrosis is often overlooked. In this review, we discuss the diverse roles of MMPs and LOX/LOXL2 in chronic organ fibrosis. Finally, we review contemporary therapeutic strategies for fibrosis treatment, based on neutralization of MMP and LOX activity, as well as the development of novel drug delivery approaches.
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•Extracellular matrix enzymes play a crucial role in tissue remodeling.•Excessive accumulation of ECM during inflammation and wound healing lead to fibrosis.•Matrix metalloproteinases (MMPs) catalyze the degradation of ECM, whereas lysyl oxidases (LOX/LOXLs) mediate ECM covalent cross-linking and stiffness.•MMPs and LOXs expression levels are altered during fibrosis and these molecules are highlighted as novel fibrotic biomarkers.•Several therapeutic tools have been developed, in order to attenuate fibrosis via targeting MMPs and LOXs.
The inflammatory response in the injured spinal cord, an immune privileged site, has been mainly associated with the poor prognosis. However, recent data demonstrated that, in fact, some leukocytes, ...namely monocytes, are pivotal for repair due to their alternative anti-inflammatory phenotype. Given the pro-inflammatory milieu within the traumatized spinal cord, known to skew monocytes towards a classical phenotype, a pertinent question is how parenchymal-invading monocytes acquire resolving properties essential for healing, under such unfavorable conditions. In light of the spatial association between resolving (interleukin (IL)-10 producing) monocytes and the glial scar matrix chondroitin sulfate proteoglycan (CSPG), in this study we examined the mutual relationship between these two components. By inhibiting the de novo production of CSPG following spinal cord injury, we demonstrated that this extracellular matrix, mainly known for its ability to inhibit axonal growth, serves as a critical template skewing the entering monocytes towards the resolving phenotype. In vitro cell culture studies demonstrated that this matrix alone is sufficient to induce such monocyte polarization. Reciprocal conditional ablation of the monocyte-derived macrophages concentrated at the lesion margins, using diphtheria toxin, revealed that these cells have scar matrix-resolving properties. Replenishment of monocytic cell populations to the ablated mice demonstrated that this extracellular remodeling ability of the infiltrating monocytes requires their expression of the matrix-degrading enzyme, matrix metalloproteinase 13 (MMP-13), a property that was found here to be crucial for functional recovery. Altogether, this study demonstrates that the glial scar-matrix, a known obstacle to regeneration, is a critical component skewing the encountering monocytes towards a resolving phenotype. In an apparent feedback loop, monocytes were found to regulate scar resolution. This cross-regulation between the glial scar and monocytes primes the resolution of this interim phase of spinal cord repair, thereby providing a fundamental platform for the dynamic healing response.
Solvent dynamics can play a major role in enzyme activity, but obtaining an accurate, quantitative picture of solvent activity during catalysis is quite challenging. Here, we combine terahertz ...spectroscopy and X-ray absorption analyses to measure changes in the coupled water-protein motions during peptide hydrolysis by a zinc-dependent human metalloprotease. These changes were tightly correlated with rearrangements at the active site during the formation of productive enzyme-substrate intermediates and were different from those in an enzyme-inhibitor complex. Molecular dynamics simulations showed a steep gradient of fast-to-slow coupled protein-water motions around the protein, active site and substrate. Our results show that water retardation occurs before formation of the functional Michaelis complex. We propose that the observed gradient of coupled protein-water motions may assist enzyme-substrate interactions through water-polarizing mechanisms that are remotely mediated by the catalytic metal ion and the enzyme active site.
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