Macrophage/microglia-producing transient increase of platelet-activating factor is involved in neuropathic pain.

Peripheral nerve injury (PNI) induces debilitating neuropathic pain symptoms, such as tactile allodynia. Accumulating evidence suggests that the expression levels of various transcripts and proteins are drastically changed after PNI. Recent lipidome analysis demonstrates increased levels of diverse lipids in chronic pain conditions. We show that PNI transiently increases platelet-activating factor (PAF) levels, a potent inflammatory phospholipid mediator, in the dorsal root ganglia (DRG) and spinal cord. We revealed that macrophage and microglia-specific PAF-producing enzyme LPLAT9/LPCAT2 knockout mice (Cx3cr1CreERT2;Lpcat2flox/flox) failed to develop mechanical allodynia and to increase PAF levels in the DRG and spinal cord after PNI. Moreover, we observed the suppression of PNI-induced PAF increase in the spinal cord of PAF receptor knockout mice, indicating a self-amplification loop of PAF production. In conclusion, macrophages and microglia enhance PAF production, contributing to PNI-induced neuropathic pain. Additionally, PAF-PAF receptor signaling is a potential target of neuropathic pain control.

Sphingosine-1-phosphate promotes liver fibrosis in metabolic dysfunction-associated steatohepatitis.

AIM: Metabolic dysfunction-associated steatohepatitis (MASH) is one of the most prevalent liver diseases and is characterized by steatosis and the accumulation of bioactive lipids. This study aims to understand the specific lipid species responsible for the progression of liver fibrosis in MASH. METHODS: Changes in bioactive lipid levels were examined in the livers of MASH mice fed a choline-deficient diet (CDD). Additionally, sphingosine kinase (SphK)1 mRNA, which generates sphingosine 1 phosphate (S1P), was examined in the livers of patients with MASH. RESULTS: CDD induced MASH and liver fibrosis were accompanied by elevated levels of S1P and increased expression of SphK1 in capillarized liver sinusoidal endothelial cells (LSECs) in mice. SphK1 mRNA also increased in the livers of patients with MASH. Treatment of primary cultured mouse hepatic stellate cells (HSCs) with S1P stimulated their activation, which was mitigated by the S1P receptor (S1PR)2 inhibitor, JTE013. The inhibition of S1PR2 or its knockout in mice suppressed liver fibrosis without reducing steatosis or hepatocellular damage. CONCLUSION: S1P level is increased in MASH livers and contributes to liver fibrosis via S1PR2.

Lysophospholipid Acyltransferase 9 Promotes Emphysema Formation via Platelet-activating Factor.

Cigarette smoking is known to be the leading cause of chronic obstructive pulmonary disease (COPD). However, the detailed mechanisms have not been elucidated. Platelet-activating factor (PAF), a potent inflammatory mediator, is involved in the pathogenesis of various respiratory diseases, such as bronchial asthma or COPD. We focused on lysophospholipid acyltransferase 9 (LPLAT9), a biosynthetic enzyme of PAF, in the pathogenesis of COPD. LPLAT9 gene expression was observed in excised COPD lungs and single-cell RNA sequencing data of alveolar macrophage (AM). LPLAT9 was predominant and upregulated in AM, particularly monocyte-derived AM, in patients with COPD. To identify the function of LPLAT9/PAF in AM on the pathogenesis of COPD, we exposed cigarette smoke (CS) to systemic LPLAT9 knockout (LPALT9-/-) mice. CS increased the number of AM, especially monocyte-derived fraction, which secreted matrix metalloprotease 12 (MMP12). Also, CS augmented LPLAT9 phosphorylation/activation on macrophage and, subsequently, PAF synthesis in mice lung. LPLAT9-/- mice lung reduced PAF production after CS exposure. Intratracheal PAF administration accumulated AM by increasing monocyte chemoattractant protein-1 (MCP1). After CS exposure, AM accumulation and subsequent pulmonary emphysema, a primary pathologic change of COPD, were reduced in LPALT9-/- mice than in LPLAT9+/+ mice. Notably, these phenotypes got worsened again by LPLAT9+/+ bone marrow transplantation in LPALT9-/- mice. Thus, CS-induced LPLAT9 activation in monocyte-derived AM aggravated pulmonary emphysema via PAF-induced further AM accumulation. These results suggest that PAF synthesized by LPLAT9 has an important role in the pathogenesis of COPD.

Overexpression of lysophospholipid acyltransferase, LPLAT10/LPCAT4/LPEAT2, in the mouse liver increases glucose-stimulated insulin secretion.

Postprandial hyperglycemia is an early indicator of impaired glucose tolerance that leads to type 2 diabetes mellitus (T2DM). Alterations in the fatty acid composition of phospholipids have been implicated in diseases such as T2DM and nonalcoholic fatty liver disease. Lysophospholipid acyltransferase 10 (LPLAT10, also called LPCAT4 and LPEAT2) plays a role in remodeling fatty acyl chains of phospholipids; however, its relationship with metabolic diseases has not been fully elucidated. LPLAT10 expression is low in the liver, the main organ that regulates metabolism, under normal conditions. Here, we investigated whether overexpression of LPLAT10 in the liver leads to improved glucose metabolism. For overexpression, we generated an LPLAT10-expressing adenovirus (Ad) vector (Ad-LPLAT10) using an improved Ad vector. Postprandial hyperglycemia was suppressed by the induction of glucose-stimulated insulin secretion in Ad-LPLAT10-treated mice compared with that in control Ad vector-treated mice. Hepatic and serum levels of phosphatidylcholine 40:7, containing C18:1 and C22:6, were increased in Ad-LPLAT10-treated mice. Serum from Ad-LPLAT10-treated mice showed increased glucose-stimulated insulin secretion in mouse insulinoma MIN6 cells. These results indicate that changes in hepatic phosphatidylcholine species due to liver-specific LPLAT10 overexpression affect the pancreas and increase glucose-stimulated insulin secretion. Our findings highlight LPLAT10 as a potential novel therapeutic target for T2DM.

A lipid index for risk of hyperlipidemia caused by anti-retroviral drugs.

HIV-associated lipodystrophy has been reported in people taking anti-retroviral therapy (ART). Lipodystrophy can cause cardiovascular diseases, affecting the quality of life of HIV-infected individuals. In this study, we propose a pharmacological lipid index to estimate the risk of hyperlipidemia caused by anti-retroviral drugs. Lipid droplets were stained in cells treated with anti-retroviral drugs and cyclosporin A. Signal intensities of lipid droplets were plotted against the drug concentrations to obtain an isodose of 10 µM of cyclosporin A, which we call the Pharmacological Lipid Index (PLI). The PLI was then normalized by EC50. PLI/EC50 values were low in early proteinase inhibitors and the nucleoside reverse transcriptase inhibitor, d4T, indicating high risk of hyperlipidemia, which is consistent with previous findings of hyperlipidemia. In contrast, there are few reports of hyperlipidemia for drugs with high PLI/EC50 scores. Data suggests that PLI/EC50 is a useful index for estimating the risk of hyperlipidemia.

LPCAT3/LPLAT12 deficiency in the liver ameliorates acetaminophen-induced acute liver injury.

Acetaminophen (APAP) is a double-edged sword, mainly depending on the dosage. A moderate dose of APAP is effective for fever and pain relief; however, an overdose induces acute liver injury. The mechanism underlying APAP-induced acute liver failure is unclear, and its treatment is limited. A recent report has shown that several oxidized phospholipids are associated with APAP-induced acute liver failure. Lysophosphatidylcholine acyltransferase 3 (Lpcat3, Lplat12), which is highly expressed in the liver, preferentially catalyzes the incorporation of arachidonate into lysophospholipids (PLs). In the present study, we investigated the roles of Lpcat3 on APAP-induced acute liver injury using liver-specific Lpcat3-knockout mice. Hepatic Lpcat3 deficiency reduced the degree of APAP-induced necrosis of hepatocytes around Zone 3 and ameliorated the elevation of hepatic injury serum marker levels, and prolonged survival. Lipidomic analysis showed that the accumulation of oxidized and hydroperoxidized phospholipids was suppressed in Lpcat3-knockout mice. The amelioration of APAP-induced acute liver injury was due not only to the reduction in the lipid synthesis of arachidonic acid PLs because of Lpcat3 deficiency, but also to the promotion of the APAP detoxification pathway by facilitating the conjugation of glutathione and N-acetyl-p-benzoquinone imine. Our findings suggest that Lpcat3 is a potential therapeutic target for treating APAP-induced acute liver injury.

Hepatic FASN deficiency differentially affects nonalcoholic fatty liver disease and diabetes in mouse obesity models.

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes are interacting comorbidities of obesity, and increased hepatic de novo lipogenesis (DNL), driven by hyperinsulinemia and carbohydrate overload, contributes to their pathogenesis. Fatty acid synthase (FASN), a key enzyme of hepatic DNL, is upregulated in association with insulin resistance. However, the therapeutic potential of targeting FASN in hepatocytes for obesity-associated metabolic diseases is unknown. Here, we show that hepatic FASN deficiency differentially affects NAFLD and diabetes depending on the etiology of obesity. Hepatocyte-specific ablation of FASN ameliorated NAFLD and diabetes in melanocortin 4 receptor-deficient mice but not in mice with diet-induced obesity. In leptin-deficient mice, FASN ablation alleviated hepatic steatosis and improved glucose tolerance but exacerbated fed hyperglycemia and liver dysfunction. The beneficial effects of hepatic FASN deficiency on NAFLD and glucose metabolism were associated with suppression of DNL and attenuation of gluconeogenesis and fatty acid oxidation, respectively. The exacerbation of fed hyperglycemia by FASN ablation in leptin-deficient mice appeared attributable to impairment of hepatic glucose uptake triggered by glycogen accumulation and citrate-mediated inhibition of glycolysis. Further investigation of the therapeutic potential of hepatic FASN inhibition for NAFLD and diabetes in humans should thus consider the etiology of obesity.

Lysophospholipid acyltransferases orchestrate the compositional diversity of phospholipids.

Lysophospholipid acyltransferases (LPLATs), in concert with glycerol-3-phosphate acyltransferases (GPATs) and phospholipase A1/2s, orchestrate the compositional diversity of the fatty chains in membrane phospholipids. Fourteen LPLAT enzymes which come from two distinct families, AGPAT and MBOAT, have been identified, and in this mini-review we provide an overview of their roles in de novo and remodeling pathways of membrane phospholipid biosynthesis. Recently new nomenclature for LPLATs has been introduced (LPLATx, where x is a number 1-14), and we also give an overview of key biological functions that have been discovered for LPLAT1-14, revealed primarily through studies of LPLAT-gene-deficient mice as well as by linkages to various human diseases.

LPGAT1/LPLAT7 regulates acyl chain profiles at the sn-1 position of phospholipids in murine skeletal muscles.

Skeletal muscle consists of both fast- and slow-twitch fibers. Phospholipids are important structural components of cellular membranes, and the diversity of their fatty acid composition affects membrane characteristics. Although some studies have shown that acyl chain species in phospholipids differ among various muscle fiber types, the mechanisms underlying these differences are unclear. To investigate this, we analyzed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules in the murine extensor digitorum longus (EDL; fast-twitch) and soleus (slow-twitch) muscles. In the EDL muscle, the vast majority (93.6%) of PC molecules was palmitate-containing PC (16:0-PC), whereas in the soleus muscle, in addition to 16:0-PC, 27.9% of PC molecules was stearate-containing PC (18:0-PC). Most palmitate and stearate were bound at the sn-1 position of 16:0- and 18:0-PC, respectively, and 18:0-PC was found in type I and IIa fibers. The amount of 18:0-PE was higher in the soleus than in the EDL muscle. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) increased the amount of 18:0-PC in the EDL. Lysophosphatidylglycerol acyltransferase 1 (LPGAT1) was highly expressed in the soleus compared with that in the EDL muscle and was upregulated by PGC-1α. LPGAT1 knockout decreased the incorporation of stearate into PC and PE in vitro and ex vivo and the amount of 18:0-PC and 18:0-PE in murine skeletal muscle with an increase in the level of 16:0-PC and 16:0-PE. Moreover, knocking out LPGAT1 decreased the amount of stearate-containing phosphatidylserine (18:0-PS), suggesting that LPGAT1 regulated the acyl chain profiles of phospholipids, namely, PC, PE, and PS, in the skeletal muscle.

Dietary omega-3 fatty acid does not improve male infertility caused by lysophospholipid acyltransferase 3 (LPLAT3/AGPAT3) deficiency.

Docosahexaenoic acid (DHA), an omega-3 fatty acid, usually presents as a constituent of phospholipids in the cellular membrane. Lysophospholipid acyltransferase 3 (LPLAT3; AGPAT3) is the primary enzyme that incorporates DHA into phospholipids. LPLAT3-KO mice show male infertility and visual dysfunction accompanied by decreased phospholipids (PLs) containing DHA (PL-DHA) in the testis and retina, respectively. In this study, we evaluated the effect of diets consisting mainly of triacylglycerol-bound DHA (fish oil) and PL-bound DHA (salmon roe oil) on the amount of PL-DHA in a broad range of tissues and on reproductive functions. Both diets elevated phosphatidylcholines (PCs)-containing DHA in most tissues of wild type (WT) mice. Although LPLAT3-KO mice acquired a minimal amount of PC-DHA in the testes and sperm by eating either of the diets, reproductive function did not improve. The present study suggests that DHA-rich diets do not restore sufficient PL-DHA to improve male infertility in LPLAT3-KO mice. Alternatively, PL-DHA can be biosynthesized by LPLAT3 but not by external supplementation, which may be necessary for normal reproductive function.

Constitutively active GPR43 is crucial for proper leukocyte differentiation.

The G protein-coupled receptors, GPR43 (free fatty acid receptor 2, FFA2) and GPR41 (free fatty acid receptor 3, FFA3), are activated by short-chain fatty acids produced under various conditions, including microbial fermentation of carbohydrates. Previous studies have implicated this receptor energy homeostasis and immune responses as well as in cell growth arrest and apoptosis. Here, we observed the expression of both receptors in human blood cells and a remarkable enhancement in leukemia cell lines (HL-60, U937, and THP-1 cells) during differentiation. A reporter assay revealed that GPR43 is coupled with Gαi and Gα12/13 and is constitutively active without any stimuli. Specific blockers of GPR43, GLPG0974 and CATPB function as inverse agonists because treatment with these compounds significantly reduces constitutive activity. In HL-60 cells, enhanced expression of GPR43 led to growth arrest through Gα12/13 . In addition, the blockage of GPR43 activity in these cells significantly impaired their adherent properties due to the reduction of adhesion molecules. We further revealed that enhanced GPR43 activity induces F-actin formation. However, the activity of GPR43 did not contribute to butyrate-induced apoptosis in differentiated HL-60 cells because of the ineffectiveness of the inverse agonist on cell death. Collectively, these results suggest that GPR43, which possesses constitutive activity, is crucial for growth arrest, followed by the proper differentiation of leukocytes.

Multiomics identifies the link between intratumor steatosis and the exhausted tumor immune microenvironment in hepatocellular carcinoma.

BACKGROUND AND AIMS: Immunotherapy has become the standard-of-care treatment for hepatocellular carcinoma (HCC), but its efficacy remains limited. To identify immunotherapy-susceptible HCC, we profiled the molecular abnormalities and tumor immune microenvironment (TIME) of rapidly increasing nonviral HCC. APPROACHES AND RESULTS: We performed RNA-seq of tumor tissues in 113 patients with nonviral HCC and cancer genome sequencing of 69 genes with recurrent genetic alterations reported in HCC. Unsupervised hierarchical clustering classified nonviral HCCs into three molecular classes (Class I, II, III), which stratified patient prognosis. Class I, with the poorest prognosis, was associated with TP53 mutations, whereas class III, with the best prognosis, was associated with cadherin-associated protein beta 1 (CTNNB1) mutations. Thirty-eight percent of nonviral HCC was defined as an immune class characterized by a high frequency of intratumoral steatosis and a low frequency of CTNNB1 mutations. Steatotic HCC, which accounts for 23% of nonviral HCC cases, presented an immune-enriched but immune-exhausted TIME characterized by T cell exhaustion, M2 macrophage and cancer-associated fibroblast (CAF) infiltration, high PD-L1 expression, and TGF-ß signaling activation. Spatial transcriptome analysis suggested that M2 macrophages and CAFs may be in close proximity to exhausted CD8+ T cells in steatotic HCC. An in vitro study showed that palmitic acid-induced lipid accumulation in HCC cells upregulated PD-L1 expression and promoted immunosuppressive phenotypes of cocultured macrophages and fibroblasts. Patients with steatotic HCC, confirmed by chemical-shift MR imaging, had significantly longer PFS with combined immunotherapy using anti-PD-L1 and anti-VEGF antibodies. CONCLUSIONS: Multiomics stratified nonviral HCCs according to prognosis or TIME. We identified the link between intratumoral steatosis and immune-exhausted immunotherapy-susceptible TIME.

Conformations of Three Types of Ultra-Long-Chain Fatty Acids in Multicomponent Lipid Bilayers.

Ultra-long-chain fatty acids (ULCFAs) are biosynthesized in certain types of tissues, but their biological roles remain unknown. Here, we report how the conformation of ULCFAs depends on the length and unsaturated-bond ratio of the ultra-long chains and the composition of the host bilayer membrane using molecular dynamics simulations. The ultra-long chain of ULCFAs flips between the two leaflets and fluctuates among three conformations: elongated, L-shaped, and turned. Furthermore, we found that the saturated ultra-long chain exhibited an elongated conformation more frequently than the unsaturated chain. In addition, the truncation of the ultra-long chain at C26 had little effect on the remaining ULCFAs. ULCFAs respond to lipid-density differences in the two leaflets, and the ratio of the elongated and turned conformations changed to reduce this difference. However, in cholesterol-containing membranes, ULCFAs exhibit no density difference after the flip-flop of cholesterol removes the difference.

Identification and characterization of LPLAT7 as an sn-1-specific lysophospholipid acyltransferase.

The main fatty acids at the sn-1 position of phospholipids (PLs) are saturated or monounsaturated fatty acids such as palmitic acid (C16:0), stearic acid (C18:0), and oleic acid (C18:1) and are constantly replaced, like unsaturated fatty acids at the sn-2 position. However, little is known about the molecular mechanism underlying the replacement of fatty acids at the sn-1 position, i.e., the sn-1 remodeling. Previously, we established a method to evaluate the incorporation of fatty acids into the sn-1 position of lysophospholipids (lyso-PLs). Here, we used this method to identify the enzymes capable of incorporating fatty acids into the sn-1 position of lyso-PLs (sn-1 lysophospholipid acyltransferase [LPLAT]). Screenings using siRNA knockdown and recombinant proteins for 14 LPLATs identified LPLAT7/lysophosphatidylglycerol acyltransferase 1 (LPGAT1) as a candidate. In vitro, we found LPLAT7 mainly incorporated several fatty acids into the sn-1 position of lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE), with weak activities toward other lyso-PLs. Interestingly, however, only C18:0-containing phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were specifically reduced in the LPLAT7-mutant cells and tissues from knockout mice, with a concomitant increase in the level of C16:0- and C18:1-containing PC and PE. Consistent with this, the incorporation of deuterium-labeled C18:0 into PLs dramatically decreased in the mutant cells, while deuterium-labeled C16:0 and C18:1 showed the opposite dynamic. Identifying LPLAT7 as an sn-1 LPLAT facilitates understanding the biological significance of sn-1 fatty acid remodeling of PLs. We also propose to use the new nomenclature, LPLAT7, for LPGAT1 since the newly assigned enzymatic activities are quite different from the LPGAT1s previously reported.

Profiling of fatty acid metabolism in the dorsal root ganglion after peripheral nerve injury.

Peripheral nerve injury (PNI) induces neuronal hyperexcitability, which underlies neuropathic pain. The emergence of RNA sequencing technologies has enabled profiling of transcriptional changes in pathological conditions. However, these approaches do not provide information regarding metabolites such as lipids that are not directly encoded by genes. Fatty acids (FAs) are some of the essential lipids in mammalian organisms and are mainly stored as membrane phospholipids. In response to various biological stimuli, FAs are rapidly released and converted into several mediators, such as eicosanoids and docosanoids. FAs themselves or their metabolites play important roles in physiology and pathology. In this study, using a comprehensive lipidomic analysis of FA metabolites, 152 species were measured in the dorsal root ganglia of mice at multiple time points after PNI. We found that PNI increased the ω-6 FA metabolites produced by cyclooxygenases but not those produced by lipoxygenases or cytochrome P450 enzymes in the dorsal root ganglia. In contrast, ω-3 FA metabolites biosynthesized by any enzyme transiently increased after nerve injury. Overall, these findings provide a new resource and valuable insights into PNI pathologies, including pain and nerve regeneration.

α-Synuclein V15A Variant in Familial Parkinson's Disease Exhibits a Weaker Lipid-Binding Property.

BACKGROUND: The α-Synuclein (α-Syn) V15A variant has been found in two Caucasian families with Parkinson's disease (PD). However, the significance of this missense variant remained unclear. OBJECTIVE: We sought to elucidate whether V15A could increase aggregation or change phospholipid affinity. METHODS: A sequencing analysis for the SNCA encoding α-Syn from 875 patients with PD and 324 control subjects was performed. Comparing with known pathogenic missense variants of α-Syn, A30P, and A53T, we analyzed the effects of V15A on binding to phospholipid membrane, self-aggregation, and seed-dependent aggregation in cultured cells. RESULTS: Genetic screening identified SNCA c.44 T>C (p.V15A) from two Japanese PD families. The missense variant V15A was extremely rare in several public databases and predicted as pathogenic using in silico tools. The amplification activity of α-Syn V15A fibrils was stronger than that of wild-type α-Syn fibrils. CONCLUSIONS: The discovery of the V15A variant from Japanese families reinforces the possibility that the V15A variant may be a causative variant for developing PD. V15A had a reduced affinity for phospholipids and increased propagation activity compared with wild-type. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Lysophosphatidylcholine acyltransferase 1 controls mitochondrial reactive oxygen species generation and survival of retinal photoreceptor cells.

Due to their high energy demands and characteristic morphology, retinal photoreceptor cells require a specialized lipid metabolism for survival and function. Accordingly, dysregulation of lipid metabolism leads to the photoreceptor cell death and retinal degeneration. Mice bearing a frameshift mutation in the gene encoding lysophosphatidylcholine acyltransferase 1 (Lpcat1), which produces saturated phosphatidylcholine (PC) composed of two saturated fatty acids, has been reported to cause spontaneous retinal degeneration in mice; however, the mechanism by which this mutation affects degeneration is unclear. In this study, we performed a detailed characterization of LPCAT1 in the retina and found that genetic deletion of Lpcat1 induces light-independent and photoreceptor-specific apoptosis in mice. Lipidomic analyses of the retina and isolated photoreceptor outer segment (OS) suggested that loss of Lpcat1 not only decreased saturated PC production but also affected membrane lipid composition, presumably by altering saturated fatty acyl-CoA availability. Furthermore, we demonstrated that Lpcat1 deletion led to increased mitochondrial reactive oxygen species levels in photoreceptor cells, but not in other retinal cells, and did not affect the OS structure or trafficking of OS-localized proteins. These results suggest that the LPCAT1-dependent production of saturated PC plays critical roles in photoreceptor maturation. Our findings highlight the therapeutic potential of saturated fatty acid metabolism in photoreceptor cell degeneration-related retinal diseases.

Lysophosphatidylcholine Acyltransferase 1 Deficiency Promotes Pulmonary Emphysema via Apoptosis of Alveolar Epithelial Cells.

Chronic obstructive pulmonary disease (COPD) is primarily caused by inhalation of cigarette smoke and is the third leading cause of death worldwide. Pulmonary surfactant, a complex of phospholipids and proteins, plays an essential role in respiration by reducing the surface tension in the alveoli. Lysophosphatidylcholine acyltransferase 1 (LPCAT1) is an enzyme that catalyzes the biosynthesis of surfactant lipids and is expressed in type 2 alveolar epithelial cells. Its dysfunction is suggested to be involved in various lung diseases; however, the relationship between LPCAT1 and COPD remains unclear. To investigate the role of LPCAT1 in the pathology of COPD, we analyzed an elastase-induced emphysema model using Lpcat1 knockout (KO) mice. In Lpcat1 KO mice, elastase-induced emphysema was significantly exacerbated with increased apoptotic cells, which was not ameliorated by supplementation with dipalmitoylphosphatidylcholine, which is a major component of the surfactant synthesized by LPCAT1. We subsequently evaluated the effects of cigarette smoking on primary human type 2 alveolar epithelial cells (hAEC2s) and found that cigarette smoke extract (CSE) downregulated the expression of Lpcat1. Furthermore, RNA sequencing analysis revealed that the apoptosis pathway was significantly enriched in CSE-treated primary hAEC2s. Finally, we downregulated the expression of Lpcat1 using small interfering RNA, which resulted in enhanced CSE-induced apoptosis in A549 cells. Taken together, cigarette smoke-induced downregulation of LPCAT1 can promote the exacerbation of pulmonary emphysema by increasing the susceptibility of alveolar epithelial cells to apoptosis, thereby suggesting that Lpcat1 is a novel therapeutic target for irreversible emphysema.

Lysophosphatidic acid receptor1/3 antagonist inhibits the activation of satellite glial cells and reduces acute nociceptive responses.

Lysophosphatidic acid (LPA) exerts various biological activities through six characterized G protein-coupled receptors (LPA1-6 ). While LPA-LPA1  signaling contributes toward the demyelination and retraction of C-fiber and induces neuropathic pain, the effects of LPA-LPA1  signaling on acute nociceptive pain is uncertain. This study investigated the role of LPA-LPA1  signaling in acute nociceptive pain using the formalin test. The pharmacological inhibition of the LPA-LPA1 axis significantly attenuated formalin-induced nociceptive behavior. The LPA1  mRNA was expressed in satellite glial cells (SGCs) in dorsal root ganglion (DRG) and was particularly abundant in SGCs surrounding large DRG neurons, which express neurofilament 200. Treatment with LPA1/3 receptor (LPA1/3 ) antagonist inhibited the upregulation of glial markers and inflammatory cytokines in DRG following formalin injection. The LPA1/3 antagonist also attenuated phosphorylation of extracellular signal-regulated kinase, especially in SGCs and cyclic AMP response element-binding protein in the dorsal horn following formalin injection. LPA amounts after formalin injection to the footpad were quantified by liquid chromatography/tandem mass spectrometry, and LPA levels were found to be increased in the innervated DRGs. Our results indicate that LPA produced in the innervated DRGs promotes the activation of SGCs through LPA1 , increases the sensitivity of primary neurons, and modulates pain behavior. These results facilitate our understanding of the pathology of acute nociceptive pain and demonstrate the possibility of the LPA1 on SGCs as a novel target for acute pain control.