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dc.contributor.authorPetrey, Aaron Christopher
dc.description.abstractThe severe pediatric disorder Mucolipidosis II (ML-II) is characterized by multiple developmental defects including pronounced skeletal, craniofacial, and cartilage abnormalities. ML-II patients have mutations in the gene encoding the catalytic activity of the enzyme GlcNAc-1- phosphotransferase leading to impaired biosynthesis of mannose-6- phosphate (Man-6-P), the key recognition marker for sorting of lysosomal hydrolases to lysosomes. Though the genetic bases for this disorder are now well established, the molecular mechanisms underlying the pathophysiology of individuals with ML-II remain poorly understood. In an effort to investigate the developmental defects of this disease we analyzed the expression level and activity of a number of lysosomal hydrolases using a zebrafish model for ML-II. The present work addresses the role of lysosomal and matrix proteases in the cartilage pathogenesis of ML-II. Several cathepsins and matrix metalloproteinases (MMPs) were found to be present at elevated levels in ML-II. Analysis of cathepsin K, an enzyme involved in bone and cartilage homeostasis, revealed the enzyme is tightly regulated during early cartilage development in zebrafish. Further studies showed cathepsin K is present at normal levels but subject to enhanced proteolytic activation in ML-II. The pharmacological or genetic suppression of cathepsin K was shown to alleviate several aspects of the craniofacial defects as well as the elevated activities of other proteases. Cathepsin K was found to be a highly Man-6-P modified enzyme capable of functioning at a pH consistent with the extracellular space, and deficient within sorted chondrocytes. By contrast, the related enzyme cathepsin D was poorly Man-6-P modified and present at normal levels in chondrocytes, suggesting cathepsin-specific hypersecretion occurs in zebrafish. Removal of specific N-glycans of cathepsin K and exogenous expression in wildtype embryos revealed that the enzyme is subject to enhanced activation upon loss of Man-6-P modification and is capable of generating cartilage phenotypes analogous to those seen in ML-II. Further studies using a feline model revealed that increased MMP activity is a general feature of ML-II, and is accompanied by the increased expression of proinflammatory cytokines. Collectively, these results indicate that the inappropriate extracellular activity of cathepsin K plays a central role in the cartilage pathogenesis of ML-II.
dc.subjectn-linked glycosylation
dc.subjectmannose 6-phosphate
dc.subjectMucolipidosis II
dc.subjectlysosomal storage disorder
dc.subjectmatrix metalloproteinase
dc.titleInvestigating Mucolipidosis II
dc.title.alternativea role for proteases in cartilage pathogenesis
dc.description.departmentBiochemistry and Molecular Biology
dc.description.majorBiochemistry and Molecular Biology
dc.description.advisorRichard Steet
dc.description.committeeRichard Steet
dc.description.committeeLance Wells
dc.description.committeeLianchun Wang
dc.description.committeeMichael Tiemeyer

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