Graduation Date

Spring 5-6-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Molecular Genetics & Cell Biology

First Advisor

Andrew T. Dudley

Abstract

Throughout fetal and adolescent development, bone growth is regulated by fine-tuned and controlled maturation of chondrocytes through a cartilaginous template called the growth plate. Bone growth rate is controlled through cell enlargement and extracellular matrix deposition, while the polarized arrangement of proliferative chondrocytes into columns aligned with the long axis of the bone potentiate growth. Chondrocytes are surrounded by a complex three-dimensional arrangement of matrix molecules, all of which are secreted by chondrocytes and assembled/remodeled to support the biological functions of the cell. Adhesion receptors found on the cell membrane of chondrocytes are crucial to the organization of matrix proteins and act to transduce mechanical forces from the matrix to the chondrocyte. The work contained in this dissertation characterizes the utility of an in vitro culture system that is sensitive enough to study cell-autonomous matrix development mechanisms and understand the contribution of adhesion molecules like CD44 and integrins in matrix development under both static and dynamic compression environments. Hydrodynamic inflation of the pericellular matrix compartment with hyaluronan and aggrecan is dependent on binding of hyaluronan to CD44. This inflation is one of the requirements for mechano-responsiveness of chondrocytes to compressive strain. Beta1 integrin is not required for expansion of the PCM compartment; however, work contained in this dissertation suggests a primary role for beta1 integrin in driving chondrocyte rotation to form proliferative columns. Intercellular adhesion between daughter chondrocytes is mediated by cadherins. The studies utilizing an allelic series of N-cadherin and beta1 integrin mutants suggest that optimal levels of adhesion are essential for chondrocyte rotation and support a model where crosstalk between the adhesion surfaces is needed to achieve tensional homeostasis. Together, the work highlights the contributions of adhesion proteins to matrix synthesis and column formation, two key components to regulate growth rate and potential of long bones.

Comments

2023 Copyright, the authors

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