Researchers evaluating age-associated vascular pathology have demonstrated that molecular imaging of matrix metalloproteinases can evaluate tissue remodeling and identify survival prospects in an experimental murine model of aortic aneurysm. The investigation, published in EJNMMI Research, utilized a positron emission tomography and computed tomography radiotracer known as 64Cu-RYM2 alongside tissue-level analytical assays to examine how advancing chronological age influences vascular enzyme activation, regional vulnerability across the aortic tree, and fatal outcomes following aneurysm induction. In the preclinical cohort, older animals exhibited significantly higher baseline and induced enzymatic activation within the vessel wall, an elevation that directly preceded structural dissection and correlated with increased mortality from catastrophic vascular rupture.

Aortic aneurysms represent a major clinical concern worldwide, contributing annually to an estimated 150,000 to 200,000 human deaths through insidious vascular expansion, acute dissection, and fatal rupture. Advanced chronological age remains one of the primary risk factors for both thoracic and abdominal aortic aneurysms, with rupture rates escalating markedly in older populations. Pathologically, aneurysmal degeneration is accompanied by the deregulation of matrix metalloproteinases, a specialized multi-gene family of zinc-dependent endopeptidases responsible for degrading extracellular matrix components within the vessel architecture. While surgical tissue specimens recovered from human patients after acute dissection or rupture exhibit substantial elevations in matrix metalloproteinase expression, post-hoc clinical tissue examination cannot distinguish whether enzymatic destruction drove the initial vascular failure or emerged as an inflammatory consequence of tissue injury.

To rigorously investigate whether aging itself drives heightened enzymatic activity and worsens aneurysm outcomes in a controlled setting, the study examined male apolipoprotein E-deficient mice alongside wild-type C57BL/6J controls across distinct age brackets. The experimental protocol contrasted young mice aged 8 to 10 weeks against aged mice older than 51 weeks, while also incorporating an intermediate cohort of fully mature adult animals aged 12 to 17 weeks for temporal and anatomical mapping. Aneurysm induction was executed in apolipoprotein E-deficient mice via the continuous subcutaneous delivery of recombinant human angiotensin II at a rate of 1,000 ng/kg/min for up to 28 days using implanted osmotic minipumps. A pre-defined subgroup of animals was designated for early tissue harvesting on day 3 post-implantation, while the primary experimental groups were monitored prospectively to evaluate rupture-free survival across the 28-day protocol.

Survival tracking across the 28-day experimental window revealed marked disparities governed by chronological age following angiotensin II exposure. Old apolipoprotein E-deficient mice demonstrated significantly lower rupture-free survival compared to their young counterparts, an outcome confirmed with statistical significance under log-rank analysis. Necropsy examinations confirmed that, excluding a single aged animal that died during diagnostic image acquisition, every recorded death within the cohorts resulted directly from catastrophic aortic rupture, including four fatalities among the eighteen young mice and six fatalities among the eleven aged animals. Morphometric analysis performed on animals surviving to the completion of the 28-day monitoring period identified established abdominal aortic aneurysms in 5 out of 14 young mice and 1 out of 4 surviving aged mice.

Non-invasive tracking of enzymatic activity in vivo was achieved through high-resolution PET/CT imaging utilizing the specialized radiopharmaceutical 64Cu-RYM2, which binds selectively to the common catalytic activation epitope exposed on activated matrix metalloproteinases. Scans performed seven days after starting angiotensin II infusion revealed that tracer uptake across the aorta was significantly elevated in aged mice relative to young animals. In the descending thoracic aorta, the maximum standardized uptake value registered at 1.36 ± 0.39 in older mice compared with 0.96 ± 0.20 in younger animals. Within the suprarenal abdominal aorta, uptake measured 1.80 ± 0.52 in the old cohort compared to 1.17 ± 0.23 in the young group, establishing that advanced chronological age intensifies active enzymatic remodeling across vulnerable aortic regions.

Importantly, early radiotracer accumulation measured on day 7 exhibited a direct quantitative association with overall 28-day survival outcomes across the experimental cohort. Animals that succumbed to fatal aortic rupture prior to day 28 displayed significantly higher suprarenal abdominal aortic radiotracer uptake than animals that survived the entire 28-day protocol, registering maximum standardized uptake values of 2.11 ± 0.45 in non-survivors versus 1.21 ± 0.25 in survivors. When the maximum standardized uptake value was evaluated as a dichotomous diagnostic metric utilizing a cut-off threshold of 1.5, survival stratification was pronounced: 100 percent of mice presenting with uptake below 1.5 survived the 28-day period, whereas only 33.3 percent of mice displaying uptake equal to or greater than 1.5 survived, demonstrating that non-invasive molecular detection of enzyme activation reflects tissue vulnerability prior to fatal collapse.

The study demonstrated that heightened vascular matrix metalloproteinase activation in older animals is present even prior to pathological disease provocation. Comparative PET/CT imaging conducted in unmanipulated control apolipoprotein E-deficient mice established that baseline suprarenal abdominal aortic uptake of 64Cu-RYM2 was significantly greater in older mice than in young controls, recording maximum standardized uptake values of 0.84 ± 0.07 versus 0.60 ± 0.05. Angiotensin II infusion subsequently drove a dramatic upward escalation of enzyme activation in both age cohorts, with the suprarenal abdominal signal rising significantly after seven days of systemic peptide exposure. Circulating blood pool radioactivity within the left ventricle and cellular fraction assays similarly showed significantly higher enzymatic baseline activity in older animals, underscoring that aging systematically shifts the homeostatic proteolytic baseline toward an activated state.

Histological and molecular examinations of aortic tissues dissected three days after pump implantation confirmed that enzymatic surges coincide with rapid vascular inflammatory recruitment before gross structural breakdown occurs. Immunostaining and quantitative reverse transcription polymerase chain reaction for the macrophage marker CD68 demonstrated significantly higher macrophage infiltration in the suprarenal abdominal aorta of aged mice compared to young animals. Fluorometric tissue zymography of protein lysates harvested at this day 3 timepoint showed marked increases in active metalloproteinase levels in older vessels, displaying a strong positive linear correlation with CD68 expression. Because tissue harvesting occurred at a time point when medial dissection is seldom present, these findings indicate that local macrophage accumulation and coordinated matrix degradation precede macroscopic tissue disruption.

Spatial mapping conducted across distinct anatomical territories of the aorta revealed pronounced regional heterogeneity in enzymatic vulnerability. By examining the ascending aorta, descending thoracic aorta, suprarenal abdominal aorta, and infrarenal abdominal aorta in intermediate-age apolipoprotein E-deficient mice, investigators observed that baseline and angiotensin II-induced matrix metalloproteinase activity was concentrated within specific segments rather than dispersed evenly along the vessel. Fluorometric zymography demonstrated that the ascending aorta harbored the highest intrinsic enzymatic levels, and following three days of angiotensin II infusion, significant enzymatic increases were strictly localized to the ascending aorta and suprarenal abdominal aorta. These two segments correspond precisely to the anatomical zones displaying the highest clinical and experimental predilection for intramural hematoma, progressive aneurysm expansion, and fatal vascular rupture.

Parallel experiments conducted in wild-type C57BL/6J mice confirmed that age-associated regional proteolytic heterogeneity develops independently of hyperlipidemia and severe atherogenesis. While young wild-type mice exhibited uniform, low-level matrix metalloproteinase activity across all four examined aortic segments, aged wild-type animals demonstrated pronounced spatial variation, characterized by significantly elevated activity within the ascending aorta relative to the descending thoracic, suprarenal, and infrarenal segments. Although apolipoprotein E-deficient mice maintained higher absolute activity levels than wild-type mice across comparable vascular beds, the presence of heightened ascending aortic remodeling in aged wild-type animals confirms that chronological aging alters vascular matrix biology intrinsically, irrespective of atherosclerotic plaque formation.

Despite the translational value of these molecular imaging observations, the authors noted several critical experimental boundaries inherent to preclinical animal models. Circulating radiotracer clearance differences between young and old animals may partially influence PET signal levels, although complementary ex vivo fluorometric zymography and autoradiography independently verified elevated tissue-level activity. Additionally, the experimental angiotensin II infusion model initiates aortic aneurysm via early medial dissection and intramural hematoma formation within days, an evolutionary sequence that diverges from classic degenerative human abdominal aortic aneurysms where dissection is uncommon. Because pan-MMP tracers such as 64Cu-RYM2 capture net activation rather than isolating specific individual metalloproteinase enzymes, comprehensive clinical translation will require validation in human patients and the ongoing development of isoform-selective molecular imaging probes.

Subject of Research: Preclinical molecular imaging of matrix metalloproteinases and survival in aged murine aortic aneurysms

Article Title: Matrix metalloproteinase imaging and survival prospects with aging in murine aortic aneurysm

Article References: Ghim, M., Varli, O., Ahmad, A. A., Neishabouri, A., Kukreja, G., Zhang, Z., Zarnegar, S., Gangemi, N., Hedayatyanfard, K., Toczek, J., Wang, L., Zhang, J., Liu, C., Liu, Y., Gropler, R. J., & Sadeghi, M. M. (2026). Matrix metalloproteinase imaging and survival prospects with aging in murine aortic aneurysm. EJNMMI Research, 16(1), Article 146. https://doi.org/10.1186/s13550-026-01521-w

Image Credits: AI Generated

DOI: 10.1186/s13550-026-01521-w

Keywords: Aortic Aneurysm, Molecular Imaging, Matrix Metalloproteinases, PET-CT Imaging, Aging Research, Vascular Remodeling, Preclinical Cardiology, Apolipoprotein E, Matrix, metalloproteinase, imaging, survival