The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Folate-mediated transgenerational inheritance of sperm DNA methylation patterns correlate with spinal axon regeneration

In mammals, the molecular mechanisms underlying transgenerational inheritance of phenotypic traits in serial generations of progeny after ancestral environmental exposures, without variation in DNA sequence, remain elusive. We've recently described transmission of a beneficial trait in rats and mice, in which F0 supplementation of methyl donors, including folic acid, generates enhanced axon regeneration after sharp spinal cord injury in untreated F1 to F3 progeny linked to differential DNA methylation levels in spinal cord tissue. To test whether the transgenerational effect of folic acid is transmitted via the germline, we performed whole-genome methylation sequencing on sperm DNA from F0 mice treated with either folic acid or vehicle control, and their F1, F2, and F3 untreated progeny. Transgenerational differentially methylated regions (DMRs) are observed in each consecutive generation and distinguish folic acid from untreated lineages, predominate outside of CpG islands and in regions of the genome that regulate gene expression, including promoters, and overlap at both the differentially methylated position (DMP) and gene levels. These findings indicate that molecular changes between generations are caused by ancestral folate supplementation. In addition, 29,719 DMPs exhibit serial increases or decreases in DNA methylation levels in successive generations of untreated offspring, correlating with a serial increase in the phenotype across generations, consistent with a 'wash-in' effect. Sibship-specific DMPs annotate to genes that participate in axon- and synapse-related pathways.

Neuronal lipid droplets play a conserved and sex-biased role in maintaining whole-body energy homeostasis

Lipids are essential for neuron development and physiology. Yet, the central hubs that coordinate lipid supply and demand in neurons remain unclear. Here, we combine invertebrate and vertebrate models to establish the presence and functional significance of neuronal lipid droplets (LD) in vivo. We find that LD are normally present in neurons in a non-uniform distribution across the brain, and demonstrate triglyceride metabolism enzymes and lipid droplet-associated proteins control neuronal LD formation through both canonical and recently-discovered pathways. Appropriate LD regulation in neurons has conserved and male-biased effects on whole-body energy homeostasis across flies and mice, specifically neurons that couple environmental cues with energy homeostasis. Mechanistically, LD-derived lipids support neuron function by providing phospholipids to sustain mitochondrial and endoplasmic reticulum homeostasis. Together, our work identifies a conserved role for LD as the organelle that coordinates lipid management in neurons, with implications for our understanding of mechanisms that preserve neuronal lipid homeostasis and function in health and disease.

Effects of 1, 2-bis (2,4, 6-tribromophenoxy) ethane and bis (2-ethylhexyl) tetrabromophthalate on serum metabolic and lipid profiles in male rats

This study explored the effects of 1, 2-bis (2,4, 6-tribromophenoxy) ethane (BTBPE) and bis (2-ethylhexyl) tetrabromophthalate (TBPH) on serum metabolites and lipids in male Sprague-Dawley (SD) rats. Rats were orally gavaged 250 mg/kg bw of BTBPE and 500 mg/kg bw of TBPH for 28 consecutive days. Serum samples were collected for metabolomics and lipidomics analysis. Orthogonal partial least squares discriminant analysis (OPLS-DA) was used to explore changes in rat metabolic patterns. Least absolute shrinkage and selection operator (LASSO) regression models were established using serum levels of total thyroxine (TT4), free thyroxine (FT4), and rats' grouping information as variables to screen for robust differential substances. SuperPred was the database to obtain potential targets. The metabolomics and lipidomics results showed that BTBPE and TBPH had an impact on rat metabolic patterns, affecting pathways such as vitamin B6 synthesis. For BTBPE treatment, pyridoxal and ceramide (Cer) 24:0;4O were selected as differential substances related to thyroid hormones. For TBPH treatment, dehydroascorbic acid, acylcarnitine (CAR) 19:0, and diglyceride (DG) 38:4 were selected as differential substances related to thyroid hormones. Serotonin 2c receptor and cyclooxygenase-2 were chosen as potential targets of BTBPE and TBPH, respectively. In conclusion, this study found that BTBPE and TBPH impacted the metabolism of rats, and this effect may be related to changes in thyroid function.

DHM/SERS reveals cellular morphology and molecular changes during iPSCs-derived activation of astrocytes

The activation of astrocytes derived from induced pluripotent stem cells (iPSCs) is of great significance in neuroscience research, and it is crucial to obtain both cellular morphology and biomolecular information non-destructively in situ, which is still complicated by the traditional optical microscopy and biochemical methods such as immunofluorescence and western blot. In this study, we combined digital holographic microscopy (DHM) and surface-enhanced Raman scattering (SERS) to investigate the activation characteristics of iPSCs-derived astrocytes. It was found that the projected area of activated astrocytes decreased by 67%, while the cell dry mass increased by 23%, and the cells changed from a flat polygonal shape to an elongated star-shaped morphology. SERS analysis further revealed an increase in the intensities of protein spectral peaks (phenylalanine 1001 cm-1, proline 1043 cm-1, etc.) and lipid-related peaks (phosphatidylserine 524 cm-1, triglycerides 1264 cm-1, etc.) decreased in intensity. Principal component analysis-linear discriminant analysis (PCA-LDA) modeling based on spectral data distinguished resting and reactive astrocytes with a high accuracy of 96.5%. The increase in dry mass correlated with the increase in protein content, while the decrease in projected area indicated the adjustment of lipid composition and cell membrane remodeling. Importantly, the results not only reveal the cellular morphology and molecular changes during iPSCs-derived astrocytes activation but also reflect their mapping relationship, thereby providing new insights into diagnosing and treating neurodegenerative diseases.

Molecular cartography within axons

Recent advances in imaging methods begin to further illuminate the inner workings of neurons. Views of the axonal landscape through the lens of in situ cryo-electron tomography (cryo-ET) provide a high-resolution atlas of the macromolecular organization in near-native conditions, leading to our growing understanding of the vital roles of compositional and structural organization in maintaining neuronal homeostasis. In this review, we discuss the latest observations concerning the fundamental components found within neuronal compartments, with special emphasis on the axon, branch points, and growth cone. We describe the similarity and difference in organization of organelles and molecules in varying compartments. Finally, we highlight outstanding questions on the dynamics and localization of various components along the axon that may be answered using orthogonal approaches.

Dynamic changes in endoplasmic reticulum morphology and its contact with the plasma membrane in motor neurons in response to nerve injury

The endoplasmic reticulum (ER) extends throughout a cell and plays a critical role in maintaining cellular homeostasis. Changes in ER shape could provide a clue to explore the mechanisms that underlie the fate determination of neurons after axon injury because the ER drastically changes its morphology under neuronal stress to maintain cellular homeostasis and recover from damage. Because of their tiny structures and richness in the soma, the detailed morphology of the ER and its dynamics have not been well analysed. In this study, the focused ion beam/scanning electron microscopy (FIB/SEM) analysis was performed to explore the ultra-structures of the ER in the somata of motor neuron with axon regenerative injury models. In normal motor neurons, ER in the somata is abundantly localised near the perinucleus and represents lamella-like structures. After injury, analysis of the ER volume and ER branching points indicated a collapse of the normal distribution and a transformation from lamella-like structures to mesh-like structures. Furthermore, accompanied by ER accumulation near the plasma membrane (PM), the contact between the ER and PM (ER-PM contacts) significantly increased after injury. The accumulation of extended-synaptotagmin 1 (E-Syt1), a tethering protein of the ER and PM that regulates Ca2+-dependent lipid transfer, was also identified by immunohistochemistry and quantitative Real-time PCR after injury. These morphological alterations of ER and the increase in ER-PM contacts may be crucial events that occur in motor neurons as a resilient response for the survival after axonal injury.

Cerebrospinal fluid neutral lipids predict progression from mild cognitive impairment to Alzheimer's disease

Genetic, metabolic, and clinical evidence links lipid dysregulation to an increased risk of Alzheimer's disease (AD). However, the role of lipids in the pathophysiological processes of AD and its clinical progression is unclear. We investigated the association between cerebrospinal fluid (CSF) lipidome and the pathological hallmarks of AD, progression from mild cognitive impairment (MCI) to AD, and the rate of cognitive decline in MCI patients. The CSF lipidome was analyzed by liquid chromatography coupled to mass spectrometry in an LC-ESI-QTOF-MS/MS platform for 209 participants: 91 AD, 92 MCI, and 26 control participants. The MCI patients were followed up for a median of 58 (± 12.5) months to evaluate their clinical progression to AD. Forty-eight (52.2%) MCI patients progressed to AD during follow-up. We found that higher CSF levels of hexacosanoic acid and ceramide Cer(d38:4) were associated with an increased risk of amyloid beta 42 (Aβ42) positivity in CSF, while levels of phosphatidylethanolamine PE(40:0) were associated with a reduced risk. Higher CSF levels of sphingomyelin SM(30:1) were positively associated with pathological levels of phosphorylated tau in CSF. Cholesteryl ester CE(11D3:1) and an unknown lipid were recognized as the most associated lipid species with MCI to AD progression. Furthermore, TG(O-52:2) was identified as the lipid most strongly associated with the rate of progression. Our results indicate the involvement of membrane and intracellular neutral lipids in the pathophysiological processes of AD and the progression from MCI to AD dementia. Therefore, CSF neutral lipids can be used as potential prognostic markers for AD.

LIPUS-induced neurogenesis:A potential therapeutic strategy for cognitive dysfunction in traumatic brain injury

Traumatic brain injury (TBI) precipitates cellular membrane degeneration, phospholipid degradation, neuronal demise, impaired brain electrical activity, and compromised neuroplasticity, ultimately leading to acute and chronic brain dysfunction. Low-intensity pulsed ultrasound (LIPUS) is an emerging brain therapy with the characteristics of non-invasive, high spatial resolution, and high stimulation depth. Herein, we established a controlled cortical impact model to investigate the potential reparative mechanisms of LIPUS in TBI, employing a multi-faceted research methodology encompassing behavioral assessments, immunofluorescence, neuroelectrophysiology, scratch detection of primary cortical neurons, metabolomics and transcriptomics. Our findings demonstrate that LIPUS promotes hippocampal neurogenesis following brain injury, accomplished through the elevation of phosphatidylcholine levels in the hippocampus of TBI mice. Consequently, LIPUS enhances neural electrical activity and augments neural plasticity within the CA1 subregion of the hippocampus, effectively restoring neuronal function and cognitive capabilities in TBI mice. These findings shed light on the promising role of LIPUS in TBI brain rehabilitation, offering new perspectives and theoretical foundations for future studies in this domain.

A CRISPR-Cas9-mediated F0 screen to identify pro-regenerative genes in the zebrafish retinal pigment epithelium

Ocular diseases resulting in death of the retinal pigment epithelium (RPE) lead to vision loss and blindness. There are currently no FDA-approved strategies to restore damaged RPE cells. Stimulating intrinsic regenerative responses within damaged tissues has gained traction as a possible mechanism for tissue repair. Zebrafish possess remarkable regenerative abilities, including within the RPE; however, our understanding of the underlying mechanisms remains limited. Here, we conducted an F0 in vivo CRISPR-Cas9-mediated screen of 27 candidate RPE regeneration genes. The screen involved injection of a ribonucleoprotein complex containing three highly mutagenic guide RNAs per target gene followed by PCR-based genotyping to identify large intragenic deletions and MATLAB-based automated quantification of RPE regeneration. Through this F0 screening pipeline, eight positive and seven negative regulators of RPE regeneration were identified. Further characterization of one candidate, cldn7b, revealed novel roles in regulating macrophage/microglia infiltration after RPE injury and in clearing RPE/pigment debris during late-phase RPE regeneration. Taken together, these data support the utility of targeted F0 screens for validating pro-regenerative factors and reveal novel factors that could regulate regenerative responses within the zebrafish RPE.

Erythrocyte Plasma Membrane Lipid Composition Mirrors That of Neurons and Glial Cells in Murine Experimental In Vitro and In Vivo Inflammation

Lipid membrane turnover and myelin repair play a central role in diseases and lesions of the central nervous system (CNS). The aim of the present study was to analyze lipid composition changes due to inflammatory conditions. We measured the fatty acid (FA) composition in erythrocytes (RBCs) and spinal cord tissue (gas chromatography) derived from mice affected by experimental allergic encephalomyelitis (EAE) in acute and remission phases; cholesterol membrane content (Filipin) and GM1 membrane assembly (CT-B) in EAE mouse RBCs, and in cultured neurons, oligodendroglial cells and macrophages exposed to inflammatory challenges. During the EAE acute phase, the RBC membrane showed a reduction in polyunsaturated FAs (PUFAs) and an increase in saturated FAs (SFAs) and the omega-6/omega-3 ratios, followed by a restoration to control levels in the remission phase in parallel with an increase in monounsaturated fatty acid residues. A decrease in PUFAs was also shown in the spinal cord. CT-B staining decreased and Filipin staining increased in RBCs during acute EAE, as well as in cultured macrophages, neurons and oligodendrocyte precursor cells exposed to inflammatory challenges. This regulation in lipid content suggests an increased cell membrane rigidity during the inflammatory phase of EAE and supports the investigation of peripheral cell membrane lipids as possible biomarkers for CNS lipid membrane concentration and assembly.

In Vitro Diagnosis and Visualization of Cerebral Ischemia/Reperfusion Injury in Rats and Protective Effects of Ferulic Acid by Raman Biospectroscopy and Machine Learning

Ischemic stroke is a major cause of mortality with complicated pathophysiological mechanisms, and hematoxylin and eosin (HE) staining is a histochemical diagnosis technique heavily relying on subjective observation. In this study, we developed a noninvasive assay using Raman spectroscopy for in vitro diagnosis and visualization of cerebral ischemia/reperfusion injury and protective effects of ferulic acid. By establishing a middle cerebral artery occlusion (MCAO) model in Sprague-Dawley male rats, we found effective interventions by ferulic acid using the neurological function score and HE staining. Raman spectra of neuronal and neuroglial cells exhibited significant intensity changes of protein, nucleotide, lipid, and carbohydrate at 780, 814, 1002, 1012, 1176, 1224, 1402, 1520, 1586, 1614, and 1752 cm^-1. Cluster vector analysis highlighted the alterations at 1002, 1080, 1298, 1430, 1478, 1508, 1586, and 1676 cm^-1. To evaluate the levels of neuron injury and intervention performance, a random forest model was developed on Raman spectral data and achieved satisfactory accuracy (0.9846), sensitivity (0.9679-0.9932), and specificity (0.9945-0.9989), ranking peaks around 1002 cm^-1 as key fingerprint for classification. Spectral phenylalanine-to-tryptophan ratio was the biomarker to visualize neuronal injury and intervention performance of ferulic acid with a resolution of 1 μm. Our results unravel the biochemical changes in neuronal cells with cerebral ischemia/reperfusion injury and ferulic acid treatment, and prove Raman spectroscopy coupled with machine learning as a power tool to classify neuron viability and evaluate the intervention performance in pharmacological research.

Chemical Exchange Saturation Transfer Magnetic Resonance Imaging for Longitudinal Assessment of Intracerebral Hemorrhage and Deferoxamine Treatment at 3T in a Mouse Model

BACKGROUND

Noninvasive imaging of molecular alterations after intracerebral hemorrhage (ICH) could provide valuable information to guide and monitor treatments. Chemical exchange saturation transfer (CEST) magnetic resonance imaging has demonstrated promises in identifying proliferation, necrosis, and changes in cellularity in brain tumors. Here, we applied CEST magnetic resonance imaging to monitor molecular changes in hematoma without and with treatment noninvasively over 2 weeks at 3T using endogenous contrast.

METHODS

CEST contrast related to proteins at 3.5 ppm (amide proton transfer) and proteins/lipids at -3.5 ppm (relayed nuclear overhauser effect [rNOE]) were examined over 14 days in a collagenase-induced ICH mouse model. Imaging findings were validated with immunohistochemistry based on the ICH neuropathology. We also examined iron-containing phantoms that mimicked iron concentrations in hematoma to ensure the iron will not attenuate the CEST contrast during disease progression. Based on the validity of the CEST contrast of hematoma, we further examined related molecular alterations under iron-chelation treatment with deferoxamine.

RESULTS

We observed the temporal and spatial differences of CEST contrasts between rNOE at -3.5 ppm and amide proton transfer at 3.5 ppm, in which the core and perihematoma could be identified by rNOE on day 3 and day 14, and amide proton transfer on day 1, day 7, and day 14. Moreover, we observed a 25.7% significant reduction (P<0.05) of rNOE contrast after deferoxamine treatment to the ICH mice on day 3, which was not observable in amide proton transfer contrast. Our histology data indicated that rNOE primarily correlated with the myelin pathology, and amide proton transfer could reflect the cellularity increase at hematoma up to day 7.

CONCLUSIONS

Significant rNOE changes correlated well with histologic findings, especially myelin lipids, and regional characteristics in hematoma indicate the uniqueness of CEST magnetic resonance imaging in monitoring molecular changes during ICH and treatment.

Oxidative Stress and Lipid Accumulation Augments Cell Death in LDLR-Deficient RPE Cells and Ldlr-/- Mice

Lipid peroxidation from oxidative stress is considered a major contributor to age-related macular degeneration (AMD). The retina is abundant with circulating low-density lipoproteins (LDL), which are taken up by LDL receptor (LDLR) in the RPE and Müller cells. The purpose of this study is to investigate the role of LDLR in the NaIO3-induced model of dry AMD. Confluent primary human RPE (hRPE) and LDLR-silenced ARPE-19 cells were stressed with 150 µM tert-butyl hydroperoxide (tBH) and caspase 3/7 activation was determined. WT and Ldlr-/- mice were administered NaIO3 (20 mg/kg) intravenously. On day 7, fundus imaging, OCT, ERG, and retinal thickness were measured. Histology, TUNEL, cleaved caspase 3 and lipid accumulation were assessed. Treatment of hRPE with tBH markedly decreased LDLR expression. Caspase 3/7 activation was significantly increased in LDLR-silenced ARPE-19 cells treated with tBH. In Ldlr-/- mice, NaIO3 administration resulted in significant (a) retinal thinning, (b) compromised photoreceptor function, (c) increased percentage of cleaved caspase 3 positive and apoptotic cells, and (d) increased lipid droplet accumulation in the RPE, Bruch membrane, choroid, and sclera, compared to WT mice. Our findings imply that LDLR loss leads to lipid accumulation and impaired retinal function, which may contribute to the development of AMD.

Protocol for assessing ex vivo lipolysis of murine adipose tissue

Here, we provide a detailed protocol for assessing exvivo lipolysis of subcutaneous and visceral white adipose tissue. We describe a robust approach to detect depot-specific changes in lipolytic potential under basal and beta-adrenergic receptor-stimulated conditions. Given that adipose tissue plays a critical role in systemic metabolic health, this experimental protocol can be used to determine changes in adipose tissue function in health and disease.

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Detailed protocol to quantitatively measure exvivo adipose tissue lipolysis in mice

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Steps to dissect adipose tissue and detect glycerol and fatty acids

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Measures adipose tissue function under normal and disease/trauma conditions

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Mass Spectrometry Imaging of Lipids in the Scent Glands of Muskrat (Ondatra zibethicus) in Different Reproductive Statuses

As a typical seasonal breeding animal, male muskrats have a pair of scent glands that can emit musky odor substances to attract females during the breeding period. The present study aimed to visualize the differences in the distribution of lipids in the scent glands of muskrats during their different reproductive statuses by imaging mass spectrometry and quantitative real-time PCR (qRT-PCR). The results revealed remarkable differences in the expression and spatial distribution of lipids detected in the scent glands of muskrats during the different reproductive statuses. In addition, the expression levels of lipid molecules PC (32:0) and LysoPC (16:0) were found to be significantly higher in the breeding season than in the non-breeding season. Moreover, the mRNA expression levels of lipid synthesis enzyme Pemt and Pla2g4b were higher in the breeding season than in the non-breeding season, and there were positive correlations between the expression intensities of lipid molecules and the expression levels of Pemt and Pla2g4b. The present study investigates the changes and distribution of the endogenous lipid in the scent glands of muskrats and elucidates that the seasonal changes in the lipid metabolism may affect the functions of the scent glands in muskrats.

Functions of Stress-Induced Lipid Droplets in the Nervous System

Lipid droplets are highly dynamic intracellular organelles that store neutral lipids such as cholesteryl esters and triacylglycerols. They have recently emerged as key stress response components in many different cell types. Lipid droplets in the nervous system are mostly observed in vivo in glia, ependymal cells and microglia. They tend to become more numerous in these cell types and can also form in neurons as a consequence of ageing or stresses involving redox imbalance and lipotoxicity. Abundant lipid droplets are also a characteristic feature of several neurodegenerative diseases. In this minireview, we take a cell-type perspective on recent advances in our understanding of lipid droplet metabolism in glia, neurons and neural stem cells during health and disease. We highlight that a given lipid droplet subfunction, such as triacylglycerol lipolysis, can be physiologically beneficial or harmful to the functions of the nervous system depending upon cellular context. The mechanistic understanding of context-dependent lipid droplet functions in the nervous system is progressing apace, aided by new technologies for probing the lipid droplet proteome and lipidome with single-cell type precision.

Role of the endoplasmic reticulum in synaptic transmission

Neurons possess a complex morphology spanning long distances and a large number of subcellular specializations such as presynaptic terminals and dendritic spines. This structural complexity is essential for maintenance of synaptic junctions and associated electrical as well as biochemical signaling events. Given the structural and functional complexity of neurons, neuronal endoplasmic reticulum is emerging as a key regulator of neuronal function, in particular synaptic signaling. Neuronal endoplasmic reticulum mediates calcium signaling, calcium and lipid homeostasis, vesicular trafficking, and proteostasis events that underlie autonomous functions of numerous subcellular compartments. However, based on its geometric complexity spanning the whole neuron, endoplasmic reticulum also integrates the activity of these autonomous compartments across the neuron and coordinates their interactions with the soma. In this article, we review recent work regarding neuronal endoplasmic reticulum function and its relationship to neurotransmission and plasticity.

A Brief Analysis of Proteomic Profile Changes during Zebrafish Regeneration

Unlike mammals, zebrafish are capable to regenerate many of their organs, however, the response of tissue damage varies across tissues. Understanding the molecular mechanism behind the robust regenerative capacity in a model organism may help to identify and develop novel treatment strategies for mammals (including humans). Hence, we systematically analyzed the current literature on the proteome profile collected from different regenerated zebrafish tissues. Our analyses underlining that several proteins and protein families responsible as a component of cytoskeleton and structure, protein synthesis and degradation, cell cycle control, and energy metabolism were frequently identified. Moreover, target proteins responsible for the initiation of the regeneration process, such as inflammation and immune response were less frequently detected. This highlights the limitation of previous proteomic analysis and suggested a more sensitive modern proteomics analysis is needed to unfold the mechanism. This brief report provides a list of target proteins with predicted functions that could be useful for further biological studies.