All ETDs from UAB

Advisory Committee Chair

Rosa Serra

Advisory Committee Members

Alan W Eberhardt

Joanne Murphy-Ullrich

Susan L Bellis

Timothy M Wick

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

Articular cartilage is a special type of hyaline cartilage present at the end of long bones and facilitates smooth functioning of joints and transfer of load. While most cartilage elements in the body are transient, articular cartilage is permanent and functions throughout life. Osteoarthritis (OA) is a joint degenerative disease and the leading cause of disability in the industrialized world. A multitude of factors including aging, orthopedic trauma, genetics etc. have been associated with OA. Transforming growth factor-ß (TGF-ß) is a multifunctional polypeptide which plays an important role in chondrocyte proliferation, differentiation and synthesis of extracellular matrix. Previously, mice with dominant negative interference of TGF-ß type II receptor (DNIIR) was shown to develop joint degeneration and exhibit human OA symptoms. Similar results were found in mice with other mutations in the TGF-ß signaling pathway, but none of these studies characterized the biomechanical, biochemical and gene expression changes in the articular cartilage of these mutants. In order to fully understand the role of TGF-ß in the maintenance of articular cartilage, we employed the DNIIR model in our studies. Biomechanical tests revealed a significant decrease in indentation stiffness in DNIIR articular cartilage as compared to wild type mice. From microarray of bovine articular chondrocytes cultured in micromass and treated/left untreated with TGF-ß, we generated direct targets of TGF-ß which included genes such as Papss2 and Plod2 that regulate global post-translational modifications of the extracellular matrix. As Papss2 is crucial for sulfation of cartilage glycosaminoglycans, we examined Papss2 expression and found marked reduction of Papss2 mRNA and protein in articular cartilage of DNIIR mice as compared to wild type. By immunofluorescence and Alcian Blue critical electrolyte staining we demonstrated that reduction in Papss2 led to a decrease in sulfation of cartilage matrix especially chondroitin-4-sulfate and upregulation of unsulfated chondroitin in the DNIIR mice with no change in aggrecan core protein. In support of TGF-&beta regulation of Papss2, we also show that Tgfbr2 homozygous null mice exhibit a severe decrease in Papss2 expression levels embryonically. Overall, we propose that TGF-ß maintains the biomechanical integrity by regulating Papss2 and sulfation of glycosaminoglycans in mouse articular cartilage.

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Engineering Commons

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