Mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) control the dendritic arbor morphology of hippocampal neurons

Comprehensive Overview of Alzheimer's Disease: Etiological Insights and Degradation Strategies

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and affects millions of individuals globally. AD is associated with cognitive decline and memory loss that worsens with aging. A statistical report using U.S. data on AD estimates that approximately 6.9 million individuals suffer from AD, a number projected to surge to 13.8 million by 2060. Thus, there is a critical imperative to pinpoint and address AD and its hallmark tau protein aggregation early to prevent and manage its debilitating effects. Amyloid-β and tau proteins are primarily associated with the formation of plaques and neurofibril tangles in the brain. Current research efforts focus on degrading amyloid-β and tau or inhibiting their synthesis, particularly targeting APP processing and tau hyperphosphorylation, aiming to develop effective clinical interventions. However, navigating this intricate landscape requires ongoing studies and clinical trials to develop treatments that truly make a difference. Genome-wide association studies (GWASs) across various cohorts identified 40 loci and over 300 genes associated with AD. Despite this wealth of genetic data, much remains to be understood about the functions of these genes and their role in the disease process, prompting continued investigation. By delving deeper into these genetic associations, novel targets such as kinases, proteases, cytokines, and degradation pathways, offer new directions for drug discovery and therapeutic intervention in AD. This review delves into the intricate biological pathways disrupted in AD and identifies how genetic variations within these pathways could serve as potential targets for drug discovery and treatment strategies. Through a comprehensive understanding of the molecular underpinnings of AD, researchers aim to pave the way for more effective therapies that can alleviate the burden of this devastating disease.

CCT and Cullin1 Regulate the TORC1 Pathway to Promote Dendritic Arborization in Health and Disease

The development of cell-type-specific dendritic arbors is integral to the proper functioning of neurons within their circuit networks. In this study, we examine the regulatory relationship between the cytosolic chaperonin CCT, key insulin pathway genes, and an E3 ubiquitin ligase (Cullin1) in dendritic development. CCT loss of function (LOF) results in dendritic hypotrophy in Drosophila Class IV (CIV) multi-dendritic larval sensory neurons, and CCT has recently been shown to fold components of the TOR (Target of Rapamycin) complex 1 (TORC1) in vitro. Through targeted genetic manipulations, we confirm that an LOF of CCT and the TORC1 pathway reduces dendritic complexity, while overexpression of key TORC1 pathway genes increases the dendritic complexity in CIV neurons. Furthermore, both CCT and TORC1 LOF significantly reduce microtubule (MT) stability. CCT has been previously implicated in regulating proteinopathic aggregation, thus, we examine CIV dendritic development in disease conditions as well. The expression of mutant Huntingtin leads to dendritic hypotrophy in a repeat-length-dependent manner, which can be rescued by Cullin1 LOF. Together, our data suggest that Cullin1 and CCT influence dendritic arborization through the regulation of TORC1 in both health and disease.

Synergistic hyperactivation of both mTORC1 and mTORC2 underlies the neural abnormalities of PTEN-deficient human neurons and cortical organoids

Mutations in the phosphatase and tensin homolog (PTEN) gene are associated with severe neurodevelopmental disorders. Loss of PTEN leads to hyperactivation of the mechanistic target of rapamycin (mTOR), which functions in two distinct protein complexes, mTORC1 and mTORC2. The downstream signaling mechanisms that contribute to PTEN mutant phenotypes are not well delineated. Here, we show that pluripotent stem cell-derived PTEN mutant human neurons, neural precursors, and cortical organoids recapitulate disease-relevant phenotypes, including hypertrophy, electrical hyperactivity, enhanced proliferation, and structural overgrowth. PTEN loss leads to simultaneous hyperactivation of mTORC1 and mTORC2. We dissect the contribution of mTORC1 and mTORC2 by generating double mutants of PTEN and RPTOR or RICTOR, respectively. Our results reveal that the synergistic hyperactivation of both mTORC1 and mTORC2 is essential for the PTEN mutant human neural phenotypes. Together, our findings provide insights into the molecular mechanisms that underlie PTEN-related neural disorders and highlight novel therapeutic targets.

Rab11 regulates autophagy at dendritic spines in an mTOR- and NMDA-dependent manner

Synaptic plasticity is a process that shapes neuronal connections during neurodevelopment and learning and memory. Autophagy is a mechanism that allows the cell to degrade its unnecessary or dysfunctional components. Autophagosomes appear at dendritic spines in response to plasticity-inducing stimuli. Autophagy defects contribute to altered dendritic spine development, autistic-like behavior in mice, and neurological disease. While several studies have explored the involvement of autophagy in synaptic plasticity, the initial steps of the emergence of autophagosomes at the postsynapse remain unknown. Here, we demonstrate a postsynaptic association of autophagy-related protein 9A (Atg9A), known to be involved in the early stages of autophagosome formation, with Rab11, a small GTPase that regulates endosomal trafficking. Rab11 activity was necessary to maintain Atg9A-positive structures at dendritic spines. Inhibition of mTOR increased Rab11 and Atg9A interaction and increased the emergence of LC3 positive vesicles, an autophagosome membrane-associated protein marker, in dendritic spines when coupled to NMDA receptor stimulation. Dendritic spines with newly formed LC3+ vesicles were more resistant to NMDA-induced morphologic change. Rab11 DN overexpression suppressed appearance of LC3+ vesicles. Collectively, these results suggest that initiation of autophagy in dendritic spines depends on neuronal activity and Rab11a-dependent Atg9A interaction that is regulated by mTOR activity.

CCT and Cullin1 regulate the TORC1 pathway to promote dendritic arborization in health and disease

The development of cell-type-specific dendritic arbors is integral to the proper functioning of neurons within their circuit networks. In this study, we examine the regulatory relationship between the cytosolic chaperonin CCT, key insulin pathway genes, and an E3 ubiquitin ligase (Cullin1) in homeostatic dendritic development. CCT loss of function (LOF) results in dendritic hypotrophy in Drosophila Class IV (CIV) multidendritic larval sensory neurons, and CCT has recently been shown to fold components of the TOR (Target of Rapamycin) complex 1 (TORC1), in vitro. Through targeted genetic manipulations, we have confirmed that LOF of CCT and the TORC1 pathway reduces dendritic complexity, while overexpression of key TORC1 pathway genes increases dendritic complexity in CIV neurons. Both CCT and TORC1 LOF significantly reduce microtubule (MT) stability. CCT has been previously implicated in regulating proteinopathic aggregation, thus we examined CIV dendritic development in disease conditions as well. Expression of mutant Huntingtin leads to dendritic hypotrophy in a repeat-length-dependent manner, which can be rescued by TORC1 disinhibition via Cullin1 LOF. Together, our data suggest that Cullin1 and CCT influence dendritic arborization through regulation of TORC1 in both health and disease.

The Key Role of Initiation Timing on Stroke Rehabilitation by Remote Ischemic Conditioning with Exercise (RICE)

OBJECTIVE

Physical therapy is an integral part of post-stroke rehabilitation. Remote ischemic conditioning (RIC) induces neuroprotection within 24 hours after stroke, during which exercise is unsafe and ineffective. We combined RIC with exercise to establish a novel rehabilitation strategy, RICE (RIC+Exercise). The aim of this study was to optimize the RICE protocol in neurorehabilitation.

METHODS

Thirty-two adult male Sprague-Dawley rats were placed in one of four groups: stroke with no rehabilitation or stroke with various RICE protocols. To further understand the mechanisms underlying neurorehabilitation, sixteen adult male Sprague-Dawley were added, each placed in one of two groups: stroke with exerciseor RIC  . Long-term functional outcomes were determined by beam balance, rota-rod, grid walk, forelimb placing, and Morris water maze tests up to 28 days after stroke (p < 0.05). Changes in neuroplasticity including synaptogenesis (assessed by measuring synaptophysin, post-synaptic density protein-95, and brain-derived neutrophic factor), angiogenesis (via vascular endothelial growth factor, Angiopoietin-1, and Angiopoietin-2), and regulatory molecules (including hypoxia inducible factor-1α, phospholipase D2 and the mechanistic target of rapamycin pathway), were all measured at both mRNA and protein levels (p < 0.05).

RESULTS

All rehabilitation groups showed significant improvement in functional outcomes and levels of synaptogenesis and angiogenesis. 5 day RICE groups, in which RIC was started five days prior to exercise, demonstrated the greatest improvement among these parameters. The results also suggested that the HIF-1α/PLD2/mTOR signaling pathway may be implicated in post-stroke neuroplasticity.

CONCLUSIONS

RICE, particularly RIC initiation at hour 6 post-reperfusion followed by exercise on day 5, enhanced post-stroke rehabilitation in rats.

Quantitative proteomic analysis reveals the effects of mu opioid agonists on HT22 cells

Introduction: At present, the mu opioid receptor is the most important neuroaesthetics receptor in anesthesiology research, and the damage that it does to the nervous system is unknown. Methods: We investigated the effects of loperamide, an agonist of the mu opioid receptor, on protein expression in HT22 cells using stable isotope labeling of amino acids in cell culture (SILAC), immobilized metal affinity chromatography (IMAC) enrichment, and high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 7,823 proteins were identified. Results and Discussion: Bioinformatic analysis revealed that mu opioid receptor agonism can induce distinct changes in the proteome of HT22 cells. These findings improve our understanding of narcotic drugs.

Insulin stimulates atypical protein kinase C-mediated phosphorylation of the neuronal adaptor FE65 to potentiate neurite outgrowth by activating ARF6-Rac1 signaling

Neurite outgrowth is a fundamental process in neurons that produces extensions and, consequently, neural connectivity. Neurite damage and atrophy are observed in various brain injuries and disorders. Understanding the intrinsic pathways of neurite outgrowth is essential for developing strategies to stimulate neurite regeneration. Insulin is a pivotal hormone in the regulation of glucose homeostasis. There is increasing evidence for the neurotrophic functions of insulin, including the induction of neurite outgrowth. However, the associated mechanism remains elusive. Here, we demonstrate that insulin potentiates neurite outgrowth mediated by the small GTPases ADP-ribosylation factor 6 (ARF6) and Ras-related C3 botulinum toxin substrate 1 (Rac1) through the neuronal adaptor FE65. Moreover, insulin enhances atypical protein kinase Cι/λ (PKCι/λ) activation and FE65 phosphorylation at serine 459 (S459) in neurons and mouse brains. In vitro and cellular assays show that PKCι/λ phosphorylated FE65 at S459. Consistently, insulin potentiates FE65 S459 phosphorylation only in the presence of PKCι/λ. Phosphomimetic studies show that an FE65 S459E mutant potently activates ARF6, Rac1, and neurite outgrowth. Notably, this phosphomimetic mutation enhances the FE65-ARF6 interaction, a process that promotes ARF6-Rac1-mediated neurite outgrowth. Likewise, insulin treatment and PKCι/λ overexpression potentiate the FE65-ARF6 interaction. Conversely, PKCι/λ knockdown suppresses the stimulatory effect of FE65 on ARF6-Rac1-mediated neurite outgrowth. The effect of insulin on neurite outgrowth is also markedly attenuated in PKCι/λ knockdown neurons, in the presence and absence of FE65. Our findings reveal a novel mechanism linking insulin with ARF6-Rac1-dependent neurite extension through the PKCι/λ-mediated phosphorylation of FE65.

Dysregulation of AMPK-mTOR signaling leads to comorbid anxiety in Dip2a KO mice

Autism is often comorbid with other psychiatric disorders. We have previously shown that Dip2a knockout (KO) induces autism-like behaviors in mice. However, the role of Dip2a in other psychiatric disorders remains unclear. In this paper, we revealed that Dip2a KO mice had comorbid anxiety. Dip2a KO led to a reduction in the dendritic length of cortical and hippocampal excitatory neurons. Molecular mechanism studies suggested that AMPK was overactivated and suppressed the mTOR cascade, contributing to defects in dendritic morphology. Deletion of Dip2a in adult-born hippocampal neurons (Dip2a conditional knockout (cKO)) increased susceptibility to anxiety upon acute stress exposure. Application of (2R,6R)-hydroxynorketamine (HNK), an inhibitor of mTOR, rescued anxiety-like behaviors in Dip2a KO and Dip2a cKO mice. In addition, 6 weeks of high-fat diet intake alleviated AMPK-mTOR signaling and attenuated the severity of anxiety in both Dip2a KO mice and Dip2a cKO mice. Taken together, these results reveal an unrecognized function of DIP2A in anxiety pathophysiology via regulation of AMPK-mTOR signaling.

Study on the active components and mechanism of Suanzaoren decoction in improving cognitive impairment caused by sleep deprivation

ETHNOPHARMACOLOGICAL RELEVANCE

Suanzaoren Decoction (SZRD) is a traditional and classic prescription for the treatment of insomnia, with a history of more than 1,000 years. It replenishes blood components, calms the nerves, reduces fever and irritability. It is commonly used in the clinical treatment of chronic fatigue syndrome, cardiac neurosis, and menopausal syndromes. Modern pharmacological studies have shown that it improves cognitive impairment; however, its mechanism of action remains unclear.

AIM OF THE STUDY

This study preliminarily investigated the potential bioactive components and mechanism of SZRD in improving cognitive impairment by exploring network pharmacology, molecular docking, and conducting in vivo experiments.

MATERIALS AND METHODS

The components of various Chinese herbs in SZRD and their disease-related targets were identified through network pharmacology and literature. Gene ontology (GO) function enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses of intersection targets were performed using the relevant database. Next, the "Components-Targets-Pathways" (C-T-P) and "Protein-Protein interaction" networks were constructed using the enrichment analysis results to further identify potential pathways, bioactive components, and hub genes. At the same time, molecular docking was used to further distinguish the key bioactive components and genes of SZRD responsible for improving cognitive impairment. Finally, the potential mechanism of action was further analysed and verified using in vivo experiments.

RESULTS

A total of 117 potential active components and 138 intersection targets were identified by network pharmacology screening. The key bioactive components, including calycosin, 5-Prenylbutein, licochalcone G, glypallichalcone, and ZINC189892, were identified by analysing the networks and molecular docking results. Hub genes included ACHE, CYP19A1, EGFR, ESR1, and ESR2. The oestrogen signalling pathway was the most important in the enrichment analysis. In vivo experiments further proved that SZRD could improve cognitive impairment by affecting the oestrogen signalling pathway and the expression of ACHE and CYP19A1.

CONCLUSIONS

Network pharmacology and in vivo experiments demonstrate that SZRD improves cognitive impairment caused by sleep disturbance through estrogen receptor pathway, which provides a basis for its clinical application.

Brain-enriched RagB isoforms regulate the dynamics of mTORC1 activity through GATOR1 inhibition

Mechanistic target of rapamycin complex 1 (mTORC1) senses nutrient availability to appropriately regulate cellular anabolism and catabolism. During nutrient restriction, different organs in an animal do not respond equally, with vital organs being relatively spared. This raises the possibility that mTORC1 is differentially regulated in different cell types, yet little is known about this mechanistically. The Rag GTPases, RagA or RagB bound to RagC or RagD, tether mTORC1 in a nutrient-dependent manner to lysosomes where mTORC1 becomes activated. Although the RagA and B paralogues were assumed to be functionally equivalent, we find here that the RagB isoforms, which are highly expressed in neurons, impart mTORC1 with resistance to nutrient starvation by inhibiting the RagA/B GTPase-activating protein GATOR1. We further show that high expression of RagB isoforms is observed in some tumours, revealing an alternative strategy by which cancer cells can retain elevated mTORC1 upon low nutrient availability.

Raptor downregulation rescues neuronal phenotypes in mouse models of Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is a neurodevelopmental disorder caused by mutations in the TSC1 or TSC2 genes, which encode proteins that negatively regulate mTOR complex 1 (mTORC1) signaling. Current treatment strategies focus on mTOR inhibition with rapamycin and its derivatives. While effective at improving some aspects of TSC, chronic rapamycin inhibits both mTORC1 and mTORC2 and is associated with systemic side-effects. It is currently unknown which mTOR complex is most relevant for TSC-related brain phenotypes. Here we used genetic strategies to selectively reduce neuronal mTORC1 or mTORC2 activity in mouse models of TSC. We find that reduction of the mTORC1 component Raptor, but not the mTORC2 component Rictor, rebalanced mTOR signaling in Tsc1 knock-out neurons. Raptor reduction was sufficient to improve several TSC-related phenotypes including neuronal hypertrophy, macrocephaly, impaired myelination, network hyperactivity, and premature mortality. Raptor downregulation represents a promising potential therapeutic intervention for the neurological manifestations of TSC.

Dopamine neuron morphology and output are differentially controlled by mTORC1 and mTORC2

The mTOR pathway is an essential regulator of cell growth and metabolism. Midbrain dopamine neurons are particularly sensitive to mTOR signaling status as activation or inhibition of mTOR alters their morphology and physiology. mTOR exists in two distinct multiprotein complexes termed mTORC1 and mTORC2. How each of these complexes affect dopamine neuron properties, and whether they have similar or distinct functions is unknown. Here, we investigated this in mice with dopamine neuron-specific deletion of Rptor or Rictor, which encode obligatory components of mTORC1 or mTORC2, respectively. We find that inhibition of mTORC1 strongly and broadly impacts dopamine neuron structure and function causing somatodendritic and axonal hypotrophy, increased intrinsic excitability, decreased dopamine production, and impaired dopamine release. In contrast, inhibition of mTORC2 has more subtle effects, with selective alterations to the output of ventral tegmental area dopamine neurons. Disruption of both mTOR complexes leads to pronounced deficits in dopamine release demonstrating the importance of balanced mTORC1 and mTORC2 signaling for dopaminergic function.

mTORC1 function in hippocampal parvalbumin interneurons: regulation of firing and long-term potentiation of intrinsic excitability but not long-term contextual fear memory and context discrimination

Hippocampal CA1 parvalbumin-expressing interneurons (PV INs) play a central role in controlling principal cell activity and orchestrating network oscillations. PV INs receive excitatory inputs from CA3 Schaffer collaterals and local CA1 pyramidal cells, and they provide perisomatic inhibition. Schaffer collateral excitatory synapses onto PV INs express Hebbian and anti-Hebbian types of long-term potentiation (LTP), as well as elicit LTP of intrinsic excitability (LTP_IE). LTP_IE requires the activation of type 5 metabotropic glutamate receptors (mGluR5) and is mediated by downregulation of potassium channels Kv1.1. It is sensitive to rapamycin and thus may involve activation of the mammalian target of rapamycin complex 1 (mTORC1). LTP_IE facilitates PV INs recruitment in CA1 and maintains an excitatory-inhibitory balance. Impaired CA1 PV INs activity or LTP affects network oscillations and memory. However, whether LTP_IE in PV INs plays a role in hippocampus-dependent memory remains unknown. Here, we used conditional deletion of the obligatory component of mTORC1, the Regulatory-Associated Protein of mTOR (Raptor), to directly manipulate mTORC1 in PV INs. We found that homozygous, but not heterozygous, conditional knock-out of Rptor resulted in a decrease in CA1 PV INs of mTORC1 signaling via its downstream effector S6 phosphorylation assessed by immunofluorescence. In whole-cell recordings from hippocampal slices, repetitive firing of CA1 PV INs was impaired in mice with either homozygous or heterozygous conditional knock-out of Rptor. High frequency stimulation of Schaffer collateral inputs that induce LTP_IE in PV INs of control mice failed to do so in mice with either heterozygous or homozygous conditional knock-out of Rptor in PV INs. At the behavioral level, mice with homozygous or heterozygous conditional knock-out of Rptor showed similar long-term contextual fear memory or contextual fear memory discrimination relative to control mice. Thus, mTORC1 activity in CA1 PV INs regulates repetitive firing and LTP_IE but not consolidation of long-term contextual fear memory and context discrimination. Our results indicate that mTORC1 plays cell-specific roles in synaptic plasticity of hippocampal inhibitory interneurons that are differentially involved in hippocampus-dependent learning and memory.

Combined overexpression of ATXN1L and mutant ATXN1 knockdown by AAV rescue motor phenotypes and gene signatures in SCA1 mice

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disease caused by a (CAG) repeat expansion in the coding sequence of ATXN1. The primary mechanism of disease in SCA1 is toxic gain of function by polyglutamine-expanded mutant ATXN1 and is compounded by partial loss of wild-type function. Addressing both disease mechanisms, we have shown that virally expressed RNA interference targeting ATXN1 can both prevent and reverse disease phenotypes in SCA1 mice, and that overexpression of the ATXN1 homolog, ataxin 1-like (ATXN1L), improves disease readouts when delivered pre-symptomatically. Here, we combined these therapeutic approaches into two, dual component recombinant adeno-associated virus (rAAV) vectors and tested their ability to reverse disease in symptomatic SCA1 mice using behavior, pathological, and next-generation sequencing assays. Mice treated with vectors expressing human ATXN1L (hATXN1L) alone showed motor improvements and changes in gene expression that reflected increases in pro-development pathways. When hATN1L was combined with miS1, a previously validated microRNA targeting h ATXN1, there was added normalization of disease allele-induced changes in gene expression along with motor improvements. Our data show the additive nature of this two-component approach for a more effective SCA1 therapy.

Hallucinogenic drugs and their potential for treating fear-related disorders: Through the lens of fear extinction

Fear-related disorders, mainly phobias and post-traumatic stress disorder, are highly prevalent, debilitating disorders that pose a significant public health problem. They are characterized by aberrant processing of aversive experiences and dysregulated fear extinction, leading to excessive expression of fear and diminished quality of life. The gold standard for treating fear-related disorders is extinction-based exposure therapy (ET), shown to be ineffective for up to 35% of subjects. Moreover, ET combined with traditional pharmacological treatments for fear-related disorders, such as selective serotonin reuptake inhibitors, offers no further advantage to patients. This prompted the search for ways to improve ET outcomes, with current research focused on pharmacological agents that can augment ET by strengthening fear extinction learning. Hallucinogenic drugs promote reprocessing of fear-imbued memories and induce positive mood and openness, relieving anxiety and enabling the necessary emotional engagement during psychotherapeutic interventions. Mechanistically, hallucinogens induce dynamic structural and functional neuroplastic changes across the fear extinction circuitry and temper amygdala's hyperreactivity to threat-related stimuli, effectively mitigating one of the hallmarks of fear-related disorders. This paper provides the first comprehensive review of hallucinogens' potential to alleviate symptoms of fear-related disorders by focusing on their effects on fear extinction and the underlying molecular mechanisms. We overview both preclinical and clinical studies and emphasize the advantages of hallucinogenic drugs over current first-line treatments. We highlight 3,4-methylenedioxymethamphetamine and ketamine as the most effective therapeutics for fear-related disorders and discuss the potential molecular mechanisms responsible for their potency with implications for improving hallucinogen-assisted psychotherapy.

Striking a balance: PIP2 and PIP3 signaling in neuronal health and disease

Phosphoinositides are membrane phospholipids involved in a variety of cellular processes like growth, development, metabolism, and transport. This review focuses on the maintenance of cellular homeostasis of phosphatidylinositol 4,5-bisphosphate (PIP₂), and phosphatidylinositol 3,4,5-trisphosphate (PIP₃). The critical balance of these PIPs is crucial for regulation of neuronal form and function. The activity of PIP₂ and PIP₃ can be regulated through kinases, phosphatases, phospholipases and cholesterol microdomains. PIP₂ and PIP₃ carry out their functions either indirectly through their effectors activating integral signaling pathways, or through direct regulation of membrane channels, transporters, and cytoskeletal proteins. Any perturbations to the balance between PIP₂ and PIP₃ signaling result in neurodevelopmental and neurodegenerative disorders. This review will discuss the upstream modulators and downstream effectors of the PIP₂ and PIP₃ signaling, in the context of neuronal health and disease.

Sex and Genotype Modulate the Dendritic Effects of Developmental Exposure to a Human-Relevant Polychlorinated Biphenyls Mixture in the Juvenile Mouse

While many neurodevelopmental disorders (NDDs) are thought to result from interactions between environmental and genetic risk factors, the identification of specific gene-environment interactions that influence NDD risk remains a critical data gap. We tested the hypothesis that polychlorinated biphenyls (PCBs) interact with human mutations that alter the fidelity of neuronal Ca²⁺ signaling to confer NDD risk. To test this, we used three transgenic mouse lines that expressed human mutations known to alter Ca²⁺ signals in neurons: (1) gain-of-function mutation in ryanodine receptor-1 (T4826I-RYR1); (2) CGG-repeat expansion in the 5′ non-coding portion of the fragile X mental retardation gene 1 (FMR1); and (3) a double mutant (DM) that expressed both mutations. Transgenic and wildtype (WT) mice were exposed throughout gestation and lactation to the MARBLES PCB mix at 0.1, 1, or 6 mg/kg in the maternal diet. The MARBLES mix simulates the relative proportions of the twelve most abundant PCB congeners found in serum from pregnant women at increased risk for having a child with an NDD. Using Golgi staining, the effect of developmental PCB exposure on dendritic arborization of pyramidal neurons in the CA1 hippocampus and somatosensory cortex of male and female WT mice was compared to pyramidal neurons from transgenic mice. A multilevel linear mixed-effects model identified a main effect of dose driven by increased dendritic arborization of cortical neurons in the 1 mg/kg PCB dose group. Subsequent analyses with genotypes indicated that the MARBLES PCB mixture had no effect on the dendritic arborization of hippocampal neurons in WT mice of either sex, but significantly increased dendritic arborization of cortical neurons of WT males in the 6 mg/kg PCB dose group. Transgene expression increased sensitivity to the impact of developmental PCB exposure on dendritic arborization in a sex-, and brain region-dependent manner. In conclusion, developmental exposure to PCBs present in the gestational environment of at-risk humans interfered with normal dendritic morphogenesis in the developing mouse brain in a sex-, genotype- and brain region-dependent manner. Overall, these observations provide proof-of-principle evidence that PCBs interact with heritable mutations to modulate a neurodevelopmental outcome of relevance to NDDs.

RalA, PLD and mTORC1 Are Required for Kinase-Independent Pathways in DGKβ-Induced Neurite Outgrowth

Diacylglycerol kinase β (DGKβ) is an enzyme that converts diacylglycerol to phosphatidic acid and is mainly expressed in the cerebral cortex, hippocampus and striatum. We previously reported that DGKβ induces neurite outgrowth and spinogenesis, contributing to higher brain functions, including emotion and memory. To elucidate the mechanisms involved in neuronal development by DGKβ, we investigated the importance of DGKβ activity in the induction of neurite outgrowth using human neuroblastoma SH-SY5Y cells. Interestingly, both wild-type DGKβ and the kinase-negative (KN) mutant partially induced neurite outgrowth, and these functions shared a common pathway via the activation of mammalian target of rapamycin complex 1 (mTORC1). In addition, we found that DGKβ interacted with the small GTPase RalA and that siRNA against RalA and phospholipase D (PLD) inhibitor treatments abolished DGKβKN-induced neurite outgrowth. These results indicate that binding of RalA and activation of PLD and mTORC1 are involved in DGKβKN-induced neurite outgrowth. Taken together with our previous reports, mTORC1 is a key molecule in both kinase-dependent and kinase-independent pathways of DGKβ-mediated neurite outgrowth, which is important for higher brain functions.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

MHY1485 enhances X-irradiation-induced apoptosis and senescence in tumor cells

The mammalian target of rapamycin (mTOR) is a sensor of nutrient status and plays an important role in cell growth and metabolism. Although inhibition of mTOR signaling promotes tumor cell death and several mTOR inhibitors have been used clinically, recent reports have shown that co-treatment with MHY1485, an mTOR activator, enhances the anti-cancer effects of anti-PD-1 antibody and 5-fluorouracil. However, it remains unclear whether MHY1485 treatment alters the effects of radiation on tumor cells. In this study, the radiosensitizing effects of MHY1485 were investigated using murine CT26 and LLC cell lines. We examined mTOR signaling, tumor cell growth, colony formation, apoptosis, senescence, oxidative stress, p21 accumulation and endoplasmic reticulum (ER) stress levels in cells treated with MHY1485 and radiation, either alone or together. We found that MHY1485 treatment inhibited growth and colony formation in both cell lines under irradiation and no-irradiation conditions, results that were not fully consistent with MHY1485's known role in activating mTOR signaling. Furthermore, we found that combined treatment with MHY1485 and radiation significantly increased apoptosis and senescence in tumor cells in association with oxidative stress, ER stress and p21 stabilization, compared to radiation treatment alone. Our results suggested that MHY1485 enhances the radiosensitivity of tumor cells by a mechanism that may differ from MHY1485's role in mTOR activation.

The Role of Hippo Signaling Pathway in the Development of the Nervous System

Hippo signaling pathway is a highly conserved and crucial signaling pathway that controls the size of tissues and organs by regulating the proliferation, differentiation, and apoptosis of cells. The nervous system is a complicated system that participates in information collection, integration, and procession. The balance of various aspects of the nervous system is vital for the normal regulation of physiological conditions of the body, like the population and distribution of nerve cells, nerve connections, and so on. Defects in these aspects may lead to cognitive, behavioral, and neurological dysfunction, resulting in various nervous system diseases. Recently, accumulating evidence proposes that Hippo pathway maintains numerous biological functions in the nervous system development, including modulating the proliferation and differentiation of nerve cells and promoting the development of synapse, corpus callosum, and cortex. In this review, we will summarize recent findings of Hippo pathway in the nervous system to improve our understanding on its function and to provide potential therapeutic strategies of nervous system diseases in the future.

Current Approaches and Future Directions for the Treatment of mTORopathies

The mechanistic target of rapamycin (mTOR) is a kinase at the center of an evolutionarily conserved signaling pathway that orchestrates cell growth and metabolism. mTOR responds to an array of intra- and extracellular stimuli and in turn controls multiple cellular anabolic and catabolic processes. Aberrant mTOR activity is associated with numerous diseases, with particularly profound impact on the nervous system. mTOR is found in two protein complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), which are governed by different upstream regulators and have distinct cellular actions. Mutations in genes encoding for mTOR regulators result in a collection of neurodevelopmental disorders known as mTORopathies. While these disorders can affect multiple organs, neuropsychiatric conditions such as epilepsy, intellectual disability, and autism spectrum disorder have a major impact on quality of life. The neuropsychiatric aspects of mTORopathies have been particularly challenging to treat in a clinical setting. Current therapeutic approaches center on rapamycin and its analogs, drugs that are administered systemically to inhibit mTOR activity. While these drugs show some clinical efficacy, adverse side effects, incomplete suppression of mTOR targets, and lack of specificity for mTORC1 or mTORC2 may limit their utility. An increased understanding of the neurobiology of mTOR and the underlying molecular, cellular, and circuit mechanisms of mTOR-related disorders will facilitate the development of improved therapeutics. Animal models of mTORopathies have helped unravel the consequences of mTOR pathway mutations in specific brain cell types and developmental stages, revealing an array of disease-related phenotypes. In this review, we discuss current progress and potential future directions for the therapeutic treatment of mTORopathies with a focus on findings from genetic mouse models.

Perspectives on ROCK2 as a Therapeutic Target for Alzheimer's Disease

Rho-associated coiled-coil containing kinase isoform 2 (ROCK2) is a member of the AGC family of serine/threonine kinases and an extensively studied regulator of actin-mediated cytoskeleton contractility. Over the past decade, new evidence has emerged that suggests ROCK2 regulates autophagy. Recent studies indicate that dysregulation of autophagy contributes to the development of misfolded tau aggregates among entorhinal cortex (EC) excitatory neurons in early Alzheimer's disease (AD). While the accumulation of tau oligomers and fibrils is toxic to neurons, autophagy facilitates the degradation of these pathologic species and represents a major cellular pathway for tau disposal in neurons. ROCK2 is expressed in excitatory neurons and pharmacologic inhibition of ROCK2 can induce autophagy pathways. In this mini-review, we explore potential mechanisms by which ROCK2 mediates autophagy and actin dynamics and discuss how these pathways represent therapeutic avenues for Alzheimer's disease.

Kinase Signaling in Dendritic Development and Disease

Dendrites undergo extensive growth and remodeling during their lifetime. Specification of neurites into dendrites is followed by their arborization, maturation, and functional integration into synaptic networks. Each of these distinct developmental processes is spatially and temporally controlled in an exquisite fashion. Protein kinases through their highly specific substrate phosphorylation regulate dendritic growth and plasticity. Perturbation of kinase function results in aberrant dendritic growth and synaptic function. Not surprisingly, kinase dysfunction is strongly associated with neurodevelopmental and psychiatric disorders. Herein, we review, (a) key kinase pathways that regulate dendrite structure, function and plasticity, (b) how aberrant kinase signaling contributes to dendritic dysfunction in neurological disorders and (c) emergent technologies that can be applied to dissect the role of protein kinases in dendritic structure and function.

Iron Deficiency and Iron Excess Differently Affect Dendritic Architecture of Pyramidal Neurons in the Hippocampus of Piglets

BACKGROUND

Both iron deficiency and overload may adversely affect neurodevelopment.

OBJECTIVES

The study assessed how changes in early-life iron status affect iron homeostasis and cytoarchitecture of hippocampal neurons in a piglet model.

METHODS

On postnatal day (PD) 1, 30 Hampshire × Yorkshire crossbreed piglets (n = 15/sex) were stratified by sex and litter and randomly assigned to experimental groups receiving low (L-Fe), adequate (A-Fe), or high (H-Fe) levels of iron supplement during the pre- (PD1-21) and postweaning periods (PD22-35). Pigs in the L-Fe, A-Fe, and H-Fe groups orally received 0, 1, and 30 mg Fe · kg weight-1 · d-1 preweaning and were fed a diet containing 30, 125, and 1000 mg Fe/kg postweaning, respectively. Heme indexes were analyzed weekly, and gene and protein expressions of iron regulatory proteins in duodenal mucosa, liver, and hippocampus were analyzed through qRT-PCR and western blot, respectively, on PD35. Hippocampal neurons stained using the Golgi-Cox method were traced and their dendritic arbors reconstructed in 3-D using Neurolucida. Dendritic complexity was quantified using Sholl and branch order analyses.

RESULTS

Pigs in the L-Fe group developed iron deficiency anemia (hemoglobin = 8.2 g/dL, hematocrit = 20.1%) on PD35 and became stunted during week 5 with lower final body weight than H-Fe group pigs (6.6 compared with 9.6 kg, P < 0.05). In comparison with A-Fe, H-Fe increased hippocampal ferritin expression by 38% and L-Fe decreased its expression by 52% (P < 0.05), suggesting altered hippocampal iron stores. Pigs in the H-Fe group had greater dendritic complexity in CA1/3 pyramidal neurons than L-Fe group pigs as shown by more dendritic intersections with Sholl rings (P ≤ 0.04) and a greater number of dendrites (P ≤ 0.016).

CONCLUSIONS

In piglets, the developing hippocampus is susceptible to perturbations by dietary iron, with deficiency and overload differentially affecting dendritic arborization.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

FGFR Regulation of Dendrite Elaboration in Adult-born Granule Cells Depends on Intracellular Mediator and Proximity to the Soma

Fibroblast Growth Factor Receptors (FGFRs) play crucial roles in promoting dendrite growth and branching during development. In mice, three FGFR genes, Fgfr1, Fgfr2, and Fgfr3, remain expressed in the adult neurogenic niche of the hippocampal dentate gyrus. However, the function of FGFRs in the dendritic maturation of adult-born neurons remains largely unexplored. Here, using conditional alleles of Fgfr1, Fgfr2, and Fgfr3 as well as Fgfr1 alleles lacking binding sites for Phospholipase-Cγ (PLCγ) and FGF Receptor Substrate (FRS) proteins, we test the requirement for FGFRs in dendritogenesis of adult-born granule cells. We find that deleting all three receptors results in a small decrease in proximal dendrite elaboration. In contrast, specifically mutating Tyr766 in FGFR1 (a PLCγ binding site) in an Fgfr2;Fgfr3 deficient background results in a dramatic increase of overall dendrite elaboration, while blocking FGFR1-FRS signaling causes proximal dendrite deficits and, to a lesser extent than Tyr766 mutants, increases distal dendrite elaboration. These findings reveal unexpectedly complex roles for FGFRs and their intracellular mediators in regulating proximal and distal dendrite elaboration, with the most notable role in suppressing distal elaboration through the PLCγbinding site.

The amino acid transporter Slc7a5 regulates the mTOR pathway and is required for granule cell development

Pathogenic mutations in the solute carrier family 7 member 5 (SLC7A5) gene, which encodes an amino acid transporter cause microcephaly and seizures, yet the mechanisms responsible for these phenotypes are unclear. Models have demonstrated that Slc7a5 deletion is embryonic lethal and that these embryos lack a fully formed telencephalon. This phenotype is similar to that of mammalian target of rapamycin (mTOR) protein kinase deletion or mTOR inhibition. Notably, in many cells, Slc7a5 import of amino acids is required to maintain mTOR activity. Slc7a5 is present within neurogenic regions during embryogenesis, is found in cultured neurons and can modulate neuronal electrophysiological properties. However, Slc7a5 is also highly expressed within endothelial cells of the blood-brain barrier where removal in conditional mice leads to severe behavioral defects and non-cell autonomous changes in neurons. Therefore, the extent that neural Slc7a5 is required for development is unclear. Here, subventricular zone neural stem cells that generate olfactory bulb granule cell neurons were electroporated with SLC7A5 or Slc7a5 short hairpin RNA encoding plasmids. Although early phases of neural development were unaltered, Slc7a5 knockdown effected late phases of GC dendrite maturation and survival. Slc7a5 knockdown also decreased mTOR pathway activity. Ras homolog enriched in brain, an mTOR activator, rescued the effect of Slc7a5 knockdown on mTOR pathway activity and dendrite arbors. The data presented here demonstrate that Slc7a5 is required for GC mTOR pathway activity, maturation and survival, which may help explain why Slc7a5 mutations prevent normal brain development and function.

The role of the mTOR pathway in models of drug-induced reward and the behavioural constituents of addiction

BACKGROUND

Exposure to drugs of abuse induces neuroadaptations in critical nodes of the so-called reward systems that are thought to mediate the transition from controlled drug use to the compulsive drug-seeking that characterizes addictive disorders. These neural adaptations are likely to require protein synthesis, which is regulated, among others, by the mechanistic target of the rapamycin kinase (mTOR) signalling cascade.

METHODS

We have performed a narrative review of the literature available in PubMed about the involvement of the mTOR pathway in drug-reward and addiction-related phenomena.

AIMS

The aim of this study was to review the underlying architecture of this complex intracellular network and to discuss the alterations of its components that are evident after exposure to drugs of abuse. The aim was also to delineate the effects that manipulations of the mTOR network have on models of drug reward and on paradigms that recapitulate some of the psychological components of addiction.

RESULTS

There is evidence for the involvement of the mTOR pathway in the acute and rewarding effects of drugs of abuse, especially psychostimulants. However, the data regarding opiates are scarce. There is a need to use sophisticated animal models of addiction to ascertain the real role of the mTOR pathway in this pathology and not just in drug-mediated reward. The involvement of this pathway in behavioural addictions and impulsivity should also be studied in detail in the future.

CONCLUSIONS

Although there is a plethora of data about the modulation of mTOR by drugs of abuse, the involvement of this signalling pathway in addictive disorders requires further research.

Maf1 regulates dendritic morphogenesis and influences learning and memory

Maf1, a general transcriptional regulator and mTOR downstream effector, is highly expressed in the hippocampus and cortex, but the function of Maf1 in neurons is not well elucidated. Here, we first demonstrate that Maf1 plays a central role in the inhibition of dendritic morphogenesis and the growth of dendritic spines both in vitro and in vivo. Furthermore, Maf1 downregulation paradoxically leads to activation of AKT-mTOR signaling, which is mediated by decreased PTEN expression. Moreover, we confirmed that Maf1 could regulate the activity of PTEN promoter by luciferase reporter assay, and proved that Maf1 could bind to the promoter of PTEN by ChIP-PCR experiment. We also demonstrate that expression of Maf1 in the hippocampus affects learning and memory in mice. Taken together, we show for the first time that Maf1 inhibits dendritic morphogenesis and the growth of dendritic spines through AKT-mTOR signaling by increasing PTEN expression.

Retinal energy metabolism in health and glaucoma

Energy metabolism refers to the processes by which life transfers energy to do cellular work. The retina's relatively large energy demands make it vulnerable to energy insufficiency. In addition, evolutionary pressures to optimize human vision have been traded against retinal ganglion cell bioenergetic fragility. Details of the metabolic profiles of the different retinal cells remain poorly understood and are challenging to resolve. Detailed immunohistochemical mapping of the energy pathway enzymes and substrate transporters has provided some insights and highlighted interspecies differences. The different spatial metabolic patterns between the vascular and avascular retinas can account for some inconsistent data in the literature. There is a consilience of evidence that at least some individuals with glaucoma have impaired RGC energy metabolism, either due to impaired nutrient supply or intrinsic metabolic perturbations. Bioenergetic-based therapy for glaucoma has a compelling pathophysiological foundation and is supported by recent successes in animal models. Recent demonstrations of visual and electrophysiological neurorecovery in humans with glaucoma is highly encouraging and motivates longer duration trials investigating bioenergetic neuroprotection.

Suppression of sirtuin 1 alleviates airway inflammation through mTOR‑mediated autophagy

Sirtuin 1 (SIRT1) is involved in the pathogenesis of allergic asthma. This study aimed to investigate whether EX-527, a specific SIRT1 inhibitor, exerted suppressive effects on allergic airway inflammation in mice submitted to ovalbumin (OVA) inhalation. In addition, this study assessed whether such a protective role was mediated by autophagy suppression though mammalian target of rapamycin (mTOR) activation. Female C57BL/6 mice were sensitized to OVA and EX-527 (10 mg/kg) was administered prior to OVA challenge. The study found that EX-527 reversed OVA-induced airway inflammation, and reduced OVA-induced increases in inflammatory cytokine expression, and total cell and eosinophil counts in bronchoalveolar lavage fluid. In addition, EX-527 enhanced mTOR activation, thereby suppressing autophagy in allergic mice. To assess whether EX-527 inhibited airway inflammation in asthma through the mTOR-mediated autophagy pathway, rapamycin was administered to mice treated with EX-527 after OVA sensitization. All effects induced by EX-527, including increased phosphorylated-mTOR and decreased autophagy, were abrogated by rapamycin treatment. Taken together, the present findings indicated that EX-527 may inhibit allergic airway inflammation by suppressing autophagy, an effect mediated by mTOR activation in allergic mice.

The Effects of YAP and Its Related Mechanisms in Central Nervous System Diseases

Yes-associated protein (YAP) is a key effector downstream of the Hippo signaling pathway and plays an important role in the development of the physiology and pathology of the central nervous system (CNS), especially regulating cell proliferation, differentiation, migration, and apoptosis. However, the roles and underlying mechanisms of YAP in CNS diseases are still puzzling. Here, this review will systematically and comprehensively summarize the biological feature, pathological role, and underlying mechanisms of YAP in normal and pathologic CNS, which aims to provide insights into the potential molecular targets and new therapeutic strategies for CNS diseases.

Complete neural stem cell (NSC) neuronal differentiation requires a branched chain amino acids-induced persistent metabolic shift towards energy metabolism

Neural stem cell (NSC) neuronal differentiation requires a metabolic shift towards oxidative phosphorylation. We now show that a branched-chain amino acids-driven, persistent metabolic shift toward energy metabolism is required for full neuronal maturation. We increased energy metabolism of differentiating neurons derived both from murine NSCs and human induced pluripotent stem cells (iPSCs) by supplementing the cell culture medium with a mixture composed of branched-chain amino acids, essential amino acids, TCA cycle precursors and co-factors. We found that treated differentiating neuronal cells with enhanced energy metabolism increased: i) total dendritic length; ii) the mean number of branches and iii) the number and maturation of the dendritic spines. Furthermore, neuronal spines in treated neurons appeared more stable with stubby and mushroom phenotype and with increased expression of molecules involved in synapse formation. Treated neurons modified their mitochondrial dynamics increasing the mitochondrial fusion and, consistently with the increase of cellular ATP content, they activated cellular mTORC1 dependent p70S6 K1 anabolism. Global transcriptomic analysis further revealed that treated neurons induce Nrf2 mediated gene expression. This was correlated with a functional increase in the Reactive Oxygen Species (ROS) scavenging mechanisms. In conclusion, persistent branched-chain amino acids-driven metabolic shift toward energy metabolism enhanced neuronal differentiation and antioxidant defences. These findings offer new opportunities to pharmacologically modulate NSC neuronal differentiation and to develop effective strategies for treating neurodegenerative diseases.

Targeted Deletion of PTEN in Kisspeptin Cells Results in Brain Region- and Sex-Specific Effects on Kisspeptin Expression and Gonadotropin Release

Kisspeptin-expressing neurons in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC) of the hypothalamus relay hormonal and metabolic information to gonadotropin-releasing hormone neurons, which in turn regulate pituitary and gonadal function. Phosphatase and tensin homolog (PTEN) blocks phosphatidylinositol 3-kinase (PI3K), a signaling pathway utilized by peripheral factors to transmit their signals. However, whether PTEN signaling in kisspeptin neurons helps to integrate peripheral hormonal cues to regulate gonadotropin release is unknown. To address this question, we generated mice with a kisspeptin cell-specific deletion of Pten (Kiss-PTEN KO), and first assessed kisspeptin protein expression and gonadotropin release in these animals. Kiss-PTEN KO mice displayed a profound sex and region-specific kisspeptin neuron hyperthrophy. We detected both kisspeptin neuron hyperthrophy as well as increased kisspeptin fiber densities in the AVPV and ARC of Kiss-PTEN KO females and in the ARC of Kiss-PTEN KO males. Moreover, Kiss-PTEN KO mice showed a reduced gonadotropin release in response to gonadectomy. We also found a hyperactivation of mTOR, a downstream PI3K target and central regulator of cell metabolism, in the AVPV and ARC of Kiss-PTEN KO females but not males. Fasting, known to inhibit hypothalamic kisspeptin expression and luteinizing hormone levels, failed to induce these changes in Kiss-PTEN KO females. We conclude that PTEN signaling regulates kisspeptin protein synthesis in both sexes and that its role as a metabolic signaling molecule in kisspeptin neurons is sex-specific.

Genetic inactivation of mTORC1 or mTORC2 in neurons reveals distinct functions in glutamatergic synaptic transmission

Although mTOR signaling is known as a broad regulator of cell growth and proliferation, in neurons it regulates synaptic transmission, which is thought to be a major mechanism through which altered mTOR signaling leads to neurological disease. Although previous studies have delineated postsynaptic roles for mTOR, whether it regulates presynaptic function is largely unknown. Moreover, the mTOR kinase operates in two complexes, mTORC1 and mTORC2, suggesting that mTOR's role in synaptic transmission may be complex-specific. To better understand their roles in synaptic transmission, we genetically inactivated mTORC1 or mTORC2 in cultured mouse glutamatergic hippocampal neurons. Inactivation of either complex reduced neuron growth and evoked EPSCs (eEPSCs), however, the effects of mTORC1 on eEPSCs were postsynaptic and the effects of mTORC2 were presynaptic. Despite postsynaptic inhibition of evoked release, mTORC1 inactivation enhanced spontaneous vesicle fusion and replenishment, suggesting that mTORC1 and mTORC2 differentially modulate postsynaptic responsiveness and presynaptic release to optimize glutamatergic synaptic transmission.

mTORC1 is involved in DGKβ-induced neurite outgrowth and spinogenesis

Diacylglycerol kinase β (DGKβ) is an enzyme converting DG to phosphatidic acid (PA) and is specifically expressed in neurons, especially those in the cerebral cortex, hippocampus and striatum. We previously reported that DGKβ induces neurite outgrowth and spinogenesis, contributing to higher brain function including emotion and memory, and plasma membrane localization of DGKβ via the C1 domain and a cluster of basic amino acids at the C-terminus is necessary for its function. To clarify the mechanisms involved in neuronal development by DGKβ, we investigated whether DGKβ activity induces neurite outgrowth using human neuroblastoma SH-SY5Y cells. DGKβ induced neurite outgrowth by activation of mammalian target of rapamycin complex 1 (mTORC1) through a kinase-dependent pathway. In addition, in primary cultured cortical and hippocampal neurons, inhibition of mTORC1 abolished DGKβ induced-neurite outgrowth, branching and spinogenesis. These results indicated that DGKβ induces neurite outgrowth and spinogenesis by activating mTORC1 in a kinase-dependent pathway.

Neuroligin 3 Regulates Dendritic Outgrowth by Modulating Akt/mTOR Signaling

Neuroligins (NLs) are a group of postsynaptic cell adhesion molecules that function in synaptogenesis and synaptic transmission. Genetic defects in neuroligin 3 (NL3), a member of the NL protein family, are associated with autism. Studies in rodents have revealed that mutations of NL3 gene lead to increased growth and complexity in dendrites in the central nervous system. However, the detailed mechanism is still unclear. In our study, we found that deficiency of NL3 led to morphological changes of the pyramidal neurons in layer II/III somatosensory cortex in mice, including enlarged somata, elongated dendritic length, and increased dendritic complexity. Knockdown of NL3 in cultured rat neurons upregulated Akt/mTOR signaling, resulting in both increased protein synthesis and dendritic growth. Treating neurons with either rapamycin to inhibit the mTOR or LY294002 to inhibit the PI3K/Akt activity rescued the morphological abnormalities resulting from either NL3 knockdown or knockout (KO). In addition, we found that the hyperactivated Akt/mTOR signaling associated with NL3 defects was mediated by a reduction in phosphatase and tensin (PTEN) expression, and that MAGI-2, a scaffold protein, interacted with both NL3 and PTEN and could be a linker between NL3 and Akt/mTOR signaling pathway. In conclusion, our results suggest that NL3 regulates neuronal morphology, especially dendritic outgrowth, by modulating the PTEN/Akt/mTOR signaling pathway, probably via MAGI-2. Thereby, this study provides a new link between NL3 and neuronal morphology.

Relevance of Translation Initiation in Diffuse Glioma Biology and its Therapeutic Potential

Cancer cells are continually exposed to environmental stressors forcing them to adapt their protein production to survive. The translational machinery can be recruited by malignant cells to synthesize proteins required to promote their survival, even in times of high physiological and pathological stress. This phenomenon has been described in several cancers including in gliomas. Abnormal regulation of translation has encouraged the development of new therapeutics targeting the protein synthesis pathway. This approach could be meaningful for glioma given the fact that the median survival following diagnosis of the highest grade of glioma remains short despite current therapy. The identification of new targets for the development of novel therapeutics is therefore needed in order to improve this devastating overall survival rate. This review discusses current literature on translation in gliomas with a focus on the initiation step covering both the cap-dependent and cap-independent modes of initiation. The different translation initiation protagonists will be described in normal conditions and then in gliomas. In addition, their gene expression in gliomas will systematically be examined using two freely available datasets. Finally, we will discuss different pathways regulating translation initiation and current drugs targeting the translational machinery and their potential for the treatment of gliomas.

PTEN in Autism and Neurodevelopmental Disorders

Phosphatase and tensin homolog (PTEN) is a classical tumor suppressor that antagonizes phosphatidylinositol 3-phosphate kinase (PI3K)/AKT signaling. Although there is a strong association of PTEN germline mutations with cancer syndromes, they have also been described in a subset of patients with autism spectrum disorders with macrocephaly characterized by impairments in social interactions and communication, repetitive behavior and, occasionally, epilepsy. To investigate PTEN's role during neurodevelopment and its implication for autism, several conditional Pten knockout mouse models have been generated. These models are valuable tools to understand PTEN's spatiotemporal roles during neurodevelopment. In this review, we will highlight the anatomical and phenotypic results from animal studies and link them to cellular and molecular findings.

Multi-omics analysis identifies mitochondrial pathways associated with anxiety-related behavior

Stressful life events are major environmental risk factors for anxiety disorders, although not all individuals exposed to stress develop clinical anxiety. The molecular mechanisms underlying the influence of environmental effects on anxiety are largely unknown. To identify biological pathways mediating stress-related anxiety and resilience to it, we used the chronic social defeat stress (CSDS) paradigm in male mice of two inbred strains, C57BL/6NCrl (B6) and DBA/2NCrl (D2), that differ in their susceptibility to stress. Using a multi-omics approach, we identified differential mRNA, miRNA and protein expression changes in the bed nucleus of the stria terminalis (BNST) and blood cells after chronic stress. Integrative gene set enrichment analysis revealed enrichment of mitochondrial-related genes in the BNST and blood of stressed mice. To translate these results to human anxiety, we investigated blood gene expression changes associated with exposure-induced panic attacks. Remarkably, we found reduced expression of mitochondrial-related genes in D2 stress-susceptible mice and in exposure-induced panic attacks in humans, but increased expression of these genes in B6 stress-susceptible mice. Moreover, stress-susceptible vs. stress-resilient B6 mice displayed more mitochondrial cross-sections in the post-synaptic compartment after CSDS. Our findings demonstrate mitochondrial-related alterations in gene expression as an evolutionarily conserved response in stress-related behaviors and validate the use of cross-species approaches in investigating the biological mechanisms underlying anxiety disorders.

Age-related changes in hippocampal AD pathology, actin remodeling proteins and spatial memory behavior of male APP/PS1 mice

Alzheimer's disease (AD) is the most common form of dementia in the elderly, characterized by amyloid-beta (Aβ) plaques and tau neurofibrillary tangles (NFTs). Synaptic plasticity impairment is one of the early pathological events in AD. Transgenic APP/PS1 mice that overproduce Aβ are one of the most extensively used AD animal models. Many studies have investigated the roles of NTF-related p-Tau, non-amyloidogenic ADAM10, amyloidogenic BACE1, Aβ proteolytic NEP and IDE in certain ages of APP/PS1 mice as well as dendritic spine-related Rictor and Profilin-1 in normal mice, but there are few studies exploring the age-related changes of these molecules in the hippocampus of APP/PS1 mice. Furthermore, current studies regarding when memory impairment occurs in these mice are controversial. Thus, we examined the changes of these molecules in APP/PS1 and control mice using Western blot in mice 2-month-old (2 m) to 10 m of age and behavior changes using the Morris water maze from 4 m to 8 m. The results showed that in APP/PS1 mice, significant changes of hippocampal p-Tau, Aβ, ADAM10, BACE1 and Rictor occurred at 6 m, NEP at 8 m, and IDE and Profilin-1 at 10 m. In control mice, changes of p-Tau, ADAM10, and BACE1 occurred at 8 m and NEP at 10 m, while IDE, Rictor and Profilin-1 remained unchanged. Importantly, the Morris water maze test revealed that spatial memory impairment was detected at 8 m but not 4 or 6 m. The above findings clearly evidence that neurochemical changes overtly precede cognitive dysfunctions in this AD model and provide novel knowledge for a better understanding of the molecular events driving AD.

Letrozole induces worse hippocampal synaptic and dendritic changes and spatial memory impairment than ovariectomy in adult female mice

Estrogens (E2) derived from ovaries and/or local de novo synthesis in the hippocampus profoundly regulate hippocampal structure and function, but the importance of local E2 versus ovarian E2 on hippocampal synaptic plasticity and spatial memory has not been well elucidated. The present study used ovariectomy (OVX) and intraperitoneal injection of an E2 synthase inhibitor, letrozole (LET), in adult female mice to investigate changes in hippocampal steroid receptor coactivator-1 (SRC-1), postsynaptic proteins, and actin polymerization dynamics with these treatments. Changes in the CA1 spine density, synapse density and spatial learning and memory after OVX and LET were also investigated. As a result, OVX and LET showed similar regulation of the expression of GluR1, spinophilin and p-Cofilin, but LET tended to induce more significant changes in SRC-1, PSD95, Rictor, Cofilin and actin depolymerization. More significant decreases in F-actin/G-actin, CA1 spine density and synapse density were also observed after LET than after OVX. Notably, LET-treated mice showed worse learning and memory impairment than OVX mice. Taken together, these results demonstrated that circulating E2 played a limited role and that hippocampus-derived E2 played a more important role in the regulation of hippocampal synaptic plasticity and hippocampus-based spatial learning and memory.

Amot and Yap1 regulate neuronal dendritic tree complexity and locomotor coordination in mice

The angiomotin (Amot)-Yes-associated protein 1 (Yap1) complex plays a major role in regulating the inhibition of cell contact, cellular polarity, and cell growth in many cell types. However, the function of Amot and the Hippo pathway transcription coactivator Yap1 in the central nervous system remains unclear. We found that Amot is a critical mediator of dendritic morphogenesis in cultured hippocampal cells and Purkinje cells in the brain. Amot function in developing neurons depends on interactions with Yap1, which is also indispensable for dendrite growth and arborization in vitro. The conditional deletion of Amot and Yap1 in neurons led to a decrease in the complexity of Purkinje cell dendritic trees, abnormal cerebellar morphology, and impairments in motor coordination. Our results indicate that the function of Amot and Yap1 in dendrite growth does not rely on interactions with TEA domain (TEAD) transcription factors or the expression of Hippo pathway-dependent genes. Instead, Amot and Yap1 regulate dendrite development by affecting the phosphorylation of S6 kinase and its target S6 ribosomal protein.

Genetic Etiologies, Diagnosis, and Treatment of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects multiple organ systems due to an inactivating variant in either TSC1 or TSC2, resulting in the hyperactivation of the mechanistic target of rapamycin (mTOR) pathway. Dysregulated mTOR signaling results in increased cell growth and proliferation. Clinically, TSC patients exhibit great phenotypic variability, but the neurologic and neuropsychiatric manifestations of the disease have the greatest morbidity and mortality. TSC-associated epilepsy occurs in nearly all patients and is often difficult to treat because it is refractory to multiple antiseizure medications. The advent of mTOR inhibitors offers great promise in the treatment of TSC-associated epilepsy and other neurodevelopmental manifestations of the disease; however, the optimal timing of therapeutic intervention is not yet fully understood.

Current concepts in the neuropathogenesis of mucolipidosis type IV

Mucolipidosis type IV (MLIV) is an autosomal recessive, lysosomal storage disorder causing progressively severe intellectual disability, motor and speech deficits, retinal degeneration often culminating in blindness, and systemic disease causing a shortened lifespan. MLIV results from mutations in the gene MCOLN1 encoding the transient receptor potential channel mucolipin-1. It is an ultra-rare disease and is currently known to affect just over 100 diagnosed individuals. The last decade has provided a wealth of research focused on understanding the role of the enigmatic mucolipin-1 protein in cell and brain function and how its absence causes disease. This review explores our current understanding of the mucolipin-1 protein in relation to neuropathogenesis in MLIV and describes recent findings implicating mucolipin-1's important role in mechanistic target of rapamycin and TFEB (transcription factor EB) signaling feedback loops as well as in the function of the greater endosomal/lysosomal system. In addition to addressing the vital role of mucolipin-1 in the brain, we also report new data on the question of whether haploinsufficiency as would be anticipated in MCOLN1 heterozygotes is associated with any evidence of neuron dysfunction or disease. Greater insights into the role of mucolipin-1 in the nervous system can be expected to shed light not only on MLIV disease but also on numerous processes governing normal brain function. This article is part of the Special Issue "Lysosomal Storage Disorders".