Lysophosphatidylcholine elicits intracellular calcium signaling in a GPR55-dependent manner

Cannabinoids' Role in Modulating Central and Peripheral Immunity in Neurodegenerative Diseases

Cannabinoids (the endocannabinoids, the synthetic cannabinoids, and the phytocannabinoids) are well known for their various pharmacological properties, including neuroprotective and anti-inflammatory features, which are fundamentally important for the treatment of neurodegenerative diseases. The aging of the global population is causing an increase in these diseases that require the development of effective drugs to be even more urgent. Taking into account the unavailability of effective drugs for neurodegenerative diseases, it seems appropriate to consider the role of cannabinoids in the treatment of these diseases. To our knowledge, few reviews are devoted to cannabinoids' impact on modulating central and peripheral immunity in neurodegenerative diseases. The objective of this review is to provide the best possible information about the cannabinoid receptors and immuno-modulation features, peripheral immune modulation by cannabinoids, cannabinoid-based therapies for the treatment of neurological disorders, and the future development prospects of making cannabinoids versatile tools in the pursuit of effective drugs.

Lysophosphatidylcholines Enriched with cis and trans Palmitoleic Acid Regulate Insulin Secretion via GPR119 Receptor

Among lipids, lysophosphatidylcholines (LPCs) with various fatty acyl chains have been identified as potential agonists of G protein-coupled receptors (GPCRs). Recently, targeting GPCRs has been switched to diabetes and obesity. Concomitantly, our last findings indicate the insulin secretagogue properties of cis and trans palmitoleic acid (16:1, n-7) resulting from GPCR activation, however, associated with different signaling pathways. We here report the synthesis of LPCs bearing two geometrical isomers of palmitoleic acids and investigation of their impact on human pancreatic β cells viability, insulin secretion, and activation of four GPCRs previously demonstrated to be targeted by free fatty acids and LPCs. Moreover, molecular modeling was exploited to investigate the probable binding sites of tested ligands and calculate their affinity toward GPR40, GPR55, GPR119, and GPR120 receptors.

Presynaptic nigral GPR55 receptors stimulate [3 H]-GABA release through [3 H]-cAMP production and PKA activation and promote motor behavior

Striatal medium-sized spiny neurons express mRNA and protein of GPR55 receptors that stimulate neurotransmitter release; thus, GPR55 could be sent to nigral striatal projections, where it might modulate GABA release and motor behavior. Here we study the presence of GPR55 receptors at striato-nigral terminals, their modulation of GABA release, their signaling pathway, and their effect on motor activity. By double immunohistochemistry, we found the colocation of GPR55 protein and substance P in the dorsal striatum. In slices of the rat substantia nigra, the GPR55 agonists LPI and O-1602 stimulated [³ H]-GABA release induced by high K⁺ depolarization in a dose-dependent manner. The antagonists CID16020046 and cannabidiol prevented agonist stimulation in a dose-dependent way. The effect of GPR55 on nigral [³ H]-GABA release was prevented by lesion of the striatum with kainic acid, which was accompanied by a decrement of GPR55 protein in nigral synaptosomes, indicating the presynaptic location of receptors. The depletion of internal Ca²⁺ stores with thapsigargin did not prevent the effect of LPI on [³ H]-GABA release, but the remotion or chelation of external calcium did. Blockade of Gi, Gs, PLC, PKC, or dopamine D1 receptor signaling proteins did not prevent the effect of GPR55 on release. However, the activation of GPR55 stimulated [³ H]-cAMP accumulation and PKA activity. Intranigral unilateral injection of LPI induces contralateral turning. This turning was prevented by CID16020046, cannabidiol, and bicuculline but not by SCH 23390. Our data indicate that presynaptic GPR55 receptors stimulate [³ H]-GABA release at striato-nigral terminals through [³ H]-cAMP production and stimulate motor behavior. This article is protected by copyright. All rights reserved.

The oncogenic lysophosphatidylinositol (LPI)/GPR55 signaling

GPR55 is a class A orphan G protein-coupled receptor that has drawn important therapeutic attention in the last decade because of its role in pathophysiological processes including vascular functions, metabolic dysfunction, neurodegenerative disorders, or bone turnover among others. Several cannabinoids of phytogenic, endogenous, and synthetic nature have shown to modulate this receptor leading to propose it as a member of the endocannabinoid system. The putative endogenous GPR55 ligand is L-α-lysophosphatidylinositol (LPI) and it has been associated with several processes that control cell survival and tumor progression. The relevance of GPR55 in cancer is currently being extensively studied in vitro and in vivo using diverse cancer models. The LPI/GPR55 axis has been reported to participate in pro-oncogenic processes including cellular proliferation, differentiation, migration, invasion, and metastasis being altered in several cancer cells via G_12/13 and G_q signaling. Moreover, GRP55 and its bioactive lipid have been proposed as potential biomarkers for cancer diagnosis. Indeed, GPR55 overexpression or high expression has been shown to correlate with cancer aggressiveness in specific tumors including acute myeloid leukemia, uveal melanoma, low grade glioma and renal cancer. This review aims to analyze and summarize current evidence on the cancerogenic role of the LPI/GPR55 axis providing a critical view of the therapeutic prospects of this promising target.

GPR55 Antagonist CID16020046 Protects against Atherosclerosis Development in Mice by Inhibiting Monocyte Adhesion and Mac-1 Expression

GPR55 recognizes several lipid molecules such as lysophosphatidylinositol. GPR55 expression was reported in human monocytes. However, its role in monocyte adhesion and atherosclerosis development has not been studied. The role of GPR55 in monocyte adhesion and atherosclerosis development was investigated in human THP-1 monocytes and ApoE^-/- mice using O-1602 (a potent agonist of GPR55) and CID16020046 (a specific GPR55 antagonist). O-1602 treatment significantly increased monocyte adhesion to human umbilical vein endothelial cells, and the O-1602-induced adhesion was inhibited by treatment with CID16020046. O-1602 induced the expression of Mac-1 adhesion molecules, whereas CID16020046 inhibited this induction. Analysis of the promoter region of Mac-1 elucidated the binding sites of AP-1 and NF-κB between nucleotides -750 and -503 as GPR55 responsive elements. O-1602 induction of Mac-1 was found to be dependent on the signaling components of GPR55, that is, Gq protein, Ca²⁺, CaMKK, and PI3K. In Apo^-/- mice, administration of CID16020046 ameliorated high-fat diet-induced atherosclerosis development. These results suggest that high-fat diet-induced GPR55 activation leads to the adhesion of monocytes to endothelial cells via induction of Mac-1, and CID16020046 blockage of GPR55 could suppress monocyte adhesion to vascular endothelial cells through suppression of Mac-1 expression, leading to protection against the development of atherosclerosis.

Aβ Oligomers Dysregulate Calcium Homeostasis by Mechanosensitive Activation of AMPA and NMDA Receptors

Alzheimer's disease, which is the most common form of dementia, is characterized by the aggregation of the amyloid β peptide (Aβ) and by an impairment of calcium homeostasis caused by excessive activation of glutamatergic receptors (excitotoxicity). Here, we studied the effects on calcium homeostasis caused by the formation of Aβ oligomeric assemblies. We found that Aβ oligomers cause a rapid influx of calcium ions (Ca2+) across the cell membrane by rapidly activating extrasynaptic N-methyl-d-aspartate (NMDA) receptors and, to a lower extent, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We also observed, however, that misfolded oligomers do not interact directly with these receptors. Further experiments with lysophosphatidylcholine and arachidonic acid, which cause membrane compression and stretch, respectively, indicated that these receptors are activated through a change in membrane tension induced by the oligomers and transmitted mechanically to the receptors via the lipid bilayer. Indeed, lysophosphatidylcholine is able to neutralize the oligomer-induced activation of the NMDA receptors, whereas arachidonic acid activates the receptors similarly to the oligomers with no additive effects. An increased rotational freedom observed for a fluorescent probe embedded within the membrane in the presence of the oligomers also indicates a membrane stretch. These results reveal a mechanism of toxicity of Aβ oligomers in Alzheimer's disease through the perturbation of the mechanical properties of lipid membranes sensed by NMDA and AMPA receptors.

Functional Characterization of the Lin28/let-7 Circuit During Forelimb Regeneration in Ambystoma mexicanum and Its Influence on Metabolic Reprogramming

The axolotl (Ambystoma mexicanum) is a caudate amphibian, which has an extraordinary ability to restore a wide variety of damaged structures by a process denominated epimorphosis. While the origin and potentiality of progenitor cells that take part during epimorphic regeneration are known to some extent, the metabolic changes experienced and their associated implications, remain unexplored. However, a circuit with a potential role as a modulator of cellular metabolism along regeneration is that formed by Lin28/let-7. In this study, we report two Lin28 paralogs and eight mature let-7 microRNAs encoded in the axolotl genome. Particularly, in the proliferative blastema stage amxLin28B is more abundant in the nuclei of blastemal cells, while the microRNAs amx-let-7c and amx-let-7a are most downregulated. Functional inhibition of Lin28 factors increase the levels of most mature let-7 microRNAs, consistent with an increment of intermediary metabolites of the Krebs cycle, and phenotypic alterations in the outgrowth of the blastema. In summary, we describe the primary components of the Lin28/let-7 circuit and their function during axolotl regeneration, acting upstream of metabolic reprogramming events.

Formation of βTC3 and MIN6 Pseudoislets Changes the Expression Pattern of Gpr40, Gpr55, and Gpr119 Receptors and Improves Lysophosphatidylcholines-Potentiated Glucose-Stimulated Insulin Secretion

The impaired spatial arrangement and connections between cells creating islets of Langerhans as well as altered expression of G protein-coupled receptors (GPCRs) often lead to dysfunction of insulin-secreting pancreatic β cells and can significantly contribute to the development of diabetes. Differences in glucose-stimulated insulin secretion (GSIS) are noticeable not only in diabetic individuals but also in model pancreatic β cells, e.g., βTC3 and MIN6 β cell lines with impaired and normal insulin secretion, respectively. Now, we compare the ability of GPCR agonists (lysophosphatidylcholines bearing fatty acid chains of different lengths) to potentiate GSIS in βTC3 and MIN6 β cell models, cultured as adherent monolayers and in a form of pseudoislets (PIs) with pancreatic MS1 endothelial cells. Our aim was also to investigate differences in expression of the GPCRs responsive to LPCs in these experimental systems. Aggregation of β cells into islet-like structures greatly enhanced the expression of Gpr40, Gpr55, and Gpr119 receptors. In contrast, the co-culture of βTC3 cells with endothelial cells converted the GPCR expression pattern closer to the pattern observed in MIN6 cells. Additionally, the efficiencies of various LPC species in βTC3-MS1 PIs also shifted toward the MIN6 cell model.

Extracellular Nucleotides Selectively Induce Migration of Chondrocytes and Expression of Type II Collagen

The migration of chondrocytes from healthy to injured tissues is one of the most important challenges during cartilage repair. Additionally, maintenance of the chondrogenic phenotype remains another limitation, especially during monolayer culture in vitro. Using both the differentiated and undifferentiated chondrogenic ATDC5 cell line, we showed that extracellular nucleotides are able to increase the migration rate of chondrocytes without affecting their chondrogenic phenotype. We checked the potency of natural nucleotides (ATP, ADP, UTP, and UDP) as well as their stable phosphorothioate analogs, containing a sulfur atom in the place of one nonbridging oxygen atom in a phosphate group. We also detected P2y1, P2y2, P2y4, P2y6, P2y12, P2y13, and P2y14 mRNA transcripts for nucleotide receptors, demonstrating that P2y1 and P2y13 are highly upregulated in differentiated ATDC5 cells. We showed that ADPβS, UDPβS, and ADP are the best stimulators of migration of differentiated chondrocytes. Additionally, ADP and ADPβS positively affected the expression of type II collagen, a structural component of the cartilage matrix.

An Updated Review of Pro- and Anti-Inflammatory Properties of Plasma Lysophosphatidylcholines in the Vascular System

Lysophosphatidylcholines are a group of bioactive lipids heavily investigated in the context of inflammation and atherosclerosis development. While present in plasma during physiological conditions, their concentration can drastically increase in certain inflammatory states. Lysophosphatidylcholines are widely regarded as potent pro-inflammatory and deleterious mediators, but an increasing number of more recent studies show multiple beneficial properties under various pathological conditions. Many of the discrepancies in the published studies are due to the investigation of different species or mixtures of lysophatidylcholines and the use of supra-physiological concentrations in the absence of serum or other carrier proteins. Furthermore, interpretation of the results is complicated by the rapid metabolism of lysophosphatidylcholine (LPC) in cells and tissues to pro-inflammatory lysophosphatidic acid. Interestingly, most of the recent studies, in contrast to older studies, found lower LPC plasma levels associated with unfavorable disease outcomes. Being the most abundant lysophospholipid in plasma, it is of utmost importance to understand its physiological functions and shed light on the discordant literature connected to its research. LPCs should be recognized as important homeostatic mediators involved in all stages of vascular inflammation. In this review, we want to point out potential pro- and anti-inflammatory activities of lysophospholipids in the vascular system and highlight recent discoveries about the effect of lysophosphatidylcholines on immune cells at the endothelial vascular interface. We will also look at their potential clinical application as biomarkers.

The Ryanodine Receptor Contributes to the Lysophosphatidylcholine-Induced Mineralization in Valvular Interstitial Cells

PURPOSE

Fibrocalcific aortic valve disease (CAVD) is caused by the deposition of calcific nodules in the aortic valve leaflets, resulting in progressive loss of function that ultimately requires surgical intervention. This process is actively mediated by the resident valvular interstitial cells (VICs), which, in response to oxidized lipids, transition from a quiescent to an osteoblast-like state. The purpose of this study was to examine if the ryanodine receptor, an intracellular calcium channel, could be therapeutically targeted to prevent this phenotypic conversion.

METHODS

The expression of the ryanodine receptor in porcine aortic VICs was characterized by qRT-PCR and immunofluorescence. Next, the VICs were exposed to lysophosphatidylcholine, an oxidized lipid commonly found in low-density lipoprotein, while the activity of the ryanodine receptor was modulated with ryanodine. The cultures were analyzed for markers of cellular mineralization, alkaline phosphatase activity, proliferation, and apoptosis.

RESULTS

Porcine aortic VICs predominantly express isoform 3 of the ryanodine receptors, and this protein mediates the cellular response to LPC. Exposure to LPC caused elevated intracellular calcium concentration in VICs, raised levels of alkaline phosphatase activity, and increased calcific nodule formation, but these changes were reversed when the activity of the ryanodine receptor was blocked.

CONCLUSIONS

Our findings suggest blocking the activity of the ryanodine receptor can attenuate the valvular mineralization caused by LPC. We conclude that oxidized lipids, such as LPC, play an important role in the development and progression of CAVD and that the ryanodine receptor is a promising target for pharmacological intervention.

Lysophosphatidylcholine Containing Anisic Acid Is Able to Stimulate Insulin Secretion Targeting G Protein Coupled Receptors

Diabetes mellitus is a worldwide health problem with high rates of mortality and morbidity. Management of diabetes mellitus by dietary components is achievable especially at the initial stage of the disease. Several studies confirmed the antidiabetic activities of simple phenolic acids and lysophosphatidylcholine (LPC). The main goal of this study was to identify new potential insulin secretion modulators obtained by combining the structures of two natural compounds, namely O-methyl derivatives of phenolic acids and phospholipids. LPC and phosphatidylcholine bearing methoxylated aromatic carboxylic acids were tested as potential agents able to improve glucose-stimulated insulin secretion (GSIS) and intracellular calcium mobilization in MIN6 β pancreatic cell line. Our results show that LPC with covalently bonded molecule of p-anisic acid at the sn-1 position was able to induce GSIS and intracellular calcium flux. Notably, 1-anisoyl-2-hydroxy-sn-glycero-3-phosphocholine did not affect the viability of MIN6 cells, suggesting its potential safe use. Furthermore, we have shown that three G protein coupled receptors, namely GPR40, GPR55, and GPR119, are targeted by this LPC derivative.

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.

Cannabinoid-sensitive receptors in cardiac physiology and ischaemia

The classical cannabinoid receptors CB1 and CB2 as well as the cannabinoid-sensitive receptor GPR55 are widely distributed throughout the mammalian body. In the cardiovascular field, CB1 and CB2 crucially impact on diseases characterized by inflammatory processes, such as atherosclerosis and acute myocardial infarction. Both receptors and their endogenous ligands anandamide and 2-arachidonoylglycerol are up-regulated in the ischaemic heart in humans and animal models. Pharmacological and genetic interventions with CB1 and CB2 vitally affect acute ischaemia-induced cardiac inflammation. Herein, CB1 rather aggravates the inflammatory response whereas CB2 mitigates inflammation via directly affecting immune cell attraction, macrophage polarization and lymphocyte clusters in the pericardial adipose tissue. Furthermore, cannabinoids and their receptors affect numerous cardiac risk factors. In this context, cannabis consumption is debated to trigger arrhythmias and even myocardial infarction. Moreover, CB1 activation is linked to impaired lipid and glucose metabolism and therefore obesity and diabetes, while its antagonism leads to the reduction of plasma triglycerides, low-density lipoprotein cholesterol, leptin, insulin and glucose. On the other hand, activation of cannabinoid-sensitive receptors can also counteract unfavourable predictors for cardiovascular diseases. In particular, hypertension can be mitigated via CB1 agonism and impaired adrenoceptor responsiveness prevented by functional GPR55. Taken together, current insights identify the cannabinoid system as promising target not only to therapeutically interfere with the vasculature, but also to affect the heart as target organ. This review discusses current knowledge regarding a direct cardiac role of the cannabinoid system and points out its feasible therapeutic manipulation in the ischaemic myocardium.

GPR55 controls functional differentiation of self-renewing epithelial progenitors for salivation

GPR55, a lipid-sensing receptor, is implicated in cell cycle control, malignant cell mobilization, and tissue invasion in cancer. However, a physiological role for GPR55 is virtually unknown for any tissue type. Here, we localize GPR55 to self-renewing ductal epithelial cells and their terminally differentiated progeny in both human and mouse salivary glands. Moreover, we find GPR55 expression downregulated in salivary gland mucoepidermoid carcinomas and GPR55 reinstatement by antitumor irradiation, suggesting that GPR55 controls renegade proliferation. Indeed, GPR55 antagonism increases cell proliferation and function determination in quasiphysiological systems. In addition, Gpr55-/- mice present ~50% enlarged submandibular glands with many more granulated ducts, as well as disordered endoplasmic reticuli and with glycoprotein content. Next, we hypothesized that GPR55 could also modulate salivation and glycoprotein content by entraining differentiated excretory progeny. Accordingly, GPR55 activation facilitated glycoprotein release by itself, inducing low-amplitude Ca2+ oscillations, as well as enhancing acetylcholine-induced Ca2+ responses. Topical application of GPR55 agonists, which are ineffective in Gpr55-/- mice, into adult rodent submandibular glands increased salivation and saliva glycoprotein content. Overall, we propose that GPR55 signaling in epithelial cells ensures both the life-long renewal of ductal cells and the continuous availability of saliva and glycoproteins for oral health and food intake.

Targeting CB1 and GPR55 Endocannabinoid Receptors as a Potential Neuroprotective Approach for Parkinson's Disease

Cannabinoid CB₁ receptors (CB₁R) and the GPR55 receptor are expressed in striatum and are potential targets in the therapy of Parkinson's disease (PD), one of the most prevalent neurodegenerative diseases in developed countries. The aim of this paper was to address the potential of ligands acting on those receptors to prevent the action of a neurotoxic agent, MPP⁺, that specifically affects neurons of the substantia nigra due to uptake via the dopamine DAT transporter. The SH-SY5Y cell line model was used as it expresses DAT and, therefore, is able to uptake MPP⁺ that inhibits complex I of the respiratory mitochondrial chain and leads to cell death. Cells were transfected with cDNAs coding for either or both receptors. Receptors in cotransfected cells formed heteromers as indicated by the in situ proximity ligation assays. Cell viability was assayed by oxygen rate consumption and by the bromide-based MTT method. Assays of neuroprotection using two concentrations of MPP⁺ showed that cells expressing receptor heteromers were more resistant to the toxic effect. After correction by effects on cell proliferation, the CB₁R antagonist, SR141716, afforded an almost full neuroprotection in CB₁R-expressing cells even when a selective agonist, ACEA, was present. In contrast, SR141716 was not effective in cells expressing CB₁/GPR55 heteromeric complexes. In addition, an agonist of GPR55, CID1792197, did not enhance neuroprotection in GPR55-expressing cells. These results show that neurons expressing heteromers are more resistant to cell death but question the real usefulness of CB₁R, GPR55, and their heteromers as targets to afford PD-related neuroprotection.

Lysophospholipases cooperate to mediate lipid homeostasis and lysophospholipid signaling

Lysophospholipids (LysoPLs) are bioactive lipid species involved in cellular signaling processes and the regulation of cell membrane structure. LysoPLs are metabolized through the action of lysophospholipases, including lysophospholipase A1 (LYPLA1) and lysophospholipase A2 (LYPLA2). A new X-ray crystal structure of LYPLA2 compared with a previously published structure of LYPLA1 demonstrated near-identical folding of the two enzymes; however, LYPLA1 and LYPLA2 have displayed distinct substrate specificities in recombinant enzyme assays. To determine how these in vitro substrate preferences translate into a relevant cellular setting and better understand the enzymes' role in LysoPL metabolism, CRISPR-Cas9 technology was utilized to generate stable KOs of Lypla1 and/or Lypla2 in Neuro2a cells. Using these cellular models in combination with a targeted lipidomics approach, LysoPL levels were quantified and compared between cell lines to determine the effect of losing lysophospholipase activity on lipid metabolism. This work suggests that LYPLA1 and LYPLA2 are each able to account for the loss of the other to maintain lipid homeostasis in cells; however, when both are deleted, LysoPL levels are dramatically increased, causing phenotypic and morphological changes to the cells.

Lysophosphatidylcholine and its phosphorothioate analogues potentiate insulin secretion via GPR40 (FFAR1), GPR55 and GPR119 receptors in a different manner

Lysophosphatidylcholine (LPC) is an endogenous ligand for GPR119 receptor, mediating glucose-stimulated insulin secretion (GSIS). We demonstrate that LPC facilitates GSIS in MIN6 pancreatic β-cell line and murine islets of Langerhans by recognizing not only GPR119 but also GPR40 (free fatty acid receptor 1) and GPR55 activated by lysophosphatidylinositol. Natural LPCs are unstable when administered in vivo limiting their therapeutic value and therefore, we present phosphorothioate LPC analogues with increased stability. All the modified LPCs under study (12:0, 14:0, 16:0, 18:0, and 18:1) significantly enhanced GSIS. The 16:0 sulfur analogue was the most potent, evoking 2-fold accentuated GSIS compared to the native counterpart. Interestingly, LPC analogues evoked GPR40-, GPR55-and GPR119-dependent [Ca²⁺]_i signaling, but did not stimulate cAMP accumulation as in the case of unmodified molecules. Thus, introduction of a phosphorothioate function not only increases LPC stability but also modulates affinity towards receptor targets and evokes different signaling pathways.

Lysophospholipids induce innate immune transdifferentiation of endothelial cells, resulting in prolonged endothelial activation

Innate immune cells express danger-associated molecular pattern (DAMP) receptors, T-cell costimulation/coinhibition receptors, and major histocompatibility complex II (MHC-II). We have recently proposed that endothelial cells can serve as innate immune cells, but the molecular mechanisms involved still await discovery. Here, we investigated whether human aortic endothelial cells (HAECs) could be transdifferentiated into innate immune cells by exposing them to hyperlipidemia-up-regulated DAMP molecules, i.e. lysophospholipids. Performing RNA-seq analysis of lysophospholipid-treated HAECs, we found that lysophosphatidylcholine (LPC) and lysophosphatidylinositol (LPI) regulate largely distinct gene programs as revealed by principal component analysis. Metabolically, LPC up-regulated genes that are involved in cholesterol biosynthesis, presumably through sterol regulatory element-binding protein 2 (SREBP2). By contrast, LPI up-regulated gene transcripts critical for the metabolism of glucose, lipids, and amino acids. Of note, we found that LPC and LPI both induce adhesion molecules, cytokines, and chemokines, which are all classic markers of endothelial cell activation, in HAECs. Moreover, LPC and LPI shared the ability to transdifferentiate HAECs into innate immune cells, including induction of potent DAMP receptors, such as CD36 molecule, T-cell costimulation/coinhibition receptors, and MHC-II proteins. The induction of these innate-immunity signatures by lysophospholipids correlated with their ability to induce up-regulation of cytosolic calcium and mitochondrial reactive oxygen species. In conclusion, lysophospholipids such as LPC and LPI induce innate immune cell transdifferentiation in HAECs. The concept of prolonged endothelial activation, discovered here, is relevant for designing new strategies for managing cardiovascular diseases.

Lysophosphatidylinositols, from Cell Membrane Constituents to GPR55 Ligands

Lysophosphatidylinositols (LPIs) are membrane constituents that alter the properties of said membranes. However, recent data showing that the once orphan receptor, GPR55, can act as a receptor for LPIs has sparked a renewed interest in LPIs as bioactive lipids. As evidence supporting the importance of LPIs and/or GPR55 is continuously accumulating and because LPI levels are altered in a number of pathologies such as obesity and cancer, the coming years should bring new, exciting discoveries to this field. In this review, we discuss the recent work on LPIs and on their molecular target, the GPR55 receptor. First, we summarize the metabolism of LPIs before outlining the cellular pathways activated by GPR55. Then, we review the actions of LPIs and GPR55 that could have potential pharmacological or therapeutic applications in several pathophysiological settings, such as cancer, obesity, pain, and inflammation.

A High-Fat Diet Rich in Saturated and Mono-Unsaturated Fatty Acids Induces Disturbance of Thyroid Lipid Profile and Hypothyroxinemia in Male Rats

SCOPE

Increasing evidence has shown that the disturbance of lipid metabolism might make a possible contribution to the pathogenesis of organ dysfunction, including thyroid, yet it is unknown whether excess intake of dietary fat interferes in thyroid lipid profile. We investigate the effects of dietary fat toward the thyroid lipid profile and thyroid function.

METHODS AND RESULTS

Male Sprague-Dawley rats are fed with high-fat diet (HFD) rich in saturated and mono-unsaturated fatty acids or chow diet for 18 weeks. LC-MS analysis of thyroid shows that total free fatty acids (FFAs) content is significantly higher in HFD rats. The concentration of highly saturated triglycerides significantly increases in HFD rats, whereas the polyunsaturated triglyceride significantly decreases, indicating the decrease in unsaturation in the HFD group. Significant increase of lysophosphatidylcholines (LPC) is observed in HFD rats. Thyroid function tests show hypothyroxinemia (total thyroxine [TT₄ ] and free thyroxine [FT₄ ]) in HFD rats, and elevated thyrotropin (TSH) concentration. The HFD rats also show decreased thyroid uptake of iodine.

CONCLUSION

Excess intake of dietary fat induces disturbance of thyroid lipid profile and hypothyroxinemia, indicating thyroid dysfunction. We speculate that it may provide a new prospect in understanding the pathogenesis of hypothyroidism.