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G-protein-coupled receptors (GPCRs) play important roles in cellular functions. However, their intracellular organization is largely unknown. Through investigation of the cannabinoid receptor 1 (CB1), we discovered periodically repeating clusters of CB1 hotspots within the axons of neurons. We observed these CB1 hotspots interact with the membrane-associated periodic skeleton (MPS) forming a complex crucial in the regulation of CB1 signaling. Furthermore, we found that CB1 hotspot periodicity increased upon CB1 agonist application, and these activated CB1 displayed less dynamic movement compared to non-activated CB1. Our results suggest that CB1 forms periodic hotspots organized by the MPS as a mechanism to increase signaling efficacy upon activation., Despite the importance of G-protein-coupled receptors in many cellular functions, their intracellular organisation is largely unknown. The authors identified periodically repeating clusters of cannabinoid receptor 1 hotspots within neuronal axons that are dynamically regulated by CB1 agonists.

Signal transduction systems enable organisms to monitor their external environments and accordingly adjust the cellular processes. In mast cells, the second messenger Ap4A binds to the histidine triad nucleotide-binding protein 1 (HINT1), disrupts its interaction with the microphthalmia-associated transcription factor (MITF), and eventually activates the transcription of genes downstream of MITF in response to immunostimulation. How the HINT1 protein recognizes and is regulated by Ap4A remain unclear. Here, using eight crystal structures, biochemical experiments, negative stain electron microscopy, and cellular experiments, we report that Ap4A specifically polymerizes HINT1 in solution and in activated rat basophilic leukemia cells. The polymerization interface overlaps with the area on HINT1 for MITF interaction, suggesting a possible competitive mechanism to release MITF for transcriptional activation. The mechanism depends precisely on the length of the phosphodiester linkage of Ap4A. These results highlight a direct polymerization signaling mechanism by the second messenger., The second messenger Ap4A contributes to mast cell activation by interacting with HINT1 but the molecular mechanism is not fully understood. Here, the authors show that Ap4A regulates downstream signaling by polymerizing HINT1 and provide insights into how specificity over other second messengers is achieved.

In-depth profiling of transmembrane proteins in the brain leads to the identification of GPCR regulators in a disease model., Transmembrane proteins play vital roles in mediating synaptic transmission, plasticity, and homeostasis in the brain. However, these proteins, especially the G protein–coupled receptors (GPCRs), are underrepresented in most large-scale proteomic surveys. Here, we present a new proteomic approach aided by deep learning models for comprehensive profiling of transmembrane protein families in multiple mouse brain regions. Our multiregional proteome profiling highlights the considerable discrepancy between messenger RNA and protein distribution, especially for region-enriched GPCRs, and predicts an endogenous GPCR interaction network in the brain. Furthermore, our new approach reveals the transmembrane proteome remodeling landscape in the brain of a mouse depression model, which led to the identification of two previously unknown GPCR regulators of depressive-like behaviors. Our study provides an enabling technology and rich data resource to expand the understanding of transmembrane proteome organization and dynamics in the brain and accelerate the discovery of potential therapeutic targets for depression treatment.

Gestational diabetes (GDM) is common in pregnancies due to the inflammation and oxidative stress-mediated insulin resistance. In the present study, GDM was induced in the Wistar rats by administering the streptozotocin to elucidate whether the administration of syringin (50 mg/kg/day) during pregnancy could improve maternal glycemia and protect against the complications of GDM. The animals were assessed for their morphological changes in the β-islets of Langerhans and their insulin-producing ability, inflammatory cytokine markers, and the involvement of TLR4/MyD88/NF-κB signaling pathway using RT-PCR. The results demonstrated that the onset of GDM demonstrated pancreatic tissue degeneration in the islets of Langerhans with a significant increase in oxidative stress and reduced antioxidant enzymes. Besides, the mRNA expression levels of TLR4, MyD88, NF-Kβ p65; NLRP3 mRNA were profoundly increased in GDM rats compared to normal pregnant rats. On the other hand, syringin administered GDM rats abrogated the oxidative stress and attenuated the level of the inflammatory cytokines. Intriguingly, the decrease in TLR4 expression and the downstream molecules of MyD88, NF-κB, and NLRP3 were also observed in syringin administered GDM rats that indicate the insulin secretion stimulatory actions of syringin through the suppression of TLR4 signaling. These novel findings of the study provide evidence that syringin could be a probable candidate to be used in the treatment of gestational diabetes in the future.

Data-independent acquisition mass spectrometry (DIA-MS) is a rapidly evolving technique that enables relatively deep proteomic profiling with superior quantification reproducibility. DIA data mining predominantly relies on a spectral library of sufficient proteome coverage that, in most cases, is built on data-dependent acquisition-based analysis of the same sample. To expand the proteome coverage for a pre-determined protein family, we report herein on the construction of a hybrid spectral library that supplements a DIA experiment-derived library with a protein family-targeted virtual library predicted by deep learning. Leveraging this DIA hybrid library substantially deepens the coverage of three transmembrane protein families (G protein coupled receptors; ion channels; and transporters) in mouse brain tissues with increases in protein identification of 37-87%, and peptide identification of 58-161%. Moreover, of the 412 novel GPCR peptides exclusively identified with the DIA hybrid library strategy, 53.6% were validated as present in mouse brain tissues based on orthogonal experimental measurement.

Super-resolution fluorescence imaging reveals a previously unknown novel structure of spectrin in inner ear hair cells., Inner ear hair cells (HCs) detect sound through the deflection of mechanosensory stereocilia. Stereocilia are inserted into the cuticular plate of HCs by parallel actin rootlets, where they convert sound-induced mechanical vibrations into electrical signals. The molecules that support these rootlets and enable them to withstand constant mechanical stresses underpin our ability to hear. However, the structures of these molecules have remained unknown. We hypothesized that αII- and βII-spectrin subunits fulfill this role, and investigated their structural organization in rodent HCs. Using super-resolution fluorescence imaging, we found that spectrin formed ring-like structures around the base of stereocilia rootlets. These spectrin rings were associated with the hearing ability of mice. Further, HC-specific, βII-spectrin knockout mice displayed profound deafness. Overall, our work has identified and characterized structures of spectrin that play a crucial role in mammalian hearing development.

Summary Data-independent acquisition mass spectrometry (DIA-MS) is a powerful technique that enables relatively deep proteomic profiling with superior quantification reproducibility. DIA data mining predominantly relies on a spectral library of sufficient proteome coverage that, in most cases, is built on data-dependent acquisition-based analysis of the same sample. To expand the proteome coverage for a pre-determined protein family, we report herein on the construction of a hybrid spectral library that supplements a DIA experiment-derived library with a protein family-targeted virtual library predicted by deep learning. Leveraging this DIA hybrid library substantially deepens the coverage of three transmembrane protein families (G protein-coupled receptors, ion channels, and transporters) in mouse brain tissues with increases in protein identification of 37%–87% and peptide identification of 58%–161%. Moreover, of the 412 novel GPCR peptides exclusively identified with the DIA hybrid library strategy, 53.6% were validated as present in mouse brain tissues based on orthogonal experimental measurement., Graphical Abstract, Highlights • A virtual library is built for a selected protein family using deep learning models • The hybrid library strategy vastly deepens the coverage for the targeted protein family • About 53.6% of novel GPCR peptides identified with the DIA hybrid library are validated • Extend the strategy to deep mapping of multiple transmembrane protein families, Analytical Chemistry; Biological Sciences; Classification of Proteins; Proteomics

Summary The axon initial segment (AIS) cytoskeleton undergoes rapid and irreversible disruption prior to cell death after injury, and loss of AIS integrity can produce profound neurological effects on the nervous system. Here we described a previously unrecognized mechanism for ischemia-induced alterations in AIS integrity. We show that in hippocampal CA1 pyramidal neurons Nav1.6 mostly preserves at the AIS after disruption of the cytoskeleton in a mouse model of middle cerebral artery occlusion. Genetic removal of neurofascin-186 leads to rapid disruption of Nav1.6 following injury, indicating that neurofascin is required for Nav1.6 maintenance at the AIS after cytoskeleton collapse. Importantly, calcineurin inhibition with FK506 fully protects AIS integrity and sufficiently prevents impairments of spatial learning and memory from injury. This study provides evidence that calcineurin activation is primarily involved in initiating disassembly of the AIS cytoskeleton and that maintaining AIS integrity is crucial for therapeutic strategies to facilitate recovery from injury., Graphical Abstract, Highlights • Ion channels are mostly retained at the AIS after ischemic injury • Neurofascin is required for clustering ion channels at the AIS after ischemia • Calcineurin inhibition protects AIS structural integrity and function from ischemia • Calcineurin inhibition protects cognitive function against impairment by ischemia, Neuroscience; Molecular Neuroscience; Cellular Neuroscience

Dysregulation of voltage-gated sodium channels (VGSCs) is associated with multiple clinical disorders, including febrile seizures (FS). The contribution of different sodium channel subtypes to environmentally triggered seizures is not well understood. Here we demonstrate that somatic and axonal sodium channels primarily mediated through NaV1.2 and NaV1.6 subtypes, respectively, behave differentially at FT, and might play distinct roles in FS generation. In contrast to sodium channels on the main axonal trunk, somatic ones are more resistant to inactivation and display significantly augmented currents, faster gating rates and kinetics of recovery from inactivation at FT, features that promote neuronal excitabilities. Pharmacological inhibition of NaV1.2 by Phrixotoxin-3 (PTx3) suppressed FT-induced neuronal hyperexcitability in brain slice, while up-regulation of NaV1.2 as in NaV1.6 knockout mice showed an opposite effect. Consistently, NaV1.6 knockout mice were more susceptible to FS, exhibiting much lower temperature threshold and shorter onset latency than wildtype mice. Neuron modeling further suggests that NaV1.2 is the major subtype mediating FT-induced neuronal hyperexcitability, and predicts potential outcomes of alterations in sodium channel subtype composition. Together, these data reveal a role of native NaV1.2 on neuronal excitability at FT and its important contribution to FS pathogenesis.

Voltage-gated K+ (K-V) channels play critical roles in shaping neuronal signals. K-V channels distributed in the perisomatic regions and thick dendrites of cortical pyramidal neurons have been extensively studied. However, the properties and regulation of K-V channels distributed in the thin axons remain unknown. In this study, by performing somatic and axonal patch-clamp recordings from layer 5 pyramidal neurons of prefrontal cortical slices, we showed that the rapidly inactivating A-currents mediated the transient K+ currents evoked by action potential (AP) waveform command (K-AP) at the soma, whereas the rapidly activating but slowly inactivating K(V)1-mediated D-currents dominated the K-AP at the axon. In addition, activation of D1-like receptors for dopamine decreased the axonal K+ currents, as a result of an increase in the activity of cAMP-PKA pathway. In contrast, activation of D2-like receptors showed an opposite effect on the axonal K+ currents. Further experiments demonstrated that functional D1-like receptors were expressed at the main axon trunk and their activation could broaden the waveforms of axonal APs. Together, these results show that axonal K-V channels were subjected to dopamine modulation, and this modulation could regulate the waveforms of propagating APs at the axon, suggesting an important role of dopaminergic modulation of axonal K-V channels in regulating neuronal signalling.

We report on an ultraviolet-enhanced supercontinuum generation in a uniform photonic crystal fiber pumped by a giant-chirped mode-locked Yb-doped fiber laser. We find theoretically and experimentally that the initial pluses with giant chirp leads more initial energy transferred to the dispersive waves in visible and ultraviolet wavelength. An extremely wide optical spectrum spanning from 370 nm to beyond 2400 nm with a broad 3 dB spectral bandwidth of 367 nm (from 431 nm to 798 nm) is obtained. Over 36% (350 mW) of the total output power locates in the visible and ultraviolet regime between 370 nm and 850 nm with a maximum spectral power density of 1.6 mW/nm at 550 nm.

Studies in rodents revealed that selective accumulation of Na(+) channel subtypes at the axon initial segment (AIS) determines action potential (AP) initiation and backpropagation in cortical pyramidal cells (PCs); however, in human cortex, the molecular identity of Na(+) channels distributed at PC axons, including the AIS and the nodes of Ranvier, remains unclear. We performed immunostaining experiments in human cortical tissues removed surgically to cure brain diseases. We found strong immunosignals of Na(+) channels and two channel subtypes, NaV1.2 and NaV1.6, at the AIS of human cortical PCs. Although both channel subtypes were expressed along the entire AIS, the peak immunosignals of NaV1.2 and NaV1.6 were found at proximal and distal AIS regions, respectively. Surprisingly, in addition to the presence of NaV1.6 at the nodes of Ranvier, NaV1.2 was also found in a subpopulation of nodes in the adult human cortex, different from the absence of NaV1.2 in myelinated axons in rodents. NaV1.1 immunosignals were not detected at either the AIS or the nodes of Ranvier of PCs; however, they were expressed at interneuron axons with different distribution patterns. Further experiments revealed that parvalbumin-positive GABAergic axon cartridges selectively innervated distal AIS regions with relatively high immunosignals of NaV1.6 but not the proximal NaV1.2-enriched compartments, suggesting an important role of axo-axonic cells in regulating AP initiation in human PCs. Together, our results show that both NaV1.2 and NaV1.6 (but not NaV1.1) channel subtypes are expressed at the AIS and the nodes of Ranvier in adult human cortical PCs, suggesting that these channel subtypes control neuronal excitability and signal conduction in PC axons.