Meprin A Impairs Epithelial Barrier Function, Enhances Monocyte

23 Meprin metalloproteases are highly expressed at the luminal interface of the intestine and 24 kidney and in certain leukocytes. Meprins cleave a variety of substrates in vitro including 25 extracellular matrix proteins, adherens junction proteins and cytokines, and have been 26 implicated in a number of inflammatory diseases. The linkage between results in vitro 27 and pathogenesis however, has not been elucidated. The current study aimed to determine 28 whether meprins are determinative factors in disrupting the barrier function of the 29 epithelium. Active meprin A or meprin B applied to the Madin-Darby canine kidney 30 (MDCK) cell monolayers increased permeability to fluorescein isothiocyanate (FITC)31 dextran and disrupted immunostaining of the tight junction protein occludin but not 32 claudin-4. Meprin A, but not meprin B, cleaved occludin in MDCK monolayers. Studies 33 with recombinant occludin demonstrated meprin A cleaves the protein between Gly100 34 and Ser101 on the first extracellular loop. In vivo experiments demonstrated that meprin 35 A infused into the mouse bladder increased the epithelium permeability to sodium 36 fluorescein. Furthermore, monocytes from meprin knockout (KO) mice on the C57BL/6 37 background were less able to migrate through an MDCK monolayer than monocytes from 38 wild-type (WT) counterparts. These results demonstrate the capability of meprin A to 39 disrupt epithelial barriers and implicate occludin as one of the important targets of 40 meprin A that may modulate inflammation. 41 42