Neuronal Homeostasis Research Articles

GM1 Oligosaccharide Ameliorates Rett Syndrome Phenotypes In Vitro and In Vivo via Trk Receptor Activation

Rett syndrome (RTT) is a severe neurodevelopmental disorder primarily caused by mutations in the methyl-CpG binding protein 2 (MECP2) gene. Despite advancements in research, no cure exists due to an incomplete understanding of the molecular effects of MeCP2 deficiency. Previous studies have identified impaired tropomyosin receptor kinase (Trk) neurotrophin (NTP) signaling and mitochondrial redox imbalances as key drivers of the pathology. Moreover, altered glycosphingolipid metabolism has been reported in RTT. GM1 ganglioside is a known regulator of the nervous system, and growing evidence indicates its importance in maintaining neuronal homeostasis via its oligosaccharide chain, coded as GM1-OS. GM1-OS directly interacts with the Trk receptors on the cell surface, triggering neurotrophic and neuroprotective pathways in neurons. In this study, we demonstrate that GM1-OS ameliorates RTT deficits in the Mecp2-null model. GM1-OS restored synaptogenesis and reduced mitochondrial oxidative stress of Mecp2-knock-out (ko) cortical neurons. When administered in vivo, GM1-OS mitigated RTT-like symptoms. Our findings indicate that GM1-OS effects were mediated by Trk receptor activation on the neuron’s plasma membrane. Overall, our results highlight GM1-OS as a promising candidate for RTT treatment.

Accumulation of F-actin drives brain aging and limits healthspan in Drosophila

The actin cytoskeleton is a key determinant of cell structure and homeostasis. However, possible tissue-specific changes to actin dynamics during aging, notably brain aging, are not understood. Here, we show that there is an age-related increase in filamentous actin (F-actin) in Drosophila brains, which is counteracted by prolongevity interventions. Critically, decreasing F-actin levels in aging neurons prevents age-onset cognitive decline and extends organismal healthspan. Mechanistically, we show that autophagy, a recycling process required for neuronal homeostasis, is disabled upon actin dysregulation in the aged brain. Remarkably, disrupting actin polymerization in aged animals with cytoskeletal drugs restores brain autophagy to youthful levels and reverses cellular hallmarks of brain aging. Finally, reducing F-actin levels in aging neurons slows brain aging and promotes healthspan in an autophagy-dependent manner. Our data identify excess actin polymerization as a hallmark of brain aging, which can be targeted to reverse brain aging phenotypes and prolong healthspan.

Modulation of autophagy by melatonin and its receptors: implications in brain disorders.

Autophagy plays a crucial role in maintaining neuronal homeostasis and function, and its disruption is linked to various brain diseases. Melatonin, an endogenous hormone that primarily acts through MT1 and MT2 receptors, regulates autophagy via multiple pathways. Growing evidence indicates that melatonin's ability to modulate autophagy provides therapeutic and preventive benefits in brain disorders, including neurodegenerative and affective diseases. In this review, we summarize the key mechanisms by which melatonin affects autophagy and explore its therapeutic potential in the treatment of brain disorders.

DTD1 modulates synaptic efficacy by maintaining D-serine and D-aspartate homeostasis.

D-serine and D-aspartate are involved in N-methyl-D-aspartate receptor (NMDAR)-related physiological and pathological processes. D-aminoacyl-tRNA deacylase 1 (DTD1) may biochemically contribute to D-serine or D-aspartate production. However, it is unclear thus far whether DTD1 regulates D-serine or D-aspartate content in neurobiological processes. In the present research, we found that DTD1 was essential to maintain the D-serine or D-aspartate homeostasis, which was consistent with the phenomenon that DTD1-deficiency resulted in changes in the quantity changes of functional NMDAR subunits in postsynaptic compartments. Moreover, DTD1 played a considerable role in regulating dendritic morphology and synaptic structure. As a consequence, DTD1 affected neurobiological events, including the synaptic strength of the CA3-to-CA1 circuit, dendritic spine density of hippocampal pyramidal neurons, and behavioral performance of mice in the Morris water maze. These findings highlight the important role of DTD1 in synaptic transmission, neuronal morphology, and spatial learning and memory and suggest an undisclosed mechanism of DTD1 that participates the regulation of D-serine or D-aspartate homeostasis in hippocampal neurons.

Manipulation of DHPS activity affects dendritic morphology and expression of synaptic proteins in primary rat cortical neurons.

Deoxyhypusine synthase (DHPS) catalyzes the initial step of hypusine incorporation into the eukaryotic initiation factor 5A (eIF5A), leading to its activation. The activated eIF5A, in turn, plays a key role in regulating the protein translation of selected mRNAs and therefore appears to be a suitable target for therapeutic intervention strategies. In the present study, we analyzed the role of DHPS-mediated hypusination in regulating neuronal homeostasis using lentivirus-based gain and loss of function experiments in primary cortical cultures from rats. This model allows us to examine the impact of DHPS function on the composition of the dendritic and synaptic compartments, which may contribute to a better understanding of cognitive function and neurodevelopment in vivo. Our findings revealed that shRNA-mediated DHPS knockdown diminishes the amount of hypusinated eIF5A (eIF5AHyp), resulting in notable alterations in neuronal dendritic architecture. Furthermore, in neurons, the synaptic composition was also affected, showing both pre- and post-synaptic changes, while the overexpression of DHPS had only a minor impact. Therefore, we hypothesize that interfering with the eIF5A hypusination caused by reduced DHPS activity impairs neuronal and synaptic homeostasis.

Unraveling autophagic imbalances and therapeutic insights in Mecp2-deficient models.

Loss-of-function mutations in MECP2 are associated to Rett syndrome (RTT), a severe neurodevelopmental disease. Mainly working as a transcriptional regulator, MeCP2 absence leads to gene expression perturbations resulting in deficits of synaptic function and neuronal activity. In addition, RTT patients and mouse models suffer from a complex metabolic syndrome, suggesting that related cellular pathways might contribute to neuropathogenesis. Along this line, autophagy is critical in sustaining developing neuron homeostasis by breaking down dysfunctional proteins, lipids, and organelles.Here, we investigated the autophagic pathway in RTT and found reduced content of autophagic vacuoles in Mecp2 knock-out neurons. This correlates with defective lipidation of LC3B, probably caused by a deficiency of the autophagic membrane lipid phosphatidylethanolamine. The administration of the autophagy inducer trehalose recovers LC3B lipidation, autophagosomes content in knock-out neurons, and ameliorates their morphology, neuronal activity and synaptic ultrastructure. Moreover, we provide evidence for attenuation of motor and exploratory impairment in Mecp2 knock-out mice upon trehalose administration. Overall, our findings open new perspectives for neurodevelopmental disorders therapies based on the concept of autophagy modulation.

Dysregulation of protein SUMOylation networks in Huntington's disease R6/2 mouse striatum.

Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded CAG repeat mutation in the Huntingtin (HTT) gene. The mutation impacts neuronal protein homeostasis and cortical/striatal circuitry. SUMOylation is a post-translational modification with broad cellular effects including via modification of synaptic proteins. Here, we used an optimised SUMO protein-enrichment and mass spectrometry method to identify the protein SUMOylation/SUMO interaction proteome in the context of HD using R6/2 transgenic and non-transgenic (NT) mice. Significant changes in enrichment of SUMOylated and SUMO-interacting proteins were observed, including those involved in presynaptic function, cytomatrix at the active zone scaffolding, cytoskeleton organization, and glutamatergic signaling. Mitochondrial and RNA-binding proteins also showed altered enrichment. Modified SUMO-associated pathways in HD tissue include clathrin-mediated endocytosis signaling, synaptogenesis signaling, synaptic long-term potentiation, and SNARE signaling. To evaluate how modulation of SUMOylation might influence functional measures of neuronal activity in HD cells in vitro, we utilised primary neuronal cultures from R6/2 and NT mice. A receptor internalization assay for the metabotropic glutamate receptor 7 (mGLUR7), a SUMO enriched protein in the mass spec, showed decreased internalization in R6/2 neurons compared to NT. siRNA-mediated knockdown of the E3 SUMO ligase Protein Inhibitor of Activated STAT1 (Pias1), which can SUMO modify mGLUR7, prevented this HD phenotype. In addition, microelectrode array analysis of primary neuronal cultures indicated early hyperactivity in HD cells, while later timepoints demonstrated deficits in several measurements of neuronal activity within cortical neurons. HD phenotypes were rescued at selected timepoints following knockdown of Pias1. Collectively, our results provide a mouse brain SUMOome resource and show that significant alterations occur within the post-translational landscape of SUMO-protein interactions of synaptic proteins in HD mice, suggesting that targeting of synaptic SUMO networks may provide a proteostatic systems-based therapeutic approach for HD and other neurological. Disorders.

Jujuboside A Regulates Calcium Homeostasis and Structural Plasticity to Alleviate Depression-Like Behavior via Shh Signaling in Immature Neurons.

Depression, a leading cause of disability worldwide, is characterized by dysfunction of immature neurons, resulting in dysregulated calcium homeostasis and impaired structural plasticity. Jujuboside A (JuA), a biologically active compound derived from Semen Ziziphi Spinosae, has demonstrated anti-anxiety and anti-insomnia properties. Recent studies suggest that JuA may be a promising antidepressant, but its underlying mechanisms remain unclear. Sprague-Dawley rats were subjected to chronic unpredictable mild stress (CUMS) to induce a depression model. JuA (12.5 mg/kg, 25 mg/kg, 50 mg/kg) was administered orally for 4weeks. Emotional and cognitive function were assessed. Monoamine neurotransmitter levels were measured using enzyme-linked immunosorbent assay (ELISA). The number of immature neurons and calcium homeostasis were evaluated by immunofluorescence. Western blotting and immunofluorescence were employed to detect the expression of Sonic hedgehog (Shh) signaling proteins. Additionally, lentiviral vector expressing Shh shRNA (LV-Shh-RNAi) were infused intracerebrally to investigate the role of Shh in JuA's antidepressant effects. JuA significantly ameliorated depressive-like behavior and cognitive dysfunction in CUMS rats, increased monoamine neurotransmitter levels in serum and hippocampal tissue, reduced the number of BrdU/DCX (bromodeoxyuridine/doublecortin)-positive immature neurons, and attenuated calcium ion (Ca2+) concentration and Ca2+/calmodulin-dependent protein kinase II (CaMKII) levels in immature neurons. JuA also markedly elevated synaptic density and prominence complexity, upregulated Shh, Gli family zinc finger 1 and 2 (Gli1/2), synaptophysin (Syn) and postsynaptic density protein-95 (PSD-95) expression in the ventral dentate gyrus (vDG). However, knockdown of Shh in the vDG counteracted JuA's therapeutic effects. These findings collectively suggest that JuA improves depressive-like behavior in CUMS rats by modulating calcium homeostasis and synaptic structural plasticity in immature neurons through the Shh signaling pathway.

Kaixinsan regulates neuronal mitochondrial homeostasis to improve the cognitive function of Alzheimer's disease by activating CaMKKβ-AMPK-PGC-1α signaling axis

BackgroundAlzheimer's disease (AD) is a neurodegenerative disease primarily characterized by cognitive impairments. With the intensification of population aging, AD has become a major health issue faced by the elderly. Kaixinsan, a classical traditional Chinese prescription consists of Panax ginseng C. A. Mey., Polygala tenuifolia Willd., Poria cocos (Schw.) Wolf and Acori Tatarinowii rhizoma, is commonly used in clinical for treating memory decline. However, its mechanism remains unclear, which hinders its popularization and application. MethodMorris water maze (MWM) was performed to evaluate the effect of Kaixinsan on improving learning and memory ability in SAMP8 (senescence-accelerated mouse prone 8, an AD model mice) mice. Nissl staining, TdT-mediated dUTP Nick End Labeling (TUNEL) and western blotting (Bax and Bcl-2) were used to confirm the effect of Kaixinsan on the neuronal structure and apoptosis of SAMP8 mice. ultra performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) was performed to identify the distribution components of the brain tissue after receiving Kaixinsan extraction. Based on the identified brain distribution components, the mechanism of Kaixinsan improving the cognitive function was predicted by network pharmacology. Then, using HSP60 as mitochondrial marker and RBFOX3 as neuron marker, immunofluorescence co-localization was used to confirm the effect of Kaixinsan on neuronal mitochondria quantity in SAMP8 mice. Using western blotting to detect the expression of predicted proteins (AMPK, CaMKKβ, PGC-1α and HSP90) affecting mitochondrial homeostasis. To further confirm the mechanism of Kaixinsa. The authors replicated SH-SY5Y cell injury model induced by Amyloid β - protein fragment 25-35 (Aβ25-35) and compared the effects of serum containing Kaixinsan on apoptosis of injured SH-SY5Y cells (detected by flow cytometer) and the expression level of apoptosis-associated protein (Bax and Bcl-2) and mitochondrial homeostasis related proteins (AMPK, CaMKKβ, PGC-1α and HSP90), with or without the addition of CaMKKβ inhibitor (STO-609). ResultsThe results indicate that Kaixinsan can improve the cognitive function of SAMP8 mice, alleviate the hippocampal tissue lesions and inhibit neuron apoptosis. Seventeen brain distribution components of Kaixinsan were identified. Based on the brain distribution components of Kaixinsan, the results of network pharmacology suggest that Kaixinsan may regulate mitochondrial homeostasis through the CaMKKβ-AMPK-PGC-1α signaling axis. In vivo experiments, The authors observed that Kaixinsan could reverse neuronal mitochondrial loss in SAMP8 mice by upregulating CaMKKβ, AMPK, HSP90 and PGC-1α to promote mitochondrial biogenesis and increase the number of neuronal mitochondria. Additionally, the in vitro experiments demonstrated that Kaixinsan can inhibit apoptosis of Aβ25-35 injured SH-SY5Y cells and upregulate mitochondrial homeostasis-related proteins CaMKKβ, AMPK and PGC-1α. However, in addition to CaMKKβ inhibitors, the neuroprotective effect disappeared. ConclusionThe results indicate that Kaixinsan can improve the cognitive function of SAMP8 mice by regulating CaMKKβ-AMPK-PGC-1α signaling axis to maintain mitochondrial homeostasis and inhibit neuronal apoptosis.

Neuroimmune Interactions in Stress and Depression: Exploring the Molecular and Cellular Mechanisms within the Neuroinflammation-depression Nexus.

The escalating global burden of stress and depression underscores an urgent need to unravel their complex interrelationships and underlying mechanisms. This investigation delves into the intricate dynamics between stress and depression, spotlighting the Neuroimmunoinflammatory Stress Model (NIIS), which elucidates the pivotal role of cellular and molecular pathways in mediating these conditions. Through an exhaustive review of literature spanning epidemiology, neurobiology, and psychoneuroimmunology, this study synthesizes the current understanding of stress and depression. It accentuates the definitional scopes, interplay, and intricacies of the NIIS model, which integrates neuroimmune-inflammatory responses into the conceptual framework of the stress-depression interaction. By identifying stress as a multifactorial reaction to perceived adversities and depression as a manifestation of prolonged stress exposure, our analysis foregrounds the NIIS model. This paradigmatic model reveals the transition from normal stress responses to pathological neuroinflammatory pathways, highlighting neurotransmitter imbalances, disruptions in neuronal and glial homeostasis, and ensuing low-grade neuroinflammation as key factors in the pathogenesis of depression under chronic stress conditions. The NIIS model identifies prolonged cellular pro-inflammatory stress of neurons and microglia as a fundamental pathological subsystem of many neuropsychiatric disorders. In turn, neuroinflammation and associated neurodegenerative processes are complications of chronic psychoemotional stress, which can clinically manifest as depression. The NIIS model views depression as the terminal stage of chronic stress, pathogenetically linked to latent neuroinflammation. This insight not only advances our understanding of their etiopathogenesis but also paves the way for developing precise therapeutic interventions.

Nilotinib as a Prospective Treatment for Alzheimer's Disease: Effect on Proteins Involved in Neurodegeneration and Neuronal Homeostasis.

Nilotinib, a tyrosine kinase inhibitor that targets the Abelson tyrosine kinase (c-Abl) signaling pathway, is FDA-approved to treat chronic myeloid leukemia. Nilotinib has properties indicative of a possible utility in neuroprotection that have prompted exploration of repurposing the drug for the treatment of Alzheimer's disease (AD) and Parkinson's disease (PD). AD is a progressive age-related neurodegenerative disorder characterized by the deposition of extracellular amyloid-β plaques and intracellular neurofibrillary tangles. It is incurable and affects approximately 50 million patients worldwide. Nilotinib reduces c-Abl phosphorylation, amyloid-β levels, and dopaminergic neuron degeneration in preclinical AD models. This study explores the effects of nilotinib on amyloid processing and mitochondrial functioning in the SH-SY5Y human neuroblastoma cell line. SH-SY5Y cells were exposed to nilotinib (1, 5, and 10 µM). Real-time PCR and immunoblot analysis were performed to quantify the expression of genes pertaining to amyloid-β processing and neuronal health. Nilotinib did not significantly change APP, BACE1, or ADAM10 mRNA levels. However, BACE1 protein was significantly increased at 1 µM, and ADAM10 was increased at 10 µM nilotinib without affecting APP protein expression. Further, nilotinib treatment did not affect the expression of genes associated with neuronal health and mitochondrial functioning. Taken together, our findings do not support the efficacy of nilotinib treatment for neuroprotection.

Neuroprotective effects of magnesium: implications for neuroinflammation and cognitive decline.

Neurodegenerative diseases, which are characterized by progressive neuronal loss and cognitive decline, are a significant concern for the aging population. Neuroinflammation, a shared characteristic of these diseases, is implicated in their pathogenesis. This article briefly summarizes the role of magnesium, an essential mineral involved in numerous enzymatic reactions and critical for neuronal bioactivity, in the context of neuroinflammation and cognitive decline. The potential neuroprotective effects of magnesium, including the mechanisms of neuroprotection by magnesium through maintaining neuronal ion homeostasis, reducing inflammation, and preventing excitotoxicity, are also described. Additionally, we discuss the impact of inadequate magnesium on neuroinflammation and its potential as a therapeutic agent for attenuating cognitive decline to improve neurodegenerative conditions.

Vanillin Mitigates the MPTP-Induced α-Synucleinopathy in a Mouse Model of Parkinson's Disease: Insights into the Involvement of Wnt/β-Catenin Signaling.

The abnormal aggregation of α-synuclein (α-syn) in the substantia nigra pars compacta (SNpc) region of the brain is characteristic of Parkinson's disease (PD), leading to the selective demise of neurons. Modifications in the post-translational processing of α-syn, phosphorylation at Ser129 in particular, are implicated in α-syn aggregation and are considered key hallmarks of PD. Furthermore, dysregulated Wnt/β-catenin signaling, influenced by glycogen synthase kinase-3 beta (GSK-3β), is implicated in PD pathogenesis. Inhibition of GSK-3β holds promise in promoting neuroprotection by enhancing the Wnt/β-catenin pathway. In our previous study utilizing 1-methyl-4-phenylpyridinium (MPP+)-administered differentiated SH-SY5Y cells and a PD mouse model, we explored Vanillin's neuroprotective properties and related mechanisms against neuronal loss induced by MPP+/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. In the current study, we elucidated the mitigating effects of Vanillin on motor impairments, P-Ser129-α-syn expression, Wnt/β-catenin signaling, and autophagic neuron death induced by MPTP in a mouse model of PD by performing motor function tests, western blot analysis and immunostaining. Our results show that Vanillin effectively modulated the motor dysfunctions, GSK-3β expression, and activity, activated the Wnt/β-catenin signaling, and reduced autophagic neuronal demise in the MPTP-lesioned mice, highlighting its neuroprotective effects. These findings underscore the complex interplay between α-syn pathology, GSK-3β, Wnt/β-catenin signaling, and autophagic-cell death in PD pathogenesis. Targeting these pathways, particularly with Vanillin, can be a promising therapeutic strategy for restoring dopaminergic (DA-ergic) neuronal homeostasis and slowing the progression of PD. Further research is crucial to resolving existing disputes and translating these discoveries into effective therapeutic interventions for PD patients.

Evaluation of altered cell-cell communication between glia and neurons in the hippocampus of 3xTg-AD mice at two time points.

Alzheimer's disease (AD) is the most common form of dementia and is characterized by progressive memory loss and cognitive decline, affecting behavior, speech, and motor abilities. The neuropathology of AD includes the formation of extracellular amyloid-β plaque and intracellular neurofibrillary tangles of phosphorylated tau, along with neuronal loss. While neuronal loss is an AD hallmark, cell-cell communication between neuronal and non-neuronal cell populations maintains neuronal health and brain homeostasis. To study changes in cellcell communication during disease progression, we performed snRNA-sequencing of the hippocampus from female 3xTg-AD and wild-type littermates at 6 and 12 months. We inferred differential cell-cell communication between 3xTg-AD and wild-type mice across time points and between senders (astrocytes, microglia, oligodendrocytes, and OPCs) and receivers (excitatory and inhibitory neurons) of interest. We also assessed the downstream effects of altered glia-neuron communication using pseudobulk differential gene expression, functional enrichment, and gene regulatory analyses. We found that glia-neuron communication is increasingly dysregulated in 12-month 3xTg-AD mice. We also identified 23 AD-associated ligand-receptor pairs that are upregulated in the 12-month-old 3xTg-AD hippocampus. Our results suggest increased AD association of interactions originating from microglia. Signaling mediators were not significantly differentially expressed but showed altered gene regulation and TF activity. Our findings indicate that altered glia-neuron communication is increasingly dysregulated and affects the gene regulatory mechanisms in neurons of 12-month-old 3xTg-AD mice.

CRTC1 in Mc4r-expressing cells is required for peripheral metabolism and systemic energy homeostasis.

Melanocortin-4-receptor (Mc4r) is a G protein-coupled receptor (GPCR) that controls systemic energy balance by regulating food intake and energy expenditure. Although the detailed molecular mechanism remains unclear, the activation of cAMP signaling in Mc4r-expressing cells reportedly suppresses food intake and increases energy expenditure. cAMP-responsive element-binding protein-regulated transcriptional co-activator-1 (CRTC1) is selectively expressed in neuronal cells and participates in transcriptional control, thereby contributing to neuronal plasticity and energy homeostasis. Considering the cAMP-dependent regulation of CRTC1 activity, CRTC1 in Mc4r- expressing cells may contribute to energy balance regulation through the melanocortin pathway. In this context, we examined the physiological contribution of CRTC1 in Mc4r-expressing cells to energy metabolism. In this study, mice with CRTC1 deficiency in Mc4r-expressing cells exhibited 1) modest obesity, glucose intolerance, insulin resistance, hyperinsulinemia, and hyperlipidemia; 2) decreased systemic energy expenditure and thermogenesis; 3) suppression of melanocortin agonist-induced adaptation of energy expenditure and food intake; 4) impaired thermogenic programs and oxidative pathway in brown adipose tissue and skeletal muscle; and 5) enhanced lipogenic programs in the liver and white adipose tissue. These results provide novel insights into the molecular mechanisms underlying the regulation of energy balance by the melanocortin system.

Bis(benzimidazol-2-yl)amine-Based DPP-4 Inhibitors Potentially Suitable for Combating Diabetes and Associated Nervous System Alterations.

Bis(benzimidazol-2-yl)amine scaffold is not present in dipeptidyl peptidase-4 (DPP-4) inhibitors published so far. Herein, the inhibitory potential of bis(benzimidazol-2-yl)amine derivatives against DPP-4 was evaluated. In non-competitive inhibition mode, three representatives 5, 6, and 7 inhibited DPP-4 in vitro with IC50 values below 50 μM. The assessed binding pocket of DPP-4 for these benzimidazoles includes the S2 extensive subsite's residues Phe357 and Arg358. None of the lead compounds showed cytotoxicity to human neuroblastoma SH-SY5Y cells at concentrations lower than 10 μM. None showed significant binding affinity at dopamine D2, D3, and histamine H1, H3 receptors, at concentrations lower than 10 μM, leading to preferable outcomes due to mutually opposite effects of these neurotransmitters on each other. The potential beneficial effects on dopamine synthesis and the survival of dopaminergic neurons could be mediated by DPP-4 inhibition. These effective noncompetitive DPP-4 inhibitors, with inhibitory potential better than reference diprotin A (relative inhibitory potency compared to diprotin A is 3.39 and 1.54 for compounds 7 and 5, respectively), with the absence of cytotoxicity to SH-SY5Y cells, are valuable candidates for further evaluation for the treatment of diabetes and associated disruption of neuronal homeostasis.

SIRT1 Regulates Mitochondrial Damage in N2a Cells Treated with the Prion Protein Fragment 106-126 via PGC-1α-TFAM-Mediated Mitochondrial Biogenesis.

Mitochondrial damage is an early and key marker of neuronal damage in prion diseases. As a process involved in mitochondrial quality control, mitochondrial biogenesis regulates mitochondrial homeostasis in neurons and promotes neuron health by increasing the number of effective mitochondria in the cytoplasm. Sirtuin 1 (SIRT1) is a NAD+-dependent deacetylase that regulates neuronal mitochondrial biogenesis and quality control in neurodegenerative diseases via deacetylation of a variety of substrates. In a cellular model of prion diseases, we found that both SIRT1 protein levels and deacetylase activity decreased, and SIRT1 overexpression and activation significantly ameliorated mitochondrial morphological damage and dysfunction caused by the neurotoxic peptide PrP106-126. Moreover, we found that mitochondrial biogenesis was impaired, and SIRT1 overexpression and activation alleviated PrP106-126-induced impairment of mitochondrial biogenesis in N2a cells. Further studies in PrP106-126-treated N2a cells revealed that SIRT1 regulates mitochondrial biogenesis through the PGC-1α-TFAM pathway. Finally, we showed that resveratrol resolved PrP106-126-induced mitochondrial dysfunction and cell apoptosis by promoting mitochondrial biogenesis through activation of the SIRT1-dependent PGC-1α/TFAM signaling pathway in N2a cells. Taken together, our findings further describe SIRT1 regulation of mitochondrial biogenesis and improve our understanding of mitochondria-related pathogenesis in prion diseases. Our findings support further investigation of SIRT1 as a potential target for therapeutic intervention of prion diseases.

Membrane tension sensing formin-binding protein 1 is a neuronal nutrient stress-responsive Golgiphagy receptor.

Nutrient stress-responsive neuronal homeostasis relies on intricate autophagic mechanisms that modulate various organelle integrity and function. The selective autophagy of the Golgi, known as Golgiphagy, regulates secretory processes by modulating vesicle trafficking during nutrient starvation. In this study, we explored a genetic screen of BAR-domain-containing proteins to elucidate the role of formin-binding protein 1 (FNBP1) as a Golgiphagy receptor in modulating Golgi dynamics in response to varying nutrient availability in neurons. Mapping the systems network of FNBP1 and its interacting proteins reveals the putative involvement of FNBP1 in autophagy and Golgi-associated processes. While nutrient depletion causes Golgi fragmentation, FNBP1 preferentially localizes to the fragmented Golgi membrane through its 284FEDYTQ289 motif during nutrient stress. Simultaneously, FNBP1 engages in molecular interactions with LC3B through a conserved 131WKQL134 LC3 interacting region, thereby sequestering the fragmented Golgi membrane in neuronal autophagosomes. Increased aggregation of GM130, abnormal clumping of RAB11-positive secretory granules, and enhanced senescent death of FNBP1-depleted starved neurons indicate disruptions of neuronal homeostasis under metabolic stress. The identification of FNBP1 as a nutrient stress-responsive Golgiphagy receptor expands our insights into the molecular mechanisms underlying Golgiphagy, establishing the crosstalk between nutrient sensing and membrane tension-sensing regulatory autophagic processes of Golgi turnover in neurons.

Characteristics of blood–brain barrier heterogeneity between brain regions revealed by profiling vascular and perivascular cells

The blood–brain barrier (BBB) protects the brain and maintains neuronal homeostasis. BBB properties can vary between brain regions to support regional functions, yet how BBB heterogeneity occurs is poorly understood. Here, we used single-cell and spatial transcriptomics to compare the mouse median eminence, one of the circumventricular organs that has naturally leaky blood vessels, with the cortex. We identified hundreds of molecular differences in endothelial cells (ECs) and perivascular cells, including astrocytes, pericytes and fibroblasts. Using electron microscopy and an aqueous-based tissue-clearing method, we revealed distinct anatomical specializations and interaction patterns of ECs and perivascular cells in these regions. Finally, we identified candidate regionally enriched EC–perivascular cell ligand–receptor pairs. Our results indicate that both molecular specializations in ECs and unique EC–perivascular cell interactions contribute to BBB functional heterogeneity. This platform can be used to investigate BBB heterogeneity in other regions and may facilitate the development of central nervous system region-specific therapeutics.

ALS-Linked VapB P56S Mutation Alters Neuronal Mitochondrial Turnover at the Synapse.

Mitochondrial population maintenance in neurons is essential for neuron function and survival. Contact sites between mitochondria and the endoplasmic reticulum (ER) are poised to regulate mitochondrial homeostasis in neurons. These contact sites can facilitate transfer of calcium and lipids between the organelles and have been shown to regulate aspects of mitochondrial dynamics. Vesicle-associated membrane protein-associated protein B (VapB) is an ER membrane protein present at a subset of ER-mitochondrial contact sites. A proline-to-serine mutation in VapB at amino acid 56 (P56S) correlates with susceptibility to amyotrophic lateral sclerosis (ALS) type 8. Given the relationship between failed mitochondrial health and neurodegenerative disease, we investigated the function of VapB in mitochondrial population maintenance. We demonstrated that transgenic expression of VapBP56S in zebrafish larvae (sex undetermined) increased mitochondrial biogenesis, causing increased mitochondrial population size in the axon terminal. Expression of wild-type VapB did not alter biogenesis but, instead, increased mitophagy in the axon terminal. Using genetic manipulations to independently increase mitochondrial biogenesis, we show that biogenesis is normally balanced by mitophagy to maintain a constant mitochondrial population size. VapBP56S transgenics fail to increase mitophagy to compensate for the increase in mitochondrial biogenesis, suggesting an impaired mitophagic response. Finally, using a synthetic ER-mitochondrial tether, we show that VapB's function in mitochondrial turnover is likely independent of ER-mitochondrial tethering by contact sites. Our findings demonstrate that VapB can control mitochondrial turnover in the axon terminal, and this function is altered by the P56S ALS-linked mutation.