Neuroprotective role of sphingolipid rheostat in excitotoxic retinal ganglion cell death

Sphingosine-1-phosphate in the regulation of diabetes mellitus: a scientometric study to an in-depth review

Diabetes is a significant global health issue, causing extensive morbidity and mortality, and represents a serious threat to human health. Recently, the bioactive lipid molecule Sphingosine-1-Phosphate has garnered considerable attention in the field of diabetes research. The aim of this study is to comprehensively understand the mechanisms by which Sphingosine-1-Phosphate regulates diabetes. Through comprehensive bibliometric analysis and an in-depth review of relevant studies, we investigated and summarized various mechanisms through which Sphingosine-1-Phosphate acts in prediabetes, type 1 diabetes, type 2 diabetes, and their complications (such as diabetic nephropathy, retinopathy, cardiovascular disease, neuropathy, etc.), including but not limited to regulating lipid metabolism, insulin sensitivity, and inflammatory responses. This scholarly work not only unveils new possibilities for using Sphingosine-1-Phosphate in diabetes treatment but also offers fresh insights and recommendations for future research directions to researchers.

Sphingosine-1-phosphate signaling regulates the ability of Müller glia to become neurogenic, proliferating progenitor-like cells

The purpose of these studies is to investigate how Sphingosine-1-phosphate (S1P) signaling regulates glial phenotype, dedifferentiation of Müller glia (MG), reprogramming into proliferating MG-derived progenitor cells (MGPCs), and neuronal differentiation of the progeny of MGPCs in the chick retina. We found that S1P-related genes are highly expressed by retinal neurons and glia, and levels of expression were dynamically regulated following retinal damage. Drug treatments that activate S1P receptor 1 (S1PR1) or increase levels of S1P suppressed the formation of MGPCs. Conversely, treatments that inhibit S1PR1 or decrease levels of S1P stimulated the formation of MGPCs. Inhibition of S1P receptors or S1P synthesis significantly enhanced the neuronal differentiation of the progeny of MGPCs. We report that S1P-related gene expression in MG is modulated by microglia and inhibition of S1P receptors or S1P synthesis partially rescues the loss of MGPC formation in damaged retinas missing microglia. Finally, we show that TGFβ/Smad3 signaling in the resting retina maintains S1PR1 expression in MG. We conclude that the S1P signaling is dynamically regulated in MG and MGPCs in the chick retina, and activation of S1P signaling depends, in part, on signals produced by reactive microglia.

Roles of Sphingosine Kinase and Sphingosine-1-Phosphate Receptor 2 in Endotoxin-Induced Acute Retinal Inflammation

PURPOSE

To investigate the roles of sphingosine kinases (SphKs) and sphingosine-1-phosphate receptors (S1PRs) in endotoxin-induced uveitis (EIU) mice.

METHODS

EIU model was induced using an intraperitoneal injection of lipopolysaccharide (LPS). The expression of SphKs and S1PRs in the retina was assessed using quantitative polymerase chain reaction (qPCR) and immunofluorescence. The effects of S1PR antagonists on the expression of inflammatory cytokines in the retina were evaluated using qPCR and western blotting. Effects of leukocyte infiltration of the retinal vessels were evaluated to determine the effects of the S1PR2 antagonist and genetic deletion of S1PR2 on retinal inflammation.

RESULTS

Retinal SphK1 expression was significantly upregulated in EIU. SphK1 was expressed in the GCL, IPL, and OPL and S1PR2 was expressed in the GCL, INL, and OPL. Positive cells in IPL and OPL of EIU retina were identified as endothelial cells. S1PR2 antagonist and genetic deletion of S1PR2 significantly suppressed the expression of IL-1α, IL-6, TNF-α, and ICAM-1, whereas S1PR1/3 antagonist did not. Use of S1PR2 antagonist and S1PR2 knockout in mice significantly ameliorated leukocyte adhesion induced by LPS.

CONCLUSION

SphK1/S1P/S1PR2 signaling was upregulated in EIU and S1PR2 inhibition suppressed inflammatory response. Targeting this signaling pathway has potential for treating retinal inflammatory diseases.

Lysophospholipid receptors in neurodegeneration and neuroprotection

The central nervous system (CNS) is one of the most complex physiological systems, and treatment of CNS disorders represents an area of major medical need. One critical aspect of the CNS is its lack of regeneration, such that damage is often permanent. The damage often leads to neurodegeneration, and so strategies for neuroprotection could lead to major medical advances. The G protein-coupled receptor (GPCR) family is one of the major receptor classes, and they have been successfully targeted clinically. One class of GPCRs is those activated by bioactive lysophospholipids as ligands, especially sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA). Research has been increasingly demonstrating the important roles that S1P and LPA, and their receptors, play in physiology and disease. In this review, I describe the role of S1P and LPA receptors in neurodegeneration and potential roles in neuroprotection. Much of our understanding of the role of S1P receptors has been through pharmacological tools. One such tool, fingolimod (also known as FTY720), which is a S1P receptor agonist but a functional antagonist in the immune system, is clinically efficacious in multiple sclerosis by producing a lymphopenia to reduce autoimmune attacks; however, there is evidence that fingolimod is also neuroprotective. Furthermore, fingolimod is neuroprotective in many other neuropathologies, including stroke, Parkinson's disease, Huntington's disease, Rett syndrome, Alzheimer's disease, and others that are discussed here. LPA receptors also appear to be involved, being upregulated in a variety of neuropathologies. Antagonists or mutations of LPA receptors, especially LPA1, are neuroprotective in a variety of conditions, including cortical development, traumatic brain injury, spinal cord injury, stroke and others discussed here. Finally, LPA receptors may interact with other receptors, including a functional interaction with plasticity related genes.

Accumulation of branched-chain amino acids deteriorates the neuroinflammatory response of Müller cells in diabetic retinopathy via leucine/Sestrin2-mediated sensing of mTOR signaling

AIMS

This study aimed to investigate branched-chain amino acid (BCAA) catabolism in diabetic retinopathy (DR).

METHODS

Wild-type and db/db mice were fed BCAAs (5 or 10 mg/kg/day) for 12 weeks, and hyperglycemia-exposed Müller cells were treated with BCAAs (2 or 5 mmol/L) for 24 and 48 h. BCAA levels were measured using MS/MS. Western blotting was performed to detect proteins. Flow cytometry, oxygen consumption rate, and Cell Counting Kit-8 assays were used to evaluate Müller cell viability. Each experiment was conducted at least thrice.

RESULTS

BCAAs and branched-chain α-keto acids (BCKAs) were increased in the retina and systemic tissues of diabetic mice, and these changes were further enhanced to approximately 2-fold by extra BCAAs compared to wild-type group. In vitro, BCAAs and BCKAs were induced in hyperglycemic Müller cells, and augmented by BCAA supplementation. The aberrant BCAA catabolism was accompanied by mTORC1 activation and subsequently induced TNF-ɑ, VEGFA, GS, and GFAP in retinas and Müller cells under diabetic conditions. The cell apoptosis rate increased by approximately 50%, and mitochondrial respiration was inhibited by hyperglycemia and BCAA in Müller cells. Additionally, mTORC1 signaling was activated by leucine in Müller cells. Knockdown of Sestrin2 or LeuRS significantly abolished the leucine-induced mTORC1 phosphorylation and protected Müller cell viability under diabetic conditions.

CONCLUSIONS

We found that BCAA catabolism is hindered in DR through mTORC1 activation. Leucine plays a key role in inducing mTORC1 by sensing Sestrin2 in Müller cells. Targeting Sestrin2 may ameliorate the toxic effects of BCAA accumulation on Müller cells in DR.

Neuroprotective effect of omidenepag on excitotoxic retinal ganglion cell death regulating COX-2-EP2-cAMP-PKA/Epac pathway via Neuron-Glia interaction

Glutamate excitotoxicity is involved in retinal ganglion cell (RGC) death in various retinal degenerative diseases, including ischemia-reperfusion injury and glaucoma. Excitotoxic RGC death is caused by both direct damage to RGCs and indirect damage through neuroinflammation of retinal glial cells. Omidenepag (OMD), a novel E prostanoid receptor 2 (EP2) agonist, is a recently approved intraocular pressure-lowering drug. The second messenger of EP2 is cyclic adenosine monophosphate (cAMP), which activates protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). In this study, we investigated the neuroprotective effects of OMD on excitotoxic RGC death by focusing on differences in cAMP downstream signaling from the perspective of glia-neuron interactions. We established a glutamate excitotoxicity model in vitro and NMDA intravitreal injection model in vivo. In vitro, rat primary RGCs were used in an RGC survival rate assay. MG5 cells (mouse microglial cell line) and A1 cells (astrocyte cell line) were used for immunocytochemistry and Western blotting to evaluate the expressions of COX-1/2, PKA, Epac1/2, pCREB, cleaved caspase-3, inflammatory cytokines, and neurotrophic factors. Mouse retinal specimens underwent hematoxylin and eosin staining, flat-mounted retina examination, and immunohistochemistry. OMD significantly suppressed excitotoxic RGC death, cleaved caspase-3 expression, and activated glia both in vitro and in vivo. Moreover, it inhibited Epac1 and inflammatory cytokine expression and promoted COX-2, pCREB, and neurotrophic factor expression. OMD may have neuroprotective effects through inhibition of the Epac pathway and promotion of the COX-2-EP2-cAMP-PKA pathway by modulating glia-neuron interaction.

Unveiling enigmatic essence of Sphingolipids: A promising avenue for glaucoma treatment

Treatment of glaucoma, the leading cause of irreversible blindness, remains challenging. The apoptotic loss of retinal ganglion cells (RGCs) in glaucoma is the pathological hallmark. Current treatments often remain suboptimal as they aim to halt RGC loss secondary to reduction of intraocular pressure. The pathophysiological targets for exploring direct neuroprotective approaches, therefore are highly relevant. Sphingolipids have emerged as significant target molecules as they are not only the structural components of various cell constituents, but they also serve as signaling molecules that regulate molecular pathways involved in cell survival and death. Investigations have shown that a critical balance among various sphingolipid species, particularly the ceramide and sphingosine-1-phosphate play a role in deciding the fate of the cell. In this review we briefly discuss the metabolic interconversion of sphingolipid species to get an insight into "sphingolipid rheostat", the dynamic balance among metabolites. Further we highlight the role of sphingolipids in the key pathophysiological mechanisms that lead to glaucomatous loss of RGCs. Lastly, we summarize the potential drug candidates that have been investigated for their neuroprotective effects in glaucoma via their effects on sphingolipid axis.

Alzheimer's disease manifests abnormal sphingolipid metabolism

Introduction

Alzheimer's disease (AD) is associated with disturbed metabolism, prompting investigations into specific metabolic pathways that may contribute to its pathogenesis and pathology. Sphingolipids have garnered attention due to their known physiological impact on various diseases.

Methods

We conducted comprehensive profiling of sphingolipids to understand their possible role in AD. Sphingolipid levels were measured in AD brains, Cerad score B brains, and controls, as well as in induced pluripotent stem (iPS) cells (AD, PS, and control), using liquid chromatography mass spectrometry.

Results

AD brains exhibited higher levels of sphingosine (Sph), total ceramide 1-phosphate (Cer1P), and total ceramide (Cer) compared to control and Cerad-B brains. Deoxy-ceramide (Deoxy-Cer) was elevated in Cerad-B and AD brains compared to controls, with increased sphingomyelin (SM) levels exclusively in Cerad-B brains. Analysis of cell lysates revealed elevated dihydroceramide (dhSph), total Cer1P, and total SM in AD and PS cells versus controls. Multivariate analysis highlighted the relevance of Sph, Cer, Cer1P, and SM in AD pathology. Machine learning identified Sph, Cer, and Cer1P as key contributors to AD.

Discussion

Our findings suggest the potential importance of Sph, Cer1P, Cer, and SM in the context of AD pathology. This underscores the significance of sphingolipid metabolism in understanding and potentially targeting mechanisms underlying AD.

Relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder

BACKGROUND

Alcohol use disorder is a chronic recurrent encephalopathy, and its pathogenesis has not been fully understood. Among possible explanations, neuroinflammation caused by the disorders of brain central immune signaling has been identified as one possible mechanism of alcohol use disorder. As the basic components of cells and important bioactive molecules, sphingolipids are essential in regulating many cellular activities. Recent studies have shown that sphingolipids-mediated neuroinflammation may be involved in the development of alcohol use disorder.

METHODS

PubMed databases were searched for literature on sphingolipids and alcohol use disorder (alcohol abuse, alcohol addiction, alcohol dependence, and alcohol misuse) including evidence of the relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder (formation, withdrawal, treatment).

RESULTS

Disorders of sphingolipid metabolism, including the different types of sphingolipids and regulatory enzyme activity, have been found in patients with alcohol use disorder as well as animal models, which in turn cause neuro-inflammation in the central nervous system. Thus, these disorders may also be an important mechanism in the development of alcohol use disorder in patients. In addition, different sphingolipids may have different or even reverse effects on alcohol use disorder.

CONCLUSIONS

The sphingolipids-mediated neuroinflammation plays an important role in the development of alcohol use disorder. This review proposes a potential approach to prevent and treat alcohol use disorders by manipulating sphingolipid metabolism.

Synergic effects of EP2 and FP receptors co-activation on Blood-Retinal Barrier and Microglia

Macular edema (ME) is caused with disruption of the blood-retinal barrier (BRB) followed by fluid accumulation in the subretinal space. Main components of the outer and inner BRB are retinal pigment epithelial (RPE) cells and retinal microvascular endothelial cells, respectively. In addition, glial cells also participate in the functional regulation of the BRB as the member of 'neurovascular unit'. Under various stresses, cells in neurovascular units secrete inflammatory cytokines. Neuroinflammation induced by these cytokines can cause BRB dysfunction by degrading barrier-related proteins and contribute to the pathophysiology of ME. Prostaglandins (PGs) are crucial lipid mediators involved in neuroinflammation. Among PGs, a novel EP2 agonist, omidenepag (OMD) acts on not only the uveoscleral pathway but also the conventional pathway, unlike F prostanoid (FP) receptor agonists. Moreover, the combination use of the EP and the FP agonist is not recommended because of the risk of inflammation. In this study, we investigated effects of OMD and latanoprost acid (LTA), a FP agonist, on BRB and microglia in vitro and in vivo. To investigate the function of outer/inner BRB and microglia, in vitro, ARPE-19 cells, human retinal microvascular endothelial cells (HRMECs), and MG5 cells were used. Cell viability, inflammatory cytokines mRNA and protein levels, barrier morphology/function, and microglial activation were evaluated using proliferation assays, qRT-PCR, ELISA, immunocytochemistry, trans-epithelial electrical resistance, and permeability assay. Moreover, after vitreous injection into the mouse, outer BRB morphology, glial activation, and cytokine expression were assessed. Each OMD and LTA alone did not affect the viability or cytokines expression of the three types of cells. In ARPE-19 cells, the co-stimulation of OMD and LTA increased the mRNA and protein levels of inflammatory cytokines (IL-6, TNF-α, and VEGF-A) and decreased the barrier function and the junction-related protein (ZO-1 and β-catenin). By contrast in HRMECs, the co-stimulation affected significant differences in the mRNA levels of some cytokine (IL-6 and TNF-α) but enhanced the barrier function. In MG5 cells, the cytokines mRNA and size of Iba1-expressed cell were increased. A non-steroidal anti-inflammatory inhibited the barrier dysfunction and the junction-related protein downregulation in ARPE-19 cells and activation of MG5 cells. Also in vivo, the co-stimulation induced outer BRB disruption, cytokine increase, and retinal glial activation. Therefore, the co-stimulation of EP2 and FP induced the inflammatory cytokine-mediated outer BRB disruption, the enhanced inner BRB function, and the microglial activation. The BRB imbalance and the intrinsic prostaglandin production may be involved in OMD-related inflammation.

Study on the action mechanism of Buyang Huanwu Decoction against ischemic stroke based on S1P/S1PR1/PI3K/Akt signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ischemic stroke is a common and frequent clinical disease. Recent studies have demonstrated that sphingolipid plays an important role in the pathological process of ischemic stroke. PI3K-Akt is a classic protective signaling pathway of cerebral ischemic injury. After acting on the S1P receptor, S1P can activate the downstream PI3K/Akt signaling pathway and play an anti-cerebral ischemia role. Buyang Huanwu Decoction (BHD) is a traditional Chinese medicine formula used to treat ischemic stroke. However, the mechanisms of BHD on ischemic stroke remain unclear based on S1P/S1PR1/PI3K/Akt signaling pathway.

AIM OF THE STUDY

The present study is intended to investigate the action mechanism of BHD on ischemic stroke based on the S1P/S1PR1/PI3K/Akt signaling pathway from multiple perspectives.

MATERIALS AND METHODS

The BHD lyophilized product was prepared by vacuum freeze-drying method, of which the chemical composition was determined by UPLC-Q-TOF/MS. The mouse permanent middle cerebral artery occlusion (pMCAO) model was established by the suture-occluded method. Male KM mice were randomly divided into seven groups: sham group, model group, FTY720 (positive control) group, BHD group, BHD + W146 (selective S1PR1 inhibitor) group, SEW2871 (selective S1PR1 agonist) group, and Calycosin group. Each group was administered continuously for 14 days and evaluated with modified neurological severity score (mNSS) and cerebral infarct volume on the 1st, 4th, 7th, and 14th days. The SphK1, SphK2, S1PR1, PI3K, Akt, and p-Akt protein in the prefrontal lobe, hippocampus, and striatum was quantified by Western blot and immunohistochemical (IHC) experiment respectively. The qRT-PCR method was employed to evaluate SphK1, SphK2, and S1PR1 mRNA expression in the above tissue.

RESULTS

BHD and Calycosin both effectively improved mNSS scores with smaller infarct volumes. The SphK1 level in the prefrontal lobe, hippocampus, and striatum of mice in the BHD group was significantly lower, and SphK2, PI3K, and p-Akt in the hippocampus and striatum were significantly higher than those in the model group. BHD significantly decreased SphK1 mRNA expression in the prefrontal lobe, hippocampus, and striatum, and significantly up-regulated SphK2 mRNA and S1PR1 mRNA expression. Additionally, SphK1 protein expression levels of the prefrontal lobe, hippocampus, and striatum in the BHD group was significantly lower than model group, and SphK2, S1PR1, PI3K, Akt, and p-Akt protein expressions levels were increased obviously. Furthermore, SEW2871 can increase S1PR1 and Akt expression, and up-regulate SphK2 and S1PR1 mRNA expression. The effect of BHD on the expression of S1P/S1PR1/PI3K/Akt signaling pathway-related proteins and mRNA were weakened by BHD + W146.

CONCLUSION

BHD and Calycosin significantly improved the symptoms of neurological deficits in pMCAO mice, reduced the cerebral infarction volume, up-regulated SphK2 and S1PR1 mRNA levels, enhanced SphK2, S1PR1, PI3K, Akt, p-Akt protein expression of the prefrontal lobe, hippocampus and striatum, and down-regulated SphK1 mRNA and protein expression, which may be helpful to clarify the mechanism of BHD through S1P/S1PR1/PI3K/Akt signaling pathway to protect against cerebral ischemic injury.

Rapamycin suppresses neuroinflammation and protects retinal ganglion cell loss after optic nerve crush

Pyroptosis, an inflammasome-mediated mode of death, plays an important role in glaucoma. It has been shown that regulating the mTOR pathway can inhibit pyroptosis. Unfortunately, whether rapamycin (RAPA), a specific inhibitor of the mTOR pathway, can inhibit optic nerve crush (ONC)-induced pyroptosis to protect retinal ganglion cells (RGCs) has not been investigated. Our research aimed to confirm the effect of intravitreal injection of RAPA on RGCs. Furthermore, we used the ONC model to explore the underlying mechanisms. First, we observed that intravitreal injection of RAPA alleviated RGC damage induced by various types of injury. We then used the ONC model to further explore the potential mechanism of RAPA. Mechanistically, RAPA not only reduced the activation of glial cells in the retina but also inhibited retinal pyroptosis-induced expression of inflammatory factors such as nucleotide-binding oligomeric domain-like receptor 3 (NLRP3), apoptosis-associated speckle-like protein containing a CARD (ASC), N-terminal of gasdermin-D (GSDMD-N), IL-18 and IL-1β. Moreover, RAPA exerted protective effects on RGC axons, possibly by inhibiting glial activation and regulating the mTOR/ROCK pathway. Therefore, this study demonstrates a novel mechanism by which RAPA protects against glaucoma and provides further evidence for its application in preclinical studies.

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".

Comprehensive transcriptional and metabolomic analysis reveals the neuroprotective mechanism of dietary gamma-aminobutyric acid response to hypoxic stress in the Chinese mitten crab (Eriocheir sinensis)

Hypoxia is one of the serious stress challenges that aquatic animals face throughout their life. Our previous study found that hypoxia stress could induce neural excitotoxicity and neuronal apoptosis in Eriocheir sinensis, and observed that gamma-aminobutyric acid (GABA) has a positive neuroprotective effect on juvenile crabs under hypoxia. To reveal the neuroprotective pathway and metabolic regulatory mechanism of GABA in E. sinensis exposed to hypoxia stress, an 8-week feeding trial and acute hypoxia challenge were performed. Subsequently, we performed a comprehensive transcriptomic and metabolomic analysis of the thoracic ganglia of juvenile crabs. Differential genes and differential metabolites were co-annotated to 11 KEGG pathways, and further significant analysis showed that only the sphingolipid signaling pathway and the arachidonic acid metabolism pathway were significantly enriched. In the sphingolipid signaling pathway, GABA treatment significantly increased long-chain ceramide content in thoracic ganglia, which exerted neuroprotective effects by activating downstream signals to inhibit hypoxia-induced apoptosis. Moreover, in the arachidonic acid metabolism pathway, GABA could increase the content of neuroprotective active substances and reduce the content of harmful metabolites by regulating the metabolism of arachidonic acid for inflammatory regulation and neuroprotection. Furthermore, the decrease of glucose and lactate levels in the hemolymph suggests the positive role of GABA in metabolic regulation. This study reveals the neuroprotective pathways and possible mechanisms of GABA in juvenile E. sinensis exposed to hypoxia stress and inspires the discovery of new targets for improving hypoxia tolerance in aquatic animals.

S1PR1 signaling attenuates apoptosis of retinal ganglion cells via modulation of cJun/Bim cascade and Bad phosphorylation in a mouse model of glaucoma

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and apoptotic retinal ganglion cell (RGC) death, and is the leading cause of irreversible blindness worldwide. Among the sphingosine 1-phosphate receptors (S1PRs) family, S1PR1 is a highly expressed subtype in the central nervous system and has gained rapid attention as an important mediator of pathophysiological processes in the brain and the retina. Our recent study showed that mice treated orally with siponimod drug exerted neuroprotection via modulation of neuronal S1PR1 in experimental glaucoma. This study identified the molecular signaling pathway modulated by S1PR1 activation with siponimod treatment in RGCs in glaucomatous injury. We investigated the critical neuroprotective signaling pathway in vivo using mice deleted for S1PR1 in RGCs. Our results showed marked upregulation of the apoptotic pathway was associated with decreased Akt and Erk1/2 activation levels in the retina in glaucoma conditions. Activation of S1PR1 with siponimod treatment significantly increased neuroprotective Akt and Erk1/2 activation and attenuated the apoptotic signaling via suppression of c-Jun/Bim cascade and by increasing Bad phosphorylation. Conversely, deletion of S1PR1 in RGCs significantly increased the apoptotic cells in the ganglion cell layer in glaucoma and diminished the neuroprotective effects of siponimod treatment on Akt/Erk1/2 activation, c-Jun/Bim cascade, and Bad phosphorylation. Our data demonstrated that activation of S1PR1 in RGCs induces crucial neuroprotective signaling that suppresses the proapoptotic c-Jun/Bim cascade and increases antiapoptotic Bad phosphorylation. Our findings suggest that S1PR1 is a potential therapeutic target for neuroprotection of RGCs in glaucoma.

Peptains block retinal ganglion cell death in animal models of ocular hypertension: implications for neuroprotection in glaucoma

Ocular hypertension is a significant risk factor for vision loss in glaucoma due to the death of retinal ganglion cells (RGCs). This study investigated the effects of the antiapoptotic peptides peptain-1 and peptain-3a on RGC death in vitro in rat primary RGCs and in mouse models of ocular hypertension. Apoptosis was induced in primary rat RGCs by trophic factor deprivation for 48 h in the presence or absence of peptains. The effects of intravitreally injected peptains on RGC death were investigated in mice subjected to retinal ischemic/reperfusion (I/R) injury and elevated intraocular pressure (IOP). I/R injury was induced in mice by elevating the IOP to 120 mm Hg for 1 h, followed by rapid reperfusion. Ocular hypertension was induced in mice by injecting microbeads (MB) or silicone oil (SO) into the anterior chamber of the eye. Retinal flatmounts were immunostained with RGC and activated glial markers. Effects on anterograde axonal transport were determined by intravitreal injection of cholera toxin-B. Peptain-1 and peptain-3a inhibited neurotrophic factor deprivation-mediated RGC apoptosis by 29% and 35%, respectively. I/R injury caused 52% RGC loss, but peptain-1 and peptain-3a restricted RGC loss to 13% and 16%, respectively. MB and SO injections resulted in 31% and 36% loss in RGCs following 6 weeks and 4 weeks of IOP elevation, respectively. Peptain-1 and peptain-3a inhibited RGC death; the loss was only 4% and 12% in MB-injected eyes and 16% and 15% in SO-injected eyes, respectively. Anterograde transport was defective in eyes with ocular hypertension, but this defect was substantially ameliorated in peptain-injected eyes. Peptains suppressed ocular hypertension-mediated retinal glial activation. In summary, our results showed that peptains block RGC somal and axonal damage and neuroinflammation in animal models of glaucoma. We propose that peptains have the potential to be developed as therapeutics against neurodegeneration in glaucoma.

Aqueous Humor Apolipoprotein Concentration and Severity of Diabetic Retinopathy in Type 2 Diabetes

An imbalance of plasma apolipoproteins has been linked to diabetic retinopathy (DR); however, there is scarce information regarding their presence in the aqueous humor (AH) and their role in DR. Here, we aimed at analysing the relationship between apolipoprotein concentrations in human AH and the severity of DR. Concentrations of apolipoproteins were measured retrospectively in patients with type 2 diabetes mellitus (T2DM) without DR (n = 23), with mild to moderate nonproliferative DR (NPDR) (n = 13), and advanced NPDR/proliferative DR (PDR) (n = 14) using a multiplex immunoassay. Compared to the non-apparent DR group, the concentrations of seven apolipoproteins were elevated in advanced NPDR/PDR (Apo AI 5.8-fold, Apo AII 4.5-fold, Apo CI 3.3-fold, Apo CIII 6.8-fold, Apo D 3.3-fold, Apo E 2.4-fold, and Apo H 6.6-fold). No significant differences were observed in apolipoprotein concentrations between patients with non-apparent DR and healthy controls (n = 17). In conclusion, the AH concentrations of apolipoproteins AI, AII, CI, CIII, D, E, and H increased in advancing stages of DR, suggesting their role in the pathogenesis of DR, which deserves further examination.

Diabetic retinopathy: Involved cells, biomarkers, and treatments

Diabetic retinopathy (DR), a leading cause of vision loss and blindness worldwide, is caused by retinal neurovascular unit dysfunction, and its cellular pathology involves at least nine kinds of retinal cells, including photoreceptors, horizontal and bipolar cells, amacrine cells, retinal ganglion cells, glial cells (Müller cells, astrocytes, and microglia), endothelial cells, pericytes, and retinal pigment epithelial cells. Its mechanism is complicated and involves loss of cells, inflammatory factor production, neovascularization, and BRB impairment. However, the mechanism has not been completely elucidated. Drug treatment for DR has been gradually advancing recently. Research on potential drug targets relies upon clear information on pathogenesis and effective biomarkers. Therefore, we reviewed the recent literature on the cellular pathology and the diagnostic and prognostic biomarkers of DR in terms of blood, protein, and clinical and preclinical drug therapy (including synthesized molecules and natural molecules). This review may provide a theoretical basis for further DR research.

Targeted Metabolomics Shows That the Level of Glutamine, Kynurenine, Acyl-Carnitines and Lysophosphatidylcholines Is Significantly Increased in the Aqueous Humor of Glaucoma Patients

The composition of the aqueous humor of patients with glaucoma is relevant to understand the underlying causes of the pathology. Information on the concentration of metabolites and small molecules in the aqueous humor of healthy subjects is limited. Among the causes of the limitations is the lack of healthy controls since, until recently, they were not surgically intervened; therefore, the aqueous humor of patients operated for cataract was used as a reference. Sixteen aqueous humor samples from healthy subjects undergoing refractive surgery and eight samples from glaucoma patients were used to assess the concentration of 188 compounds using chromatography and mass spectrometry. The concentration of 80 of the 188 was found to be reliable, allowing comparison of data from the two groups (glaucoma and control). The pattern found in the controls is similar to, but not the same as, that reported using samples from “controls” undergoing cataract surgery. Comparing data from glaucoma patients and healthy subjects, 57 of the 80 compounds were significantly (p < 0.05) altered in the aqueous humor. Kynurenine and glutamine, but not glutamate, were significantly increased in the glaucoma samples. Furthermore, 10 compounds were selected considering a statistical score of p < 0.0001 and the degree of change of more than double or less than half. The level of C10 (decanoyl)-carnitine decreased, while the concentration of spermidine and various acyl-carnitines and lysophosphatidylcholines increased in glaucoma. Principal component analysis showed complete segregation of controls and cases using the data for the 10 selected compounds. The receiver operating characteristic curve these 10 compounds and for glutamine allowed finding cut-off values and significant sensitivity and specificity scores. The concentration of small metabolites in the aqueous humor of glaucoma patients is altered even when they take medication and are well controlled. The imbalance affects membrane components, especially those of the mitochondria, suggesting that mitochondrial abnormalities are a cause or consequence of glaucoma. The increase in glutamine in glaucoma is also relevant because it could be a means of keeping the concentration of glutamate under control, thus avoiding its potential to induce the death of neurons and retinal cells. Equally notable was the increase in kynurenine, which is essential in the metabolism of nicotine adenine dinucleotides.