Optic Nerve Lipidomics Reveal Impaired Glucosylsphingosine Lipids Pathway in Glaucoma

FABP5 regulates ROS-NLRP3 inflammasome in glutamate-induced retinal excitotoxic glaucomatous model

Fatty acid binding proteins (FABPs) are a class of small molecular mass intracellular lipid chaperone proteins that bind to hydrophobic ligands, such as long-chain fatty acids. FABP5 expression was significantly upregulated in the N-methyl-d-aspartic acid (NMDA) model, the microbead-induced chronic glaucoma model, and the DBA/2J mice. Previous studies have demonstrated that FABP5 can mediate mitochondrial dysfunction and oxidative stress in ischemic neurons, but the role of FABP5 in oxidative stress and cell death in retina NMDA injury models is unclear. In this study, we found that FABP5 is significantly altered in a model of glutamate excitotoxicity and is regulated by Stat3. Inhibition of FABP5 alleviated oxidative stress imbalance and activation of NLRP3 inflammasome, reduced the release of inflammatory factors, and ultimately attenuated glutamate excitotoxicity-induced retinal ganglion cell loss. Meanwhile, caspase1 inhibitors could alleviate the retinal ganglion cell loss induced by glutamate excitotoxicity. In conclusion, FABP5 inhibition protects retina ganglion cells from excitotoxic damage by suppressing the ROS-NLRP3 inflammasome pathway. FABP5 maybe a promising new target for glaucoma diagnosis and treatment.

Glial Cell Activation and Immune Responses in Glaucoma: A Systematic Review of Human Postmortem Studies of the Retina and Optic Nerve

Although researched extensively the understanding regarding mechanisms underlying glaucoma pathogenesis remains limited. Further, the exact mechanism behind neuronal death remains elusive. The role of neuroinflammation in retinal ganglion cell (RGC) death has been prominently theorised. This review provides a comprehensive summary of neuroinflammatory responses in glaucoma. A systematic search of Medline and Embase for articles published up to 8th March 2023 yielded 32 studies using post-mortem tissues from glaucoma patients. The raw data were extracted from tables and text to calculate the standardized mean differences (SMDs). These studies utilized post-mortem tissues from glaucoma patients, totalling 490 samples, compared with 380 control samples. Among the included studies, 27 reported glial cell activation based on changes to cellular morphology and molecular staining. Molecular changes were predominantly attributed to astrocytes (62.5%) and microglia (15.6%), with some involvement of Muller cells. These glial cell changes included amoeboid microglial cells with increased CD45 or HLA-DR intensity and hypertrophied astrocytes with increased glial fibrillary acidic protein labelling. Further, changes to extracellular matrix proteins like collagen, galectin, and tenascin-C suggested glial cells' influence on structural changes in the optic nerve head. The activation of DAMPs-driven immune response and the classical complement cascade was reported and found to be associated with activated glial cells in glaucomatous tissue. Increased pro-inflammatory markers such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also linked to glial cells. Glial cell activation was also associated with mitochondrial, vascular, metabolic and antioxidant component disruptions. Association of the activated glial cells with pro-inflammatory responses, dysregulation of homeostatic components and antigen presentation indicates that glial cell responses influence glaucoma progression. However, the exact mechanism triggering these responses and underlying interactions remains unexplored. This necessitates further research using human samples for an increased understanding of the precise role of neuroinflammation in glaucoma progression.

Lack of ceramide synthase 5 protects retinal ganglion cells from ocular hypertensive injury

Ceramides with varying acyl-chain lengths can have unique biological actions and hence, cellular responses to ceramides may depend not on their overall concentration but on that of individual ceramide species. The purpose of this study was to determine individual ceramide species impacting retinal ganglion cell (RGC) loss under the ocular hypertensive condition. Induced pluripotent stem cell (iPSC)-derived RGCs and primary cultures of human astrocytes were used to determine the effect of individual ceramide species on both RGC viability and astrocyte secretion of inflammatory cytokines in vitro. In in vivo experiments with wild-type (WT) and ceramide synthase 5 (CerS5) knockout mice, intraocular pressure was unilaterally elevated with microbead injection. Retinal function and morphology were evaluated using pattern electroretinography (pERG) and immunofluorescence, respectively. Ceramide levels were determined by LC-MS/MS analysis. Exposure to C16:0-, C18:0-, C18:1-, C20:0- and C24:0-ceramides significantly reduces RGC viability in vitro, with the very long chain C24:0-ceramide being the most neurotoxic; treatment with C18:0-, C18:1- and C24:0-ceramides stimulates an increase of TNF-α secretion by astrocytes. The retinas of CerS5 KO mice have significantly reduced levels of C16:0- and C18:1-ceramides compared to WT; ocular hypertensive eyes of these mice maintain higher pERG amplitudes and RGC numbers compared to WT. Individual ceramides with different chain lengths have different effects on RGCs and astrocytes. Our results demonstrate that suppressing C16:0- and C18:1-ceramide species effectively protects RGCs against ocular hypertensive injury. These results provide a basis for targeting specific ceramide species in the treatment of glaucoma.

Potential Immune-Inflammatory Proteome Biomarkers for Guiding the Treatment of Patients with Primary Acute Angle-Closure Glaucoma Caused by COVID-19

Primary acute angle-closure glaucoma (PAACG) is a sight-threatening condition that can lead to blindness. With the increasing incidence of COVID-19, a multitude of people are experiencing acute vision loss and severe swelling of the eyes and head. These patients were then diagnosed with acute angle closure, with or without a history of PACG. However, the mechanism by which viral infection causes PACG has not been clarified. This is the first study to explore the specific inflammatory proteomic landscape in SARS-CoV-2-induced PAACG. The expression of 92 inflammation-related proteins in 19 aqueous humor samples from PAACGs or cataract patients was detected using the Olink Target 96 Inflammation Panel based on a highly sensitive and specific proximity extension assay technology. The results showed that 76 proteins were significantly more abundant in the PAACG group than in the cataract group. Notably, the top eight differentially expressed proteins were IL-8, MCP-1, TNFRSF9, DNER, CCL4, Flt3L, CXCL10, and CD40. Generally, immune markers are related to inflammation, macrophage activation, and viral infection, revealing the crucial role of macrophages in the occurrence of PAACGs caused by SARS-CoV-2.

Concept of Normativity in Multi-Omics Analysis of Axon Regeneration

Transcriptomes and proteomes can be normalized with a handful of RNAs or proteins (or their peptides), such as GAPDH, β-actin, RPBMS, and/or GAP43. Even with hundreds of standards, normalization cannot be achieved across different molecular mass ranges for small molecules, such as lipids and metabolites, due to the non-linearity of mass by charge ratio for even the smallest part of the spectrum. We define the amount (or range of amounts) of metabolites and/or lipids per a defined amount of a protein, consistently identified in all samples of a multiple-model organism comparison, as the normative level of that metabolite or lipid. The defined protein amount (or range) is a normalized value for one cohort of complete samples for which intrasample relative protein quantification is available. For example, the amount of citrate (a metabolite) per µg of aconitate hydratase (normalized protein amount) identified in the proteome is the normative level of citrate with aconitase. We define normativity as the amount of metabolites (or amount range) detected when compared to normalized protein levels. We use axon regeneration as an example to illustrate the need for advanced approaches to the normalization of proteins. Comparison across different pharmacologically induced axon regeneration mouse models entails the comparison of axon regeneration, studied at different time points in several models designed using different agents. For the normalization of the proteins across different pharmacologically induced models, we perform peptide doping (fixed amounts of known peptides) in each sample to normalize the proteome across the samples. We develop Regen V peptides, divided into Regen III (SEB, LLO, CFP) and II (HH4B, A1315), for pre- and post-extraction comparisons, performed with the addition of defined, digested peptides (bovine serum albumin tryptic digest) for protein abundance normalization beyond commercial labeled relative quantification (for example, 18-plex tandem mass tags). We also illustrate the concept of normativity by using this normalization technique on regenerative metabolome/lipidome profiles. As normalized protein amounts are different in different biological states (control versus axon regeneration), normative metabolite or lipid amounts are expected to be different for specific biological states. These concepts and standardization approaches are important for the integration of different datasets across different models of axon regeneration.

A Look into Ocular Diseases: The Pivotal Role of Omics Sciences in Ophthalmology Research

Precision medicine is a new medical approach which considers both population characteristics and individual variability to provide customized healthcare. The transition from traditional reactive medicine to personalized medicine is based on a biomarker-driven process and a deep knowledge of biological mechanisms according to which the development of diseases occurs. In this context, the advancements in high-throughput omics technologies represent a unique opportunity to discover novel biomarkers and to provide an unbiased picture of the biological system. One of the medical fields in which omics science has started to be recently applied is that of ophthalmology. Ocular diseases are very common, and some of them could be highly disabling, thus leading to vision loss and blindness. The pathogenic mechanism of most ocular diseases may be dependent on various genetic and environmental factors, whose effect has not been yet completely understood. In this context, large-scale omics approaches are fundamental to have a comprehensive evaluation of the whole system and represent an essential tool for the development of novel therapies. This Review summarizes the recent advancements in omics science applied to ophthalmology in the last ten years, in particular by focusing on proteomics, metabolomics and lipidomics applications from an analytical perspective. The role of high-efficiency separation techniques coupled to (high-resolution) mass spectrometry ((HR)MS) is also discussed, as well as the impact of sampling, sample preparation and data analysis as integrating parts of the analytical workflow.

A study protocol to characterise pathophysiological and molecular markers of rheumatic heart disease and degenerative aortic stenosis using multiparametric cardiovascular imaging and multiomics techniques

INTRODUCTION

Rheumatic heart disease (RHD), degenerative aortic stenosis (AS), and congenital valve diseases are prevalent in sub-Saharan Africa. Many knowledge gaps remain in understanding disease mechanisms, stratifying phenotypes, and prognostication. Therefore, we aimed to characterise patients through clinical profiling, imaging, histology, and molecular biomarkers to improve our understanding of the pathophysiology, diagnosis, and prognosis of RHD and AS.

METHODS

In this cross-sectional, case-controlled study, we plan to recruit RHD and AS patients and compare them to matched controls. Living participants will undergo clinical assessment, echocardiography, CMR and blood sampling for circulatory biomarker analyses. Tissue samples will be obtained from patients undergoing valve replacement, while healthy tissues will be obtained from cadavers. Immunohistology, proteomics, metabolomics, and transcriptome analyses will be used to analyse circulatory- and tissue-specific biomarkers. Univariate and multivariate statistical analyses will be used for hypothesis testing and identification of important biomarkers. In summary, this study aims to delineate the pathophysiology of RHD and degenerative AS using multiparametric CMR imaging. In addition to discover novel biomarkers and explore the pathomechanisms associated with RHD and AS through high-throughput profiling of the tissue and blood proteome and metabolome and provide a proof of concept of the suitability of using cadaveric tissues as controls for cardiovascular disease studies.

Lipid mediators in glaucoma: Unraveling their diverse roles and untapped therapeutic potential

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and visual field loss, and remains a leading cause of irreversible blindness. Elevated intraocular pressure (IOP) is a critical risk factor that requires effective management. Emerging research underscores dual roles of bioactive lipid mediators in both IOP regulation, and the modulation of neurodegeneration and neuroinflammation in glaucoma. Bioactive lipids, encompassing eicosanoids, specialized pro-resolving mediators (SPMs), sphingolipids, and endocannabinoids, have emerged as crucial players in these processes, orchestrating inflammation and diverse effects on aqueous humor dynamics and tissue remodeling. Perturbations in these lipid mediators contribute to retinal ganglion cell loss, vascular dysfunction, oxidative stress, and neuroinflammation. Glaucoma management primarily targets IOP reduction via pharmacological agents and surgical interventions, with prostaglandin analogues at the forefront. Intriguingly, additional lipid mediators offer promise in attenuating inflammation and providing neuroprotection. Here we explore these pathways to shed light on their intricate roles, and to unveil novel therapeutic avenues for glaucoma management.

Association between glaucoma susceptibility with combined defects in mitochondrial oxidative phosphorylation and fatty acid beta oxidation

Glaucoma is one of the leading causes of visual impairment and blindness worldwide, and is characterized by the progressive damage of retinal ganglion cells (RGCs) and the atrophy of the optic nerve head (ONH). The exact cause of RGC loss and optic nerve damage in glaucoma is not fully understood. The high energy demands of these cells imply a higher sensitivity to mitochondrial defects. Moreover, it has been postulated that the optic nerve is vulnerable towards damage from oxidative stress and mitochondrial dysfunction. To investigate this further, we conducted a pooled analysis of mitochondrial variants related to energy production, specifically focusing on oxidative phosphorylation (OXPHOS) and fatty acid β-oxidation (FAO). Our findings revealed that patients carrying non-synonymous (NS) mitochondrial DNA (mtDNA) variants within the OXPHOS complexes had an almost two-fold increased risk of developing glaucoma. Regarding FAO, our results demonstrated that longer-chain acylcarnitines (AC) tended to decrease, while shorter-chain AC tended to increase in patients with glaucoma. Furthermore, we observed that the knocking down cpt1a (a key rate-limiting enzyme involved in FAO) in zebrafish induced a degenerative process in the optic nerve and RGC, which resembled the characteristics observed in glaucoma. In conclusion, our study provides evidence that genes encoding mitochondrial proteins involved in energy metabolisms, such as OXPHOS and FAO, are associated with glaucoma. These findings contribute to a better understanding of the molecular mechanisms underlying glaucoma pathogenesis and may offer potential targets for therapeutic interventions in the future.

Optimized Lipidomics Extraction of Sphingosine and Sphinganine from Optic Nerve for Signaling Studies

Interconvertible sphingolipid metabolites represent germane constituents of eukaryotic membranes and are vital in the regulation of cellular homeostasis, proliferation, survival, and induction of autophagy. This protocol describes a step-by-step method for extractions of sphingosine and sphinganine from mammalian tissue samples, particularly from the murine optic nerve. These lipids are partitioned into a binary mixture of chloroform and methanol in a modified Bligh and Dyer method. This is followed with reverse phase ultrahigh-performance liquid chromatography fractionation with a C18+ column and subsequent tandem mass spectrometry (UHPLC-MS-MS) analysis of the biological abundance. These free sphingoid bases dissociate to form structurally distinctive carbocation product ions that can be confirmed with annotations of lipidomic databases or in-house fragmentation software.

Ocular Treatments Targeting Separate Prostaglandin Receptors in Mice Exhibit Alterations in Intraocular Pressure and Optic Nerve Lipidome

Background: Prostaglandin (PG) receptor agonists are the first-line eyedrop medication treatment for glaucoma. The pathophysiology of this disease is not completely known, and elevated intraocular pressure (IOP) is the key risk factor. The membranes of the axons (of the retinal ganglion cells) passing through the optic nerve (ON) head experience significant damage. Lipids are an essential component of the cell's membranes, and their profile changes owing to neurodegeneration. In this investigation, three agonists for distinct PG receptors were used to lower IOP and to determine their effect on the ON lipids. We utilized DBA/2J mice as a model of progressive IOP increase and C57BL/6J mice as a model of ON crush. Methods: DBA/2J and C57BL/6J mice were treated daily for 2 weeks with Latanoprost, PF-04217329, or Rivenprost. The IOP was measured every 2 days and pattern electroretinogram was conducted for DBA/2J throughout the study. Lipidomics of ONs were performed for each model and treatment group. Results: Of the tested compounds, Latanoprost and Rivenprost were the most effective agents decreasing IOP in DBA/2J mice. Triglyceride levels increased in the ONs of DBA/2J mouse model, but phosphatidylethanolamine levels underwent highest level changes in the C57BL/6J mouse model when treated with Latanoprost. Conclusions: Topical ocular FP- and EP4-receptor agonists appreciably lowered IOP in the DBA/2J mice representing pigmentary glaucoma. The observed changes in ON lipidomics in the different models of neurodegeneration suggest possible use of such measures in the development of more effective medicines for both IOP reduction and ON protection.

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

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

Plasma metabolite profile for primary open-angle glaucoma in three US cohorts and the UK Biobank

Glaucoma is a progressive optic neuropathy and a leading cause of irreversible blindness worldwide. Primary open-angle glaucoma is the most common form, and yet the etiology of this multifactorial disease is poorly understood. We aimed to identify plasma metabolites associated with the risk of developing POAG in a case-control study (599 cases and 599 matched controls) nested within the Nurses' Health Studies, and Health Professionals' Follow-Up Study. Plasma metabolites were measured with LC-MS/MS at the Broad Institute (Cambridge, MA, USA); 369 metabolites from 18 metabolite classes passed quality control analyses. For comparison, in a cross-sectional study in the UK Biobank, 168 metabolites were measured in plasma samples from 2,238 prevalent glaucoma cases and 44,723 controls using NMR spectroscopy (Nightingale, Finland; version 2020). Here we show higher levels of diglycerides and triglycerides are adversely associated with glaucoma in all four cohorts, suggesting that they play an important role in glaucoma pathogenesis.

Is fat the future for saving sight? Bioactive lipids and their impact on glaucoma

Glaucoma is characterized by a continuous loss of retinal ganglion cells. The cause of glaucoma is associated with an increase in intraocular pressure (IOP), but the underlying pathophysiology is diverse and, in most cases, unknown. There is an indisputable unmet need to identify new pathways involved in glaucoma pathogenesis. Increasing evidence suggests that bioactive lipids may be critical in the development and progression of glaucoma. Preclinical and clinical bioactive lipid targets exist and are being developed. In this review, we aim to shed light on the potential of bioactive lipids for the prevention, diagnosis, prognosis, and treatment of glaucoma by asking the question "is fat the future for saving sight".

Region-resolved multi-omics of the mouse eye

The eye is a complex organ consisting of multiple compartments with unique and specialized properties, and small disturbances in one eye region can result in impaired vision and blindness. Although there have been advancements in ocular research, the hierarchical molecular network in region-wide resolution, indicating the division of labor and crosstalk among different eye regions, is not yet comprehensively illuminated. Here, we present an atlas of region-resolved proteome and lipidome of mouse eye. Multiphoton microscopy-guided laser microdissection combined with in-depth label-free proteomics identifies 13,536 proteins across various mouse eye regions. Further integrative analysis of spectral imaging, label-free proteome, and imaging mass spectrometry of the lipidome and phosphoproteome reveals distinctive molecular features, including proteins and lipids of various anatomical mouse eye regions. These deposited datasets and our open proteome server integrating all information provide a valuable resource for future functional and mechanistic studies of mouse eye and ocular disease.

Isobaric Incorporation of C13-Histidine for the Assessment of Remyelination

Multiple sclerosis is a demyelinating disease of the central nervous system characterized by the loss of the myelin sheath-the nonconductive membrane surrounding neuronal axons. Demyelination interrupts neuronal transmission, which can impair neurological pathways and present a variety of neurological deficits. Prolonged demyelination can damage neuronal axons resulting in irreversible neuronal damage. Efforts have been made to identify agents that can promote remyelination. However, the assessment of remyelination that new therapies promote can be challenging. The method described in this chapter addresses this challenge by using isobaric C13-histidine as a tag for monitoring its incorporation into myelin proteins and thus monitoring the remyelination process.

Compared to Fishmeal, Dietary Soybean Meal Improves the Reproductive Performance of Female Yellow Catfish (Pelteobagrus fulvidraco) Broodstock

To investigate the effects of different dietary protein sources on the reproductive performance of female broodstock, yellow catfish (Pelteobagrus fulvidraco) were fed with three experimental diets using fishmeal (FM), soybean meal (SBM), and rapeseed meal (RSM) as main protein sources, respectively. Females (initial weight: 64.56 ± 0.45 g) were distributed into 9 net cages for feeding trial. Results indicated that 30% dietary SBM improved the reproductive performance for higher gonadosomatic index (GSI), relative fecundity, total egg production, egg diameter, and hatching rate. In addition, SBM and RSM diets resulted in higher estradiol (E2), vitellogenin (VTG), luteinizing hormones (LH), and lower follicle-stimulating hormone (FSH) and testosterone (T) in plasma (P < 0.05) of female broodstock. Dietary SBM and RSM also resulted in lower mesenteric fat index (MFI), plasma total cholesterol (TC), plasma total bilirubin (T-Bil) contents, and gonadal cortisol concentrations, while dietary SBM downregulated the transcription levels of steroidogenesis-related proteins by negative feedback (P < 0.05). The results demonstrated that dietary SBM and RSM could promote sex steroid hormone and VTG biosynthesis and showed hypocholesterolemic effects. Besides, 30% dietary SBM inclusion could improve the reproductive performance of female yellow catfish broodstock.

Integrated multi-omics reveals the molecular mechanisms underlying efficient phosphorus use under phosphate deficiency in elephant grass (Pennisetum purpureum)

Phosphorus (P) is an essential macronutrient element for plant growth, and deficiency of inorganic phosphate (Pi) limits plant growth and yield. Elephant grass (Pennisetum purpureum) is an important fodder crop cultivated widely in tropical and subtropical areas throughout the world. However, the mechanisms underlying efficient P use in elephant grass under Pi deficiency remain poorly understood. In this study, the physiological and molecular responses of elephant grass leaves and roots to Pi deficiency were investigated. The results showed that dry weight, total P concentration, and P content decreased in Pi-deprived plants, but that acid phosphatase activity and P utilization efficiency (PUE) were higher than in Pi-sufficient plants. Regarding Pi starvation-responsive (PSR) genes, transcriptomics showed that 59 unigenes involved in Pi acquisition and transport (especially 18 purple acid phosphatase and 27 phosphate transporter 1 unigenes) and 51 phospholipase unigenes involved in phospholipids degradation or Pi-free lipids biosynthesis, as well as 47 core unigenes involved in the synthesis of phenylpropanoids and flavonoids, were significantly up-regulated by Pi deprivation in leaves or roots. Furthermore, 43 unigenes related to Pi-independent- or inorganic pyrophosphate (PPi)-dependent bypass reactions were markedly up-regulated in Pi-deficient leaves, especially five UDP-glucose pyrophosphorylase and 15 phosphoenolpyruvate carboxylase unigenes. Consistent with PSR unigene expression changes, metabolomics revealed that Pi deficiency significantly increased metabolites of Pi-free lipids, phenylpropanoids, and flavonoids in leaves and roots, but decreased phospholipid metabolites. This study reveals the mechanisms underlying the responses to Pi starvation in elephant grass leaves and roots, which provides candidate unigenes involved in efficient P use and theoretical references for the development of P-efficient elephant grass varieties.

Sphingomyelinases in retinas and optic nerve heads: Effects of ocular hypertension and ischemia

Sphingomyelinases (SMase), enzymes that catalyze the hydrolysis of sphingomyelin to ceramide, are important sensors for inflammatory cytokines and apoptotic signaling. Studies have provided evidence that increased SMase activity can contribute to retinal injury. In most tissues, two major SMases are responsible for stress-induced increases in ceramide: acid sphingomyelinase (ASMase) and Mg2+-dependent neutral sphingomyelinase (NSMase). The purposes of the current study were to determine the localization of SMases and their substrates in the retina and optic nerve head and to investigate the effects of ocular hypertension and ischemia on ASMase and NSMase activities. Tissue and cellular localization of ASMase and NSMase were determined by immunofluorescence imaging. Tissue localization of sphingomyelin in retinas was further determined by Matrix-Assisted Laser Desorption/Ionization mass spectrometry imaging. Tissue levels of sphingomyelins and ceramide were determined by liquid chromatography with tandem mass spectrometry. Sphingomyelinase activities under basal conditions and following acute ischemic and ocular hypotensive stress were measured using the Amplex Red Sphingomyelinase Assay Kit. Our data show that ASMase is in the optic nerve head and the retinal ganglion cell layer. NSMase is in the optic nerve head, photoreceptor and retinal ganglion cell layers. Both ASMase and NSMase were identified in human induced pluripotent stem cell-derived retinal ganglion cells and optic nerve head astrocytes. The retina and optic nerve head each exhibited unique distribution of sphingomyelins with the abundance of very long chain species being higher in the optic nerve head than in the retina. Basal activities for ASMase in retinas and optic nerve heads were 54.98 ± 2.5 and 95.6 ± 19.5 mU/mg protein, respectively. Ocular ischemia significantly increased ASMase activity to 86.2 ± 15.3 mU/mg protein in retinas (P = 0.03) but not in optic nerve heads (81.1 ± 15.3 mU/mg protein). Ocular hypertension significantly increased ASMase activity to 121.6 ± 7.3 mU/mg protein in retinas (P < 0.001) and 267.0 ± 66.3 mU/mg protein in optic nerve heads (P = 0.03). Basal activities for NSMase in retinas and optic nerve heads were 12.3 ± 2.1 and 37.9 ± 8.7 mU/mg protein, respectively. No significant change in NSMase activity was measured following ocular ischemia or hypertension. Our results provide evidence that both ASMase and NSMase are expressed in retinas and optic nerve heads; however, basal ASMase activity is significantly higher than NSMase activity in retinas and optic nerve heads. In addition, only ASMase activity was significantly increased in ocular ischemia or hypertension. These data support a role for ASMase-mediated sphingolipid metabolism in the development of retinal ischemic and hypertensive injuries.

Temporal Alterations of Sphingolipids in Optic Nerves Following Indirect Traumatic Optic Neuropathy

Purpose

To identify optic nerve (ON) lipid alterations associated with sonication-induced traumatic optic neuropathy (TON).

Design

Experimental study.

Subjects

A mouse model of indirect TON was generated using sound energy concentrated focally at the entrance of the optic canal using a laboratory sonifier with a microtip probe.

Methods

Analyses of datasets generated from high-performance liquid chromatography-electrospray tandem mass spectrometry of ONs dissected from the head of the ON to the optic chiasm at 1 day, 7 days, and 14 days postsonication compared with that in nonsonicated controls.

Main Outcome Measures

Lipid abundance alterations in postsonicated ONs were evaluated using 1-way analysis of variance (false discovery rate-adjusted significant P value < 0.01), lipid-related gene sets, biochemical properties, and receiver operating characteristic to identify lipids associated with optic neuropathy.

Results

There were 28 lipid species with significantly different abundances across the control and postsonication groups. The 2 most significantly upregulated lipids included a sphingomyelin (SM) species, SM(d40:7), and a hexosylceramide (CerG1) species, CerG1(d18:1/24:2). Hexosylceramide (d18:1/24:2) was noted to have a stepwise increasing trend from day 1 to day 14 after sonication-induced optic neuropathy. Investigation of biophysical properties showed notable enrichment of lipids with high and above-average transition temperatures at day 14 after sonication. Lipid-related gene set analysis revealed enrichment in sphingolipid and glycosphingolipid metabolic processes. The best classifier to differentiate day 14 postsonication from controls, based on area under the receiver operating characteristic curve, was CerG1(d18:1/24:2) (area under the receiver operating characteristic curve: 1).

Conclusions

Temporal alterations in sphingolipid metabolism and biochemical properties were observed in the ON of mice after sonication-induced optic neuropathy, with notable elevations in sphingomyelin and hexosylceramide species. Hexosylceramide (d18:1/24:2) may be associated with damage after indirect trauma, indicating that lipid membrane abnormalities may be a mediator of pathology due to trauma.

Lyso-Lipid-Induced Oligodendrocyte Maturation Underlies Restoration of Optic Nerve Function

Protein hyperdeimination and deficiency of lyso-phospholipids (LPC 18:1) has been associated with the pathology of demyelinating disease in both humans and mice. We uncovered interesting biology of LPC 18:1, in which LPC 18:1 induced optic nerve function restoration through oligodendrocyte maturation and remyelination in mouse model systems. Our in vitro studies show LPC 18:1 protection against neuron-ectopic hyperdeimination and stimulation of oligodendrocyte maturation, while in vivo investigations recorded optic nerve function improvement following optic nerve injections of LPC 18:1, in contrast with LPC 18:0. Thus, just a change in a single bond renders a dramatic alternation in biological function. The incorporation of isobaric C13-histidine in newly synthesized myelin proteins and quantitative proteome shifts are consistent with remyelination underlying restoration in optic nerve function. These results suggest that exogenous LPC 18:1 may provide a therapeutic avenue for stemming vision loss in demyelinating diseases.

Analysis of lipidomics profile of Carya cathayensis nuts and lipid dynamic changes during embryonic development

Hickory (Carya cathayensis) nuts contain higher amount of lipids, and possess high nutritional value and substantial health benefits. However, their lipid composition and dynamic changes during embryogenesis have not been thoroughly investigated. Therefore, lipidomics profile and lipid dynamic changes during embryonic development were analyzed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Totally, 544 kinds of lipids were identified in mature hickory nuts with higher proportions of glycerolipids (59.94%) and glycerophospholipids (38.66%). Notably, diacylglycerols showed gradual uptrends, which corresponded with total glycerolipid and glycerophospholipid at middle and late stage of embryogenesis, suggesting the pivotal role of diacylglycerols in the accumulation of glycerolipids and glycerophospholipids. Moreover, triacylglycerols, diacylglycerols, phosphatidylethanolamines and phosphatidylcholines had high relative content with abundance of unsaturated fatty acids, specifically oleic acid, linoleic acid and linolenic acid, localized mainly at sn-2 lipid position. Together, our study provides innovative perspectives for studying the nutritional benefits of hickory nut lipids.

Proteome Characterization of Glaucoma Aqueous Humor

Glaucoma is the leading cause of irreversible blindness worldwide. The proteome characterization of glaucoma is not clearly understood. A total of 175 subjects, including 57 primary acute angle-closure glaucoma (PAACG), 50 primary chronic angle-closure glaucoma (PCACG), 35 neovascular glaucoma (NVG), and 33 cataract patients, were enrolled and comparison proteomic analysis was provided. The samples were randomly divided into discovery group or validation group, whose aqueous humor proteome was analyzed by data-independent acquisition or by parallel reaction monitoring. The common proteome features of three types of glaucoma were immune response, lipid metabolism, and cell death. Three proteins, VTN, SERPIND1, and CD14, showed significant upregulation in glaucoma and could discriminate glaucoma from cataract. Mutual differential proteomic analysis of PAACG, PCACG, and NVG showed different proteome characterization of the three types of glaucoma. NVG was characterized with activated angiogenesis. PAACG was characterized with activation of inflammation response. SERPIND1 was discovered to play vital role in glaucoma occurrences, which is associated with eye transparency decrease and glucose metabolism. This study would provide insights in understanding proteome characterization of glaucoma and benefit the clinical application of AH proteome.

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Aqueous humor proteome of different glaucoma (PACG, NVG) was profiled.

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Potential protein biomarkers for glaucoma were proposed.

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Potential mechanism of glaucoma was described.

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SERPIND1 was discovered to have potential value for glaucoma diagnosis.

An overview of lipidomics utilizing cadaver derived biological samples

INTRODUCTION

We present lipidomic studies that have utilized cadaveric biological samples, including tissues and bodily fluids (excluding blood or serum). Analyses of lipids from cadaveric-derived tissues play vital roles in many different fields, such as in anthropogeny to understand food habits of ancient people, in forensics for postmortem analyses, and in biomedical research to study human diseases.

AREAS COVERED

The goal of the review is to demonstrate how cadavers can be utilized for study of lipidome to get biological insight in different fields. Several important considerations need to be made when analyzing lipids from cadaver samples. For example, what important postmortem changes occur due to environmental or other intrinsic factors that introduce deviations in the observed differences versus true differences? Do these factors affect distinct classes of lipids differently? How do we arrive at a reasonable level of certainty that the observed differences are truly biological rather than artifacts of sample collection, changes during transportation, or variations in analytical procedures? These are pressing questions that need to be addressed when performing lipidomics investigations utilizing postmortem tissues, which inherently presents hurdles and unknowns beginning with harvesting methods, transportation logistics, and at analytical techniques. In our review, we have purposefully omitted blood and serum studies since they pose greater challenges in this regard. Several studies have been carried out with cadaveric tissues and fluids that support the successful use of cases of these samples; however, many control studies are still necessary to provide insight into full potential of the cadaveric tissue and fluid resources. Most importantly, additional control studies will allow us to gain important insights into the opportunities lipidomics presents for biomedical studies of complex human disease and disorders. Another goal of the review is to generate awareness about limitations and pitfalls of use of cadaver materials for study of lipidome.

EXPERT OPINION

We comment on the current state of lipidomics studies that utilize cadaveric tissues, provide a few pertinent examples, and discuss perspectives on both future technological directions and the applications they will enable.

Multifactorial Pathogenic Processes of Retinal Ganglion Cell Degeneration in Glaucoma towards Multi-Target Strategies for Broader Treatment Effects

Glaucoma is a chronic neurodegenerative disease characterized by apoptosis of retinal ganglion cell (RGC) somas, degeneration of axons, and loss of synapses at dendrites and axon terminals. Glaucomatous neurodegeneration encompasses multiple triggers, multiple cell types, and multiple molecular pathways through the etiological paths with biomechanical, vascular, metabolic, oxidative, and inflammatory components. As much as intrinsic responses of RGCs themselves, divergent responses and intricate interactions of the surrounding glia also play decisive roles for the cell fate. Seen from a broad perspective, multitarget treatment strategies have a compelling pathophysiological basis to more efficiently manipulate multiple pathogenic processes at multiple injury sites in such a multifactorial neurodegenerative disease. Despite distinct molecular programs for somatic and axonal degeneration, mitochondrial dysfunction and glia-driven neuroinflammation present interdependent processes with widespread impacts in the glaucomatous retina and optic nerve. Since dysfunctional mitochondria stimulate inflammatory responses and proinflammatory mediators impair mitochondria, mitochondrial restoration may be immunomodulatory, while anti-inflammatory treatments protect mitochondria. Manipulation of these converging routes may thus allow a unified treatment strategy to protect RGC axons, somas, and synapses. This review presents an overview of recent research advancements with emphasis on potential treatment targets to achieve the best treatment efficacy to preserve visual function in glaucoma.

Ocular phenotypes in a mouse model of impaired glucocerebrosidase activity

Mutations in the GBA1 gene encoding glucocerebrosidase (GCase) are linked to Gaucher (GD) and Parkinson's Disease (PD). Since some GD and PD patients develop ocular phenotypes, we determined whether ocular phenotypes might result from impaired GCase activity and the corresponding accumulation of glucosylceramide (GluCer) and glucosylsphingosine (GluSph) in the Gba1^D409V/D409V knock-in (Gba KI/KI; "KI") mouse. Gba KI mice developed age-dependent pupil dilation deficits to an anti-muscarinic agent; histologically, the iris covered the anterior part of the lens with adhesions between the iris and the anterior surface of the lens (posterior synechia). This may prevent pupil dilation in general, beyond an un-responsiveness of the iris to anti-muscarinics. Gba KI mice displayed atrophy and pigment dispersion of the iris, and occlusion of the iridocorneal angle by pigment-laden cells, reminiscent of secondary open angle glaucoma. Gba KI mice showed progressive thinning of the retina consistent with retinal degeneration. GluSph levels were increased in the anterior and posterior segments of the eye, suggesting that accumulation of lipids in the eye may contribute to degeneration in this compartment. We conclude that the Gba KI model provides robust and reproducible eye phenotypes which may be used to test for efficacy and establish biomarkers for GBA1-related therapies.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

Alteration in Lysophospholipids and Converting Enzymes in Glaucomatous Optic Nerves

Purpose

To determine whether lysophospholipid (LPL) profiles and corresponding conversion enzymes in the LPL pathways are altered in the optic nerve (ON) between human control and glaucoma samples.

Methods

Lipids extracted from control (n = 11) and glaucomatous (n = 12) ON samples using the Bligh and Dyer method were subjected to high-resolution mass spectrometry on a Q-exactive mass spectrometer coupled with a high-performance liquid chromatography (Accela 600) system. Analysis was performed for LPLs (lysophosphatidylcholines, lysophosphatidylserines, lysophosphatidylethanolamines, lysophosphatidylinositols, and lysosphingomyelines) using LipidSearch v.4.1, MZmine v.2.0, and MetaboAnalyst v.4.0. LPL synthesis and degradation pathway maps, utilizing UniProt and BRENDA database entries as needed, were created using Kyoto Encyclopedia of Genes and Genomes (KEGG)-based tools. The mRNA expression level in normal and glaucomatous human ON were analyzed using Gene Expression Omnibus (GEO) entry GSE45570. Protein amounts were determined using PHAST gel and dot blot and were used for normalization of protein amounts across samples. Western blot, ELISA, and protein quantification were performed using established protocols.

Results

Principal component analysis of ON LPL profile placed control and glaucomatous ONs in two distinct separate groups. Mass spectrometric analysis of ON revealed decrease in lysophosphatidic acid, lysophosphatidylethanolamine, lysophosphatidylcholine, and significant increase in diacylglycerol in glaucomatous ON. Statistical analysis of LPL conversion enzymes revealed significant overexpression of phosphatidate phosphatase LPIN2, phospholipid phosphatase 3, phosphatidylcholine-sterol acyltransferase, and calcium-dependent phospholipase 2, and significant downregulation of glycerol-3-phosphate acyltransferase 4 at mRNA level in glaucomatous ON. Western blot and ELISA confirmed proteomic differences between normal and diseased ON.

Conclusions

Our analysis revealed alterations in specific LPL levels and corresponding select enzyme-level changes in glaucomatous ON.

UPLC-MS/MS-based Lipidomic Profiles Revealed Aberrant Lipids Associated with Invasiveness of Silent Corticotroph Adenoma

CONTEXT

The accumulation of aberrant lipids and abnormal lipid metabolism in silent corticotroph adenomas (SCAs) could contribute to changes in clinical phenotypes, especially sphenoid sinus invasion.

OBJECTIVE

To systematically investigate lipidomic and transcriptomic alterations associated with invasiveness and their potential molecular mechanisms in SCAs and to provide candidate biomarkers for predicting invasiveness and novel treatment options for invasive SCAs by targeting lipids.

METHODS

Fifty-four SCAs (34 invasive/20 noninvasive) were subjected to lipidomic analysis based on ultraperformance liquid chromatography mass spectrometry, and 42 clinically nonfunctioning pituitary adenomas (23 invasive/19 noninvasive) were subjected to transcriptomic analysis. Differential analysis was performed to determine differential lipids and genes between invasive and noninvasive tumors. A functionally connected network was constructed with the molecular pathways as cores. Multiple machine learning methods were applied to identify the most critical lipids, which were further used to construct a lipidomic signature to predict invasive SCAs by multivariate logistic regression, and its performance was evaluated by receiver operating characteristic analysis.

RESULTS

Twenty-eight differential lipids were identified, and a functionally connected network was constructed with 2 lipids, 17 genes, and 4 molecular pathways. Connectivity Map (CMap) analysis further revealed 32 potential drugs targeting 4 genes and related pathways. The 4 most critical lipids were identified as risk factors contributing to the invasive phenotype. A lipidomic signature was constructed and showed excellent performance in discriminating invasive and noninvasive SCAs.

CONCLUSIONS

The lipidomic signature could serve as a promising predictor for the invasive SCA phenotype and provide potential therapeutic targets for SCAs.

A broad perspective on the molecular regulation of retinal ganglion cell degeneration in glaucoma

Glaucoma is a complex neurodegenerative disease involving RGC axons, somas, and synapses at dendrites and axon terminals. Recent research advancements in the field have revealed a bigger picture of glaucomatous neurodegeneration that encompasses multiple stressors, multiple injury sites, multiple cell types, and multiple signaling pathways for asynchronous degeneration of RGCs during a chronic disease period. Optic nerve head is commonly viewed as the critical site of injury in glaucoma, where early injurious insults initiate distal and proximal signaling for axonal and somatic degeneration. Despite compartmentalized processes for degeneration of RGC axons and somas, there are intricate interactions between the two compartments and mechanistic overlaps between the molecular pathways that mediate degeneration in axonal and somatic compartments. This review summarizes the recent progress in the molecular understanding of RGC degeneration in glaucoma and highlights various etiological paths with biomechanical, metabolic, oxidative, and inflammatory components. Through this growing body of knowledge, the glaucoma community moves closer toward causative treatment of this blinding disease.

Myelin Basic Protein Phospholipid Complexation Likely Competes with Deimination in Experimental Autoimmune Encephalomyelitis Mouse Model

Multiple sclerosis has complex pathogenesis encompassing a variety of components (immunologic, genetic, and environmental). The autoimmunogenicity against the host's myelin basic protein is a major contributor. An increase in myelin basic protein deimination (a post-translational modification) and a change in phospholipid composition have been associated with multiple sclerosis. The interaction of myelin basic protein with phospholipids in the myelin membrane is an important contributor to the stability and maintenance of proper myelin sheath function. The study of this aspect of multiple sclerosis is an area that has yet to be fully explored and that the present study seeks to understand. Several biochemical methods, a capillary electrophoresis coupled system and mass spectrometry, were used in this study. These methods identified four specific phospholipids complexing with myelin basic protein. We show that lysophosphatidylcholine 18:1 provides a robust competitive effect against hyper-deimination. Our data suggest that lysophosphatidylcholine 18:1 has a different biochemical behavior when compared to other phospholipids and lysophosphatidylcholines 14:0, 16:0, and 18:0.

Elusive Roles of the Different Ceramidases in Human Health, Pathophysiology, and Tissue Regeneration

Ceramide and sphingosine are important interconvertible sphingolipid metabolites which govern various signaling pathways related to different aspects of cell survival and senescence. The conversion of ceramide into sphingosine is mediated by ceramidases. Altogether, five human ceramidases—named acid ceramidase, neutral ceramidase, alkaline ceramidase 1, alkaline ceramidase 2, and alkaline ceramidase 3—have been identified as having maximal activities in acidic, neutral, and alkaline environments, respectively. All five ceramidases have received increased attention for their implications in various diseases, including cancer, Alzheimer’s disease, and Farber disease. Furthermore, the potential anti-inflammatory and anti-apoptotic effects of ceramidases in host cells exposed to pathogenic bacteria and viruses have also been demonstrated. While ceramidases have been a subject of study in recent decades, our knowledge of their pathophysiology remains limited. Thus, this review provides a critical evaluation and interpretive analysis of existing literature on the role of acid, neutral, and alkaline ceramidases in relation to human health and various diseases, including cancer, neurodegenerative diseases, and infectious diseases. In addition, the essential impact of ceramidases on tissue regeneration, as well as their usefulness in enzyme replacement therapy, is also discussed.