Age and Sex Dependency of Thoracic Aortopathy in a Mouse Model of Marfan Syndrome

Thoracic aortic aneurysm is one of the manifestations of Marfan syndrome (MFS) that is known to affect men more severely than women. However, the incidence of MFS is similar between men and women. The aim of this study is to show that during pathological aortic dilation, sex-dependent severity of thoracic aortopathy in a mouse model of Marfan syndrome translates into sex-dependent alterations in cells and matrix of the ascending aorta, consequently affecting aortic biomechanics. Fibrillin1 C1041G/+ were used as a mouse model of MFS. Ultrasound measurements from 3-12 months showed increased aortic diameter in Marfan aorta with larger percent increase in diameter for males compared to females. Immunohistochemistry showed decreased contractile smooth muscle cells in Marfan aortic wall compared to healthy aorta, which was accompanied by decreased contractility measured by wire myography. Elastin autofluorescence, second harmonic generation microscopy of collagen fibers and passive biomechanical assessments using myography showed more severe damage to elastin fibers, increased medial fibrosis, and increased stiffness of the aortic wall in MFS males but not females. Male and female heterozygotes showed increased expression of Sca-1-positive adventitial progenitor cells vs. controls at young ages. In agreement with clinical data, Marfan mice demonstrate sex-dependent severity of thoracic aortopathy. It was also shown that aging exacerbates the disease state especially for males. Our findings suggest that female mice are protected from progression of aortic dilation at early ages, leading to a lag in aneurysm growth.

Polarization-Sensitive Second Harmonic Generation Microscopy for Investigations of Diseased Collagenous Tissues

The advancement of non-invasive quantitative optical diagnosis techniques such as polarization-sensitive second harmonic generation microscopy (PSHG) for diseases such as cancer presents opportunities for improving disease understanding and survival rates. Here, novel and developing techniques in PSHG microscopy applied for the differentiation of cancerous or diseased tissues are presented, including circular dichroism, modulation of laser linear polarization, detection of outgoing linear laser polarization, and double-Stokes Mueller. Typically, initial cancer diagnosis is performed by visual inspection of stained biopsy or surgical resection tissue sections under bright-field microscopy, however, early diagnosis is challenging due to variability in morphological interpretation of the tissues, and because cancer initiation regions can be small and easy to miss. Therefore, pathologists could benefit in identifying cancer on biopsy or surgical resection sections by using unbiased quantitative automated technologies with high spatial resolution and improved disease specificity that can check the entire slide pixel-by-pixel. Second harmonic generation microscopy offers the opportunity to measure ultrastructural alterations in collagenous scaffolds of organ tissues virtually background free on submicron-sized tissue regions. The approach is particularly interesting for cancer diagnosis applications, because during cancer initiation and progression, the collagen in the affected tissue extracellular matrix is often deregulated and becomes disorganized. This mini-review contains a thorough summary of PSHG techniques that have interrogated diseased tissues, and discusses their technical variations and successes in disease discrimination.