Endothelial MT1-MMP targeting limits intussusceptive angiogenesis and colitis via TSP1/nitric oxide axis

Pathological angiogenesis contributes to cancer progression and chronic inflammatory diseases. In inflammatory bowel disease, the microvasculature expands by intussusceptive angiogenesis (IA), a poorly characterized mechanism involving increased blood flow and splitting of pre-existing capillaries. In this report, mice lacking the protease MT1-MMP in endothelial cells (MT1iΔEC ) presented limited IA in the capillary plexus of the colon mucosa assessed by 3D imaging during 1% DSS-induced colitis. This resulted in better tissue perfusion, preserved intestinal morphology, and milder disease activity index. Combined in vivo intravital microscopy and lentiviral rescue experiments with in vitro cell culture demonstrated that MT1-MMP activity in endothelial cells is required for vasodilation and IA, as well as for nitric oxide production via binding of the C-terminal fragment of MT1-MMP substrate thrombospondin-1 (TSP1) to CD47/αvβ3 integrin. Moreover, TSP1 levels were significantly higher in serum from IBD patients and in vivo administration of an anti-MT1-MMP inhibitory antibody or a nonamer peptide spanning the αvβ3 integrin binding site in TSP1 reduced IA during mouse colitis. Our results identify MT1-MMP as a new actor in inflammatory IA and a promising therapeutic target for inflammatory bowel disease.

The protease MT1-MMP drives a combinatorial proteolytic program in activated endothelial cells

The mechanism by which proteolytic events translate into biological responses is not well understood. To explore the link of pericellular proteolysis to events relevant to capillary sprouting within the inflammatory context, we aimed at the identification of the collection of substrates of the protease MT1-MMP in endothelial tip cells induced by inflammatory stimuli. We applied quantitative proteomics to endothelial cells (ECs) derived from wild-type and MT1-MMP-null mice to identify the substrate repertoire of this protease in TNF-α-activated ECs. Bioinformatics analysis revealed a combinatorial MT1-MMP proteolytic program, in which combined rather than single substrate processing would determine biological decisions by activated ECs, including chemotaxis, cell motility and adhesion, and vasculature development. MT1-MMP-deficient ECs inefficiently processed several of these substrates (TSP1, CYR61, NID1, and SEM3C), validating the model. This novel concept of MT1-MMP-driven combinatorial proteolysis in angiogenesis might be extendable to proteolytic actions in other cellular contexts.

Altered apoptosis of inflammatory neutrophils in MMP-9-deficient mice is due to lower expression and activity of caspase-3

Matrix metalloproteinase 9 (MMP-9) is a Zn(2+)-dependent endopeptidase that degrades some of the components of basement membranes and extracellular matrix and thus participates in leukocyte infiltration during inflammation. In a model of zymosan peritonitis, neutrophil infiltration in MMP-deficient (MMP-9(-/-)) mice was significantly weaker at the time of their maximal influx in wild-type mice (6h). However, during the late stages of peritonitis (24h) an extended accumulation of neutrophils was observed in MMP-9(-/-)versus the wild-type mice. Recently, we reported that the ratio of apoptosis of inflammatory leukocytes is impaired in MMP-9(-/-) mice during late peritonitis and the process depends on COX-1-driven PGE(2). Here we scrutinized the alterations in apoptotic mechanisms by comparisons between MMP-9(-/-) and the wild-type mice. Altered apoptosis occurred only during late (24h) peritonitis and concerned only neutrophils, and not macrophages, mast cells or lymphocytes. Furthermore, expression and activity of caspases was altered in MMP-9(-/-) animals, delayed for caspase-8 and -9, and decreased in the case of caspase-3. Also the expression of Bax/Bcl-2 proteins was changed in MMP-9(-/-) mice. These changes, and in particular the impaired neutrophil apoptosis and weaker caspase-3 activity, were restored by the selective COX-1 inhibition. We conclude that in mice lacking MMP-9 the enhanced COX-1-PGE(2) decreases caspase-3 expression and activity leading to impaired apoptosis of inflammatory neutrophils resulting in abnormal accumulation of the cells at the inflammatory focus. The data also reinforce the notion that MMP-9 is a key enzyme in neutrophil biology.

Inflammatory macrophages, and not only neutrophils, die by apoptosis during acute peritonitis

The central paradigm says that during inflammation, after completing their function, granulocytes die apoptotically in periphery to avoid destruction of self-tissues. Here we aimed to investigate the kinetic aspect of inflammatory leukocyte apoptosis and verify whether apart from neutrophils also other inflammatory leukocytes numerously undergo apoptosis. We observed that in physiological conditions, less than 7% of either resident peritoneal macrophages or lymphocytes die apoptotically. The studies on a model of acute zymosan-induced peritoneal inflammation revealed that there are two waves of inflammatory leukocyte apoptosis. The first wave corresponds to the time of maximal neutrophil accumulation in peritoneum (6h) and the apoptotic death indeed concerns mostly neutrophils (over 30% of those cells), but also more macrophages die at this time (>10%). The second wave (at 3 days) concerns mostly macrophages (20% versus 3-6% for other populations) and coincides with the resolution of inflammation and the dominant presence of macrophages. In contrast, numbers of apoptotic T (1-3%) and B (approximately 5%) cells do not significantly change during the whole peritonitis. The two waves of apoptosis concur with an increase of caspase-8, -9 and -3 at the transcript and activity levels. The apoptosis inducer TNF-alpha is produced only during first hours while nitric oxide throughout all inflammation. Moreover, during the whole course of peritonitis the expression of pro-apoptotic Bax dominates over anti-apoptotic Bcl-2. In conclusion, we characterized kinetics of apoptotic death of inflammatory leukocytes during acute peritoneal inflammation and revealed that both phagocyte populations (neutrophils and macrophages) die numerously in peritoneum.

Iteration model of starch hydrolysis by amylolytic enzymes

An elaborate computer program to simulate the process of starch hydrolysis by amylolytic enzymes was been developed. It is based on the Monte Carlo method and iteration kinetic model, which predict productive and non-productive amylase complexes with substrates. It describes both multienzymatic and multisubstrate reactions simulating the "real" concentrations of all components versus the time of the depolymerization reaction the number of substrates, intermediate products, and final products are limited only by computer memory. In this work, it is assumed that the "proper" substrate for amylases is the glucoside linkages in starch molecules. Dynamic changes of substrate during the simulation adequately influence the increase or decrease of reaction velocity, as well as the kinetics of depolymerization. The presented kinetic model, can be adapted to describe most enzymatic degradations of a polymer. This computer program has been tested on experimental data obtained for alpha- and beta-amylases.