25-Hydroxycholesterol-Induced Oxiapoptophagy in L929 Mouse Fibroblast Cell Line

Oxysterol 25-hydroxycholesterol activation of ferritinophagy inhibits the development of squamous intraepithelial lesion of cervix in HPV-positive patients

Squamous intraepithelial lesion of cervix (SIL) in human papillomavirus (HPV)-positive patient often undergoes a silent and long-course development, and most of them with high-grade transit to cervical squamous cell carcinoma (CSCC). The oxysterol 25-hydroxycholesterol (25-HC) is associated with HPV inhibition, autophagy and cholesterol synthesis, however, its function in this long process of SIL development remain unclear. In this study, we demonstrate that 25-HC generation is inhibited through HSIL-to-CSCC transition. The 25-HC activates ferritinophagy in the early stage of SIL, promoting the vulnerability of HSILs to ferroptosis. Therefore, maintaining 25-HC level is crucial for suppressing HSIL progression and holds promise for developing novel clinical therapies for CSCC.

Oxysterols in Vascular Cells and Role in Atherosclerosis

Atherosclerosis is a major cardiovascular complication of diseases associated with elevated oxidative stress such as type 2 diabetes and metabolic syndrome. In these situations, low-density lipoproteins (LDL) undergo oxidation. Oxidized LDL displays proatherogenic activities through multiple and complex mechanisms which lead to dysfunctions of vascular cells (endothelial cells, smooth muscle cells, and macrophages). Oxidized LDLs are enriched in oxidized products of cholesterol called oxysterols formed either by autoxidation, enzymatically, or by both mechanisms. Several oxysterols have been shown to accumulate in atheroma plaques and to play a key role in atherogenesis. Depending on the type of oxysterols, various biological effects are exerted on vascular cells to regulate the formation of macrophage foam cells, endothelial integrity, adhesion and transmigration of monocytes, plaque progression, and instability. Most of these effects are linked to the ability of oxysterols to induce cellular oxidative stress and cytotoxicity mainly through apoptosis and proinflammatory mediators. Like for excess cholesterol, high-density lipoproteins (HDL) can exert antiatherogenic activity by stimulating the efflux of oxysterols that have accumulated in foamy macrophages.

25-Hydroxycholesterol in health and diseases

Cholesterol is an essential structural component of all membranes of mammalian cells where it plays a fundamental role not only in cellular architecture, but also, for example, in signaling pathway transduction, endocytosis process, receptor functioning and recycling, or cytoskeleton remodeling. Consequently, intracellular cholesterol concentrations are tightly regulated by complex processes, including cholesterol synthesis, uptake from circulating lipoproteins, lipid transfer to these lipoproteins, esterification, and metabolization into oxysterols that are intermediates for bile acids. Oxysterols have been considered for long time as sterol waste products, but a large body of evidence has clearly demonstrated that they play key roles in central nervous system functioning, immune cell response, cell death, or migration and are involved in age-related diseases, cancers, autoimmunity, or neurological disorders. Among all the existing oxysterols, this review summarizes basic as well as recent knowledge on 25-hydroxycholesterol which is mainly produced during inflammatory or infectious situations and that in turn contributes to immune response, central nervous system disorders, atherosclerosis, macular degeneration, or cancer development. Effects of its metabolite 7α,25-dihydroxycholesterol are also presented and discussed.

25-Hydroxycholesterol-induced Osteoblast Oxiapoptophagy Is Involved in the Pathophysiological Process of Osteoporosis

BACKGROUND/AIM

25-hydroxycholesterol (25-HC) plays important roles in lipid metabolism, inflammatory responses, and apoptosis, but its pathophysiological association with osteoporosis (OP) has not been verified in osteoblasts. Hence, we studied the pathophysiological linkage and underlying cellular mechanisms of 25-HC in human osteoblast-like MG-63 cells and an ovariectomy-induced osteoporotic mouse model.

MATERIALS AND METHODS

To investigate the pathophysiological linkage between 25-HC-induced osteoblast oxiapoptophagy and OP, 25-HC ELISA assay, MTT assay, cell live/dead staining, hematoxylin and eosin staining, DAPI staining, flow cytometry analysis, western blot, caspase-3 staining, reactive oxygen species (ROS) assay, autophagy staining, immunocytochemistry, Micro-CT image analysis and immunocytochemistry were performed in MG-63 cells and ovariectomy-induced OP animals.

RESULTS

The expression of cholesterol-25-hydroxylase (CH25H), an enzyme catalyzing the conversion of cholesterol to 25-HC, and the production of 25-HC were increased by lipopolysaccharide in MG-63 cells. Cytotoxicity was increased by 25-HC in MG-63 cells. Apoptosis with condensed chromatin and altered morphology was induced by 25-HC through cleavage of caspases-8, -9, and -3 in MG-63 cells. 25-HC induced oxidative stress in MG-63 cells via elevation of ROS production, cyclooxygenase-2, and inducible nitric oxide synthase. Furthermore, the expression of autophagy biomarkers, including beclin-1 and microtubule-associated protein 1A/1B-light chain 3, was elevated by 25-HC in MG-63 cells. In addition, p53 expression was increased, whereas Akt phosphorylation was suppressed in 25-HC-incubated MG-63 cells. The expression of CH25H, cleaved caspase-3, and beclin-1 were up-regulated in the femoral bone of ovariectomy-induced mouse osteoporotic animals.

CONCLUSION

25-HC plays a role in OP via the induction of oxiapoptophagic osteoblast death.

Reoxygenation Modulates the Adverse Effects of Hypoxia on Wound Repair

Hypoxia is a major stressor and a prominent feature of pathological conditions, such as bacterial infections, inflammation, wounds, and cardiovascular defects. In this study, we investigated whether reoxygenation has a protective effect against hypoxia-induced acute injury and burn using the C57BL/6 mouse model. C57BL/6 mice were exposed to hypoxia and treated with both acute and burn injuries and were in hypoxia until wound healing. Next, C57BL/6 mice were exposed to hypoxia for three days and then transferred to normoxic conditions for reoxygenation until wound healing. Finally, skin wound tissue was collected to analyze healing-related markers, such as inflammation, vascularization, and collagen. Hypoxia significantly increased inflammatory cell infiltration and decreased vascular and collagen production, and reoxygenation notably attenuated hypoxia-induced infiltration of inflammatory cells, upregulation of pro-inflammatory cytokine levels (IL-6 and TNF-α) in the wound, and remission of inflammation in the wound. Immunofluorescence analysis showed that reoxygenation increased the expression of the angiogenic factor α-SMA and decreased ROS expression in burn tissues compared to hypoxia-treated animals. Moreover, further analysis by qPCR showed that reoxygenation could alleviate the expression of hypoxic-induced inflammatory markers (IL-6 and TNF), increase angiogenesis (SMA) and collagen synthesis (Col I), and thus promote wound healing. It is suggested that oxygen can be further evaluated in combination with oxygen-releasing materials as a supplementary therapy for patients with chronic hypoxic wounds.

Oxiapoptophagy in Age-Related Diseases. Comment on Ouyang et al. 7-Ketocholesterol Induces Oxiapoptophagy and Inhibits Osteogenic Differentiation in MC3T3-E1 Cells. Cells 2022, 11, 2882

Due to the increase in life span and life expectancy, which can, however, be more or less pronounced depending on the economic, social and cultural context [...].

Implications of High-Density Cholesterol Metabolism for Oocyte Biology and Female Fertility

Cholesterol is an essential component of animal cells. Different regulatory mechanisms converge to maintain adequate levels of this lipid because both its deficiency and excess are unfavorable. Low cell cholesterol content promotes its synthesis and uptake from circulating lipoproteins. In contrast, its excess induces the efflux to high-density lipoproteins (HDL) and their transport to the liver for excretion, a process known as reverse cholesterol transport. Different studies suggest that an abnormal HDL metabolism hinders female fertility. HDL are the only lipoproteins detected in substantial amounts in follicular fluid (FF), and their size and composition correlate with embryo quality. Oocytes obtain cholesterol from cumulus cells via gap junctions because they cannot synthesize cholesterol de novo and lack HDL receptors. Recent evidence has supported the possibility that FF HDL play a major role in taking up excess unesterified cholesterol (UC) from the oocyte. Indeed, genetically modified mouse models with disruptions in reverse cholesterol transport, some of which show excessive circulating UC levels, exhibit female infertility. Cholesterol accumulation can affect the egg´s viability, as reported in other cell types, and activate the plasma membrane structure and activity of membrane proteins. Indeed, in mice deficient for the HDL receptor Scavenger Class B Type I (SR-B1), excess circulating HDL cholesterol and UC accumulation in oocytes impairs meiosis arrest and hinders the developmental capacity of the egg. In other cells, the addition of cholesterol activates calcium channels and dysregulates cell death/survival signaling pathways, suggesting that these mechanisms may link altered HDL cholesterol metabolism and infertility. Although cholesterol, and lipids in general, are usually not evaluated in infertile patients, one study reported high circulating UC levels in women showing longer time to pregnancy as an outcome of fertility. Based on the evidence described above, we propose the existence of a well-regulated and largely unexplored system of cholesterol homeostasis controlling traffic between FF HDL and oocytes, with significant implications for female fertility.

GPR183 Regulates 7α,25-Dihydroxycholesterol-Induced Oxiapoptophagy in L929 Mouse Fibroblast Cell

7α,25-dihydroxycholesterol (7α,25-DHC) is an oxysterol synthesized from 25-hydroxycholesterol by cytochrome P450 family 7 subfamily B member 1 (CYP7B1) and is a monooxygenase (oxysterol-7α-hydroxylase) expressed under inflammatory conditions in various cell types. In this study, we verified that 7α,25-DHC-induced oxiapoptophagy is mediated by apoptosis, oxidative stress, and autophagy in L929 mouse fibroblasts. MTT assays and live/dead cell staining revealed that cytotoxicity was increased by 7α,25-DHC in L929 cells. Consequentially, cells with condensed chromatin and altered morphology were enhanced in L929 cells incubated with 7α,25-DHC for 48 h. Furthermore, apoptotic population was increased by 7α,25-DHC exposure through the cascade activation of caspase-9, caspase-3, and poly (ADP-ribose) polymerase in the intrinsic pathway of apoptosis in these cells. 7α,25-DHC upregulated reactive oxygen species (ROS) in L929 cells. Expression of autophagy biomarkers, including beclin-1 and LC3, was significantly increased by 7α,25-DHC treatment in L929 cells. 7α,25-DHC inhibits the phosphorylation of Akt associated with autophagy and increases p53 expression in L929 cells. In addition, inhibition of G-protein-coupled receptor 183 (GPR183), a receptor of 7α,25-DHC, using GPR183 specific antagonist NIBR189 suppressed 7α,25-DHC-induced apoptosis, ROS production, and autophagy in L929 cells. Collectively, GPR183 regulates 7α,25-DHC-induced oxiapoptophagy in L929 cells.