Dynamic Control of Synaptic Adhesion and Organizing Molecules in Synaptic Plasticity

Synapses play a critical role in establishing and maintaining neural circuits, permitting targeted information transfer throughout the brain. A large portfolio of synaptic adhesion/organizing molecules (SAMs) exists in the mammalian brain involved in synapse development and maintenance. SAMs bind protein partners, forming trans-complexes spanning the synaptic cleft or cis-complexes attached to the same synaptic membrane. SAMs play key roles in cell adhesion and in organizing protein interaction networks; they can also provide mechanisms of recognition, generate scaffolds onto which partners can dock, and likely take part in signaling processes as well. SAMs are regulated through a portfolio of different mechanisms that affect their protein levels, precise localization, stability, and the availability of their partners at synapses. Interaction of SAMs with their partners can further be strengthened or weakened through alternative splicing, competing protein partners, ectodomain shedding, or astrocytically secreted factors. Given that numerous SAMs appear altered by synaptic activity, in vivo, these molecules may be used to dynamically scale up or scale down synaptic communication. Many SAMs, including neurexins, neuroligins, cadherins, and contactins, are now implicated in neuropsychiatric and neurodevelopmental diseases, such as autism spectrum disorder, schizophrenia, and bipolar disorder and studying their molecular mechanisms holds promise for developing novel therapeutics.

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The AF-6 Homolog Canoe Acts as a Rap1 Effector During Dorsal Closure of the Drosophila Embryo

Genetics ◽

10.1093/genetics/165.1.159 ◽

2003 ◽

Vol 165 (1) ◽

pp. 159-169

Author(s):

Benjamin Boettner ◽

Phoebe Harjes ◽

Satoshi Ishimaru ◽

Michael Heke ◽

Hong Qing Fan ◽

...

Keyword(s):

Molecular Mechanisms ◽

Genetic Interaction ◽

Critical Role ◽

Adherens Junction ◽

Small Gtpases ◽

Drosophila Embryo ◽

Dorsal Closure ◽

Cell Sheets ◽

Jnk Pathway

Abstract Rap1 belongs to the highly conserved Ras subfamily of small GTPases. In Drosophila, Rap1 plays a critical role in many different morphogenetic processes, but the molecular mechanisms executing its function are unknown. Here, we demonstrate that Canoe (Cno), the Drosophila homolog of mammalian junctional protein AF-6, acts as an effector of Rap1 in vivo. Cno binds to the activated form of Rap1 in a yeast two-hybrid assay, the two molecules colocalize to the adherens junction, and they display very similar phenotypes in embryonic dorsal closure (DC), a process that relies on the elongation and migration of epithelial cell sheets. Genetic interaction experiments show that Rap1 and Cno act in the same molecular pathway during DC and that the function of both molecules in DC depends on their ability to interact. We further show that Rap1 acts upstream of Cno, but that Rap1, unlike Cno, is not involved in the stimulation of JNK pathway activity, indicating that Cno has both a Rap1-dependent and a Rap1-independent function in the DC process.

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The potential renal toxicity of silver nanoparticles after repeated oral exposure and its underlying mechanisms

BMC Nephrology ◽

10.1186/s12882-021-02428-5 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Hamed Nosrati ◽

Manijeh Hamzepoor ◽

Maryam Sohrabi ◽

Massoud Saidijam ◽

Mohammad Javad Assari ◽

...

Keyword(s):

Silver Nanoparticles ◽

Molecular Mechanisms ◽

Renal Toxicity ◽

Periodic Acid ◽

Critical Role ◽

Oral Exposure ◽

Control Group ◽

Rt Pcr ◽

Periodic Acid Schiff

Abstract Background Silver nanoparticles (AgNPs) can accumulate in various organs after oral exposure. The main objective of the current study is to evaluate the renal toxicity induced by AgNPs after repeated oral exposure and to determine the relevant molecular mechanisms. Methods In this study, 40 male Wistar rats were treated with solutions containing 30, 125, 300, and 700 mg/kg of AgNPs. After 28 days of exposure, histopathological changes were assessed using hematoxylin-eosin (H&E), Masson’s trichrome, and periodic acid-Schiff (PAS) staining. Apoptosis was quantified by TUNEL and immunohistochemistry of caspase-3, and the level of expression of the mRNAs of growth factors was determined using RT-PCR. Results Histopathologic examination revealed degenerative changes in the glomeruli, loss of tubular architecture, loss of brush border, and interrupted tubular basal laminae. These changes were more noticeable in groups treated with 30 and 125 mg/kg. The collagen intensity increased in the group treated with 30 mg/kg in both the cortex and the medulla. Apoptosis was much more evident in middle-dose groups (i.e., 125 and 300 mg/kg). The results of RT-PCR indicated that Bcl-2 and Bax mRNAs upregulated in the treated groups (p < 0.05). Moreover, the data related to EGF, TNF-α, and TGF-β1 revealed that AgNPs induced significant changes in gene expression in the groups treated with 30 and 700 mg/kg compared to the control group. Conclusion Our observations showed that AgNPs played a critical role in in vivo renal toxicity.

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Hydroxychloroquine Synergizes With The PI3K Inhibitor BKM120 to Exhibit Antitumor Efficacy Independent of Autophagy

10.21203/rs.3.rs-691658/v1 ◽

2021 ◽

Author(s):

Xin Peng ◽

Shaolu Zhang ◽

Wenhui Jiao ◽

Zhenxing Zhong ◽

Yuqi Yang ◽

...

Keyword(s):

Tumor Cells ◽

Cell Biology ◽

Molecular Mechanisms ◽

Critical Role ◽

Single Agent ◽

Antitumor Efficacy ◽

Antitumor Effects ◽

Autophagy Inhibitor

Abstract Background: The critical role of phosphoinositide 3-kinase (PI3K) activation in tumor cell biology has prompted massive efforts to develop PI3K inhibitors (PI3Kis) for cancer therapy. However, recent results from clinical trials have shown only a modest therapeutic efficacy of single-agent PI3Kis in solid tumors. Targeting autophagy has controversial context-dependent effects in cancer treatment. As a FDA-approved lysosomotropic agent, hydroxychloroquine (HCQ) has been well tested as an autophagy inhibitor in preclinical models. Here, we elucidated the novel mechanism of HCQ alone or in combination with PI3Ki BKM120 in the treatment of cancer.Methods: The antitumor effects of HCQ and BKM120 on three different types of tumor cells were assessed by in vitro PrestoBlue assay, colony formation assay and in vivo zebrafish and nude mouse xenograft models. The involved molecular mechanisms were investigated by MDC staining, LC3 puncta formation assay, immunofluorescent assay, flow cytometric analysis of apoptosis and ROS, qRT-PCR, Western blot, comet assay, homologous recombination (HR) assay and immunohistochemical staining. Results: HCQ significantly sensitized cancer cells to BKM120 in vitro and in vivo. Interestingly, the sensitization mediated by HCQ could not be phenocopied by treatment with other autophagy inhibitors (Spautin-1, 3-MA and bafilomycin A1) or knockdown of the essential autophagy genes Atg5/Atg7, suggesting that the sensitizing effect might be mediated independent of autophagy status. Mechanistically, HCQ induced ROS production and activated the transcription factor NRF2. In contrast, BKM120 prevented the elimination of ROS by inactivation of NRF2, leading to accumulation of DNA damage. In addition, HCQ activated ATM to enhance HR repair, a high-fidelity repair for DNA double-strand breaks (DSBs) in cells, while BKM120 inhibited HR repair by blocking the phosphorylation of ATM and the expression of BRCA1/2 and Rad51. Conclusions: Our study revealed that HCQ and BKM120 synergistically increased DSBs in tumor cells and therefore augmented apoptosis, resulting in enhanced antitumor efficacy. Our findings provide a new insight into how HCQ exhibits antitumor efficacy and synergizes with PI3Ki BKM120, and warn that one should consider the “off target” effects of HCQ when used as autophagy inhibitor in the clinical treatment of cancer.

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FC 006PP2A PHOSPHATASE INHIBITION IS ANTI-FIBROTIC THROUGH SER77 PHOSPHORYLATION-MEDIATED ARNT/ARNT HOMODIMER FORMATION

Nephrology Dialysis Transplantation ◽

10.1093/ndt/gfab124.003 ◽

2021 ◽

Vol 36 (Supplement_1) ◽

Author(s):

Gunsmaa Nyamsuren ◽

Gregor Christof Rapp ◽

Björn Tampe ◽

Michael Zeisberg

Keyword(s):

Molecular Mechanisms ◽

Therapeutic Potential ◽

Critical Role ◽

Phosphorylation Site ◽

Receptor Expression ◽

Proximity Ligation Assay ◽

Proximity Ligation ◽

Aryl Hydrocarbon ◽

Ureter Obstruction

Abstract Background and Aims Aryl hydrocarbon receptor nuclear translocator (ARNT) mediates anti-fibrotic activity in kidney and liver through induction of ALK3-receptor expression and subsequently increased Smad1/5/8 signaling. While expression of ARNT can be pharmacologically induced by sub-immunosuppressive doses of FK506 or by GPI1046, its anti-fibrotic activity is only realized when ARNT-ARNT homodimers form, as opposed to formation of ARNT-AHR or ARNT-HIF1α heterodimers. Mechanisms underlying ARNTs dimerization decision to specifically form ARNT-ARNT homodimers and possible cues to specifically induce ARNT homodimerization have been previously unknown. We here aimed to elucidate the molecular mechanisms underlying control of ARNT dimerization decision and to explore its therapeutic potential. Method We analyzed dimerization of recombinant and native ARNT by immunoprecipitation, MALDI-TOF mass spectrometry, and LS-MS/MS analysis and proximity ligation assay. Phosphorylation sites were mapped through generation of phosphorylation site mutants and through pharmacological inhibition. For in vivo analysis we challenged mice with model of unilateral ureter obstruction and carbon tetrachloride to induce fibrosis in kidney and liver. Results Here we report that inhibition of PP2A phosphatase activity increases intracellular accumulation of ARNT-ARNT homodimers. This effect is dependent on enhanced ARNT-ARNT homodimerization and decreased ARNT proteolytic degradation, but independent of ARNT transcription (which remains unchanged upon PP2A inhibition). We further identify that Ser77 phosphorylation plays a critical role in ARNT homodimerization, as ARNT-ARNT homodimers do not form with Ser77/Asp-mutant ARNT proteins. In light of previous studies which identified anti-fibrotic activity upon increased ARNT expression, we further demonstrate attenuated fibrosis upon monotherapy with the PP2A inhibitor LB100, and additive anti-fibrotic activities upon combination with pharmacological inducers of ARNT expression FK506 or GPI1046 in murine models of kidney and liver fibrosis. Conclusion Our study provides additional evidence for the anti-fibrotic activity of ARNT and reveals Ser77 phosphorylation as a novel pharmacological target to realize the therapeutic potential of increased ARNT transactivation activity.

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UBE3A-mediated PTPA ubiquitination and degradation regulate PP2A activity and dendritic spine morphology

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1820131116 ◽

2019 ◽

Vol 116 (25) ◽

pp. 12500-12505 ◽

Cited By ~ 7

Author(s):

Jie Wang ◽

Sen-Sen Lou ◽

Tingting Wang ◽

Rong-Jie Wu ◽

Guangying Li ◽

...

Keyword(s):

Ubiquitin Ligase ◽

Dendritic Spine ◽

Isotope Labeling ◽

Neurodevelopmental Disorder ◽

Critical Role ◽

Motor Impairment ◽

Autism Spectrum ◽

Loss Of Function ◽

Pp2a Activity

Deficiency in the E3 ubiquitin ligase UBE3A leads to the neurodevelopmental disorder Angelman syndrome (AS), while additional dosage of UBE3A is linked to autism spectrum disorder. The mechanisms underlying the downstream effects of UBE3A gain or loss of function in these neurodevelopmental disorders are still not well understood, and effective treatments are lacking. Here, using stable-isotope labeling of amino acids in mammals and ubiquitination assays, we identify PTPA, an activator of protein phosphatase 2A (PP2A), as a bona fide ubiquitin ligase substrate of UBE3A. Maternal loss of Ube3a (Ube3am−/p+) increased PTPA level, promoted PP2A holoenzyme assembly, and elevated PP2A activity, while maternal 15q11–13 duplication containing Ube3a down-regulated PTPA level and lowered PP2A activity. Reducing PTPA level in vivo restored the defects in dendritic spine maturation in Ube3am−/p+ mice. Moreover, pharmacological inhibition of PP2A activity with the small molecule LB-100 alleviated both reduction in excitatory synaptic transmission and motor impairment in Ube3am−/p+ mice. Together, our results implicate a critical role of UBE3A-PTPA-PP2A signaling in the pathogenesis of UBE3A-related disorders and suggest that PP2A-based drugs could be potential therapeutic candidates for treatment of UBE3A-related disorders.

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Ligation of CD137 receptor prevents and reverses established anergy of CD8+ cytolytic T lymphocytes in vivo

Blood ◽

10.1182/blood-2003-06-2184 ◽

2004 ◽

Vol 103 (1) ◽

pp. 177-184 ◽

Cited By ~ 68

Author(s):

Ryan A. Wilcox ◽

Koji Tamada ◽

Dallas B. Flies ◽

Gefeng Zhu ◽

Andrei I. Chapoval ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Molecular Mechanisms ◽

Transplant Rejection ◽

Critical Role ◽

Tumor Necrosis Factor Receptor ◽

T Cell Anergy ◽

Cell Anergy ◽

Induced Tolerance

Abstract T-cell anergy is a tolerance mechanism defined as a hyporesponsive status of antigen-specific T cells upon prior antigen encounter and is believed to play a critical role in the evasion of tumor immunity and the amelioration of allogeneic transplant rejection. Molecular mechanisms in controlling T-cell anergy are less known. We show here that administration of an agonistic monoclonal antibody (mAb) to CD137, a member of the tumor necrosis factor receptor superfamily, prevents the induction of CD8+ cytolytic T-lymphocyte (CTL) anergy by soluble antigens. More importantly, CD137 mAb restores the functions of established anergic CTLs upon reencountering their cognate antigen. As a result, infusion of CD137 mAb inhibits progressive tumor growth that is caused by soluble tumor antigen-induced tolerance in a P815R model. CD137 mAb also restores proliferation and effector functions of anergic alloreactive 2C T cells in a bone marrow transplantation model. Our results indicate that ligation of CD137 receptor delivers a regulatory signal for T-cell anergy and implicate manipulation of the CD137 pathway as a new approach to break T-cell tolerance.

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Acid-sensing ion channels regulate spontaneous inhibitory activity in the hippocampus: possible implications for epilepsy

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2015.0431 ◽

2016 ◽

Vol 371 (1700) ◽

pp. 20150431 ◽

Cited By ~ 13

Author(s):

O. Ievglevskyi ◽

D. Isaev ◽

O. Netsyk ◽

A. Romanov ◽

M. Fedoriuk ◽

...

Keyword(s):

Ion Channels ◽

Hippocampal Neurons ◽

Hippocampal Slices ◽

Synaptic Activity ◽

Mammalian Brain ◽

Strong Increase ◽

Life And Death ◽

Acid Sensing Ion Channels

Acid-sensing ion channels (ASICs) play an important role in numerous functions in the central and peripheral nervous systems ranging from memory and emotions to pain. The data correspond to a recent notion that each neuron and many glial cells of the mammalian brain express at least one member of the ASIC family. However, the mechanisms underlying the involvement of ASICs in neuronal activity are poorly understood. However, there are two exceptions, namely, the straightforward role of ASICs in proton-based synaptic transmission in certain brain areas and the role of the Ca 2+ -permeable ASIC1a subtype in ischaemic cell death. Using a novel orthosteric ASIC antagonist, we have found that ASICs specifically control the frequency of spontaneous inhibitory synaptic activity in the hippocampus. Inhibition of ASICs leads to a strong increase in the frequency of spontaneous inhibitory postsynaptic currents. This effect is presynaptic because it is fully reproducible in single synaptic boutons attached to isolated hippocampal neurons. In concert with this observation, inhibition of the ASIC current diminishes epileptic discharges in a low Mg 2+ model of epilepsy in hippocampal slices and significantly reduces kainate-induced discharges in the hippocampus in vivo . Our results reveal a significant novel role for ASICs. This article is part of the themed issue ‘Evolution brings Ca 2+ and ATP together to control life and death’.

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Age-related changes in microglial physiology: the role for healthy brain ageing and neurodegenerative disorders

e-Neuroforum ◽

10.1515/nf-2016-a057 ◽

2017 ◽

Vol 23 (4) ◽

Cited By ~ 4

Author(s):

Olga Garaschuk

Keyword(s):

Neurodegenerative Disorders ◽

Healthy Aging ◽

Molecular Mechanisms ◽

Brain Parenchyma ◽

Immune Defense ◽

Synaptic Activity ◽

Mammalian Brain ◽

Age Related ◽

Brain Ageing ◽

The Brain

AbstractMicroglia are the main immune cells of the brain contributing, however, not only to brain’s immune defense but also to many basic housekeeping functions such as development and maintenance of functional neural networks, provision of trophic support for surrounding neurons, monitoring and modulating the levels of synaptic activity, cleaning of accumulating extracellular debris and repairing microdamages of the brain parenchyma. As a consequence, age-related alterations in microglial function likely have a manifold impact on brain’s physiology. In this review, I discuss the recent data about physiological properties of microglia in the adult mammalian brain; changes observed in the brain innate immune system during healthy aging and the probable biological mechanisms responsible for them as well as changes occurring in humans and mice during age-related neurodegenerative disorders along with underlying cellular/molecular mechanisms. Together these data provide a new conceptual framework for thinking about the role of microglia in the context of age-mediated brain dysfunction.

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ADF/n-cofilin–dependent actin turnover determines platelet formation and sizing

Blood ◽

10.1182/blood-2010-03-274340 ◽

2010 ◽

Vol 116 (10) ◽

pp. 1767-1775 ◽

Cited By ~ 56

Author(s):

Markus Bender ◽

Anita Eckly ◽

John H. Hartwig ◽

Margitta Elvers ◽

Irina Pleines ◽

...

Keyword(s):

Actin Filament ◽

Molecular Mechanisms ◽

Critical Role ◽

Actin Dynamics ◽

Complex Process ◽

First Time ◽

Late Stages ◽

Platelet Formation

Abstract The cellular and molecular mechanisms orchestrating the complex process by which bone marrow megakaryocytes form and release platelets remain poorly understood. Mature megakaryocytes generate long cytoplasmic extensions, proplatelets, which have the capacity to generate platelets. Although microtubules are the main structural component of proplatelets and microtubule sliding is known to drive proplatelet elongation, the role of actin dynamics in the process of platelet formation has remained elusive. Here, we tailored a mouse model lacking all ADF/n-cofilin–mediated actin dynamics in megakaryocytes to specifically elucidate the role of actin filament turnover in platelet formation. We demonstrate, for the first time, that in vivo actin filament turnover plays a critical role in the late stages of platelet formation from megakaryocytes and the proper sizing of platelets in the periphery. Our results provide the genetic proof that platelet production from megakaryocytes strictly requires dynamic changes in the actin cytoskeleton.

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Function and Plasticity of Electrical Synapses in the Mammalian Brain: Role of Non-Junctional Mechanisms

10.20944/preprints202112.0384.v1 ◽

2021 ◽

Author(s):

Sebastian Curti ◽

Federico Davoine ◽

Antonella Dapino

Keyword(s):

Molecular Mechanisms ◽

Mammalian Brain ◽

Synaptic Membrane ◽

Electrical Transmission ◽

Electrical Synapses ◽

Electrophysiological Properties ◽

Voltage Dependent ◽

Theoretical Evidence ◽

Circuit Function

Electrical transmission between neurons is largely mediated by gap junctions. These junctions allow the direct flow of electric current between neurons, and in mammals are mostly composed of the protein connexin (Cx)36. Circuits of electrically coupled neurons are widespread in these animals, plus, experimental and theoretical evidence supports the notion that, beyond synchronicity, these circuits are able to perform sophisticated operations like lateral excitation and inhibition, noise reduction, as well as the ability to selectively respond upon coincident excitatory inputs. Although once considered stereotyped and unmodifiable, we now know that electrical synapses are subject to modulation and, by reconfiguring neural circuits, these modulations can alter relevant operations. The strength of electrical synapses depends on gap junction conductance, as well as on its functional interaction with the electrophysiological properties of coupled neurons. In particular, voltage dependent channels of the non-synaptic membrane critically determine the efficacy of transmission at these contacts. Consistently, modulatory actions on these channels have been shown to represent relevant mechanisms of plasticity of electrical synaptic transmission. Here we review recent evidence on the regulation of electrical synapses of mammals, the underlying molecular mechanisms, and the possible ways in which they affect circuit function.

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