Blockade of the Lysophosphatidylserine Lipase ABHD12 Potentiates Ferroptosis in Cancer Cells

Inhalation of nicotine-containing electronic cigarette vapor exacerbates the features of COPD by inducing ferroptosis in βENaC-overexpressing mice

Introduction

Chronic obstructive pulmonary disease (COPD) is currently listed as the 3rd leading cause of death in the United States. Accumulating data shows the association between COPD occurrence and the usage of electronic nicotine delivery systems (ENDS) in patients. However, the underlying pathogenesis mechanisms of COPD have not been fully understood.

Methods

In the current study, bENaC-overexpressing mice (bENaC mice) were subjected to whole-body ENDS exposure. COPD related features including emphysema, mucus accumulation, inflammation and fibrosis are examined by tissue staining, FACS analysis, cytokine measurement. Cell death and ferroptosis of alveolar epithelial cells were further evaluated by multiple assays including staining, FACS analysis and lipidomics.

Results

ENDS-exposed mice displayed enhanced emphysema and mucus accumulation, suggesting that ENDS exposure promotes COPD features. ENDS exposure also increased immune cell number infiltration in bronchoalveolar lavage and levels of multiple COPD-related cytokines in the lungs, including CCL2, IL-4, IL-13, IL-10, M-CSF, and TNF-α. Moreover, we observed increased fibrosis in ENDS-exposed mice, as evidenced by elevated collagen deposition and a-SMA+ myofibroblast accumulation. By investigating possible mechanisms for how ENDS promoted COPD, we demonstrated that ENDS exposure induced cell death of alveolar epithelial cells, evidenced by TUNEL staining and Annexin V/PI FACS analysis. Furthermore, we identified that ENDS exposure caused lipid dysregulations, including TAGs (9 species) and phospholipids (34 species). As most of these lipid species are highly associated with ferroptosis, we confirmed ENDS also enhanced ferroptosis marker CD71 in both type I and type II alveolar epithelial cells.

Discussion

Overall, our data revealed that ENDS exposure exacerbates features of COPD in bENaC mice including emphysema, mucus accumulation, abnormal lung inflammation, and fibrosis, which involves the effect of COPD development by inducing ferroptosis in the lung.

The cell biology of ferroptosis

Ferroptosis is a non-apoptotic cell death mechanism characterized by iron-dependent membrane lipid peroxidation. Here, we review what is known about the cellular mechanisms mediating the execution and regulation of ferroptosis. We first consider how the accumulation of membrane lipid peroxides leads to the execution of ferroptosis by altering ion transport across the plasma membrane. We then discuss how metabolites and enzymes that are distributed in different compartments and organelles throughout the cell can regulate sensitivity to ferroptosis by impinging upon iron, lipid and redox metabolism. Indeed, metabolic pathways that reside in the mitochondria, endoplasmic reticulum, lipid droplets, peroxisomes and other organelles all contribute to the regulation of ferroptosis sensitivity. We note how the regulation of ferroptosis sensitivity by these different organelles and pathways seems to vary between different cells and death-inducing conditions. We also highlight transcriptional master regulators that integrate the functions of different pathways and organelles to modulate ferroptosis sensitivity globally. Throughout this Review, we highlight open questions and areas in which progress is needed to better understand the cell biology of ferroptosis.

A role for pH dynamics regulating transcription factor DNA binding selectivity

Intracellular pH (pHi) dynamics regulates diverse cell processes such as proliferation, dysplasia, and differentiation, often mediated by the protonation state of a functionally critical histidine residue in endogenous pH sensing proteins. How pHi dynamics can directly regulate gene expression and whether transcription factors can function as pH sensors has received limited attention. We tested the prediction that transcription factors with a histidine in their DNA binding domain (DBD) that forms hydrogen bonds with nucleotides can have pH-regulated activity, which is relevant to more than 85 transcription factors in distinct families, including FOX, KLF, SOX and MITF/Myc. Focusing on FOX family transcription factors, we used unbiased SELEX-seq to identify pH-dependent DNA binding motif preferences, then confirm pH-regulated binding affinities for FOXC2, FOXM1, and FOXN1 to a canonical FkhP DNA motif that are 2.5 to 7.5 greater at pH 7.0 compared with pH 7.5. For FOXC2, we also find greater activity for an FkhP motif at lower pHi in cells and that pH-regulated binding and activity are dependent on a conserved histidine (His122) in the DBD. RNA-seq with FOXC2 also reveals pH-dependent differences in enriched promoter motifs. Our findings identify pH-regulated transcription factor-DNA binding selectivity with relevance to how pHi dynamics can regulate gene expression for myriad cell behaviours.

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

Ferroptosis and ferroptosis-inducing nanomedicine as a promising weapon in combination therapy of prostate cancer

Incidence and mortality of prostate cancer (PCa) rank in the top five among male tumors. However, single treatment modalities are often restricted due to biochemical recurrence and drug resistance, necessitating the development of new approaches for the combination treatment of castration-resistant and neuroendocrine PCa. Ferroptosis is characterized by the accumulation of iron-overload-mediated lipid peroxidation and has shown promising outcomes in anticancer treatment, prompting us to present a review reporting the application of ferroptosis in the treatment of PCa. First, the process and mechanism of ferroptosis are briefly reviewed. Second, research advances combining ferroptosis-inducing agents and clinical treatment regimens, which exhibit a "two-pronged approach" effect, are further summarized. Finally, the recent progress on ferroptosis-inducing nanomaterials for combination anticancer therapy is presented. This review is expected to provide novel insights into ferroptosis-based combination treatment in drug-resistant PCa.

ABHD12 contributes to tumorigenesis and sorafenib resistance by preventing ferroptosis in hepatocellular carcinoma

Sorafenib induces ferroptosis, making it a useful treatment against advanced liver hepatocellular carcinoma (LIHC). However, sorafenib resistance is extremely common among LIHC patients. Here, we used a comprehensive approach to investigate the effects of ABHD12, which regulates tumorigenesis and sorafenib resistance in LIHC. We validated ABHD12 expression was upregulated in LIHC tissue, which correlated with worse overall survival and related to tumor size or stage. ABHD12 facilitated a pro-tumorigenic phenotype involving increased cell proliferation, migration, and clonogenicity as well as sorafenib resistance. Knockout of ABHD12 sensitized liver cancer cells to sorafenib-induced ferroptosis. Co-delivery of sorafenib and ABHD12 inhibitor into a nude mouse model enhanced therapeutic efficacy for LIHC. Our study demonstrates that ABHD12 contributes to tumor growth and sorafenib resistance in liver cancer, which indicate the promising potential of ABHD12 in diagnosis and prognosis as well as highlight the potential therapeutic applications for co-delivery of sorafenib and ABHD12 inhibitor.

Hippo pathway in intestinal diseases: focusing on ferroptosis

The incidence of intestinal diseases, such as inflammatory bowel disease, gastric cancer, and colorectal cancer, has steadily increased over the past decades. The Hippo pathway is involved in cell proliferation, tissue and organ damage, energy metabolism, tumor formation, and other physiologic processes. Ferroptosis is a form of programmed cell death characterized by the accumulation of iron and lipid peroxides. The Hippo pathway and ferroptosis are associated with various intestinal diseases; however, the crosstalk between them is unclear. This review elaborates on the current research on the Hippo pathway and ferroptosis in the context of intestinal diseases. We summarized the connection between the Hippo pathway and ferroptosis to elucidate the underlying mechanism by which these pathways influence intestinal diseases. We speculate that a mutual regulatory mechanism exists between the Hippo pathway and ferroptosis and these two pathways interact in several ways to regulate intestinal diseases.

Lipid Quality Control and Ferroptosis: From Concept to Mechanism

Cellular quality control systems sense and mediate homeostatic responses to prevent the buildup of aberrant macromolecules, which arise from errors during biosynthesis, damage by environmental insults, or imbalances in enzymatic and metabolic activity. Lipids are structurally diverse macromolecules that have many important cellular functions, ranging from structural roles in membranes to functions as signaling and energy-storage molecules. As with other macromolecules, lipids can be damaged (e.g., oxidized), and cells require quality control systems to ensure that nonfunctional and potentially toxic lipids do not accumulate. Ferroptosis is a form of cell death that results from the failure of lipid quality control and the consequent accumulation of oxidatively damaged phospholipids. In this review, we describe a framework for lipid quality control, using ferroptosis as an illustrative example to highlight concepts related to lipid damage, membrane remodeling, and suppression or detoxification of lipid damage via preemptive and damage-repair lipid quality control pathways. Expected final online publication date for the Annual Review of Biochemistry , Volume 93 is June 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Ferroptosis, a subtle talk between immune system and cancer cells: To be or not to be?

Ferroptosis, an established form of programmed cell death discovered in 2012, is characterized by an imbalance in iron metabolism, lipid metabolism, and antioxidant metabolism. Activated CD8 + T cells can trigger ferroptosis in tumor cells by releasing interferon-γ, which initiates the ferroptosis program. Despite the remarkable progress made in treating various tumors with immunotherapy, such as anti-PD1/PDL1, there are still significant challenges to overcome, including limited treatment options and drug resistance. In this review, we exam the potential biological significance of the ferroptosis phenotype using bioinformatics and review the latest advancements in understanding the mechanism of ferroptosis-mediated anti-tumor immunotherapy. Furthermore, we revisit the host immune system, immune microenvironment, ferroptotic defense system, metabolic reprogramming, and key genes that regulate the occurrence and resistance of ferroptosis of tumor cell. Additionally, several immune-combined ferroptosis treatment strategies were put forward to improve immunotherapy efficacy and to provide new insights into reversing anti-tumor immune drug resistance.

Current insights into the functional roles of ferroptosis in musculoskeletal diseases and therapeutic implications

Ferroptosis is a novel type of cell death associated with iron accumulation and excessive lipid peroxidation. Elucidating the underlying molecular mechanisms of ferroptosis is intensively related to the development and treatment of multiple diseases, including musculoskeletal disorders. Moreover, in vitro and in vivo studies have shown the importance of oxidative stress in musculoskeletal conditions such as osteoporosis, osteoarthritis, rheumatoid arthritis, and osteosarcoma. Ferroptosis-derived clinical management of musculoskeletal diseases offers tremendous and attractive opportunities. Notably, ferroptosis agonists have been proven to enhance the sensitivity of osteosarcoma cells to conventional therapeutic strategies. In this review, we have mainly focused on the implications of ferroptosis regulation in the pathophysiology and therapeutic response of musculoskeletal disorders. Understanding roles of ferroptosis for controlling musculoskeletal diseases might provide directions for ferroptosis-driven therapies, which could be promising for the development of novel therapeutic strategies.

Targeting lipid metabolism for ferroptotic cancer therapy

It has been 10 years since the concept of ferroptosis was put forward and research focusing on ferroptosis has been increasing continuously. Ferroptosis is driven by iron-dependent lipid peroxidation, which can be antagonized by glutathione peroxidase 4 (GPX4), ferroptosis inhibitory protein 1 (FSP1), dihydroorotate dehydrogenase (DHODH) and Fas-associated factor 1 (FAF1). Various cellular metabolic events, including lipid metabolism, can modulate ferroptosis sensitivity. It is worth noting that the reprogramming of lipid metabolism in cancer cells can promote the occurrence and development of tumors. The metabolic flexibility of cancer cells opens the possibility for the coordinated targeting of multiple lipid metabolic pathways to trigger cancer cells ferroptosis. In addition, cancer cells must obtain immortality, escape from programmed cell death including ferroptosis, to promote cancer progression, which provides new perspectives for improving cancer therapy. Targeting the vulnerability of ferroptosis has received attention as one of the significant possible strategies to treat cancer given its role in regulating tumor cell survival. We review the impact of iron and lipid metabolism on ferroptosis and the potential role of the crosstalk of lipid metabolism reprogramming and ferroptosis in antitumor immunity and sum up agents targeting lipid metabolism and ferroptosis for cancer therapy.

Ferroptosis in osteosarcoma: A promising future

The incidence of osteosarcoma (OS) is increasing year by year, and the prognosis of patients with advanced OS is extremely poor due to the tendency of recurrence and chemotherapy resistance after surgery. Ferroptosis is a novel form of programmed cell death (PCD) that kills cells through iron-dependent lipid peroxidation. Current studies have shown that ferroptosis is closely related to OS and could reduce chemotherapy resistance to a certain extent, which has great therapeutic potential. In this paper, we review the regulatory mechanism of ferroptosis and its research progress in OS, hoping to provide new help for the clinical treatment of OS.

Ferroptosis turns 10: Emerging mechanisms, physiological functions, and therapeutic applications

Ferroptosis, a form of cell death driven by iron-dependent lipid peroxidation, was identified as a distinct phenomenon and named a decade ago. Ferroptosis has been implicated in a broad set of biological contexts, from development to aging, immunity, and cancer. This review describes key regulators of this form of cell death within a framework of metabolism, ROS biology, and iron biology. Key concepts and major unanswered questions in the ferroptosis field are highlighted. The next decade promises to yield further breakthroughs in the mechanisms governing ferroptosis and additional ways of harnessing ferroptosis for therapeutic benefit.

Nutritional and Metabolic Control of Ferroptosis

Ferroptosis is a type of regulated cell death characterized by an excessive lipid peroxidation of cellular membranes caused by the disruption of the antioxidant defense system and/or an imbalanced cellular metabolism. Ferroptosis differentiates from other forms of regulated cell death in that several metabolic pathways and nutritional aspects, including endogenous antioxidants (such as coenzyme Q₁₀, vitamin E, and di/tetrahydrobiopterin), iron handling, energy sensing, selenium utilization, amino acids, and fatty acids, directly regulate the cells' sensitivity to lipid peroxidation and ferroptosis. As hallmarks of ferroptosis have been documented in a variety of diseases, including neurodegeneration, acute organ injury, and therapy-resistant tumors, the modulation of ferroptosis using pharmacological tools or by metabolic reprogramming holds great potential for the treatment of ferroptosis-associated diseases and cancer therapy. Hence, this review focuses on the regulation of ferroptosis by metabolic and nutritional cues and discusses the potential of nutritional interventions for therapy by targeting ferroptosis. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Identification of a Small Molecule That Enhances Ferroptosis via Inhibition of Ferroptosis Suppressor Protein 1 (FSP1)

Glutathione peroxidase 4 (GPX4) is an intracellular enzyme that oxidizes glutathione while reducing lipid peroxides and is a promising target for cancer therapy. To date, several GPX4 inhibitors have been reported to exhibit cytotoxicity against cancer cells. However, some cancer cells are less sensitive to the known GPX4 inhibitors. This study aimed to explore compounds showing synergistic effects with GPX4 inhibitors. We screened a chemical library and identified a compound named NPD4928, whose cytotoxicity was enhanced in the presence of a GPX4 inhibitor. Furthermore, we identified ferroptosis suppressor protein 1 as its target protein. The results indicate that NPD4928 enhanced the sensitivity of various cancer cells to GPX4 inhibitors, suggesting that the combination might have therapeutic potential via the induction of ferroptosis.

Generation of singlet oxygen via iron-dependent lipid peroxidation and its role in Ferroptosis

Ferroptosis is a cell death pathway mediated by iron-dependent accumulation of lipid peroxide. However, the specific downstream molecular events of iron-dependent lipid peroxidation are yet to be elucidated. In this study, based on various spectral analyses, we have found evidence that singlet oxygen is produced through the Russell mechanism during the self-reaction of lipid peroxyl radicals generated via iron-dependent lipid peroxidation regardless of the presence of cholesterol. Significantly reduced generation of singlet oxygen was observed in the absence of iron. The generated singlet oxygen accelerated the oxidative damage of lipid membranes by propagating lipid peroxidation and facilitated ferroptotic cancer cell death initiated by erastin. In this work, singlet oxygen has been revealed to be a new reactive species that participates in ferroptosis, thus improving the understanding on iron-dependent lipid peroxidation and the mechanism of ferroptosis.

The mechanisms and therapeutic targets of ferroptosis in cancer

INTRODUCTION

Ferroptosis, a form of programmed cell death, is mediated primarily by lipid peroxidation via a unique iron-dependent process. The mechanisms of ferroptosis involve the metabolisms of amino acids, irons, and lipids, and the regulation of antioxidant systems. Evidence supports the roles of ferroptosis in cancer, while metabolic reprogramming (a hallmark of cancer) renders tumor cells highly vulnerable to ferroptosis and thus provides a rationale for ferroptosis-targeted therapy for cancer.

AREA COVERED

This article examines the current understanding of the mechanisms and related signaling pathways involving ferroptosis; it focuses on novel targets in cancer and its treatment and drug resistance. The development of ferroptosis-targeted therapy, especially in combination with conventional or non-conventional therapies, are considered with dilemmas and key questions in this research area.

EXPERT OPINION

An increasing number of potential targets and ferroptosis inducers (FINs) have been identified to treat cancer. However, no specific FIN has entered clinical trials thus far, likely due to poor efficacy and high toxicity in vivo. Thus, new FINs with high selectivity and bioavailability are required to target tumor cells more specifically and potently. Particularly, the combination of FINs with chemotherapy, radiotherapy, targeted therapy, and immunotherapy warrants clinical investigation in the future.

Emerging Role of Ferroptosis in the Pathogenesis of Ischemic Stroke: A New Therapeutic Target?

Ischemic stroke is one of the main causes of high morbidity, mortality, and disability worldwide; however, the treatment methods are limited and do not always achieve satisfactory results. The pathogenesis of ischemic stroke is complex, defined by multiple mechanisms; among them, programmed death of neuronal cells plays a significant role. Ferroptosis is a novel type of regulated cell death characterized by iron redistribution or accumulation and increased lipid peroxidation in the membrane. Ferroptosis is implicated in many pathological conditions, such as cancer, neurodegenerative diseases, and ischemia-reperfusion injury. In this review, we summarize current research findings on ferroptosis, including possible molecular mechanisms and therapeutic applications of ferroptosis regulators, with a focus on the involvement of ferroptosis in the pathogenesis and treatment of ischemic stroke. Understanding the role of ferroptosis in ischemic stroke will throw some light on the development of methods for diagnosis, treatment, and prevention of this devastating disease.

Targeting ferroptosis in osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumour in children and adolescents, with high degree of malignancy and an extremely poor prognosis. Ferroptosis, a non-traditional mode of regulated cell death (RCD) characterised by iron-dependent accumulation of lipid reactive oxygen species (ROS), is closely associated with a variety of cancers. It has been demonstrated that ferroptosis can regulate OS progression and exert an essential role in the treatment of OS, which is potentially of great value. By targeting ferroptosis in OS, the present review article summarises the relevant mechanisms and therapeutic applications along with discussing current limitations and future directions, which may provide a new strategy for the treatment of OS.

α/β-Hydrolase Domain (ABHD) Inhibitors as New Potential Therapeutic Options against Lipid-Related Diseases

Much of the experimental evidence in the literature has linked altered lipid metabolism to severe diseases such as cancer, obesity, cardiovascular pathologies, diabetes, and neurodegenerative diseases. Therefore, targeting key effectors of the dysregulated lipid metabolism may represent an effective strategy to counteract these pathological conditions. In this context, α/β-hydrolase domain (ABHD) enzymes represent an important and diversified family of proteins, which are involved in the complex environment of lipid signaling, metabolism, and regulation. Moreover, some members of the ABHD family play an important role in the endocannabinoid system, being designated to terminate the signaling of the key endocannabinoid regulator 2-arachidonoylglycerol. This Perspective summarizes the research progress in the development of ABHD inhibitors and modulators: design strategies, structure-activity relationships, action mechanisms, and biological studies of the main ABHD ligands will be highlighted.

Juggling with lipids, a game of Russian roulette

Lipid peroxidation (LPO) is the molecular mechanism involved in oxidative damage of cellular membranes and the hallmark of a nonapoptotic form of cell death, known as ferroptosis. This iron-dependent cell death is an emerging strategy in cancer treatment and one of the central cell death mechanisms accounting for early cell loss and organ dysfunction in both neurodegenerative disease and ischemia-reperfusion injury. Although the biological roles of LPO products have attracted considerable attention, not only for their pathological mechanisms but also for their potential clinical application as biomarkers, the existence of a common lethal lipid death signal generated during ferroptosis remains poorly explored. A better understanding of the LPO process, however, may unleash unprecedented opportunities for therapeutic intervention of as-yet incurable diseases.

The Metabolic Underpinnings of Ferroptosis

Acute or chronic cellular stress resulting from aberrant metabolic and biochemical processes may trigger a pervasive non-apoptotic form of cell death, generally known as ferroptosis. Ferroptosis is unique among the different cell death modalities, as it has been mostly linked to pathophysiological conditions and because several metabolic pathways, such as (seleno)thiol metabolism, fatty acid metabolism, iron handling, mevalonate pathway, and mitochondrial respiration, directly impinge on the cells' sensitivity toward lipid peroxidation and ferroptosis. Additionally, key cellular redox systems, such as selenium-dependent glutathione peroxidase 4 and the NAD(P)H/ferroptosis suppressor protein-1/ubiquinone axis, are at play that constantly surveil and neutralize oxidative damage to cellular membranes. Since this form of cell death emerges to be the root cause of a number of diseases and since it offers various pharmacologically tractable nodes for therapeutic intervention, there has been overwhelming interest in the last few years aiming for a better molecular understanding of the ferroptotic death process.

Emerging mechanisms and applications of ferroptosis in the treatment of resistant cancers

The development of chemotherapy drugs has promoted anticancer treatment, but the effect on tumours is not clear because of treatment resistance; thus, it is necessary to further understand the mechanism of cell death to explore new therapeutic targets. As a new type of programmed cell death, ferroptosis is increasingly being targeted in the treatment of many cancers with clinical drugs and experimental compounds. Ferroptosis is stimulated in tumours with inherently high levels of ferrous ions by a reaction with abundant polyunsaturated fatty acids and the inhibition of antioxidant enzymes, which can overcome treatment resistance in cancers mainly through GPX4. In this review, we focus on the intrinsic cellular regulators against ferroptosis in cancer resistance, such as GPX4, NRF2 and the thioredoxin system. We summarize the application of novel compounds and drugs to circumvent treatment resistance. We also introduce the application of nanoparticles for the treatment of resistant cancers. In conclusion, targeting ferroptosis represents a considerable strategy for resistant cancer treatment.

The Lysophosphatidylserines-An Emerging Class of Signalling Lysophospholipids

Lysophospholipids are potent hormone-like signalling biological lipids that regulate many important biological processes in mammals (including humans). Lysophosphatidic acid and sphingosine-1-phosphate represent the best studied examples for this lipid class, and their metabolic enzymes and/or cognate receptors are currently under clinical investigation for treatment of various neurological and autoimmune diseases in humans. Over the past two decades, the lysophsophatidylserines (lyso-PSs) have emerged as yet another biologically important lysophospholipid, and deregulation in its metabolism has been linked to various human pathophysiological conditions. Despite its recent emergence, an exhaustive review summarizing recent advances on lyso-PSs and the biological pathways that this bioactive lysophospholipid regulates has been lacking. To address this, here, we summarize studies that led to the discovery of lyso-PS as a potent signalling biomolecule, and discuss the structure, its detection in biological systems, and the biodistribution of this lysophospholipid in various mammalian systems. Further, we describe in detail the enzymatic pathways that are involved in the biosynthesis and degradation of this lipid and the putative lyso-PS receptors reported in the literature. Finally, we discuss the various biological pathways directly regulated by lyso-PSs in mammals and prospect new questions for this still emerging biomedically important signalling lysophospholipid.

Bioactive lipids, inflammation and chronic diseases

Endogenous bioactive lipids are part of a complex network that modulates a plethora of cellular and molecular processes involved in health and disease, of which inflammation represents one of the most prominent examples. Inflammation serves as a well-conserved defence mechanism, triggered in the event of chemical, mechanical or microbial damage, that is meant to eradicate the source of damage and restore tissue function. However, excessive inflammatory signals, or impairment of pro-resolving/anti-inflammatory pathways leads to chronic inflammation, which is a hallmark of chronic pathologies. All main classes of endogenous bioactive lipids - namely eicosanoids, specialized pro-resolving lipid mediators, lysoglycerophopsholipids and endocannabinoids - have been consistently involved in the chronic inflammation that characterises pathologies such as cancer, diabetes, atherosclerosis, asthma, as well as autoimmune and neurodegenerative disorders and inflammatory bowel diseases. This review gathers the current knowledge concerning the involvement of endogenous bioactive lipids in the pathogenic processes of chronic inflammatory pathologies.

Mapping the Neuroanatomy of ABHD16A, ABHD12, and Lysophosphatidylserines Provides New Insights into the Pathophysiology of the Human Neurological Disorder PHARC

Lysophosphatidylserine (lyso-PS), a lysophospholipid derived from phosphatidylserine (PS), has emerged as a potent signaling lipid in mammalian physiology. In vivo, the metabolic serine hydrolases ABHD16A and ABHD12 are major lipases that biosynthesize and degrade lyso-PS, respectively. Of biomedical relevance, deleterious mutations to ABHD12 cause accumulation of lyso-PS in the brain, and this deregulated lyso-PS metabolism leads to the human genetic neurological disorder PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract). While the roles of ABHD16A and ABHD12 in lyso-PS metabolism in the mammalian brain are well established, the anatomical and (sub)cellular localizations of both lipases and the functional cross-talk between them with respect to regulating lyso-PS lipids remain under investigated. Here, using subcellular organelle fractionation, biochemical assays, and immunofluorescence-based high-resolution microscopy, we show that the PS lipase ABHD16A is an endoplasmic reticulum-localized enzyme, an organelle intricately regulating cellular PS levels. In addition, leveraging immunohistochemical analysis using genetic ABHD16A and ABHD12 knockout mice as important controls, we map the anatomical distribution of both of these lipases in tandem in the murine brain and show for the first time the distinct localization of these lipases to different regions and cells of the cerebellum. We complement the aforementioned immunohistochemical studies by quantitatively measuring lyso-PS concentrations in various brain regions using mass spectrometry and find that the cerebellar lyso-PS levels are most affected by deletion of ABHD16A (decreased) or ABHD12 (increased). Taken together, our studies provide new insights into lyso-PS signaling in the cerebellum, the most atrophic brain region in human PHARC subjects.

ABHD12 and LPCAT3 Interplay Regulates a Lyso-phosphatidylserine-C20:4 Phosphatidylserine Lipid Network Implicated in Neurological Disease

PHARC (polyneuropathy, hearing loss, cerebellar ataxia, retinitis pigmentosa, and cataract) is a human neurological disorder caused by deleterious mutations in the ABHD12 gene, which encodes an integral membrane lyso-phosphatidylserine (lyso-PS) lipase. Pharmacological or genetic disruption of ABHD12 leads to higher levels of lyso-PS lipids in human cells and the central nervous system (CNS) of mice. ABHD12 loss also causes rapid rewiring of PS content, resulting in selective increases in the level of arachidonoyl (C20:4) PS and decreases in the levels of other PS species. The biochemical basis for ABHD12-dependent PS remodeling and its pathophysiological significance remain unknown. Here, we show that genetic deletion of the lysophospholipid acyltransferase LPCAT3 blocks accumulation of brain C20:4 PS in mice lacking ABHD12 and concurrently produces hyper-increases in the level of lyso-PS in these animals. These lipid changes correlate with exacerbated auditory dysfunction and brain microgliosis in mice lacking both ABHD12 and LPCAT3. Taken together, our findings reveal that ABHD12 and LPCAT3 coordinately regulate lyso-PS and C20:4 PS content in the CNS and point to lyso-PS lipids as the likely bioactive metabolites contributing to PHARC-related neuropathologies.