FGF14 is a regulator of KCNQ2/3 channels

Identification and characterisation of pathogenic and non-pathogenic FGF14 repeat expansions

Repeat expansions in FGF14 cause autosomal dominant late-onset cerebellar ataxia (SCA27B) with estimated pathogenic thresholds of 250 (incomplete penetrance) and 300 AAG repeats (full penetrance), but the sequence of pathogenic and non-pathogenic expansions remains unexplored. Here, we demonstrate that STRling and ExpansionHunter accurately detect FGF14 expansions from short-read genome data using outlier approaches. By combining long-range PCR and nanopore sequencing in 169 patients with cerebellar ataxia and 802 controls, we compare FGF14 expansion alleles, including interruptions and flanking regions. Uninterrupted AAG expansions are significantly enriched in patients with ataxia from a lower threshold (180-200 repeats) than previously reported based on expansion size alone. Conversely, AAGGAG hexameric expansions are equally frequent in patients and controls. Distinct 5' flanking regions, interruptions and pre-repeat sequences correlate with repeat size. Furthermore, pure AAG (pathogenic) and AAGGAG (non-pathogenic) repeats form different secondary structures. Regardless of expansion size, SCA27B is a recognizable clinical entity characterized by frequent episodic ataxia and downbeat nystagmus, similar to the presentation observed in a family with a previously unreported nonsense variant (SCA27A). Overall, this study suggests that SCA27B is a major overlooked cause of adult-onset ataxia, accounting for 23-31% of unsolved patients. We strongly recommend re-evaluating pathogenic thresholds and integrating expansion sequencing into the molecular diagnostic process.

Spinocerebellar ataxia 27B: a frequent and slowly progressive autosomal-dominant cerebellar ataxia-experience from an Italian cohort

BACKGROUND

Autosomal-dominant spinocerebellar ataxia (ADCA) due to intronic GAA repeat expansion in FGF14 (SCA27B) is a recent, relatively common form of late-onset ataxia.

OBJECTIVE

Here, we aimed to: (1) investigate the relative frequency of SCA27B in different clinically defined disease subgroups with late-onset ataxia collected among 16 tertiary Italian centers; (2) characterize phenotype and diagnostic findings of patients with SCA27B; (3) compare the Italian cohort with other cohorts reported in recent studies.

METHODS

We screened 396 clinically diagnosed late-onset cerebellar ataxias of unknown cause, subdivided in sporadic cerebellar ataxia, ADCA, and multisystem atrophy cerebellar type. We identified 72 new genetically defined subjects with SCA27B. Then, we analyzed the clinical, neurophysiological, and imaging features of 64 symptomatic cases.

RESULTS

In our cohort, the prevalence of SCA27B was 13.4% (53/396) with as high as 38.5% (22/57) in ADCA. The median age of onset of SCA27B patients was 62 years. All symptomatic individuals showed evidence of impaired balance and gait; cerebellar ocular motor signs were also frequent. Episodic manifestations at onset occurred in 31% of patients. Extrapyramidal features (17%) and cognitive impairment (25%) were also reported. Brain magnetic resonance imaging showed cerebellar atrophy in most cases (78%). Pseudo-longitudinal assessments indicated slow progression of ataxia and minimal functional impairment.

CONCLUSION

Patients with SCA27B in Italy present as an adult-onset, slowly progressive cerebellar ataxia with predominant axial involvement and frequent cerebellar ocular motor signs. The high consistency of clinical features in SCA27B cohorts in multiple populations paves the way toward large-scale, multicenter studies.

Live imaging of excitable axonal microdomains in ankyrin-G-GFP mice

The axon initial segment (AIS) constitutes not only the site of action potential initiation, but also a hub for activity-dependent modulation of output generation. Recent studies shedding light on AIS function used predominantly post-hoc approaches since no robust murine in vivo live reporters exist. Here, we introduce a reporter line in which the AIS is intrinsically labeled by an ankyrin-G-GFP fusion protein activated by Cre recombinase, tagging the native Ank3 gene. Using confocal, superresolution, and two-photon microscopy as well as whole-cell patch-clamp recordings in vitro, ex vivo, and in vivo, we confirm that the subcellular scaffold of the AIS and electrophysiological parameters of labeled cells remain unchanged. We further uncover rapid AIS remodeling following increased network activity in this model system, as well as highly reproducible in vivo labeling of AIS over weeks. This novel reporter line allows longitudinal studies of AIS modulation and plasticity in vivo in real-time and thus provides a unique approach to study subcellular plasticity in a broad range of applications.

Downbeat nystagmus: a clinical and pathophysiological review

Downbeat nystagmus (DBN) is a neuro-otological finding frequently encountered by clinicians dealing with patients with vertigo. Since DBN is a finding that should be understood because of central vestibular dysfunction, it is necessary to know how to frame it promptly to suggest the correct diagnostic-therapeutic pathway to the patient. As knowledge of its pathophysiology has progressed, the importance of this clinical sign has been increasingly understood. At the same time, clinical diagnostic knowledge has increased, and it has been recognized that this sign may occur sporadically or in association with others within defined clinical syndromes. Thus, in many cases, different therapeutic solutions have become possible. In our work, we have attempted to systematize current knowledge about the origin of this finding, the clinical presentation and current treatment options, to provide an overview that can be used at different levels, from the general practitioner to the specialist neurologist or neurotologist.

Loss of Intracellular Fibroblast Growth Factor 14 (iFGF14) Increases the Excitability of Mature Hippocampal and Cortical Pyramidal Neurons

Mutations in FGF14 , which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia type 27 (SCA27), a multisystem disorder associated with progressive deficits in motor coordination and cognitive function. Mice ( Fgf14 -/- ) lacking iFGF14 display similar phenotypes, and we have previously shown that the deficits in motor coordination reflect reduced excitability of cerebellar Purkinje neurons, owing to the loss of iFGF14-mediated regulation of the voltage-dependence of inactivation of the fast transient component of the voltage-gated Na + (Nav) current, I NaT . Here, we present the results of experiments designed to test the hypothesis that loss of iFGF14 also attenuates the intrinsic excitability of mature hippocampal and cortical pyramidal neurons. Current-clamp recordings from adult mouse hippocampal CA1 pyramidal neurons in acute in vitro slices, however, revealed that repetitive firing rates were higher in Fgf14 -/- , than in wild type (WT), cells. In addition, the waveforms of individual action potentials were altered in Fgf14 -/- hippocampal CA1 pyramidal neurons, and the loss of iFGF14 reduced the time delay between the initiation of axonal and somal action potentials. Voltage-clamp recordings revealed that the loss of iFGF14 altered the voltage-dependence of activation, but not inactivation, of I NaT in CA1 pyramidal neurons. Similar effects of the loss of iFGF14 on firing properties were evident in current-clamp recordings from layer 5 visual cortical pyramidal neurons. Additional experiments demonstrated that the loss of iFGF14 does not alter the distribution of anti-Nav1.6 or anti-ankyrin G immunofluorescence labeling intensity along the axon initial segments (AIS) of mature hippocampal CA1 or layer 5 visual cortical pyramidal neurons in situ . Taken together, the results demonstrate that, in contrast with results reported for neonatal (rat) hippocampal pyramidal neurons in dissociated cell culture, the loss of iFGF14 does not disrupt AIS architecture or Nav1.6 localization/distribution along the AIS of mature hippocampal (or cortical) pyramidal neurons in situ .

A Developmental Switch in Cholinergic Mechanisms of Modulation in the Medial Nucleus of the Trapezoid Body

The medial nucleus of the trapezoid body (MNTB) has been intensively investigated as a primary source of inhibition in brainstem auditory circuitry. MNTB-derived inhibition plays a critical role in the computation of sound location, as temporal features of sounds are precisely conveyed through the calyx of Held/MNTB synapse. In adult gerbils, cholinergic signaling influences sound-evoked responses of MNTB neurons via nicotinic acetylcholine receptors (nAChRs; Zhang et al., 2021) establishing a modulatory role for cholinergic input to this nucleus. However, the cellular mechanisms through which acetylcholine (ACh) mediates this modulation in the MNTB remain obscure. To investigate these mechanisms, we used whole-cell current and voltage-clamp recordings to examine cholinergic physiology in MNTB neurons from Mongolian gerbils (Meriones unguiculatus) of both sexes. Membrane excitability was assessed in brain slices, in pre-hearing (postnatal days 9-13) and post-hearing onset (P18-20) MNTB neurons during bath application of agonists and antagonists of nicotinic (nAChRs) and muscarinic receptors (mAChRs). Muscarinic activation induced a potent increase in excitability most prominently prior to hearing onset with nAChR modulation emerging at later time points. Pharmacological manipulations further demonstrated that the voltage-gated K+ channel KCNQ (Kv7) is the downstream effector of mAChR activation that impacts excitability early in development. Cholinergic modulation of Kv7 reduces outward K+ conductance and depolarizes resting membrane potential. Immunolabeling revealed expression of Kv7 channels as well as mAChRs containing M1 and M3 subunits. Together, our results suggest that mAChR modulation is prominent but transient in the developing MNTB and that cholinergic modulation functions to shape auditory circuit development.

Fibroblast growth factor 13-mediated regulation of medium spiny neuron excitability and cocaine self-administration

Cocaine use disorder (CUD) is a prevalent neuropsychiatric disorder with few existing treatments. Thus, there is an unmet need for the identification of new pharmacological targets for CUD. Previous studies using environmental enrichment versus isolation paradigms have found that the latter induces increased cocaine self-administration with correlative increases in the excitability of medium spiny neurons (MSN) of the nucleus accumbens shell (NAcSh). Expanding upon these findings, we sought in the present investigation to elucidate molecular determinants of these phenomena. To that end, we first employed a secondary transcriptomic analysis and found that cocaine self-administration differentially regulates mRNA for fibroblast growth factor 13 (FGF13), which codes for a prominent auxiliary protein of the voltage-gated Na+ (Nav) channel, in the NAcSh of environmentally enriched rats (i.e., resilient behavioral phenotype) compared to environmentally isolated rats (susceptible phenotype). Based upon this finding, we used in vivo genetic silencing to study the causal functional and behavioral consequences of knocking down FGF13 in the NAcSh. Functional studies revealed that knockdown of FGF13 in the NAcSh augmented excitability of MSNs by increasing the activity of Nav channels. These electrophysiological changes were concomitant with a decrease in cocaine demand elasticity (i.e., susceptible phenotype). Taken together, these data support FGF13 as being protective against cocaine self-administration, which positions it well as a pharmacological target for CUD.

Fibroblast growth factor signaling in axons: from development to disease

The fibroblast growth factor (FGF) family regulates various and important aspects of nervous system development, ranging from the well-established roles in neuronal patterning to more recent and exciting functions in axonal growth and synaptogenesis. In addition, FGFs play a critical role in axonal regeneration, particularly after spinal cord injury, confirming their versatile nature in the nervous system. Due to their widespread involvement in neural development, the FGF system also underlies several human neurological disorders. While particular attention has been given to FGFs in a whole-cell context, their effects at the axonal level are in most cases undervalued. Here we discuss the endeavor of the FGF system in axons, we delve into this neuronal subcompartment to provide an original view of this multipurpose family of growth factors in nervous system (dys)function. Video Abstract.

CKII Control of Axonal Plasticity Is Mediated by Mitochondrial Ca2+ via Mitochondrial NCLX

Mitochondrial Ca²⁺ efflux by NCLX is a critical rate-limiting step in mitochondria signaling. We previously showed that NCLX is phosphorylated at a putative Casein Kinase 2 (CKII) site, the serine 271 (S271). Here, we asked if NCLX is regulated by CKII and interrogated the physiological implications of this control. We found that CKII inhibitors down-regulated NCLX-dependent Ca²⁺ transport activity in SH-SY5Y neuronal cells and primary hippocampal neurons. Furthermore, we show that the CKII phosphomimetic mutants on NCLX inhibited (S271A) and constitutively activated (S271D) NCLX transport, respectively, rendering it insensitive to CKII inhibition. These phosphomimetic NCLX mutations also control the allosteric regulation of NCLX by mitochondrial membrane potential (ΔΨm). Since the omnipresent CKII is necessary for modulating the plasticity of the axon initial segment (AIS), we interrogated, in hippocampal neurons, if NCLX is required for this process. Similarly to WT neurons, NCLX-KO neurons can exhibit homeostatic plasticity following M-channel block. However, while WT neurons utilize a CKII-sensitive distal relocation of AIS Na⁺ and Kv7 channels to decrease their intrinsic excitability, we did not observe such translocation in NCLX-KO neurons. Thus, our results indicate that NCLX is regulated by CKII and is a crucial link between CKII signaling and fast neuronal plasticity.

Excitatory and inhibitory hippocampal neurons differ in their homeostatic adaptation to chronic M-channel modulation

A large body of studies has investigated bidirectional homeostatic plasticity both in vitro and in vivo using numerous pharmacological manipulations of activity or behavioral paradigms. However, these experiments rarely explored in the same cellular system the bidirectionality of the plasticity and simultaneously on excitatory and inhibitory neurons. M-channels are voltage-gated potassium channels that play a crucial role in regulating neuronal excitability and plasticity. In cultured hippocampal excitatory neurons, we previously showed that chronic exposure to the M-channel blocker XE991 leads to adaptative compensations, thereby triggering at different timescales intrinsic and synaptic homeostatic plasticity. This plastic adaptation barely occurs in hippocampal inhibitory neurons. In this study, we examined whether this homeostatic plasticity induced by M-channel inhibition was bidirectional by investigating the acute and chronic effects of the M-channel opener retigabine on hippocampal neuronal excitability. Acute retigabine exposure decreased excitability in both excitatory and inhibitory neurons. Chronic retigabine treatment triggered in excitatory neurons homeostatic adaptation of the threshold current and spontaneous firing rate at a time scale of 4–24 h. These plastic changes were accompanied by a substantial decrease in the M-current density and by a small, though significant, proximal relocation of Kv7.3-FGF14 segment along the axon initial segment. Thus, bidirectional homeostatic changes were observed in excitatory neurons though not symmetric in kinetics and mechanisms. Contrastingly, in inhibitory neurons, the compensatory changes in intrinsic excitability barely occurred after 48 h, while no homeostatic normalization of the spontaneous firing rate was observed. Our results indicate that excitatory and inhibitory hippocampal neurons differ in their adaptation to chronic alterations in neuronal excitability induced by M-channel bidirectional modulation.

The Deletion of GluK2 Alters Cholinergic Control of Neuronal Excitability

Kainate receptors (KARs) are key regulators of synaptic circuits by acting at pre- and postsynaptic sites through either ionotropic or metabotropic actions. KARs can be activated by kainate, a potent neurotoxin, which induces acute convulsions. Here, we report that the acute convulsive effect of kainate mostly depends on GluK2/GluK5 containing KARs. By contrast, the acute convulsive activity of pilocarpine and pentylenetetrazol is not alleviated in the absence of KARs. Unexpectedly, the genetic inactivation of GluK2 rather confers increased susceptibility to acute pilocarpine-induced seizures. The mechanism involves an enhanced excitability of GluK2-/- CA3 pyramidal cells compared with controls upon pilocarpine application. Finally, we uncover that the absence of GluK2 increases pilocarpine modulation of Kv7/M currents. Taken together, our findings reveal that GluK2-containing KARs can control the excitability of hippocampal circuits through interaction with the neuromodulatory cholinergic system.

Glycogen Synthase Kinase 3: Ion Channels, Plasticity, and Diseases

Glycogen synthase kinase 3β (GSK3) is a multifaceted serine/threonine (S/T) kinase expressed in all eukaryotic cells. GSK3β is highly enriched in neurons in the central nervous system where it acts as a central hub for intracellular signaling downstream of receptors critical for neuronal function. Unlike other kinases, GSK3β is constitutively active, and its modulation mainly involves inhibition via upstream regulatory pathways rather than increased activation. Through an intricate converging signaling system, a fine-tuned balance of active and inactive GSK3β acts as a central point for the phosphorylation of numerous primed and unprimed substrates. Although the full range of molecular targets is still unknown, recent results show that voltage-gated ion channels are among the downstream targets of GSK3β. Here, we discuss the direct and indirect mechanisms by which GSK3β phosphorylates voltage-gated Na⁺ channels (Na_v1.2 and Na_v1.6) and voltage-gated K⁺ channels (K_v4 and K_v7) and their physiological effects on intrinsic excitability, neuronal plasticity, and behavior. We also present evidence for how unbalanced GSK3β activity can lead to maladaptive plasticity that ultimately renders neuronal circuitry more vulnerable, increasing the risk for developing neuropsychiatric disorders. In conclusion, GSK3β-dependent modulation of voltage-gated ion channels may serve as an important pharmacological target for neurotherapeutic development.

The IGSF1, Wnt5a, FGF14, and ITPR1 Gene Expression and Prognosis Hallmark of Prostate Cancer

Background

Prostate cancer is considered as the second leading cause of cancer related death in men worldwide and the third frequent cancer among Iranian men. Despite the use of PSA as the only biomarker for early diagnosis of prostate cancer, its application in clinical settings is under debate. Therefore, the introduction of new molecular markers for early detection of prostate cancer is needed.

Methods

In the present study we intended to evaluate the expression of IGSF1, Wnt5a, FGF14, and ITPR1 in prostate cancer specimens by real time PCR. Biopsy samples of 40 prostate cancer cases and 41 healthy Iranian men were compared to determine the relative gene expression of IGSF1, Wnt5a, FGF14, and ITPR1 by real time PCR.

Results

Our results showed that Wnt5a, FGF14, and IGSF1 were significantly overexpressed in the prostate cancer patients while the mean relative expression of ITPR1 showed a significant decrease in PCa samples compared to healthy controls.

Conclusion

According to results of the present study, the combination panel of IGSF1, Wnt5a, FGF14, and ITPR1 genes could be considered as potential genetic markers for prostate cancer diagnosis. However further studies on larger populations and investigating the clinicopathological relevance of these genes is needed.

Poly-dipeptides produced from C9orf72 hexanucleotide repeats cause selective motor neuron hyperexcitability in ALS

SignificanceThe GGGGCC hexanucleotide repeat expansion in the chromosome 9 open reading frame 72 (C9orf72) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS). Despite myriad studies on the toxic effects of poly-dipeptides produced from the C9orf72 repeats, the mechanisms underlying the selective hyperexcitability of motor cortex that characterizes the early stages of C9orf72 ALS patients remain elusive. Here, we show that the proline-arginine poly-dipeptides cause hyperexcitability in cortical motor neurons by increasing persistent sodium currents conducted by the Nav1.2/β4 sodium channel complex, which is highly expressed in the motor cortex. These findings provide the basis for understanding how the C9orf72 mutation causes motor neuron hyperactivation that can lead to the motor neuron death in C9orf72 ALS.

Exploring the Genomic Patterns in Human and Mouse Cerebellums Via Single-Cell Sequencing and Machine Learning Method

In mammals, the cerebellum plays an important role in movement control. Cellular research reveals that the cerebellum involves a variety of sub-cell types, including Golgi, granule, interneuron, and unipolar brush cells. The functional characteristics of cerebellar cells exhibit considerable differences among diverse mammalian species, reflecting a potential development and evolution of nervous system. In this study, we aimed to recognize the transcriptional differences between human and mouse cerebellum in four cerebellar sub-cell types by using single-cell sequencing data and machine learning methods. A total of 321,387 single-cell sequencing data were used. The 321,387 cells included 4 cell types, i.e., Golgi (5,048, 1.57%), granule (250,307, 77.88%), interneuron (60,526, 18.83%), and unipolar brush (5,506, 1.72%) cells. Our results showed that by using gene expression profiles as features, the optimal classification model could achieve very high even perfect performance for Golgi, granule, interneuron, and unipolar brush cells, respectively, suggesting a remarkable difference between the genomic profiles of human and mouse. Furthermore, a group of related genes and rules contributing to the classification was identified, which might provide helpful information for deepening the understanding of cerebellar cell heterogeneity and evolution.

Targetable Pathways in Advanced Bladder Cancer: FGFR Signaling

Bladder cancer is the 10th most commonly diagnosed cancer in the world, accounting for around 573,000 new cases and 213,000 deaths in 2020. The current standard treatment for locally advanced bladder cancer is neoadjuvant cisplatin (NAC)-based chemotherapy followed by cystectomy. The significant progress being made in the genomic and molecular understandings of bladder cancer has uncovered the genetic alterations and signaling pathways that drive bladder cancer progression. These developments have led to a dramatic increase in the evaluation of molecular agents targeting at these alterations. One example is Erdafitinib, a first-in-class FGFR inhibitor being approved as second-line treatment for locally advanced or metastatic urothelial carcinoma with FGFR mutations. Immunotherapy has also been approved as second-line treatment for advanced and metastatic bladder cancer. Preclinical studies suggest targeted therapy combined with immunotherapy has the potential to markedly improve patient outcome. Given the prevalence of FGFR alternations in bladder cancer, here we review recent preclinical and clinical studies on FGFR inhibitors and analyze possible drug resistance mechanisms to these agents. We also discuss FGFR inhibitors in combination with other therapies and its potential to improve outcome.

A Variation in FGF14 Is Associated with Downbeat Nystagmus in a Genome-Wide Association Study

Downbeat nystagmus (DBN) is a frequent form of acquired persisting central fixation nystagmus, often associated with other cerebellar ocular signs, such as saccadic smooth pursuit or gaze-holding deficits. Despite its distinct clinical features, the underlying etiology of DBN often remains unclear. Therefore, a genome-wide association study (GWAS) was conducted in 106 patients and 2609 healthy controls of European ancestry to identify genetic variants associated with DBN. A genome-wide significant association (p < 5 × 10^-8) with DBN was found for a variation on chromosome 13 located within the fibroblast growth factor 14 gene (FGF14). FGF14 is expressed in Purkinje cells (PCs) and a reduction leads to a decreased spontaneous firing rate and excitability of PCs, compatible with the pathophysiology of DBN. In addition, mutations in the FGF14 gene cause spinocerebellar ataxia type 27. Suggestive associations (p < 1 × 10^-05) could be detected for 15 additional LD-independent loci, one of which is also located in the FGF14 gene. An association of a region containing the dihydrofolate reductase (DHFR) and MutS Homolog 3 (MSH3) genes on chromosome 5 was slightly below the genome-wide significance threshold. DHFR is relevant for neuronal regulation, and a dysfunction is known to induce cerebellar damage. Among the remaining twelve suggestive associations, four genes (MAST4, TPPP, FTMT, and IDS) seem to be involved in cerebral pathological processes. Thus, this GWAS analysis has identified a potential genetic contribution to idiopathic DBN, including suggestive associations to several genes involved in postulated pathological mechanisms of DBN (i.e., impaired function of cerebellar PCs).

Ca2+-saturated calmodulin binds tightly to the N-terminal domain of A-type fibroblast growth factor homologous factors

Voltage-gated sodium channels (Na_vs) are tightly regulated by multiple conserved auxiliary proteins, including the four fibroblast growth factor homologous factors (FGFs), which bind the Na_v EF-hand like domain (EFL), and calmodulin (CaM), a multifunctional messenger protein that binds the Na_V IQ motif. The EFL domain and IQ motif are contiguous regions of Na_V cytosolic C-terminal domains (CTD), placing CaM and FGF in close proximity. However, whether the FGFs and CaM act independently, directly associate, or operate through allosteric interactions to regulate channel function is unknown. Titrations monitored by steady-state fluorescence spectroscopy, structural studies with solution NMR, and computational modeling demonstrated for the first time that both domains of (Ca²⁺)₄-CaM (but not apo CaM) directly bind two sites in the N-terminal domain (NTD) of A-type FGF splice variants (FGF11A, FGF12A, FGF13A, and FGF14A) with high affinity. The weaker of the (Ca²⁺)₄-CaM-binding sites was known via electrophysiology to have a role in long-term inactivation of the channel but not known to bind CaM. FGF12A binding to a complex of CaM associated with a fragment of the Na_V1.2 CTD increased the Ca²⁺-binding affinity of both CaM domains, consistent with (Ca²⁺)₄-CaM interacting preferentially with its higher-affinity site in the FGF12A NTD. Thus, A-type FGFs can compete with Na_V IQ motifs for (Ca²⁺)₄-CaM. During spikes in the cytosolic Ca²⁺ concentration that accompany an action potential, CaM may translocate from the Na_V IQ motif to the FGF NTD, or the A-type FGF NTD may recruit a second molecule of CaM to the channel.

Fibroblast Growth Factor-14 Acts as Tumor Suppressor in Lung Adenocarcinomas

Investigation of the molecular dynamics in lung cancer is crucial for the development of new treatment strategies. Fibroblast growth factor (FGF) 14 belongs to the FGF family, which might play a crucial role in cancer progression. We analyzed lung adenocarcinoma (LUAC) patients samples and found that FGF14 was downregulated, correlating with reduced survival and oncogenic mutation status. FGF14 overexpression in lung cancer cell lines resulted in decreased proliferation, colony formation, and migration, as well as increased expression of epithelial markers and a decreased expression of mesenchymal markers, indicating a mesenchymal to epithelial transition in vitro. We verified these findings using small interfering RNA against FGF14 and further confirmed the suppressive effect of FGF14 in a NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ immunodeficient xenograft tumor model. Moreover, FGF14 overexpressing tumor cell RNA sequencing data suggests that genes affected by FGF14 were related to the extracellular matrix, playing a role in proliferation and migration. Notably, newly identified FGF14 target genes, adenosine deaminase RNA specific B1 (ADARB1), collagen and calcium-binding epidermal growth factor domain-containing protein 1 (CCBE1), α1 chain of collagen XI (COL11A1), and mucin 16 (MUC16) expression was negatively correlated with overall survival when FGF14 was downregulated in LUAC. These findings led us to suggest that FGF14 regulates proliferation and migration in LUAC.

High-Resolution mRNA and Secretome Atlas of Human Enteroendocrine Cells

Enteroendocrine cells (EECs) sense intestinal content and release hormones to regulate gastrointestinal activity, systemic metabolism, and food intake. Little is known about the molecular make-up of human EEC subtypes and the regulated secretion of individual hormones. Here, we describe an organoid-based platform for functional studies of human EECs. EEC formation is induced in vitro by transient expression of NEUROG3. A set of gut organoids was engineered in which the major hormones are fluorescently tagged. A single-cell mRNA atlas was generated for the different EEC subtypes, and their secreted products were recorded by mass-spectrometry. We note key differences to murine EECs, including hormones, sensory receptors, and transcription factors. Notably, several hormone-like molecules were identified. Inter-EEC communication is exemplified by secretin-induced GLP-1 secretion. Indeed, individual EEC subtypes carry receptors for various EEC hormones. This study provides a rich resource to study human EEC development and function.

Control of neuronal excitability by GSK-3beta: Epilepsy and beyond

Glycogen synthase kinase 3beta (GSK-3β) is an enzyme with a variety of cellular functions in addition to the regulation of glycogen metabolism. In the central nervous system, different intracellular signaling pathways converge on GSK-3β through a cascade of phosphorylation events that ultimately control a broad range of neuronal functions in the development and adulthood. In mice, genetically removing or increasing GSK-3β cause distinct functional and structural neuronal phenotypes and consequently affect cognition. Precise control of GSK-3β activity is important for such processes as neuronal migration, development of neuronal morphology, synaptic plasticity, excitability, and gene expression. Altered GSK-3β activity contributes to aberrant plasticity within neuronal circuits leading to neurological, psychiatric disorders, and neurodegenerative diseases. Therapeutically targeting GSK-3β can restore the aberrant plasticity of neuronal networks at least in animal models of these diseases. Although the complete repertoire of GSK-3β neuronal substrates has not been defined, emerging evidence shows that different ion channels and their accessory proteins controlling excitability, neurotransmitter release, and synaptic transmission are regulated by GSK-3β, thereby supporting mechanisms of synaptic plasticity in cognition. Dysregulation of ion channel function by defective GSK-3β activity sustains abnormal excitability in the development of epilepsy and other GSK-3β-linked human diseases.

The emerging molecular mechanism of m6A modulators in tumorigenesis and cancer progression

N⁶-methyladenosine (m⁶A) is the most abundant RNA modification; m⁶A modifications are installed by methyltransferases, removed by demethylases and recognized by reader proteins. M⁶A plays crucial roles in a variety of biological processes by regulating target RNA translation, splicing, nuclear export, and decay. Since the establishment of methylated RNA immunoprecipitation-sequencing methodology, over three hundred articles about m⁶A modulators, including "writers", "erasers" and "readers", have been reported in the last four years. In addition, an increasing number of molecular mechanisms underlying m⁶A RNA methylation in human cancers have been comprehensively clarified. The recently emerged molecular mechanisms of m⁶A modulators in cancer cell proliferation, cell cycle progression, migration and invasion, apoptosis, and autophagy remain to be summarized. Hence, this review specifically summarizes these recent advances in the understanding of m⁶A molecular mechanisms in tumorigenesis and cancer progression. In addition, we discuss the prospect of using an m⁶A methylation modulator as a new diagnostic biomarker and therapeutic target for human cancers.

M-Current Inhibition in Hippocampal Excitatory Neurons Triggers Intrinsic and Synaptic Homeostatic Responses at Different Temporal Scales

Persistent alterations in neuronal activity elicit homeostatic plastic changes in synaptic transmission and/or intrinsic excitability. However, it is unknown whether these homeostatic processes operate in concert or at different temporal scales to maintain network activity around a set-point value. Here we show that chronic neuronal hyperactivity, induced by M-channel inhibition, triggered intrinsic and synaptic homeostatic plasticity at different timescales in cultured hippocampal pyramidal neurons from mice of either sex. Homeostatic changes of intrinsic excitability occurred at a fast timescale (1-4 h) and depended on ongoing spiking activity. This fast intrinsic adaptation included plastic changes in the threshold current and a distal relocation of FGF14, a protein physically bridging Na_v1.6 and K_v7.2 channels along the axon initial segment. In contrast, synaptic adaptations occurred at a slower timescale (∼2 d) and involved decreases in miniature EPSC amplitude. To examine how these temporally distinct homeostatic responses influenced hippocampal network activity, we quantified the rate of spontaneous spiking measured by multielectrode arrays at extended timescales. M-Channel blockade triggered slow homeostatic renormalization of the mean firing rate (MFR), concomitantly accompanied by a slow synaptic adaptation. Thus, the fast intrinsic adaptation of excitatory neurons is not sufficient to account for the homeostatic normalization of the MFR. In striking contrast, homeostatic adaptations of intrinsic excitability and spontaneous MFR failed in hippocampal GABAergic inhibitory neurons, which remained hyperexcitable following chronic M-channel blockage. Our results indicate that a single perturbation such as M-channel inhibition triggers multiple homeostatic mechanisms that operate at different timescales to maintain network mean firing rate.SIGNIFICANCE STATEMENT Persistent alterations in synaptic input elicit homeostatic plastic changes in neuronal activity. Here we show that chronic neuronal hyperexcitability, induced by M-type potassium channel inhibition, triggered intrinsic and synaptic homeostatic plasticity at different timescales in hippocampal excitatory neurons. The data indicate that the fast adaptation of intrinsic excitability depends on ongoing spiking activity but is not sufficient to provide homeostasis of the mean firing rate. Our results show that a single perturbation such as M-channel inhibition can trigger multiple homeostatic processes that operate at different timescales to maintain network mean firing rate.

FGF14-related episodic ataxia: delineating the phenotype of Episodic Ataxia type 9

We report four patients from two families who presented attacks of childhood-onset episodic ataxia associated with pathogenic mutations in the FGF14 gene. Attacks were triggered by fever, lasted several days, and had variable frequencies. Nystagmus and/or postural tremor and/or learning disabilities were noticed in individuals harboring FGF14 mutation with or without episodic ataxia. These cases and literature data delineate the FGF14-mutation-related episodic ataxia phenotype: wide range of age at onset (from childhood to adulthood), variable durations and frequencies, triggering factors including fever, and association to chronic symptoms. We propose to add FGF14-related episodic ataxia to the list of primary episodic ataxia as Episodic Ataxia type 9.

Antibiotics and Host-Tailored Probiotics Similarly Modulate Effects on the Developing Avian Microbiome, Mycobiome, and Host Gene Expression

Alternative approaches are greatly needed to reduce the need for antibiotic use in food animal production. This study utilized a pipeline for the development of a host-tailored probiotic to enhance performance in commercial turkeys and modulate their microbiota, similar to the effects of low-dose antibiotic administration. We determined that a host-tailored probiotic, developed in the context of the commercial turkey gut microbiome, was more effective at modulating these parameters than a nontailored probiotic cocktail. Furthermore, the host-tailored probiotic mimicked many of the effects of a low-dose antibiotic growth promoter. Surprisingly, the effects of the antibiotic growth promoter and host-tailored probiotic were observed across kingdoms, illustrating the coordinated interkingdom effects of these approaches. This work suggests that tailored approaches to probiotic development hold promise for modulating the avian host and its microbiota.

The microbiome is important to all animals, including poultry, playing a critical role in health and performance. Low-dose antibiotics have historically been used to modulate food production animals and their microbiome. Identifying alternatives to antibiotics conferring similar modulatory properties has been elusive. The purpose of this study was to determine if a host-tailored probiotic could recapitulate effects of a low-dose antibiotic on host response and the developing microbiome. Over 13 days of life, turkey poults were supplemented continuously with a low-dose antibiotic or oral supplementation of a prebiotic with or without two different probiotics (8 cage units, n = 80 per group). Gastrointestinal bacterial and fungal communities of poults were characterized by 16S rRNA gene and ITS2 amplicon sequencing. Localized and systemic host gene expression was assessed using transcriptome sequencing (RNA-Seq), kinase activity was assessed by avian-specific kinome peptide arrays, and performance parameters were assessed. We found that development of the early-life microbiome of turkey poults was tightly ordered in a tissue- and time-specific manner. Low-dose antibiotic and turkey-tailored probiotic supplementation, but not nontailored probiotic supplementation, elicited similar shifts in overall microbiome composition during development compared to controls. Treatment-induced bacterial changes were accompanied by parallel shifts in the fungal community and host gene expression and enhanced performance metrics. These results were validated in pen trials that identified further additive effects of the turkey-tailored probiotic combined with different prebiotics. Alternative approaches to low-dose antibiotic use in poultry are feasible and can be optimized utilizing the indigenous poultry microbiome. Similar approaches may also be beneficial for humans.

Genome-wide Association Study of Maximum Habitual Alcohol Intake in >140,000 U.S. European and African American Veterans Yields Novel Risk Loci

BACKGROUND

Habitual alcohol use can be an indicator of alcohol dependence, which is associated with a wide range of serious health problems.

METHODS

We completed a genome-wide association study in 126,936 European American and 17,029 African American subjects in the Veterans Affairs Million Veteran Program for a quantitative phenotype based on maximum habitual alcohol consumption.

RESULTS

ADH1B, on chromosome 4, was the lead locus for both populations: for the European American sample, rs1229984 (p = 4.9 × 10-47); for African American, rs2066702 (p = 2.3 × 10-12). In the European American sample, we identified three additional genome-wide-significant maximum habitual alcohol consumption loci: on chromosome 17, rs77804065 (p = 1.5 × 10-12), at CRHR1 (corticotropin-releasing hormone receptor 1); the protein product of this gene is involved in stress and immune responses; and on chromosomes 8 and 10. European American and African American samples were then meta-analyzed; the associated region at CRHR1 increased in significance to 1.02 × 10-13, and we identified two additional genome-wide significant loci, FGF14 (p = 9.86 × 10-9) (chromosome 13) and a locus on chromosome 11. Besides ADH1B, none of the five loci have prior genome-wide significant support. Post-genome-wide association study analysis identified genetic correlation to other alcohol-related traits, smoking-related traits, and many others. Replications were observed in UK Biobank data. Genetic correlation between maximum habitual alcohol consumption and alcohol dependence was 0.87 (p = 4.78 × 10-9). Enrichment for cell types included dopaminergic and gamma-aminobutyric acidergic neurons in midbrain, and pancreatic delta cells.

CONCLUSIONS

The present study supports five novel alcohol-use risk loci, with particularly strong statistical support for CRHR1. Additionally, we provide novel insight regarding the biology of harmful alcohol use.

Characterisation of endogenous players in fibroblast growth factor-regulated functions of hypothalamic tanycytes and energy-balance nuclei

The mammalian hypothalamus regulates key homeostatic and neuroendocrine functions ranging from circadian rhythm and energy balance to growth and reproductive cycles via the hypothalamic-pituitary and hypothalamic-thyroid axes. In addition to its neurones, tanycytes are taking centre stage in the short- and long-term augmentation and integration of diverse hypothalamic functions, although the genetic regulators and mediators of their involvement are poorly understood. Exogenous interventions have implicated fibroblast growth factor (FGF) signalling, although the focal point of the action of FGF and any role for putative endogenous players also remains elusive. We carried out a comprehensive high-resolution screen of FGF signalling pathway mediators and modifiers using a combination of in situ hybridisation, immunolabelling and transgenic reporter mice, aiming to map their spatial distribution in the adult hypothalamus. Our findings suggest that β-tanycytes are the likely focal point of exogenous and endogenous action of FGF in the third ventricular wall, utilising FGF receptor (FGFR)1 and FGFR2 IIIc isoforms, but not FGFR3. Key IIIc-activating endogenous ligands include FGF1, 2, 9 and 18, which are expressed by a subset of ependymal and parenchymal cells. In the parenchymal compartment, FGFR1-3 show divergent patterns, with FGFR1 being predominant in neuronal nuclei and expression of FGFR3 being associated with glial cell function. Intracrine FGFs are also present, suggestive of multiple modes of FGF function. Our findings provide a testable framework for understanding the complex role of FGFs with respect to regulating the metabolic endocrine and neurogenic functions of hypothalamus in vivo.

New insights into ion channel-dependent signalling during left-right patterning

The left-right organizer (LRO) in the mouse consists of pit cells within the depression, located at the end of the developing notochord, also known as the embryonic node and crown cells lining the outer periphery of the node. Cilia on pit cells are posteriorly tilted, rotate clockwise and generate leftward fluid flow. Primary cilia on crown cells are required to interpret the directionality of fluid movement and initiate flow-dependent gene transcription. Crown cells express PC1-L1 and PC2, which may form a heteromeric polycystin channel complex on primary cilia. It is still only poorly understood how fluid flow activates the ciliary polycystin complex. Besides polycystin channels voltage gated channels like HCN4 and KCNQ1 have been implicated in establishing asymmetry. How this electrical network of ion channels initiates left-sided signalling cascades and differential gene expression is currently only poorly defined.

Paroxysmal Movement Disorders: Recent Advances

PURPOSE OF REVIEW

Recent advancements in next-generation sequencing (NGS) have enabled techniques such as whole exome sequencing (WES) and whole genome sequencing (WGS) to be used to study paroxysmal movement disorders (PMDs). This review summarizes how the recent genetic advances have altered our understanding of the pathophysiology and treatment of the PMDs. Recently described disease entities are also discussed.

RECENT FINDINGS

With the recognition of the phenotypic and genotypic heterogeneity that occurs amongst the PMDs, an increasing number of gene mutations are now implicated to cause the disorders. PMDs can also occur as part of a complex phenotype. The increasing complexity of PMDs challenges the way we view and classify them. The identification of new causative genes and their genotype-phenotype correlation will shed more light on the underlying pathophysiology and will facilitate development of genetic testing guidelines and identification of novel drug targets for PMDs.

Subcellular control of membrane excitability in the axon

Ion channels are microscopic pore proteins in the membrane that open and close in response to chemical and electrical stimuli. This simple concept underlies rapid electrical signaling in the brain as well as several important aspects of neural plasticity. Although the soma accounts for less than 1% of many neurons by membrane area, it has been the major site of measuring ion channel function. However, the axon is one of the longest processes found in cellular biology and hosts a multitude of critical signaling functions in the brain. Not only does the axon initiate and rapidly propagate action potentials (APs) across the brain but it also forms the presynaptic terminals that convert these electrical inputs into chemical outputs. Here, we review recent advances in the physiological role of ion channels within the diverse landscape of the axon and presynaptic terminals.

Gene expression in retinal ischemic post-conditioning

PURPOSE

The pathophysiology of retinal ischemia involves mechanisms including inflammation and apoptosis. Ischemic post-conditioning (Post-C), a brief non-lethal ischemia, induces a long-term ischemic tolerance, but the mechanisms of ischemic post-conditioning in the retina have only been described on a limited basis. Accordingly, we conducted this study to determine the molecular events in retinal ischemic post-conditioning and to identify targets for therapeutic strategies for retinal ischemia.

METHODS

To determine global molecular events in ischemic post-conditioning, a comprehensive study of the transcriptome of whole retina was performed. We utilized RNA sequencing (RNA-Seq), a recently developed, deep sequencing technique enabling quantitative gene expression, with low background noise, dynamic detection range, and discovery of novel genes. Rat retina was subjected to ischemia in vivo by elevation of intraocular pressure above systolic blood pressure. At 24 h after ischemia, Post-C or sham Post-C was performed by another, briefer period of ischemia, and 24 h later, retinas were collected and RNA processed.

RESULTS

There were 71 significantly affected pathways in post-conditioned/ischemic vs. normals and 43 in sham post conditioned/ischemic vs. normals. Of these, 28 were unique to Post-C and ischemia. Seven biological pathways relevant to ischemic injury, in Post-C as opposed to sham Post-C, were examined in detail. Apoptosis, p53, cell cycle, JAK-STAT, HIF-1, MAPK and PI3K-Akt pathways significantly differed in the number as well as degree of fold change in genes between conditions.

CONCLUSION

Post-C is a complex molecular signaling process with a multitude of altered molecular pathways. We identified potential gene candidates in Post-C. Studying the impact of altering expression of these factors may yield insight into new methods for treating or preventing damage from retinal ischemic disorders.

M-current inhibition rapidly induces a unique CK2-dependent plasticity of the axon initial segment

Alterations in synaptic input, persisting for hours to days, elicit homeostatic plastic changes in the axon initial segment (AIS), which is pivotal for spike generation. Here, in hippocampal pyramidal neurons of both primary cultures and slices, we triggered a unique form of AIS plasticity by selectively targeting M-type K⁺ channels, which predominantly localize to the AIS and are essential for tuning neuronal excitability. While acute M-current inhibition via cholinergic activation or direct channel block made neurons more excitable, minutes to hours of sustained M-current depression resulted in a gradual reduction in intrinsic excitability. Dual soma-axon patch-clamp recordings combined with axonal Na⁺ imaging and immunocytochemistry revealed that these compensatory alterations were associated with a distal shift of the spike trigger zone and distal relocation of FGF14, Na⁺, and K_v7 channels but not ankyrin G. The concomitant distal redistribution of FGF14 together with Na_v and K_v7 segments along the AIS suggests that these channels relocate as a structural and functional unit. These fast homeostatic changes were independent of l-type Ca²⁺ channel activity but were contingent on the crucial AIS protein, protein kinase CK2. Using compartmental simulations, we examined the effects of varying the AIS position relative to the soma and found that AIS distal relocation of both Na_v and K_v7 channels elicited a decrease in neuronal excitability. Thus, alterations in M-channel activity rapidly trigger unique AIS plasticity to stabilize network excitability.

Post-translational dysfunctions in channelopathies of the nervous system

Channelopathies comprise various diseases caused by defects of ion channels. Modifications of their biophysical properties are common and have been widely studied. However, ion channels are heterogeneous multi-molecular complexes that are extensively modulated and undergo a maturation process comprising numerous steps of structural modifications and intracellular trafficking. Perturbations of these processes can give rise to aberrant channels that cause pathologies. Here we review channelopathies of the nervous system associated with dysfunctions at the post-translational level (folding, trafficking, degradation, subcellular localization, interactions with associated proteins and structural post-translational modifications). We briefly outline the physiology of ion channels' maturation and discuss examples of defective mechanisms, focusing in particular on voltage-gated sodium channels, which are implicated in numerous neurological disorders. We also shortly introduce possible strategies to develop therapeutic approaches that target these processes. This article is part of the Special Issue entitled 'Channelopathies.'

Intracellular Fibroblast Growth Factor 14: Emerging Risk Factor for Brain Disorders

The finely tuned regulation of neuronal firing relies on the integrity of ion channel macromolecular complexes. Minimal disturbances of these tightly regulated networks can lead to persistent maladaptive plasticity of brain circuitry. The intracellular fibroblast growth factor 14 (FGF14) belongs to the nexus of proteins interacting with voltage-gated Na+ (Na_v) channels at the axonal initial segment. Through isoform-specific interactions with the intracellular C-terminal tail of neuronal Na_v channels (Na_v1.1, Na_v1.2, Na_v1.6), FGF14 controls channel gating, axonal targeting and phosphorylation in neurons effecting excitability. FGF14 has been also involved in synaptic transmission, plasticity and neurogenesis in the cortico-mesolimbic circuit with cognitive and affective behavioral outcomes. In translational studies, interest in FGF14 continues to rise with a growing list of associative links to diseases of the cognitive and affective domains such as neurodegeneration, depression, anxiety, addictive behaviors and recently schizophrenia, suggesting its role as a converging node in the etiology of complex brain disorders. Yet, a full understanding of FGF14 function in neurons is far from being complete and likely to involve other functions unrelated to the direct regulation of Na_v channels. The goal of this Mini Review article is to provide a summary of studies on the emerging role of FGF14 in complex brain disorders.

Conditional knockout of Fgf13 in murine hearts increases arrhythmia susceptibility and reveals novel ion channel modulatory roles

The intracellular fibroblast growth factors (iFGF/FHFs) bind directly to cardiac voltage gated Na⁺ channels, and modulate their function. Mutations that affect iFGF/FHF-Na⁺ channel interaction are associated with arrhythmia syndromes. Although suspected to modulate other ionic currents, such as Ca²⁺ channels based on acute knockdown experiments in isolated cardiomyocytes, the in vivo consequences of iFGF/FHF gene ablation on cardiac electrical activity are still unknown. We generated inducible, cardiomyocyte-restricted Fgf13 knockout mice to determine the resultant effects of Fgf13 gene ablation. Patch clamp recordings from ventricular myocytes isolated from Fgf13 knockout mice showed a ~25% reduction in peak Na⁺ channel current density and a hyperpolarizing shift in steady-state inactivation. Electrocardiograms on Fgf13 knockout mice showed a prolonged QRS duration. The Na⁺ channel blocker flecainide further prolonged QRS duration and triggered ventricular tachyarrhythmias only in Fgf13 knockout mice, suggesting that arrhythmia vulnerability resulted, at least in part, from a loss of functioning Na⁺ channels. Consistent with these effects on Na⁺ channels, action potentials in Fgf13 knockout mice, compared to Cre control mice, exhibited slower upstrokes and reduced amplitude, but unexpectedly had longer durations. We investigated candidate sources of the prolonged action potential durations in myocytes from Fgf13 knockout mice and found a reduction of the transient outward K⁺ current (I_to). Fgf13 knockout did not alter whole-cell protein levels of Kv4.2 and Kv4.3, the I_to pore-forming subunits, but did decrease Kv4.2 and Kv4.3 at the sarcolemma. No changes were seen in the sustained outward K⁺ current or voltage-gated Ca²⁺ current, other candidate contributors to the increased action potential duration. These results implicate that FGF13 is a critical cardiac Na⁺ channel modulator and Fgf13 knockout mice have increased arrhythmia susceptibility in the setting of Na⁺ channel blockade. The unanticipated effect on I_to revealed new FGF13 properties and the unexpected lack of an effect on voltage-gated Ca²⁺ channels highlight potential compensatory changes in vivo not readily revealed with acute Fgf13 knockdown in cultured cardiomyocytes.