Claudio Acuna

KCNQ1 encodes a voltage-gated potassium channel implicated in peripheral and neurological disorders, but its role in human neurodevelopment remains unclear. We generated KCNQ1 knockout (KO) human induced pluripotent stem cells and differentiated them into neural stem cells (NSCs) and cortical neurons. KCNQ1 -deficient NSCs show impaired neurite outgrowth, linked to reduced cell adhesion and disrupted neural cell adhesion molecule signalling, a phenotype reproduced by pharmacological KCNQ1 inhibition. Multi-omics and follow-up analyses reveal mitochondrial dysfunction, including reduced mitochondrial copy number and ATP synthase expression. KO cells also show impaired insulin signalling, with diminished insulin receptor gene expression and altered RAS-MAPK and PI3K-AKT pathways. In differentiated neuronal cultures, KCNQ1 loss decreases synaptic activity and maintains an immature transcriptional profile. Together, these findings identify a role for KCNQ1 in regulating cell adhesion, mitochondrial function, insulin signalling, and neuronal maturation, expanding our understanding of processes that may contribute to neurological manifestations associated with KCNQ1 -related disorders.

The axon initial segment (AIS) and nodes of Ranvier (NoR) are essential for action potential initiation and propagation. They share many features of their molecular architecture, and their assembly mechanisms converge on the membrane-associated periodic skeleton (MPS). Here, we identify Paralemmin-2 (Palm2) as a component of both the AIS and NoR. Palm2 depletion shortens the AIS and reduces neuronal excitability. Endogenous Palm2 in the AIS is non-periodic, but upon overexpression it associates with the MPS, localizing to actin rings and reducing βIV-spectrin abundance and periodicity. In NoR of the central and peripheral nervous system, Palm2 localizes to different subdomains - nodal or paranodal, respectively. Palm2, and its homolog Palm1, bind the deubiquitinase USP7, implicating paralemmins in proteostasis at the MPS. The complementary localizations of Palm2 and Palm1 at the AIS/NoR or axon shafts, respectively, parallel the distributions of β-spectrin and ankyrin isoforms between these axonal compartments. We propose that Palm2 modulates the submembrane cytoskeleton and its membrane attachment, and thus contributes to the assembly, functioning and remodeling of the AIS and NoR.

Presynaptic scaffold proteins, including liprin-α, RIM, and ELKS, are pivotal to the assembly of the active zone and regulating the coupling of calcium signals and neurotransmitter release, yet the underlying mechanism remains poorly understood. Here, we determined the crystal structure of the liprin-α2/RIM1 complex, revealing a multifaceted intermolecular interaction that drives the liprin-α/RIM assembly. Neurodevelopmental disease-associated mutations block the formation of the complex. Disrupting this interaction in cultured human neurons impairs synaptic transmission and reduces the readily releasable pool of synaptic vesicles. Super-resolution imaging analysis supports a role for liprin-α in recruiting RIM1 to the active zone, presumably by promoting the liquid–liquid phase separation (LLPS) of RIM1. Strikingly, the liprin-α/RIM interaction modulates the competitive distribution of ELKS1 and voltage-gated Ca²⁺ channels (VGCCs) in RIM1 condensates. Disrupting the liprin-α/RIM interaction significantly decreased VGCC accumulation in the condensed phase and rendered release more sensitive to the slow calcium buffer EGTA, suggesting an increased physical distance between VGCC and vesicular calcium sensors. Together, our findings provide a plausible mechanism of the liprin-α/RIM complex in regulating the coupling of calcium channels and primed synaptic vesicles via LLPS for efficient synaptic transmission and uncover the pathological implication of liprin-α mutations in neurodevelopmental disorders.

Heat acclimation is an adaptive process that improves physiological performance and supports survival in the face of increasing environmental temperatures, but the underlying mechanisms are not well understood. Here we identified a discrete group of neurons in the mouse hypothalamic preoptic area (POA) that rheostatically increase their activity over the course of heat acclimation, a property required for mice to become heat tolerant. In non-acclimated mice, peripheral thermoafferent pathways via the parabrachial nucleus activate POA neurons and mediate acute heat-defense mechanisms. However, long-term heat exposure promotes the POA neurons to gain intrinsically warm-sensitive activity, independent of thermoafferent parabrachial input. This newly gained cell-autonomous warm sensitivity is required to recruit peripheral heat tolerance mechanisms in acclimated animals. This pacemaker-like, warm-sensitive activity is driven by a combination of increased sodium leak current and enhanced utilization of the Na_V1.3 ion channel. We propose that this salient neuronal plasticity mechanism adaptively drives acclimation to promote heat tolerance.

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.

Presynaptic scaffold proteins, including liprin-α, RIM, and ELKS, are pivotal to the assembly of the active zone and regulating the coupling of calcium signals and neurotransmitter release, yet the underlying mechanism remains poorly understood. Here, we determined the crystal structure of the liprin-α2/RIM1 complex, revealing a multifaceted intermolecular interaction that drives the liprin-α/RIM assembly. Neurodevelopmental disease-associated mutations block the formation of the complex. Disrupting this interaction in neurons impairs synaptic transmission and reduces the readily releasable pool of synaptic vesicles. Super-resolution imaging analysis supports a role for liprin-α in recruiting RIM1 to the active zone, presumably by promoting the liquid-liquid phase separation (LLPS) of RIM1. Strikingly, the liprin-α/RIM interaction modulates the competitive distribution of ELKS1 and voltage-gated calcium channels (VGCCs) in RIM1 condensates. Disrupting the liprin-α/RIM interaction significantly decreased VGCC accumulation in the condensed phase and rendered release more sensitive to the slow calcium buffer EGTA, suggesting an increased physical distance between VGCC and vesicular calcium sensors. Together, our findings provide a plausible mechanism of the liprin-α/RIM complex in regulating the coupling of calcium channels and primed synaptic vesicles via LLPS for efficient synaptic transmission and uncover the pathological implication of liprin-α mutations in neurodevelopmental disorders.

Glioblastomas are heterogeneous brain tumors, notorious for their invasive behavior and resistance to therapy. Neuron-to-glioma synapses have been identified to promote glioblastoma invasion and proliferation. However, a comprehensive characterization of tumor-connected neurons has been hampered by a lack of technologies. Here, we adapted retrograde tracing with a modified rabies virus system to characterize and manipulate connected neuron-tumor networks. Glioblastoma rapidly integrated into neural circuits across the brain engaging in widespread functional communication, with acetylcholinergic and glutamatergic neurons driving glioblastoma progression. We uncovered patient-specific and tumor cell state-dependent differences in synaptogenic gene expression driving neuron-tumor connectivity and subsequent invasivity. Importantly, radiotherapy enhanced neuron-tumor connectivity by increased neuronal activity. In turn, simultaneous inhibition of AMPA receptors and radiotherapy showed increased therapeutic effects, indicative of a role for neuron-to-glioma synapses in contributing to therapeutic resistance. Lastly, rabies-mediated genetic ablation of tumor-connected neurons halted glioblastoma progression, offering a novel viral strategy to target glioblastoma. Together, this study provides a comprehensive framework for basic research and clinical translation of synaptic neuron-cancer interactions to target glioblastoma.

The formation of mammalian synapses entails the precise alignment of presynaptic release sites with postsynaptic receptors but how nascent cell–cell contacts translate into assembly of presynaptic specializations remains unclear. Guided by pioneering work in invertebrates, we hypothesized that in mammalian synapses, liprin-α proteins directly link trans -synaptic initial contacts to downstream steps. Here we show that, in human neurons lacking all four liprin-α isoforms, nascent synaptic contacts are formed but recruitment of active zone components and accumulation of synaptic vesicles is blocked, resulting in ‘empty’ boutons and loss of synaptic transmission. Interactions with presynaptic cell adhesion molecules of either the LAR-RPTP family or neurexins via CASK are required to localize liprin-α to nascent synaptic sites. Liprin-α subsequently recruits presynaptic components via a direct interaction with ELKS proteins. Thus, assembly of human presynaptic terminals is governed by a hierarchical sequence of events in which the recruitment of liprin-α proteins by presynaptic cell adhesion molecules is a critical initial step.

Toscana virus is a major cause of arboviral disease in humans in the Mediterranean basin during summer. However, early virus-host cell interactions and entry mechanisms remain poorly characterized. Investigating iPSC-derived human neurons and cell lines, we found that virus binding to the cell surface was specific, and 50% of bound virions were endocytosed within 10 min. Virions entered Rab5a+ early endosomes and, subsequently, Rab7a+ and LAMP-1+ late endosomal compartments. Penetration required intact late endosomes and occurred within 30 min following internalization. Virus entry relied on vacuolar acidification, with an optimal pH for viral membrane fusion at pH 5.5. The pH threshold increased to 5.8 with longer pre-exposure of virions to the slightly acidic pH in early endosomes. Strikingly, the particles remained infectious after entering late endosomes with a pH below the fusion threshold. Overall, our study establishes Toscana virus as a late-penetrating virus and reveals an atypical use of vacuolar acidity by this virus to enter host cells.

Toscana virus is a major cause of arboviral disease in humans in the Mediterranean basin during summer. However, early virus-host cell interactions and entry mechanisms remain poorly characterized. Investigating iPSC-derived human neurons and cell lines, we found that virus binding to the cell surface was specific but inefficient, and 50% of bound virions were endocytosed within 10 min. Virions entered Rab5a+ early endosomes and, subsequently, Rab7a+ and LAMP-1+ late endosomal compartments. Penetration required intact late endosomes and occurred within 30 min following internalization. Virus entry relied on vacuolar acidification, with an optimal pH for viral membrane fusion at pH 5.5. The pH threshold increased to 5.8 with longer pre-exposure of virions to the slightly acidic pH in early endosomes. Strikingly, the particles remained infectious after entering late endosomes with a pH below the fusion threshold. Overall, our study establishes Toscana virus as a late-penetrating virus and reveals an atypical use of vacuolar acidity by this virus to enter host cells.