The fate of vascular smooth muscle cells in Marfan aortic aneurysm
Embargo Date
2027-11-13
OA Version
Citation
Abstract
Vascular smooth muscle cells (VSMCs) function in the aortic vasculature as contractile units, regulating vessel diameter and blood flow, in a complex dynamic with the extracellular environment. Upon vascular injury, and in response to various physiological mediators, VSMCs de-differentiate to a non-contractile synthetic phenotype, that displays an array of physiological properties including increased proliferation rate, matrix metalloprotease (MMP) secretion, and extracellular matrix (ECM) production. These synthetic functions can lead to VSMC apoptosis, maladaptive ECM remodeling, or vessel hyperplasia, respectively, and contribute towards aortic pathogenesis. Aortic aneurysm (AA) is the most clinically fatal manifestation of the autosomal dominant genetic disorder Marfan Syndrome (MFS), which is characterized by medial degeneration, vessel thickening and weakening, and increased risk for aortic dissection. Mutations of fibrillin-1 (Fbn1) are widely understood to be the primary genetic contributor to MFS. Fbn1 is a microfibrillar protein that plays an important role in elastic lamellae formation and overall medial structure and function. Given the limitations and barriers to genotherapy, research on other medicinal and therapeutical treatments targeting the mechanism of MFS AA pathogenesis is warranted. Understanding VSMC switching or other concurrent disease processes, such as inflammatory mediators, and structural degeneration, a primary contributer to medial degeneration, is crucial to develop novel therapies. In this study, I sought to explore the morphological and structural features of the aneurysmal aorta of a mouse model of MFS when compared to wildtype (WT) aortas by staining with Hematoxylin and Eosin (H&E). I further sought to analyze the pathophysiological features of model MFS AA and other related models (MFS mice lacking anti-oxidant enzymes situin-1 or glutaredoxin-1), that exhibit exacerbated aneurysm, by immunofluorescence (IF) staining using primary antibody markers for contractile VSMCs (calponin), macrophages (F4/80), and proliferating VSMCs (KLF4).The H&E staining results showed minimal visual differences in WT and MFS structural integrity, besides mild VSMC disorganization, which infers a level of elastic lamellae disruption. Moreover, there were significant differences in the tissue quality and structural integrity of the medial layer when comparing more severe forms of MFS AA to WT aortas, revealing elastin fragmentation, cellular disorganization, and medial degeneration in the Fbn1-/- and Glrx-/- Fbn1-/- groups. The IF staining results showed limited variability in the average calponin fluorescence intensity per area of aorta between genotypic groups, which indicates that there is little contractile VSMC loss in MFS and related models of AA when compared to WT. Futhermore, there was a significant increase in the average F4/80 fluorescence intensity per area of aorta in MFS model mice, and especially MFS mice with VSMC specific Sirtuin-1 (SirT1) knockout (KO), when compared to WT aortas. Variability in the KLF4 flourescence intensity per area results between groups highlights the complexity of VSMC phenotypic switching. In conclusion, these results seem to indicate that macrophages play a more significant role in MFS and related AA pathogenesis, rather than the loss of contractile VSMCs due to phenotypic switching, however further trials are needed to increase the sample size and external validity of the study. The pathophysiological mechanism of MFS AA should be further exploited to reveal new targets for therapeutic intervention.
Description
2024