Decellularization Following Fixation of Explanted Aortic Valves as a Strategy for Preserving Native Mechanical Properties and Function

Mechanical or biological aortic valves are incorporated in physical cardiac simulators for surgical training, educational purposes, and device testing. They suffer from limitations including either a lack of anatomical and biomechanical accuracy or a short lifespan, hence limiting the authentic hands-on learning experience. Medical schools utilize hearts from human cadavers for teaching and research, but these formaldehyde-fixed aortic valves contort and stiffen relative to native valves. Here, we compare a panel of different chemical treatment methods on explanted porcine aortic valves and evaluate the microscopic and macroscopic features of each treatment with a primary focus on mechanical function. A surfactant-based decellularization method after formaldehyde fixation is shown to have mechanical properties close to those of the native aortic valve. Valves treated in this method were integrated into a custom-built left heart cardiac simulator to test their hemodynamic performance. This decellularization, post-fixation technique produced aortic valves which have ultimate stress and elastic modulus in the range of the native leaflets. Decellularization of fixed valves reduced the valvular regurgitation by 60% compared to formaldehyde-fixed valves. This fixation method has implications for scenarios where the dynamic function of preserved valves is required, such as in surgical trainers or device test rigs.

Metformin alleviates the calcification of aortic valve interstitial cells through activating the PI3K/AKT pathway in an AMPK dependent way

Background Calcific aortic valve disease (CAVD) is the most prevalent valvular disease worldwide. However, no effective treatment could delay or prevent the progression of the disease due to the poor understanding of its pathological mechanism. Many studies showed that metformin exerted beneficial effects on multiple cardiovascular diseases by mediating multiple proteins such as AMPK, NF-κB, and AKT. This study aims to verify whether metformin can inhibit aortic calcification through the PI3K/AKT signaling pathway. Methods We first analyzed four microarray datasets to screen differentially expressed genes (DEGs) and signaling pathways related to CAVD. Then aortic valve samples were used to verify selected genes and pathways through immunohistochemistry (IHC) and western blot (WB) assays. Aortic valve interstitial cells (AVICs) were isolated from non-calcific aortic valves and then cultured with phosphate medium (PM) with or without metformin to verify whether metformin can inhibit the osteogenic differentiation and calcification of AVICs. Finally, we used inhibitors and siRNA targeting AMPK, NF-κB, and AKT to study the mechanism of metformin. Results We screened 227 DEGs; NF-κB and PI3K/AKT signaling pathways were implicated in the pathological mechanism of CAVD. IHC and WB experiments showed decreased AMPK and AKT and increased Bax in calcific aortic valves. PM treatment significantly reduced AMPK and PI3K/AKT signaling pathways, promoted Bax/Bcl2 ratio, and induced AVICs calcification. Metformin treatment ameliorated AVICs calcification and apoptosis by activating the PI3K/AKT signaling pathway. AMPK activation and NF-κB inhibition could inhibit AVICs calcification induced by PM treatment; however, AMPK and AKT inhibition reversed the protective effect of metformin. Conclusions This study, for the first time, demonstrates that metformin can inhibit AVICs in vitro calcification by activating the PI3K/AKT signaling pathway; this suggests that metformin may provide a potential target for the treatment of CAVD. And the PI3K/AKT signaling pathway emerges as an important regulatory axis in the pathological mechanism of CAVD.

COP Cells in States of Bone Anabolism and Abnormal Calcification/Ossification

Circulating osteogenic progenitor (COP) cells are a population of cells in the peripheral blood with the capacity for bone formation, as well as broader differentiation into mesoderm-like cells in vitro. There are several pathologies of accelerated bone formation and physiological responses to injury in which COP cells have been theorized to play a role. These include fracture, vascular calcification, and subtypes of heterotopic ossification (HO). Overall, the available studies suggest COP cells are likely to be mobilized in response to fracture, home to the site of injury, undergo a maturation process, and contribute to the osteogenesis and angiogenesis required for fracture healing. HO is the pathological process of bone formation in nonskeletal tissue and can be acquired or hereditary. COP cells may seed sites of injury and inflammation that precede the formation of endochondral bone identified in both genetic and nongenetic forms of HO. Vascular calcification is a common occurrence in older adults and is strongly associated with poorer cardiovascular health outcomes. It appears that COP cells, particularly those expressing hematopoietic and vascular markers such as CD45 and CD34, contribute to the calcification and ossification of atherosclerotic plaques and aortic valves, and that they correlate to the severity of the calcification. Whether COP cells are attracted to sites of injury and inflammation and so are highly associated with fracture, vascular calcification/ossification and HO, or whether they underlie these processes at a more mechanistic level, remains to be more clearly demonstrated.