Spatiotemporal expression and localization of matrix metalloproteinas-9 in a murine model of thoracic aortic aneurysm

ObjectiveMatrix metalloproteinase-9 (MMP-9) has been widely described to play a critical role in aneurysm development. The goal of this study was to determine the spatiotemporal changes in MMP-9 expression and abundance in the early stages of aortic dilatation during the course of thoracic aortic aneurysm (TAA) formation in a mouse model.MethodsIn this study, TAAs were surgically induced in a transgenic reporter mouse strain expressing the β-galactosidase (β-gal) gene under control of the MMP-9 promoter. Terminal studies were performed during the early stages of TAA development at 1 week (n = 6), 2 weeks (n = 6), and 4 weeks (n = 6) post-TAA induction surgery. Changes in aortic outer diameter were determined in vivo by video micrometry. MMP-9 transcriptional activity (β-gal staining) and protein content (immunohistochemistry) were quantified at each time point and expressed as a percentage of unoperated reference control mice (n = 6).ResultsAortic dilatation was evident at 1 week and reached maximal size at 2 weeks (21% ± 6% increase from baseline, P < .05). MMP-9 transcriptional activity was detected at 1 week post-TAA induction (722% ± 323%, P = .19), reached a maximum within the adventitia at 2 weeks (1770% ± 505%, P < .05), and returned to baseline by 4 weeks (167% ± 47%, P = .21). MMP-9 transcription at 2 weeks colocalized with fibroblasts and smooth muscle cells. MMP-9 protein content within the aortic adventitia was increased at 2 weeks post-TAA induction (413% ± 124%, P < .05) and remained elevated at 4 weeks (222% ± 41%, P < .05). MMP-9 staining was most intense at the adventitial–medial border and could be detected throughout the elastic media.ConclusionsThese findings demonstrate a unique spatiotemporal pattern of MMP-9 transcriptional activation and protein content in the developing TAA. Colocalization studies suggest that early dilatation may be driven in part by MMP-9 produced by endogenous cells residing within the aortic vascular wall.Clinical RelevanceThe detection of thoracic abdominal aneurysm (TAA) formation and progression remains clinically difficult to manage. TAA development is a multifactorial process influenced by both cellular and extracellular mechanisms that converge on common maladaptive signaling pathways that alter the vascular environment. Active remodeling of the vascular extracellular matrix has been directly implicated in aortic dilatation and aneurysm development, and multiple studies have shown that matrix metalloproteinase-9 (MMP-9) has a critical role in this process. Thus, the goal of this study was to define the spatiotemporal relationship between MMP-9 expression/abundance and the initiation of aortic dilatation in the developing TAA. Understanding when and where MMP-9 is expressed locally defines a therapeutic window during which disruption of MMP-9 activity may aid in attenuating TAA progression

Alterations in membrane type-1 matrix metalloproteinase abundance after the induction of thoracic aortic aneurysm in a murine model

Thoracic aortic aneurysms (TAAs) develop as a result of dysregulated extracellular matrix remodeling mediated by several matrix metalloproteinases (MMPs). Membrane type-1 MMP (MT1-MMP) is the prototypical member of a unique family of membrane-bound MMPs, possessing multiple substrates and functions. The present study tested the hypothesis that MT1-MMP expression, abundance, and activity would be elevated during TAA development and that this protease is produced primarily by mesenchymal cells within the thoracic aorta. Descending thoracic aortas were harvested from C57BL/6J mice at multiple time points (2, 4, 8, and 16 wk, n = 15 each) post-TAA induction (0.5M CaCl2, 15 min) and compared with reference controls (n = 15). The expression and abundance of MT1-MMP, MMP-2, and tissue inhibitor of metalloproteinase (TIMP)-2 were assessed by quantitative PCR and immunoblot analysis. MT1-MMP activity was determined by fluorescent peptide assay. MT1-MMP was localized within the aortic wall by immunohistochemistry. MT1-MMP abundance and localization in live animals (8 wk post-TAA induction vs. control) was determined by microultrasound imaging with an MT1-MMP-targeted microbubble contrast agent. Aortic diameter was increased 172 ± 7% at 16 wk post-TAA induction (P < 0.05). MT1-MMP and MMP-2 mRNA levels were elevated at 2 wk post-TAA induction (P < 0.05). MT1-MMP protein abundance increased progressively to a maximum of 178 ± 26% at 16 wk post-TAA induction, whereas MMP-2 and TIMP-2 peaked at 2 wk post-TAA induction (526 ± 93% and 376 ± 48%, respectively, P < 0.05). MT1-MMP colocalized with fibroblasts, and MT1-MMP-targeted contrast binding was elevated in 8-wk TAA-induced mice versus control mice (217 ± 53% vs. 81 ± 8%, P < 0.05). In conclusion, these novel results suggest that MT1-MMP plays a dynamic multifunctional role in TAA development and, therefore, may provide a significant target for therapeutic strategies

Plasma Aβ42/40 and cognitive variability are associated with cognitive function in Black Americans: Findings from the AA‐FAIM cohort

Abstract Introduction It is critical to develop more inclusive Alzheimer's disease (AD) research protocols to ensure that historically excluded groups are included in preclinical research and have access to timely diagnosis and treatment. If validated in racialized groups, plasma AD biomarkers and measures of subtle cognitive dysfunction could provide avenues to expand diversity in preclinical AD research. We sought to evaluate the utility of two easily obtained, low‐burden disease markers, plasma amyloid beta (Aβ)42/40, and intra‐individual cognitive variability (IICV), to predict concurrent and longitudinal cognitive performance in a sample of Black adults. Methods Two hundred fifty‐seven Black participants enrolled in the African Americans Fighting Alzheimer's in Midlife (AA‐FAIM) study underwent at least one cognitive assessment visit; a subset of n = 235 had plasma samples. Baseline IICV was calculated as the standard deviation across participants’ z scores on five cognitive measures: Rey Auditory Verbal Learning Test Delayed Recall, Trail Making Test Parts A and B (Trails A and B), and Boston Naming Test. Using mixed effects regression models, we compared concurrent and longitudinal models to baseline plasma Aβ42/40 or IICV by age interactions. PrecivityAD assays quantified baseline plasma Aβ42/40. Results IICV was associated with concurrent/baseline performance on several outcomes but did not modify associations between age and cognitive decline. In contrast, plasma Aβ42/40 was unrelated to baseline cognitive performance, but a pattern emerged in interactions with age in longitudinal models of Trails A and B and Rey Auditory Verbal Learning Test total learning trials. Although not significant after correcting for multiple comparisons, low Aβ42/40 was associated with faster cognitive declines over time. Discussion Our results are promising as they extend existing findings to an Black American sample using low‐cost, low‐burden methods that can be implemented outside of a research center, thus supporting efforts for inclusive AD biomarker research