Tian-Le Xu

Summary: For decades, ischemic neuronal death was understood largely as a story about glutamate. Acid-sensing ion channels (ASICs) have revised that account. When cerebral blood flow stops, the penumbra can develop prolonged extracellular acidosis, and experimental studies implicate ASIC1a in mediating sufficient Ca²⁺ entry to injure neurons even when glutamate receptors are blocked, a contribution shaped by channel expression, subunit composition, and the intracellular signaling context. However, sustained acidosis does not necessarily imply sustained channel opening, given ASIC1a desensitization. Besides acidosis, glutamate, polyamines, a paradoxical intracellular alkalization, and oxidative stress can enhance ASIC1a activity or expression, and the channel also signals through a non-conducting route, recruiting RIPK1 to trigger necroptosis independently of ion flux. The relative contributions of these conducting and non-conducting mechanisms in vivo remain incompletely defined. Endogenous mechanisms may constrain injury by internalizing the channel, altering subunit expression, including conditioning-associated ASIC2a upregulation, and degrading ASIC1a through estrogen signaling. We argue that these responses are better understood as constraints on injury than as a genuine survival program, a distinction with mechanistic and therapeutic consequences. Critically, the contribution of these mechanisms may vary over time. The same channel acts as a target of homeostatic regulation before stroke, a driver of death during ischemia, a potential target at reperfusion when acidosis persists but restored flow finally permits drug delivery, and an impediment to repair for weeks afterward. The question in ASIC-targeted neuroprotection is not only whether to inhibit the channel, but also when and for how long.

Conspectus: Spatial precision of endogenous biological signaling is dictated by submicrometer microdomains. Traditional pharmacological modalities lack spatial resolution needed to interrogate discrete coordinates, whereas genetic methods often lack rapid kinetic control needed to capture dynamic signaling networks. While photochemical tools offer noninvasive, spatiotemporally resolved control, their biological translation is limited by UV phototoxicity, nonspecific ROS damage, and the difficulty to achieve true subcellular localization. We summarize our development of proximity-activated photocatalytic pharmacology via spatially confined small-molecule release, focusing on mechanistic evolution of biocompatible, metal-free photocatalytic deboronative hydroxylation of organoboronates. We present a paradigm where reaction fidelity is governed not by intrinsic photochemical properties of substrates but by physical coordinates of the localized photocatalyst and short-lived reactive species generated within defined spatial boundaries. This platform operates through localized generation of transient intermediates, specifically superoxide anions (O2·–) and H2O2, whose intracellular diffusion is constrained by native cellular quenching machinery. By exploiting steep concentration gradients of species, we establish a high-resolution reaction sphere for photocatalytic bond cleavage to enable precise interrogation of biological microdomains. Our research program progressed through three distinct generations to span increasingly complex biological scales: • First generation (cellular scale): We established a visible-light-driven small-molecule release system using biocompatible organic xanthene dyes and physiological ascorbates. Operating through a single-electron transfer pathway, this manifold selectively reduces molecular oxygen to O2·– to drive bioorthogonal deboronative hydroxylation while bypassing cytotoxic energy transfer pathways. • Second generation (subcellular scale): We achieved subcellular precision by engineering targeted chemical scaffolds and hybrid genetically targeted platforms (e.g., SNAP-FL) to restrict photocatalytic activity to specific organelle coordinates. By advancing to fully genetically encoded 12 kDa miniature photoenzymes (miniSOG), we eliminated exogenous chemical catalyst requirements. Together, these methods enabled us to map compartment-specific drug toxicities, drive selective mitochondrial depolarization, and achieve nucleus-specific epitranscriptomic remodeling of m6A RNA methylation. • Third generation (circuit scale): We deployed these platforms to decipher complex architecture of the mammalian nervous system. By expressing membrane-anchored SNAP-FL at projection-specific synaptic terminals, we achieved optochemical neuromodulation in acute brain slices within seconds. Ultimately, this enabled cell-type-specific photocatalytic pharmacology in vivo, facilitating the selective release of GABABR agonists within NaV1.8+ terminals to functionally delineate peripheral neural circuits driving pruritus in mice. By transitioning from bulk cellular activation to localized, genetically directed modulation, we provide a unified mechanistic framework that demonstrates how photocatalyst localization and confined reactive species dynamics dictate complex biological outcomes across multiple spatiotemporal scales.

Chronic pain is frequently accompanied by affective disturbances, yet existing analgesics provide limited efficacy and raise substantial safety concerns. The proton-gated ion channel ASIC1a contributes to nociceptive sensitisation and affective pain processing, but the lack of tools that selectively target human ASIC1a has hindered translational progress. Here, we identify a nanobody that selectively recognises human ASIC1a and enhances its endocytosis, thereby reducing surface channel availability and suppressing proton-evoked currents. Using a humanised ASIC1a knock-in mouse model, we combine molecular, electrophysiological, and behavioural approaches to dissect the functional consequences of human ASIC1a modulation in vivo. We show that human ASIC1a expressed in both the anterior cingulate cortex and peripheral nociceptors contributes to inflammatory hypersensitivity and anxiety-like behaviours in chronic pain. Targeted adeno-associated virus-mediated expression of the nanobody in the anterior cingulate cortex, as well as local peripheral delivery of purified nanobody protein, produces analgesic effects accompanied by improvements in affective behaviour. These findings define a trafficking-based mode of human ASIC1a regulation that can be selectively engaged by nanobody binding, supporting nanobody-mediated modulation of human ASIC1a as a translationally tractable strategy for rebalancing the sensory and emotional dimensions of chronic pain.

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric condition characterized by persistent fear memory, hyperarousal, and social impairment. Mounting evidence highlights the critical role of social stress, such as bullying, in triggering PTSD. However, progress in elucidating the underlying mechanisms and developing effective treatments has been hindered by the lack of animal models that accurately recapitulate the multidimensional etiology of social trauma-related PTSD. To address this gap, we developed a novel triple-composite social bullying (SB) model in mice, which integrates social aggression, physiological pain, and psychological isolation to mimic the pathogenesis of PTSD induced by social bullying. Mice subjected to social bullying paradigm exhibited robust PTSD-like phenotypes, including anxiety- and depression-like behaviors, enhanced cue-induced fear responses, along with a prominent social avoidance phenotype that was not observed in the conventional foot shock (FS) model. Systemic administration of fluoxetine (10 mg/kg, intraperitoneal injection) significantly alleviated these behavioral deficits. Paralleled with these behavioral changes, neural hyperactivation in brain regions associated with fear and stress (anterior cingulate cortex [ACC], basolateral amygdala [BLA]), suppressed activity in the dorsal hippocampus (dHIP), reduced dendritic complexity in limbic areas, elevated expression of the FKBP51-glucocorticoid receptor (GR) complex, and increased cortisol levels. Collectively, this study demonstrates that the SB model faithfully recapitulates the core clinical manifestations of social trauma-induced PTSD across behavioral, neural, cellular, and molecular dimensions. The model thus provides a rigorously validated preclinical tool for investigating mechanisms of social trauma-related PTSD and screening potential therapeutic interventions.

Engrams are formed by activity-dependent recruitment of subsets of excitatory principal neurons, whereas inhibitory neurons mediate memory lability and stability. It remains elusive whether specific types of interneurons are preferentially engaged in determining the fate of memory. Here we show, in male mice undergoing cued fear memory training and extinction, that neuropeptide Y (NPY)-expressing (NPY⁺) GABA-ergic interneurons in ventral CA1 (vCA1) exert both fast GABA-ergic inhibition to facilitate memory acquisition and slow NPY-mediated inhibition to facilitate extinction. Specifically, the calcium dynamics of NPY⁺ neurons and NPY release in vCA1 ramp up as extinction learning progresses and the behavioral state switches from ‘fear-on’ to ‘fear-off’. We show that NPY is necessary and sufficient to control the rate and degree of memory extinction by acting on two nonoverlapping subensembles composed of NPY receptor 1 (NPY1R)-expressing and NPY2R-expressing neurons, thereby gating early fast and late slow stages of extinction, respectively. Thus, subtype-specific, slow peptidergic inhibition from interneurons regulates engram lability versus stability.

Post-traumatic stress disorder (PTSD) is a severe psychiatric disorder that develops in the months and years following exposure to severe trauma. Despite growing research, there remain gaps in understanding the full pathophysiology of PTSD, so that treatments are not universally effective, contributing to a significant public health burden. Therefore, it is necessary to explore novel therapeutic approaches. Anesthetics have recently been shown as a novel therapeutic agent with promising results in the treatment of PTSD. This review summarizes key mechanisms of anesthetics, including N-methyl-D-aspartate (NMDA) receptor antagonists, α2-adrenergic receptor agonists, Gamma-Aminobutyric Acid (GABA)-A Receptor-related anesthetics and opioids, and their translational potential to treatment of PTSD.

Detecting and utilizing salience information are essential for organisms to prioritize behaviorally relevant stimuli. While the prefrontal cortex is critical for cognition and learning, how it leverages salience information remains unclear. We report that chandelier cells (ChCs) in the medial prefrontal cortex (mPFC), a unique GABAergic interneuron, encode salience information and influence learning. Using cell-type-specific calcium signal recording in male mice, we demonstrate that ChCs respond robustly to stimuli across modalities, with responses dependent on stimulus salience, as determined by novelty and intensity. Circuit-specific manipulations reveal that ChC salience coding is attributable to synaptic inputs from the anterior insular cortex and paraventricular thalamus. Furthermore, ChCs acquire salience-coding property for behaviorally relevant stimuli through associative learning. Notably, bidirectional manipulations of ChC-mediated salience detection correspondingly led to improved or impaired associative learning. Together, these findings establish mPFC ChCs as a key circuit element for processing salience information to shape learning and behavior.