A Novel Approach to Assess the In Situ Versus Ex Vivo Mechanical Behaviors of the Coronary Artery

Single-Cell RNA sequencing investigation of female-male differences under PAD conditions

Peripheral arterial disease (PAD) is an age-related medical condition affecting mostly muscular arteries of the limb. It is the 3rd leading cause of atherosclerotic morbidity. The mechanical environment of endothelial cells (ECs) in PAD is characterized by disturbed blood flow (d-flow) and stiff extracellular matrices. In PAD, the stiffness of arteries is due to decreased elastin function and increased collagen content. These flow and stiffness parameters are largely missing from current models of PAD. It has been previously proven that ECs exposed to d-flow or stiff substrates lead to proatherogenic pathways, but the effect of both, d-flow and stiffness, on EC phenotype has not been fully investigated. In this study, we sought to explore the effect of sex on proatherogenic pathways that could result from exposing endothelial cells to a d-flow and stiff environment. We utilized the scRNA-seq tool to analyze the gene expression of ECs exposed to the different mechanical conditions both in vitro and in vivo. We found that male ECs exposed to different mechanical stimuli presented higher expression of genes related to fibrosis and d-flow in vitro. We validated our findings in vivo by exposing murine carotid arteries to d-flow via partial carotid artery ligation. Since women have delayed onset of arterial stiffening and subsequent PAD, this work may provide a framework for some of the pathways in which biological sex interacts with sex-based differences in PAD.

Quantifying stent-induced damage in coronary arteries by investigating mechanical and structural alterations

Vascular damage develops with diverging severity during and after percutaneous coronary intervention with stent placement and is the prevailing stimulus for in-stent restenosis. Previous work has failed to link mechanical data obtained in a realistic in vivo or in vitro environment with data collected during imaging processes. We investigated whether specimens of porcine right coronary arteries soften when indented with a stent strut shaped structure, and if the softening results from damage mechanisms inside the fibrillar collagen structure. To simulate the multiaxial loading scenario of a stented coronary artery, we developed the testing device 'LAESIO' that can measure differences in the stress-stretch behavior of the arterial wall before and after the indentation of a strut-like stamp. The testing protocol was optimized according to preliminary experiments, more specifically equilibrium and relaxation tests. After chemical fixation of the specimens and subsequent tissue clearing, we performed three-dimensional surface and second-harmonic generation scans on the deformed specimens. We analyzed and correlated the mechanical response with structural parameters of high-affected tissue located next to the stamp indentation and low-affected tissue beyond the injured area. The results reveal that damage mechanisms, like tissue compression as well as softening, fiber dispersion, and the lesion extent, are direction-dependent, and the severity of them is linked to the strut orientation, indentation pressure, and position. The findings highlight the need for further investigations by applying the proposed methods to human coronary arteries. Additional data and insights might help to incorporate the observed damage mechanisms into material models for finite element analyses to perform more accurate simulations of stent-implantations.