Calcification of bioprosthetic valves (BVs) implanted in aortic position can result in gradual deterioration and necessitate aortic valve replacement. The molecular mechanism of calcium deposition on BV leaflets has been investigated, but remains to be fully elucidated. The present study aimed to identify explanted bioprosthetic valve (eBV)-specific proteins using a proteomics approach and to unveil their biochemical and histological involvements in calcium deposition on BV leaflets. Calcification, fibrosis, and glycosylation of the valves were histologically assessed using Von Kossa, Masson's Trichrome and Alcian Blue staining, as well as immunostaining. Protein expression in the explanted biological valves was analysed using proteomics and western blotting. In a histological evaluation, αSMA-positive myofibroblasts were not observed in eBV, whereas severe fibrosis occurred around calcified areas. SDS-PAGE revealed three major bands with considerably increased intensity in BV leaflets that were identified as plasminogen and fibrinogen gamma chain (100 kDa), and fibrinogen beta chain (50 and 37 kDa) by mass analysis. Immunohistochemistry showed that fibrinogen β-chain was distributed throughout the valve tissue. On the contrary, plasminogen was strongly stained in CD68-positive macrophages, as evidenced by immunofluorescence. The results suggest that two important blood coagulation-related proteins, plasminogen and fibrinogen, might affect the progression of BV degeneration.

• We found crucial differences in cellular and collagen contents between the native and bioprosthetic valves. • Proteomics uncovered an accumulation of blood proteins as a macrophage activator in the interstitial spaces. • Excessive cell accumulations of apoptotic macrophages were found in the pericardium-derived bioprostheses. • Structural improvements by increasing collagen density of bioprostheses are one of the effective anti-deterioration therapies.

Postoperative pericardial adhesions are considered a risk factor for redo cardiac surgery. Several large- and medium-size animal models of pericardial adhesions have been reported, but small animal models for investigating the development of anti-adhesion materials and molecular mechanisms of this condition are lacking. In this study, we aimed to establish a simple mouse model of pericardial adhesions to address this gap. We administered blood, minocycline, picibanil, and talc into the murine pericardial cavity via one-shot injection. Micro-computed tomography analyses of contrast agent-injected mice were carried out for methodological evaluation. We investigated various dosages and treatment durations for molecules identified to be inducers of pericardial adhesion. The adhesive grade was quantified by scoring the strength and volume of adhesion tissues at sacrificed time points. Histological staining with hematoxylin and eosin and Masson’s trichrome, and immunostaining for F4/80 or αSMA was performed to investigate the structural features of pericardial adhesions, and pathological features of the pericardial adhesion tissue were compared with human clinical specimens. Administration of talc resulted in the most extensive pericardial adhesions. Micro-computed tomography imaging data confirmed that accurate injection into the pericardial cavity was achieved. We found the optimal condition for the formation of strong pericardial adhesions to be injection of 2.5 mg/g talc for 2 weeks. Furthermore, histological analysis showed that talc administration led to an invasion of myofibroblasts and macrophages in the pericardial cavity and epicardium, consistent with pathological findings in patients with left ventricular assistive devices. We successfully established a simple mouse model of talc-induced pericardial adhesions, which mimics human pathology and could contribute to solving the clinical issues related to pericardial adhesions.

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by synovitis, bone and cartilage destruction, and increased fracture risk with bone loss. Although disease–modifying antirheumatic drugs have dramatically improved clinical outcomes, these therapies are not universally effective in all patients because of the heterogeneity of RA pathogenesis. Therefore, it is necessary to elucidate the molecular mechanisms underlying RA pathogenesis, including associated bone loss, in order to identify novel therapeutic targets. In this study, we found that Budding uninhibited by benzimidazoles 1 (BUB1) was highly expressed in RA patients’ synovium and murine ankle tissue with arthritis. As CD45⁺CD11b⁺ myeloid cells are a Bub1 highly expressing population among synovial cells in mice, myeloid cell–specific Bub1 conditional knockout (Bub1^ΔLysM) mice were generated. Bub1^ΔLysM mice exhibited reduced femoral bone mineral density when compared with control (Ctrl) mice under K/BxN serum–transfer arthritis, with no significant differences in joint inflammation or bone erosion based on a semi–quantitative erosion score and histological analysis. Bone histomorphometry revealed that femoral bone mass of Bub1^ΔLysM under arthritis was reduced by increased osteoclastic bone resorption. RNA-seq and subsequent Gene Set Enrichment Analysis demonstrated a significantly enriched nuclear factor-kappa B pathway among upregulated genes in receptor activator of nuclear factor kappa B ligand (RANKL)–stimulated bone marrow–derived macrophages (BMMs) obtained from Bub1^ΔLysM mice. Indeed, osteoclastogenesis using BMMs derived from Bub1^ΔLysM was enhanced by RANKL and tumor necrosis factor-α or RANKL and IL-1β treatment compared with Ctrl. Finally, osteoclastogenesis was increased by Bub1 inhibitor BAY1816032 treatment in BMMs derived from wildtype mice. These data suggest that Bub1 expressed in macrophages plays a protective role against inflammatory arthritis–associated bone loss through inhibition of inflammation–mediated osteoclastogenesis. Rheumatoid arthritis (RA) is a disease caused by an abnormal immune system, resulting in inflammation, swelling, and bone destruction in the joints, along with systemic bone loss. While new medications have dramatically improved treatment efficacy, these therapies are not universally effective for all patients. Therefore, we need to understand the regulatory mechanisms behind RA, including associated bone loss, to develop better therapies. In this study, we found that Budding uninhibited by benzimidazoles 1 (Bub1) was highly expressed in inflamed joints, especially in myeloid cells, which are a type of immune cells. To explore its role, we created myeloid cell–specific Bub1 conditional knockout (cKO) mice and induced arthritis to analyze its role during arthritis. The cKO mice exhibited lower bone mineral density when compared with control mice under inflammatory arthritis because of increased osteoclastic bone resorption, without significant differences in joint inflammation or bone erosion. Further investigation showed that Bub1 prevents excessive osteoclast differentiation induced by inflammation in bone marrow macrophages. These data suggest that Bub1 in macrophages protects against bone loss caused by inflammatory arthritis, offering potential insights for developing treatments that focus on bone health.

The characterization of aortic valve interstitial cells (VICs) cultured under optimal conditions is essential for understanding the molecular mechanisms underlying aortic valve stenosis. Here, we propose 2% hypoxia as an optimum VIC culture condition. Leaflets harvested from patients with aortic valve regurgitation were digested using collagenase and VICs were cultured under the 2% hypoxic condition. A significant increase in VIC growth was observed in 2% hypoxia (hypo-VICs), compared to normoxia (normo-VICs). RNA-sequencing revealed that downregulation of oxidative stress-marker genes (such as superoxide dismutase) and upregulation of cell cycle accelerators (such as cyclins) occurred in hypo-VICs. Accumulation of reactive oxygen species was observed in normo-VICs, indicating that low oxygen tension can avoid oxidative stress with cell-cycle arrest. Further mRNA quantifications revealed significant upregulation of several mesenchymal and hematopoietic progenitor markers, including CD34, in hypo-VICs. The stemness of hypo-VICs was confirmed using osteoblast differentiation assays, indicating that hypoxic culture is beneficial for maintaining growth and stemness, as well as for avoiding senescence via oxidative stress. The availability of hypoxic culture was also demonstrated in the molecular screening using proteomics. Therefore, hypoxic culture can be helpful for the identification of therapeutic targets and the evaluation of VIC molecular functions in vitro.