Graduation Year

2007

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Molecular Pharmacology and Physiology

Major Professor

Paul E. Gottschall, Ph.D.

Keywords

Proteoglycan, Brevican, Plasticity, ADAMTS, Extracellular matrix

Abstract

The extracellular environment of the central nervous system (CNS) through which neuritic processes must traverse during development or after injury is complex, and may vary from stabile conditions to a milieu favorable for neural plasticity and growth. The extracellular space in the CNS accounts for about 20% of brain volume and is composed of aggregating complexes of several different extracellular matrix (ECM) molecules. The ECM supports neural networks and acts as a barrier for neurite extention, depending on the type of molecules involved and the various signals they induce. One mechansim that may produce an environment favoring plasticity is the proteolytic cleavage of ECM. Brevican belongs to the lectican family of aggregating, chondroitin sulfate-containing proteoglycans (CSPGs) and is abundant in brain ECM complexes. It is localized peri-synaptically, inhibits neurite outgrowth, and is thought to stabilize synaptic networks in the adult.

Interestingly, a significant proportion of brevican in the CNS is observed as a fragment of the protein core formed by proteolytic cleavage. Endogenous matrix-degrading proteinases, such as the MMPs (matrix metalloproteinases) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs), cleave brevican and other lecticans potentially promoting neural plasticity. Cleavage of brevican and similar lectican family members may "loosen" the aggregated complexes and change the extracellular environment to one that is more permissive toward neural plasticity. After injury, during inflammation or with disease, alterations in the ECM may influence development and/or progression of neurological disease.

The purpose of these studies was to investigate the catabolism of brevican in the ECM and its potential role in neural plasticity under each of these influences, taking an in depth look at how brevican is processed after (1) undergoing a classical model of neural plasticity, the entorhinal cortex lesion (ECL); (2) a disease state that is thought to have dysregulated neural and synaptic plasticity; and (3) how brevican catabolism and neural plasticity is effected by deleting the protease responsible for the cleavage of lecticans in a mouse model. Overall, these experiments provide evidence that the proteolytic cleavage of brevican, and lecticans in general, may play an important role in the regulation of neural plasticity.

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