Bone morphogenetic protein 4 alleviates nonalcoholic steatohepatitis by inhibiting hepatic ferroptosis

Cutting edge: ferroptosis in metabolic dysfunction-associated steatotic liver disease (MASLD) pathogenesis and therapy

Ferroptosis denotes a distinct form of controlled cell death marked by substantial iron buildup and significant lipid peroxidation, playing a crucial role in several disease processes linked to cell death. Given the liver's essential functions in iron and lipid metabolism and its vulnerability to oxidative damage, more research has investigated the correlation between ferroptosis and numerous hepatic diseases, including metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD). NAFLD has arisen as a worldwide public health concern due to elevated morbidity and high death rates. The pathogenesis of MASLD remains incompletely elucidated. Recent data suggests that ferroptosis is crucial in the pathophysiology of MASLD; nevertheless, the specific processes by which ferroptosis influences MASLD remain unclear. The present review summarizes the molecular processes of ferroptosis and its intricate regulatory networks, outlines the differing impacts of ferroptosis at different stages of MASLD, and examines possible approaches targeting ferroptosis for the therapy of MASLD, suggesting a novel approach for its management.

Exploring the Role of Metabolic Hyperferritinaemia (MHF) in Steatotic Liver Disease (SLD) and Hepatocellular Carcinoma (HCC)

The increasing prevalence of the spectrum of Steatotic Liver Disease (SLD), including Metabolic-Associated Steatotic Liver Disease (MASLD), Metabolic-Associated Steatohepatitis (MASH), and progression to Cirrhosis and Hepatocellular Carcinoma (HCC) has led to intense research in disease pathophysiology, with many studies focusing on the role of iron. Iron overload, which is often observed in patients with SLD as a part of metabolic hyperferritinaemia (MHF), particularly in the reticuloendothelial system (RES), can exacerbate steatosis. This imbalance in iron distribution, coupled with a high-fat diet, can further promote the progression of SLD by means of oxidative stress triggering inflammation and activating hepatic stellate cells (HSCs), therefore leading to fibrosis and progression of simple steatosis to the more severe MASH. The influence of iron overload in disease progression has also been shown by the complex role of ferroptosis, a type of cell death driven by iron-dependent lipid peroxidation. Ferroptosis depletes the liver's antioxidant capacity, further contributing to the development of MASH, while its role in MASH-related HCC is potentially linked to alternations in the tumour microenvironment, as well as ferroptosis resistance. The iron-rich steatotic hepatic environment becomes prone to hepatocarcinogenesis by activation of several pro-carcinogenic mechanisms including epithelial-to-mesenchymal transition and deactivation of DNA damage repair. Biochemical markers of iron overload and deranged metabolism have been linked to all stages of SLD and its associated HCC in multiple patient cohorts of diverse genetic backgrounds, enhancing our daily clinical understanding of this interaction. Further understanding could lead to enhanced therapies for SLD management and prevention.

Diosgenin alleviates lipid accumulation in NAFLD through the pathways of ferroptosis defensive and executive system

The most prevalent liver condition globally is non-alcoholic fatty liver disease (NAFLD), for which no approved therapies currently exist. Diosgenin, an important component in plants from the Leguminosae, Dioscoreaceae, and Solanaceae families, has demonstrated considerable anti-inflammatory and antioxidant effects. Nonetheless, the specific mechanism by which it may act in managing NAFLD remains unclear. Our research aims to explore the effects and molecular mechanisms of DG on NAFLD by utilizing both in vivo and in vitro experimental approaches. To investigate the effect of DG on hepatic steatosis, we used Sprague-Dawley rats induced by a high-fat diet (HFD) and HepG2 cells exposed to free fatty acids. Oil red O staining and hematoxylin-eosin (H&E) staining were used to explore lipid accumulation and hepatic degeneration. ROS staining, SOD, MDA, and Fe2+kits were used to detect the indexes related to oxidative stress in ferroptosis in hepatic tissues and cells. IFSP1 and pcDNA3.1-ACSL4 plasmid were used to knock down Ferroptosis suppressor protein1 (FSP1) and promote the expression of acyl-CoA synthetase long-chain family member 4 (ACSL4) in HepG2 cells. DG improved lipid metabolism disorders and liver damage induced by a high-fat diet in rats with NAFLD. Furthermore, the administration of DG notably decreased oxidative stress levels and liver Fe2+ concentrations in rats. Additionally, in vitro experiments demonstrated that DG treatment markedly attenuated ferroptosis and ROS accumulation in HepG2 cells induced by FFAs. Moreover, overexpression of hepatic ACSL4 expression by pcDNA3.1-ACSL4 plasmid promoted the regulatory effects of DG on LPCAT3 and ALOX15. Our research shows that DG can alleviate NAFLD by regulating the FSP1/COQ10 pathway of the ferroptosis defense system and the ACSL4/LPCAT3/ALOX15 pathway of the ferroptosis execution system. Therefore, DG may serve as a novel inhibitor of ferroptosis for the treatment of NAFLD.

BMP4-GPX4 can improve the ferroptosis phenotype of retinal ganglion cells and enhance their differentiation ability after retinal stem cell transplantation in glaucoma with high intraocular pressure

Activation of bone morphogenetic protein (BMP) 4 signaling promotes the survival of retinal ganglion cell (RGC) after acute injury. In this study, we investigated the role of the BMP4 signaling pathway in regulating the degeneration of retinal ganglion cells (RGCs) in a mouse glaucoma model and its potential application in retinal stem cell. Our results demonstrate that BMP4-GPX4 not only reduces oxidative stress and iron accumulation but also promotes neuroprotective factors that support the survival of transplanted RSCs into the host retina. These findings suggest a novel therapeutic approach for glaucoma involving the modulation of the BMP4-GPX4 pathway to protect RGCs and improve visual function through enhanced RSC differentiation.

Sulfone-Embedded NIR Fluorophore with Large Stokes Shift for Monitoring Viscosity Changes during NAFLD-Induced Ferroptosis

The accumulation of lipids in hepatocytes in nonalcoholic fatty liver disease (NAFLD) leads to an increase in reactive oxygen species and changes in the intracellular microenvironment, while ferroptosis is the result of the accumulation of iron-dependent lipid peroxidation. Studies have shown that ferroptosis plays an important role in the pathogenesis of NAFLD. Herein, we have developed a viscosity-sensitive fluorescence probe PTSO with near-infrared emission and a large Stokes shift, which were achieved by introducing the sulfone group into the dioxothiochromen-malononitrile fluorophore as an electron-withdrawing group. This probe showed satisfactory selectivity and sensitivity toward viscosity. Importantly, probe PTSO could discriminate between normal and tumor cells, and was further employed in monitoring the viscosity changes during NAFLD-induced ferroptosis. With the help of probe PTSO, our results have validated the close relationship between viscosity and ferroptosis in NAFLD at both cellular and tissue levels, potentially offering novel insights for the clinical diagnosis and treatment of NAFLD.

Osteokines in Nonalcoholic Fatty Liver Disease

PURPOSE OF REVIEW

To critically summarize evidence on the potential role of osteokines in the pathogenesis and progression of nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

There are emerging data supporting that certain osteokines, which are specific bone-derived proteins, may beneficially or adversely affect hepatic metabolism, and their alterations in the setting of osteoporosis or other bone metabolic diseases may possibly contribute to the development and progression of NAFLD. There is evidence showing a potential bidirectional association between NAFLD and bone metabolism, which may imply the existence of a liver-bone axis. In this regard, osteocalcin, osteoprotegerin, bone morphogenic protein 4 (BMP4) and BMP6 appear to have a positive impact on the liver, thus possibly alleviating NAFLD, whereas osteopontin, receptor activator of nuclear factor kappa Β ligand (RANKL), sclerostin, periostin, BMP8B, and fibroblast growth factor 23 (FGF23) appear to have a negative impact on the liver, thus possibly exacerbating NAFLD. The potential implication of osteokines in NAFLD warrants further animal and clinical research in the field that may possibly result in novel therapeutic targets for NAFLD in the future.

Serum uric acid and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by over 5% hepatic fat accumulation without secondary causes. The prevalence of NAFLD has escalated in recent years due to shifts in dietary patterns and socioeconomic status, making it the most prevalent chronic liver disease and a significant public health concern globally. Serum uric acid (SUA) serves as the end product of purine metabolism in the body and is intricately linked to metabolic syndrome. Elevated SUA levels have been identified as an independent risk factor for the incidence and progression of NAFLD. This paper reviews the relationship between SUA and NAFLD, the underlying mechanisms of SUA involved in NAFLD, and the potential benefits of SUA-lowering therapy in treating NAFLD. The aim is to raise awareness of SUA management in patients with NAFLD, and to encourage further investigation into pharmacological interventions in this area.

Targeting cell death in NAFLD: mechanisms and targeted therapies

Nonalcoholic fatty liver disease (NAFLD) is a group of chronic liver disease which ranges from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) and is characterized by lipid accumulation, inflammation activation, fibrosis, and cell death. To date, a number of preclinical studies or clinical trials associated with therapies targeting fatty acid metabolism, inflammatory factors and liver fibrosis are performed to develop effective drugs for NAFLD/NASH. However, few therapies are cell death signaling-targeted even though the various cell death modes are present throughout the progression of NAFLD/NASH. Here we summarize the four types of cell death including apoptosis, necroptosis, pyroptosis, and ferroptosis in the NAFLD and the underlying molecular mechanisms by which the pathogenic factors such as free fatty acid and LPS induce cell death in the pathogenesis of NAFLD. In addition, we also review the effects of cell death-targeted therapies on NAFLD. In summary, our review provides comprehensive insight into the roles of various cell death modes in the progression of NAFLD, which we hope will open new avenues for therapeutic intervention.

Salvianolic acid A attenuates non-alcoholic fatty liver disease by regulating the AMPK-IGFBP1 pathway

Non-alcoholic fatty liver disease (NAFLD) affects approximately a quarter of the population and, to date, there is no approved drug therapy for this condition. Individuals with type 2 diabetes mellitus (T2DM) are at a significantly elevated risk of developing NAFLD, underscoring the urgency of identifying effective NAFLD treatments for T2DM patients. Salvianolic acid A (SAA) is a naturally occurring phenolic acid that is an important component of the water-soluble constituents isolated from the roots of Salvia miltiorrhiza Bunge. SAA has been demonstrated to possess anti-inflammatory and antioxidant stress properties. Nevertheless, its potential in ameliorating diabetes-associated NAFLD has not yet been fully elucidated. In this study, diabetic ApoE-/- mice were employed to establish a NAFLD model via a Western diet. Following this, they were treated with different doses of SAA (10 mg/kg, 20 mg/kg) via gavage. The study demonstrated a marked improvement in liver injury, lipid accumulation, inflammation, and the pro-fibrotic phenotype after the administration of SAA. Additionally, RNA-seq analysis indicated that the primary pathway by which SAA alleviates diabetes-induced NAFLD involves the cascade pathways of lipid metabolism. Furthermore, SAA was found to be effective in the inhibition of lipid accumulation, mitochondrial dysfunction and ferroptosis. A functional enrichment analysis of RNA-seq data revealed that SAA treatment modulates the AMPK pathway and IGFBP-1. Further experimental results demonstrated that SAA is capable of inhibiting lipid accumulation through the activation of the AMPK pathway and IGFBP-1.

Targeting the regulation of iron homeostasis as a potential therapeutic strategy for nonalcoholic fatty liver disease

With aging and the increasing incidence of obesity, nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. NAFLD mainly includes simple hepatic steatosis, nonalcoholic steatohepatitis (NASH), liver fibrosis and hepatocellular carcinoma (HCC). An imbalance in hepatic iron homeostasis is usually associated with the progression of NAFLD and induces iron overload, reactive oxygen species (ROS) production, and lipid peroxide accumulation, which leads to ferroptosis. Ferroptosis is a unique type of programmed cell death (PCD) that is characterized by iron dependence, ROS production and lipid peroxidation. The ferroptosis inhibition systems involved in NAFLD include the solute carrier family 7 member 11 (SLC7A11)/glutathione (GSH)/glutathione peroxidase 4 (GPX4) and ferroptosis suppressor protein 1 (FSP1)/coenzyme Q10 (CoQ10)/nicotinamide adenine dinucleotide phosphate (NADPH) regulatory axes. The main promotion system involved is the acyl-CoA synthetase long-chain family (ACSL4)/arachidonic lipoxygenase 15 (ALOX15) axis. In recent years, an increasing number of studies have focused on the multiple roles of iron homeostasis imbalance and ferroptosis in the progression of NAFLD. This review highlights the latest studies about iron homeostasis imbalance- and ferroptosis-associated NAFLD, mainly including the physiology and pathophysiology of hepatic iron metabolism, hepatic iron homeostasis imbalance during the development of NAFLD, and key regulatory molecules and roles of hepatic ferroptosis in NAFLD. This review aims to provide innovative therapeutic strategies for NAFLD.

MitoQ protects against carbon tetrachloride-induced hepatocyte ferroptosis and acute liver injury by suppressing mtROS-mediated ACSL4 upregulation

Ferroptosis has been shown to be involved in carbon tetrachloride (CCl4)-induced acute liver injury (ALI). The mitochondrion-targeted antioxidant MitoQ can eliminate the production of mitochondrial reactive oxygen species (mtROS). This study investigated the role of MitoQ in CCl4-induced hepatocytic ferroptosis and ALI. MDA and 4HNE were elevated in CCl4-induced mice. In vitro, CCl4 exposure elevated the levels of oxidized lipids in HepG2 cells. Alterations in the mitochondrial ultrastructure of hepatocytes were observed in the livers of CCl4-evoked mice. Ferrostatin-1 (Fer-1) attenuated CCl4-induced hepatic lipid peroxidation, mitochondrial ultrastructure alterations and ALI. Mechanistically, acyl-CoA synthetase long-chain family member 4 (ACSL4) was upregulated in CCl4-exposed human hepatocytes and mouse livers. The ACSL4 inhibitor rosiglitazone alleviated CCl4-induced hepatic lipid peroxidation and ALI. ACSL4 knockdown inhibited oxidized lipids in CCl4-exposed human hepatocytes. Moreover, CCl4 exposure decreased the mitochondrial membrane potential and OXPHOS subunit levels and increased the mtROS level in HepG2 cells. Correspondingly, MitoQ pretreatment inhibited the upregulation of ACSL4 in CCl4-evoked mouse livers and HepG2 cells. MitoQ attenuated lipid peroxidation in vivo and in vitro after CCl4 exposure. Finally, MitoQ pretreatment alleviated CCl4-induced hepatocytic ferroptosis and ALI. These findings suggest that MitoQ protects against hepatocyte ferroptosis in CCl4-induced ALI via the mtROS-ACSL4 pathway.

Endothelial TET2 regulates the white adipose browning and metabolism via fatty acid oxidation in obesity

Obesity is a complex metabolic disorder, manifesting as excessive accumulation of body fat. Ten-Eleven Translocation-2 (TET2) has garnered significant attention in the context of obesity due to its crucial role in epigenetic regulation and metabolic homeostasis. In this study, we aimed to investigate the effect of endothelial TET2 on obesity and explore the potential mechanism. We generated endothelial cell-specific TET2 deficiency mice and investigated endothelial TET2 using transcriptomic and epigenomic analyses. We determined the downregulation of endothelial TET2 in white adipose tissues. Furthermore, we identified that endothelial TET2 loss aggravated high-fat diet-induced obesity by inhibiting vascularization and thus suppressing white adipose tissue browning. Mechanistically, endothelial TET2 modulates obesity by engaging in endothelial fatty acid oxidation and angiocrine-mediated secretion of bone morphogenetic protein 4 (BMP4), in which nuclear factor-erythroid 2-related factor 2 (NRF2) serves as a key mediator. Our study reveals that endothelial TET2 regulates white adipose tissue browning by interacting with NRF2 to facilitate fatty acid oxidation and lipolysis in adipocytes.

BMP4 inhibits corneal neovascularization by interfering with tip cells in angiogenesis

Corneal neovascularization (CNV) can lead to impaired corneal transparency, resulting in vision loss or blindness. The primary pathological mechanism underlying CNV is an imbalance between pro-angiogenic and anti-angiogenic factors, with inflammation playing a crucial role. Notably, a vascular endothelial growth factor（VEGF）-A gradient triggers the selection of single endothelial cells（ECs） into primary tip cells that guide sprouting, while a dynamic balance between tip and stalk cells maintains a specific ratio to promote CNV. Despite the central importance of tip-stalk cell selection and shuffling, the underlying mechanisms remain poorly understood. In this study, we examined the effects of bone morphogenetic protein 4 (BMP4) on VEGF-A-induced lumen formation in human umbilical vein endothelial cells (HUVECs) and CD34-stained tip cell formation. In vivo, BMP4 inhibited CNV caused by corneal sutures. This process was achieved by BMP4 decreasing the protein expression of VEGF-A and VEGFR2 in corneal tissue after corneal suture injury. By observing the ultrastructure of the cornea, BMP4 inhibited the sprouting of tip cells and brought forward the appearance of intussusception. Meanwhile, BMP4 attenuated the inflammatory response by inhibiting neutrophil extracellular traps （NETs）formation through the NADPH oxidase-2（NOX-2）pathway. Our results indicate that BMP4 inhibits the formation of tip cells by reducing the generation of NETs, disrupting the dynamic balance of tip and stalk cells and thereby inhibiting CNV, suggesting that BMP4 may be a potential therapeutic target for CNV.

High glucose promotes the progression of colorectal cancer by activating the BMP4 signaling and inhibited by glucagon-like peptide-1 receptor agonist

BACKGROUND

The detailed molecular mechanism between type 2 diabetes mellitus (T2DM) and colorectal cancer (CRC) is still uncertain. Bone morphogenetic protein 4 (BMP4) dysregulation is implicated in T2DM and CRC, respectively. This study aims to investigate whether BMP4 can mediate the interaction of CRC with T2DM.

METHODS

We firstly explored the expression of BMP4 in The Cancer Genome Altas (TCGA) databases and CRC patients with or without DM from the Shanghai Tenth People's Hospital. The diabetic model of CRC cell lines in vitro and the mice model in vivo were developed to explore the BMP4 expression during CRC with or without diabetes. Further inhibition of BMP4 to observe its effects on CRC. Also, glucagon-like peptide-1 receptor agonist (GLP-1RA) was used to verify the underlying mechanism of hypoglycemic drugs on CRC via BMP4.

RESULTS

BMP4 expression was upregulated in CRC patients, and significantly higher in CRC patients with diabetes (P < 0.05). High glucose-induced insulin resistance (IR)-CRC cells and diabetic mice with metastasis model of CRC had increased BMP4 expression, activated BMP4-Smad1/5/8 pathway, and improved proliferative and metastatic ability mediated by epithelial-mesenchymal transition (EMT). And, treated CRC cells with exogenously BMP inhibitor-Noggin or transfected with lentivirus (sh-BMP4) could block the upregulated metastatic ability of CRC cells induced by IR. Meanwhile, GLP-1R was downregulated by high glucose-induced IR while unregulated by BMP4 inhibitor noggin, and treated GLP-1RA could suppress the proliferation of CRC cells induced by IR through downregulated BMP4.

CONCLUSIONS

BMP4 increased by high glucose promoted the EMT of CRC. The mechanism of the BMP4/Smad pathway was related to the susceptible metastasis of high glucose-induced IR-CRC. The commonly used hypoglycemic drug, GLP-1RA, inhibited the growth and promoted the apoptosis of CRC through the downregulation of BMP4. The result of our study suggested that BMP4 might serve as a therapeutic target in CRC patients with diabetes.

Ferroptosis inhibitor liproxstatin-1 alleviates metabolic dysfunction-associated fatty liver disease in mice: potential involvement of PANoptosis

Ferroptosis is a new form of regulated cell death characterized by excessive iron accumulation and uncontrollable lipid peroxidation. The role of ferroptosis in metabolic dysfunction-associated fatty liver disease (MAFLD) is not fully elucidated. In this study we compared the therapeutic effects of ferroptosis inhibitor liproxstatin-1 (LPT1) and iron chelator deferiprone (DFP) in MAFLD mouse models. This model was established in mice by feeding a high-fat diet with 30% fructose in water (HFHF) for 16 weeks. The mice then received LPT1 (10 mg·kg-1·d-1, ip) or DFP (100 mg·kg-1·d-1, ig) for another 2 weeks. We showed that both LPT1 and DFP treatment blocked the ferroptosis markers ACSL4 and ALOX15 in MAFLD mice. Furthermore, LPT1 treatment significantly reduced the liver levels of triglycerides and cholesterol, lipid peroxidation markers 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA), and ameliorated the expression of lipid synthesis/oxidation genes (Pparα, Scd1, Fasn, Hmgcr and Cpt1a), insulin resistance, mitochondrial ROS content and liver fibrosis. Importantly, LPT1 treatment potently inhibited hepatic apoptosis (Bax/Bcl-xL ratio and TUNEL+ cell number), pyroptosis (cleavages of Caspase-1 and GSDMD) and necroptosis (phosphorylation of MLKL). Moreover, LPT1 treatment markedly inhibited cleavages of PANoptosis-related caspase-8 and caspase-6 in MAFLD mouse liver. In an in vitro MAFLD model, treatment with LPT1 (100 nM) prevented cultured hepatocyte against cell death induced by pro-PANoptosis molecules (TNF-α, LPS and nigericin) upon lipid stress. On the contrary, DFP treatment only mildly attenuated hepatic inflammation but failed to alleviate lipid deposition, insulin resistance, apoptosis, pyroptosis and necroptosis in MAFLD mice. We conclude that ferroptosis inhibitor LPT1 protects against steatosis and steatohepatitis in MAFLD mice, which may involve regulation of PANoptosis, a coordinated cell death pathway that involves apoptosis, pyroptosis and necroptosis. These results suggest a potential link between ferroptosis and PANoptosis.

Dissecting the potential role of ferroptosis in liver diseases: an updated review

Ferroptosis is a novel form of cell death, manifested by iron-dependent, non-apoptotic manner resulting from the intracellular accumulation of large clusters of reactive oxygen species (ROS) and lipid peroxides due to abnormal iron metabolism. Since the liver is the main organ of human body for storing iron, it is essential to perform in-depth investigation on the role and mechanistic basis of ferroptosis in the context of divergent liver diseases. We previously summarized the emerging role of ferroptosis among various liver diseases, however, the past few years have been a surge in research establishing ferroptosis as the molecular basis or treatment option. This review article concentrated on the accumulating research progress of ferroptosis in a range of liver diseases such as acute liver injury/failure (ALI/ALF), immune-mediated hepatitis, alcoholic liver disease (ALD), nonalcoholic fatty liver disease and liver fibrosis. Ferroptosis may be a promising target for the prevention and treatment of various liver diseases, providing a strategy for exploring new therapeutic avenues for these entities.