A role for LYNX2 in anxiety-related behavior

Pesticide-Induced Alterations in Locomotor Activity, Anxiety, and Depression-like Behavior Are Mediated through Oxidative Stress-Related Autophagy: A Persistent Developmental Study in Mice

Chlorpyrifos (CPF), dichlorvos (DDV), and cypermethrin (CP), as commonly used pesticides, have been implicated in inducing neuropsychiatric disorders, such as anxiety, depression-like behaviors, and locomotor activity impairment. However, the exact molecular mechanisms of these adverse effects, particularly in both sexes and their next-generation effects, remain unclear. In this study, we conducted behavioral analysis, along with cellular assays (monodansylcadaverine staining) and molecular investigations (qRT-PCR and western blotting of mTOR, P62, and Beclin-1) to clear the potential role of autophagy in pesticide-induced behavioral alterations. For this purpose, 42 adult female and 21 male inbred ICR mice (F0) were distributed into seven groups. Maternal mice (F0) and 112 F1 offspring were exposed to 0.5 and 1 ppm of CPF, DDV, and CP through drinking water. F1 male and female animals were studied to assess the sex-specific effects of pesticides on brain tissue. Our findings revealed pronounced anxiogenic effects and impaired locomotor activity in mice. F1 males exposed to CPF (1 ppm) exhibited significantly elevated depression-like behaviors compared to other groups. Moreover, pesticide exposure reduced mTOR and P62 levels, while enhancing the Beclin-1 gene and protein expression. These changes in autophagy signaling pathways, coupled with oxidative and neurogenic damage in the cerebral cortex and hippocampus, potentially contribute to heightened locomotor activity, anxiety, and depression-like behaviors following pesticide exposure. This study underscores the substantial impact of pesticides on both physiological and behavioral aspects, emphasizing the necessity for comprehensive assessments and regulatory considerations for pesticide use. Additionally, the identification of sex-specific responses presents a crucial dimension for pharmaceutical sciences, highlighting the need for tailored therapeutic interventions and further research in this field.

Association of serum Ly6/PLAUR domain-containing protein 1 levels with skin sclerosis in systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease characterized by aberrant immune activation, vascular injury, and fibrosis of the skin and internal organs. Ly6/PLAUR domain-containing protein 1 (LYPD1) was reported to be secreted and to have various physiological functions such as anti-angiogenic effects. Here we investigated serum LYPD1 levels in SSc patients and the association of serum LYPD1 levels with clinical features of SSc. Serum samples were obtained from 75 SSc patients and 22 healthy individuals as controls. We measured serum LYPD1 levels using enzyme-linked immunosorbent assay kits. Then, the relationship between serum LYPD1 levels and clinical features of SSc was analyzed. Serum LYPD1 levels in diffuse cutaneous SSc (dcSSc) patients were significantly higher than those in the limited cutaneous SSc (lcSSc) patients (median [25-75th percentiles], 1693.43 [1086.61-1917.57] vs. 904.55 [714.356-1285.56] pg/mL), while there were no significant differences in the serum LYPD1 levels between lcSSc and healthy controls (904.55 [714.356-1285.56] vs. 750.71 pg/mL [544.00-912.14]). Further analysis revealed that serum LYPD1 levels in patients correlated with skin thickness scores and serum interleukin (IL)-6 levels, which were known to reflect the extent of skin thickening in SSc. Moreover, serum LYPD1 levels showed a decrease with improvement in skin thickness after treatment, along with a decrease in serum IL-6 levels. These results indicate that LYPD1 might be a potential marker for monitoring skin sclerosis and evaluating the efficacy of skin fibrosis treatment in SSc patients.

A diagnostic model based on bioinformatics and machine learning to differentiate bipolar disorder from schizophrenia and major depressive disorder

Bipolar disorder (BD) showed the highest suicide rate of all psychiatric disorders, and its underlying causative genes and effective treatments remain unclear. During diagnosis, BD is often confused with schizophrenia (SC) and major depressive disorder (MDD), due to which patients may receive inadequate or inappropriate treatment, which is detrimental to their prognosis. This study aims to establish a diagnostic model to distinguish BD from SC and MDD in multiple public datasets through bioinformatics and machine learning and to provide new ideas for diagnosing BD in the future. Three brain tissue datasets containing BD, SC, and MDD were chosen from the Gene Expression Omnibus database (GEO), and two peripheral blood datasets were selected for validation. Linear Models for Microarray Data (Limma) analysis was carried out to identify differentially expressed genes (DEGs). Functional enrichment analysis and machine learning were utilized to identify. Least absolute shrinkage and selection operator (LASSO) regression was employed for identifying candidate immune-associated central genes, constructing protein-protein interaction networks (PPI), building artificial neural networks (ANN) for validation, and plotting receiver operating characteristic curve (ROC curve) for differentiating BD from SC and MDD and creating immune cell infiltration to study immune cell dysregulation in the three diseases. RBM10 was obtained as a candidate gene to distinguish BD from SC. Five candidate genes (LYPD1, HMBS, HEBP2, SETD3, and ECM2) were obtained to distinguish BD from MDD. The validation was performed by ANN, and ROC curves were plotted for diagnostic value assessment. The outcomes exhibited the prediction model to have a promising diagnostic value. In the immune infiltration analysis, Naive B, Resting NK, and Activated Mast Cells were found to be substantially different between BD and SC. Naive B and Memory B cells were prominently variant between BD and MDD. In this study, RBM10 was found as a candidate gene to distinguish BD from SC; LYPD1, HMBS, HEBP2, SETD3, and ECM2 serve as five candidate genes to distinguish BD from MDD. The results obtained from the ANN network showed that these candidate genes could perfectly distinguish BD from SC and MDD (76.923% and 81.538%, respectively).

Nicotinic acetylcholine receptors in cancer: Limitations and prospects

Nicotinic acetylcholine receptors (nAChRs) have long been considered to solely mediate neurotransmission. However, their widespread distribution in the human body suggests a more diverse physiological role. Additionally, the expression of nAChRs is increased in certain cancers, such as lung cancer, and has been associated with cell proliferation, epithelial-to-mesenchymal cell transition, angiogenesis and apoptosis prevention. Several compounds that interact with these receptors have been identified as potential therapeutic agents. They have been tested as drugs for treating nicotine addiction, alcoholism, depression, pain and Alzheimer's disease. This review focuses on nAChR-mediated signalling in cancer, presenting opportunities for the development of innovative nAChR-based anticancer drugs. It displays the differences in expression of each nAChR subunit between normal and cancer cells for selected cancer types, highlighting their possible involvement in specific cases. Antagonists of nAChRs that could complement existing cancer therapies are summarised and critically discussed. We hope that this review will stimulate further research on the role of nAChRs in cancer potentially leading to innovative cancer therapies.

Pre/postnatal taurine supplementation improves neurodevelopment and brain function in mice offspring: A persistent developmental study from puberty to maturity

Taurine (TAU) is a sulfur-containing amino acid abundantly found in the human body. Endogenously, TAU is synthesized from cysteine in the liver. However, newborns rely entirely on TAU's dietary supply (milk). There is no investigation on the effect of long-term TAU administration on next-generation neurological development. The current study evaluated the effect of long-term TAU supplementation during the maternal gestational and litter weaning time on several neurological parameters in mice offspring. Moreover, the effects of TAU on mitochondrial function and oxidative stress biomarkers as plausible mechanisms of its action in the whole brain and hippocampus have been evaluated. TAU (0.5 % and 1 % w/v) was dissolved in the drinking water of pregnant mice (Day one of pregnancy), and amino acid supplementation was continued during the weaning time (post-natal day; PND = 21) until litters maturity (PND = 65). It was found that TAU significantly improved cognitive function, memory performance, reflexive motor activity, and emotional behaviors in F1-mice generation. TAU measurement in the brain and hippocampus revealed higher levels of this amino acid. TAU and ATP levels were also significantly higher in the mitochondria isolated from the whole brain and hippocampus. Based on these data, TAU could be suggested as a supplement during pregnancy or in pediatric formula. The effects of TAU on cellular mitochondrial function and energy metabolism might play a fundamental role in the positive effects of this amino acid observed in this investigation.

Aβ1-42 Accumulation Accompanies Changed Expression of Ly6/uPAR Proteins, Dysregulation of the Cholinergic System, and Degeneration of Astrocytes in the Cerebellum of Mouse Model of Early Alzheimer Disease

Alzheimer disease (AD) is a widespread neurodegenerative disease characterized by the accumulation of oligomeric toxic forms of β-amyloid (Aβ1-42) and dysfunction of the cholinergic system in the different brain regions. However, the exact mechanisms of AD pathogenesis and the role of the nicotinic acetylcholine receptors (nAChRs) in the disease progression remain unclear. Here, we revealed a decreased expression of a number of the Ly6/uPAR proteins targeting nAChRs in the cerebellum of 2xTg-AD mice (model of early AD) in comparison with non-transgenic mice both at mRNA and protein levels. We showed that co-localization of one of them, - neuromodulator Lynx1, with α7-nAChR was diminished in the vicinity of cerebellar astrocytes of 2xTg-AD mice, while Aβ1-42 co-localization with this receptor present was increased. Moreover, the expression of anti-inflammatory transcription factor KLF4 regulating transcription of the Ly6/uPAR genes was decreased in the cerebellum of 2xTg-AD mice, while expression of inflammatory cytokine TNF-α was increased. Based on these data together with observed astrocyte degeneration in the cerebellum of 2xTg-AD mice, we suggest the mechanism by which expression of the Ly6/uPAR proteins upon Aβ pathology results in dysregulation of the cholinergic system and particularly of α7-nAChR function in the cerebellum. This leads to enhanced neuroinflammation and cerebellar astrocyte degeneration.

Low Dopamine D2 Receptor Expression Drives Gene Networks Related to GABA, cAMP, Growth and Neuroinflammation in Striatal Indirect Pathway Neurons

Background

A salient effect of addictive drugs is to hijack the dopamine reward system, an evolutionarily conserved driver of goal-directed behavior and learning. Reduced dopamine type 2 receptor availability in the striatum is an important pathophysiological mechanism for addiction that is both consequential and causal for other molecular, cellular, and neuronal network differences etiologic for this disorder. Here, we sought to identify gene expression changes attributable to innate low expression of the Drd2 gene in the striatum and specific to striatal indirect medium spiny neurons (iMSNs).

Methods

Cre-conditional, translating ribosome affinity purification (TRAP) was used to purify and analyze the translatome (ribosome-bound messenger RNA) of iMSNs from mice with low/heterozygous or wild-type Drd2 expression in iMSNs. Complementary electrophysiological recordings and gene expression analysis of postmortem brain tissue from human cocaine users were performed.

Results

Innate low expression of Drd2 in iMSNs led to differential expression of genes involved in GABA (gamma-aminobutyric acid) and cAMP (cyclic adenosine monophosphate) signaling, neural growth, lipid metabolism, neural excitability, and inflammation. Creb1 was identified as a likely upstream regulator, among others. In human brain, expression of FXYD2, a modulatory subunit of the Na/K pump, was negatively correlated with DRD2 messenger RNA expression. In iMSN-TRAP-Drd2HET mice, increased Cartpt and reduced S100a10 (p11) expression recapitulated previous observations in cocaine paradigms. Electrophysiology experiments supported a higher GABA tone in iMSN-Drd2HET mice.

Conclusions

This study provides strong molecular evidence that, in addiction, inhibition by the indirect pathway is constitutively enhanced through neural growth and increased GABA signaling.

Arsenic exposure induced anxiety-like behaviors in male mice via influencing the GABAergic Signaling in the prefrontal cortex

Arsenic contamination in drinking water causes a global public health problem. Emerging evidence suggests that arsenic may act as an environmental risk factor for anxiety disorders. However, the exact mechanism underlying the adverse effects has not been fully elucidated. This study aimed to evaluate the anxiety-like behaviors of mice exposed to arsenic trioxide (As2O3), to observe the neuropathological changes, and to explore the link between the GABAergic system and behavioral manifestations. For this purpose, male C57BL/6 mice were exposed to various doses of As2O3 (0, 0.15, 1.5, and 15 mg/L) through drinking water for 12 weeks. Anxiety-like behaviors were assessed using the open field test (OFT), light/dark choice test, and elevated zero maze (EZM). Neuronal injuries in the cerebral cortex and hippocampus were assessed by light microscopy with H&E and Nissl staining. Ultrastructural alteration in the cerebral cortex was assessed by transmission electron microscope (TEM). The expression levels of GABAergic system-related molecules (i.e., glutamate decarboxylase, GABA transporter, and GABAB receptor subunits) in the prefrontal cortex (PFC) were determined by qRT-PCR and western blotting. Arsenic exposure showed a striking anxiogenic effect on mice, especially in the group exposed to 15 mg/L As2O3. Light microscopy showed neuron necrosis and reduced cell counts. TEM revealed marked ultrastructural changes, including the vacuolated mitochondria, disrupted Nissl bodies, an indentation in the nucleus membrane, and delamination of myelin sheath in the cortex. In addition, As2O3 influenced the GABAergic system in the PFC by decreasing the expression of the glutamate decarboxylase 1 (GAD1) and the GABAB2 receptor subunit, but not the GABAB1 receptor subunit. To sum up, sub-chronic exposure to As2O3 is associated with increased anxiety-like behaviors, which may be mediated by altered GABAergic signaling in the PFC. These findings shed light on the mechanisms responsible for the neurotoxic effects of arsenic and therefore more cautions should be taken.

Lynx1 and the family of endogenous mammalian neurotoxin-like proteins and their roles in modulating nAChR function

The promise of nicotinic receptors as a therapeutic target has yet to be fully realized, despite solid data supporting their involvement in neurological and neuropsychiatric diseases. The reasons for this are likely complex and manifold, having to do with the widespread action of the cholinergic system and the biophysical mechanism of action of nicotinic receptors leading to fast desensitization and down-regulation. Conventional drug development strategies tend to focus on receptor subtype-specific action of candidate therapeutics, although the broad agonist, nicotine, is being explored in the clinic. The potential negative effects of nicotine make the search for alternate strategies warranted. Prototoxins are a promising yet little-explored avenue of nicotinic receptor drug development. Nicotinic receptors in the brain belong to a complex of proteins, including those that bind to the extracellular face of the receptor, as well as chaperones that bind the intracellular domain, etc. Lynx prototoxins have allosteric modularity effects on receptor function and number and have been implicated in complex in vivo processes such as neuroplasticity, learning, and memory. Their mechanism of action and binding specificity on sets of nAChR subtypes present intriguing possibilities for more efficacious and nuanced therapeutic targeting than nicotinic receptor subtypes alone. An allosteric drug may restrict its actions to physiologically relevant time points, which tend to be correlated with salient events which would be encoded into long-term memory storage. Rather than blanketing the brain with a steady and prolonged elevation of agonist, an allosteric nAChR compound could avoid side effects and loss of efficacy over time. This review details the potential strengths and challenges of prototoxin proteins as therapeutic targets, and some of the utility of such therapeutics based on the emerging understanding of cholinergic signaling in a growing number of complex neural processes.

Human LY6 gene family: potential tumor-associated antigens and biomarkers of prognosis in uterine corpus endometrial carcinoma

The human Lymphocyte antigen-6 (LY6) gene family has recently gained interest for its possible role in tumor progression. We have carried out in silico analyses of all known LY6 gene expression and amplification in different cancers using TNMplot and cBioportal. We also have analyzed patient survival by Kaplan-Meier plotter after mining the TCGA database. We report that upregulated expression of many LY6 genes is associated with poor survival in uterine corpus endometrial carcinoma (UCEC) cancer patients. Importantly, the expression of several LY6 genes is elevated in UCEC when compared to the expression in normal uterine tissue. For example, LY6K expression is 8.25× higher in UCEC compared to normal uterine tissue, and this high expression is associated with poor survival with a hazard ratio of 2.42 (p-value = 0.0032). Therefore, some LY6 gene products may serve as tumor-associated antigens in UCEC, biomarkers for UCEC detection, and possibly targets for directing UCEC patient therapy. Further analysis of tumor-specific expression of LY6 gene family members and LY6-triggered signaling pathways is needed to uncover the function of LY6 proteins and their ability to endow tumor survival and poor prognosis in UCEC patients.

Xanomeline restores endogenous nicotinic acetylcholine receptor signaling in mouse prefrontal cortex

Cholinergic synapses in prefrontal cortex are vital for attention, but this modulatory system undergoes substantial pre- and post-synaptic alterations during adulthood. To examine the integrated impact of these changes, we optophysiologically probe cholinergic synapses ex vivo, revealing a clear decline in neurotransmission in middle adulthood. Pharmacological dissection of synaptic components reveals a selective reduction in postsynaptic nicotinic receptor currents. Other components of cholinergic synapses appear stable, by contrast, including acetylcholine autoinhibition, metabolism, and excitation of postsynaptic muscarinic receptors. Pursuing strategies to strengthen cholinergic neurotransmission, we find that positive allosteric modulation of nicotinic receptors with NS9283 is effective in young adults but wanes with age. To boost nicotinic receptor availability, we harness the second messenger pathways of the preserved excitatory muscarinic receptors with xanomeline. This muscarinic agonist and cognitive-enhancer restores nicotinic signaling in older mice significantly, in a muscarinic- and PKC-dependent manner. The rescued nicotinic component regains youthful sensitivity to allosteric enhancement: treatment with xanomeline and NS9283 restores cholinergic synapses in older mice to the strength, speed, and receptor mechanism of young adults. Our results reveal a new and efficient strategy to rescue age-related nicotinic signaling deficits, demonstrating a novel pathway for xanomeline to restore cognitively-essential endogenous cholinergic neurotransmission.

Chrna5 and lynx prototoxins identify acetylcholine super-responder subplate neurons

Attention depends on cholinergic excitation of prefrontal neurons but is sensitive to perturbation of α5-containing nicotinic receptors encoded by Chrna5. However, Chrna5-expressing (Chrna5+) neurons remain enigmatic, despite their potential as a target to improve attention. Here, we generate complex transgenic mice to probe Chrna5+ neurons and their sensitivity to endogenous acetylcholine. Through opto-physiological experiments, we discover that Chrna5+ neurons contain a distinct population of acetylcholine super-responders. Leveraging single-cell transcriptomics, we discover molecular markers conferring subplate identity on this subset. We determine that Chrna5+ super-responders express a unique complement of GPI-anchored lynx prototoxin genes (Lypd1, Ly6g6e, and Lypd6b), predicting distinct nicotinic receptor regulation. To manipulate lynx regulation of endogenous nicotinic responses, we developed a pharmacological strategy guided by transcriptomic predictions. Overall, we reveal Chrna5-Cre mice as a transgenic tool to target the diversity of subplate neurons in adulthood, yielding new molecular strategies to manipulate their cholinergic activation relevant to attention disorders.

Orientational Preferences of GPI-Anchored Ly6/uPAR Proteins

Ly6/uPAR proteins regulate many essential functions in the nervous and immune systems and epithelium. Most of these proteins contain single β-structural LU domains with three protruding loops and are glycosylphosphatidylinositol (GPI)-anchored to a membrane. The GPI-anchor role is currently poorly studied. Here, we investigated the positional and orientational preferences of six GPI-anchored proteins in the receptor-unbound state by molecular dynamics simulations. Regardless of the linker length between the LU domain and GPI-anchor, the proteins interacted with the membrane by polypeptide parts and N-/O-glycans. Lynx1, Lynx2, Lypd6B, and Ly6H contacted the membrane by the loop regions responsible for interactions with nicotinic acetylcholine receptors, while Lypd6 and CD59 demonstrated unique orientations with accessible receptor-binding sites. Thus, GPI-anchoring does not guarantee an optimal 'pre-orientation' of the LU domain for the receptor interaction.

New Three-Finger Protein from Starfish Asteria rubens Shares Structure and Pharmacology with Human Brain Neuromodulator Lynx2

Three-finger proteins (TFPs) are small proteins with characteristic three-finger β-structural fold stabilized by the system of conserved disulfide bonds. These proteins have been found in organisms from different taxonomic groups and perform various important regulatory functions or act as components of snake venoms. Recently, four TFPs (Lystars 1–4) with unknown function were identified in the coelomic fluid proteome of starfish A. rubens. Here we analyzed the genomes of A. rubens and A. planci starfishes and predicted additional five and six proteins containing three-finger domains, respectively. One of them, named Lystar5, is expressed in A. rubens coelomocytes and has sequence homology to the human brain neuromodulator Lynx2. The three-finger structure of Lystar5 close to the structure of Lynx2 was confirmed by NMR. Similar to Lynx2, Lystar5 negatively modulated α4β2 nicotinic acetylcholine receptors (nAChRs) expressed in X. laevis oocytes. Incubation with Lystar5 decreased the expression of acetylcholine esterase and α4 and α7 nAChR subunits in the hippocampal neurons. In summary, for the first time we reported modulator of the cholinergic system in starfish.

High and fluctuating levels of ovarian hormones induce an anxiogenic effect, which can be modulated under stress conditions: Evidence from an assisted reproductive rodent model

Elevated levels of endogenous ovarian hormones are conditions commonly experienced by women undergoing assisted reproductive technologies (ART). Additionally, infertility-associated stress and treatment routines are factors that together may have a highly negative impact on female emotionality, which can be aggravated when several cycles of ART are needed to attempt pregnancy. This study aimed to investigate the effect of high and fluctuating levels of gonadal hormones induced by repeated ovarian stimulation on the stress response in rodents. To mimic the context of ART, female rats were exposed to an unpredictable chronic mild stress (UCMS) paradigm for four weeks. During this time, three cycles of ovarian stimulation (superovulation) (150 IU/Kg of PMSG and 75 IU/Kg of hCG) were applied, with intervals of two estrous cycles between them. The rats were distributed into four groups: Repeated Superovulation/UCMS; Repeated Superovulation/No Stress; Saline/UCMS; and Saline/No Stress. Anxiety-like and depressive-like behaviors were evaluated in a light-dark transition box and by splash test, respectively. Corticosterone, estradiol, progesterone, and biometric parameters were assessed. Data were analyzed using a two-way Generalized Linear Model (GzLM). Our results showed that repeated ovarian stimulation exerts by itself an expressive anxiogenic effect. Surprisingly, when high and fluctuating levels of ovarian hormones were combined with chronic stress, anxiety-like behavior was no longer observed, and a depressive-like state was not detected. Our findings suggest that females subjected to emotional overload induced by repeated ovarian stimulation and chronic stress seem to trigger the elaboration of adaptive coping strategies.

Biophysical characterization of lynx-nicotinic receptor interactions using atomic force microscopy

Nicotinic acetylcholine receptors (nAChRs) are broadly expressed in the central and peripheral nervous systems, playing essential roles in cholinergic neurotransmission. The lynx family proteins, a subset of the Ly6/uPAR superfamily expressed in multiple brain regions, have been shown to bind to nAChRs and modulate their function via allosteric regulation. The binding interactions between lynx and nAChRs, however, have not been systematically quantified and compared. In this work, we characterized the interactions between lynx1 or lynx2 and α3β4- or α7-nAChRs using single-molecule atomic force microscopy (AFM). The AFM technique allows the quantification of the off-rate of lynx-nAChR binding and of the energetic barrier width between the bound state and transition state, providing a biophysical means to compare the selectivity of lynx proteins for nAChR subtypes. Results indicate that lynx1 has a marginal preference for α7- over α3β4-nAChRs. Strikingly, lynx2 exhibits a two order of magnitude stronger affinity for α3β4- compared to α7-nAChRs. Together, the AFM assay serves as a valuable tool for the biophysical characterization of lynx-nAChR binding affinities. Revealing the differential affinities of lynx proteins for nAChR subtypes will help elucidate how lynx regulates nAChR-dependent functions in the brain, including nicotine addiction and other critical pathways.

Differential Expression Patterns of Lynx Proteins and Involvement of Lynx1 in Prepulse Inhibition

Negative allosteric modulators, such as lynx1 and lynx2, directly interact with nicotinic acetylcholine receptors (nAChRs). The nAChRs are integral to cholinergic signaling in the brain and have been shown to mediate different aspects of cognitive function. Given the interaction between lynx proteins and these receptors, we examined whether these endogenous negative allosteric modulators are involved in cognitive behaviors associated with cholinergic function. We found both cell-specific and overlapping expression patterns of lynx1 and lynx2 mRNA in brain regions associated with cognition, learning, memory, and sensorimotor processing, including the prefrontal cortex (PFC), cingulate cortex, septum, hippocampus, amygdala, striatum, and pontine nuclei. Since lynx proteins are thought to play a role in conditioned associations and given the expression patterns across brain regions, we first assessed whether lynx knockout mice would differ in a cognitive flexibility task. We found no deficits in reversal learning in either the lynx1^–/– or lynx2^–/– knockout mice. Thereafter, sensorimotor gating was examined with the prepulse inhibition (PPI) assessment. Interestingly, we found that both male and female lynx1^–/– mice exhibited a deficit in the PPI behavioral response. Given the comparable expression of lynx2 in regions involved in sensorimotor gating, we then examined whether removal of the lynx2 protein would lead to similar behavioral effects. Unexpectedly, we found that while male lynx2^–/– mice exhibited a decrease in the baseline startle response, no differences were found in sensorimotor gating for either male or female lynx2^–/– mice. Taken together, these studies provide insight into the expression patterns of lynx1 and lynx2 across multiple brain regions and illustrate the modulatory effects of the lynx1 protein in sensorimotor gating.

Human Three-Finger Protein Lypd6 Is a Negative Modulator of the Cholinergic System in the Brain

Lypd6 is a GPI-tethered protein from the Ly-6/uPAR family expressed in the brain. Lypd6 enhances the Wnt/β-catenin signaling, although its action on nicotinic acetylcholine receptors (nAChRs) have been also proposed. To investigate a cholinergic activity of Lypd6, we studied a recombinant water-soluble variant of the human protein (ws-Lypd6) containing isolated “three-finger” LU-domain. Experiments at different nAChR subtypes expressed in Xenopus oocytes revealed the negative allosteric modulatory activity of ws-Lypd6. Ws-Lypd6 inhibited ACh-evoked currents at α3β4- and α7-nAChRs with IC₅₀ of ∼35 and 10 μM, respectively, and the maximal amplitude of inhibition of 30–50%. EC₅₀ of ACh at α3β4-nAChRs (∼30 μM) was not changed in the presence of 35 μM ws-Lypd6, while the maximal amplitude of ACh-evoked current was reduced by ∼20%. Ws-Lypd6 did not elicit currents through nAChRs in the absence of ACh. Application of 1 μM ws-Lypd6 significantly inhibited (up to ∼28%) choline-evoked current at α7-nAChRs in rat hippocampal slices. Similar to snake neurotoxin α-bungarotoxin, ws-Lypd6 suppressed the long-term potentiation (LTP) in mouse hippocampal slices. Colocalization of endogenous GPI-tethered Lypd6 with α3β4- and α7-nAChRs was detected in primary cortical and hippocampal neurons. Ws-Lypd6 interaction with the extracellular domain of α7-nAChR was modeled using the ensemble protein-protein docking protocol. The interaction of all three Lypd6 loops (“fingers”) with the entrance to the orthosteric ligand-binding site and the loop C of the primary receptor subunit was predicted. The results obtained allow us to consider Lypd6 as the endogenous negative modulator involved in the regulation of the cholinergic system in the brain.

Nicotinic acetylcholine receptor redux: Discovery of accessories opens therapeutic vistas

The neurotransmitter acetylcholine (ACh) acts in part through a family of nicotinic ACh receptors (nAChRs), which mediate diverse physiological processes including muscle contraction, neurotransmission, and sensory transduction. Pharmacologically, nAChRs are responsible for tobacco addiction and are targeted by medicines for hypertension and dementia. Nicotinic AChRs were the first ion channels to be isolated. Recent studies have identified molecules that control nAChR biogenesis, trafficking, and function. These nAChR accessories include protein and chemical chaperones as well as auxiliary subunits. Whereas some factors act on many nAChRs, others are receptor specific. Discovery of these regulatory mechanisms is transforming nAChR research in cells and tissues ranging from central neurons to spinal ganglia to cochlear hair cells. Nicotinic AChR-specific accessories also enable drug discovery on high-confidence targets for psychiatric, neurological, and auditory disorders.

Pain and itch processing by subpopulations of molecularly diverse spinal and trigeminal projection neurons

A remarkable molecular and functional heterogeneity of the primary sensory neurons and dorsal horn interneurons transmits pain- and or itch-relevant information, but the molecular signature of the projection neurons that convey the messages to the brain is unclear. Here, using retro-TRAP (translating ribosome affinity purification) and RNA sequencing, we reveal extensive molecular diversity of spino- and trigeminoparabrachial projection neurons. Among the many genes identified, we highlight distinct subsets of Cck+ -, Nptx2+ -, Nmb+ -, and Crh+ -expressing projection neurons. By combining in situ hybridization of retrogradely labeled neurons with Fos-based assays, we also demonstrate significant functional heterogeneity, including both convergence and segregation of pain- and itch-provoking inputs into molecularly diverse subsets of NK1R- and non-NK1R-expressing projection neurons.

Multidimensional Intersection of Nicotine, Gene Expression, and Behavior

The cholinergic system plays a crucial role in nervous system function with important effects on developmental processes, cognition, attention, motivation, reward, learning, and memory. Nicotine, the reinforcing component of tobacco and e-cigarettes, directly acts on the cholinergic system by targeting nicotinic acetylcholine receptors (nAChRs) in the brain. Activation of nAChRs leads to a multitude of immediate and long-lasting effects in specific cellular populations, thereby affecting the addictive properties of the drug. In addition to the direct actions of nicotine in binding to and opening nAChRs, the subsequent activation of circuits and downstream signaling cascades leads to a wide range of changes in gene expression, which can subsequently alter further behavioral expression. In this review, we provide an overview of the actions of nicotine that lead to changes in gene expression and further highlight evidence supporting how these changes can often be bidirectional, thereby inducing subsequent changes in behaviors associated with further drug intake.

Interaction between zinc, the GPR39 zinc receptor and the serotonergic system in depression

Zinc signalling has a crucial impact on the proper functioning of the brain. Disturbances within the zincergic system may lead to neuropsychological disorders, including major depression. Studying this disease and designing effective treatment is hampered by its heterogeneous etiology and the diversified nature of the symptoms. Over the years, studies have shown that zinc deficiency and disturbances in the expression profile of the zinc receptor - GPR39 - might be a useful neurobiological indicator of a pathological state. Zinc levels and the zinc receptor are altered by classic antidepressant treatment, which indicates possible reciprocity between the monoaminergic system and zinc signalling. Disruptions in this specific interplay might be a cause of a pathological depressive state, and restoring balance and cooperation between those systems might be key to a successful form of pharmacotherapy. In this review, we aim to describe interactions between the serotonergic and zincergic systems and to highlight their significance in the pathophysiology and treatment of depression.

Anti-LYPD1/CD3 T-Cell-Dependent Bispecific Antibody for the Treatment of Ovarian Cancer

Ovarian cancer is a diverse class of tumors with very few effective treatment options and suboptimal response rates in early clinical studies using immunotherapies. Here we describe LY6/PLAUR domain containing 1 (LYPD1) as a novel target for therapeutic antibodies for the treatment of ovarian cancer. LYPD1 is broadly expressed in both primary and metastatic ovarian cancer with ∼70% prevalence in the serous cancer subset. Bispecific antibodies targeting CD3 on T cells and a tumor antigen on cancer cells have demonstrated significant clinical activity in hematologic cancers. We have developed an anti-LYPD1/CD3 T-cell-dependent bispecific antibody (TDB) to redirect T-cell responses to LYPD1 expressing ovarian cancer. Here we characterize the nonclinical pharmacology of anti-LYPD1/CD3 TDB and show induction of a robust polyclonal T-cell activation and target dependent killing of LYPD1 expressing ovarian cancer cells resulting in efficient in vivo antitumor responses in PBMC reconstituted immune-deficient mice and human CD3 transgenic mouse models. Anti-LYPD1/CD3 TDB is generally well tolerated at high-dose levels in mice, a pharmacologically relevant species, and showed no evidence of toxicity or damage to LYPD1 expressing tissues.

Structural Diversity and Dynamics of Human Three-Finger Proteins Acting on Nicotinic Acetylcholine Receptors

Ly-6/uPAR or three-finger proteins (TFPs) contain a disulfide-stabilized β-structural core and three protruding loops (fingers). In mammals, TFPs have been found in epithelium and the nervous, endocrine, reproductive, and immune systems. Here, using heteronuclear NMR, we determined the three-dimensional (3D) structure and backbone dynamics of the epithelial secreted protein SLURP-1 and soluble domains of GPI-anchored TFPs from the brain (Lynx2, Lypd6, Lypd6b) acting on nicotinic acetylcholine receptors (nAChRs). Results were compared with the data about human TFPs Lynx1 and SLURP-2 and snake α-neurotoxins WTX and NTII. Two different topologies of the β-structure were revealed: one large antiparallel β-sheet in Lypd6 and Lypd6b, and two β-sheets in other proteins. α-Helical segments were found in the loops I/III of Lynx2, Lypd6, and Lypd6b. Differences in the surface distribution of charged and hydrophobic groups indicated significant differences in a mode of TFPs/nAChR interactions. TFPs showed significant conformational plasticity: the loops were highly mobile at picosecond-nanosecond timescale, while the β-structural regions demonstrated microsecond-millisecond motions. SLURP-1 had the largest plasticity and characterized by the unordered loops II/III and cis-trans isomerization of the Tyr39-Pro40 bond. In conclusion, plasticity could be an important feature of TFPs adapting their structures for optimal interaction with the different conformational states of nAChRs.

ALKBH5 suppresses malignancy of hepatocellular carcinoma via m6A-guided epigenetic inhibition of LYPD1

Background

N6-methyladenosine (m⁶A) modification is an emerging layer of epigenetic regulation which is widely implicated in the tumorigenicity of hepatocellular carcinoma (HCC), offering a novel perspective for investigating molecular pathogenesis of this disease. The role of AlkB homolog 5 (ALKBH5), one of the m⁶A demethylases, has not been fully explored in HCC. Here we clarify the biological profile and potential mechanisms of ALKBH5 in HCC.

Methods

Expression of ALKBH5 and its correlation with clinicopathological characteristics of HCC were evaluated using tissue microarrays and online datasets. And biological effects of ALKBH5 in HCC were determined in vitro and in vivo. Subsequently, methylated RNA immunoprecipitation sequencing (MeRIP-seq) combined with RNA sequencing (RNA-seq), and following m⁶A dot blot, MeRIP-qPCR, RIP-qPCR or dual luciferase reporter assays were employed to screen and validate the candidate targets of ALKBH5.

Results

We demonstrated that ALKBH5 was down-regulated in HCC, and decreased ALKBH5 expression was an independent prognostic factor of worse survival in HCC patients. Functionally, ALKBH5 suppressed the proliferation and invasion capabilities of HCC cells in vitro and in vivo. Mechanistically, ALKBH5-mediated m⁶A demethylation led to a post-transcriptional inhibition of LY6/PLAUR Domain Containing 1 (LYPD1), which could be recognized and stabilized by the m⁶A effector IGF2BP1. In addition, we identified that LYPD1 induced oncogenic behaviors of tumors in contrast to ALKBH5. Dysregulation of ALKBH5/LYPD1 axis impelled the progression of HCC.

Conclusion

Our study reveals that ALKBH5, characterized as a tumor suppressor, attenuates the expression of LYPD1 via an m⁶A-dependent manner in HCC cells. Our findings enrich the landscape of m⁶A-modulated tumor malignancy, and provide new insights into potential biomarkers and therapeutic targets of HCC treatment.

Lynx Prototoxins: Roles of Endogenous Mammalian Neurotoxin-Like Proteins in Modulating Nicotinic Acetylcholine Receptor Function to Influence Complex Biological Processes

The cholinergic system modulates many biological functions, due to the widespread distribution of cholinergic neuronal terminals, and the diffuse release of its neurotransmitter, acetylcholine. Several layers of regulation help to refine and control the scope of this excitatory neurotransmitter system. One such regulatory mechanism is imparted through endogenous toxin-like proteins, prototoxins, which largely control the function of nicotinic receptors of the cholinergic system. Prototoxins and neurotoxins share the distinct three finger toxin fold, highly effective as a receptor binding protein, and the former are expressed in the mammalian brain, immune system, epithelium, etc. Prototoxins and elapid snake neurotoxins appear to be related through gene duplication and divergence from a common ancestral gene. Protein modulators can provide a graded response of the cholinergic system, and within the brain, stabilize neural circuitry through direct interaction with nicotinic receptors. Understanding the roles of each prototoxin (e.g., lynx1, lynx2/lypd1, PSCA, SLURP1, SLURP2, Lypd6, lypd6b, lypdg6e, PATE-M, PATE-B, etc.), their binding specificity and unique expression profile, has the potential to uncover many fascinating cholinergic-dependent mechanisms in the brain. Each family member can provide a spatially restricted level of control over nAChR function based on its expression in the brain. Due to the difficulty in the pharmacological targeting of nicotinic receptors in the brain as a result of widespread expression patterns and similarities in receptor sequences, unique interfaces between prototoxin and nicotinic receptor could provide more specific targeting than nicotinic receptors alone. As such, this family is intriguing from a long-term therapeutic perspective.

Acetylcholine signaling system in progression of lung cancers

The neurotransmitter acetylcholine (ACh) acts as an autocrine growth factor for human lung cancer. Several lines of evidence show that lung cancer cells express all of the proteins required for the uptake of choline (choline transporter 1, choline transporter-like proteins) synthesis of ACh (choline acetyltransferase, carnitine acetyltransferase), transport of ACh (vesicular acetylcholine transport, OCTs, OCTNs) and degradation of ACh (acetylcholinesterase, butyrylcholinesterase). The released ACh binds back to nicotinic (nAChRs) and muscarinic receptors on lung cancer cells to accelerate their proliferation, migration and invasion. Out of all components of the cholinergic pathway, the nAChR-signaling has been studied the most intensely. The reason for this trend is due to genome-wide data studies showing that nicotinic receptor subtypes are involved in lung cancer risk, the relationship between cigarette smoke and lung cancer risk as well as the rising popularity of electronic cigarettes considered by many as a "safe" alternative to smoking. There are a small number of articles which review the contribution of the other cholinergic proteins in the pathophysiology of lung cancer. The primary objective of this review article is to discuss the function of the acetylcholine-signaling proteins in the progression of lung cancer. The investigation of the role of cholinergic network in lung cancer will pave the way to novel molecular targets and drugs in this lethal malignancy.

Molecular Mechanisms Associated with Nicotine Pharmacology and Dependence

Tobacco dependence is a leading cause of preventable disease and death worldwide. Nicotine, the main psychoactive component in tobacco cigarettes, has also been garnering increased popularity in its vaporized form, as derived from e-cigarette devices. Thus, an understanding of the molecular mechanisms underlying nicotine pharmacology and dependence is required to ascertain novel approaches to treat drug dependence. In this chapter, we review the field's current understanding of nicotine's actions in the brain, the neurocircuitry underlying drug dependence, factors that modulate the function of nicotinic acetylcholine receptors, and the role of specific genes in mitigating the vulnerability to develop nicotine dependence. In addition to nicotine's direct actions in the brain, other constituents in nicotine and tobacco products have also been found to alter drug use, and thus, evidence is provided to highlight this issue. Finally, currently available pharmacotherapeutic strategies are discussed, along with an outlook for future therapeutic directions to achieve to the goal of long-term nicotine cessation.

Sensory Neuron Diversity in the Inner Ear Is Shaped by Activity

In the auditory system, type I spiral ganglion neurons (SGNs) convey complex acoustic information from inner hair cells (IHCs) to the brainstem. Although SGNs exhibit variation in physiological and anatomical properties, it is unclear which features are endogenous and which reflect input from synaptic partners. Using single-cell RNA sequencing, we derived a molecular classification of mouse type I SGNs comprising three subtypes that express unique combinations of Ca2+ binding proteins, ion channel regulators, guidance molecules, and transcription factors. Based on connectivity and susceptibility to age-related loss, these subtypes correspond to those defined physiologically. Additional intrinsic differences among subtypes and across the tonotopic axis highlight an unexpectedly active role for SGNs in auditory processing. SGN identities emerge postnatally and are disrupted in a mouse model of deafness that lacks IHC-driven activity. These results elucidate the range, nature, and origins of SGN diversity, with implications for treatment of congenital deafness.

Augmenting the antinociceptive effects of nicotinic acetylcholine receptor activity through lynx1 modulation

Neuronal nicotinic acetylcholine receptors (nAChRs) of the cholinergic system have been linked to antinociception, and therefore could be an alternative target for pain alleviation. nAChR activity has been shown to be regulated by the nicotinic modulator, lynx1, which forms stable complexes with nAChRs and has a negative allosteric action on their function. The objective in this study was to investigate the contribution of lynx1 to nicotine-mediated antinociception. Lynx1 contribution was investigated by mRNA expression analysis and electrophysiological responses to nicotine in the dorsal raphe nucleus (DRN), a part of the pain signaling pathway. In vivo antinociception was investigated in a test of nociception, the hot-plate analgesia assay with behavioral pharmacology. Lynx1/α4β2 nAChR interactions were investigated using molecular dynamics computational modeling. Nicotine evoked responses in serotonergic and GABAergic neurons in the DRN are augmented in slices lacking lynx1 (lynx1KO). The antinociceptive effect of nicotine and epibatidine is enhanced in lynx1KO mice and blocked by mecamylamine and DHβE. Computer simulations predict preferential binding affinity of lynx1 to the α:α interface that exists in the stoichiometry of the low sensitivity (α4)₃(β2)₂ nAChRs. Taken together, these data point to a role of lynx1 in mediating pain signaling in the DRN through preferential affinity to the low sensitivity α4β2 nAChRs. This study suggests that lynx1 is a possible alternative avenue for nociceptive modulation outside of opioid-based strategies.

Three-Finger Proteins from the Ly6/uPAR Family: Functional Diversity within One Structural Motif

The discovery in higher animals of proteins from the Ly6/uPAR family, which have structural homology with snake "three-finger" neurotoxins, has generated great interest in these molecules and their role in the functioning of the organism. These proteins have been found in the nervous, immune, endocrine, and reproductive systems of mammals. There are two types of the Ly6/uPAR proteins: those associated with the cell membrane by GPI-anchor and secreted ones. For some of them (Lynx1, SLURP-1, SLURP-2, Lypd6), as well as for snake α-neurotoxins, the target of action is nicotinic acetylcholine receptors, which are widely represented in the central and peripheral nervous systems, and in many other tissues, including epithelial cells and the immune system. However, the targets of most proteins from the Ly6/uPAR family and the mechanism of their action remain unknown. This review presents data on the structural and functional properties of the Ly6/uPAR proteins, which reveal a variety of functions within a single structural motif.

Loss of Lypd6 leads to reduced anxiety-like behaviour and enhanced responses to nicotine

Nicotine consumption through smoking affects anxious states in humans. However, the precise role of nicotinic acetylcholine receptor (nAChR) circuitry in the regulation of anxiety remains elusive. The Lynx protein Lypd6 is highly enriched in synaptic loci and has been previously identified as an endogenous inhibitor of neuronal nAChR function in vitro. Here, we investigate the effect of Lypd6 in anxiety-related behaviour and examine the molecular underpinnings of its function in the brain. We employ the marble burying (MB) and elevated zero maze (EZM) tests in Lypd6 knock-out (KO) and wild-type (WT) mice and find that loss of Lypd6 leads to decreased digging behaviour in the MB test and increased time spent in the open area in the EZM test. Moreover, we demonstrate that acute nicotine administration reduces digging in the MB test in both KO and WT mice and further accentuates the inherent genotype difference. Using in vitro electrophysiology in dorsal raphe nuclei (DRN) neurons from Lypd6 KO mice, we show that nicotine-evoked whole-cell currents are enhanced in the absence of Lypd6. Collectively, these data are the first to indicate the involvement of Lypd6 in circuits associated with anxiety and suggest that a possible underlying neurobiological mechanism is the modulation of cholinergic responses in the DRN.

Getting a Handle on Neuropharmacology by Targeting Receptor-Associated Proteins

Targeted therapy for neuropsychiatric disorders requires selective modulation of dysfunctional neuronal pathways. Receptors relevant to CNS disorders typically have associated proteins discretely expressed in specific neuronal pathways; these accessory proteins provide a new dimension for drug discovery. Recent studies show that targeting a TARP auxiliary subunit of AMPA receptors selectively modulates neuronal excitability in specific forebrain pathways relevant to epilepsy. Other medicinally important ion channels, gated by glutamate, γ-aminobutyric acid (GABA), and acetylcholine, also have associated proteins, which may be druggable. This emerging pharmacology of receptor-associated proteins provides a new approach for improving drug efficacy while mitigating side effects.

Involvement of Lypge in the formation of eye and pineal gland in zebrafish

The proteins of Ly-6 (lymphocyte antigen-6) family are involved in the regulation of immunoreaction, cell migration and adhesion, and neuronal excitability. However, little is known about the function of Ly-6 proteins in embryogenesis. Herein, we identified a GPI anchored Ly-6 member named ly6 expressed in pineal gland and eye (lypge). Dynamic expression pattern of lypge was revealed by whole mount in situ hybridization. It was strikingly expressed in the pineal gland and cone photoreceptor, and its expression was regulated by orthodenticle homolog 5 (otx5) which has been shown to control the expression of many pineal genes. In addition, we demonstrated that lypge was rhythmically expressed in larvae from 4dpf on. Moreover, knockdown of lypge resulted in small head and small eye formed in zebrafish embryos. These suggest that Lypge is involved in the formation of the eye and pineal gland in early development of zebrafish.

Early Pheromone Experience Modifies a Synaptic Activity to Influence Adult Pheromone Responses of C. elegans

Experiences during early development can influence neuronal functions and modulate adult behaviors [1, 2]. However, the molecular mechanisms underlying the long-term behavioral effects of these early experiences are not fully understood. The C. elegans ascr#3 (asc-ΔC9; C9) pheromone triggers avoidance behavior in adult hermaphrodites [3-7]. Here, we show that hermaphrodites that are briefly exposed to ascr#3 immediately after birth exhibit increased ascr#3-specific avoidance as adults, indicating that ascr#3-experienced animals form a long-lasting memory or imprint of this early ascr#3 exposure [8]. ascr#3 imprinting is mediated by increased synaptic activity between the ascr#3-sensing ADL neurons and their post-synaptic SMB motor neuron partners via increased expression of the odr-2 glycosylated phosphatidylinositol (GPI)-linked signaling gene in the SMB neurons. Our study suggests that the memory for early ascr#3 experience is imprinted via alteration of activity of a single synaptic connection, which in turn shapes experience-dependent plasticity in adult ascr#3 responses.

Identification of Ly2 members as antimicrobial peptides from zebrafish Danio rerio

The emergence of multidrug-resistant (MDR) microbes caused by overuse of antibiotics leads to urgent demands for novel antibiotics exploration. Our recent data showed that Ly2.1–3 (a novel lymphocyte antigen 6 (Ly6) gene cluster) were proteins with cationic nature and rich in cysteine content, that are characteristic of antimicrobial peptides (AMPs) and their expression were all significantly up-regulated after challenge with lipopolysaccharide (LPS). These strongly suggested that Ly2.1–3 are potential AMPs, but firm evidence are lacking. Here, we clearly showed that the recombinant proteins of Ly2.1–3 were capable of killing Gram-negative bacteria Aeromonas hydrophila and Escherichia coli, while they had little bactericidal activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis. We also showed that recombinant proteins Ly2.1–3 (rLy2.1–3) were able to bind to the Gram-negative bacteria A. hydrophila, E. coli and the microbial signature molecule LPS, but not to the Gram-positive bacteria S. aureus and B. subtilis as well as the microbial signature molecule LTA. Moreover, the Scatchard analysis revealed that rLy2.1–3 could specifically bind to LPS. Finally, we found that Ly2.1–3 were not cytotoxic to mammalian cells. All these together indicate that Ly2.1–3 can function as AMPs.

Nicotinic regulation of experience-dependent plasticity in visual cortex

While the cholinergic neuromodulatory system and muscarinic acetylcholine receptors (AChRs) have been appreciated as permissive factors for developmental critical period plasticity in visual cortex, it was unknown why plasticity becomes limited after the critical period even in the presence of massive cholinergic projections to visual cortex. In this review we highlighted the recent progresses that started to shed light on the role of the nicotinic cholinergic neuromodulatory signaling on limiting juvenile form of plasticity in the adult brain. We introduce the Lynx family of proteins and Lynx1 as its representative, as endogenous proteins structurally similar to α-bungarotoxin with the ability to bind and modulate nAChRs to effectively regulate functional and structural plasticity. Remarkably, Lynx family members are expressed in distinct subpopulations of GABAergic interneurons, placing them in unique positions to potentially regulate the convergence of GABAergic and nicotinic neuromodulatory systems to regulate plasticity. Continuing studies of the potentially differential roles of Lynx family of proteins may further our understanding of the fundamentals of molecular and cell type-specific mechanisms of plasticity that we may be able to harness through nicotinic cholinergic signaling.

Functional interaction between Lypd6 and nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) affect multiple physiological functions in the brain and their functions are modulated by regulatory proteins of the Lynx family. Here, we report for the first time a direct interaction of the Lynx protein LY6/PLAUR domain-containing 6 (Lypd6) with nAChRs in human brain extracts, identifying Lypd6 as a novel regulator of nAChR function. Using protein cross-linking and affinity purification from human temporal cortical extracts, we demonstrate that Lypd6 is a synaptically enriched membrane-bound protein that binds to multiple nAChR subtypes in the human brain. Additionally, soluble recombinant Lypd6 protein attenuates nicotine-induced hippocampal inward currents in rat brain slices and decreases nicotine-induced extracellular signal-regulated kinase phosphorylation in PC12 cells, suggesting that binding of Lypd6 is sufficient to inhibit nAChR-mediated intracellular signaling. We further show that perinatal nicotine exposure in rats (4 mg/kg/day through minipumps to dams from embryonic day 7 to post-natal day 21) significantly increases Lypd6 protein levels in the hippocampus in adulthood, which did not occur after exposure to nicotine in adulthood only. Our findings suggest that Lypd6 is a versatile inhibitor of cholinergic signaling in the brain, and that Lypd6 is dysregulated by nicotine exposure during early development. Regulatory proteins of the Lynx family modulate the function of nicotinic receptors (nAChRs). We report for the first time that the Lynx protein Lypd6 binds to nAChRs in human brain extracts, and that recombinant Lypd6 decreases nicotine-induced ERK phosphorylation and attenuates nicotine-induced hippocampal inward currents. Our findings suggest that Lypd6 is a versatile inhibitor of cholinergic signaling in the brain.

Organization, evolution and functions of the human and mouse Ly6/uPAR family genes

Members of the lymphocyte antigen-6 (Ly6)/urokinase-type plasminogen activator receptor (uPAR) superfamily of proteins are cysteine-rich proteins characterized by a distinct disulfide bridge pattern that creates the three-finger Ly6/uPAR (LU) domain. Although the Ly6/uPAR family proteins share a common structure, their expression patterns and functions vary. To date, 35 human and 61 mouse Ly6/uPAR family members have been identified. Based on their subcellular localization, these proteins are further classified as GPI-anchored on the cell membrane, or secreted. The genes encoding Ly6/uPAR family proteins are conserved across different species and are clustered in syntenic regions on human chromosomes 8, 19, 6 and 11, and mouse Chromosomes 15, 7, 17, and 9, respectively. Here, we review the human and mouse Ly6/uPAR family gene and protein structure and genomic organization, expression, functions, and evolution, and introduce new names for novel family members.

The prototoxin LYPD6B modulates heteromeric α3β4-containing nicotinic acetylcholine receptors, but not α7 homomers

Prototoxins are a diverse family of membrane-tethered molecules expressed in the nervous system that modulate nicotinic cholinergic signaling, but their functions and specificity have yet to be completely explored. We tested the selectivity and efficacy of leukocyte antigen, PLAUR (plasminogen activator, urokinase receptor) domain-containing (LYPD)-6B on α3β4-, α3α5β4-, and α7-containing nicotinic acetylcholine receptors (nAChRs). To constrain stoichiometry, fusion proteins encoding concatemers of human α3, β4, and α5 (D and N variants) subunits were expressed in Xenopus laevis oocytes and tested with or without LYPD6B. We used the 2-electrode voltage-clamp method to quantify responses to acetylcholine (ACh): agonist sensitivity (EC50), maximal agonist-induced current (Imax), and time constant (τ) of desensitization. For β4-α3-α3-β4-α3 and β4-α3-β4-α3-α3, LYPD6B decreased EC50 from 631 to 79 μM, reduced Imax by at least 59%, and decreased τ. For β4-α3-α5D-β4-α3 and β4-α3-β4-α-α5D, LYPD6B decreased Imax by 63 and 32%, respectively. Thus, LYPD6B acted only on (α3)3(β4)2 and (α3)2(α5D)(β4)2 and did not affect the properties of (α3)2(β4)3, α7, or (α3)2(α5N)(β4)2 nAChRs. Therefore, LYPD6B acts as a mixed modulator that enhances the sensitivity of (α3)3(β4)2 nAChRs to ACh while reducing ACh-induced whole-cell currents. LYPD6B also negatively modulates α3β4 nAChRs that include the α5D common human variant, but not the N variant associated with nicotine dependence.

Human Secreted Ly-6/uPAR Related Protein-1 (SLURP-1) Is a Selective Allosteric Antagonist of α7 Nicotinic Acetylcholine Receptor

SLURP-1 is a secreted toxin-like Ly-6/uPAR protein found in epithelium, sensory neurons and immune cells. Point mutations in the slurp-1 gene cause the autosomal inflammation skin disease Mal de Meleda. SLURP-1 is considered an autocrine/paracrine hormone that regulates growth and differentiation of keratinocytes and controls inflammation and malignant cell transformation. The majority of previous studies of SLURP-1 have been made using fusion constructs containing, in addition to the native protein, extra polypeptide sequences. Here we describe the activity and pharmacological profile of a recombinant analogue of human SLURP-1 (rSLURP-1) differing from the native protein only by one additional N-terminal Met residue. rSLURP-1 significantly inhibited proliferation (up to ~ 40%, EC₅₀ ~ 4 nM) of human oral keratinocytes (Het-1A cells). Application of mecamylamine and atropine,—non-selective inhibitors of nicotinic acetylcholine receptors (nAChRs) and muscarinic acetylcholine receptors, respectively, and anti-α7-nAChRs antibodies revealed α7 type nAChRs as an rSLURP-1 target in keratinocytes. Using affinity purification from human cortical extracts, we confirmed that rSLURP-1 binds selectively to the α7-nAChRs. Exposure of Xenopus oocytes expressing α7-nAChRs to rSLURP-1 caused a significant non-competitive inhibition of the response to acetylcholine (up to ~ 70%, IC₅₀ ~ 1 μM). It was shown that rSLURP-1 binds to α7-nAChRs overexpressed in GH₄C_l cells, but does not compete with ¹²⁵I-α-bungarotoxin for binding to the receptor. These findings imply an allosteric antagonist-like mode of SLURP-1 interaction with α7-nAChRs outside the classical ligand-binding site. Contrary to rSLURP-1, other inhibitors of α7-nAChRs (mecamylamine, α-bungarotoxin and Lynx1) did not suppress the proliferation of keratinocytes. Moreover, the co-application of α-bungarotoxin with rSLURP-1 did not influence antiproliferative activity of the latter. This supports the hypothesis that the antiproliferative activity of SLURP-1 is related to ‘metabotropic’ signaling pathway through α7-nAChR, that activates intracellular signaling cascades without opening the receptor channel.

Structural Analysis and Deletion Mutagenesis Define Regions of QUIVER/SLEEPLESS that Are Responsible for Interactions with Shaker-Type Potassium Channels and Nicotinic Acetylcholine Receptors

Ly6 proteins are endogenous prototoxins found in most animals. They show striking structural and functional parallels to snake α-neurotoxins, including regulation of ion channels and cholinergic signaling. However, the structural contributions of Ly6 proteins to regulation of effector molecules is poorly understood. This question is particularly relevant to the Ly6 protein QUIVER/SLEEPLESS (QVR/SSS), which has previously been shown to suppress excitability and synaptic transmission by upregulating potassium (K) channels and downregulating nicotinic acetylcholine receptors (nAChRs) in wake-promoting neurons to facilitate sleep in Drosophila. Using deletion mutagenesis, co-immunoprecipitations, ion flux assays, surface labeling and confocal microscopy, we demonstrate that only loop 2 is required for many of the previously described properties of SSS in transfected cells, including interactions with K channels and nAChRs. Collectively our data suggest that QVR/SSS, and by extension perhaps other Ly6 proteins, target effector molecules using limited protein motifs. Mapping these motifs may be useful in rational design of drugs that mimic or suppress Ly6-effector interactions to modulate nervous system function.

Cholinergic Targets in Lung Cancer

Lung cancers express an autocrine cholinergic loop in which secreted acetylcholine can stimulate tumor growth through both nicotinic and muscarinic receptors. Because activation of mAChR and nAChR stimulates growth; tumor growth can be stimulated by both locally synthesized acetylcholine as well as acetylcholine from distal sources and from nicotine in the high percentage of lung cancer patients who are smokers. The stimulation of lung cancer growth by cholinergic agonists offers many potential new targets for lung cancer therapy. Cholinergic signaling can be targeted at the level of choline transport; acetylcholine synthesis, secretion and degradation; and nicotinic and muscarinic receptors. In addition, the newly describe family of ly-6 allosteric modulators of nicotinic signaling such as lynx1 and lynx2 offers yet another new approach to novel lung cancer therapeutics. Each of these targets has their potential advantages and disadvantages for the development of new lung cancer therapies which are discussed in this review.

Mechanisms of inhibition and potentiation of α4β2 nicotinic acetylcholine receptors by members of the Ly6 protein family

α4β2 nicotinic acetylcholine receptors (nAChRs) are abundantly expressed throughout the central nervous system and are thought to be the primary target of nicotine, the main addictive substance in cigarette smoking. Understanding the mechanisms by which these receptors are regulated may assist in developing compounds to selectively interfere with nicotine addiction. Here we report previously unrecognized modulatory properties of members of the Ly6 protein family on α4β2 nAChRs. Using a FRET-based Ca(2+) flux assay, we found that the maximum response of α4β2 receptors to agonist was strongly inhibited by Ly6h and Lynx2 but potentiated by Ly6g6e. The mechanisms underlying these opposing effects appear to be fundamentally distinct. Receptor inhibition by Lynx2 was accompanied by suppression of α4β2 expression at the cell surface, even when assays were preceded by chronic exposure of cells to an established chaperone, nicotine. Receptor inhibition by Lynx2 also was resistant to pretreatment with extracellular phospholipase C, which cleaves lipid moieties like those that attach Ly6 proteins to the plasma membrane. In contrast, potentiation of α4β2 activity by Ly6g6e was readily reversible by pretreatment with phospholipase C. Potentiation was also accompanied by slowing of receptor desensitization and an increase in peak currents. Collectively our data support roles for Lynx2 and Ly6g6e in intracellular trafficking and allosteric potentiation of α4β2 nAChRs, respectively.