Hyperglycemia inhibits AAA expansion: examining the role of lysyl oxidase.

Abdominal aortic aneurysm (AAA) is a common, progressive, and potentially fatal dilation of the most distal aortic segment. Multiple studies with longitudinal follow-up of AAA have identified markedly slower progression among patients affected with diabetes. Understanding the molecular pathway responsible for the growth inhibition could have implications for therapy in nondiabetic patients with AAA. Toward this end, we investigated the effects of hyperglycemia in a murine model of AAA and a carefully monitored cohort of patients with AAA from the Noninvasive Treatment of AAA-Clinical Trial (NTA3CT). In mice with hyperglycemia, AAA growth was inhibited to a similar degree (∼30%) as seen in patients with diabetes. AAA growth correlated inversely to levels of hyperglycemia in mice and patients with AAA. Inhibiting lysyl oxidase (LOX) activity increases aneurysm growth and matrix degradation in this model. Hyperglycemia increased LOX concentration in aortic smooth muscle cells (SMCs) but not in murine AAA tissue. Inhibiting LOX activity completely blocked the growth-inhibitory effect of hyperglycemia. Lysyl oxidase-like 2 (LOXL2), the primary arterial isoform of LOX, is expressed in the same area as type IV collagen along the outer media in murine AAA tissue. There is a significant inverse correlation between LOXL2 and AAA growth rates in patients. Taken together, these studies suggest a role for LOXL2-mediated type IV collagen crosslinking in slowing AAA growth in the setting of hyperglycemia. AAA grows slower in patients affected by diabetes. This growth inhibition is lost when the enzyme lysyl oxidase (LOX) is blocked in diabetic mice. The predominant arterial isoform of LOX, LOX-like 2 (LOXL2), overlaps with type IV collagen in the outer media of murine aneurysm tissue. Circulating LOXL2 correlates inversely with AAA growth in patients. Type IV collagen cross-linking by LOXL2 may play a role in the AAA growth inhibition associated with diabetes.