Reduced Sox7 contributes to abnormal valve development resulting in congenital aortic stenosis
Authors: Yu Y , Feng W , Hong N , Zhang Q I , Liu G , Chen Y , Wu Y , Qian Z , Jin L , Ding X , Zhao P , Chen A F 
Published: October 2024

Abstract

Background
Abnormal valve development is the most common congenital heart malformation. During valve remodeling, abnormal changes in valve cell proliferation, apoptosis, and extracellular matrix synthesis affect valve development, resulting in malformations. The molecular mechanisms underlying pathophysiology of aortic stenos is remain unclear.

Purpose
We would like to explore how Sox7 is involved in aortic valve development.

Methods and Results
We proved Sox7 was mainly expressed in endocardial and mesenchymal cells of aortic valves by immunofluorescence staining determined by at different stages of mice (E10.5～8 weeks) and human embryos and RNA-seq of E9.5 mouse embryonic hearts. We constructed a conditional Sox7 floxed allele in endothelial cells using an endocardial specific Cre. Echocardiography data showed that Nfat-KO mice had increased blood velocity, pressure gradient across aortic valves, left ventricular mass and dilated aortic roots. Then, HE and Sirius red staining to examine histological changes in aortic valves of Nfat-KO mice were performed, and we observed a remarkable increase in the size and increased staining of fibrotic cells in aortic valves of KO mice.
Next, we collected embryonic hearts of Sox7 CNC-specific knockout mice (WNT1-KO) and controls at E16.5. According to HE staining results and echocardiography analysis, there was no difference in aortic valves between WNT1-KO mice and controls. Meanwhile, we collected Nfat-KO mice and control embryos at E11.5 days. HE staining results showed that EndMT process was not impaired. Interestingly, leaflets and cusps of Nfat-KO mice showed significantly augmented proliferation levels, decreased apoptosis levels, and calcium deposition in fibrin layer.
A significant decrease in MMP9 levels were observed in both mRNA and protein levels. Co-transfection of Sox7-expressing vector and MMP9 luciferase in MEEC suggested that Sox7 significantly activated MMP9.
We used adenovirus to overexpress Sox7 in valvular interstitial cells. Compared with that in control group, the Sox7-overexpression group increased protein level of MMP9 and cleaved caspase-3, and increased Tunel-positive rate and lower Ki-67 positive rate.
Finally, we detected expression of Sox7 protein in human fetal aortic valves derived from patients with aortic stenosis using immunofluorescence. The results demonstrated that the number of Sox7 positive mesenchymal cells in human fetal aortic valves of patients was significantly lower than that in control group.

Conclusion
We demonstrated that targeted inactivation of Sox7 in the endocardium of mice affects valve development and leads to aortic stenosis. Mechanistically, no influence of Sox7 on the EndMT process of the OFT cushion. Moreover, CNC-derived Sox7 was not involved in aortic valve development. Interestingly, we found that Sox7 regulated ECM remodeling through matrix MMP9 and Sox7 had an impact on apoptosis, proliferation, and calcification.