Jennifer H. Cox

LPS responsiveness and neutrophil chemotaxis in vivo require PMN MMP-8 activity.

We identify matrix metalloproteinase (MMP)-8, the polymorphonuclear (PMN) leukocyte collagenase, as a critical mediator initiating lipopolysaccharide (LPS)-responsiveness in vivo. PMN infiltration towards LPS is abrogated in Mmp8-null mice. MMP-8 cleaves LPS-induced CXC chemokine (LIX) at Ser4∼Val5 and Lys79∼Arg80. LIX bioactivity is increased upon N-terminal cleavage, enhancing intracellular calcium mobilization and chemotaxis upon binding its cognate receptor, CXCR2. As there is no difference in PMN chemotaxis in Mmp8-null mice compared with wild-type mice towards synthetic analogues of MMP-8-cleaved LIX, MMP-8 is not essential for extravasation or cell migration in collagenous matrices in vivo. However, with biochemical redundancy between MMPs 1, 2, 9, and 13, which also cleave LIX at position 4∼5, it was surprising to observe such a markedly reduced PMN infiltration towards LPS and LIX in Mmp8-/- mice. This lack of physiological redundancy in vivo identifies MMP-8 as a key mediator in the regulation of innate immunity. Comparable results were found with CXCL8/IL-8 and CXCL5/ENA-78, the human orthologues of LIX. MMP-8 cleaves CXCL8 at Arg5-Ser6 and at Val7-Leu8 in CXCL5 to activate respective chemokines. Hence, rather than collagen, these PMN chemoattractants are important MMP-8 substrates in vivo; PMN-derived MMP-8 cleaves and activates LIX to execute an in cis PMN-controlled feed-forward mechanism to orchestrate the initial inflammatory response and promote LPS responsiveness in tissue.

Macrophage-specific metalloelastase (MMP-12) truncates and inactivates ELR CXC chemokines and generates CCL2, -7, -8, and -13 antagonists: potential role of the macrophage in terminating polymorphonuclear leukocyte influx

Through the activity of macrophage-specific matrix metalloproteinase-12 (MMP-12), we found that macrophages dampen the lipopolysaccharide (LPS)-induced influx of polymorphonuclear leukocytes (PMNs)-thus providing a new mechanism for the termination of PMN recruitment in acute inflammation. MMP-12 specifically cleaves human ELR(+) CXC chemokines (CXCL1, -2, -3, -5, and -8) at E-LR, the critical receptor-binding motif or, for CXCL6, carboxyl-terminal to it. Murine (m) MMP-12 also cleaves mCXCL1, -2, and -3 at E-LR. MMP-12-cleaved mCXCL2 (macrophage-inflammatory protein-2 [MIP-2]) and mCXCL3 (dendritic cell inflammatory protein-1 [DCIP-1]) lost chemotactic activity. Furthermore, MMP-12 processed and inactivated monocyte chemotactic proteins CCL2, -7, -8, and -13 at position 4-5 generating CCR antagonists. Indeed, PMNs and macrophages in bronchoalveolar lavage fluid were significantly increased 72 hours after intranasal instillation of LPS in Mmp12(-/-) mice compared with wild type. Specificity occurred at 2 levels. Macrophage MMP-1 and MMP-9 did not cleave in the ELR motif. Second, unlike human ELR(+)CXC chemokines, mCXCL5 (LPS-induced CXC chemokine [LIX]) was not inactivated. Rather, mMMP-12 cleavage at Ser4-Val5 activated the chemokine, promoting enhanced PMN early infiltration in wild-type mice compared with Mmp12(-/-) mice 8 hours after LPS challenge in air pouches. We propose that the macrophage, specifically through MMP-12, assists in orchestrating the regulation of acute inflammatory responses by precise proteolysis of ELR(+)CXC and CC chemokines.

Proteolytic processing of SDF-1α reveals a change in receptor specificity mediating HIV-associated neurodegeneration

Proteolytic cleavage of constitutively expressed proteins can generate peptides with novel bioactive properties. Matrix metalloproteinase (MMP)-2 cleaves the 4 amino-terminal residues of the chemokine, stromal cell-derived factor (SDF)-1α, yielding a highly neurotoxic molecule, SDF(5-67), which fails to bind to its cognate receptor, CXCR4. Herein, we detected SDF(5-67) in brain monocytoid cells of HIV-infected persons, particularly in those with HIV-associated dementia. SDF(5-67) activated cell type-specific expression of proinflammatory genes including IL-1β, TNFα, indoleamine 2′,3′-dioxygenase (IDO), and IL-10 in both astrocytic and monocytoid cells (P < 0.05). Unlike SDF-1α, SDF(5-67) caused neuronal membrane perturbations with ensuing neurotoxicity and apoptosis (P < 0.05) through engagement of an inducible receptor. CXCR3 antagonists and siRNA-mediated knockdown of CXCR3 inhibited SDF(5-67)-stimulated neurophysiological changes, neuronal death, and neuroimmune activation (P < 0.05). Moreover SDF(5-67) bound directly to CXCR3 in a competitive manner, mediated by its amino terminus. In vivo neuroinflammation, neuronal loss, and neurobehavioral abnormalities caused by SDF(5-67) (P < 0.05) were prevented by a CXCR3 antagonist. These studies reveal additive neuropathogenic properties exerted by a proteolytically cleaved chemokine as consequences of a change in receptor specificity, culminating in neurodegeneration.

Matrix Metalloproteinase Processing of CXCL11/I-TAC Results in Loss of Chemoattractant Activity and Altered Glycosaminoglycan Binding

The CXCR3 chemokine receptor regulates the migration of Th1 lymphocytes and responds to three ligands: CXCL9/MIG, CXCL10/IP-10, and CXCL11/I-TAC. We screened for potential regulation of T cell responses by matrix metalloproteinase (MMP) processing of these important chemokines. The most potent of the CXCR3 ligands, CXCL11, was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry as a substrate of the PMN-specific MMP-8, macrophage-specific MMP-12, and the general leukocyte MMP-9. The 73-amino acid residue CXCL11 is processed at both the amino and carboxyl termini to generate CXCL11-(5–73), -(5–63), and -(5–58) forms. NH2-terminal truncation results in loss of agonistic properties, as shown in calcium mobilization and chemotaxis experiments using CXCR3 transfectants and human T lymphocytes. Moreover, CXCL11-(5–73) is a CXCR3 antagonist and interestingly shows enhanced affinity to heparin. However, upon COOH-terminal truncation to position 58 there is loss of antagonist activity and heparin binding. Together this highlights an unexpected site for receptor interaction and that the carboxyl terminus is critical for glycosaminoglycan binding, an essential function for the formation of chemokine gradients in vivo. Hence, MMP activity might regulate CXCL11 tissue gradients in two ways. First, the potential of CXCL11-(5–73) to compete active CXCL11 from glycosaminoglycans might lead to the formation of an antagonistic haptotactic chemokine gradient. Second, upon further truncation, MMPs disperse the CXCL11 gradients in a novel way by proteolytic loss of a COOH-terminal GAG binding site. Hence, these results reveal potential new roles in down-regulating Th1 lymphocyte chemoattraction through MMP processing of CXCL11.

Network Analyses Reveal Pervasive Functional Regulation Between Proteases in the Human Protease Web

Network modeling of interactions between proteases and their inhibitors reveals a network of new protein connections and cascades in the protease web.

Stromal cell-derived factors 1α and 1β, inflammatory protein-10 and interferon-inducible T cell chemo-attractant are novel substrates of dipeptidyl peptidase 8

N‐terminal truncation of chemokines by proteases including dipeptidyl peptidase (DP) IV significantly alters their biological activity; generally ablating cognate G‐protein coupled receptor engagement and often generating potent receptor antagonists. DP8 is a recently recognised member of the prolyl oligopeptidase gene family that includes DPIV. Since DPIV is known to process chemokines we surveyed 27 chemokines for cleavage by DP8. We report DP8 cleavage of the N‐terminal two residues of IP10 (CXCL10), ITAC (CXCL11) and SDF‐1 (CXCL12). This has implications for DP8 substrate specificity. Chemokine cleavage and inactivation may occur in vivo upon cell lysis and release of DP8 or in the inactivation of internalized chemokine/receptor complexes.

Ablation of Matrix Metalloproteinase-9 Increases Severity of Viral Myocarditis in Mice

Background— Coxsackievirus B3 (CVB3) causes human myocarditis, which can result in cardiac damage, maladaptive remodeling, and heart failure. Matrix metalloproteinases (MMP)-8 and -9 have been identified in virus-infected myocardium, but their particular roles and underlying mechanisms of effect are unknown. For the first time, we examine the severity of CVB3-induced myocarditis in MMP-8–and MMP-9–deficient mice. Methods and Results— CVB3-infected MMP-8 and MMP-9 knockout (KO) mice and corresponding wild-type (WT) mice were euthanized and harvested at 9 days after infection. Expression of MMP-2, -8, -12, and -13 and tissue inhibitors of MMPs was assessed by zymography or immunoblotting on harvested hearts, and in situ hybridization was performed to detect active infection. Infected MMP-9 KO mice had greater myocardial injury and foci of infection than WT mice despite similar pancreatic infection. Increased fibrosis (10.6±2.7% versus 7.1±2.6%, P=0.04), viral titer, as well as decreased cardiac output, were evident in MMP-9 KO compared with WT mice as assessed by picrosirius red staining, plaque assay, and echocardiography, respectively. Immune infiltration was also greatly increased in MMP-9 KO compared with WT mice (15.2±12.6% versus 2.0±3.0%, P<0.002). Myocardial interferon-&bgr;1, interferon-&ggr;, interleukin-6, interleukin-10, and macrophage inflammatory protein-1&agr; expression was elevated in MMP-9 KO mice as measured by quantitative real-time polymerase chain reaction and ELISA. In contrast, MMP-8 KO mice had the same degree of cardiac injury, fibrosis, and viral infection as their WT counterparts. Conclusions— During acute CVB3 infection, MMP-9 appears necessary to halt virus propagation in the heart, promote proper immune infiltration and remodeling, and preserve cardiac output.

Collagenase-2 Deficiency or Inhibition Impairs Experimental Autoimmune Encephalomyelitis in Mice

Matrix metalloproteinases (MMPs) have been implicated in a variety of human diseases, including neuroimmunological disorders such as multiple sclerosis. However, the recent finding that some MMPs play paradoxical protective roles in these diseases has made necessary the detailed study of the specific function of each family member in their pathogenesis. To determine the relevance of collagenase-2 (MMP-8) in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, we have performed two different analyses involving genetic and biochemical approaches. First, we have analyzed the development of EAE in mutant mouse deficient in MMP-8, with the finding that the absence of this proteolytic enzyme is associated with a marked reduction in the clinical symptoms of EAE. We have also found that MMP-8-/- mice exhibit a marked reduction in central nervous system-infiltrating cells and demyelinating lesions. As a second approach, we have carried out a pharmacological inhibition of MMP-8 with a selective inhibitor against this protease (IC50 = 0.4 nm). These studies have revealed that the administration of the MMP-8 selective inhibitor to mice with EAE also reduces the severity of the disease. Based on these findings, we conclude that MMP-8 plays an important role in EAE development and propose that this enzyme may be a novel therapeutic target in human neuro-inflammatory diseases such as multiple sclerosis.

Matrix metalloproteinase 8 deficiency in mice exacerbates inflammatory arthritis through delayed neutrophil apoptosis and reduced caspase 11 expression

OBJECTIVE Neutrophil accumulation is balanced by both cell infiltration and cell clearance, the controls of which are pivotal in the pathogenesis of rheumatoid arthritis (RA) and other chronic inflammatory diseases. Of the neutrophil-specific proteases, matrix metalloproteinase 8 (MMP-8; also known as neutrophil collagenase or collagenase 2) is traditionally viewed as being crucial for collagen degradation and hence cell migration and infiltration. This study was undertaken to examine the role of MMP-8 in a murine model of spontaneous RA. METHODS MMP-8(-/-) mice were backcrossed onto the Fas-defective MRL/lpr background, a mouse strain characterized by systemic autoimmunity including spontaneous autoimmune arthritis. Arthritis was induced with Freunds complete adjuvant and clinical disease and histologic parameters were assessed. RESULTS MMP-8(-/-) mice had earlier and more severe joint inflammation than their MMP-8(+/+) counterparts, coupled with a massive accumulation of neutrophils in synovial tissue, an unexpected result considering the commonly held view that MMP-8 has important extracellular matrix-degradative functions. Protease and protease inhibitor analysis of MMP-8(-/-) mouse neutrophils by CLIP-CHIP microarray revealed very little additional change in protease levels except for low expression of the apoptosis initiator caspase 11. This was confirmed at the protein level in unstimulated, lipopolysaccharide-treated, and interferon-γ-treated MMP-8(-/-) mouse neutrophils. Downstream of caspase 11, the activity of the apoptosis executioner caspase 3 was consequently reduced in MMP-8(-/-) mouse neutrophils, translating to reduced neutrophil apoptosis and cell accumulation compared with wild-type mouse cells. CONCLUSION Our findings indicate that MMP-8 is not essential for neutrophil migration in arthritis and likely other autoimmune diseases. Rather, MMP-8 is important for normal rates of neutrophil apoptosis and hence regulates cell clearance. Because MMP-8 deficiency leads to an exaggerated accumulation of neutrophil infiltrates due to delayed apoptosis and concurrent pathologic changes associated with dramatically increased neutrophil infiltration, MMP-8 is antiinflammatory and therefore a drug antitarget in the treatment of arthritis.

Active site specificity profiling datasets of matrix metalloproteinases (MMPs) 1, 2, 3, 7, 8, 9, 12, 13 and 14

The data described provide a comprehensive resource for the family-wide active site specificity portrayal of the human matrix metalloproteinase family. We used the high-throughput proteomic technique PICS (Proteomic Identification of protease Cleavage Sites) to comprehensively assay 9 different MMPs. We identified more than 4300 peptide cleavage sites, spanning both the prime and non-prime sides of the scissile peptide bond allowing detailed subsite cooperativity analysis. The proteomic cleavage data were expanded by kinetic analysis using a set of 6 quenched-fluorescent peptide substrates designed using these results. These datasets represent one of the largest specificity profiling efforts with subsequent structural follow up for any protease family and put the spotlight on the specificity similarities and differences of the MMP family. A detailed analysis of this data may be found in Eckhard et al. (2015) [1]. The raw mass spectrometry data and the corresponding metadata have been deposited in PRIDE/ProteomeXchange with the accession number PXD002265.