Nianlong Yan

BACKGROUND: Endothelial-to-mesenchymal transition (EndMTE) is implicated in atherosclerosis by contributing to endothelial dysfunction (ED). SMS2 (sphingomyelin synthase 2), a key enzyme in sphingomyelin synthesis, plays a significant role in both ED and atherosclerosis. Nonetheless, the precise mechanisms of SMS2-associated ED, and its potential modulation via EndMT remain unexplored in the context of ED and atherosclerosis progression. METHODS: To investigate this, we inhibited SMS2 activity using the inhibitor Ly93 and performed RNA sequencing on human umbilical vein endothelial cells. Furthermore, we validated the potential mechanisms of EndMT in human umbilical vein endothelial cells, Apo E ^−/− mice, and human atherosclerotic plaques. RESULTS: SMS2 inhibition suppressed EndMT by blocking the Wnt/β-catenin pathway. This blockade attenuated PPARγ (peroxisome proliferator-activated receptor gamma) ubiquitination-mediated degradation via PPARγ-β-catenin interaction, ultimately reducing CPT1A expression and fatty acid oxidation. In vivo, endothelial cell-specific overexpression of SMS2 in ApoE ^−/− mice enhances atherosclerosis, and SMS2 positively correlates with Wnt/β-catenin, EndMT, and ED, but inversely correlates with PPARγ activity and fatty acid oxidation. Furthermore, in the unstable atherosclerosis plaques of humans, the expression of SMS2 in endothelial cells is significantly higher compared with that in stable plaques. The relationship between SMS2 and Wnt/β-catenin, EndMT, ED, PPARγ, and fatty acid oxidation aligns with the aforementioned findings. CONCLUSIONS: SMS2 can activate the Wnt/β-catenin pathway, which is inversely correlated with the activity of PPARγ and fatty acid oxidation. This process facilitates EndMT and ED, ultimately contributing to the initiation and development of atherosclerosis. These findings suggest that inhibition of endothelial SMS2 activity with Ly93 could be beneficial for the treatment of atherosclerosis.

Endothelial dysfunction (ED) is the initiation of atherosclerosis (AS). Our previous studies have found that cholesterol metabolism and the Wnt/β-catenin pathway can affect endoplasmic reticulum stress (ER stress), which ultimately leads to ED. However, the effects of cholesterol efflux on ED, which are caused by oxidative stress and the correlation among ER stress, Wnt/β-catenin pathway, and cholesterol efflux, are not clear during ED. To uncover them, the expressions of liver X receptors (LXRα and LXRβ) and ATP-binding cassette protein A1 (ABCA1) and G1 (ABCG1) in HUVECs (human umbilical vein endothelial cells) were measured under oxidative stress. Moreover, HUVECs were treated with LXR-623 (LXR agonist), cholesterol, tunicamycin, and salinomycin alone or together. The results indicated that oxidative stress-induced ED could deregulate the expressions of LXRα and LXRβ and trigger the ER stress and Wnt/β-catenin pathway, resulting thereafter in the accumulation of cholesterol. Furthermore, similar results were shown after treatment with cholesterol; however, the activation of liver X receptor (LXR) could reverse these changes. Furthermore, other results demonstrated that tunicamycin-induced ER stress could stimulate the accumulation of cholesterol and the Wnt/β-catenin pathway, further leading to ED. Inversely, salinomycin could reverse the above effects by deregulating the Wnt/β-catenin pathway. Collectively, our results showed that cholesterol efflux is partly responsible for the oxidative stress-induced ED; in addition, ER stress, the Wnt/β-catenin pathway, and cholesterol metabolism can interact with each other to promote ED.

Many articles have demonstrated that extracellular neutrophil traps (NETs) are often described as part of the antibacterial function. However, since the components of NETs are non-specific, excessive NETs usually cause inflammation and tissue damage. Endothelial dysfunction (ED) caused by NETs is the major focus of tissue damage, which is highly related to many inflammatory diseases. Therefore, this review summarizes the latest advances in the primary and secondary mechanisms between NETs and ED regarding inflammation as a mediator. Moreover, the detailed molecular mechanisms with emphasis on the disadvantages from NETs are elaborated: NETs can use its own enzymes, release particles as damage-associated molecular patterns (DAMPs) and activate the complement system to interact with endothelial cells (ECs), drive ECs damage and eventually aggravate inflammation. In view of the role of NETs-induced ED in different diseases, we also discussed possible molecular mechanisms and the treatments of NETs-related diseases.

Cholesterol metabolism affects endoplasmic reticulum (ER) stress and modulates epithelial-mesenchymal transition (EMT). Our previous study demonstrated that 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) attenuated EMT by blocking the transforming growth factor (TGF)-β/Smad signaling pathway and activating ER stress in MDA-MB-231 cells. To further assess the detailed mechanisms between cholesterol metabolism, ER stress, and EMT, LXR-623 (an agonist of LXRα) and simvastatin were used to increase and decrease cholesterol efflux and synthesis, respectively. Here, we found that high HP-β-CD concentrations could locally increase cholesterol levels in the ER by decreasing LXRα expression and increasing Hydroxymethylglutaryl-Coenzyme A reductase (HMGCR) expression in MDA-MB-231 and BT-549 cells, which triggered ER stress and inhibited EMT. Meanwhile, tunicamycin-induced ER stress blocked the TGF-β/Smad signaling pathway. However, low HP-β-CD concentrations can decrease the level of membrane cholesterol, enhance the TGF-β receptor I levels in lipid rafts, which helped to activate TGF-β/Smad signaling pathway, inhibit ER stress and elevate EMT. Based on our findings, the use of high HP-β-CD concentration can lead to cholesterol accumulation in the ER, thereby inducing ER stress, which directly suppresses TGF-β pathway-induced EMT. However, HP-β-CD is proposed to deplete membrane cholesterol at low concentrations and concurrently inhibit ER stress and induce EMT by promoting the TGF-β signaling pathways.

Triple negative breast cancer (TNBC) has significantly threatened human health. Many aspects of TNBC are closely related to Wnt/β-catenin pathway, and cell apoptosis induced by endoplasmic reticulum stress (ER stress) in TNBC may act as a potential target of non-chemotherapy treatment. However, how ER stress interacts with this pathway in TNBC has not yet been understood. Here, the tunicamycin and LiCl have been applied to MDA-MB-231. The related proteins expression was measured by western blotting. Moreover, acridine orange/ethidium bromide (AO/EB) staining was applied to test the apoptosis degree of the cells, and cell viability was tested by MTT experiment. Then, we found the ER stress and apoptosis degree of MDA-MB-231 were induced after treatment with tunicamycin. Besides, tunicamycin dose dependently inhibited both Wnt/β-catenin pathway and cells viability. Licl, an activator of Wnt/β-catenin signaling pathway, could significantly inhibit cell apoptosis. In conclusion, our study found that the activation of ER stress could promote the MDA-MB-231 apoptosis by repressing Wnt/β-catenin pathway, which provides some promising prospects and basic mechanism to the further research.

Atherosclerosis (AS) is the most common cardiovascular disease, and reverse cholesterol transport (RCT) plays an important role in maintaining cholesterol homeostasis. Both endoplasmic reticulum (ER) stress and LXRα can affect the metabolism of cholesterol. However, whether ER stress can modulate cholesterol metabolism by LXRα in hepatocytes and macrophages remains unclear. Therefore, in this study, we aimed to explore the relationship between ER stress induced by tunicamycin and LXRα in hepatocytes and macrophages and clarify their possible mechanisms and roles in AS. C57BL/6 mice and Huh-7 and THP-1 cells were treated with tunicamycin and LXR-623 (an agonist of LXRα) alone or in combination. Tunicamycin-induced ER stress caused liver injury; promoted the accumulation of cholesterol and triglycerides; inhibited the expression of LXRα, ABCA1 and ABCG1 in the livers of mice, thus reducing serum high-density lipoprotein (HDL)-C, low-density lipoprotein (LDL)-C, total cholesterol and triglyceride levels; however, LXR-623 could attenuate ER stress and reverse these changes. We also obtained the same results in Huh-7 and THP-1 cells. ER stress induced by tunicamycin could clearly be reversed by activating LXRα because it promoted cholesterol efflux by enhancing the expression of ABCA1 and ABCG1 in hepatocytes and macrophages, contributing to attenuation of the development of AS.