Size matters: the relationship between MMP-9 expression and aortic diameter

Area of Science:

• Cardiovascular Biology
• Molecular Biology
• Aortic Disease Research

Background:

• Increased matrix metalloproteinase (MMP)-9 expression is documented in abdominal aortic aneurysms (AAAs).
• No prior studies have investigated the correlation between aortic diameter and MMP-9 expression levels.
• Elastolysis, a key process in AAA formation, occurs early, suggesting a link between aortic size and MMP-9 activity.

Purpose of the Study:

• To quantify MMP-9 messenger RNA (mRNA) levels in AAAs of varying diameters.
• To establish the relationship between AAA size and MMP-9 expression.
• To investigate the role of MMP-9 in AAA expansion and progression.

Main Methods:

• MMP-9 mRNA levels were quantified using competitive polymerase chain reaction (PCR) in AAA tissues (n=19) and normal aortas (n=4).
• Levels were normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA to control for reverse transcription efficiency.
• AAA diameter was measured using computed tomography (CT) scans.

Main Results:

• MMP-9 mRNA levels were significantly elevated in moderate-sized AAAs (5.0–6.9 cm) compared to small (<4.9 cm) or large (>7 cm) AAAs and normal aortas.
• A fourfold increase in MMP-9/GAPDH mRNA transcripts was observed in moderate AAAs (98.06±15.19) versus small AAAs (20.87±5.15) and large AAAs (27.16±14.56).
• Normalization to patient height, risk factors, age, or sex did not alter these findings.

Conclusions:

• MMP-9 mRNA expression peaks in moderate-diameter (5–6.9 cm) AAAs.
• Elevated MMP-9 expression in moderate AAAs may drive their continued expansion.
• Lower MMP-9 levels in larger AAAs (>7 cm) suggest other enzymes or mechanical stress contribute to rapid expansion and rupture risk.