Sphingolipid-mediated calcium signaling and its pathological effects

Characterization of functionally relevant G protein-coupled receptors in endometriotic epithelial cells

Endometriosis is a chronic inflammatory disease characterized by the invasion of endometrial cells outside the uterine cavity. Current treatments for the disease, whose typical symptoms are pain and infertility, are unsatisfactory, relying on the surgical removal of the lesions and hormonal therapies with high symptom relapse and collateral effects, respectively. The aim of the present study was to exploit the rationale for G protein-coupled receptors (GPCRs) as non-hormonal therapeutic targets for this disease. To this end, human endometriotic epithelial cells 12Z were employed to characterize GPCR-mediated increases in intracellular Ca2+ concentrations ([Ca2+]i) using fluo-4, and cell invasion was measured using Boyden chamber assays. The results showed that the GPCR ligands oxytocin, bradykinin, histamine, lysophosphatidic acid, and sphingosine 1-phosphate (S1P) efficiently increased [Ca2+]i and induced cell invasion in endometriotic cells. In contrast, neuropeptide S, previously identified as a pro-invasive mediator, did not increase [Ca2+]i in 12Z cells. Notably, pretreatment with pertussis toxin significantly reduced S1P-dependent [Ca2+]i increase and cell invasion, highlighting the involvement of Gi-mediated signaling. Employing specific agonists and/or antagonists of S1P receptor isoforms, we demonstrated that S1P1/S1P3/S1P5, but not S1P2/S1P4 mediated the [Ca2+]i increases in this cellular model. Moreover, activation of S1P1/S1P4/S1P5, but not S1P2/S1P3, efficiently stimulated cell invasion. Taken together, we identified several GPCRs that are functionally relevant in human endometriotic epithelial cells and may potentially serve as targets for non-hormonal therapy of endometriosis.

Early plasma ceramide and sphingomyelin levels reflect APOE genotype but not familial Alzheimer's disease gene mutations in female 5xFAD mice, with brain-region specific sphingolipid alterations

Pathophysiological changes associated with Alzheimer's disease (AD) begin decades before dementia onset, with age and APOE ε4 genotype as major risk factors [1-4]. Primary risk factors for developing AD include aging and number of copies of the apolipoprotein E (APOE) ε4 allele. Altered sphingolipid metabolism is increasingly implicated in early AD. However, the relationship between early plasma and brain sphingolipid changes-particularly in the context of APOE genotype-remains poorly defined. In this study, we analyzed plasma and brain sphingolipid profiles in transgenic AD mice carrying human APOE3 or APOE4 variants, with or without familial AD mutations (E3FAD and E4FAD). Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we assessed 110 sphingolipid species across four major classes (ceramides (Cers), hexosylceramides (HexCers), lactosylceramides (LacCers), and sphingomyelins (SMs)) at 2, 4, and 6 months in plasma and at 6 months in brain tissue in the cortex, hippocampus, striatum, and cerebellum. Our results demonstrate that early plasma sphingolipid alterations are largely driven by APOE genotype rather than AD pathology. Specifically, APOE4 carriers showed significant increases in SM species and reductions in Cer species compared to APOE3 carriers, independent of age or AD genotype. Brain lipid profiles showed minimal changes across genotypes after region correction. However, combined p-value analyses revealed APOE- and EFAD-dependent differences in the composition of primarily cortical sphingolipids. ROC analyses demonstrated high discriminative power of plasma sphingolipids for APOE, but not for AD genotype. These findings suggest that early plasma lipid profiles in female 5xFAD mice are more strongly influenced by APOE genotype than by overt AD pathology, potentially reflecting systemic pathways linked to APOE4-associated AD risk, while early disease-associated changes in the brain appear to be subtle and region-specific. These results underscore the importance of accounting for APOE genotype in early-stage AD lipidomic studies and in the interpretation of peripheral lipid biomarkers.

Negative regulation of cannabinoid receptor 2‑induced tumorigenic effect by sphingosine‑1‑phosphate receptor 5 activation

G protein‑coupled receptors (GPCR), also known as seven‑transmembrane proteins, serve a role in transmitting extracellular information into the cellular environment. Type 2 cannabinoid receptors (CB2) and type 5 sphingosine‑1‑phosphate receptor (S1P5) are GPCRs that are activated by biolipids and involved in tumor progression in various cancer types. At present, effects of crosstalk between CB2 and S1P5 receptors on tumor cell proliferation and migration in gliomas are not fully understood. The present study screened S1Ps for potential interactions with CB2 using bioluminescence resonance energy transfer analysis. S1P5 interacted strongly and specifically with CB2. 293T cells were transfected with CB2 tagged with Venus and S1P5 tagged with mCherry to investigate the cellular localization of both receptors. After 24 h, Confocal microscopy analysis revealed that, in the absence of agonists, both receptors were predominantly localized at the plasma membrane. Notably, both receptors were co‑internalized from the membrane to the cytoplasm upon individual and combined activation. The effects of co‑activation of both receptors on tumor progression were investigated using U‑87 MG, the human glioblastoma cell line. Activation of CB2 induced an increase in cell migration and proliferation, which were downregulated following the co‑activation of S1P5. Furthermore, activation of S1P5 significantly attenuated the upregulation of tumor progression‑related genes, including zinc finger protein 91, activating transcription factor 3, Ki67, basic transcription factor 3, and p21, induced by CB2 activation. This suggests that S1P5 exerts a negative regulatory effect on CB2‑mediated tumor progression. The present findings provide evidence of the crosstalk between CB2 and S1P5.

Small Extracellular Vesicles with a High Sphingomyelin Content Isolated from Hypertensive Diabetic db/db Mice Inhibits Calcium Mobilization and Augments Amiloride-Sensitive Epithelial Sodium Channel Activity

Extracellular vesicles (EVs) contain bioactive lipids that play a key role in pathophysiology. We hypothesized that EVs released from salt-loaded hypertensive diabetic db/db mice have increased bioactive lipid content that inhibits intracellular calcium mobilization and increases the activity of renal epithelial sodium channels (ENaC). An enrichment of sphingomyelins (SMs) was found in small urinary EVs (uEVs) isolated from salt-loaded hypertensive diabetic db/db mice (n = 4) compared to non-salt loaded db/db mice with diabetes alone (n = 4). Both groups of mice were included in the same cohort to control for variability. Cultured mouse cortical collecting duct (mpkCCD) cells loaded with a calcium reporter dye and challenged with small uEVs from hypertensive diabetic db/db mice showed a decrease in calcium mobilization when compared to cells treated with small uEVs from diabetic db/db mice. The amiloride-sensitive transepithelial current was increased in mpkCCD cells treated with small uEVs with abundant sphingomyelin content from hypertensive diabetic db/db mice in a dose- and time-dependent manner. Similar results were observed in mpkCCD cells and Xenopus 2F3 cells treated with exogenous sphingomyelin in a time-dependent manner. Single-channel patch clamp studies showed a decrease in ENaC activity in cells transiently transfected with sphingomyelin synthase 1/2 specific siRNA compared to non-targeting siRNA. These data suggest EVs with high sphingomyelin content positively regulate renal ENaC activity in a mechanism involving an inhibition of calcium mobilization.

Root-Knot Nematode Early Infection Suppresses Immune Response and Elicits the Antioxidant System in Tomato

The immune response in plants is regulated by several phytohormones and involves the overexpression of defense genes, including the pathogenesis-related (PR-) genes. The data reported in this paper indicate that nematodes can suppress the immune response by inhibiting the expression of defense genes. Transcripts from nine defense genes were detected by qRT-PCR in the roots of tomato plants at three and seven days post-inoculation (dpi) with living juveniles (J2s) of Meloidogyne incognita (root-knot nematodes, RKNs). All the salicylic acid (SA)-responsive genes tested (PR-1, PR-2, PR-4b, PR-5) were down-regulated in response to nematode infection. On the contrary, the expression of jasmonic acid (JA)-responsive genes, including ACO (encoding the enzyme 1-aminocyclopropane-1-carboxylic acid oxidase, which catalyzes the last step of ethylene (ET) biosynthesis) and JERF3 (Jasmonate Ethylene Response Factor 3), was unaffected by the infection. Conversely, the effect of nematode attack on the activities of the defense enzymes endoglucanase and endochitinase, encoded by PR-2 and PR-3, respectively, changed depending on the tested dpi. At 5 dpi, both enzymes were inhibited in inoculated plants compared to healthy controls. The genes encoding glutathione peroxidase (GPX) and catalase (CAT), both part of the antioxidant plant system, were highly overexpressed. Additionally, the activity of the antioxidant enzymes superoxide dismutase (SOD), CAT, and ascorbate peroxidase (APX) was enhanced in infected roots. Isoelectrofocusing of root extracts revealed novel SOD isoforms in samples from inoculated plants. Furthermore, plants were pre-treated with an array of key compounds, including hormone generators, inhibitors of SA or JA-mediated defense pathways, reactive oxygen species (ROS) scavengers and generators, inhibitors of ROS generation, and compounds that interfere with calcium-mediated metabolism. After treatments, plants were inoculated with RKNs, and nematodes were allowed to complete their life cycle. Factors of plant growth and infection level in treated plants were compared with those from untreated inoculated plants. Generally, compounds that decreased SA and/or ROS levels increased infection severity, while those that reduced JA/ET levels did not affect infection rates. ROS generators induced resistance against the pests. Compounds that silence calcium signaling by preventing its intake augmented infection symptoms. The data shown in this paper indicate that SA-mediated plant immune responses are consistently suppressed during the early stages of nematode infection, and this restriction is associated with the activation of the antioxidant ROS-scavenging system.

Molecular, immunological, and physiological evidences of a sphingosine-activated plasma membrane Ca2+-channel in Trypanosoma equiperdum

The hemoparasite Trypanosoma equiperdum belongs to the Trypanozoon subgenus and includes several species that are pathogenic to animals and humans in tropical and subtropical areas across the world. As with all eukaryotic organisms, Ca2+ is essential for these parasites to perform cellular processes thus ensuring their survival across their life cycle. Despite the established paradigm to study proteins related to Ca2+ homeostasis as potential drug targets, so far little is known about Ca2+ entry into trypanosomes. Therefore, in the present study, the presence of a plasma membrane Ca2+-channel in T. equiperdum (TeCC), activated by sphingosine and inhibited by verapamil, is described. The TeCC was cloned and analyzed using bioinformatic resources, which confirmed the presence of several domains, motifs, and a topology similar to the Ca2+ channels found in higher eukaryotes. Biochemical and confocal microscopy assays using antibodies raised against an internal region of human L-type Ca2+ channels indicate the presence of a protein with similar predicted molar mass to the sequence analyzed, located at the plasma membrane of T. equiperdum. Physiological assays based on Fura-2 signals and Mn2+ quenching performed on whole parasites showed a unidirectional Ca2+ entry, which is activated by sphingosine and blocked by verapamil, with the distinctive feature of insensitivity to nifedipine and Bay K 8644. This suggests a second Ca2+ entry for T. equiperdum, different from the store-operated Ca2+ entry (SOCE) previously described. Moreover, the evidence presented here for the TeCC indicates molecular and pharmacological differences with their mammal counterparts, which deserve further studies to evaluate the potential of this channel as a drug target.

High-Density Lipoproteins at the Interface between the NLRP3 Inflammasome and Myocardial Infarction

Despite significant therapeutic advancements, morbidity and mortality following myocardial infarction (MI) remain unacceptably high. This clinical challenge is primarily attributed to two significant factors: delayed reperfusion and the myocardial injury resulting from coronary reperfusion. Following reperfusion, there is a rapid intracellular pH shift, disruption of ionic balance, heightened oxidative stress, increased activity of proteolytic enzymes, initiation of inflammatory responses, and activation of several cell death pathways, encompassing apoptosis, necroptosis, and pyroptosis. The inflammatory cell death or pyroptosis encompasses the activation of the intracellular multiprotein complex known as the NLRP3 inflammasome. High-density lipoproteins (HDL) are endogenous particles whose components can either promote or mitigate the activation of the NLRP3 inflammasome. In this comprehensive review, we explore the role of inflammasome activation in the context of MI and provide a detailed analysis of how HDL can modulate this process.

Plasma Ceramides and Sphingomyelins and Sudden Cardiac Death in the Cardiovascular Health Study

Importance

Sphingolipids, including ceramides and sphingomyelins, may influence the pathophysiology and risk of sudden cardiac death (SCD) through multiple biological activities. Whether the length of the fatty acid acylated to plasma sphingolipid species is associated with SCD risk is not known.

Objective

To determine whether the saturated fatty acid length of plasma ceramides and sphingomyelins influences the association with SCD risk.

Design, Setting, and Participants

In this cohort study, multivariable Cox proportional hazards regression models were used to examine the association of sphingolipid species with SCD risk. The study population included 4612 participants in the Cardiovascular Health Study followed up prospectively for a median of 10.2 (IQR, 5.5-11.6) years. Baseline data were collected from January 1992 to December 1995 during annual examinations. Data were analyzed from February 11, 2020, to September 9, 2023.

Exposures

Eight plasma sphingolipid species (4 ceramides and 4 sphingomyelins) with saturated fatty acids of 16, 20, 22, and 24 carbons.

Main Outcome and Measure

Association of plasma ceramides and sphingomyelins with saturated fatty acids of different lengths with SCD risk.

Results

Among the 4612 CHS participants included in the analysis (mean [SD] age, 77 [5] years; 2724 [59.1%] women; 6 [0.1%] American Indian; 4 [0.1%] Asian; 718 [15.6%] Black; 3869 [83.9%] White, and 15 [0.3%] Other), 215 SCD cases were identified. In adjusted Cox proportional hazards regression analyses, plasma ceramides and sphingomyelins with palmitic acid (Cer-16 and SM-16) were associated with higher SCD risk per higher SD of log sphingolipid levels (hazard ratio [HR] for Cer-16, 1.34 [95% CI, 1.12-1.59]; HR for SM-16, 1.37 [95% CI, 1.12-1.67]). Associations did not differ by baseline age, sex, race, or body mass index. No significant association of SCD with sphingolipids with very-long-chain saturated fatty acids was observed after correction for multiple testing (HR for ceramide with arachidic acid, 1.06 [95% CI, 0.90-1.24]; HR for ceramide with behenic acid, 0.92 [95% CI, 0.77-1.10]; HR for ceramide with lignoceric acid, 0.92 [95% CI, 0.77-1.09]; HR for sphingomyelin with arachidic acid, 0.83 [95% CI, 0.71-0.98]; HR for sphingomyelin with behenic acid, 0.84 [95% CI, 0.70-1.00]; HR for sphingomyelin with lignoceric acid, 0.86 [95% CI, 0.72-1.03]).

Conclusions and Relevance

The findings of this large, population-based cohort study of SCD identified that higher plasma levels of Cer-16 and SM-16 were associated with higher risk of SCD. Future studies are needed to examine the underlying mechanism of these associations.

Sphingolipids: From structural components to signaling hubs

In late November 2019, Prof. Lina M. Obeid passed away from cancer, a disease she spent her life researching and studying its intricate molecular underpinnings. Along with her husband, Prof. Yusuf A. Hannun, Obeid laid down the foundations of sphingolipid biochemistry and oversaw its remarkable evolution over the years. Lipids are a class of macromolecules that are primarily associated with cellular architecture. In fact, lipids constitute the perimeter of the cell in such a way that without them, there cannot be cells. Hence, much of the early research on lipids identified the function of this class of biological molecules as merely structural. Nevertheless, unlike proteins, carbohydrates, and nucleic acids, lipids are elaborately diverse as they are not made up of monomers in polymeric forms. This diversity in structure is clearly mirrored by functional pleiotropy. In this chapter, we focus on a major subset of lipids, sphingolipids, and explore their historic rise from merely inert structural components of plasma membranes to lively and necessary signaling molecules that transmit various signals and control many cellular processes. We will emphasize the works of Lina Obeid since she was an integral pillar of the sphingolipid research world.

Boldine Alters Serum Lipidomic Signatures after Acute Spinal Cord Transection in Male Mice

Traumatic spinal cord injury (SCI) results in wide-ranging cellular and systemic dysfunction in the acute and chronic time frames after the injury. Chronic SCI has well-described secondary medical consequences while acute SCI has unique metabolic challenges as a result of physical trauma, in-patient recovery and other post-operative outcomes. Here, we used high resolution mass spectrometry approaches to describe the circulating lipidomic and metabolomic signatures using blood serum from mice 7 d after a complete SCI. Additionally, we probed whether the aporphine alkaloid, boldine, was able to prevent SCI-induced changes observed using these 'omics platforms'. We found that SCI resulted in large-scale changes to the circulating lipidome but minimal changes in the metabolome, with boldine able to reverse or attenuate SCI-induced changes in the abundance of 50 lipids. Multiomic integration using xMWAS demonstrated unique network structures and community memberships across the groups.

Sphingosine phosphate lyase insufficiency syndrome: a systematic review

BACKGROUND

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) or nephrotic syndrome type-14 is caused by biallelic mutations in SGPL1. Here, we conducted a systematic review to delineate the characteristics of SPLIS patients.

METHODS

A literature search was performed in PubMed, Web of Science, and Scopus databases, and eligible studies were included. For all patients, demographic, clinical, laboratory, and molecular data were collected and analyzed.

RESULTS

Fifty-five SPLIS patients (54.9% male, 45.1% female) were identified in 19 articles. Parental consanguinity and positive family history were reported in 70.9% and 52.7% of patients, respectively. Most patients (54.9%) primarily manifested within the first year of life, nearly half of whom survived, while all patients with a prenatal diagnosis of SPLIS (27.5%) died at a median [interquartile (IQR)] age of 2 (1.4-5.3) months (P = 0.003). The most prevalent clinical feature was endocrinopathies, including primary adrenal insufficiency (PAI) (71.2%) and hypothyroidism (32.7%). Kidney disorders (42, 80.8%) were mainly in the form of steroid-resistant nephrotic syndrome (SRNS) and progressed to end-stage kidney disease (ESKD) in 19 (36.5%) patients at a median (IQR) age of 6 (1.4-42.6) months. Among 30 different mutations in SGPL1, the most common was c.665G > A (p.Arg222Gln) in 11 (20%) patients. Twenty-six (49.1%) patients with available outcome were deceased at a median (IQR) age of 5 (1.5-30.5) months, mostly following ESKD (23%) or sepsis/septic shock (23%).

CONCLUSION

In patients with PAI and/or SRNS, SGPL1 should be added to diagnostic genetic panels, which can provide an earlier diagnosis of SPLIS and prevention of ESKD and other life-threatening complications.

Ichthyosis linked to sphingosine 1-phosphate lyase insufficiency is due to aberrant sphingolipid and calcium regulation

Sphingosine 1-phosphate lyase (SGPL1) insufficiency (SPLIS) is a syndrome which presents with adrenal insufficiency, steroid-resistant nephrotic syndrome, hypothyroidism, neurological disease, and ichthyosis. Where a skin phenotype is reported, 94% had abnormalities such as ichthyosis, acanthosis, and hyperpigmentation. To elucidate the disease mechanism and the role SGPL1 plays in the skin barrier we established clustered regularly interspaced short palindromic repeats-Cas9 SGPL1 KO and a lentiviral-induced SGPL1 overexpression (OE) in telomerase reverse-transcriptase immortalised human keratinocytes (N/TERT-1) and thereafter organotypic skin equivalents. Loss of SGPL1 caused an accumulation of S1P, sphingosine, and ceramides, while its overexpression caused a reduction of these species. RNAseq analysis showed perturbations in sphingolipid pathway genes, particularly in SGPL1_KO, and our gene set enrichment analysis revealed polar opposite differential gene expression between SGPL1_KO and _OE in keratinocyte differentiation and Ca2+ signaling genesets. SGPL1_KO upregulated differentiation markers, while SGPL1_OE upregulated basal and proliferative markers. The advanced differentiation of SGPL1_KO was confirmed by 3D organotypic models that also presented with a thickened and retained stratum corneum and a breakdown of E-cadherin junctions. We conclude that SPLIS associated ichthyosis is a multifaceted disease caused possibly by sphingolipid imbalance and excessive S1P signaling, leading to increased differentiation and an imbalance of the lipid lamellae throughout the epidermis.

Sphingosine 1-phosphate attenuates neuronal dysfunction induced by amyloid-β oligomers through endocytic internalization of NMDA receptors

Soluble oligomers arising from the aggregation of the amyloid beta peptide (Aβ) have been identified as the main pathogenic agents in Alzheimer's disease (AD). Prefibrillar oligomers of the 42-residue form of Aβ (Aβ₄₂ O) show membrane-binding capacity and trigger the disruption of Ca²⁺ homeostasis, a causative event in neuron degeneration. Since bioactive lipids have been recently proposed as potent protective agents against Aβ toxicity, we investigated the involvement of sphingosine 1-phosphate (S1P) signalling pathway in Ca²⁺ homeostasis in living neurons exposed to Aβ₄₂ O. We show that both exogenous and endogenous S1P rescued neuronal Ca²⁺ dyshomeostasis induced by toxic Aβ₄₂ O in primary rat cortical neurons and human neuroblastoma SH-SY5Y cells. Further analysis revealed a strong neuroprotective effect of S1P₁ and S1P₄ receptors, and to a lower extent of S1P₃ and S1P₅ receptors, which activate the G_i -dependent signalling pathways, thus resulting in the endocytic internalization of the extrasynaptic GluN2B-containing N-methyl-D-aspartate receptors (NMDARs). Notably, the S1P beneficial effect can be sustained over time by sphingosine kinase-1 overexpression, thus counteracting the down-regulation of the S1P signalling induced by Aβ₄₂ O. Our findings disclose underlying mechanisms of S1P neuronal protection against harmful Aβ₄₂ O, suggesting that S1P and its signalling axis can be considered promising targets for therapeutic approaches for AD.

Sphingolipids and their role in health and disease in the central nervous system

Sphingolipids (SLs) are lipids derived from sphingosine, and their metabolism involves a broad and complex network of reactions. Although SLs are widely distributed in the body, it is well known that they are present in high concentrations within the central nervous system (CNS). Under physiological conditions, their abundance and distribution in the CNS depend on brain development and cell type. Consequently, SLs metabolism impairment may have a significant impact on the normal CNS function, and has been associated with several disorders, including sphingolipidoses, Parkinson's, and Alzheimer's. This review summarizes the main SLs characteristics and current knowledge about synthesis, catabolism, regulatory pathways, and their role in physiological and pathological scenarios in the CNS.

Regulation of the lysosome by sphingolipids: potential role in aging

Sphingolipids are a class of bioactive complex lipids that have been closely associated with aging and aging-related diseases. However, the mechanism through which sphingolipids control aging has long been a mystery. Emerging studies reveal that sphingolipids exert tight control over lysosomal homeostasis and function, as evidenced by sphingolipid-related diseases, including but not limited to lysosomal storage disorders. These diseases are defined by primary lysosomal defects and a few secondary defects such as mitochondrial dysfunction. Intriguingly, recent research indicates that the majority of these defects are also associated with aging, implying that sphingolipid-related diseases and aging may share common mechanisms. We propose that the lysosome is a pivotal hub for sphingolipid-mediated aging regulation. This review discusses the critical roles of sphingolipid metabolism in regulating various lysosomal functions, with an emphasis on how such regulation may contribute to aging and aging-related diseases.

Polychlorinated environmental toxicants affect sphingolipid metabolism during neurogenesis in vitro

Sphingolipids (SLs) are important signaling molecules and functional components of cellular membranes. Although SLs are known as crucial regulators of neural cell physiology and differentiation, modulations of SLs by environmental neurotoxicants in neural cells and their neuronal progeny have not yet been explored. In this study, we used in vitro models of differentiated neuron-like cells, which were repeatedly exposed during differentiation to model environmental toxicants, and we analyzed changes in sphingolipidome, cellular morphology and gene expression related to SL metabolism or neuronal differentiation. We compared these data with the results obtained in undifferentiated neural cells with progenitor-like features. As model polychlorinated organic pollutants, we used 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3'-dichlorobiphenyl (PCB11) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153). PCB153 revealed itself as the most prominent deregulator of SL metabolism and as potent toxicant during early phases of in vitro neurogenesis. TCDD exerted only minor changes in the levels of analysed lipid species, however, it significantly changed the rate of pro-neuronal differentiation and deregulated expression of neuronal markers during neurogenesis. PCB11 acted as a potent disruptor of in vitro neurogenesis, which induced significant alterations in SL metabolism and cellular morphology in both differentiated neuron-like models (differentiated NE4C and NG108-15 cells). We identified ceramide-1-phosphate, lactosylceramides and several glycosphingolipids to be the most sensitive SL species to exposure to polychlorinated pollutants. Additionally, we identified deregulation of several genes related to SL metabolism, which may be explored in future as potential markers of developmental neurotoxicity.

Nogo-A Modulates the Synaptic Excitation of Hippocampal Neurons in a Ca2+-Dependent Manner

A tight regulation of the balance between inhibitory and excitatory synaptic transmission is a prerequisite for synaptic plasticity in neuronal networks. In this context, the neurite growth inhibitor membrane protein Nogo-A modulates synaptic plasticity, strength, and neurotransmitter receptor dynamics. However, the molecular mechanisms underlying these actions are unknown. We show that Nogo-A loss-of-function in primary mouse hippocampal cultures by application of a function-blocking antibody leads to higher excitation following a decrease in GABA_ARs at inhibitory and an increase in the GluA1, but not GluA2 AMPAR subunit at excitatory synapses. This unbalanced regulation of AMPAR subunits results in the incorporation of Ca²⁺-permeable GluA2-lacking AMPARs and increased intracellular Ca²⁺ levels due to a higher Ca²⁺ influx without affecting its release from the internal stores. Increased neuronal activation upon Nogo-A loss-of-function prompts the phosphorylation of the transcription factor CREB and the expression of c-Fos. These results contribute to the understanding of the molecular mechanisms underlying the regulation of the excitation/inhibition balance and thereby of plasticity in the brain.

TMEM135 is a Novel Regulator of Mitochondrial Dynamics and Physiology with Implications for Human Health Conditions

Transmembrane proteins (TMEMs) are integral proteins that span biological membranes. TMEMs function as cellular membrane gates by modifying their conformation to control the influx and efflux of signals and molecules. TMEMs also reside in and interact with the membranes of various intracellular organelles. Despite much knowledge about the biological importance of TMEMs, their role in metabolic regulation is poorly understood. This review highlights the role of a single TMEM, transmembrane protein 135 (TMEM135). TMEM135 is thought to regulate the balance between mitochondrial fusion and fission and plays a role in regulating lipid droplet formation/tethering, fatty acid metabolism, and peroxisomal function. This review highlights our current understanding of the various roles of TMEM135 in cellular processes, organelle function, calcium dynamics, and metabolism.

Aging and β3-adrenergic stimulation alter mitochondrial lipidome of adipose tissue

Mitochondrial abundance and thermogenic capacity are two imperative components that distinguish brown, beige and white adipose tissues. Most importantly, the lipid composition is vital for maintaining the quantity, quality and function of mitochondria. Therefore, we employed quantitative lipidomics to probe the mitochondrial lipidome of adipose tissues. The mitochondrial lipidome reveals β3-adrenergic stimulation and aging drastically altered the levels of phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio and acyl chain desaturation. Precisely, PC36:2 and PE38:4 levels correlate with the increased brown and beige fat activity in young mice. While aging increased lysoPC species in white adipose tissue (WAT) mitochondria, CL-316,243 administration reduced lysoPC species and increased lyso-PE18:1 and 18:2 content during WAT browning. Also, non-thermogenic mitochondria accumulate sphingomyelin (SM), phosphatidylserine (PS), phosphatidic acid (PA) and ether-linked PC (ePC). Similarly, enrichment of phosphatidylglycerol (PG) and cardiolipin (CL) levels are associated with thermogenic mitochondria. Also, our in vitro experiment supports that blocking the de novo sphingolipid synthesis pathway by myriocin, SPT1 inhibitor increased the thermogenic capacity and oxygen consumption rate in mature adipocytes. Overall, our study suggests mitochondria of brown, beige and white adipose tissues own a unique pattern of lipid molecular species and their levels are altered by aging and CL-316,243 administration.

Drug-Induced Lipid Remodeling in Leishmania Parasites

Leishmania parasites efficiently develop resistance against several types of drugs including antimonials, the primary antileishmanial drug historically implemented. The resistance to antimonials is considered to be a major risk factor for effective leishmaniasis treatment. To detect biomarkers/biopatterns for the differentiation of antimony-resistant Leishmania strains, we employed untargeted global mass spectrometry to identify intracellular lipids present in antimony sensitive and resistant parasites before and after antimony exposure. The lipidomic profiles effectively differentiated the sensitive and resistant phenotypes growing with and without antimony pressure. Resistant phenotypes were characterized by significant downregulation of phosphatidylcholines, sphingolipid decrease, and lysophosphatidylcholine increase, while sensitive phenotypes were characterized by the upregulation of triglycerides with long-chain fatty acids and a tendency toward the phosphatidylethanolamine decrease. Our findings suggest that the changes in lipid composition in antimony-resistant parasites contribute to the physiological response conducted to combat the oxidative stress unbalance caused by the drug. We have identified several lipids as potential biomarkers associated with the drug resistance.

A comprehensive overview of the complex world of the endo- and sarcoplasmic reticulum Ca2+-leak channels

Inside cells, the endoplasmic reticulum (ER) forms the largest Ca²⁺ store. Ca²⁺ is actively pumped by the SERCA pumps in the ER, where intraluminal Ca²⁺-binding proteins enable the accumulation of large amount of Ca²⁺. IP₃ receptors and the ryanodine receptors mediate the release of Ca²⁺ in a controlled way, thereby evoking complex spatio-temporal signals in the cell. The steady state Ca²⁺ concentration in the ER of about 500 μM results from the balance between SERCA-mediated Ca²⁺ uptake and the passive leakage of Ca²⁺. The passive Ca²⁺ leak from the ER is often ignored, but can play an important physiological role, depending on the cellular context. Moreover, excessive Ca²⁺ leakage significantly lowers the amount of Ca²⁺ stored in the ER compared to normal conditions, thereby limiting the possibility to evoke Ca²⁺ signals and/or causing ER stress, leading to pathological consequences. The so-called Ca²⁺-leak channels responsible for Ca²⁺ leakage from the ER are however still not well understood, despite over 20 different proteins have been proposed to contribute to it. This review has the aim to critically evaluate the available evidence about the various channels potentially involved and to draw conclusions about their relative importance.

Targeting the Sphingosine-1-Phosphate Axis for Developing Non-narcotic Pain Therapeutics

Chronic pain is a life-altering condition affecting millions of people. Current treatments are inadequate and prolonged therapies come with severe side effects, especially dependence and addiction to opiates. Identification of non-narcotic analgesics is of paramount importance. Preclinical and clinical studies suggest that sphingolipid metabolism alterations contribute to neuropathic pain development. Functional sphingosine-1-phosphate (S1P) receptor 1 (S1PR1) antagonists, such as FTY720/fingolimod, used clinically for non-pain conditions, are emerging as non-narcotic analgesics, supporting the repurposing of fingolimod for chronic pain treatment and energizing drug discovery focused on S1P signaling. Here, we summarize the role of S1P in pain to highlight the potential of targeting the S1P axis towards development of non-narcotic therapeutics, which, in turn, will hopefully help lessen misuse of opioid pain medications and address the ongoing opioid epidemic.

Inhibition of sphingolipid synthesis improves outcomes and survival in GARP mutant wobbler mice, a model of motor neuron degeneration

Numerous mutations that impair retrograde membrane trafficking between endosomes and the Golgi apparatus lead to neurodegenerative diseases. For example, mutations in the endosomal retromer complex are implicated in Alzheimer's and Parkinson's diseases, and mutations of the Golgi-associated retrograde protein (GARP) complex cause progressive cerebello-cerebral atrophy type 2 (PCCA2). However, how these mutations cause neurodegeneration is unknown. GARP mutations in yeast, including one causing PCCA2, result in sphingolipid abnormalities and impaired cell growth that are corrected by treatment with myriocin, a sphingolipid synthesis inhibitor, suggesting that alterations in sphingolipid metabolism contribute to cell dysfunction and death. Here we tested this hypothesis in wobbler mice, a murine model with a homozygous partial loss-of-function mutation in Vps54 (GARP protein) that causes motor neuron disease. Cytotoxic sphingoid long-chain bases accumulated in embryonic fibroblasts and spinal cords from wobbler mice. Remarkably, chronic treatment of wobbler mice with myriocin markedly improved their wellness scores, grip strength, neuropathology, and survival. Proteomic analyses of wobbler fibroblasts revealed extensive missorting of lysosomal proteins, including sphingolipid catabolism enzymes, to the Golgi compartment, which may contribute to the sphingolipid abnormalities. Our findings establish that altered sphingolipid metabolism due to GARP mutations contributes to neurodegeneration and suggest that inhibiting sphingolipid synthesis might provide a useful strategy for treating these disorders.

Sphingosine-1-Phosphate in the Tumor Microenvironment: A Signaling Hub Regulating Cancer Hallmarks

As a key hub of malignant properties, the cancer microenvironment plays a crucial role intimately connected to tumor properties. Accumulating evidence supports that the lysophospholipid sphingosine-1-phosphate acts as a key signal in the cancer extracellular milieu. In this review, we have a particular focus on glioblastoma, representative of a highly aggressive and deleterious neoplasm in humans. First, we highlight recent advances and emerging concepts for how tumor cells and different recruited normal cells contribute to the sphingosine-1-phosphate enrichment in the cancer microenvironment. Then, we describe and discuss how sphingosine-1-phosphate signaling contributes to favor cancer hallmarks including enhancement of proliferation, stemness, invasion, death resistance, angiogenesis, immune evasion and, possibly, aberrant metabolism. We also discuss the potential of how sphingosine-1-phosphate control mechanisms are coordinated across distinct cancer microenvironments. Further progress in understanding the role of S1P signaling in cancer will depend crucially on increasing knowledge of its participation in the tumor microenvironment.

De novo transcriptome profile of coccolithophorid alga Emiliania huxleyi CCMP371 at different calcium concentrations with proteome analysis

The haptophyte alga Emiliania huxleyi is the most abundant coccolithophore in the modern ocean and produces elaborate calcite crystals, called coccolith, in a separate intracellular compartment known as the coccolith vesicle. Despite the importance of biomineralization in coccolithophores, the molecular mechanism underlying it remains unclear. Understanding this precise machinery at the molecular level will provide the knowledge needed to enable further manipulation of biomineralization. In our previous study, altering the calcium concentration modified the calcifying ability of E. huxleyi CCMP371. Therefore in this study, we tested E. huxleyi cells acclimated to three different calcium concentrations (0, 0.1, and 10 mM). To understand the whole transcript profile at different calcium concentrations, RNA-sequencing was performed and used for de novo assembly and annotation. The differentially expressed genes (DEGs) among the three different calcium concentrations were analyzed. The functional classification by gene ontology (GO) revealed that 'intrinsic component of membrane' was the most enriched of the GO terms at the ambient calcium concentration (10 mM) compared with the limited calcium concentrations (0 and 0.1 mM). Moreover, the DEGs in those comparisons were enriched mainly in 'secondary metabolites biosynthesis, transport and catabolism' and 'signal transduction mechanisms' in the KOG clusters and 'processing in endoplasmic reticulum', and 'ABC transporters' in the KEGG pathways. Furthermore, metabolic pathways involved in protein synthesis were enriched among the differentially expressed proteins. The results of this study provide a molecular profile for understanding the expression of transcripts and proteins in E. huxleyi at different calcium concentrations, which will help to identify the detailed mechanism of its calcification.