Proteases and protease inhibitors operate in the pericellular environment to provide proteolysis essential for cytokine/growth factor maturation, matrix remodeling, signaling receptor activation, ion channel activity, and more. Our Section studies the biochemistry, biology, and pathology of cell surface proteolysis, with emphasis on determining its contribution to the development, homeostasis, regeneration, and malignant transformation of oral tissues, thereby providing a foundation for developing improved treatments of diseases of the oral cavity. Research accomplished Identification of a fibrosis-protective role of intracellular collagen degradation: Our previous research has shown that the collagen endocytosis receptor, uPARAP, predominantly is expressed in bone-forming tissues and that it is important for collagen turnover during osteogenesis. uPARAP, however, frequently becomes expressed by various mesenchymal cell populations after tissue injury, suggesting that it could be involved in regulating collagen deposition in healing tissues and, therefore, could have a fibrosis-protective role. To challenge this hypothesis, we investigated the expression and functional role of uPARAP in liver cirrhosis induced by chronic CCl4 exposure in collaboration with Lars Engelholm and Niels Behrendt, University of Copenhagen. uPARAP expression was low in the unchallenged mouse liver, but the receptor became highly expressed in hepatic stellate cells after injury. High uPARAP expression in hepatic stellate cells was also observed in fibrotic human liver. Furthermore, genetic elimination of uPARAP markedly increased collagen deposition during hepatic regeneration, resulting in increased liver fibrosis. In collaboration with Allison Eddy, University of Washington, Seattle, a similar injury-induced upregulation of uPARAP in myofibroblasts and macrophages and a fibrosis protective role of uPARAP, were observed after experimental kidney injury. Taken together, these studies reveal a novel and important role of the intracellular collagen degradation pathway in the protection of adult organs from injury-induced scarring. Identification of capillary morphogenesis protein-2 in maintenance of collagen homeostasis and mouse parturition: Capillary morphogenesis protein-2 (CMG2) is a recently identified cell surface receptor for collagen. Mutations in CMG2 have been shown to cause two human autosomal recessive disorders, juvenile hyaline fibromatosis and infantile systemic hyalinosis, both characterized by excess hyaline material deposition in connective tissues. To better understand the role of CMG2 in physiology, we performed detailed histological analyses of the CMG2-deficient mice. While no morphological or histological defects were observed in male mice deficient in CMG2, CMG2-deficient female mice were unable to produce any offspring due to a specific defect in parturition. We found that deletion of CMG2 resulted in a diffuse deposition of collagen within the myometrium of females, causing remarkable morphological changes to their uteri. This collagen accumulation also led to loss a of myometrial smooth muscle cells, likely disabling uterine contractile function during parturition. As a consequence, even though pregnant CMG2-deficient mice were able to carry the gestation to full term, they were unable to deliver pups. However, the fully-developed fetuses could be successfully delivered by Cesarean section and survived to adulthood when fostered. These data provide evidence that CMG2 is critical for maintaining collagen homeostasis and reveal an indispensable role of the receptor in murine parturition. Establishment of a link between reduced pericellular proteolysis, chronic epithelial inflammation, and inflammation-associated carcinogenesis: The genesis of many complex inflammatory/immune disorders (asthma, atopic dermatitis, eczema, inflammatory bowel disease IBD, and primary Sjgrens syndrome) recently has been linked to subtle defects in the epithelial barrier, causing enhanced or altered exposure of the immune system to antigens expressed by the commensal microbiota. In collaborations with Toni Antalis, university of Maryland, we therefore explored the long-term consequences of intestinal epithelial barrier impairment, caused by reduced matriptase proteolytic activity, on immune homeostasis. Interestingly, elimination of matriptase from the gastrointestinal tract resulted in a syndrome that closely resembled human inflammatory bowel disease (IBD), which was promoted by exposure of the colonic mucosa to the commensal microbiota. This inflammatory syndrome rapidly progressed to colon adenocarcinoma, which strikingly resembled human colitis-associated colorectal cancers. This finding demonstrates that inflammation-associated carcinogenesis can be initiated and promoted solely by an intrinsic intestinal permeability barrier perturbation. Interestingly, inflamed colonic tissues from individuals with IBD (Crohn's disease as well as ulcerative colitis) displayed significantly reduced matriptase protein and mRNA, and cytokines implicated in barrier disruption during IBD strongly suppressed matriptase expression in colonic epithelial monolayers. Taken together, these studies provide a tentative and intriguing link between the derailment of a matriptase-dependent proteolytic pathway and the initiation of human complex inflammatory/immune disorders. A HAI-1 and HAI-2-regulated prostasin (CAP1/PRSS8)-matriptase axis that is active in multiple steps of development: Vertebrate embryogenesis is dependent upon a series of precisely coordinated cell proliferation, migration, and differentiation events. Recently, the execution of these events was shown to be guided in part by extracellular cues provided by focal pericellular proteolysis by a newly identified family of membrane-anchored serine proteases. We have found that two of these membrane-anchored serine proteases, prostasin and matriptase, constitute a single proteolytic signaling cascade that is active at multiple stages of development. Furthermore, we show that failure to precisely regulate the enzymatic activity of both prostasin and matriptase by two developmentally co-expressed transmembrane serine protease inhibitors, hepatocyte growth factor activator inhibitor-1 and -2, causes an array of developmental defects, including clefting of the embryonic ectoderm, lack of placental labyrinth formation, and inability to close the neural tube. Our study also provides evidence that the failure to regulate the prostasin-matriptase cascade may derail morphogenesis independent of the activation of known protease-regulated developmental signaling pathways. Because hepatocyte growth factor activator inhibitor-deficiency in humans is known to cause an assortment of common and rare developmental abnormalities, the aberrant activity of the prostasin-matriptase cascade identified in our study may importantly contribute to genetic as well as sporadic birth defects in humans.
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