TAM receptor deficiency affects adult hippocampal neurogenesis

Whole-Exome Sequencing in Family Trios Reveals De Novo Mutations Associated with Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease characterized by insulin deficiency and loss of pancreatic islet β-cells. The objective of this study is to identify de novo mutations in 13 trios from singleton families that contribute to the genetic basis of T1DM through the application of whole-exome sequencing (WES). Of the 13 families sampled for this project, 12 had de novo variants, with Family 7 having the highest number (nine) of variants linked to T1DM/autoimmune pathways, whilst Family 4 did not have any variants past the filtering steps. There were 10 variants of 7 genes reportedly associated with T1DM (MST1; TDG; TYRO3; IFIHI; GLIS3; VEGFA; TYK2). There were 20 variants of 13 genes that were linked to endocrine, metabolic, or autoimmune diseases. Our findings demonstrate that trio-based WES is a powerful approach for identifying new candidate genes for the pathogenesis of T1D. Genotyping and functional annotation of the discovered de novo variants in a large cohort is recommended to ascertain their association with disease pathogenesis.

An insight into the TAM system in Alzheimer's disease

The TAM receptors may help delay the progression of Alzheimer's disease (AD). AD is the most common neurodegenerative disease associated with human aging. The TAM receptors, derived from the first letter of its three constituents -Tyro3, Axl, and Mertk, are associated with immune responses, cellular differentiation and migration, and clearance of apoptotic cells and debris, with the two canonical ligands, Growth Arrest Specific 6 (Gas6) and ProS1. Several kinds of research have indicated the participation of the TAM system in AD pathology. Also, the TAMs regulate multiple features of microglia, the significant sensors of disorder in the central nervous system (CNS). In this review, we describe the biology of the TAM receptors and ligands in the CNS. Then, we discuss the relationship between the TAM system and AD, specially focusing on its functional expression in the microglia. Finally, we also summarize some agents that could interfere with the TAM signaling pathways and discuss potential difficulties and strategies for drug development.

Adrenoceptors as potential target for add-on immunomodulatory therapy in multiple sclerosis

This review summarizes recent findings related to the role of the sympathetic nervous system (SNS) in pathogenesis of multiple sclerosis (MS) and its commonly used experimental model - experimental autoimmune encephalomyelitis (EAE). They indicate that noradrenaline, the key end-point mediator of the SNS, acting through β-adrenoceptor, has a contributory role in the early stages of MS/EAE development. This stage is characterized by the SNS hyperactivity (increased release of noradrenaline) reflecting the net effect of different factors, such as the disease-associated inflammation, stress, vitamin D hypovitaminosis, Epstein-Barr virus infection and dysbiosis. Thus, the administration of propranolol, a non-selective β-adrenoceptor blocker, readily crossing the blood-brain barrier, to experimental rats before the autoimmune challenge and in the early (preclinical/prodromal) phase of the disease mitigates EAE severity. This phenomenon has been ascribed to the alleviation of neuroinflammation (due to attenuation of primarily microglial activation/proinflammatory functions) and the diminution of the magnitude of the primary CD4+ T-cell autoimmune response (the effect associated with impaired autoantigen uptake by antigen presenting cells and their migration into draining lymph nodes). The former is partly related to breaking of the catecholamine-dependent self-amplifying microglial feed-forward loop and the positive feedback loop between microglia and the SNS, leading to down-regulation of the SNS hyperactivity and its enhancing influence on microglial activation/proinflammatory functions and the magnitude of autoimmune response. The effects of propranolol are shown to be more prominent in male EAE animals, the phenomenon important as males (like men) are likely to develop clinically more severe disease. Thus, these findings could serve as a firm scientific background for formulation of a new sex-specific immune-intervention strategy for the early phases of MS (characterized by the SNS hyperactivity) exploiting anti-(neuro)inflammatory and immunomodulatory properties of propranolol and other relatively cheap and safe adrenergic drugs with similar therapeutic profile.

Phosphatidylserine in the Nervous System: Cytoplasmic Regulator of the AKT and PKC Signaling Pathways and Extracellular "Eat-Me" Signal in Microglial Phagocytosis

Phosphatidylserine (PtdSer) is an important anionic phospholipid found in eukaryotic cells and has been proven to serve as a beneficial factor in the treatment of neurodegenerative diseases. PtdSer resides in the inner leaflet of the plasma membrane, where it is involved in regulating the AKT and PKC signaling pathways; however, it becomes exposed to the extracellular leaflet during neurodevelopmental processes and neurodegenerative diseases, participating in microglia-mediated synaptic and neuronal phagocytosis. In this paper, we review several characteristics of PtdSer, including the synthesis and translocation of PtdSer, the functions of cytoplasmic and exposed PtdSer, and different PtdSer-detection materials used to further understand the role of PtdSer in the nervous system.

Regulation and bioinformatic analysis of circ_0015891/miR-129-1-3p axis in methamphetamine-induced dopaminergic apoptosis

Methamphetamine (METH) abuse can result in severe neurotoxicity, for which the mechanism is not yet clear. In the present study, we investigated the role of noncoding RNAs in METH-induced dopaminergic neurotoxicity, and analyzed the underlying mechanism using bioinformatic methods. We confirmed by flow cytometry that miR-129-1-3p is involved in promoting dopaminergic apoptosis under METH treatment and its role could be inhibited by a high concentration of circ_0015891. Also, we combined transcriptomic data with bioinformatics to explore the downstream mechanism of miR-129-1-3p regulation of METH-induced apoptosis, highlighted the potentially pivotal figure of response to nutrition. Further bioinformatic analysis of circ_0015891 was conducted as well and showed that circ_0015891 was the sponge of various microRNAs that effect apoptosis by different mechanisms. Collectively, we found a novel circ_0015891/miR-129-1-3p axis that may be a promising therapeutic target for METH-induced dopaminergic neurotoxicity.

Specifically Targeted Transport of Plasma Membrane Transporters: From Potential Mechanisms for Regulating Cell Health or Disease to Applications

Normal substrate transport and signal transmission are the premise to ensure the health of biological somatic cells. Therefore, a comprehensive understanding of the molecular mechanism of intercellular substrate transport is of great significance for clinical treatment. In order to better understand the membrane protein through its interaction with receptors, to help maintain a healthy cell and the molecular mechanisms of disease, in this paper, we seek to clarify, first of all, the recognition mechanism for different types of membrane protein receptors; pathogen invasion using the transport pathway involved in the membrane; and the latest specific target sites of various kinds of membrane transport carriers; to provide an explanation and summary of the system. Secondly, the downstream receptor proteins and specific substrates of different membrane transporters were classified systematically; the functional differences of different subclasses and their relationship with intracellular transport disorders were analyzed to further explore the potential relationship between cell transport disorders and diseases. Finally, the paper summarizes the use of membrane transporter-specific targets for drug design and development from the latest research results; it points out the transporter-related results in disease treatment; the application prospects and the direction for drug development and disease treatment providing a new train of thought; also for disease-specific targeted therapy, it provides a certain reference value.

Immunosuppression and Neuroinflammation in Stroke Pathobiology

Over the preceding decades, there have been substantial advances in our knowledge of the pathophysiology of stroke. One such advance has been an increased understanding of the multifarious crosstalk in which the nervous and immune systems engage in order to maintain homeostasis. By interrupting the immune-nervous nexus, it is thought that stroke induces change in both systems. Additionally, it has been found that both innate and adaptive immunosuppression play protective roles against the effects of stroke. The release of danger-/damage-associated molecular patterns (DAMPs) activates Toll-like receptors (TLRs), contributing to the harmful inflammatory effects of ischemia/reperfusion injury after stroke; the Tyro3, Axl, and MerTK (TAM)/Gas6 system, however, has been shown to suppress inflammation via downstream signaling molecules that inhibit TLR signaling. Anti-inflammatory cytokines have also been found to promote neuroprotection following stroke. Additionally, adaptive immunosuppression merits further consideration as a potential endogenous protective mechanism. In this review, we highlight recent studies regarding the effects and mechanism of immunosuppression on the pathophysiology of stroke, with the hope that a better understanding of the function of both of innate and adaptive immunity in this setting will facilitate the development of effective therapies for post-stroke inflammation.

MERTK Inhibition: Potential as a Treatment Strategy in EGFR Tyrosine Kinase Inhibitor-Resistant Non-Small Cell Lung Cancer

Epidermal growth factor tyrosine kinase inhibitors (EGFR-TKIs) are currently the most effective treatment for non-small cell lung cancer (NSCLC) patients, who carry primary EGFR mutations. However, the patients eventually develop drug resistance to EGFR-TKIs after approximately one year. In addition to the acquisition of the EGFR T790M mutation, the activation of alternative receptor-mediated signaling pathways is a common mechanism for conferring the insensitivity of EGFR-TKI in NSCLC. Upregulation of the Mer receptor tyrosine kinase (MERTK), which is a member of the Tyro3-Axl-MERTK (TAM) family, is associated with a poor prognosis of many cancers. The binding of specific ligands, such as Gas6 and PROS1, to MERTK activates phosphoinositide 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) cascades, which are the signaling pathways shared by EGFR. Therefore, the inhibition of MERTK can be considered a new therapeutic strategy for overcoming the resistance of NSCLC to EGFR-targeted agents. Although several small molecules and monoclonal antibodies targeting the TAM family are being developed and have been described to enhance the chemosensitivity and converse the resistance of EGFR-TKI, few have specifically been developed as MERTK inhibitors. The further development and investigation of biomarkers which can accurately predict MERTK activity and the response to MERTK inhibitors and MERTK-specific drugs are vitally important for obtaining appropriate patient stratification and increased benefits in clinical applications.

Embryonic Microglia Interact with Hypothalamic Radial Glia during Development and Upregulate the TAM Receptors MERTK and AXL following an Insult

Despite a growing appreciation for microglial influences on the developing brain, the responsiveness of microglia to insults during gestation remains less well characterized, especially in the embryo when microglia themselves are still maturing. Here, we asked if fetal microglia could coordinate an innate immune response to an exogenous insult. Using time-lapse imaging, we showed that hypothalamic microglia actively surveyed their environment by near-constant "touching" of radial glia projections. However, following an insult (i.e., IUE or AAV transduction), this seemingly passive touching became more intimate and long lasting, ultimately resulting in the retraction of radial glial projections and degeneration into small pieces. Mechanistically, the TAM receptors MERTK and AXL were upregulated in microglia following the insult, and Annexin V treatment inhibited radial glia breakage and engulfment by microglia. These data demonstrate a remarkable responsiveness of embryonic microglia to insults during gestation, a critical window for neurodevelopment.

Anti-Axl antibody treatment reduces the severity of experimental autoimmune encephalomyelitis

BACKGROUND

Multiple sclerosis is an immune-mediated disease of the central nervous system (CNS) characterized by inflammation, oligodendrocytes loss, demyelination, and damaged axons. Tyro3, Axl, and MerTK belong to a family of receptor tyrosine kinases that regulate innate immune responses and CNS homeostasis. During experimental autoimmune encephalomyelitis (EAE), the mRNA expression of MerTK, Gas6, and Axl significantly increase, whereas Tyro3 and ProS1 remain unchanged. We have shown that Gas6 is neuroprotective during EAE, and since Gas6 activation of Axl may be necessary for conferring neuroprotection, we sought to determine whether α-Axl or α-MerTK antibodies, shown by others to activate their respective receptors in vivo, could effectively reduce inflammation and neurodegeneration.

METHODS

Mice received either α-Axl, α-MerTK, IgG isotype control, or PBS before the onset of EAE symptoms. EAE clinical course, axonal damage, demyelination, cytokine production, and immune cell activation in the CNS were used to determine the severity of EAE.

RESULTS

α-Axl antibody treatment significantly decreased the EAE clinical indices of female mice during chronic EAE and of male mice during both acute and chronic phases. The number of days mice were severely paralyzed also significantly decreased with α-Axl treatment. Inflammatory macrophages/microglia and the extent of demyelination significantly decreased in the spinal cords of α-Axl-treated mice during chronic EAE, with no differences in the production of pro-inflammatory cytokines. α-MerTK antibody did not influence EAE induction or progression.

CONCLUSION

Our data suggests that the beneficial effect of Gas6/Axl signaling observed in mice administered with Gas6 can be partially preserved by administering an activating α-Axl antibody, but not α-MerTK.

Anti-inflammation and anti-apoptosis effects of growth arrest-specific protein 6 in acute liver injury induced by LPS/D-GalN in mice

Purpose

To investigate the effect of growth arrest-specific protein 6 (Gas6) on acute liver injury in mice and related mechanisms.

Methods

Thirty C57BL/6 (6-8 weeks old) mice were randomly divided into control, LPS/D-GalN, and LPS/D-GalN+Gas6 groups (10 mice in each group). The LPS/D-GalN group was intraperitoneally administered with LPS (0.25 mg/Kg) and D-GalN (400 mg/Kg) for 5h. The LPS/D-GalN+Gas6 group was intraperitoneally administered with rmGas6 one hour before intraperitoneal application of LPS/D-GalN. All subjects were sacrificed at 5 h for blood and tissue analysis. The expression of protein and mRNA was assessed by western blotting and RT-PCR, respectively.

Results

Compared with the control group, AST, ALT, IL-1β, TNF-α, IL-6 IL-10, MPO activity were increased in the LPS/D-GalN group. However, they were significantly inhibited by Gas6. Gas6 markedly suppressed the expression of apoptosis-related protein induced by LPS/D-GalN. Moreover, Gas6 attenuated the activation of the NF-κB signaling pathway in acute liver injury induced by LPS/D-GalN.

Conclusions

Gas6 alleviates acute liver injury in mice through regulating NF-κB signaling pathways. Gas6 can be a potential therapeutic agent in treating LPS/D-GalN-induced acute liver injury in the future.

Genome-wide association analysis of hippocampal volume identifies enrichment of neurogenesis-related pathways

Adult neurogenesis occurs in the dentate gyrus of the hippocampus during adulthood and contributes to sustaining the hippocampal formation. To investigate whether neurogenesis-related pathways are associated with hippocampal volume, we performed gene-set enrichment analysis using summary statistics from a large-scale genome-wide association study (N = 13,163) of hippocampal volume from the Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium and two year hippocampal volume changes from baseline in cognitively normal individuals from Alzheimer's Disease Neuroimaging Initiative Cohort (ADNI). Gene-set enrichment analysis of hippocampal volume identified 44 significantly enriched biological pathways (FDR corrected p-value < 0.05), of which 38 pathways were related to neurogenesis-related processes including neurogenesis, generation of new neurons, neuronal development, and neuronal migration and differentiation. For genes highly represented in the significantly enriched neurogenesis-related pathways, gene-based association analysis identified TESC, ACVR1, MSRB3, and DPP4 as significantly associated with hippocampal volume. Furthermore, co-expression network-based functional analysis of gene expression data in the hippocampal subfields, CA1 and CA3, from 32 normal controls showed that distinct co-expression modules were mostly enriched in neurogenesis related pathways. Our results suggest that neurogenesis-related pathways may be enriched for hippocampal volume and that hippocampal volume may serve as a potential phenotype for the investigation of human adult neurogenesis.

CX3CR1-deficient microglia shows impaired signalling of the transcription factor NRF2: Implications in tauopathies

TAU protein aggregation is the main characteristic of neurodegenerative diseases known as tauopathies. Low-grade chronic inflammation is also another hallmark that indicates crosstalk between damaged neurons and glial cells. Previously, we have demonstrated that neurons overexpressing TAU^P301L release CX3CL1, which activates the transcription factor NRF2 signalling to limit over-activation in microglial cells in vitro and in vivo. However, the connection between CX3CL1/CX3CR1 and NRF2 system and its functional implications in microglia are poorly described. We evaluated CX3CR1/NRF2 axis in the context of tauopathies and its implication in neuroinflammation. Regarding the molecular mechanisms that connect CX3CL1/CX3CR1 and NRF2 systems, we observed that in primary microglia from Cx3cr1^-/- mice the mRNA levels of Nrf2 and its related genes were significantly decreased, establishing a direct linking between both systems. To determine functional relevance of CX3CR1, migration and phagocytosis assays were evaluated. CX3CR1-deficient microglia showed impaired cell migration and deficiency of phagocytosis, as previously described for NRF2-deficient microglia, reinforcing the idea of the relevance of the CX3CL1/CX3CR1 axis in these events. The importance of these findings was evident in a tauopathy mouse model where the effects of sulforaphane (SFN), an NRF2 inducer, were examined on neuroinflammation in Cx3cr1^+/+ and Cx3cr1^-/- mice. Interestingly, the treatment with SFN was able to modulate astrogliosis but failed to reduce microgliosis in Cx3cr1^-/- mice. These findings suggest an essential role of the CX3CR1/NRF2 axis in microglial function and in tauopathies. Therefore, polymorphisms with loss of function in CX3CR1 or NRF2 have to be taken into account for the development of therapeutic strategies.

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CX3CR1-deficient primary microglial cells present impaired expression of the transcription factor NRF2 signature.

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TAM receptors expression is decreased in CX3CR1-deficient microglia.

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AXL receptor is a NRF2-dependent gene.

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Loss of CX3CR1 expression led to impaired phagocytosis and migration of microglia.

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Sulforaphane treatment did not reverse rAAV-TAU^P301L induced microgliosis in CX3CR1-deficient mice.

Role of the End-Point Mediators of Sympathoadrenal and Sympathoneural Stress Axes in the Pathogenesis of Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

The role of stress effector systems in the initiation and progression of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), the most commonly used experimental model of MS, has strongly been suggested. To corroborate this notion, alterations in activity of the sympathoadrenal and sympathoneural axes of sympathoadrenal system (a major communication pathway between the central nervous system and the immune system), mirrored in altered release of their end-point mediators (adrenaline and noradrenaline, respectively), are shown to precede (in MS) and/or occur during development of MS and EAE in response to immune cell activation (in early phase of disease) and disease-related damage of sympathoadrenal system neurons and their projections (in late phase of disease). To add to the complexity, innate immunity cells and T-lymphocytes synthesize noradrenaline that may be implicated in a local autocrine/paracrine self-amplifying feed-forward loop to enhance myeloid-cell synthesis of proinflammatory cytokines and inflammatory injury. Furthermore, experimental manipulations targeting noradrenaline/adrenaline action are shown to influence clinical outcome of EAE, in a disease phase-specific manner. This is partly related to the fact that virtually all types of cells involved in the instigation and progression of autoimmune inflammation and target tissue damage in EAE/MS express functional adrenoceptors. Although catecholamines exert majority of immunomodulatory effects through β₂-adrenoceptor, a role for α-adrenoceptors in EAE pathogenesis has also been indicated. In this review, we summarize all aforementioned aspects of immunopathogenetic action of catecholamines in EAE/MS as possibly important for designing new strategies targeting their action to prevent/mitigate autoimmune neuroinflammation and tissue damage.

Targeting the BDNF/TrkB pathway for the treatment of tumors

Neurotrophins are a family of growth factors that regulate neural survival, development, function and plasticity in the central and the peripheral nervous system. There are four neurotrophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and NT-4. Among them, BDNF is the most studied due to its high expression in the brain. Over the past two decades, BDNF and its receptor tropomyosin receptor kinase B (TrkB) have been reported to be upregulated in a wide range of tumors. This activated signal stimulates a series of downstream pathways, including phosphoinositide 3-kinase/protein kinase B, Ras-Raf-mitogen activated protein kinase kinase-extracellular signal-regulated kinases, the phospholipase-C-γ pathway and the transactivation of epidermal growth factor receptor. Activation of these signaling pathways induces oncogenic effects by increasing cancer cell growth, proliferation, survival, migration and epithelial to mesenchymal transition, and decreasing anoikis, relapse and chemotherapeutic sensitivity. The present review summarizes recent findings to discuss the role of BDNF in tumors, the underlying molecular mechanism, targeting Trk receptors for treatment of cancers and its potential risk.

Melatonin induces mechanisms of brain resilience against neurodegeneration

Melatonin is an endogenous pleiotropic molecule which orchestrates regulatory functions and protective capacity against age-related ailments. The increase in circulating levels of melatonin through dietary supplements intensifies its health benefits. Investigations in animal models have shown that melatonin protects against Alzheimer's disease (AD)-like pathology, although clinical studies have not been conclusive. We hypothesized that melatonin induces changes in the brain that prevent or attenuate AD by increasing resilience. Therefore, we treated healthy nontransgenic (NoTg) and AD transgenic (3xTg-AD) 6-month-old mice with a daily dose of 10 mg/kg of melatonin until 12 months of age. As expected, melatonin reversed cognitive impairment and dementia-associated behaviors of anxiety and apathy and reduced amyloid and tau burden in 3xTg-AD mice. Remarkably, melatonin induced cognitive enhancement and higher wellness level-related behavior in NoTg mice. At the mechanism level, NF-κB and proinflammatory cytokine expressions were decreased in both NoTg and 3xTg-AD mice. The SIRT1 pathway of longevity and neuroprotection was also activated in both mouse strains after melatonin dosing. Furthermore, we explored new mechanisms and pathways not previously associated with melatonin treatment such as the ubiquitin-proteasome proteolytic system and the recently proposed neuroprotective Gas6/TAM pathway. The upregulation of proteasome activity and the modulation of Gas6 and its receptors by melatonin were similarly displayed by both NoTg and 3xTg-AD mice. Therefore, these results confirm the potential of melatonin treatment against AD pathology, by way of opening new pathways in its mechanisms of action, and demonstrating that melatonin induces cognitive enhancement and brain resilience against neurodegenerative processes.

Sulforaphane rescues amyloid-β peptide-mediated decrease in MerTK expression through its anti-inflammatory effect in human THP-1 macrophages

Background

Mer tyrosine kinase (MerTK) activity necessary for amyloid-stimulated phagocytosis strongly implicates that MerTK dysregulation might contribute to chronic inflammation implicated in Alzheimer’s disease (AD) pathology. However, the precise mechanism involved in the regulation of MerTK expression by amyloid-β (Aβ) in proinflammatory environment has not yet been ascertained.

Methods

The objective of this study was to determine the underlying mechanism involved in Aβ-mediated decrease in MerTK expression through Aβ-mediated regulation of MerTK expression and its modulation by sulforaphane in human THP-1 macrophages challenged with Aβ1-42. We used protein preparation, Ca²⁺ influx fluorescence imaging, nuclear fractionation, Western blotting techniques, and small interfering RNA (siRNA) knockdown to perform our study.

Results

Aβ1-42 elicited a marked decrease in MerTK expression along with increased intracellular Ca²⁺ level and induction of proinflammatory cytokines such as IL-1β and TNF-α. Ionomycin A and thapsigargin also increased intracellular Ca²⁺ levels and production of IL-1β and TNF-α, mimicking the effect of Aβ1-42. In contrast, the Aβ1-42-evoked responses were attenuated by depletion of Ca²⁺ with ethylene glycol tetraacetic acid. Furthermore, recombinant IL-1β or TNF-α elicited a decrease in MerTK expression. However, immunodepletion of IL-1β or TNF-α with neutralizing antibodies significantly inhibited Aβ1-42-mediated downregulation of MerTK expression. Notably, sulforaphane treatment potently inhibited Aβ1-42-induced intracellular Ca²⁺ level and rescued the decrease in MerTK expression by blocking nuclear factor-κB (NF-κB) nuclear translocation, thereby decreasing IL-1β and TNF-α production upon Aβ1-42 stimulation. Such adverse effects of sulforaphane were replicated by BAY 11-7082, a NF-κB inhibitor. Moreover, sulforaphane’s anti-inflammatory effects on Aβ1-42-induced production of IL-1β and TNF-α were significantly diminished by siRNA-mediated knockdown of MerTK, confirming a critical role of MerTK in suppressing Aβ1-42-induced innate immune response.

Conclusion

These findings implicate that targeting of MerTK with phytochemical sulforaphane as a mechanism for preventing Aβ1-42-induced neuroinflammation has potential to be applied in AD therapeutics.

Axl Mediates ZIKA Virus Entry in Human Glial Cells and Modulates Innate Immune Responses

ZIKA virus (ZIKV) is an emerging pathogen responsible for neurological disorders and congenital microcephaly. However, the molecular basis for ZIKV neurotropism remains poorly understood. Here, we show that Axl is expressed in human microglia and astrocytes in the developing brain and that it mediates ZIKV infection of glial cells. Axl-mediated ZIKV entry requires the Axl ligand Gas6, which bridges ZIKV particles to glial cells. Following binding, ZIKV is internalized through clathrin-mediated endocytosis and traffics to Rab5+ endosomes to establish productive infection. During entry, the ZIKV/Gas6 complex activates Axl kinase activity, which downmodulates interferon signaling and facilitates infection. ZIKV infection of human glial cells is inhibited by MYD1, an engineered Axl decoy receptor, and by the Axl kinase inhibitor R428. Our results highlight the dual role of Axl during ZIKV infection of glial cells: promoting viral entry and modulating innate immune responses. Therefore, inhibiting Axl function may represent a potential target for future antiviral therapies.

The tyrosine kinase receptor Tyro3 enhances lifespan and neuropeptide Y (Npy) neuron survival in the mouse anorexia (anx) mutation

Severe appetite and weight loss define the eating disorder anorexia nervosa, and can also accompany the progression of some neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS). Although acute loss of hypothalamic neurons that produce appetite-stimulating neuropeptide Y (Npy) and agouti-related peptide (Agrp) in adult mice or in mice homozygous for the anorexia (anx) mutation causes aphagia, our understanding of the factors that help maintain appetite regulatory circuitry is limited. Here we identify a mutation (C19T) that converts an arginine to a tryptophan (R7W) in the TYRO3 protein tyrosine kinase 3 (Tyro3) gene, which resides within the anx critical interval, as contributing to the severity of anx phenotypes. Our observation that, like Tyro3-/- mice, anx/anx mice exhibit abnormal secondary platelet aggregation suggested that the C19T Tyro3 variant might have functional consequences. Tyro3 is expressed in the hypothalamus and other brain regions affected by the anx mutation, and its mRNA localization appeared abnormal in anx/anx brains by postnatal day 19 (P19). The presence of wild-type Tyro3 transgenes, but not an R7W-Tyro3 transgene, doubled the weight and lifespans of anx/anx mice and near-normal numbers of hypothalamic Npy-expressing neurons were present in Tyro3-transgenic anx/anx mice at P19. Although no differences in R7W-Tyro3 signal sequence function or protein localization were discernible in vitro, distribution of R7W-Tyro3 protein differed from that of Tyro3 protein in the cerebellum of transgenic wild-type mice. Thus, R7W-Tyro3 protein localization deficits are only detectable in vivo Further analyses revealed that the C19T Tyro3 mutation is present in a few other mouse strains, and hence is not the causative anx mutation, but rather an anx modifier. Our work shows that Tyro3 has prosurvival roles in the appetite regulatory circuitry and could also provide useful insights towards the development of interventions targeting detrimental weight loss.

Growth Arrest Specific 6 Concentration is Increased in the Cerebrospinal Fluid of Patients with Alzheimer's Disease

Growth arrest specific 6 (Gas6) has neurotrophic and neuroinflammatory functions, and may play a role in Alzheimer's disease (AD). In keeping with this hypothesis, we observed that cerebrospinal fluid (CSF) Gas6 is increased in AD patients compared to controls (63 versus 67 subjects; median value 13.3 versus 9.1 ng/ml; p < 0.0001). Thereafter, we assessed whether CSF Gas6 concentration was correlated to the following parameters: disease duration, MMSE score two years after clinical diagnosis, AD CSF biomarkers, and years of formal schooling. We detected an inverse correlation between CSF Gas6 levels at diagnosis and both disease duration (p < 0.0001) and decrease in the MMSE score two years later (p < 0.0001). Conversely, we found no correlation between CSF Gas6 and both AD biomarkers and years of formal schooling. In conclusion, our results suggest that upregulation of CSF Gas6 may be part of a defensive response aimed at counteracting AD progression.