Diffusion of MMPs on the Surface of Collagen Fibrils: The Mobile Cell Surface – Collagen Substratum Interface

Remodeling of the extracellular matrix catalyzed by MMPs is central to morphogenetic phenomena during development and wound healing as well as in numerous pathologic conditions such as fibrosis and cancer. We have previously demonstrated that secreted MMP-2 is tethered to the cell surface and activated by MT1-MMP/TIMP-2-dependent mechanism. The resulting cell-surface collagenolytic complex (MT1-MMP)2/TIMP-2/MMP-2 can initiate (MT1-MMP) and complete (MMP-2) degradation of an underlying collagen fibril. The following question remained: What is the mechanism of substrate recognition involving the two structures of relatively restricted mobility, the cell surface enzymatic complex and a collagen fibril embedded in the ECM? Here we demonstrate that all the components of the complex are capable of processive movement on a surface of the collagen fibril. The mechanism of MT1-MMP movement is a biased diffusion with the bias component dependent on the proteolysis of its substrate, not adenosine triphosphate (ATP) hydrolysis. It is similar to that of the MMP-1 Brownian ratchet we described earlier. In addition, both MMP-2 and MMP-9 as well as their respective complexes with TIMP-1 and -2 are capable of Brownian diffusion on the surface of native collagen fibrils without noticeable dissociation while the dimerization of MMP-9 renders the enzyme immobile. Most instructive is the finding that the inactivation of the enzymatic activity of MT1-MMP has a detectable negative effect on the cell force developed in miniaturized 3D tissue constructs. We propose that the collagenolytic complex (MT1-MMP)2/TIMP-2/MMP-2 represents a Mobile Cell Surface – Collagen Substratum Interface. The biological implications of MT1-MMP acting as a molecular ratchet tethered to the cell surface in complex with MMP-2 suggest a new mechanism for the role of spatially regulated peri-cellular proteolysis in cell-matrix interactions

Iron Sucrose Impairs Phagocytic Function and Promotes Apoptosis in Polymorphonuclear Leukocytes

BACKGROUND: With the recent implementation of bundling reimbursement policy the use of intravenous (IV) iron preparations for the management of anemia in the ESRD population has dramatically increased. Iron overload increases the risk of infections in individuals with or without kidney disease. IV iron administration in ESRD patients impairs bacteriocidal capacity of PMNs against Escherichia Coli. These preparations consist of an elemental iron core and a carbohydrate shell. In addition to the iron core the carbohydrate shell may affect PMNs. We therefore examined the effect of iron sucrose, a commonly used preparation, on phagocytic capacity of PMNs from a group of normal individuals against Gram positive (Staphylococcus Aureus) and Gram negative (E. Coli) bacteria. METHODS: Iron sucrose was added to heparinized blood samples at pharmacologically-relevant concentrations and incubated for 4 and 24 hours at 37° C to simulate in vivo condition. Blood samples mixed with equal volume of saline solution served as controls. To isolate the effects of the carbohydrate shell, blood samples were co-treated with the iron chelator, desferrioxamine. RESULTS: Iron sucrose caused significant PMN apoptosis and dose-dependent suppression of phagocytic function against both Gram positive and negative bacteria. These abnormalities were prevented by desferrioxamine which precluded contribution of the carbohydrate shell to the PMN dysfunction. CONCLUSIONS: At pharmacologically-relevant concentrations iron sucrose promotes apoptosis and inhibits phagocytic activities of PMNs. The deleterious effect of iron sucrose is mediated by its elemental iron core, not its carbohydrate shell, and as such may be shared by other IV iron preparations