Rosiglitazone inhibits acyl-CoA synthetase activity and fatty acid partitioning to diacylglycerol and triacylglycerol via a peroxisome proliferator-activated receptor-gamma-independent mechanism in human arterial smooth muscle cells and macrophages

The ferroptosis mediator ACSL4 fails to prevent disease progression in mouse models of MASLD

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an increasingly prevalent condition and a major risk factor for chronic liver damage, potentially leading to steatohepatitis and HCC. It is already known that patients with MASLD show increased systemic and hepatic iron concentrations as well as perturbed lipid metabolism, suggesting the involvement of ferroptosis in the development and progression of MASLD. Consequently, inhibition of ferroptosis represents a potential therapeutic option for patients with MASLD.

METHODS

We investigated whether liver parenchymal cell-specific deletion (LPC-KO) of the pro-ferroptotic gene acyl-CoA synthetase long-chain family member 4 (ACSL4LPC-KO) reduces MASLD onset and progression in mice. ACSL4LPC-KO and wild-type littermates were fed a choline-deficient high-fat diet (CD-HFD) or a Western diet for 20 weeks (CD-HFD and Western diet) or 40 weeks (CD-HFD only) to monitor MASLD progression and metabolic syndrome development.

RESULTS

In contrast to the recently published studies by Duan et al, our results show no significant differences between ACSL4LPC-KO and wild-type mice with regard to the development of MASLD or the progression of metabolic syndrome. Furthermore, no differences were observed in metabolic parameters (ie, weight gain, glucose tolerance test, hepatic steatosis) or MASLD-associated inflammatory response.

CONCLUSIONS

Our analyses, therefore, suggest that loss of ACSL4 has no effect on the progression of MASLD induced by CD-HFD or the Western diet. The discrepancy between our and previously published results could be due to differences in the diets or the influence of a distinct microbiome, so the results obtained with hepatocyte-specific ACSL4LPC-KO should be taken with caution.

The role of ACSL4 in stroke: mechanisms and potential therapeutic target

Stroke, as a neurological disorder with a poor overall prognosis, has long plagued the patients. Current stroke therapy lacks effective treatments. Ferroptosis has emerged as a prominent subject of discourse across various maladies in recent years. As an emerging therapeutic target, notwithstanding its initial identification in tumor cells associated with brain diseases, it has lately been recognized as a pivotal factor in the pathological progression of stroke. Acyl-CoA synthetase long-chain family member 4 (ACSL4) is a potential target and biomarker of catalytic unsaturated fatty acids mediating ferroptosis in stroke. Specifically, the upregulation of ACSL4 leads to heightened accumulation of lipid peroxidation products and reactive oxygen species (ROS), thereby exacerbating the progression of ferroptosis in neuronal cells. ACSL4 is present in various tissues and involved in multiple pathways of ferroptosis. At present, the pharmacological mechanisms of targeting ACSL4 to inhibit ferroptosis have been found in many drugs, but the molecular mechanisms of targeting ACSL4 are still in the exploratory stage. This paper introduces the physiopathological mechanism of ACSL4 and the current status of the research involved in ferroptosis crosstalk and epigenetics, and summarizes the application status of ACSL4 in modern pharmacology research, and discusses the potential application value of ACSL4 in the field of stroke.

Iron homeostasis and ferroptosis in muscle diseases and disorders: mechanisms and therapeutic prospects

The muscular system plays a critical role in the human body by governing skeletal movement, cardiovascular function, and the activities of digestive organs. Additionally, muscle tissues serve an endocrine function by secreting myogenic cytokines, thereby regulating metabolism throughout the entire body. Maintaining muscle function requires iron homeostasis. Recent studies suggest that disruptions in iron metabolism and ferroptosis, a form of iron-dependent cell death, are essential contributors to the progression of a wide range of muscle diseases and disorders, including sarcopenia, cardiomyopathy, and amyotrophic lateral sclerosis. Thus, a comprehensive overview of the mechanisms regulating iron metabolism and ferroptosis in these conditions is crucial for identifying potential therapeutic targets and developing new strategies for disease treatment and/or prevention. This review aims to summarize recent advances in understanding the molecular mechanisms underlying ferroptosis in the context of muscle injury, as well as associated muscle diseases and disorders. Moreover, we discuss potential targets within the ferroptosis pathway and possible strategies for managing muscle disorders. Finally, we shed new light on current limitations and future prospects for therapeutic interventions targeting ferroptosis.

Intricating connections: the role of ferroptosis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic inflammatory and autoimmune disease with multiple tissue damage. However, the pathology remains elusive, and effective treatments are lacking. Multiple types of programmed cell death (PCD) implicated in SLE progression have recently been identified. Although ferroptosis, an iron-dependent form of cell death, has numerous pathophysiological features similar to those of SLE, such as intracellular iron accumulation, mitochondrial dysfunction, lipid metabolism disorders and concentration of damage associated-molecular patterns (DAMPs), only a few reports have demonstrated that ferroptosis is involved in SLE progression and that the role of ferroptosis in SLE pathogenesis continues to be neglected. Therefore, this review elucidates the potential intricate relationship between SLE and ferroptosis to provide a reliable theoretical basis for further research on ferroptosis in the pathogenesis of SLE.

Molecular mechanisms of ferroptosis in cardiovascular disease

Ferroptosis is a newly recognized type of regulated cell death that is characterized by the accumulation of iron and lipid peroxides in cells. Studies have shown that ferroptosis plays a significant role in the pathogenesis of various diseases, including cardiovascular diseases. In cardiovascular disease, ferroptosis is associated with ischemia-reperfusion injury, myocardial infarction, heart failure, and atherosclerosis. The molecular mechanisms underlying ferroptosis include the iron-dependent accumulation of lipid peroxidation products, glutathione depletion, and dysregulation of lipid metabolism, among others. This review aims to summarize the current knowledge of the molecular mechanisms of ferroptosis in cardiovascular disease and discuss the potential therapeutic strategies targeting ferroptosis as a treatment for cardiovascular disease.

The role of ferroptosis in osteoarthritis: Progress and prospects

Osteoarthritis (OA) is the most prevalent degenerative joint disease, marked by cartilage degeneration, synovitis, and subchondral bone changes. The absence of effective drugs and treatments to decelerate OA's progression highlights a significant gap in clinical practice. Ferroptosis, an iron-dependent cell death driven by lipid peroxidation, has emerged as a research focus in osteoarthritic chondrocytes. This form of cell death is characterized by imbalances in iron and increased lipid peroxidation within osteoarthritic chondrocytes. Key antioxidant mechanisms, such as Glutathione Peroxidase 4 (GPX4) and the Nuclear Factor Erythroid 2-Related Factor 2 (NRF2) pathway, are vital in countering ferroptosis in osteoarthritic chondrocytes. This review collates recent findings on ferroptosis in osteoarthritic chondrocytes, emphasizing iron regulation, lipid peroxidation, and antioxidative responses. It also explores emerging therapeutics aimed at mitigating OA by targeting ferroptosis in chondrocytes.

Intestinal DHA-PA-PG axis promotes digestive organ expansion by mediating usage of maternally deposited yolk lipids

Although the metabolism of yolk lipids such as docosahexaenoic acid (DHA) is pivotal for embryonic development, the underlying mechanism remains elusive. Here we find that the zebrafish hydroxysteroid (17-β) dehydrogenase 12a (hsd17b12a), which encodes an intestinal epithelial-specific enzyme, is essential for the biosynthesis of long-chain polyunsaturated fatty acids in primitive intestine of larval fish. The deficiency of hsd17b12a leads to severe developmental defects in the primitive intestine and exocrine pancreas. Mechanistically, hsd17b12a deficiency interrupts DHA synthesis from essential fatty acids derived from yolk-deposited triglycerides, and consequently disrupts the intestinal DHA-phosphatidic acid (PA)-phosphatidylglycerol (PG) axis. This ultimately results in developmental defects of digestive organs, primarily driven by ferroptosis. Our findings indicate that the DHA-PA-PG axis in the primitive intestine facilitates the uptake of yolk lipids and promotes the expansion of digestive organs, thereby uncovering a mechanism through which DHA regulates embryonic development.

ACSL4-mediated lipid rafts prevent membrane rupture and inhibit immunogenic cell death in melanoma

Chemotherapy including platinum-based drugs are a possible strategy to enhance the immune response in advanced melanoma patients who are resistant to immune checkpoint blockade (ICB) therapy. However, the immune-boosting effects of these drugs are a subject of controversy, and their impact on the tumor microenvironment are poorly understood. In this study, we discovered that lipid peroxidation (LPO) promotes the formation of lipid rafts in the membrane, which mediated by Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) impairs the sensitivity of melanoma cells to platinum-based drugs. This reduction primarily occurs through the inhibition of immunogenic ferroptosis and pyroptosis by reducing cell membrane pore formation. By disrupting ACSL4-mediaged lipid rafts via the removal of membrane cholesterol, we promoted immunogenic cell death, transformed the immunosuppressive environment, and improved the antitumor effectiveness of platinum-based drugs and immune response. This disruption also helped reverse the decrease in CD8+ T cells while maintaining their ability to secrete cytokines. Our results reveal that ACSL4-dependent LPO is a key regulator of lipid rafts formation and antitumor immunity, and that disrupting lipid rafts has the potential to enhance platinum-based drug-induced immunogenic ferroptosis and pyroptosis in melanoma. This novel strategy may augment the antitumor immunity of platinum-based therapy and further complement ICB therapy.

Rosiglitazone retards the progression of iron overload-induced osteoarthritis by impeding chondrocyte ferroptosis

Ferroptosis is implicated in several diseases, including iron overload-induced osteoarthritis (IOOA), which is marked by oxidative stress, iron imbalance, and lipid peroxidation. Given rosiglitazone's (RSG) ability to inhibit lipid peroxidation and ferroptosis, this study aims to assess its therapeutic potential for treating IOOA. Our in vitro results show that RSG targets acyl-CoA synthetase long-chain family member 4 to mitigate impairments induced by interleukin-1 beta and ferric ammonium citrate, including cell apoptosis, senescence, inflammatory responses, extracellular matrix degradation, and ferroptosis. RSG reduced intracellular iron content, alleviated oxidative stress and lipid peroxidation, mitigated damage to membrane-bound organelles, and enhanced glucose transport. Additionally, pre-treatment with RSG imparted anti-ferroptotic properties to chondrocytes. In vivo, RSG alleviated cartilage degradation, inflammatory responses, and ferroptosis in mice with IOOA. In conclusion, RSG exhibits chondroprotective and anti-ferroptotic effects by suppressing lipid peroxidation and restoring iron homeostasis, highlighting its potential for treating IOOA.

PPARγ alleviates preeclampsia development by regulating lipid metabolism and ferroptosis

The study aims to explore the effect of PPARγ signaling on ferroptosis and preeclampsia (PE) development. Serum and placental tissue are collected from healthy subjects and PE patients. The PPARγ and Nrf2 decreases in the PE. Rosiglitazone intervention reverses hypoxia-induced trophoblast ferroptosis and decreases lipid synthesis by regulating Nfr2 and SREBP1. Compared to the Hypoxia group, the migratory and invasive abilities enhance after rosiglitazone and ferr1 treatment. Rosiglitazone reduces the effect of hypoxia and erastin. The si-Nrf2 treatment attenuats the effects of rosiglitazone on proliferation, migration, and invasion. The si-Nrf2 does not affect SREBP1 expression. PPARγ agonists alleviates ferroptosis in the placenta of the PE rats. The study confirms that PPARγ signaling and ferroptosis-related indicators were dysregulated in PE. PPARγ/Nrf2 signaling affects ferroptosis by regulating lipid oxidation rather than SREBP1-mediated lipid synthesis. In conclusion, our study find that PPARγ can alleviate PE development by regulating lipid oxidation and ferroptosis.

Targeting Dysregulated Lipid Metabolism in Cancer with Pharmacological Inhibitors

Metabolic plasticity is recognised as a hallmark of cancer cells, enabling adaptation to microenvironmental changes throughout tumour progression. A dysregulated lipid metabolism plays a pivotal role in promoting oncogenesis. Oncogenic signalling pathways, such as PI3K/AKT/mTOR, JAK/STAT, Hippo, and NF-kB, intersect with the lipid metabolism to drive tumour progression. Furthermore, altered lipid signalling in the tumour microenvironment contributes to immune dysfunction, exacerbating oncogenesis. This review examines the role of lipid metabolism in tumour initiation, invasion, metastasis, and cancer stem cell maintenance. We highlight cybernetic networks in lipid metabolism to uncover avenues for cancer diagnostics, prognostics, and therapeutics.

Ferroptosis and its modulators: A raising target for cancer and Alzheimer's disease

The process of ferroptosis, a recently identified form of regulated cell death (RCD) is associated with the overloading of iron species and lipid-derived ROS accumulation. Ferroptosis is induced by various mechanisms such as inhibiting system Xc, glutathione depletion, targeting excess iron, and directly inhibiting GPX4 enzyme. Also, ferroptosis inhibition is achieved by blocking excessive lipid peroxidation by targeting different pathways. These mechanisms are often related to the pathophysiology and pathogenesis of diseases like cancer and Alzheimer's. Fundamentally distinct from other forms of cell death, such as necrosis and apoptosis, ferroptosis differs in terms of biochemistry, functions, and morphology. The mechanism by which ferroptosis acts as a regulatory factor in many diseases remains elusive. Studying the activation and inhibition of ferroptosis as a means to mitigate the progression of various diseases is a highly intriguing and actively researched topic. It has emerged as a focal point in etiological research and treatment strategies. This review systematically summarizes the different mechanisms involved in the inhibition and induction of ferroptosis. We have extensively explored different agents that can induce or inhibit ferroptosis. This review offers current perspectives on recent developments in ferroptosis research, highlighting the disease's etiology and presenting references to enhance its understanding. It also explores new targets for the treatment of cancer and Alzheimer's disease.

Acyl-CoA synthase ACSL4: an essential target in ferroptosis and fatty acid metabolism

ABSTRACT

Long-chain acyl-coenzyme A (CoA) synthase 4 (ACSL4) is an enzyme that esterifies CoA into specific polyunsaturated fatty acids, such as arachidonic acid and adrenic acid. Based on accumulated evidence, the ACSL4-catalyzed biosynthesis of arachidonoyl-CoA contributes to the execution of ferroptosis by triggering phospholipid peroxidation. Ferroptosis is a type of programmed cell death caused by iron-dependent peroxidation of lipids; ACSL4 and glutathione peroxidase 4 positively and negatively regulate ferroptosis, respectively. In addition, ACSL4 is an essential regulator of fatty acid (FA) metabolism. ACSL4 remodels the phospholipid composition of cell membranes, regulates steroidogenesis, and balances eicosanoid biosynthesis. In addition, ACSL4-mediated metabolic reprogramming and antitumor immunity have attracted much attention in cancer biology. Because it facilitates the cross-talk between ferroptosis and FA metabolism, ACSL4 is also a research hotspot in metabolic diseases and ischemia/reperfusion injuries. In this review, we focus on the structure, biological function, and unique role of ASCL4 in various human diseases. Finally, we propose that ACSL4 might be a potential therapeutic target.

Targeting ferroptosis opens new avenues for the development of novel therapeutics

Ferroptosis is an iron-dependent form of regulated cell death with distinct characteristics, including altered iron homeostasis, reduced defense against oxidative stress, and abnormal lipid peroxidation. Recent studies have provided compelling evidence supporting the notion that ferroptosis plays a key pathogenic role in many diseases such as various cancer types, neurodegenerative disease, diseases involving tissue and/or organ injury, and inflammatory and infectious diseases. Although the precise regulatory networks that underlie ferroptosis are largely unknown, particularly with respect to the initiation and progression of various diseases, ferroptosis is recognized as a bona fide target for the further development of treatment and prevention strategies. Over the past decade, considerable progress has been made in developing pharmacological agonists and antagonists for the treatment of these ferroptosis-related conditions. Here, we provide a detailed overview of our current knowledge regarding ferroptosis, its pathological roles, and its regulation during disease progression. Focusing on the use of chemical tools that target ferroptosis in preclinical studies, we also summarize recent advances in targeting ferroptosis across the growing spectrum of ferroptosis-associated pathogenic conditions. Finally, we discuss new challenges and opportunities for targeting ferroptosis as a potential strategy for treating ferroptosis-related diseases.

Inhibition of ACSL4 ameliorates tubular ferroptotic cell death and protects against fibrotic kidney disease

Ferroptosis is a recently recognized form of regulated cell death, characterized by iron-dependent accumulation of lipid peroxidation. Ample evidence has depicted that ferroptosis plays an essential role in the cause or consequence of human diseases, including cancer, neurodegenerative disease and acute kidney injury. However, the exact role and underlying mechanism of ferroptosis in fibrotic kidney remain unknown. Acyl-CoA synthetase long-chain family member 4 (ACSL4) has been demonstrated as an essential component in ferroptosis execution by shaping lipid composition. In this study, we aim to discuss the potential role and underlying mechanism of ACSL4-mediated ferroptosis of tubular epithelial cells (TECs) during renal fibrosis. The unbiased gene expression studies showed that ACSL4 expression was tightly associated with decreased renal function and the progression of renal fibrosis. To explore the role of ACSL4 in fibrotic kidney, ACSL4 specific inhibitor rosiglitazone (ROSI) was used to disturb the high expression of ACSL4 in TECs induced by TGF-β, unilateral ureteral obstruction (UUO) and fatty acid (FA)-modeled mice in vivo, and ACSL4 siRNA was used to knockdown ACSL4 in TGF-β-induced HK2 cells in vitro. The results demonstrated that inhibition and knockdown of ACSL4 effectively attenuated the occurrence of ferroptosis in TECs and alleviated the interstitial fibrotic response. In addition, the expression of various profibrotic cytokines all decreased after ROSI-treated in vivo and in vitro. Further investigation showed that inhibition of ACSL4 obviously attenuates the progression of renal fibrosis by reducing the proferroptotic precursors arachidonic acid- and adrenic acid- containing phosphatidylethanolamine (AA-PE and AdA-PE). In conclusion, these results suggest ACSL4 is essential for tubular ferroptotic death during kidney fibrosis development and ACSL4 inhibition is a viable therapeutic approach to preventing fibrotic kidney diseases.

The ACSL4 Network Regulates Cell Death and Autophagy in Diseases

Lipid metabolism, cell death, and autophagy are interconnected processes in cells. Dysregulation of lipid metabolism can lead to cell death, such as via ferroptosis and apoptosis, while lipids also play a crucial role in the regulation of autophagosome formation. An increased autophagic response not only promotes cell survival but also causes cell death depending on the context, especially when selectively degrading antioxidant proteins or organelles that promote ferroptosis. ACSL4 is an enzyme that catalyzes the formation of long-chain acyl-CoA molecules, which are important intermediates in the biosynthesis of various types of lipids. ACSL4 is found in many tissues and is particularly abundant in the brain, liver, and adipose tissue. Dysregulation of ACSL4 is linked to a variety of diseases, including cancer, neurodegenerative disorders, cardiovascular disease, acute kidney injury, and metabolic disorders (such as obesity and non-alcoholic fatty liver disease). In this review, we introduce the structure, function, and regulation of ACSL4; discuss its role in apoptosis, ferroptosis, and autophagy; summarize its pathological function; and explore the potential implications of targeting ACSL4 in the treatment of various diseases.

ACSL4-Mediated Ferroptosis and Its Potential Role in Central Nervous System Diseases and Injuries

As an iron-dependent regulated form of cell death, ferroptosis is characterized by iron-dependent lipid peroxidation and has been implicated in the occurrence and development of various diseases, including nervous system diseases and injuries. Ferroptosis has become a potential target for intervention in these diseases or injuries in relevant preclinical models. As a member of the Acyl-CoA synthetase long-chain family (ACSLs) that can convert saturated and unsaturated fatty acids, Acyl-CoA synthetase long-chain familymember4 (ACSL4) is involved in the regulation of arachidonic acid and eicosapentaenoic acid, thus leading to ferroptosis. The underlying molecular mechanisms of ACSL4-mediated ferroptosis will promote additional treatment strategies for these diseases or injury conditions. Our review article provides a current view of ACSL4-mediated ferroptosis, mainly including the structure and function of ACSL4, as well as the role of ACSL4 in ferroptosis. We also summarize the latest research progress of ACSL4-mediated ferroptosis in central nervous system injuries and diseases, further proving that ACSL4-medicated ferroptosis is an important target for intervention in these diseases or injuries.

Fighting age-related orthopedic diseases: focusing on ferroptosis

Ferroptosis, a unique type of cell death, is characterized by iron-dependent accumulation and lipid peroxidation. It is closely related to multiple biological processes, including iron metabolism, polyunsaturated fatty acid metabolism, and the biosynthesis of compounds with antioxidant activities, including glutathione. In the past 10 years, increasing evidence has indicated a potentially strong relationship between ferroptosis and the onset and progression of age-related orthopedic diseases, such as osteoporosis and osteoarthritis. Therefore, in-depth knowledge of the regulatory mechanisms of ferroptosis in age-related orthopedic diseases may help improve disease treatment and prevention. This review provides an overview of recent research on ferroptosis and its influences on bone and cartilage homeostasis. It begins with a brief overview of systemic iron metabolism and ferroptosis, particularly the potential mechanisms of ferroptosis. It presents a discussion on the role of ferroptosis in age-related orthopedic diseases, including promotion of bone loss and cartilage degradation and the inhibition of osteogenesis. Finally, it focuses on the future of targeting ferroptosis to treat age-related orthopedic diseases with the intention of inspiring further clinical research and the development of therapeutic strategies.

MiR-23b Promotes Porcine Preadipocyte Differentiation via SESN3 and ACSL4

Genetic improvement of pork quality is one of the hot topics in pig germplasm innovation. Backfat thickness and intramuscular fat content are important indexes of meat quality. MiRNAs are becoming recognized as a crucial regulator of adipose development. Therefore, it is crucial to understand how miR-23b regulates fat metabolism at the molecular level. In the present study, Oil Red O staining, and Western blot were used to evaluate the effect of miR-23b on the differentiation of porcine preadipocytes. Dual-luciferase reporter gene assay, pulldown, and RIP were used to reveal the mechanism of miR-23b regulating cell differentiation. The findings demonstrated that miR-23b promotes the expression of adipogenic factors and increases the content of lipid droplets, thus promoting the differentiation of preadipocytes. Further research found that miR-23b can directly bind to the 3’UTR of SESN3 to regulate adipogenic differentiation. In addition, it was speculated that miR-23b controls cell differentiation by positively regulating the expression of ACSL4 in other ways. Here, we demonstrate that miR-23b promotes the differentiation of porcine preadipocytes by targeting SESN3 and promoting the expression of ACSL4. The present study is meaningful to the improvement of pork quality and the development of animal husbandry.

Therapeutic potential of deuterium-stabilized (R)-pioglitazone-PXL065-for X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (ALD) results from ABCD1 gene mutations which impair Very Long Chain Fatty Acids (VLCFA; C26:0 and C24:0) peroxisomal import and β-oxidation, leading to accumulation in plasma and tissues. Excess VLCFA drives impaired cellular functions (e.g. disrupted mitochondrial function), inflammation, and neurodegeneration. Major disease phenotypes include: adrenomyeloneuropathy (AMN), progressive spinal cord axonal degeneration, and cerebral ALD (C-ALD), inflammatory white matter demyelination and degeneration. No pharmacological treatment is available to-date for ALD. Pioglitazone, an anti-diabetic thiazolidinedione, exerts potential benefits in ALD models. Its mechanisms are genomic (PPARγ agonism) and nongenomic (mitochondrial pyruvate carrier-MPC, long-chain acyl-CoA synthetase 4-ACSL4, inhibition). However, its use is limited by PPARγ-driven side effects (e.g. weight gain, edema). PXL065 is a clinical-stage deuterium-stabilized (R)-enantiomer of pioglitazone which lacks PPARγ agonism but retains MPC activity. Here, we show that incubation of ALD patient-derived cells (both AMN and C-ALD) and glial cells from Abcd1-null mice with PXL065 resulted in: normalization of elevated VLCFA, improved mitochondrial function, and attenuated indices of inflammation. Compensatory peroxisomal transporter gene expression was also induced. Additionally, chronic treatment of Abcd1-null mice lowered VLCFA in plasma, brain and spinal cord and improved both neural histology (sciatic nerve) and neurobehavioral test performance. Several in vivo effects of PXL065 exceeded those achieved with pioglitazone. PXL065 was confirmed to lack PPARγ agonism but retained ACSL4 activity of pioglitazone. PXL065 has novel actions and mechanisms and exhibits a range of potential benefits in ALD models; further testing of this molecule in ALD patients is warranted.

CRISPR/Cas9 Screens Reveal that Hexokinase 2 Enhances Cancer Stemness and Tumorigenicity by Activating the ACSL4-Fatty Acid β-Oxidation Pathway

Metabolic reprogramming is often observed in carcinogenesis, but little is known about the aberrant metabolic genes involved in the tumorigenicity and maintenance of stemness in cancer cells. Sixty-seven oncogenic metabolism-related genes in liver cancer by in vivo CRISPR/Cas9 screening are identified. Among them, acetyl-CoA carboxylase 1 (ACC1), aldolase fructose-bisphosphate A (ALDOA), fatty acid binding protein 5 (FABP5), and hexokinase 2 (HK2) are strongly associated with stem cell properties. HK2 further facilitates the maintenance and self-renewal of liver cancer stem cells. Moreover, HK2 enhances the accumulation of acetyl-CoA and epigenetically activates the transcription of acyl-CoA synthetase long-chain family member 4 (ACSL4), leading to an increase in fatty acid β-oxidation activity. Blocking HK2 or ACSL4 effectively inhibits liver cancer growth, and GalNac-siHK2 administration specifically targets the growth of orthotopic tumor xenografts. These results suggest a promising therapeutic strategy for the treatment of liver cancer.

Altered Basal Lipid Metabolism Underlies the Functional Impairment of Naive CD8+ T Cells in Elderly Humans

Aging is associated with functional deficits in the naive T cell compartment, which compromise the generation of de novo immune responses against previously unencountered Ags. The mechanisms that underlie this phenomenon have nonetheless remained unclear. We found that naive CD8+ T cells in elderly humans were prone to apoptosis and proliferated suboptimally in response to stimulation via the TCR. These abnormalities were associated with dysregulated lipid metabolism under homeostatic conditions and enhanced levels of basal activation. Importantly, reversal of the bioenergetic anomalies with lipid-altering drugs, such as rosiglitazone, almost completely restored the Ag responsiveness of naive CD8+ T cells. Interventions that favor lipid catabolism may therefore find utility as adjunctive therapies in the elderly to promote vaccine-induced immunity against targetable cancers and emerging pathogens, such as seasonal influenza viruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

ACSL4 Directs Intramuscular Adipogenesis and Fatty Acid Composition in Pigs

Simple Summary

In the livestock industry, intramuscular fat content is an important indicator of the meat quality of domestic animals. The variations of the Acyl-CoA Synthetase Long-Chain Family Member 4 (ACSL4) gene locus are associated with intramuscular fat content in different pig populations, but the detailed molecular function of ACSL4 in pig intramuscular adipogenesis remains obscure. Our study reveals the function of ACSL4 in pig intramuscular adipogenesis and provides new clues for improving the palatability of meat and enhancing the nutritional value of pork for human health.

Abstract

The intramuscular fat is a major quality trait of meat, affecting sensory attributes such as flavor and texture. Several previous GWAS studies identified Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) gene as the candidate gene to regulate intramuscular fat content in different pig populations, but the underlying molecular function of ACSL4 in adipogenesis within pig skeletal muscle is not fully investigated. In this study, we isolated porcine endogenous intramuscular adipocyte progenitors and performed ACSL4 loss- and gain-of-function experiments during adipogenic differentiation. Our data showed that ACSL4 is a positive regulator of adipogenesis in intramuscular fat cells isolated from pigs. More interestingly, the enhanced expression of ACSL4 in pig intramuscular adipocytes could increase the cellular content of monounsaturated and polyunsaturated fatty acids, such as gamma-L eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA). The above results not only confirmed the function of ACSL4 in pig intramuscular adipogenesis and meat quality attributes, but also provided new clues for the improvement of the nutritional value of pork for human health.

Synthesis of novel thiazolidinic-phthalimide derivatives evaluated as new multi-target antiepileptic agents

Epilepsy is a disease that affects millions of people around the globe and has a multifactorial cause. Inflammation is a process that can be involved in the development of seizures. Thus, the present study proposed the design and synthesis of new candidates for antiepileptic drugs that would also control the inflammatory process. Nine new derivatives of the substituted thiazophthalimide hybrid core were obtained with satisfactory purity ≥99% and yields between 27% and 87%. All compounds showed cell viability values greater than 90% in the culture of PBMC cells from healthy volunteers and, therefore, were not considered cytotoxic. These compounds modulated proinflammatory cytokines IFN-y and IL-17A and can mitigate inflammation. Acute toxicity studies of compound 7i in an animal model indicated that the compound has low toxicity and an LD50 greater than 2 g/kg in healthy adult rats. The same compound did not show positive results for anticonvulsant activity through the PTZ test. However, 7i demonstrates the interaction with the target GABA-A receptor in silico, indicating a possible activity as an agonist of that receptor. Thus, further studies are needed to investigate the anticonvulsant activity, in particular, using models in which the inflammatory process triggers epileptic seizures.

Fatty acid metabolism and acyl-CoA synthetases in the liver-gut axis

Fatty acids are energy substrates and cell components which participate in regulating signal transduction, transcription factor activity and secretion of bioactive lipid mediators. The acyl-CoA synthetases (ACSs) family containing 26 family members exhibits tissue-specific distribution, distinct fatty acid substrate preferences and diverse biological functions. Increasing evidence indicates that dysregulation of fatty acid metabolism in the liver-gut axis, designated as the bidirectional relationship between the gut, microbiome and liver, is closely associated with a range of human diseases including metabolic disorders, inflammatory disease and carcinoma in the gastrointestinal tract and liver. In this review, we depict the role of ACSs in fatty acid metabolism, possible molecular mechanisms through which they exert functions, and their involvement in hepatocellular and colorectal carcinoma, with particular attention paid to long-chain fatty acids and small-chain fatty acids. Additionally, the liver-gut communication and the liver and gut intersection with the microbiome as well as diseases related to microbiota imbalance in the liver-gut axis are addressed. Moreover, the development of potentially therapeutic small molecules, proteins and compounds targeting ACSs in cancer treatment is summarized.

Acsbg1-dependent mitochondrial fitness is a metabolic checkpoint for tissue Treg cell homeostasis

Regulatory T (Treg) cells are critical for immunological tolerance and immune homeostasis. Treg cells strongly rely on mitochondrial metabolism and show a lower level of glycolysis. However, little is known about the role of lipid metabolism in the regulation of Treg cell homeostasis. Some members of the ACSL family of acyl-coenzyme A (CoA) synthases are expressed in T cells, but their function remains unclear. A combination of RNA-sequencing and proteome analyses shows that Acsbg1, a member of ACSL, is selectively expressed in Treg cells. We show that the genetic deletion of Acsbg1 not only causes mitochondrial dysfunction, but it also dampens other metabolic pathways. The extrinsic supplementation of Acsbg1-deficient Treg cells with oleoyl-CoA restores the phenotype of the Treg metabolic signature. Furthermore, this pathway in ST2+ effector Treg cells enhances immunosuppressive capacity in airway inflammation. Thus, Acsbg1 serves as a metabolic checkpoint governing Treg cell homeostasis and the resolution of lung inflammation.

ACSL family: The regulatory mechanisms and therapeutic implications in cancer

Accumulating evidence shows that deregulation of fatty acid (FA) metabolism is associated with the development of cancer. Long-chain acyl-coenzyme A synthases (ACSLs) are responsible for activating long-chain FAs and are frequently deregulated in cancers. Among the five mammalian ACSL family members, ACSL1 is involved in the TNFα-mediated pro-inflammatory phenotype and mainly facilitates cancer progression. ACSL3 is an androgen-responsive gene. High ACSL3 expression has been detected in a variety of cancers, including melanoma, triple-negative breast cancer (TNBC) and high-grade non-small cell lung carcinoma (NSCLC), and correlates with worse prognosis of patients with these diseases. ACSL4 can exert opposing roles acting as a tumor suppressor or as an oncogene depending on the specific cancer type and tissue environment. Moreover, ACSL4 behaves as a crucial regulator in ferroptosis that is defined as a cell death process caused by iron-dependent peroxidation of lipids. ACSL5 is nuclear-coded and expressed in the mitochondria and physiologically participates in the pro-apoptotic sensing of cells. ACSL5 mainly acts as a tumor suppressor in cancers. ACSL6 downregulation has been observed in many forms of cancers, except in colorectal cancer (CRC). Here, we address the differential regulatory mechanisms of the ACSL family members as well as their functions in carcinogenesis. Moreover, we enumerate the clinical therapeutic implications of ACSLs, which might serve as valuable biomarkers and therapeutic targets for precision cancer treatment.

Inhibition of Acyl-CoA Synthetase Long-Chain Family Member 4 Facilitates Neurological Recovery After Stroke by Regulation Ferroptosis

Background

Ischemic stroke is the main cause of disability worldwide, leading to a serious socioeconomic burden. Ferroptosis is a non-apoptotic form of programmed cell death and is related to various diseases. Acyl-CoA synthetase long-chain family member 4 (ACSL4) is considered a target of ferroptosis, but its specific role in ischemic stroke remains unclear. In this study, we investigate whether the inhibition of ACSL4 promotes the recovery of neurological function in a way that prevents ferroptosis.

Methods

A transient cerebral ischemia model was established for mice by middle cerebral artery occlusion (MCAO); glutathione peroxidase 4 (GPx4), ACSL4 and cyclooxygenase 2 (COX2) were detected by Western blot, and changes to mitochondria were observed by a transmission electron microscope. A kit was used to determine iron levels and lipid peroxide indicators, such as glutathione peroxidase (GPx), reduced glutathione (GSH), total glutathione/oxidized glutathione (GSH/GSSG), lipid peroxidation, reactive oxygen species, superoxide and malonaldehyde. Following MCAO, a ferroptosis inhibitor, liproxstatin-1, was administered intranasally immediately at a concentration of 10 mg/kg. Rosiglitazone was used to inhibit ACSL4 and was administered intravenously 1 h before MCAO at a concentration of 0.4 mg/kg. Brain injury was determined by neurological deficit scores, neuroscore (28-point), corner test and gait analyses, at 24 and 72 h after stroke. Brain infarct volume was determined by 2, 3, 5-Triphenyltetrazolium chloride (TTC) staining at 72 h after stroke.

Results

After MCAO, GPx4 protein expression decreased, ACSL4 and COX2 protein expression increased, GPx activity decreased and iron accumulation. Transmission electron microscopy confirmed that the outer mitochondrial membrane of neurons had ruptured and mitochondrial cristae had decreased or disappeared. Liproxstatin-1 could significantly attenuate the decrease of GPx4 and the increase of COX2 after MCAO, dramatically reducing iron accumulation and decreasing GPx activity, accompanied by a marked reduction in changes in lipid peroxidation indicators. The use of rosiglitazone to inhibit ACSL4 could significantly improve neurological function and reduce the brain infarct volume at 72 h after stroke. Importantly, inhibiting ACSL4 could significantly attenuate the decline of GPx4 after MCAO and markedly attenuate iron accumulation and a decrease in GPx activity. Additionally, changes in lipid peroxidation indicators were also significantly inhibited.

Conclusion

This study indicates that inhibiting ACSL4 can promote the recovery of neurological function after stroke by suppression of ferroptosis.

New inhibitor targeting Acyl-CoA synthetase 4 reduces breast and prostate tumor growth, therapeutic resistance and steroidogenesis

Acyl-CoA synthetase 4 (ACSL4) is an isoenzyme of the fatty acid ligase-coenzyme-A family taking part in arachidonic acid metabolism and steroidogenesis. ACSL4 is involved in the development of tumor aggressiveness in breast and prostate tumors through the regulation of various signal transduction pathways. Here, a bioinformatics analysis shows that the ACSL4 gene expression and proteomic signatures obtained using a cell model was also observed in tumor samples from breast and cancer patients. A well-validated ACSL4 inhibitor, however, has not been reported hindering the full exploration of this promising target and its therapeutic application on cancer and steroidogenesis inhibition. In this study, ACSL4 inhibitor PRGL493 was identified using a homology model for ACSL4 and docking based virtual screening. PRGL493 was then chemically characterized through nuclear magnetic resonance and mass spectroscopy. The inhibitory activity was demonstrated through the inhibition of arachidonic acid transformation into arachidonoyl-CoA using the recombinant enzyme and cellular models. The compound blocked cell proliferation and tumor growth in both breast and prostate cellular and animal models and sensitized tumor cells to chemotherapeutic and hormonal treatment. Moreover, PGRL493 inhibited de novo steroid synthesis in testis and adrenal cells, in a mouse model and in prostate tumor cells. This work provides proof of concept for the potential application of PGRL493 in clinical practice. Also, these findings may prove key to therapies aiming at the control of tumor growth and drug resistance in tumors which express ACSL4 and depend on steroid synthesis.

ACSL4 is a predictive biomarker of sorafenib sensitivity in hepatocellular carcinoma

Sorafenib is the first-line treatment of advanced hepatocellular carcinoma (HCC). However, there is a lack of validated biomarkers to predict sorafenib sensitivity. In this study we investigated the role of ACSL4, a positive-activating enzyme of ferroptosis, in sorafenib-induced cell death and HCC patient outcome. We showed that ACSL4 protein expression was negatively associated with IC50 values of sorafenib in a panel of HCC cell lines (R = -0.952, P < 0.001). Knockdown of ACSL4 expression by specific siRNA/sgRNA significantly attenuated sorafenib-induced lipid peroxidation and ferroptosis in Huh7 cells, and also rescued sorafenib-induced inhibition of xenograft tumor growth in vivo. We selected 29 HCC patients with surgery as primary treatment and sorafenib as postoperative adjunct therapy from a hospital-based cohort. A high proportion (66.7%) of HCC patients who had complete or partial responses to sorafenib treatment (according to the revised RECIST guideline) had higher ACSL4 expression in the pretreated HCC tissues, compared with those who had stable or progressed tumor growth (23.5%, P = 0.029). Since ACSL4 expression was independent of sorafenib treatment, it could serve as a useful predictive biomarker. Taken together, this study demonstrates that ACSL4 is essential for sorafenib-induced ferroptosis and useful for predicting sorafenib sensitivity in HCC. This study may have important translational impacts in precise treatment of HCC.

Small Molecule Regulators of Ferroptosis

Ferroptosis is a dedicated mode of cell death involving iron, reactive oxygen species and lipid peroxidation. Involved in processes such as glutathione metabolism, lysosomal iron retention or interference with lipid metabolism, leading either to activation or inhibition of ferroptosis. Given the implications of ferroptosis in diseases such as cancer, aging, Alzheimer and infectious diseases, new molecular mechanisms underlying ferroptosis and small molecules regulators that target those mechanisms have prompted a great deal of interest. Here, we discuss the current scenario of small molecules modulating ferroptosis and critically assess what is known about their mechanisms of action.

Inhibition of ACSL4 attenuates ferroptotic damage after pulmonary ischemia-reperfusion

Lung ischemia-reperfusion (IR) injury is a common clinical pathology associated with high mortality. Ferroptosis, a novel mode of cell death elicited by iron-dependent phospholipid peroxidation, has been implicated in ischemic events. Acyl-CoA synthetase long-chain family member 4 (ACSL4) is one of the main enzymes in pro-ferroptotic lipid metabolism. In this study, the involvement of ferroptotic death in different durations of reperfusion was evaluated by assessing the iron content, malondialdehyde, and glutathione levels, ferroptosis-related protein expression, and mitochondria morphology. The roles of ferroptosis-specific inhibitor, liproxastin-1 (Lip-1), and ACSL4 modulation in a preventive regimen were assessed in vivo and in vitro. The hallmarks of pulmonary function, such as histological lung injury score, wet/dry ratio, and oxygenation index, were evaluated as well. Results showed that lung IR increased the tissue iron content and lipid peroxidation accumulation, along with key protein (GPX4 and ACSL4) expression alteration during reperfusion. Pretreatment with Lip-1 inhibited ferroptosis and ameliorated lung IR-induced injury in animal and cell models. In addition, administering ACSL4 inhibitor rosiglitazone before ischemia diminished the ferroptotic damage in IR-injured lung tissue, consistent with the protective effect of ACSL4 knockdown on lung epithelial cells subjected to hypoxia/reoxygenation. Thus, this study delineated that IR-induced ferroptotic cell death in lung tissue and ACSL4 were correlated with this process. Inhibition of ferroptosis and ACSL4 mitigated the ferroptotic damage in IR-induced lung injury by reducing lipid peroxidation and increasing the glutathione and GPX4 levels.

Identification of MiR-211-5p as a tumor suppressor by targeting ACSL4 in Hepatocellular Carcinoma

BACKGROUND

Liver cancer is among the most common malignancy worldwide. Hepatocellular carcinoma (HCC), the principal histological subtype of liver cancer, is globally the third most common cause of cancer-related mortality. The high rates of recurrence and metastasis contribute to the poor prognosis of HCC patients. In recent years, increasing evidence has shown that microRNAs (miRNAs) are involved in the tumorigenesis, progression, and prognosis of HCC.

METHODS

To screen for key candidate miRNAs in HCC, three microarray datasets were downloaded from Gene Expression Omnibus (GEO). The sole common differentially expressed miRNA (DEmiR) observed in the above three datasets using a Venn diagram was microRNA-211-5p (miR-211-5p). The expression of miR-211-5p from HCC tissues was measured in several HCC cell lines. Additionally, using Kaplan-Meier plots, the potential prognostic value of miR-211-5p in HCC was analyzed. Cell counting kit-8 (CCK-8) and transwell assays examined the ability of miR-211-5p to induce cell proliferation, migration, and invasion in HCC cultures. The interaction of miR-211-5p and Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) was assessed both theoretically and using a luciferase reporter assay. Finally, the ability of miR-211-5p to modulate tumorigenesis in HCC in vivo was assessed after establishing a xenograft model.

RESULTS

qRT-PCR demonstrated that the relative expression of miR-211-5p was considerably down-regulated in HCC tissues and cell lines compared with normal tissue. Kaplan-Meier plots indicated that HCC patients with decreased expression of miR-211-5p had poor overall survival. Upregulation of miR-211-5p in vitro consistently suppressed cell proliferation, migration, and invasion. In contrast, enhanced expression of ACSL4 promoted a malignant phenotype in HCC cells. Importantly, we discovered that ACSL4 was a direct downstream target of miR-211-5p in HCC, and that miR-211-5p suppressed the malignant phenotype by inhibition of ACSL4 expression. Furthermore, miR-211-5p overexpression impaired tumorigenesis and growth of HCC in vivo.

CONCLUSIONS

Targeting miR-211-5p and the downstream gene ACSL4 will possibly provide novel insight and represents a promising approach to future therapy of HCC patients.

Long-Chain Acyl-CoA Synthetase 1 Role in Sepsis and Immunity: Perspectives From a Parallel Review of Public Transcriptome Datasets and of the Literature

A potential role for the long-chain acyl-CoA synthetase family member 1 (ACSL1) in the immunobiology of sepsis was explored during a hands-on training workshop. Participants first assessed the robustness of the potential gap in biomedical knowledge identified via an initial screen of public transcriptome data and of the literature associated with ACSL1. Increase in ACSL1 transcript abundance during sepsis was confirmed in several independent datasets. Querying the ACSL1 literature also confirmed the absence of reports associating ACSL1 with sepsis. Inferences drawn from both the literature (via indirect associations) and public transcriptome data (via correlation) point to the likely participation of ACSL1 and ACSL4, another family member, in inflammasome activation in neutrophils during sepsis. Furthermore, available clinical data indicate that levels of ACSL1 and ACSL4 induction was significantly higher in fatal cases of sepsis. This denotes potential translational relevance and is consistent with involvement in pathways driving potentially deleterious systemic inflammation. Finally, while ACSL1 expression was induced in blood in vitro by a wide range of pathogen-derived factors as well as TNF, induction of ACSL4 appeared restricted to flagellated bacteria and pathogen-derived TLR5 agonists and IFNG. Taken together, this joint review of public literature and omics data records points to two members of the acyl-CoA synthetase family potentially playing a role in inflammasome activation in neutrophils. Translational relevance of these observations in the context of sepsis and other inflammatory conditions remain to be investigated.

Macrophage fatty acid metabolism and atherosclerosis: The rise of PUFAs

Among the pathways involved in the regulation of macrophage functions, the metabolism of unsaturated fatty acids is central. Indeed, unsaturated fatty acids act as precursors of bioactive molecules such as prostaglandins, leukotrienes, resolvins and related compounds. As components of phospholipids, they have a pivotal role in cell biology by regulating membrane fluidity and membrane-associated cellular processes. Finally, polyunsaturated fatty acids (PUFAs) are also endowed with ligand properties for numerous membrane or nuclear receptors. Although myeloid cells are dependent on the metabolic context for the uptake of essential FAs, recent studies showed that these cells autonomously handle the synthesis of n-3 and n-6 long chain PUFAs such as arachidonic acid and eicosapentaenoic acid. Moreover, targeting PUFA metabolism in macrophages influences pathological processes, including atherosclerosis, by modulating macrophage functions. Omics evidence also supports a role for macrophage PUFA metabolism in the development of cardiometabolic diseases in humans. Currently, there is a renewed interest in the role of n-3/n-6 PUFAs and their oxygenated derivatives in the onset of atherosclerosis and plaque rupture. Purified n-3 FA supplementation appears as a potential strategy in the treatment and prevention of cardiovascular diseases. In this context, the ability of immune cells to handle and to synthesize very long chain PUFA must absolutely be integrated and better understood.

Liver-specific knockdown of long-chain acyl-CoA synthetase 4 reveals its key role in VLDL-TG metabolism and phospholipid synthesis in mice fed a high-fat diet

Long-chain acyl-CoA synthetase 4 (ACSL4) has a unique substrate specificity for arachidonic acid. Hepatic ACSL4 is coregulated with the phospholipid (PL)-remodeling enzyme lysophosphatidylcholine (LPC) acyltransferase 3 by peroxisome proliferator-activated receptor δ to modulate the plasma triglyceride (TG) metabolism. In this study, we investigated the acute effects of hepatic ACSL4 deficiency on lipid metabolism in adult mice fed a high-fat diet (HFD). Adenovirus-mediated expression of a mouse ACSL4 shRNA (Ad-shAcsl4) in the liver of HFD-fed mice led to a 43% reduction of hepatic arachidonoyl-CoA synthetase activity and a 53% decrease in ACSL4 protein levels compared with mice receiving control adenovirus (Ad-shLacZ). Attenuated ACSL4 expression resulted in a substantial decrease in circulating VLDL-TG levels without affecting plasma cholesterol. Lipidomics profiling revealed that knocking down ACSL4 altered liver PL compositions, with the greatest impact on accumulation of abundant LPC species (LPC 16:0 and LPC 18:0) and lysophosphatidylethanolamine (LPE) species (LPE 16:0 and LPE 18:0). In addition, fasting glucose and insulin levels were higher in Ad-shAcsl4-transduced mice versus control (Ad-shLacZ). Glucose tolerance testing further indicated an insulin-resistant phenotype upon knockdown of ACSL4. These results provide the first in vivo evidence that ACSL4 plays a role in plasma TG and glucose metabolism and hepatic PL synthesis of hyperlipidemic mice.

Identification of a novel function of hepatic long-chain acyl-CoA synthetase-1 (ACSL1) in bile acid synthesis and its regulation by bile acid-activated farnesoid X receptor

Long-chain acyl-CoA synthetase 1 (ACSL1) plays a pivotal role in fatty acid β‑oxidation in heart, adipose tissue and skeletal muscle. However, key functions of ACSL1 in the liver remain largely unknown. We investigated acute effects of hepatic ACSL1 deficiency on lipid metabolism in adult mice under hyperlipidemic and normolipidemic conditions. We knocked down hepatic ACSL1 expression using adenovirus expressing a ACSL1 shRNA (Ad-shAcsl1) in mice fed a high-fat diet or a normal chow diet. Hepatic ACSL1 depletion generated a hypercholesterolemic phenotype in mice fed both diets with marked elevations of total cholesterol, LDL-cholesterol and free cholesterol in circulation and accumulations of cholesterol in the liver. Furthermore, SREBP2 pathway in ACSL1 depleted livers was severely repressed with a 50% reduction of LDL receptor protein levels. In contrast to the dysregulated cholesterol metabolism, serum triglycerides, free fatty acid and phospholipid levels were unaffected. Mechanistic investigations of genome-wide gene expression profiling and pathway analysis revealed that ACSL1 depletion repressed expressions of several key enzymes for bile acid biosynthesis, consequently leading to reduced liver bile acid levels and altered bile acid compositions. These results are the first demonstration of a requisite role of ACSL1 in bile acid biosynthetic pathway in liver tissue. Furthermore, we discovered that Acsl1 is a novel molecular target of the bile acid-activated farnesoid X receptor (FXR). Activation of FXR by agonist obeticholic acid repressed the expression of ACSL1 protein and mRNA in the liver of FXR wild-type mice but not in FXR knockout mice.

Smooth muscle glucose metabolism promotes monocyte recruitment and atherosclerosis in a mouse model of metabolic syndrome

Metabolic syndrome contributes to cardiovascular disease partly through systemic risk factors. However, local processes in the artery wall are becoming increasingly recognized to exacerbate atherosclerosis both in mice and humans. We show that arterial smooth muscle cell (SMC) glucose metabolism markedly synergizes with metabolic syndrome in accelerating atherosclerosis progression, using a low-density lipoprotein receptor-deficient mouse model. SMCs in proximity to atherosclerotic lesions express increased levels of the glucose transporter GLUT1. Cytokines, such as TNF-α produced by lesioned arteries, promote GLUT1 expression in SMCs, which in turn increases expression of the chemokine CCL2 through increased glycolysis and the polyol pathway. Furthermore, overexpression of GLUT1 in SMCs, but not in myeloid cells, accelerates development of larger, more advanced lesions in a mouse model of metabolic syndrome, which also exhibits elevated levels of circulating Ly6Chi monocytes expressing the CCL2 receptor CCR2. Accordingly, monocyte tracing experiments demonstrate that targeted SMC GLUT1 overexpression promotes Ly6Chi monocyte recruitment to lesions. Strikingly, SMC-targeted GLUT1 overexpression fails to accelerate atherosclerosis in mice that do not exhibit the metabolic syndrome phenotype or monocytosis. These results reveal a potentially novel mechanism whereby arterial smooth muscle glucose metabolism synergizes with metabolic syndrome to accelerate monocyte recruitment and atherosclerosis progression.

A role for long-chain acyl-CoA synthetase-4 (ACSL4) in diet-induced phospholipid remodeling and obesity-associated adipocyte dysfunction

Objective

Regulation of fatty acid (FA) metabolism is central to adipocyte dysfunction during diet-induced obesity (DIO). Long-chain acyl-CoA synthetase-4 (ACSL4) has been hypothesized to modulate the metabolic fates of polyunsaturated FA (PUFA), including arachidonic acid (AA), but the in vivo actions of ACSL4 are unknown. The purpose of our studies was to determine the in vivo role of adipocyte ACSL4 in regulating obesity-associated adipocyte dysfunction.

Methods

We developed a novel mouse model with adipocyte-specific ablation of ACSL4 (Ad-KO) using loxP Cre recombinase technology. Metabolic phenotyping of Ad-KO mice relative to their floxed littermates (ACSL4^floxed) was performed, including body weight and body composition over time; insulin and glucose tolerance tests; and energy expenditure, activity, and food intake in metabolic cages. Adipocytes were isolated for ex vivo adipocyte oxygen consumption by Clark electrode and lipidomics analysis. In vitro adipocyte analysis including oxygen consumption by Seahorse and real-time PCR analysis were performed to confirm our in vivo findings.

Results

Ad-KO mice were protected against DIO, adipocyte death, and metabolic dysfunction. Adipocytes from Ad-KO mice fed high-fat diet (HFD) had reduced incorporation of AA into phospholipids (PL), free AA, and levels of the AA lipid peroxidation product 4-hydroxynonenal (4-HNE). Additionally, adipocytes from Ad-KO mice fed HFD had reduced p53 activation and increased adipocyte oxygen consumption (OCR), which we demonstrated are direct effects of 4-HNE on adipocytes in vitro.

Conclusion

These studies are the first to elucidate ACSL4's in vivo actions to regulate the incorporation of AA into PL and downstream effects on DIO-associated adipocyte dysfunction. By reducing the incorporation of AA into PL and free fatty acid pools in adipocytes, Ad-KO mice were significantly protected against HFD-induced increases in adipose and liver fat accumulation, adipocyte death, gonadal white adipose tissue (gWAT) inflammation, and insulin resistance (IR). Additionally, deficiency of adipocyte ACSL4 expression in mice fed a HFD resulted in increased gWAT adipocyte OCR and whole body energy expenditure (EE).

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ACSL4 expression is upregulated in murine white adipocytes during diet-induced obesity.

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Mice with adipocyte-specific ablation of ACSL4 (Ad-KO) are protected against diet-induced obesity, adipocyte death and metabolic dysfunction.

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Lipidomics profiling of isolated adipocytes from Ad-KO mice fed a high-fat diet (HFD) had reduced arachidonic acid (AA) in phospholipids.

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Adipocytes from Ad-KO mice fed HFD had reduced free AA and levels of the AA lipid peroxidation product 4-hydroxynonenal (4-HNE).

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Adipocytes from Ad-KO mice fed HFD had reduced p53 activation and increased adipocyte oxygen consumption (OCR).

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P53 activation and inhibited adipocyte OCR are direct effects of 4-HNE on adipocytes in vitro.

Phosphatidylserine decarboxylase CT699, lysophospholipid acyltransferase CT775, and acyl-ACP synthase CT776 provide membrane lipid diversity to Chlamydia trachomatis

De novo lipid synthesis and scavenging of fatty acids (FA) are processes essential for the formation of the membrane of the human pathogen Chlamydia trachomatis (C.t.). Host FA are assimilated via esterification by the bacterial acyl-acyl carrier protein (ACP) synthase AasC but inhibitors of the host acyl-CoA synthetase enymes ACSL also impaired growth of C.t. in human cells. In E. coli, activity of AasC was sensitive to triacsin C and rosiglitazone G. The absence of a triacsin C-insensitive pathway and the increased inhibition by rosiglitazone G confirmed the sensitivity of the bacterial acyl-ACP synthase to these drugs in infected human cells. We found no evidence that the human ACSL enzymes are required for lipid formation by C.t. The broad substrate specificity of acyltransferase CT775 provides C.t. with the capacity to incorporate straight-chain and bacterial specific branched-chain fatty acids. CT775 accepts both acyl-ACP and acyl-CoA as acyl donors and, 1- or 2-acyl isomers of lysophosphoplipids as acyl acceptors. The enzyme responsible for remodeling of human phosphatidylserine to bacterial phosphatidylethanolamine was identified as CT699. These findings provide evidence that the pathogen has the ability to extend the lipid diversity of its membrane.

The α6β4 integrin promotes resistance to ferroptosis

Lipid peroxidation in the plasma membrane can cause ferroptosis, a form of regulated necrosis. Brown et al. show that matrix detachment can induce ferroptosis, and the α6β4 integrin impedes that process by suppressing expression of the proferroptotic enzyme ACSL4.

Increases in lipid peroxidation can cause ferroptosis, a form of cell death triggered by inhibition of glutathione peroxidase 4 (GPX4), which catalyzes the reduction of lipid peroxides and is a target of ferroptosis inducers, such as erastin. The α6β4 integrin protects adherent epithelial and carcinoma cells from ferroptosis induced by erastin. In addition, extracellular matrix (ECM) detachment is a physiologic trigger of ferroptosis, which is evaded by α6β4. The mechanism that enables α6β4 to evade ferroptosis involves its ability to protect changes in membrane lipids that are proferroptotic. Specifically, α6β4-mediated activation of Src and STAT3 suppresses expression of ACSL4, an enzyme that enriches membranes with long polyunsaturated fatty acids and is required for ferroptosis. Adherent cells lacking α6β4 require an inducer, such as erastin, to undergo ferroptosis because they sustain GPX4 expression, despite their increase in ACSL4. In contrast, ECM detachment of cells lacking α6β4 is sufficient to trigger ferroptosis because GPX4 is suppressed. This causal link between α6β4 and ferroptosis has implications for cancer biology and therapy.

Overexpression of Acyl-CoA Ligase 4 (ACSL4) in Patients with Hepatocellular Carcinoma and its Prognosis

Background

Recently, accumulating studies have found that ACSL4 dysregulation is related to a great number of malignant tumors. The purpose of the present study was to explore the relationship between ACSL4 expression level and clinical prognosis of hepatocellular carcinoma (HCC) patients.

Material/Methods

The Oncomine and TCGA databases were used to predict the expression of ACSL4 mRNA in HCC and its association with HCC prognosis. Further, immunohistochemistry was performed to verify the ACSL4 protein expression in 116 paired HCC and adjacent normal tissues. Kaplan-Meier and cox analysis were performed to validate the correlation between ACSL4 expression and HCC prognosis.

Results

We first used the Oncomine database to find that ACSL4 mRNA expression level was significantly higher in HCC tissues than that in normal tissues (p all <0.001). The results were consistent with those in the TCGA database. Then, immunohistochemical results demonstrated that the ACSL4 positive expression rate was 70.7% in HCC tissues. ACSL4 differential expression level was significantly related to Edmondson grade (p=0.010), AFP (p=0.001) and TNM stage (p=0.012). Survival analysis revealed that both overall survival (OS) and disease-free survival (DFS) time were remarkably reduced in HCC patients with ACSL4 high expression (p=0.001 and 0.000, respectively). Moreover, Cox multivariate analysis demonstrated that ACSL4 expression was the only independent prognostic factor for both OS and DFS (both p values=0.001).

Conclusions

Taken together, our study demonstrated that ACSL4 was overexpressed in HCC, and it will be a new potential therapeutic target for HCC as an independent adverse prognostic parameter.

Association of long-chain acyl-coenzyme A synthetase 5 expression in human breast cancer by estrogen receptor status and its clinical significance

The lipid metabolic enzymes are considered candidate therapeutic targets for breast cancer. Long-chain acyl-coenzyme A (CoA) synthase (ACSL) is one of lipid metabolic enzymes and converts free-fatty acid to fatty acid-CoA. Five ACSL isoforms including ACSL1, ACSL3, ACSL4, ACSL5 and ACSL6 are identified in human. High ACSL4 expression has been observed in aggressive breast cancer phenotype. However, the role of other isoforms is still little-known. We therefore, analyzed the expression of ACSL isoforms in each subtype of breast cancer within METABRIC dataset and cancer cell line encyclopedia dataset. The expression levels of ACSL1, ACSL4 and ACSL5 in estrogen receptor (ER)-negative group were higher than that in ER-positive group. Similar expression pattern was detected among breast cancer cell lines MCF-7 (ER-positive) and MDA-MB-231 (ER-negative). Treatment of ACSL inhibitor triacsin C which inhibited enzyme activity of ACSL 1, 3, 4 and 5 suppressed cell growth of MCF-7 and MDA-MB-231. Our results further showed that high ACSL5 expression was associated with good prognosis in patients with both ER-positive and ER-negative breast cancer through KM plotter analysis. These results suggest that ACSL1, ACSL4 and ACSL5 expression is regulated by ER signaling pathways and ACSL5 is a potential novel biomarker for predicting prognosis of breast cancer patients.

Characterization of Acyl-CoA synthetase isoforms in pancreatic beta cells: Gene silencing shows participation of ACSL3 and ACSL4 in insulin secretion

Long-chain acyl-CoA synthetases (ACSLs) convert fatty acids to fatty acyl-CoAs to regulate various physiologic processes. We characterized the ACSL isoforms in a cell line of homogeneous rat beta cells (INS-1 832/13 cells) and human pancreatic islets. ACSL4 and ACSL3 proteins were present in the beta cells and human and rat pancreatic islets and concentrated in insulin secretory granules and less in mitochondria and negligible in other intracellular organelles. ACSL1 and ACSL6 proteins were not seen in INS-1 832/13 cells or pancreatic islets. ACSL5 protein was seen only in INS-1 832/13 cells. With shRNA-mediated gene silencing we developed stable ACSL knockdown cell lines from INS-1 832/13 cells. Glucose-stimulated insulin release was inhibited ∼50% with ACSL4 and ACSL3 knockdown and unaffected in cell lines with knockdown of ACSL5, ACLS6 and ACSL1. Lentivirus shRNA-mediated gene silencing of ACSL4 and ACSL3 in human pancreatic islets inhibited glucose-stimulated insulin release. ACSL4 and ACSL3 knockdown cells showed inhibition of ACSL enzyme activity more with arachidonate than with palmitate as a substrate, consistent with their preference for unsaturated fatty acids as substrates. ACSL4 knockdown changed the patterns of fatty acids in phosphatidylserines and phosphatidylethanolamines. The results show the involvement of ACLS4 and ACLS3 in insulin secretion.

Oxidized arachidonic and adrenic PEs navigate cells to ferroptosis

Enigmatic lipid peroxidation products have been claimed as the proximate executioners of ferroptosis-a specialized death program triggered by insufficiency of glutathione peroxidase 4 (GPX4). Using quantitative redox lipidomics, reverse genetics, bioinformatics and systems biology, we discovered that ferroptosis involves a highly organized oxygenation center, wherein oxidation in endoplasmic-reticulum-associated compartments occurs on only one class of phospholipids (phosphatidylethanolamines (PEs)) and is specific toward two fatty acyls-arachidonoyl (AA) and adrenoyl (AdA). Suppression of AA or AdA esterification into PE by genetic or pharmacological inhibition of acyl-CoA synthase 4 (ACSL4) acts as a specific antiferroptotic rescue pathway. Lipoxygenase (LOX) generates doubly and triply-oxygenated (15-hydroperoxy)-diacylated PE species, which act as death signals, and tocopherols and tocotrienols (vitamin E) suppress LOX and protect against ferroptosis, suggesting a homeostatic physiological role for vitamin E. This oxidative PE death pathway may also represent a target for drug discovery.

Acyl-CoA synthetase-4, a new regulator of mTOR and a potential therapeutic target for enhanced estrogen receptor function in receptor-positive and -negative breast cancer

Although the role of acyl-CoA synthetase 4 (ACSL4) in mediating an aggressive phenotype is well accepted, there is little evidence as to the early steps through which ACSL4 increases tumor growth and progression. In this study, and by means of the stable transfection of MCF-7 cells with ACSL4 using the tetracycline Tet-Off system (MCF-7 Tet-Off/ACSL4), we identify the mTOR pathway as one of the main specific signatures of ACSL4 expression and demonstrate the partial involvement of the lipoxygenase pathway in the activation of mTOR. The specificity of ACSL4 action on mTOR signaling is also determined by doxycycline inhibition of ACSL4 expression in MCF-7 Tet-Off/ACSL4 cells, by the expression of ACSL4 in the non-aggressive T47D breast cancer cell line and by knocking down this enzyme expression in the MDA-MB-231 breast cancer cells, which constitutively express ACSL4. ACSL4 regulates components of the two complexes of the mTOR pathway (mTORC1/2), along with upstream regulators and substrates.

We show that mTOR inhibitor rapamycin and ACSL4 inhibitor rosiglitazone can act in combination to inhibit cell growth. In addition, we demonstrate a synergistic effect on cell growth inhibition by the combination of rosiglitazone and tamoxifen, an estrogen receptor α (ERα) inhibitor. Remarkably, this synergistic effect is also evident in the triple negative MDA-MB-231 cells in vitro and in vivo.

These results suggest that ACSL4 could be a target to restore tumor hormone dependence in tumors with poor prognosis for disease-free and overall survival, in which no effective specifically targeted therapy is readily available.

Chlamydia trachomatis growth and development requires the activity of host Long-chain Acyl-CoA Synthetases (ACSLs)

The obligate-intracellular pathogen Chlamydia trachomatis (Ct) has undergone considerable genome reduction with consequent dependence on host biosynthetic pathways, metabolites and enzymes. Long-chain acyl-CoA synthetases (ACSLs) are key host-cell enzymes that convert fatty acids (FA) into acyl-CoA for use in metabolic pathways. Here, we show that the complete host ACSL family [ACSL1 and ACSL3-6] translocates into the Ct membrane-bound vacuole, termed inclusion, and remains associated with membranes of metabolically active forms of Ct throughout development. We discovered that three different pharmacologic inhibitors of ACSL activity independently impede Ct growth in a dose-dependent fashion. Using an FA competition assay, host ACSLs were found to activate Ct branched-chain FAs, suggesting that one function of the ACSLs is to activate Ct FAs and host FAs (recruited from the cytoplasm) within the inclusion. Because the ACSL inhibitors can deplete lipid droplets (LD), we used a cell line where LD synthesis was switched off to evaluate whether LD deficiency affects Ct growth. In these cells, we found no effect on growth or on translocation of ACSLs into the inclusion. Our findings support an essential role for ACSL activation of host-cell and bacterial FAs within the inclusion to promote Ct growth and development, independent of LDs.