FABP3 protein promotes α-synuclein oligomerization associated with 1-methyl-1,2,3,6-tetrahydropiridine-induced neurotoxicity

[Elucidation of the pathology of mental disorders focusing on polyunsaturated fatty acids and FABPs]

Polyunsaturated fatty acids (PUFAs) are essential for brain development and function, and an imbalance of brain PUFAs is linked to mental disorders like autism and schizophrenia. However, the cellular and molecular mechanisms underlying the effects of PUFAs on the brain remain largely unknown. Since they are insoluble in water, specific transporters like fatty acid binding proteins (FABPs), are required for transport and function of PUFAs within cells. We focused on the relationship between FABP-mediated homeostasis of brain PUFAs and neural plasticity. We found that FABP3, with a high affinity for n-6 PUFAs, is predominantly expressed in the GABAergic inhibitory interneurons of the anterior cingulate cortex (ACC) in the adult mouse brain. FABP3 knockout (KO) mice show increased GABA synthesis and inhibitory synaptic transmission in the ACC. We also found that FABP7 controls lipid raft function in astrocytes, and astrocytes lacking FABP7 exhibit changes in response to external stimuli. Furthermore, in FABP7 KO mice, dendritic protrusion formation in pyramidal neurons becomes abnormal, and we have reported a decrease in spine density and excitatory synaptic transmission. Here, we introduced recent advances in the understanding of the functions of PUFAs and FABPs in the brain, focusing especially on FABP3 and FABP7, in relation to human mental disorders.

Pharmacological inhibition of FABP7 by MF 6 counteracts cerebellum dysfunction in an experimental multiple system atrophy mouse model

Multiple system atrophy (MSA) is a rare, fatal neurodegenerative disease characterized by the accumulation of misfolded α-synuclein (αSyn) in glial cells, leading to the formation of glial cytoplasmic inclusions (GCI). We previous found that glial fatty acid-binding protein 7 (FABP7) played a crucial role in alpha-synuclein (αSyn) aggregation and toxicity in oligodendrocytes, inhibition of FABP7 by a specific inhibitor MF 6 reduced αSyn aggregation and enhanced cell viability in cultured cell lines and mouse oligodendrocyte progenitor cells. In this study we investigated whether MF 6 ameliorated αSyn-associated pathological processes in PLP-hαSyn transgenic mice (PLP-αSyn mice), a wildly used MSA mouse model with overexpressing αSyn in oligodendroglia under the proteolipid protein (PLP) promoter. PLP-αSyn mice were orally administered MF6 (0.1, 1 mg ·kg-1 ·d-1) for 32 days starting from the age of 6 months. We showed that oral administration of MF 6 significantly improved motor function assessed in a pole test, and reduced αSyn aggregation levels in both cerebellum and basal ganglia of PLP-αSyn mice. Moreover, MF 6 administration decreased oxidative stress and inflammation levels, and improved myelin levels and Purkinje neuron morphology in the cerebellum. By using mouse brain tissue slices and αSyn aggregates-treated KG-1C cells, we demonstrated that MF 6 reduced αSyn propagation to Purkinje neurons and oligodendrocytes through regulating endocytosis. Overall, these results suggest that MF 6 improves cerebellar functions in MSA by inhibiting αSyn aggregation and propagation. We conclude that MF 6 is a promising compound that warrants further development for the treatment of MSA.

On the Dynamic Mechanism of Long-Flexible Fatty Acid Binding to Fatty Acid Binding Protein: Resolving the Long-Standing Debate

Fatty acids (FAs) are one of the essential energy sources for physiological processes, and they play a vital role in regulating immune and inflammatory responses, promoting cell differentiation and apoptosis, and inhibiting tumor growth. These functions are carried out by FA binding proteins (FABPs) that recognize and transport FAs. Although the crystal structure of the FA-FABPs complex has long been characterized, the mechanism behind FA binding and dissociation from FABP remains unclear. This study employed conventional MD simulations and enhanced sampling technologies to investigate the atomic-scale complexes of heart fatty acid binding proteins and stearic acid (SA). The results revealed two primary pathways for the binding or dissociation of the flexible long-chain ligand, with the orientation of the SA carboxyl head during dissociation determining the chosen path. Conformational changes in the portal region of FABP during the ligand binding/unbinding were found to be trivial, and the overturn of the ″cap″ or the unfolding of the α2 helix was not required. This study resolves the long-standing debate on the binding mechanism of SA with the long-flexible tail to FABP, which significantly improves the understanding of the transport mechanism of FABPs and the development of related therapeutic agents.

The Multifunctional Family of Mammalian Fatty Acid-Binding Proteins

Fatty acid-binding proteins (FABPs) are small lipid-binding proteins abundantly expressed in tissues that are highly active in fatty acid (FA) metabolism. Ten mammalian FABPs have been identified, with tissue-specific expression patterns and highly conserved tertiary structures. FABPs were initially studied as intracellular FA transport proteins. Further investigation has demonstrated their participation in lipid metabolism, both directly and via regulation of gene expression, and in signaling within their cells of expression. There is also evidence that they may be secreted and have functional impact via the circulation. It has also been shown that the FABP ligand binding repertoire extends beyond long-chain FAs and that their functional properties also involve participation in systemic metabolism. This article reviews the present understanding of FABP functions and their apparent roles in disease, particularly metabolic and inflammation-related disorders and cancers.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

Are EPB41 and alpha-synuclein diagnostic biomarkers of sport-related concussion? Findings from the NCAA and Department of Defense CARE Consortium

BACKGROUND

Current protein biomarkers are only moderately predictive at identifying individuals with mild traumatic brain injury or concussion. Therefore, more accurate diagnostic markers are needed for sport-related concussion.

METHODS

This was a multicenter, prospective, case-control study of athletes who provided blood samples and were diagnosed with a concussion or were a matched non-concussed control within the National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research, and Education Consortium conducted between 2015 and 2019. The blood was collected within 48 h of injury to identify protein abnormalities at the acute and subacute timepoints. Athletes with concussion were divided into 6 h post-injury (0-6 h post-injury) and after 6 h post-injury (7-48 h post-injury) groups. We applied a highly multiplexed proteomic technique that used a DNA aptamers assay to target 1305 proteins in plasma samples from athletes with and without sport-related concussion.

RESULTS

A total of 140 athletes with concussion (79.3% males; aged 18.71 ± 1.10 years, mean ± SD) and 21 non-concussed athletes (76.2% males; 19.14 ± 1.10 years) were included in this study. We identified 338 plasma proteins that significantly differed in abundance (319 upregulated and 19 downregulated) in concussed athletes compared to non-concussed athletes. The top 20 most differentially abundant proteins discriminated concussed athletes from non-concussed athletes with an area under the curve (AUC) of 0.954 (95% confidence interval: 0.922‒0.986). Specifically, after 6 h of injury, the individual AUC of plasma erythrocyte membrane protein band 4.1 (EPB41) and alpha-synuclein (SNCA) were 0.956 and 0.875, respectively. The combination of EPB41 and SNCA provided the best AUC (1.000), which suggests this combination of candidate plasma biomarkers is the best for diagnosing concussion in athletes after 6 h of injury.

CONCLUSION

Our data suggest that proteomic profiling may provide novel diagnostic protein markers and that a combination of EPB41 and SNCA is the most predictive biomarker of concussion after 6 h of injury.

α-Synuclein decoy peptide protects mice against α-synuclein-induced memory loss

AIMS

We previously found that a decoy peptide derived from the C-terminal sequence of α-Synuclein (αSyn) prevents cytotoxic αSyn aggregation caused by fatty acid-binding protein 3 (FABP3) in vitro. In this study, we continued to utilize αSyn-derived peptides to further validate their effects on αSyn neurotoxicity and behavioral impairments in αSyn preformed fibrils (PFFs)-injected mouse model of Parkinson's disease (PD).

METHODS

Mice were injected with αSyn PFFs in the bilateral olfactory bulb (OB) and then were subjected to behavioral analysis at 2-week intervals post-injection. Peptides nasal administration was initiated one week after injection. Changes in phosphorylation of αSyn and neuronal damage in the OB were measured using immunostaining at week 4. The effect of peptides on the interaction between αSyn and FABP3 was examined using co-immunoprecipitation.

RESULTS

αSyn PFF-injected mice showed significant memory loss but no motor function impairment. Long-term nasal treatment with peptides effectively prevented memory impairment. In peptide-treated αSyn PFF-injected mice, the peptides entered the OB smoothly through the nasal cavity and were mainly concentrated in neurons in the mitral cell layer, significantly suppressing the excessive phosphorylation of αSyn and reducing the formation of αSyn-FABP3 oligomers, thereby preventing neuronal death. The addition of peptides also blocked the interaction of αSyn and FABP3 at the recombinant protein level, and its effect was strongest at molar concentrations comparable to those of αSyn and FABP3.

CONCLUSIONS

Our findings suggest that the αSyn decoy peptide represents a novel therapeutic approach for reducing the accumulation of toxic αSyn-FABP3 oligomers in the brain, thereby preventing the progression of synucleinopathies.

Fatty acid-binding proteins 3 and 5 are involved in the initiation of mitochondrial damage in ischemic neurons

We have previously shown that a fatty acid-binding protein7 (FABP7) inhibitor ameliorates cerebral ischemia-reperfusion injury in mice, suggesting an association between FABPs and ischemic neuronal injury. However, the precise role of FABPs in ischemic neuronal injury remains unclear. In this study, we investigated the role of FABPs in ischemia-reperfusion neuronal injury. FABP3, FABP5, and FABP7 were upregulated in the ischemic penumbra regions in mice. However, only FABP3 and FABP5 were expressed in injured neurons. Furthermore, FABP3 and FABP5 accumulated in the mitochondria of ischemic neurons. Overexpressing either FABP3 or FABP5 aggravated the reduced mitochondrial membrane potential and induced cell death in human neuroblastoma SH-SY5Y cells during oxidative stress. This damage was mediated by the formation of BAX-containing pores in the mitochondrial membrane. Moreover, FABP5 mediates lipid peroxidation and generates toxic by-products (i.e., 4-HNE) in SH-SY5Y cells. HY11-08 (HY08), a novel FABP3 and 5 inhibitor that does not act on FABP7, significantly reduced cerebral infarct volume and blocked FABP3/5-induced mitochondrial damage, including lipid peroxidation and BAX-related apoptotic signaling. Thus, FABP3 and FABP5 are key players in triggering mitochondrial damage in ischemic neurons. In addition, the novel FABP inhibitor, HY08, may be a potential neuroprotective treatment for ischemic stroke.

Protein Misfolding and Aggregation in the Brain: Common Pathogenetic Pathways in Neurodegenerative and Mental Disorders

Mental disorders represent common brain diseases characterized by substantial impairments of social and cognitive functions. The neurobiological causes and mechanisms of psychopathologies still have not been definitively determined. Various forms of brain proteinopathies, which include a disruption of protein conformations and the formation of protein aggregates in brain tissues, may be a possible cause behind the development of psychiatric disorders. Proteinopathies are known to be the main cause of neurodegeneration, but much less attention is given to the role of protein impairments in psychiatric disorders' pathogenesis, such as depression and schizophrenia. For this reason, the aim of this review was to discuss the potential contribution of protein illnesses in the development of psychopathologies. The first part of the review describes the possible mechanisms of disruption to protein folding and aggregation in the cell: endoplasmic reticulum stress, dysfunction of chaperone proteins, altered mitochondrial function, and impaired autophagy processes. The second part of the review addresses the known proteins whose aggregation in brain tissue has been observed in psychiatric disorders (amyloid, tau protein, α-synuclein, DISC-1, disbindin-1, CRMP1, SNAP25, TRIOBP, NPAS3, GluA1, FABP, and ankyrin-G).

Fatty Acid-Binding Proteins: Their Roles in Ischemic Stroke and Potential as Drug Targets

Stroke is among the leading causes of death and disability worldwide. However, despite long-term research yielding numerous candidate neuroprotective drugs, there remains a lack of effective neuroprotective therapies for ischemic stroke patients. Among the factors contributing to this deficiency could be that single-target therapy is insufficient in addressing the complex and extensive mechanistic basis of ischemic brain injury. In this context, lipids serve as an essential component of multiple biological processes and play important roles in the pathogenesis of numerous common neurological diseases. Moreover, in recent years, fatty acid-binding proteins (FABPs), a family of lipid chaperone proteins, have been discovered to be involved in the onset or development of several neurodegenerative diseases, including Alzheimer’s and Parkinson’s disease. However, comparatively little attention has focused on the roles played by FABPs in ischemic stroke. We have recently demonstrated that neural tissue-associated FABPs are involved in the pathological mechanism of ischemic brain injury in mice. Here, we review the literature published in the past decade that has reported on the associations between FABPs and ischemia and summarize the relevant regulatory mechanisms of FABPs implicated in ischemic injury. We also propose candidate FABPs that could serve as potential therapeutic targets for ischemic stroke.

Effects of inhibitors of SLC9A-type sodium-protein exchangers on Survival Motor Neuron 2 (SMN2) mRNA splicing and expression

Spinal muscular atrophy (SMA) is an autosomal recessive, pediatric-onset disorder caused by the loss of spinal motor neurons thereby leading to muscle atrophy. SMA is caused by the loss of or mutations in the survival motor neuron 1 (SMN1) gene. SMN1 is duplicated in humans to give rise to the paralogous SMN2 gene. This paralog is nearly identical except for a cytosine to thymine (C-to-T) transition within an exonic splicing enhancer (ESE) element within exon 7. As a result, the majority of SMN2 transcripts lack exon 7 (SMNΔ7) which produces a truncated and unstable SMN protein. Since SMN2 copy number is inversely related to disease severity, it is a well-established target for SMA therapeutics development. 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of sodium/proton exchangers (NHEs), has previously been shown to increase exon 7 inclusion and SMN protein levels in SMA cells. In this study, NHE inhibitors were evaluated for their ability to modulate SMN2 expression. EIPA as well as 5-(N,N-hexamethylene)amiloride (HMA) increase exon 7 inclusion in SMN2 splicing reporter lines as well as in SMA fibroblasts. The EIPA-induced exon 7 inclusion occurs via a unique mechanism that does not involve previously identified splicing factors. Transcriptome analysis identified novel targets, including TIA1 and FABP3, for further characterization. EIPA and HMA are more selective at inhibiting the NHE5 isoform, which is expressed in fibroblasts as well as in neuronal cells. These results show that NHE5 inhibition increases SMN2 expression and may be a novel target for therapeutics development. Significance Statement This study demonstrates a molecular mechanism by which inhibitors of the sodium-protein exchanger increase the alternative splicing of SMN2 in spinal muscular atrophy cells. NHE5 selective inhibitors increase the inclusion of full-length SMN2 mRNAs by targeting TIA1 and FABP3 expression, which is distinct from other small molecule regulators of SMN2 alternative splicing. This study provides a novel means to increase full-length SMN2 expression and a novel target for therapeutics development.

Chitosan oligosaccharides exert neuroprotective effects via modulating the PI3K/Akt/Bcl-2 pathway in a Parkinsonian model

Parkinson's disease (PD), the second most common neurodegenerative disease, is a threat to patients due to the inability to prevent or decelerate disease progression. Currently, most clinical drugs for the treatment of PD are synthetic drugs that always present undesirable adverse or toxic effects. Chitosan oligosaccharide (COS) is a natural oligosaccharide that has been considered relatively safe and studied in the therapeutic effects on different types of neuronal disorders. In this study, we separated four COS monomers (COSs) including chitobiose (COS2), chitotriose (COS3), chitotetraose (COS4) and chitopentaose (COS5) to explore their structure-activity relationship in PD mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Techniques including TLC, HPLC, MS, and NMR were applied to investigate the purity and structure of the COSs. After the oral administration of COSs, behavior indexes, pathological indexes, cytokines, and expression of proteins in the nigrostriatal pathway of the mice were analyzed. The results showed that the four COSs were fully deacetylated and the purity was >90%. Additionally, the neurobehavioral deficits of the PD mice were improved by treatment with COSs. The results further proved that COSs could protect the TH-labelled dopaminergic neurons via reducing the overexpression of α-synuclein, alleviating neuroinflammation, and activating the PI3K/Akt/Bcl-2 pathway to reduce apoptosis. COS3 exhibited a better effect on protecting dopaminergic neurons; however, COS2 provided a better effect on reducing the overexpression of α-synuclein. To conclude, the neuroprotective activity makes COSs a viable candidate as an ingredient for healthcare products.

Fatty acid-binding protein 7 triggers α-synuclein oligomerization in glial cells and oligodendrocytes associated with oxidative stress

We previously show that fatty acid-binding protein 3 (FABP3) triggers α-synuclein (Syn) accumulation and induces dopamine neuronal cell death in Parkinson disease mouse model. But the role of fatty acid-binding protein 7 (FABP7) in the brain remains unclear. In this study we investigated whether FABP7 was involved in synucleinopathies. We showed that FABP7 was co-localized and formed a complex with Syn in Syn-transfected U251 human glioblastoma cells, and treatment with arachidonic acid (100 M) significantly promoted FABP7-induced Syn aggregation, which was associated with cell death. We demonstrated that synthetic FABP7 ligand 6 displayed a high affinity against FABP7 with K_d value of 209 nM assessed in 8-anilinonaphthalene-1-sulfonic acid (ANS) assay; ligand 6 improved U251 cell survival via disrupting the FABP7-Syn interaction. We showed that activation of phospholipase A2 (PLA2) by psychosine (10 M) triggered oligomerization of endogenous Syn and FABP7, and induced cell death in both KG-1C human oligodendroglia cells and oligodendrocyte precursor cells (OPCs). FABP7 ligand 6 (1 M) significantly decreased Syn oligomerization and aggregation thereby prevented KG-1C and OPC cell death. This study demonstrates that FABP7 triggers α-synuclein oligomerization through oxidative stress, while FABP7 ligand 6 can inhibit FABP7-induced Syn oligomerization and aggregation, thereby rescuing glial cells and oligodendrocytes from cell death.

Amelioration of rotenone-induced alterations in energy/redox system, stress response and cytoskeleton proteins by octanoic acid in zebrafish: A proteomic study

Rotenone is used to generate Parkinson's disease (PD)-like symptoms in experimental animals. Octanoic acid (C8), is the principal fatty acid of medium-chain triglycerides in ketogenic diets. Beneficial effects of ketogenic diets were shown in PD. We applied proteomic methods to reveal the effects of octanoic acid in rotenone toxicity in zebrafish to gain information on the use of ketogenic diets in PD. Zebrafish were exposed to 5 μg/ml rotenone and octanoic acid (20 and 60 mg/ml) for 30 days. LC-MS/MS analysis was performed. Raw files were analyzed by Proteome Discoverer 2.4 software, peptide lists were searched against Danio rerio proteins. STRING database was used for protein annotations or interactions. 2317 unique proteins were quantified, 302 proteins were differentially expressed. Proteins involved in cell organization, biogenesis, transport, response to stimulus were most frequently expressed. Our study is first to report that the alterations in the expressions of proteins related to energy and redox system, stress response, and cytoskeleton proteins caused by rotenone exposure were normalized by octanoic acid treatment in zebrafish.

CSF and Serum Levels of Inflammatory Markers in PD: Sparse Correlation, Sex Differences and Association With Neurodegenerative Biomarkers

Background

An involvement of the central-nervous and peripheral, innate and adaptive immune system in the pathogenesis of Parkinson's disease (PD) is nowadays well established.

Objectives

We face several open questions in preparation of clinical trials aiming at disease-modification by targeting the immune system: Do peripheral (blood) inflammatory profiles reflect central (CSF) inflammatory processes? Are blood/CSF inflammatory markers associated with CSF levels of neurodegenerative/PD-specific biomarkers?

Methods

Using a multiplex assay we assessed 41 inflammatory markers in CSF/serum pairs in 453 sporadic PD patients. We analyzed CSF/serum correlation as well as associations of inflammatory markers with clinical outcome measures (UPDRS-III, H&Y, MoCA) and with CSF levels of α-synuclein, Aβ1−42, t-Tau, p181-Tau and NFL. All analyses were stratified by sex as the immune system shows relevant sex-specific differences.

Results

Correlations between CSF and serum were sparse and detected in only 25% (9 out of 36) of the analysable inflammatory markers in male PD patients and in only 38% (12 out of 32) of female PD patients. The most important pro-inflammatory mediators associated with motor and cognitive decline as well as with neurodegenerative/PD-specific biomarkers were FABP, ICAM-1, IL-8, MCP-1, MIP-1-beta, and SCF. Results were more robust for CSF than for serum.

Interpretation

Levels of central-nervous and peripheral inflammatory markers might be regulated independently of each other with CSF inflammatory markers reflecting CNS pathology more accurately than peripheral markers. These findings along with sex-specific characteristics have to be considered when designing clinical trials aiming at disease-modification by targeting the immune system.

Essential roles of exosome and circRNA_101093 on ferroptosis desensitization in lung adenocarcinoma

Background

Resistance to ferroptosis, a regulated cell death caused by iron‐dependent excessive accumulation of lipid peroxides, has recently been linked to lung adenocarcinoma (LUAD). Intracellular antioxidant systems are required for protection against ferroptosis. The purpose of the present study was to investigate whether and how extracellular system desensitizes LUAD cells to ferroptosis.

Methods

Established human lung fibroblasts MRC‐5, WI38, and human LUAD H1650, PC9, H1975, H358, A549, and H1299 cell lines, tumor and matched normal adjacent tissues of LUAD, and plasma from healthy individuals and LUAD patients were used in this study. Immunohistochemistry and immunoblotting were used to analyze protein expression, and quantitative reverse transcription‐PCR was used to analyze mRNA expression. Cell viability, cell death, and the lipid reactive oxygen species generation were measured to evaluate the responses to ferroptosis. Exosomes were observed using transmission electron microscope. The localization of arachidonic acid (AA) was detected using click chemistry labeling followed by confocal microscopy. Interactions between RNAs and proteins were detected using RNA pull‐down, RNA immunoprecipitation and photoactivatable ribonucleoside‐enhanced crosslinking and immunoprecipitation methods. Proteomic analysis was used to investigate RNA‐regulated proteins, and metabolomic analysis was performed to analyze metabolites. Cell‐derived xenograft, patient‐derived xenograft, cell‐implanted intrapulmonary LUAD mouse models and plasma/tissue specimens from LUAD patients were used to validate the molecular mechanism.

Results

Plasma exosome from LUAD patients specifically reduced lipid peroxidation and desensitized LUAD cells to ferroptosis. A potential explanation is that exosomal circRNA_101093 (cir93) maintained an elevation in intracellular cir93 in LUAD to modulate AA, a poly‐unsaturated fatty acid critical for ferroptosis‐associated increased peroxidation in the plasma membrane. Mechanistically, cir93 interacted with and increased fatty acid‐binding protein 3 (FABP3), which transported AA and facilitated its reaction with taurine. Thus, global AA was reduced, whereas N‐arachidonoyl taurine (NAT, the product of AA and taurine) was induced. Notably, the role of NAT in suppressing AA incorporation into the plasma membrane was also revealed. In pre‐clinical in vivo models, reducing exosome improved ferroptosis‐based treatment.

Conclusion

Exosome and cir93 are essential for desensitizing LUAD cells to ferroptosis, and blocking exosome may be helpful for future LUAD treatment.

Changes in median eminence of fatty acid-binding protein 3 in a mouse model of pain

AIMS

Fatty acid-binding protein (FABP) regulates polyunsaturated fatty acid (PUFA) intracellular trafficking and signal transduction. Our previous studies demonstrated that the alteration of PUFA in the hypothalamus is involved in pain process. However, how FABP subtypes change during pain remain unclear. Here, we examined the expression changes and localization in the hypothalamic FABP subtype in postoperative pain model mice.

METHODS

Paw incision-induced postoperative methods were adopted as a pain model in male ddY mice. Mechanical allodynia was examined using the von Frey test. The analysis of several FABPs mRNA was measured by real-time PCR, and cellular localization of its protein level was measured by immunofluorescent study.

RESULTS

Postoperative pain mouse elicited mechanical allodynia on Day 2 after paw incision, and mRNA expression of FABP3 increased significantly in the hypothalamus in the postoperative pain mouse model compared to that in control mice. FABP3 protein expressed in the median eminence and the arcuate nucleus, and colocalized with Iba-1, which is a microglial cell marker. Its protein level significantly increased in the median eminence on Day 2 after incision and returned to the control level on Day 4 after incision.

CONCLUSIONS

Our findings indicate that FABP3 in the median eminence may change in pain stimuli and may represent a molecular link controlling pain.

Fat and Protein Combat Triggers Immunological Weapons of Innate and Adaptive Immune Systems to Launch Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second-most common neurodegenerative disease in the world, affecting up to 10 million people. This disease mainly happens due to the loss of dopaminergic neurons accountable for memory and motor function. Partial glucocerebrosidase enzyme deficiency and the resultant excess accumulation of glycosphingolipids and alpha-synuclein (α-syn) aggregation have been linked to predominant risk factors that lead to neurodegeneration and memory and motor defects in PD, with known and unknown causes. An increasing body of evidence uncovers the role of several other lipids and their association with α-syn aggregation, which activates the innate and adaptive immune system and sparks brain inflammation in PD. Here, we review the emerging role of a number of lipids, i.e., triglyceride (TG), diglycerides (DG), glycerophosphoethanolamines (GPE), polyunsaturated fatty acids (PUFA), sphingolipids, gangliosides, glycerophospholipids (GPL), and cholesterols, and their connection with α-syn aggregation as well as the induction of innate and adaptive immune reactions that trigger neuroinflammation in PD.

[Role of fatty acid-binding protein 7 and novel therapeutic approach in synucleinopathies]

The synucleinopathies are neurodegenerative disease caused by abnormal accumulation of the 140-amino acid-containing protein α-synuclein (αSyn), including Parkinson's disease (PD), diffuse Lewy body dementia (DLBD), and multiple system atrophy (MSA). In patients with PD and DLBD, αSyn is misfolded in neurons, and its aggregation forms Lewy bodies (LB) and Lewy neurites (LN). On the other hand, in patients with MSA, αSyn accumulates primarily in oligodendrocytes (OLGs) and forms glial inclusion bodies (GCIs), a typical pathological feature of MSA. We recently demonstrated a making complex between αSyn and fatty acid-binding proteins (FABPs) in synucleinopathies and received wide attention. Fatty acid-binding protein 3 (FABP3) in dopamine nerves, and fatty acid-binding protein 7 (FABP7) in glial cells promoted αSyn accumulation and aggregation, respectively and caused cell death. Here, we introduced the current studies about the role of αSyn and FABP7 in MSA and novel therapeutic approach targeting for FABP7.

Fatty Acid Binding Protein 3 (FABP3) and Apolipoprotein E4 (ApoE4) as Lipid Metabolism-Related Biomarkers of Alzheimer's Disease

Background: Lipid metabolism-related biomarkers gain increasing researchers interest in the field of neurodegenerative disorders. Mounting evidence have indicated the role of fatty acid-binding proteins and pathology lipid metabolism in Alzheimer’s Disease (AD). The imbalance of fatty acids (FA) and lipids may negatively affect brain functions related to neurodegenerative disorders. The ApoE4 and FABP3 proteins may reflect processes leading to neurodegeneration. This study aimed to evaluate the relationship between the CSF levels of FABP3 and ApoE4 proteins and cognitive decline as well as the diagnostic performance of these candidate biomarkers in AD and mild cognitive impairment (MCI). Methods: A total of 70 subjects, including patients with AD, MCI, and non-demented controls, were enrolled in the study. CSF concentrations of FABP3 and ApoE4 were measured using immunoassay technology. Results: Significantly higher CSF concentrations of FABP3 and ApoE4 were observed in AD patients compared to MCI subjects and individuals without cognitive impairment. Both proteins were inversely associated with Aβ42/40 ratio: ApoE4 (rho = −0.472, p < 0.001), and FABP3 (rho = −0.488, p < 0.001) in the whole study group, respectively. Additionally, FABP3 was negatively correlated with Mini-Mental State Examination score in the whole study cohort (rho = −0.585 p < 0.001). Conclusion: Presented results indicate the pivotal role of FABP3 and ApoE4 in AD pathology as lipid-related biomarkers, but studies on larger cohorts are needed.

Dietary intake and plasma levels of polyunsaturated fatty acids in early-stage Parkinson's disease

Polyunsaturated fatty acids (PUFA) are important for neuronal function and may contribute to the development of neurodegenerative diseases. Here, we investigated the correlation between dietary intake and plasma concentrations of PUFA and their associations with clinical severity in early-stage Parkinson’s disease (PD). In a case–control study with 38 patients with PD and 33 controls, we assessed dietary intake using food frequency questionnaires and simultaneously measured the plasma levels of five PUFA. No differences were observed in dietary total energy and lipid intake, including PUFA, between patients with PD and controls. However, α-linolenic acid (ALA), linoleic acid (LA), and arachidonic acid (AA) plasma levels were lower in patients with PD. The association between dietary intake and plasma PUFA concentrations was not significant in patients with PD. ALA and LA plasma levels were inversely correlated with motor severity in patients with PD, while docosahexaenoic acid and AA plasma levels were positively correlated with non-motor symptoms after controlling for age and sex.

Biophysical and structural studies reveal marginal stability of a crucial hydrocarbon biosynthetic enzyme acyl ACP reductase

Acyl-ACP reductase (AAR) is one of the two key cyanobacterial enzymes along with aldehyde deformylating oxygenase (ADO) involved in the synthesis of long-chain alkanes, a drop-in biofuel. The enzyme is prone to aggregation when expressed in Escherichia coli, leading to varying alkane levels. The present work attempts to investigate the crucial structural aspects of AAR protein associated with its stability and folding. Characterization by dynamic light scattering experiment and intact mass spectrometry revealed that recombinantly expressed AAR in E. coli existed in multiple-sized protein particles due to diverse lipidation. Interestingly, while thermal- and urea-based denaturation of AAR showed 2-state unfolding transition in circular dichroism and intrinsic fluorescent spectroscopy, the unfolding process of AAR was a 3-state pathway in GdnHCl solution suggesting that the protein milieu plays a significant role in dictating its folding. Apparent standard free energy \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {\Delta {\text{G}}_{{{\text{NU}}}}^{{{\text{H}}_{2} {\text{O}}}} } \right)$$\end{document}ΔGNUH2O of ~ 4.5 kcal/mol for the steady-state unfolding of AAR indicated borderline stability of the protein. Based on these evidences, we propose that the marginal stability of AAR are plausible contributing reasons for aggregation propensity and hence the low catalytic activity of the enzyme when expressed in E. coli for biofuel production. Our results show a path for building superior biocatalyst for higher biofuel production.

Impact of Fatty Acid-Binding Proteins in α-Synuclein-Induced Mitochondrial Injury in Synucleinopathy

Synucleinopathies are diverse diseases with motor and cognitive dysfunction due to progressive neuronal loss or demyelination, due to oligodendrocyte loss in the brain. While the etiology of neurodegenerative disorders (NDDs) is likely multifactorial, mitochondrial injury is one of the most vital factors in neuronal loss and oligodendrocyte dysfunction, especially in Parkinson’s disease, dementia with Lewy body, multiple system atrophy, and Krabbe disease. In recent years, the abnormal accumulation of highly neurotoxic α-synuclein in the mitochondrial membrane, which leads to mitochondrial dysfunction, was well studied. Furthermore, fatty acid-binding proteins (FABPs), which are members of a superfamily and are essential in fatty acid trafficking, were reported to trigger α-synuclein oligomerization in neurons and glial cells and to target the mitochondrial outer membrane, thereby causing mitochondrial loss. Here, we provide an updated overview of recent findings on FABP and α-synuclein interactions and mitochondrial injury in NDDs.

Fatty Acid-Binding Proteins Aggravate Cerebral Ischemia-Reperfusion Injury in Mice

Fatty acid-binding proteins (FABPs) regulate the intracellular dynamics of fatty acids, mediate lipid metabolism and participate in signaling processes. However, the therapeutic efficacy of targeting FABPs as novel therapeutic targets for cerebral ischemia is not well established. Previously, we synthesized a novel FABP inhibitor, i.e., FABP ligand 6 [4-(2-(5-(2-chlorophenyl)-1-(4-isopropylphenyl)-1H-pyrazol-3-yl)-4-fluorophenoxy)butanoic acid] (referred to here as MF6). In this study, we analyzed the ability of MF6 to ameliorate transient middle cerebral artery occlusion (tMCAO) and reperfusion-induced injury in mice. A single MF6 administration (3.0 mg/kg, per os) at 0.5 h post-reperfusion effectively reduced brain infarct volumes and neurological deficits. The protein-expression levels of FABP3, FABP5 and FABP7 in the brain gradually increased after tMCAO. Importantly, MF6 significantly suppressed infarct volumes and the elevation of FABP-expression levels at 12 h post-reperfusion. MF6 also inhibited the promotor activity of FABP5 in human neuroblastoma cells (SH-SY5Y). These data suggest that FABPs elevated infarct volumes after ischemic stroke and that inhibiting FABPs ameliorated the ischemic injury. Moreover, MF6 suppressed the inflammation-associated prostaglandin E2 levels through microsomal prostaglandin E synthase-1 expression in the ischemic hemispheres. Taken together, the results imply that the FABP inhibitor MF6 can potentially serve as a neuroprotective therapeutic for ischemic stroke.

An α-synuclein decoy peptide prevents cytotoxic α-synuclein aggregation caused by fatty acid binding protein 3

α-synuclein (αSyn) is a protein known to form intracellular aggregates during the manifestation of Parkinson’s disease. Previously, it was shown that αSyn aggregation was strongly suppressed in the midbrain region of mice that did not possess the gene encoding the lipid transport protein fatty acid binding protein 3 (FABP3). An interaction between these two proteins was detected in vitro, suggesting that FABP3 may play a role in the aggregation and deposition of αSyn in neurons. To characterize the molecular mechanisms that underlie the interactions between FABP3 and αSyn that modulate the cellular accumulation of the latter, in this report, we used in vitro fluorescence assays combined with fluorescence microscopy, transmission electron microscopy, and quartz crystal microbalance assays to characterize in detail the process and consequences of FABP3–αSyn interaction. We demonstrated that binding of FABP3 to αSyn results in changes in the aggregation mechanism of the latter; specifically, a suppression of fibrillar forms of αSyn and also the production of aggregates with an enhanced cytotoxicity toward mice neuro2A cells. Because this interaction involved the C-terminal sequence region of αSyn, we tested a peptide derived from this region of αSyn (αSynP130-140) as a decoy to prevent the FABP3–αSyn interaction. We observed that the peptide competitively inhibited binding of αSyn to FABP3 in vitro and in cultured cells. We propose that administration of αSynP130-140 might be used to prevent the accumulation of toxic FABP3-αSyn oligomers in cells, thereby preventing the progression of Parkinson’s disease.

Fatty Acid-Binding Protein 3 Expression in the Brain and Skin in Human Synucleinopathies

Parkinson’s disease (PD) and multiple system atrophy are types of adult-onset neurodegenerative disorders named synucleinopathies, which are characterized by prominent intracellular α-synuclein (αSyn) aggregates. We have previously found that αSyn aggregates and the vulnerability of dopaminergic neurons in the mouse brain are partly associated with the expression of fatty acid-binding protein 3 (FABP3, heart FABP). However, it remains to be elucidated whether FABP3 accumulation is associated with αSyn aggregates in human tissues. Here, we histologically studied FABP3 expression in human tissues obtained from patients with synucleinopathies, patients with Alzheimer disease (AD) and controls. We found that (1) a variety of neurons expressed the FABP3 protein in human brain tissues, (2) FABP3 was colocalized with αSyn aggregates in the brains of individuals with synucleinopathies but not with amyloid β or p-tau aggregates in the brains of individuals with AD, and (3) FABP3 was not present in p-αSyn deposits in biopsied skin tissues from individuals with PD. These findings suggest that FABP3 expression is associated with αSyn aggregation in synucleinopathies and provide new insights into the involvement of FABP3 in synucleinopathies.

Suppression of α-synuclein propagation after intrastriatal injection in FABP3 null mice

Accumulation and aggregation of α-synuclein (αSyn) trigger neuronal loss in the substantia nigra pars compacta (SNpc), which in turn causes motor symptoms in Parkinson's disease. We previously demonstrated that fatty acid-binding protein 3 (FABP3), an intracellular fatty acid carrier protein, enhances αSyn neurotoxicity in SNpc and motor impairments after intranigral injection of αSyn fibrils. However, the temporal profile of αSyn fibril spread and their toxicity remains unclear. In the present study, we investigated the temporal profile of αSyn fibril spread and its toxicity, which induces intracellular fibril formation. Monomeric and fibrillar aSyn assemblies were labeled with ATTO550 to distinguish the exogenous form from the endogenous species and injected into bilateral striatum in Fabp3^+/+ (wild type) and Fabp3^-/- mice. Accumulation of both monomeric and fibrillar exogenous αSyn in the SNpc was drastically decreased in Fabp3^-/- mice compared to that in the Fabp3^+/+ counterparts. Deletion of Fabp3 also prevented exogenous αSyn fibril-induced seeding of the endogenous αSyn into aggregates containing phosphorylated and filamentous forms in the SNpc. Consistent with these results, loss of dopaminergic neurons and subsequent impaired motor behavior were attenuated in Fabp3^-/- mice. These results highlight the crucial role of FABP3 in pathogenic αSyn accumulation and its seeding ability. Taken together, FABP3 could be a potential therapeutic target against αSyn propagation in synucleinopathies.

Development of an α-synuclein knockdown peptide and evaluation of its efficacy in Parkinson's disease models

Convincing evidence supports the premise that reducing α-synuclein levels may be an effective therapy for Parkinson's disease (PD); however, there has been lack of a clinically applicable α-synuclein reducing therapeutic strategy. This study was undertaken to develop a blood-brain barrier and plasma membrane-permeable α-synuclein knockdown peptide, Tat-βsyn-degron, that may have therapeutic potential. The peptide effectively reduced the level of α-synuclein via proteasomal degradation both in cell cultures and in animals. Tat-βsyn-degron decreased α-synuclein aggregates and microglial activation in an α-synuclein pre-formed fibril model of spreading synucleinopathy in transgenic mice overexpressing human A53T α-synuclein. Moreover, Tat-βsyn-degron reduced α-synuclein levels and significantly decreased the parkinsonian toxin-induced neuronal damage and motor impairment in a mouse toxicity model of PD. These results show the promising efficacy of Tat-βsyn-degron in two different animal models of PD and suggest its potential use as an effective PD therapeutic that directly targets the disease-causing process.

Possible involvement of fatty acid binding proteins in psychiatric disorders

Polyunsaturated fatty acids (PUFAs) are essential for brain development and function. Increasing evidence has shown that an imbalance of PUFAs is associated with various human psychiatric disorders, including autism and schizophrenia. However, the mechanisms underlying the effects of PUFAs on brain functions at cellular and molecular levels remain unclear. Since PUFAs are insoluble in water, specific transporters are required to deliver PUFAs to appropriate intracellular compartments. Fatty acid-binding proteins (FABPs), the cellular chaperones of PUFAs, are involved in PUFA intracellular trafficking, signal transduction, and gene transcription. Therefore, we focused on the relationship between FABP-regulated PUFA homeostasis in the brain and neuronal plasticity. The authors previously reported that FABP3, which preferentially binds to n-6 PUFAs, is strongly expressed in the gamma-aminobutyric acid (GABAergic) inhibitory interneurons of the adult mouse anterior cingulate cortex (ACC), which is a component of the limbic cortex and is important for the coordination of cognitive and emotional behaviors. Interestingly, Fabp3 KO mice show increased GABA synthesis and abnormal excitatory/inhibitory balance in the ACC. In addition, studies have indicated that FABP7, which preferentially binds to n-3 PUFAs, controls lipid raft function in astrocytes, and astrocytic Fabp7 deficiency results in an altered response of astrocytes to external stimuli. Furthermore, Fabp7 KO mice exhibit aberrant dendritic morphology, and decreased spine density and excitatory synaptic transmission in pyramidal neurons. This review summarizes relationship between PUFAs or FABPs and human psychiatric disorders and discusses recent progress in elucidating the function of FABPs, especially FABP3 and 7, in the brain.

Dopamine D2 Long Receptors Are Critical for Caveolae-Mediated α-Synuclein Uptake in Cultured Dopaminergic Neurons

α-synuclein accumulation into dopaminergic neurons is a pathological hallmark of Parkinson's disease. We previously demonstrated that fatty acid-binding protein 3 (FABP3) is critical for α-synuclein uptake and propagation to accumulate in dopaminergic neurons. FABP3 is abundant in dopaminergic neurons and interacts with dopamine D2 receptors, specifically the long type (D_2L). Here, we investigated the importance of dopamine D_2L receptors in the uptake of α-synuclein monomers and their fibrils. We employed mesencephalic neurons derived from dopamine D_2L ^-/-, dopamine D2 receptor null (D2 null), FABP3^-/-, and wild type C57BL6 mice, and analyzed the uptake ability of fluorescence-conjugated α-synuclein monomers and fibrils. We found that D_2L receptors are co-localized with FABP3. Immunocytochemistry revealed that TH⁺ D2L^-/- or D2 null neurons do not take up α-synuclein monomers. The deletion of α-synuclein C-terminus completely abolished the uptake to dopamine neurons. Likewise, dynasore, a dynamin inhibitor, and caveolin-1 knockdown also abolished the uptake. D_2L and FABP3 were also critical for α-synuclein fibrils uptake. D_2L and accumulated α-synuclein fibrils were well co-localized. These data indicate that dopamine D_2L with a caveola structure coupled with FABP3 is critical for α-synuclein uptake by dopaminergic neurons, suggesting a novel pathogenic mechanism of synucleinopathies, including Parkinson's disease.

Impaired Acquisition of Nicotine-Induced Conditioned Place Preference in Fatty Acid-Binding Protein 3 Null Mice

Nicotine causes psychological dependence through its interactions with nicotinic acetylcholine receptors in the brain. We previously demonstrated that fatty acid-binding protein 3 (FABP3) colocalizes with dopamine D2 receptors (D2Rs) in the dorsal striatum, and FABP3 deficiency leads to impaired D2R function. Moreover, D2R null mice do not exhibit increased nicotine-induced conditioned place preference (CPP) following chronic nicotine administration. To investigate the role of FABP3 in nicotine-induced CPP, FABP3 knockout (FABP3^-/-) mice were evaluated using a CPP apparatus following consecutive nicotine administration (0.5 mg/kg) for 14 days. Importantly, nicotine-induced CPP was suppressed in the conditioning, withdrawal, and relapse phases in FABP3^-/- mice. To resolve the mechanisms underlying impaired nicotine-induced CPP in these mice, we assessed c-Fos expression and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) signaling in both dopamine D1 receptor (D1R)- and D2R-positive neurons in the nucleus accumbens (NAc). Notably, 64% of dopamine receptor-positive neurons in the mouse NAc expressed both D1R and D2R. Impaired nicotine-induced CPP was correlated with lack of responsiveness of both CaMKII and ERK phosphorylation. The number of D2R-positive neurons was increased in FABP3^-/- mice, while the number of D1R-positive neurons and the responsiveness of c-Fos expression to nicotine were decreased. The aberrant c-Fos expression was closely correlated with CaMKII but not ERK phosphorylation levels in the NAc of FABP3^-/- mice. Taken together, these results indicate that impaired D2R signaling due to lack of FABP3 may affect D1R and c-Fos signaling and underlie nicotine-induced CPP behaviors.

Crucial Role of FABP3 in αSyn-Induced Reduction of Septal GABAergic Neurons and Cognitive Decline in Mice

In synucleinopathies, while motor symptoms are thought to be attributed to the accumulation of misfolded α-synuclein (αSyn) in nigral dopaminergic neurons, it remains to be elucidated how cognitive decline arises. Here, we investigated the effects of distinct αSyn strains on cognition and the related neuropathology in the medial septum/diagonal band (MS/DB), a key region for cognitive processing. Bilateral injection of αSyn fibrils into the dorsal striatum potently impaired cognition in mice. The cognitive decline was accompanied by accumulation of phosphorylated αSyn at Ser129 and reduction of gamma-aminobutyric acid (GABA)-ergic but not cholinergic neurons in the MS/DB. Since we have demonstrated that fatty acid-binding protein 3 (FABP3) is critical for αSyn neurotoxicity in nigral dopaminergic neurons, we investigated whether FABP3 also participates in αSyn pathology in the MS/DB and cognitive decline. FABP3 was highly expressed in GABAergic but rarely in cholinergic neurons in the MS/DB. Notably, Fabp3 deletion antagonized the accumulation of phosphorylated αSyn, decrease in GABAergic neurons, and cognitive impairment caused by αSyn fibrils. Overall, the present study indicates that FABP3 mediates αSyn neurotoxicity in septal GABAergic neurons and the resultant cognitive impairment, and that FABP3 in this subpopulation could be a therapeutic target for dementia in synucleinopathies.

Fatty Acid Binding Protein 5 Mediates Cell Death by Psychosine Exposure through Mitochondrial Macropores Formation in Oligodendrocytes

Oligodendrocytes, the myelinating cells in the central nervous system (CNS), are critical for producing myelin throughout the CNS. The loss of oligodendrocytes is associated with multiple neurodegenerative disorders mediated by psychosine. However, the involvement of psychosine in the critical biochemical pathogenetic mechanism of the loss of oligodendrocytes and myelin in krabbe disease (KD) remains unclear. Here, we addressed how oligodendrocytes are induced by psychosine treatment in both KG-1C human oligodendroglial cells and mouse oligodendrocyte precursor cells. We found that fatty acid binding protein 5 (FABP5) expressed in oligodendrocytes accelerates mitochondria-induced glial death by inducing mitochondrial macropore formation through voltage-dependent anion channels (VDAC-1) and BAX. These two proteins mediate mitochondrial outer membrane permeabilization, thereby leading to the release of mitochondrial DNA and cytochrome C into the cytosol, and the activation of apoptotic caspases. Furthermore, we confirmed that the inhibition of FABP5 functions by shRNA and FABP5-specific ligands blocking mitochondrial macropore formation, thereby rescuing psychosine-induced oligodendrocyte death. Taken together, we identified FABP5 as a critical factor in mitochondrial injury associated with psychosine-induced apoptosis in oligodendrocytes.

Interaction of Alpha-Synuclein With Lipids: Mitochondrial Cardiolipin as a Critical Player in the Pathogenesis of Parkinson's Disease

Alpha-Synuclein (α-Syn) is a central protein in the pathogenesis of synucleinopathies, a group of neurodegenerative disorders including Parkinson’s disease (PD). Although its role in neurotransmission is well established, the precise role of this protein in disease pathogenesis is still not fully understood. It is, however, widely regarded to be associated with the misfolding and accumulation of toxic intracellular aggregates. In fact, α-Syn is the most abundant protein component of Lewy bodies and Lewy neurites, which are also characterized by a high lipid content. Lipids, the main constituents of cellular membranes, have been implicated in many aspects of PD-related processes. α-Syn interacts with membrane phospholipids and free fatty acids via its N-terminal domain, and altered lipid-protein complexes might enhance both its binding to synaptic and mitochondrial membranes and its oligomerization. Several studies have highlighted a specific interaction of α-Syn with the phospholipid cardiolipin (CL), a major constituent of mitochondrial membranes. By interacting with CL, α-Syn is able to disrupt mitochondrial membrane integrity, leading to mitochondrial dysfunction. Additionally, externalized CL is able to facilitate the refolding of toxic α-Syn species at the outer mitochondrial membrane. In this review, we discuss how α-Syn/lipid interactions, in particular the α-Syn/CL interaction at the mitochondrial membrane, may affect α-Syn aggregation and mitochondrial dysfunction and may thus represent an important mechanism in the pathogenesis of PD.

Interrelations of Alzheimer´s disease candidate biomarkers neurogranin, fatty acid-binding protein 3 and ferritin to neurodegeneration and neuroinflammation

There is growing evidence that promising biomarkers of inflammation in Alzheimer´s disease (AD) and other neurodegenerative diseases correlate strongest to levels of tau or neurofilament, indicating an inflammatory response to neuronal damage or death. To test this hypothesis, we investigated three AD candidate markers (ferritin, fatty acid binding protein 3 (FABP-3), and neurogranin) in interrelation to established AD and inflammatory protein markers. We further aimed to determine if such interrelations would be evident in pathological subjects only or also under non-pathological circumstances. Cerebrospinal fluid levels of the three proteins were quantified in samples from the University Clinic of Bonn (UKB) Department of Neurodegenerative Diseases & Geriatric Psychiatry, Germany. Data were analyzed based on clinical or biomarker-defined stratification of subjects with adjustment for covariates age, sex, and APOE status. Levels of ferritin, FABP-3 and neurogranin were elevated in subjects with pathological levels of t-tau independent of beta-amyloid status. The three markers correlated with each other, tau isoforms, age, and those inflammatory markers previously described as related to neurodegeneration, predominantly sTREM2, macrophage migration inhibitory factor, soluble vascular endothelial growth factor receptor, soluble vascular cell adhesion molecule 1 (sVCAM-1), and C1q. These interrelations existed in subjects with pathological and sub-pathological tau levels, in particular for FABP-3 and neurogranin. Relations to ferritin were independent of absolute levels of tau, too, but showed differing trajectories between pathological and non-pathological subjects. A specific set of inflammatory markers is highly related to markers of neuronal damage such as tau, neurogranin, or FABP-3. These proteins could be used as readouts of the inflammatory response during the neurodegeneration phase of AD.

Anti-Epileptic Effects of FABP3 Ligand MF1 through the Benzodiazepine Recognition Site of the GABAA Receptor

Recently, we developed the fatty acid-binding protein 3 (FABP3) ligand MF1 (4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid) as a therapeutic candidate for α-synucleinopathies. MF1 shows affinity towards γ-aminobutyric acid type-A (GABA_A) receptor, but its effect on the receptor remains unclear. Here, we investigate the pharmacological properties of MF1 on the GABA_A receptor overexpressed in Neuro2A cells. While MF1 (1–100 μm) alone failed to evoke GABA currents, MF1 (1 μm) promoted GABA currents during GABA exposure (1 and 10 μm). MF1-promoted GABA currents were blocked by flumazenil (10 μm) treatment, suggesting that MF1 enhances receptor function via the benzodiazepine recognition site. Acute and chronic administration of MF1 (0.1, 0.3 and 1.0 mg/kg, p.o.) significantly attenuated status epilepticus (SE) and the mortality rate in pilocarpine (PILO: 300 mg/kg, i.p.)-treated mice, similar to diazepam (DZP: 5.0 mg/kg, i.p.). The anti-epileptic effects of DZP (5.0 mg/kg, i.p.) and MF1 (0.3 mg/kg, p.o.) were completely abolished by flumazenil (25 mg/kg, i.p.) treatment. Pentylenetetrazol (PTZ: 90 mg/kg, i.p.)-induced seizures in mice were suppressed by DZP (5.0 mg/kg, i.p.), but not MF1. Collectively, this suggests that MF1 is a mild enhancer of the GABA_A receptor and exercises anti-epileptic effects through the receptor’s benzodiazepine recognition site in PILO-induced SE models.

Analysis of binding affinity and docking of novel fatty acid-binding protein (FABP) ligands

Fatty acid-binding proteins (FABPs) belong to a family of proteins that transports fatty acids in the cytosol and regulates cellular functions like membrane phospholipid synthesis, lipid metabolism, and mitochondrial β oxidation. In this study, we synthesized ten novel derivatives from BMS309403, a biphenyl azole compound specific for FABP4, and analyzed their affinity and specificity for FABP3, FABP4, and FABP5, which possess 60% of homology in amino acid sequence. Here, we used 1-anilinonaphthalene 8-sulfonic acid (ANS) displacement assay and found that Ligand 1 has highest affinity for FABP3, with comparable affinity for FABP4 and FABP5. The apparent dissociation constant of BMS309403 was identical to that of arachidonic acid and docosahexaenoic acid. Docking studies with X-ray structural data showed that these novel derivatives obtained by the substitution of phenoxyacetic acid in BMS309403 but not BMS309403 have high or moderate affinity for FABP3. We further found that substitution of a phenyl group and alkyl group caused steric hindrance between 16F, the portal loop and 115L, 117L, respectively, leading to decrease in their affinity for FABPs. In conclusion, our study provides a novel strategy for development of specific ligand for each FABP.

Fatty Acid Binding Protein 3 Enhances the Spreading and Toxicity of α-Synuclein in Mouse Brain

Oligomerization and/or aggregation of α-synuclein (α-Syn) triggers α-synucleinopathies such as Parkinson’s disease and dementia with Lewy bodies. It is known that α-Syn can spread in the brain like prions; however, the mechanism remains unclear. We demonstrated that fatty acid binding protein 3 (FABP3) promotes propagation of α-Syn in mouse brain. Animals were injected with mouse or human α-Syn pre-formed fibrils (PFF) into the bilateral substantia nigra pars compacta (SNpc). Two weeks after injection of mouse α-Syn PFF, wild-type (WT) mice exhibited motor and cognitive deficits, whereas FABP3 knock-out (Fabp3^−/−) mice did not. The number of phosphorylated α-Syn (Ser-129)-positive cells was significantly decreased in Fabp3^−/− mouse brain compared to that in WT mice. The SNpc was unilaterally infected with AAV-GFP/FABP3 in Fabp3^−/− mice to confirm the involvement of FABP3 in the development of α-Syn PFF toxicity. The number of tyrosine hydroxylase (TH)- and phosphorylated α-Syn (Ser-129)-positive cells following α-Syn PFF injection significantly decreased in Fabp3^−/− mice and markedly increased by AAV-GFP/FABP3 infection. Finally, we confirmed that the novel FABP3 inhibitor MF1 significantly antagonized motor and cognitive impairments by preventing α-Syn spreading following α-Syn PFF injection. Overall, FABP3 enhances α-Syn spreading in the brain following α-Syn PFF injection, and the FABP3 ligand MF1 represents an attractive therapeutic candidate for α-synucleinopathy.

Novel fatty acid-binding protein 3 ligand inhibits dopaminergic neuronal death and improves motor and cognitive impairments in Parkinson's disease model mice

The main symptom of Parkinson's disease (PD) is motor dysfunction and remarkably approximately 30-40% of PD patients exhibit cognitive impairments. Recently, we have developed MF8, a heart-type fatty acid-binding protein (FABP3)-specific ligand, which can inhibit α-synuclein (α-syn) oligomerization induced by arachidonic acid in FABP3 overexpressing neuro2A cells. The present study aimed to determine whether MF8 attenuates dopaminergic neuronal death and motor and cognitive impairments in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice model. MF8 can penetrate the blood-brain barrier and its peak brain concentration (21.5 ± 2.1 nM) was achieved 6 h after the oral administration (1.0 mg/kg). We also compared its effects and pharmacological action with those of L-DOPA (3,4-dihydroxy-l-phenylalanine). PD model mice were developed by administering MPTP (25 mg/kg, i.p.) once a day for five consecutive days. Twenty-four hours after the final MPTP injection, mice were administered MF8 (0.3, 1.0 mg/kg, p.o.) or L-DOPA (25 mg/kg, i.p.) once a day for 28 consecutive days and subjected to behavioral and histochemical studies. MF8 (1.0 mg/kg, p.o.), but not L-DOPA, inhibited the dopaminergic neuronal death in the ventral tegmental area and the substantia nigra pars compacta region of the MPTP-treated mice. MF8 also improved both, motor and cognitive functions, while L-DOPA ameliorated only motor dysfunction. Taken together, our results showed that MF8 attenuated the MPTP-induced dopaminergic neuronal death associated with PD pathology. We present MF8 as a novel disease-modifying therapeutic molecule for PD, which acts via a mechanism different from that of L-DOPA.

Kir6.1 Heterozygous Mice Exhibit Aberrant Amygdala-Dependent Cued Fear Memory

ATP-sensitive K⁺ (K_ATP) channels are predominantly expressed in the brain and consist of four identical inward-rectifier potassium ion channel subunits (Kir6.1 or Kir6.2) and four identical high-affinity sulfonylurea receptor subunits (SUR1, SUR2A, or SUR2B). We previously observed that chronic corticosterone-treated (CORT) mice exhibited enhanced anxiety-like behaviors and cued fear memory. In the present study, the protein and mRNA expression levels of Kir6.1, but not Kir6.2, were decreased in the lateral amygdala (LA) of CORT mice. Heterozygous Kir6.1-null (Kir6.1^+/-) mice also showed enhanced tone (cued) fear memory and long-term potentiation (LTP) in the cortico-LA pathway compared to those in wild-type mice. However, LTP was not enhanced in the hippocampal CA1 regions of Kir6.1^+/- mice. Consistent with increased cued fear memory, both Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) activities were significantly elevated in the LAs of Kir6.1^+/- mice after tone stimulation. Our results indicate that increased CaMKII and ERK activities may induce LTP in the LA in Kir6.1^+/- mice, leading to aberrant cued fear memory. The changes in neural plasticity in the LA of Kir6.1^+/- mice were associated with anxiety-like behaviors and may be related to the pathogenic mechanisms of anxiety disorders in human patients.

Fatty Acid-Binding Protein 3 is Critical for α-Synuclein Uptake and MPP+-Induced Mitochondrial Dysfunction in Cultured Dopaminergic Neurons

α-Synuclein is an abundant neuronal protein that accumulates in insoluble inclusions in Parkinson′s disease and other synucleinopathies. Fatty acids partially regulate α-Synuclein accumulation, and mesencephalic dopaminergic neurons highly express fatty acid-binding protein 3 (FABP3). We previously demonstrated that FABP3 knockout mice show decreased α-Synuclein oligomerization and neuronal degeneration of tyrosine hydroxylase (TH)-positive neurons in vivo. In this study, we newly investigated the importance of FABP3 in α-Synuclein uptake, 1-methyl-4-phenylpyridinium (MPP⁺)-induced axodendritic retraction, and mitochondrial dysfunction. To disclose the issues, we employed cultured mesencephalic neurons derived from wild type or FABP3^−/− C57BL6 mice and performed immunocytochemical analysis. We demonstrated that TH⁺ neurons from FABP3^+/+ mice take up α-Synuclein monomers while FABP3^−/− TH⁺ neurons do not. The formation of filamentous α-Synuclein inclusions following treatment with MPP⁺ was observed only in FABP3^+/+, and not in FABP3^−/− neurons. Notably, detailed morphological analysis revealed that FABP^−/− neurons did not exhibit MPP⁺-induced axodendritic retraction. Moreover, FABP3 was also critical for MPP⁺-induced reduction of mitochondrial activity and the production of reactive oxygen species. These data indicate that FABP3 is critical for α-Synuclein uptake in dopaminergic neurons, thereby preventing synucleinopathies, including Parkinson′s disease.

Clinical Therapeutic Strategy and Neuronal Mechanism Underlying Post-Traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is characterized by an exaggerated response to contextual memory and impaired fear extinction, with or without mild cognitive impairment, learning deficits, and nightmares. PTSD is often developed by traumatic events, such as war, terrorist attack, natural calamities, etc. Clinical and animal studies suggest that aberrant susceptibility of emotion- and fear-related neurocircuits, including the amygdala, prefrontal cortex (PFC), and hippocampus may contribute to the development and retention of PTSD symptoms. Psychological and pharmacological therapy, such as cognitive behavioral therapy (CBT), and treatment with anti-depressive agents and/or antipsychotics significantly attenuate PTSD symptoms. However, more effective therapeutics are required for improvement of quality of life in PTSD patients. Previous studies have reported that ω3 long-chain polyunsaturated fatty acid (LCPUFA) supplements can suppress the development of PTSD symptoms. Fatty acid binding proteins (FABPs) are essential for LCPUFA intracellular trafficking. In this review, we have introduced Fabp3 null mice as an animal model of PTSD with impaired fear extinction. Moreover, we have addressed the neuronal circuits and novel therapeutic strategies for PTSD symptoms.

Cellular α-synuclein pathology is associated with bioenergetic dysfunction in Parkinson's iPSC-derived dopamine neurons

Parkinson's disease (PD) is the second most common neurodegenerative disorder and a central role for α-synuclein (αSyn; SNCA) in disease aetiology has been proposed based on genetics and neuropathology. To better understand the pathological mechanisms of αSyn, we generated induced pluripotent stem cells (iPSCs) from healthy individuals and PD patients carrying the A53T SNCA mutation or a triplication of the SNCA locus and differentiated them into dopaminergic neurons (DAns). iPSC-derived DAn from PD patients carrying either mutation showed increased intracellular αSyn accumulation, and DAns from patients carrying the SNCA triplication displayed oligomeric αSyn pathology and elevated αSyn extracellular release. Transcriptomic analysis of purified DAns revealed perturbations in expression of genes linked to mitochondrial function, consistent with observed reduction in mitochondrial respiration, impairment in mitochondrial membrane potential, aberrant mitochondrial morphology and decreased levels of phosphorylated DRP1Ser616. Parkinson's iPSC-derived DAns showed increased endoplasmic reticulum stress and impairments in cholesterol and lipid homeostasis. Together, these data show a correlation between αSyn cellular pathology and deficits in metabolic and cellular bioenergetics in the pathology of PD.

Cerebrospinal fluid biomarkers for understanding multiple aspects of Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a multifactorial age-related brain disease. Numerous pathological events run forth in the brain leading to AD. There is an initial long, dormant phase before the clinical symptoms become evident. There is a need to diagnose the disease at the preclinical stage since therapeutic interventions are most likely to be effective if initiated early. Undoubtedly, the core cerebrospinal fluid (CSF) biomarkers have a good diagnostic accuracy and have been used in clinical trials as end point measures. However, looking into the multifactorial nature of AD and the overlapping pathology with other forms of dementia, it is important to integrate the core CSF biomarkers with a broader panel of other biomarkers reflecting different aspects of pathology. The review is focused upon a panel of biomarkers that relate to different aspects of AD pathology, as well as various studies that have evaluated their diagnostic potential. The panel includes markers of neurodegeneration: neurofilament light chain and visinin-like protein (VILIP-1); markers of amyloidogenesis and brain amyloidosis: apolipoproteins; markers of inflammation: YKL-40 and monocyte chemoattractant protein 1; marker of synaptic dysfunction: neurogranin. These markers can highlight on the state and stage-associated changes that occur in AD brain with disease progression. A combination of these biomarkers would not only aid in preclinical diagnosis, but would also help in identifying early brain changes during the onset of disease. Successful treatment strategies can be devised by understanding the contribution of these markers in different aspects of disease pathogenesis.

Fatty Acid Signaling Mechanisms in Neural Cells: Fatty Acid Receptors

Fatty acids (FAs) are typically associated with structural and metabolic roles, as they can be stored as triglycerides, degraded by β-oxidation or used in phospholipids’ synthesis, the main components of biological membranes. It has been shown that these lipids exhibit also regulatory functions in different cell types. FAs can serve as secondary messengers, as well as modulators of enzymatic activities and substrates for cytokines synthesis. More recently, it has been documented a direct activity of free FAs as ligands of membrane, cytosolic, and nuclear receptors, and cumulative evidence has emerged, demonstrating its participation in a wide range of physiological and pathological conditions. It has been long known that the central nervous system is enriched with poly-unsaturated FAs, such as arachidonic (C20:4ω-6) or docosohexaenoic (C22:6ω-3) acids. These lipids participate in the regulation of membrane fluidity, axonal growth, development, memory, and inflammatory response. Furthermore, a whole family of low molecular weight compounds derived from FAs has also gained special attention as the natural ligands for cannabinoid receptors or key cytokines involved in inflammation, largely expanding the role of FAs as precursors of signaling molecules. Nutritional deficiencies, and alterations in lipid metabolism and lipid signaling have been associated with developmental and cognitive problems, as well as with neurodegenerative diseases. The molecular mechanism behind these effects still remains elusive. But in the last two decades, different families of proteins have been characterized as receptors mediating FAs signaling. This review focuses on different receptors sensing and transducing free FAs signals in neural cells: (1) membrane receptors of the family of G Protein Coupled Receptors known as Free Fatty Acid Receptors (FFARs); (2) cytosolic transport Fatty Acid-Binding Proteins (FABPs); and (3) transcription factors Peroxisome Proliferator-Activated Receptors (PPARs). We discuss how these proteins modulate and mediate direct regulatory functions of free FAs in neural cells. Finally, we briefly discuss the advantages of evaluating them as potential targets for drug design in order to manipulate lipid signaling. A thorough characterization of lipid receptors of the nervous system could provide a framework for a better understanding of their roles in neurophysiology and, potentially, help for the development of novel drugs against aging and neurodegenerative processes.

Inhibition of MPTP-induced α-synuclein oligomerization by fatty acid-binding protein 3 ligand in MPTP-treated mice

Accumulation and aggregation of α-synuclein (αSyn) triggers dopaminergic (DAergic) neuronal loss in Parkinson's disease (PD). This pathological event is partly facilitated by the presence of long-chain polyunsaturated fatty acids (LC-PUFAs), including arachidonic acid. The intracellular transport and metabolism of LC-PUFAs are mediated by fatty acid-binding proteins (FABPs). We previously reported that heart-type FABP (FABP3) interacts with αSyn, thereby promoting αSyn oligomerization in DAergic neurons in the substantia nigra pars compacta (SNpc) following 1-methyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. This αSyn oligomerization is prevented in Fabp3 gene knock out mice. We document a novel FABP3 ligand, MF1 (4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy)butanoic acid), that inhibits αSyn accumulation in DA neurons, thereby inhibiting the oligomerization of αSyn, loss of DAergic neurons, and PD-like motor deficits in MPTP-treated mice. Chronic oral administration of MF1 (0.3 or 1.0 mg/kg/day) significantly improved motor impairments and inhibited MPTP-induced accumulation and oligomerization of αSyn in the SNpc, and in turn prevented loss of tyrosine hydroxylase (TH)-positive cells in the SNpc. MF1 administration (0.1, 0.3, or 1.0 mg/kg/day) also restored MPTP-induced cognitive impairments. Although chronic administration of l-DOPA (3,4-dihydroxl-l-phenylalanine; 25 mg/kg/day, i.p.) also improved motor deficits, it failed to improve the cognitive impairments. In addition, l-DOPA failed to inhibit DAergic neuronal loss and αSyn pathologies in the SNpc. In summary, the novel FABP3 ligand MF1 rescues MPTP-induced behavioural and neuropathological features, suggesting that MF1 may be a disease-modifying drug candidate for synucleinopathies.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.