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Aneurysms occur when the structure or function of the connective tissue within the vascular wall is compromised, often during the continuous remodeling process it undergoes to maintain structural integrity.(6) These defects can occur as a congenital condition or be acquired over time with progressive weakening of the wall. Increased expression of matrix metalloproteases (MMPs) and decreased expression of tissue inhibitors of metalloproteinases (TIMPs) often contributes to this degradation.(6) MMPs, which require metal ions such as zinc for their activity, are instrumental in the process of remodeling the extracellular matrix, to include vascular remodeling.(5) Additionally, MMPs play a prominent role in tumorigenesis due to their prominent role in cell turnover and migration, and regulating signal pathways of cell growth, inflammation and angiogenesis leading to a large body of research on these proteinases.(4) Specific to angiogenesis, MMP-2 and MMP-9 are cited as both pro and anti-angiogenic while MMP-1, MMP-7, and MMP-14 are specifically pro- while MMP-12 is anti-angiogenic.(4) MMPs are produced by a variety of cell types and regulated by growth factor and cytokine secretion. Their activity is tightly controlled as they are rapidly depleted by TIMPs produced by most mesenchymal cells.(5) When this MMP/TIMP balance is altered, such as occurs with inflammation in atherosclerosis or vasculitis, the risk of aneurysm formation increases.(6)
References:
1. Allison N. Anemic virgin female rabbits. Lab Anim. 2003;32(2):23-25.
2. Bray MV, Weir EC, Brownstein DG, Delano ML. Endometrial venous aneurysms in three New Zealand white rabbits. Lab Anim Sci. 1992;42(2):360-362.
3. Garibaldi BA, Fox JG, Otto G, Murphy JC, Pecquet-Goad ME. Hematuria in rabbits. Lab Anim Sci. 1987;37(6):769.
4. Kessenbrock K, Plaks V, Werb Z. Matrix metalloproteinases: regulators of the tumor microenvironment. Cell. 2010;141:52-67.
5. Kumar V, Abbas AK, Aster JC. Inflammation and repair. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2015:105.
6. Mitchell RN. Blood vessels. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2015:501-502.
7. Percy DH, Barthold SW. Rabbit. In: Pathology of Laboratory Rodents and Rabbits. 3rd ed. Hoboken, NJ: Wiley-Blackwell; 2008:253-307.