P53 upregulation by USP7-engaging molecular glues.

Molecular glues are typically small chemical molecules that act at the interface between a target protein and degradation machinery to trigger ternary complex formation. Identifying molecular glues is challenging. There is a scarcity of target-specific upregulating molecular glues, which are highly anticipated for numerous targets, including P53. P53 is degraded in proteasomes through polyubiquitination by specific E3 ligases, whereas deubiquitinases (DUBs) remove polyubiquitination conjugates to counteract these E3 ligases. Thus, small-molecular glues that enhance P53 anchoring to DUBs may stabilize P53 through deubiquitination. Here, using small-molecule microarray-based technology and unbiased screening, we identified three potential molecular glues that may tether P53 to the DUB, USP7, and elevate the P53 level. Among the molecular glues, bromocriptine (BC) is an FDA-approved drug with the most robust effects. BC was further verified to increase P53 stability via the predicted molecular glue mechanism engaging USP7. Consistent with P53 upregulation in cancer cells, BC was shown to inhibit the proliferation of cancer cells in vitro and suppress tumor growth in a xenograft model. In summary, we established a potential screening platform and identified potential molecular glues upregulating P53. Similar strategies could be applied to the identification of other types of molecular glues that may benefit drug discovery and chemical biology studies.

Phase transition and lysosomal degradation of expanded CAG repeat RNA suppress global protein synthesis.

Phase transitions (PT) of biomolecules are heavily involved in neurodegenerative disorders. Almost all previous studies were focusing on the PT of misfolded proteins whereas RNA molecules containing expanded repeats such as the CAG repeats are also able to undergo PT in vitro, a process called RNA gelation. Meanwhile, the expanded CAG repeat (eCAGr) RNA forms condensates that are largely observed only in the nuclei and exhibit liquid-like properties without obvious gelation. Thus, whether eCAGr RNA gelation occurs in cells and what function it is involved in remained elusive. We recently discovered that eCAGr RNA forms solid-like RNA gels in the cytoplasm, but they are rapidly cleared by the lysosomes via an autophagy-independent but LAMP2C-depdent pathway, making their presence in the cytoplasm difficult to be observed. We further revealed that these RNA gels sequester EEF2 in the cells and thus suppress global protein synthesis. In vivo expression of eCAGr RNA alone without detectable protein expression in the mouse model led to neurodegeneration-relevant electrophysiological and behavioral phenotypes, demonstrating its possible pathogenic roles.

Gelation of cytoplasmic expanded CAG RNA repeats suppresses global protein synthesis.

RNA molecules with the expanded CAG repeat (eCAGr) may undergo sol-gel phase transitions, but the functional impact of RNA gelation is completely unknown. Here, we demonstrate that the eCAGr RNA may form cytoplasmic gel-like foci that are rapidly degraded by lysosomes. These RNA foci may significantly reduce the global protein synthesis rate, possibly by sequestering the translation elongation factor eEF2. Disrupting the eCAGr RNA gelation restored the global protein synthesis rate, whereas enhanced gelation exacerbated this phenotype. eEF2 puncta were significantly enhanced in brain slices from a knock-in mouse model and from patients with Huntington's disease, which is a CAG expansion disorder expressing eCAGr RNA. Finally, neuronal expression of the eCAGr RNA by adeno-associated virus injection caused significant behavioral deficits in mice. Our study demonstrates the existence of RNA gelation inside the cells and reveals its functional impact, providing insights into repeat expansion diseases and functional impacts of RNA phase transition.

Protein Kinase C Controls the Excitability of Cortical Pyramidal Neurons by Regulating Kv2.2 Channel Activity.

The family of voltage-gated potassium Kv2 channels consists of the Kv2.1 and Kv2.2 subtypes. Kv2.1 is constitutively highly phosphorylated in neurons and its function relies on its phosphorylation state. Whether the function of Kv2.2 is also dependent on its phosphorylation state remains unknown. Here, we investigated whether Kv2.2 channels can be phosphorylated by protein kinase C (PKC) and examined the effects of PKC-induced phosphorylation on their activity and function. Activation of PKC inhibited Kv2.2 currents and altered their steady-state activation in HEK293 cells. Point mutations and specific antibodies against phosphorylated S481 or S488 demonstrated the importance of these residues for the PKC-dependent modulation of Kv2.2. In layer II pyramidal neurons in cortical slices, activation of PKC similarly regulated native Kv2.2 channels and simultaneously reduced the frequency of action potentials. In conclusion, this study provides the first evidence to our knowledge that PKC-induced phosphorylation of the Kv2.2 channel controls the excitability of cortical pyramidal neurons.

Neuritin improves the neurological functional recovery after experimental intracerebral hemorrhage in mice.

Stroke is one of the leading causes of death worldwide, with intracerebral hemorrhage (ICH) being the most lethal subtype. Neuritin (Nrn) is a neurotropic factor that has been reported to have neuroprotective effects in acute brain and spinal cord injury. However, whether Nrn has a protective role in ICH has not been investigated. In this study, ICH was induced in C57BL/6 J mice by injection of collagenase VII, while the overexpression of Nrn in the striatum was induced by an adeno-associated virus serotype 9 (AAV9) vector. We found that compared with GFP-ICH mice, Nrn-ICH mice showed improved performance in the corner, cylinder and forelimb tests after ICH, and showed less weight loss and more rapid weight recovery. Overexpression of Nrn reduced brain lesions, edema, neuronal death and white matter and synaptic integrity dysfunction caused by ICH. Western blot results showed that phosphorylated PERK and ATF4 were significantly inhibited, while phosphorylation of Akt/mammalian target of rapamycin was increased in the Nrn-ICH group, compared with the GFP-ICH group. Whole cell recording from motor neurons indicated that overexpression of Nrn reversed the decrease of spontaneous excitatory postsynaptic currents (sEPSCs) and action potential frequencies induced by ICH. These data show that Nrn improves neurological deficits in mice with ICH by reducing brain lesions and edema, inhibiting neuronal death, and possibly by increasing neuronal connections.

A deletion in the RD105 region confers resistance to multiple drugs in Mycobacterium tuberculosis.

BACKGROUND: The emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), especially those that are multidrug resistant poses a serious threat to global tuberculosis control. However, the mechanism underlying the occurrence of drug resistance against more than one drug is poorly understood. Given that the Beijing/W strains are associated with outbreaks and multidrug resistance, they may harbor a genetic advantage and provide useful insight into the disease. One marker found in all Beijing/W Mtb strains is a deletion of RD105 region that results in a gene fusion, Rv0071/74, with a variable number (3-9 m) of VDP (V: Val, D: Asp; P: Pro) repeats (coded by gtggacccg repeat sequences) at the N-terminal. Here, we report that this variable number of VDP repeats in Rv0071/74 regulates the development of multidrug resistance. RESULTS: We collected and analyzed 1255 Beijing/W clinical strains. The results showed that the number of VDP repeats in Rv0071/74 was related to the development of multidrug resistance, and the deletion of Rv0071/74-9 m from Beijing/W clinical strain restored drug susceptibility. Rv0071/74-9 m also increased resistance to multiple drugs when transferred to different mycobacterial strains. Cell-free assays indicate that the domain carrying 4-9 VDP repeats (4-9 m) showed a variable binding affinity with peptidoglycan and Rv0071/74 cleaves peptidoglycan. Furthermore, Rv0071/74-9 m increased cell wall thickness and reduced the intracellular concentration of antibiotics. CONCLUSIONS: These findings not only identify Rv0071/74 with VDP repeats as a newly identified multidrug resistance gene but also provide a new model for the development of multiple drug resistance.

Neuritin promotes neurite and spine growth in rat cerebellar granule cells via L-type calcium channel-mediated calcium influx.

Neuritin is a neurotrophic factor that is activated by neural activity and neurotrophins. Its major function is to promote neurite growth and branching; however, the underlying mechanisms are not fully understood. To address this issue, this study investigated the effects of neuritin on neurite and spine growth and intracellular Ca2+ concentration in rat cerebellar granule neurons (CGNs). Incubation of CGNs for 24 h with neuritin increased neurite length and spine density; this effect was mimicked by insulin and abolished by inhibiting insulin receptor (IR) or mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) activity. Calcium imaging and western blot analysis revealed that neuritin enhanced the increase in intracellular Ca2+ level induced by high K+ , and stimulated the cell surface expression of CaV 1.2 and CaV 1.3 α subunits of the L-type calcium channel, which was suppressed by inhibition of IR or mitogen-activated protein kinase kinase/ERK. Treatment with inhibitors of L-type calcium channels, calmodulin, and calcineurin (CaN) abrogated the effects of neuritin on neurite length and spine density. A similar result was obtained by silencing nuclear factor of activated T cells c4, which is known to be activated by neuritin in CGNs. These results indicate that IR and ERK signaling as well as the Ca2+ /CaN/nuclear factor of activated T cells c4 axis mediate the effects of neuritin on neurite and spine growth in CGNs. OPEN PRACTICES: Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/ Cover Image for this issue: doi: 10.1111/jnc.14195.

Functions and the related signaling pathways of the neurotrophic factor neuritin.

Neuritin is a member of the neurotrophic factor family, which is activated by neural activity and neurotrophins, and promotes neurite growth and branching. It has shown to play an important role in neuronal plasticity and regeneration. It is also involved in other biological processes such as angiogenesis, tumorigenesis and immunomodulation. Thus far, however, the primary mechanisms of neuritin, including whether or not it acts through a receptor or which downstream signals might be activated following binding, are not fully understood. Recent evidence suggests that neuritin may be a potential therapeutic target in several neurodegenerative diseases. This review focuses on the recent advances in studies regarding the newly identified functions of neuritin and the signaling pathways related to these functions. We also discuss current hot topics and difficulties in neuritin research.

Neuritin Enhances Synaptic Transmission in Medial Prefrontal Cortex in Mice by Increasing CaV3.3 Surface Expression.

Neuritin is a neurotrophic factor involved in neural development and synaptic plasticity. However, its role in modulating synaptic transmission remains unclear. Here, we investigated the effects of neuritin on miniature excitatory postsynaptic currents (mEPSCs) and glutamate release in the medial prefrontal cortex (mPFC) in mice. Incubation of mPFC slices with neuritin for 45 min significantly increased mEPSC frequency and glutamate release as measured by high-performance liquid chromatography, which was mimicked by insulin and abrogated by an insulin receptor (IR) inhibitor. Neuritin-induced upregulation of synaptic transmission was correlated with activation of ERK, and inhibition of mitogen-activated protein kinases/extracellular signal-regulated kinases (MEK/ERK) activity attenuated the neuritin-induced increase in mEPSC frequency and glutamate release. T-type calcium channel inhibitors but not the L-type inhibitor abolished the inward calcium current and the effects of neuritin on mEPSC frequency and glutamate release. Western blotting of membrane proteins showed that neuritin promoted surface expression of CaV3.3 α-subunit, which was also eliminated by inhibition of IR or MEK/ERK activity. The effects of neuritin on mEPSC frequency, glutamate release, and CaV3.3 α-subunit expression were inhibited by an intracellular protein-transport inhibitor. These results confirm involvement of the IR and ERK signaling pathway, and provide novel insights into the mechanisms of neuritin function in synaptic transmission.

Effect of 1.8 GHz radiofrequency electromagnetic radiation on novel object associative recognition memory in mice.

Mounting evidence suggests that exposure to radiofrequency electromagnetic radiation (RF-EMR) can influence learning and memory in rodents. In this study, we examined the effects of single exposure to 1.8 GHz RF-EMR for 30 min on subsequent recognition memory in mice, using the novel object recognition task (NORT). RF-EMR exposure at an intensity of >2.2 W/kg specific absorption rate (SAR) power density induced a significant density-dependent increase in NORT index with no corresponding changes in spontaneous locomotor activity. RF-EMR exposure increased dendritic-spine density and length in hippocampal and prefrontal cortical neurons, as shown by Golgi staining. Whole-cell recordings in acute hippocampal and medial prefrontal cortical slices showed that RF-EMR exposure significantly altered the resting membrane potential and action potential frequency, and reduced the action potential half-width, threshold, and onset delay in pyramidal neurons. These results demonstrate that exposure to 1.8 GHz RF-EMR for 30 min can significantly increase recognition memory in mice, and can change dendritic-spine morphology and neuronal excitability in the hippocampus and prefrontal cortex. The SAR in this study (3.3 W/kg) was outside the range encountered in normal daily life, and its relevance as a potential therapeutic approach for disorders associated with recognition memory deficits remains to be clarified.

Growth differentiation factor-15 promotes glutamate release in medial prefrontal cortex of mice through upregulation of T-type calcium channels.

Growth differentiation factor-15 (GDF-15) has been implicated in ischemic brain injury and synapse development, but its involvement in modulating neuronal excitability and synaptic transmission remain poorly understood. In this study, we investigated the effects of GDF-15 on non-evoked miniature excitatory post-synaptic currents (mEPSCs) and neurotransmitter release in the medial prefrontal cortex (mPFC) in mice. Incubation of mPFC slices with GDF-15 for 60 min significantly increased the frequency of mEPSCs without effect on their amplitude. GDF-15 also significantly elevated presynaptic glutamate release, as shown by HPLC. These effects were blocked by dual TGF-ß type I receptor (TßRI) and TGF-ß type II receptor (TßRII) antagonists, but not by a TßRI antagonist alone. Meanwhile, GDF-15 enhanced pERK level, and inhibition of MAPK/ERK activity attenuated the GDF-15-induced increases in mEPSC and glutamate release. Blocking T-type calcium channels reduced the GDF-15 induced up-regulation of synaptic transmission. Membrane-protein extraction and use of an intracellular protein-transport inhibitor showed that GDF-15 promoted CaV3.1 and CaV3.3 α-subunit expression by trafficking to the membrane. These results confirm previous findings in cerebellar granule neurons, in which GDF-15 induces its neurobiological effects via TßRII and activation of the ERK pathway, providing novel insights into the mechanism of GDF-15 function in cortical neurons.

GDF-15 enhances intracellular Ca2+ by increasing Cav1.3 expression in rat cerebellar granule neurons.

GDF-15 (growth/differentiation factor 15) is a novel member of the TGF (transforming growth factor)-ß superfamily that has critical roles in the central and peripheral nervous systems. We reported previously that GDF-15 increased delayed rectifier outward K(+) currents and Kv2.1 α subunit expression through TßRII (TGF-ß receptor II) to activate Src kinase and Akt/mTOR (mammalian target of rapamycin) signalling in rat CGNs (cerebellar granule neurons). In the present study, we found that treatment of CGNs with GDF-15 for 24 h increased the intracellular Ca(2+) concentration ([Ca(2+)]i) in response to membrane depolarization, as determined by Ca(2+) imaging. Whole-cell current recordings indicated that GDF-15 increased the inward Ca(2+) current (ICa) without altering steady-state activation of Ca(2+) channels. Treatment with nifedipine, an inhibitor of L-type Ca(2+) channels, abrogated GDF-15-induced increases in [Ca(2+)]i and ICa The GDF-15-induced increase in ICa was mediated via up-regulation of the Cav1.3 α subunit, which was attenuated by inhibiting Akt/mTOR and ERK (extracellular-signal-regulated kinase) pathways and by pharmacological inhibition of Src-mediated TßRII phosphorylation. Given that Cav1.3 is not only a channel for Ca(2+) influx, but also a transcriptional regulator, our data confirm that GDF-15 induces protein expression via TßRII and activation of a non-Smad pathway, and provide novel insight into the mechanism of GDF-15 function in neurons.

Screening and identification of immunoactive peptide mimotopes for the enhanced serodiagnosis of tuberculosis.

Although serological detection is a practical strategy for early detection and diagnosis of tuberculosis (TB), inconsistent and imprecise estimates of sensitivity and specificity block its development and application for clinic. New or alternative serological antigens with improved accuracy are urgently needed. A phage-displayed random peptide library was employed to screen for immunoactive peptides using specific immunoglobulin G (IgG) of TB patients as target molecules. With two screening strategies, 20 single phages displaying different sequences were obtained and no sequence homology was found among these phages. From the results of phage-ELISA, H12, TB6, TB15, and TB18 phages showed higher affinity to IgGs from TB patients(S/N ≥2.1) and were identified as the positive clones. Significant differences in the detection values of sera from 47 TB patients and 37 healthy individuals were found for these four phage clones. According to the reactivity of 284 human sera to synthetic H12, TB6, TB15, and TB18 peptides as determined by ELISA, TB15 showed significantly higher areas under the curve (AUC) and sensitivity than other peptides, providing a lead molecule for the development of new serology diagnostic strategies for TB.

Direct identification and discernment of Mycobacterium avium and Mycobacterium intracellulare using a real-time RNA isothermal amplification and detection method.

The purpose of this work was to establish a real-time simultaneous amplification and testing method for identification and discernment of Mycobacterium avium and Mycobacterium intracellulare (SAT-MAC assay) and to evaluate the efficiency with which this method can detect isolated strains and clinical sputum specimens. The specific 16S rRNA sequences of M. avium and M. intracellulare were used as targets to design RNA probes and a reverse transcription primer containing T7 promoter. RNA isothermal amplification and real-time fluorescence detection were performed at 42 °C. SAT-MAC assay, culture tests on Lowenstein-Jensen (L-J) culture medium and PCR-sequencing were used to test the clinical isolated strains and sputum specimens. The limit of detection (LOD) of M. avium and M. intracellulare by SAT-MAC was found to be 30 CFU/mL and 20 CFU/mL. SAT-MAC showed high specificity in 21 species of mycobacteria standard strains and 5 species of non-mycobacteria bacteria. Using PCR-sequencing as the reference method, both rates of SAT-MAC assay for identifying M. avium and M. intracellulare from clinical isolates were 100% (259/259). Consistent with the results of L-J culture combined PCR-sequencing, the coincidence rate of SAT-MAC assay in clinical sputum specimens was 100% (369/369) for M. avium and 99.19% (366/369) for Mycobacterium intracellular. The SAT-MAC assay can identify and distinguish M. avium and M. intracellulare rapidly and accurately. It may be suitable for use in clinical microbiology laboratories.

Neuritin reverses deficits in murine novel object associative recognition memory caused by exposure to extremely low-frequency (50 Hz) electromagnetic fields.

Animal studies have shown that electromagnetic field exposure may interfere with the activity of brain cells, thereby generating behavioral and cognitive disturbances. However, the underlying mechanisms and possible preventions are still unknown. In this study, we used a mouse model to examine the effects of exposure to extremely low-frequency (50 Hz) electromagnetic fields (ELF MFs) on a recognition memory task and morphological changes of hippocampal neurons. The data showed that ELF MFs exposure (1 mT, 12 h/day) induced a time-dependent deficit in novel object associative recognition memory and also decreased hippocampal dendritic spine density. This effect was observed without corresponding changes in spontaneous locomotor activity and was transient, which has only been seen after exposing mice to ELF MFs for 7-10 days. The over-expression of hippocampal neuritin, an activity-dependent neurotrophic factor, using an adeno-associated virus (AAV) vector significantly increased the neuritin level and dendritic spine density. This increase was paralleled with ELF MFs exposure-induced deficits in recognition memory and reductions of dendritic spine density. Collectively, our study provides evidence for the association between ELF MFs exposure, impairment of recognition memory, and resulting changes in hippocampal dendritic spine density. Neuritin prevented this ELF MFs-exposure-induced effect by increasing the hippocampal spine density.

Identification and application of ssDNA aptamers against H37Rv in the detection of Mycobacterium tuberculosis.

Microscopy of direct smear with the Ziehl-Neelsen stain is still broadly used in tuberculosis diagnosis. However, this method suffers from low specificity and is difficult to distinguish Mycobacterium tuberculosis (MTB) from nontuberculosis mycobacterial (NTM), since all mycobacterial species are positive in Ziehl-Neelsen stain. In this study, we utilized whole cell SELEX to obtain species-specific aptamers for increasing the specificity of MTB detection. Whole cell SELEX was performed in MTB reference strain H37Rv by two selection processes based on enzyme-linked plate or Eppendorf tube, respectively. To increase success rate of generating aptamers, the selection processes were systematically monitored to understand the dynamic evolution of aptamers against complex structure of target bacteria. Two preponderant groups and ten high-affinity aptamers were obtained by analyzing the dynamic evolution. Preponderant aptamer MA1 from group I showed relatively high binding affinity with apparent dissociation constant (KD value) of 12.02 nM. Sandwich ELISA assay revealed five aptamer combinations effectively bound MTB strains in preliminary evaluation, especially the combination based on aptamer MA2 (another preponderant aptamer from group II) and MA1. Further evaluated in many other strains, MA2/MA1 combination effectively identified MTB from NTM or other pathogenic bacteria, and displayed the high specificity and sensitivity. Binding analysis of aptamer MA1 or MA2 by fluorescence microscopy observation showed high binding reactivity with H37Rv, low apparent cross-reactivity with M. marinum, and no apparent cross-reactivity with Enterobacter cloacae. Taken together, this study provides attractive candidate species-specific aptamers to effectively capture or discriminate MTB strains.

Detection of Mycobacterium tuberculosis based on H37R(v) binding peptides using surface functionalized magnetic microspheres coupled with quantum dots ­ a nano detection method for Mycobacterium tuberculosis.

Despite suffering from the major disadvantage of low sensitivity, microscopy of direct smear with the Ziehl-Neelsen stain is still broadly used for detection of acid-fast bacilli and diagnosis of tuberculosis. Here, we present a unique detection method of Mycobacterium tuberculosis (MTB) using surface functionalized magnetic microspheres (MMSs) coupled with quantum dots (QDs), conjugated with various antibodies and phage display-derived peptides. The principle is based upon the conformation of the sandwich complex composed of bacterial cells, MMSs, and QDs. The complex system is tagged with QDs for providing the fluorescent signal as part of the detection while magnetic separation is achieved by MMSs. The peptide ligand H8 derived from the phage display library Ph.D.-7 is developed for MTB cells. Using the combinations of MMS-polyclonal antibody+QD-H8 and MMS-H8+QD-H8, a strong signal of 10(3) colony forming units (CFU)/mL H37R(v) was obtained with improved specificity. MS-H8+QD-H8 combination was further optimized by adjusting the concentrations of MMSs, QDs, and incubation time for the maximum detection signal. The limit of detection for MTB was found to reach 10(3) CFU/mL even for the sputum matrices. Positive sputum samples could be distinguished from control. Thus, this novel method is shown to improve the detection limit and specificity of MTB from the sputum samples, and to reduce the testing time for accurate diagnosis of tuberculosis, which needs further confirmation of more clinical samples.