Segmental differences in the orientation of smooth muscle cells in the tunica media of porcine aortae

Myocardial Bridge and Atherosclerosis, an Intimal Relationship

PURPOSE OF REVIEW

This review investigates the relationship between myocardial bridges (MBs), intimal thickening in coronary arteries, and Atherosclerotic cardiovascular disease. It focuses on the role of mechanical forces, such as circumferential strain, in arterial wall remodeling and aims to clarify how MBs affect coronary artery pathology.

REVIEW FINDINGS

MBs have been identified as influential in modulating coronary artery intimal thickness, demonstrating a protective effect against thickening within the MB segment and an increase in thickness proximal to the MB. This is attributed to changes in mechanical stress and hemodynamics. Research involving arterial hypertension models and vein graft disease has underscored the importance of circumferential strain in vascular remodeling and intimal hyperplasia. Understanding the complex dynamics between MBs, mechanical strain, and vascular remodeling is crucial for advancing our knowledge of coronary artery disease mechanisms. This could lead to improved management strategies for cardiovascular diseases, highlighting the need for further research into MB-related vascular changes.

Histological mapping of healing of the small and large intestine – a quantitative study in a porcine model

BACKGROUND

Gastrointestinal anastomoses are performed in many patients every year. The pathogenesis of aberrant anastomotic healing and the causes of intestinal leakage are not fully understood. The present study gathered and critically evaluated histological quantitative data to deepen current knowledge of anastomotic healing in the small and large intestine and its complications and outline the options for further experimental in vivo research in large porcine animal models.

METHODS

Three groups of porcine intestinal anastomoses were compared: small intestine without defect (SI; n=7), small intestine with an additional defect (SID; n=8), and large intestine (LI; n=7). Multilevel sampling (2,112 micrographs) and stereological methods were used for histological quantification of proliferation (Ki-67 immunohistochemistry), neutrophil infiltration (myeloperoxidase staining), vascularity (von Willebrand factor) and type I and type III collagen formation (picrosirius red in polarized light) within the region of anastomosis compared to the region outside of anastomosis.

RESULTS

Quantitative histological evaluation revealed the following results. i) Proliferation, vascularity, and collagen, but not neutrophils, were more highly expressed within the anastomosis than outside of the anastomosis region. ii) Porcine large and small intestine were not interchangeable based on histological evaluation of surgical experiments. The presence or absence of an additional experimental defect strongly affected healing, but the healing seemed complete after 21 days. iii) The microscopic structure of small intestine segments was more affected by their proximity to the anastomosis than the structure of large intestine segments.

CONCLUSIONS

Histological quantification was more laborious than the previously used semiquantitative scoring system evaluating the healing rate of intestinal anastomoses, but it provided detailed maps of biological processes within individual intestine layers. The primary data collected in the study are open and available for power sample analyses to calculate the minimum numbers of samples justified in future experiments on porcine intestines. The porcine intestine is a promising animal model with translational potential for human surgery.

Efficient computational modelling of smooth muscle orientation and function in the aorta

Understanding the mechanical effects of smooth muscle cell (SMC) contraction on the initiation and the propagation of cardiovascular diseases such as aortic dissection is critical. Framed by elastic lamellar sheets in the lamellar unit, there are SMCs in the media with a distinct radial tilt, which indicates their contribution to the radial strength. However, the mechanical effects of this type of anisotropy have not been fully discussed. Therefore, in this study, we propose a constitutive framework that models the passive and active mechanics of the aorta, taking into account the dispersed nature of the aortic constituents by applying the discrete fibre dispersion method. We suggest an isoparametric approach by evaluating various numerical integration methods and introducing a non-uniform discretization of the unit hemisphere to increase its computational efficiency. Finally, the constitutive parameters are fitted to layer-specific experimental data and initial computational results are briefly presented. The radial tilt of SMCs is also analysed, which has a noticeable influence on the mechanical behaviour of the aorta. In the absence of sufficient experimental data, the results indicate that the active contribution of SMCs has a remarkable impact on the mechanics of the healthy aorta.

Senescent Cells in Early Vascular Ageing and Bone Disease of Chronic Kidney Disease-A Novel Target for Treatment

Together with bone-mineral disorders, premature vascular ageing is a common feature of the uremic phenotype. A detailed understanding of mechanisms involved remains unclear and warrants further research. Available treatment options for end stage renal disease are principally dialysis and organ transplantation, as other treatment alternatives have proven insufficient. Chronic kidney disease (CKD) has been proposed as a model of early vascular and bone ageing, with accumulating evidence supporting the contribution of cellular senescence and the senescence-associated secretory phenotype (SASP) to cardiovascular pathology in CKD. Correspondingly, novel therapies based around the use of senolytic compounds and nuclear factor-erythroid-2-related factor 2 (Nrf2) agonists, have been suggested as attractive novel treatment options. In this review, we detail the contribution of the uremic environment to these processes underpinning ageing and how these relate to vascular health.

Novel Methodology for Characterizing Regional Variations in the Material Properties of Murine Aortas

Many vascular disorders, including aortic aneurysms and dissections, are characterized by localized changes in wall composition and structure. Notwithstanding the importance of histopathologic changes that occur at the microstructural level, macroscopic manifestations ultimately dictate the mechanical functionality and structural integrity of the aortic wall. Understanding structure-function relationships locally is thus critical for gaining increased insight into conditions that render a vessel susceptible to disease or failure. Given the scarcity of human data, mouse models are increasingly useful in this regard. In this paper, we present a novel inverse characterization of regional, nonlinear, anisotropic properties of the murine aorta. Full-field biaxial data are collected using a panoramic-digital image correlation (p-DIC) system. An inverse method, based on the principle of virtual power (PVP), is used to estimate values of material parameters regionally for a microstructurally motivated constitutive relation. We validate our experimental-computational approach by comparing results to those from standard biaxial testing. The results for the nondiseased suprarenal abdominal aorta from apolipoprotein-E null mice reveal material heterogeneities, with significant differences between dorsal and ventral as well as between proximal and distal locations, which may arise in part due to differential perivascular support and localized branches. Overall results were validated for both a membrane and a thick-wall model that delineated medial and adventitial properties. Whereas full-field characterization can be useful in the study of normal arteries, we submit that it will be particularly useful for studying complex lesions such as aneurysms, which can now be pursued with confidence given the present validation.

A method for three-dimensional quantification of vascular smooth muscle orientation: application in viable murine carotid arteries

When studying in vivo arterial mechanical behaviour using constitutive models, smooth muscle cells (SMCs) should be considered, while they play an important role in regulating arterial vessel tone. Current constitutive models assume a strictly circumferential SMC orientation, without any dispersion. We hypothesised that SMC orientation would show considerable dispersion in three dimensions and that helical dispersion would be greater than transversal dispersion. To test these hypotheses, we developed a method to quantify the 3D orientation of arterial SMCs. Fluorescently labelled SMC nuclei of left and right carotid arteries of ten mice were imaged using two-photon laser scanning microscopy. Arteries were imaged at a range of luminal pressures. 3D image processing was used to identify individual nuclei and their orientations. SMCs showed to be arranged in two distinct layers. Orientations were quantified by fitting a Bingham distribution to the observed orientations. As hypothesised, orientation dispersion was much larger helically than transversally. With increasing luminal pressure, transversal dispersion decreased significantly, whereas helical dispersion remained unaltered. Additionally, SMC orientations showed a statistically significant (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$p < 0.05$$\end{document}p<0.05) mean right-handed helix angle in both left and right arteries and in both layers, which is a relevant finding from a developmental biology perspective. In conclusion, vascular SMC orientation (1) can be quantified in 3D; (2) shows considerable dispersion, predominantly in the helical direction; and (3) has a distinct right-handed helical component in both left and right carotid arteries. The obtained quantitative distribution data are instrumental for constitutive modelling of the artery wall and illustrate the merit of our method.