Increased LDL receptor by SREBP2 or SREBP2-induced lncRNA LDLR-AS promotes triglyceride accumulation in fish

Hawthorn leaf flavonoids alleviate the deterioration of atherosclerosis by inhibiting SCAP-SREBP2-LDLR pathway through sPLA2-ⅡA signaling in macrophages in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Hawthorn leaves are a combination of the dried leaves of the Rosaceae plants, i.e., Crataegus pinnatifida Bge. or Crataegus pinnatifida Bge. var. major N. E. Br., is primarily cultivated in East Asia, North America, and Europe. hawthorn leaf flavonoids (HLF) are the main part of extraction. The HLF have demonstrated potential in preventing hypertension, inflammation, hyperlipidemia, and atherosclerosis. However, the potential pharmacological mechanism behind its anti-atherosclerotic effect has yet to be explored.

AIM OF THE STUDY

The in vivo and in vitro effects of HLF on lipid-mediated foam cell formation were investigated, with a specific focus on the levels of secreted phospholipase A2 type IIA (sPLA2-II A) in macrophage cells.

MATERIALS AND METHODS

The primary constituents of HLF were analyzed using ultra-high performance liquid chromatography and liquid chromatography-tandem mass spectrometry. In vivo, HLF, at concentrations of 5 mg/kg, 20 mg/kg, and 40 mg/kg, were administered to apolipoprotein E knockout mice (ApoE-/-) fed by high-fat diet (HFD) for 16 weeks. Aorta and serum samples were collected to identify lesion areas and lipids through mass spectrometry analysis to dissect the pathological process. RAW264.7 cells were incubated with oxidized low-density lipoprotein (ox-LDL) alone, or ox-LDL combined with different doses of HLF (100, 50, and 25 μg/ml), or ox-LDL plus 24-h sPLA2-IIA inhibitors, for cell biology analysis. Lipids and inflammatory cytokines were detected using biochemical analyzers and ELISA, while plaque size and collagen content of plaque were assessed by HE and the Masson staining of the aorta. The lipid deposition in macrophages was observed by Oil Red O staining. The expression of sPLA2-IIA and SCAP-SREBP2-LDLR was determined by RT-qPCR and Western blot analysis.

RESULTS

The chemical profile of HLF was studied using UPLC-Q-TOF-MS/MS, allowing the tentative identification of 20 compounds, comprising 1 phenolic acid, 9 flavonols and 10 flavones, including isovitexin, vitexin-4″-O-glucoside, quercetin-3-O-robibioside, rutin, vitexin-2″-O-rhamnoside, quercetin, etc. HLF decreased total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and non-high-density lipoprotein cholesterol (non-HDL-C) levels in ApoE-/- mice (P < 0.05), reduced ox-LDL uptake, inhibited level of inflammatory factors, such as IL-6, IL-8, TNF-α, and IL-1ꞵ (P < 0.001), and alleviated aortic plaques with a thicker fibrous cap. HLF effectively attenuated foam cell formation in ox-LDL-treated RAW264.7 macrophages, and reduced levels of intracellular TC, free cholesterol (FC), cholesteryl ester (CE), IL-6, TNF-α, and IL-1β (P < 0.001). In both in vivo and in vitro experiments, HLF significantly downregulated the expression of sPLA2-IIA, SCAP, SREBP2, LDLR, HMGCR, and LOX-1 (P < 0.05). Furthermore, sPLA2-IIA inhibitor effectively mitigated inflammatory release in RAW264.7 macrophages and regulated SCAP-SREBP2-LDLR signaling pathway by inhibiting sPLA2-IIA secretion (P < 0.05).

CONCLUSION

HLF exerted a protective effect against atherosclerosis through inhibiting sPLA2-IIA to diminish SCAP-SREBP2-LDLR signaling pathway, to reduce LDL uptake caused foam cell formation, and to slow down the progression of atherosclerosis in mice.

Dietary palm oil enhances Sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis through inducing endoplasmic reticulum stress in muscle of large yellow croaker (Larimichthys crocea)

Sterol regulatory element-binding protein 2 (SREBP2) is considered to be a major regulator to control cholesterol homoeostasis in mammals. However, the role of SREBP2 in teleost remains poorly understand. Here, we explored the molecular characterisation of SREBP2 and identified SREBP2 as a key modulator for 3-hydroxy-3-methylglutaryl-coenzyme A reductase and 7-dehydrocholesterol reductase, which were rate-limiting enzymes of cholesterol biosynthesis. Moreover, dietary palm oil in vivo or palmitic acid (PA) treatment in vitro elevated cholesterol content through triggering SREBP2-mediated cholesterol biosynthesis in large yellow croaker. Furthermore, our results also found that PA-induced activation of SREBP2 was dependent on the stimulating of endoplasmic reticulum stress (ERS) in croaker myocytes and inhibition of ERS by 4-Phenylbutyric acid alleviated PA-induced SREBP2 activation and cholesterol biosynthesis. In summary, our findings reveal a novel insight for understanding the role of SREBP2 in the regulation of cholesterol metabolism in fish and may deepen the link between dietary fatty acid and cholesterol biosynthesis.

Low intake of ruminant trans fatty acids ameliorates the disordered lipid metabolism in C57BL/6J mice fed a high-fat diet

Currently, the health benefits of ruminant trans fatty acids (R-TFA) are still controversial. Our previous investigations indicated that R-TFA at higher dosages (1.3% and 4% E) caused disordered lipid metabolism in mice; however, through collecting R-TFA intake data in 9 provinces of China, it was suggested that, in 2021, the range of R-TFA intake for Chinese residents was about 0.053-0.307 g d-1. Based on the 2022 Nutritional Dietary Guidelines for Chinese Residents, the recommended daily energy supply from R-TFA was about 0.11%-0.15% E. However, the health effects of R-TFA at a lower dosage are still unknown; therefore, our current research aims to further explore the effects of R-TFA on health. Through in vivo experiments, it was shown that R-TFA (0.15% E) decreased body weight gain and serum cholesterol levels in C57BL/6J mice fed a high-fat diet, while it had no significant effect on mice fed a low-fat diet. Besides, hepatic histopathology analysis suggested that R-TFA (0.15% E) ameliorated the degree of hepatic steatosis and reduced intrahepatocyte lipid droplet accumulation in C57BL/6J mice fed a high-fat diet. Through lipidomics analysis, we further screened 8 potential lipid metabolites that participate in regulating the dysregulation of lipid metabolism. Finally, it was suggested that R-TFA (0.15% E) down-regulated the expression of genes related to inflammation and cholesterol synthesis while up-regulated the expression of genes related to cholesterol clearance, which might partially explain the salutary effect of R-TFA (0.15% E) in ameliorating the hepatic steatosis and improving disordered lipid metabolism in mice fed a high-fat diet. Our current research will provide a reference for the intake of R-TFA and, furthermore, give some insights into understanding the health effects of R-TFA.

Effect of Copper Exposure on the Cholesterol Metabolism in Broiler Liver

Copper (Cu) is a kind of widely used dietary supplement in poultry production, and a common environmental pollutant at the same time. Excess Cu exposure has been reported to accumulate in the liver and induce cytotoxicity, but the effect of Cu toxicity on hepatic cholesterol metabolism is still uncertain. Herein, we aimed to reveal the effect of excess Cu on the liver and primary hepatocytes of broilers at various concentrations. We found that 110 mg/kg Cu supplement remarkably increased blood cholesterol levels by detecting serum TC, LDL-C, and HDL-C in the broilers, while there was no significant difference in 220 and 330 mg/kg Cu supplements. In addition, high Cu exposure resulted in severe hepatic steatosis and hepatic cord derangement in the broilers. Oil red O staining of primary hepatocytes showed that Cu treatment caused intracellular neutral lipid accumulation. However, the hepatic TC content indicated a downward trend in both liver tissues and hepatocytes after Cu exposure. Furthermore, the expression of cholesterol metabolism-related indicators (SREBP2, HMGCR, LDLR, and CYP7A1) was notably decreased in the Cu-treated groups. While the expression of the key enzyme of cholesterol esterification (ACAT2) did not change significantly. Taken together, our findings preliminarily revealed excess Cu-induced hepatic cholesterol metabolism dysfunction, providing a deeper understanding of the molecular mechanisms of Cu-induced hepatotoxicity.

Targeting PCSK9 reduces cancer cell stemness and enhances antitumor immunity in head and neck cancer

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been demonstrated to play a critical role in regulating cholesterol homeostasis and T cell antitumor immunity. However, the expression, function, and therapeutic value of PCSK9 in head and neck squamous cell carcinoma (HNSCC) remain largely unexplored. Here, we found that the expression of PCSK9 was upregulated in HNSCC tissues, and higher PCSK9 expression indicated poorer prognosis in HNSCC patients. We further found that pharmacological inhibition or siRNA downregulating PCSK9 expression suppressed the stemness-like phenotype of cancer cells in an LDLR-dependent manner. Moreover, PCSK9 inhibition enhanced the infiltration of CD8⁺ T cells and reduced the myeloid-derived suppressor cells (MDSCs) in a 4MOSC1 syngeneic tumor-bearing mouse model, and it also enhanced the antitumor effect of anti-PD-1 immune checkpoint blockade (ICB) therapy. Together, these results indicated that PCSK9, a traditional hypercholesterolemia target, may be a novel biomarker and therapeutic target to enhance ICB therapy in HNSCC.

Long noncoding RNA lincsc5d regulates hepatic cholesterol synthesis by modulating sterol C5 desaturase in large yellow croaker

Although long noncoding RNA (lncRNA) plays a vital role in cholesterol metabolism, very little information is available in fish. Thus, a 10-week feeding experiment was performed to estimate the effects of lncRNA on cholesterol metabolism in large yellow croaker fed with fish oil (FO), soybean oil (SO), olive oil (OO), and palm oil (PO) diets. Results showed that fish fed with OO and PO diets had higher liver total cholesterol (TC) and cholesterol ester (CE) contents compared with fish fed with FO diets. Analysis of the KEGG pathway showed that the steroid biosynthesis pathway was enriched in comparisons FO vs SO, FO vs OO, and FO vs PO. Meanwhile, sterol C5 desaturase (SC5D), a cholesterol synthase, was up-regulated in the steroid biosynthesis pathway. SC5D was widely expressed in all tissues examined, and the highest expression of SC5D was detected in brain. More importantly, a novel lncRNA associated with sc5d gene was identified by RNA sequencing and named as lincsc5d. The tissue distribution of lincsc5d was similar to that of sc5d. A nuclear/cytoplasmic RNA separation assay showed that lincsc5d was a nucleus-enriched lncRNA. qRT-PCR results demonstrated that lincsc5d was markedly up-regulated in the SO, OO, and PO groups. Furthermore, the results of TC content and the lincsc5d and sc5d expression in hepatocytes agreed with in vivo results. In conclusion, this study indicated that vegetable oils, especially OO and PO, increased hepatic cholesterol levels by promoting cholesterol synthesis, and lncRNA lincsc5d and sc5d might be involved in cholesterol synthesis.