Effects of Matrix Metalloproteinase 9 single nucleotide polymorphisms on the basic biology of the protease and its clinical association with abdominal aortic aneurysm

Matrix Metalloproteinase-9 (MMP-9) is the most structurally complex member of the MMP superfamily. With numerous substrates such as cell surface proteins, cryptic signaling molecules, latent extracellular proteases inhibitors, and structural ECM scaffolds, MMP-9 is considered to be a dynamic modifier of extracellular and intracellular events essential for normal physiology and a key player in many diseases. The MMP-9 gene has a number of single nucleotide polymorphisms (SNPs) and a deeper understanding of the functional consequences of these SNPs is essential in order to better understand this gene.;In this dissertation, I examined the functional consequences of MMP-9 SNPs through an in vitro characterization of the most prevalent MMP-9 SNPs followed by a clinical association study between these SNPs and patients with aortic abdominal aneurysm (AAA). Novel SNPs with alterations of the promoter and/ or enzymatic activity were identified. The clinical genetic association study demonstrated significant association between SNPs with a functional phenotype and the presence of AAA. An analysis of one SNP (N38S, rs41427445) that resulted in a profound decrease in the expression of MMP-9 protein revealed a novel mechanism of gene regulation through creation or destruction of a SNP-dependent miRNA binding site within the coding exon of MMP-9. This finding is novel in describing a SNP-dependent miRNA regulation of a gene and by revealing the coding exon as a major site of such regulation. N38S is also a site for N-glycosylation and discovery of the SNP-dependent miRNA mechanism allowed us to express the N-glycosylation deficient MMP-9 protein that enabled an examination of the role of N-glycosylation in the biology of this endopeptidase. Secretion of MMP-9 was greatly affected by the removal of N-glycosylation with N-glycosylation deficient MMP-9 trapped in the endoplasmic reticulum (ER) unable to progress down the normal secretory cascade. We believe the normal presence of N-glycosylation cloaks a high affinity protein: protein interaction between MMP-9 and ER-resident proteins enabling MMP-9 secretion.;Discoveries described in this work have implications for future clinical association studies, fundamental cell biology, and a better understanding of the biology of MMP-9.