2.1 KNOCK-OUT OF MATRIX METALLOPROTEINASE-12 EXACERBATES COMPROMISED MECHANICAL HOMEOSTASIS IN ARTERIAL AGING

Abstract

Background: Matrix metalloproteinase-12 (MMP12) may modulate arterial stiffening with age [1]. We aimed to study the effect of aging on biaxial arterial stiffness in wild-type (WT) and MMP12 knock-out (MMP12-/-) mice. Methods and Results: After euthanasia, descending thoracic (DTA) and suprarenal abdominal (SAA) aortas of young and old, WT (ages 21 ± 0 and 103 ± 1 weeks; mean ± SE) and MMP12-/- (13 ± 0 and 52 ± 0 weeks) male mice were dissected and cannulated on glass pipettes in a computer-controlled biaxial testing device. Pressure-diameter tests were performed at 95%/100%/105% of estimated in vivo stretch; axial force-length tests at pressures of 10/60/100/140 mmHg. Data were fitted using a four-fiber constitutive model [2]. WT and MMP12-/- blood pressures were comparable (133/88 vs. 126/93 mmHg; SBP/DBP; telemetry); WT aging did not influence blood pressure [3]. All metrics are therefore presented at a common pressure (figure). At first sight, MMP12-/- aging resembles WT aging: increased wall thickness (figure, panel A) leading to decreased circumferential stress (B) and decreased stored strain energy (C) [3–5]. However, in WT aging, circumferential material stiffness decreased, which did not occur in MMP12-/- (D). Structural stiffness and pulse wave velocity remained constant in WT mice but increased in MMP12-/- (E-F). Discussion: Our findings suggest that in both WT and MMP12-/-, mechanical homeostasis with aging was compromised, a finding that was exacerbated with MMP12-/-. MMP12-/- was previously reported to reduce age-associated stiffening [1]. This contradictory finding may be explained by the use of atomic force microscopy in [1] (measuring compressive stiffness) versus our use of tensile biaxial testing.