Faculty Bibliography

De novo protein synthesis is required for long-lasting synaptic plasticity and memory, but it comes with a great metabolic cost. In the mammalian brain, it remains unclear which cell types and biological mechanisms are critical for sensing and responding to increased metabolic demand. Here, we demonstrate that microglia, the resident macrophages of the brain, are required for metabolic coupling between endothelial cells, astrocytes, and neurons, which fuels protein synthesis in active neurons. Increasing metabolic demand via a motor task stimulates microglia to secrete the hypoxia-responsive protein CYR61, which increases glucose transporter expression in brain vasculature. Depleting microglia reduces training-induced metabolic fluxes and neuronal protein synthesis, which can be reproduced by blocking CYR61 signaling. Thus, we define a neuroimmune metabolic circuit that is required for on-demand protein synthesis in mouse motor cortex.

Educational initiatives that address the gap between basic/preclinical and clinical practices are important to effectively translate basic science discoveries to benefit patients. The ILAE Neurobiology Commission conducted a pilot project aimed at exposing basic and preclinical scientists engaged in epilepsy research to general clinical issues pertaining to the diagnosis and care of people with epilepsy. This aim was addressed through a two-week-long, on-site clinical training program for 50 basic scientists in 21 epilepsy centers across 18 countries in the six ILAE regions (with a maximum of 3 basic scientists per center). The learning objectives and the training module were discussed and defined by the project organizing committee, which consisted of Neurobiology Commission members and a team of epileptologists representing different geographical regions. The training activities were conducted at each epilepsy center under the local supervision of clinical tutors. Each basic scientist was exposed to 50.3 ± 23.3 (range 16-89) hours of intensive and dedicated clinical training, coordinated by 2-3 tutors per center, assisted by 6.8 ± 3.6 colleagues. A structured test consisting of 17 general clinical epilepsy questions was completed by the trainees before and after the training activity. The learning assessment was based on the comparison between responses to the exit and entry tests. After the on-site clinical exposure, the proportion of correct answers increased to 87% compared to 61% in the entry test. Structured post-training questionnaires demonstrated very high satisfaction of trainees and all involved tutors across the different aspects of the training module. This global pilot study demonstrated that on-site attendance by basic scientists in specialized clinical settings up-scaled their knowledge of clinical epileptology and facilitated networking with clinicians. Expansion of this pilot to further centers should be considered to understand how exposure to clinical practice affects research direction and quality of translational epilepsy research. PLAIN LANGUAGE SUMMARY: Epilepsy research has long benefitted from collaboration between scientists and clinicians. Early exposure of researchers to people with epilepsy and their care teams may strengthen future impact. This pilot study tested a two-week immersive experience where small teams of basic scientists shadowed clinicians during their work at hospitals around the world. Questionnaires showed high satisfaction among both groups. Results support expanding such training, with the backing of the International League Against epilepsy and aligned centers, to build understanding, interest, and long-term commitment, ensuring bench research is informed by and translates to clinical practice and improved quality of life for patients.

Ameloblasts are specialized epithelial cells that form enamel during the secretory and maturation stages, the latter involving an increase in Ca²⁺ transport to mineralize the enamel crystals. During enamel formation, ameloblasts travel several microns while secreting a matrix and are surrounded by several cell layers in the confined space of the enamel organ. Presumably, ameloblasts are subjected to mechanical stimuli e.g. pressure, stretch. Mechanosensitive (MS) or stretch-gated channels are expressed in the membranes of many cells including mineralizing cells. The opening of MS channels occurs in response to physical stimuli and results in the influx of ions. Piezo1 is a non-selective class of MS channel permeable to Ca²⁺ and hence it may contribute to Ca²⁺ homeostasis in ameloblasts. Here we show that secretory and maturation stage ameloblasts express similar protein levels of Piezo1. Cultured rat primary secretory and maturation stage ameloblasts showed stretch-activated currents by patch-clamp. Ameloblasts loaded with the cytosolic Ca²⁺ indicator Fura-2 were also stimulated with the Piezo1-selective activator Yoda1. We show that ameloblasts are sensitive to Piezo1 stimulation which evoked an increase in cytosolic Ca²⁺. This effect was inhibited by Piezo1 blockers. Mechanical analysis of the incisors of Piezo1 cKO mice showed no alterations in hardness or elastic modulus relative to littermate control mice. Our work provides the first evidence that Piezo1 channels are functional in both ameloblast stages and their activation leads to an elevation in cytosolic Ca²⁺, however, Piezo1 does not appear to be essential for enamel mineralization.

The decisional reference point, the central mechanism underlying behavioral economics, conditions our evaluations of all reinforcers. Whether a given event is experienced as positive or negative depends on this reference point. A pathological elevation of the reference point would lead a person to experience once pleasurable activities as negative reinforcers. Thus, it has been hypothesized that a reference point pathology may play a critical role in the symptomology of major depressive disorder (MDD). Here, we test the hypothesis that the reference point is pathologically elevated and dynamically inflexible in patients suffering with MDD compared to healthy controls. We find that depression is associated with a significant elevation of the reference point, and the magnitude of this elevation correlates with disease severity. The ability of patients with MDD to dynamically adjust their reference point to the environment is also dysfunctional. Our findings link the previously demonstrated treatment of depression by deep brain stimulation to modulation of the reference point in the anterior cingulate cortex and identify pathology in the dynamics of reference point setting as a potential cognitive mechanism in the disorder. Finally, these results reveal that a three-minute video game-like task measuring the reference point strongly correlates with depression severity. After further testing for clinical validity, this rapid assay may serve as a potential tool for assessing and monitoring depression.

A social hierarchy is an ordered ranking of individuals that arises through their interactions and governs relative access to resources and social influence. This form of social organization is pervasive across animal species and has a crucial role in shaping survival and reproductive outcomes. Across species, the routes to high status vary widely. As social groups become more complex, the basis of hierarchy shifts from simple residency rules to fighting-based dominance and finally to alliance-based systems. In this Review, we first examine the neuroendocrine and subcortical mechanisms that support status transitions in residency-based hierarchies. We then discuss plasticity within hypothalamic and mesolimbic circuits that underlie fighting-outcome-based social learning, through which fighting-based hierarchies emerge. Finally, we explore alliance-based hierarchies in cognitively complex species, in which individuals attain status through coalition formation, cooperation and reputation. We review evidence that cortical regions encode information about the strengths, emotions, experiences and intentions of other individuals and use this to navigate complex social interactions and attain status. As social hierarchies have shifted from primarily fighting-based to increasingly alliance-based strategies over evolutionary time, neural control of status has, thus, transitioned from subcortical social behaviour circuits to a more elaborated cortical network in humans.

Episignatures are increasingly valuable for variant interpretation in rare neurodevelopmental disorders, especially when optimized to capture the impact of specific variant types and locations across a gene. Here, we generated a next-generation DNA methylation (DNAm) episignature for Kabuki syndrome type 1 (KS1) using the largest cohort studied to date, aiming to clarify the epigenomic and phenotypic effects of diverse KMT2D variant types and positions. Genome-wide DNAm profiles were obtained for 110 individuals with KMT2D variants and 854 controls using microarrays and long-read sequencing (LRS). Differentially methylated loci were enriched in genes involved in embryonic and nervous system development and were leveraged to construct a support-vector machine classifier for detecting pathogenic KMT2D variants. The classifier achieved 97% sensitivity and 100% specificity in validation cohorts and outperformed in silico tools, demonstrating stronger concordance with clinical presentation. Missense variants in the C-terminal region (exon 48) of KMT2D and the N-terminal plant homeodomain (PHD)-type zinc fingers were predominantly classified as pathogenic, highlighting regions enriched for pathogenic variants. Missense variants in the central region (exons 31-39) were more often predicted benign for KS1, consistent with potential association with a different syndrome, highlighting the classifier's specificity for KS1. Test performance was consistent across array and LRS platforms, and classifier scores reflected levels of mosaicism detected by LRS. The KS1 episignature also positively classified pathogenic KDM6A variants associated with KS2. These findings represent a significant advance in the evolution of episignature development, demonstrating diagnostic and interpretive value of a KS1 signature in resolving uncertain or complex cases.

The capacity of hippocampal circuits to transform inputs into downstream outputs is fundamental to navigation and memory, yet the circuit-level mechanisms that enable this flexibility in adapting to experience remain unclear. Here we approach this problem by performing large-scale (up to 1,024 channel) recordings across the hippocampal-retrosplenial cortex (RSC) circuit in behaving mice, enabling simultaneous access to spiking activity in dentate gyrus (DG), CA3, CA2, CA1 and RSC. On the basis of a linear dimensionality-reduction technique known as partial canonical correlation analysis, we identify low-dimensional communication subspaces¹ between two regions while accounting for influences from a third area. These subspaces captured distinct input-output transformations in the CA1 region, linking upstream hippocampal activity (DG, CA3 and CA2) to downstream cortical targets (RSC). Intrinsic firing properties and anatomical location constrained subspace memberships-members were mapped to deep sublayers of the CA3-CA1-RSC axis during both spatial and non-spatial tasks. These subspaces could recombine overlapping neuronal pools to support distinct interareal interactions across changing experiences and brain states. Reactivation patterns of CA1-CA3 subspaces, but not those of CA1-RSC, during post-experience sleep correlated with replay, reflecting a plasticity-stability balance in the input-output transformation along the hippocampal-retrosplenial axis. Our findings suggest a model in which hippocampal-neocortical communication reconfigures predetermined circuit motifs to flexibly encode experiences.

Protease-activated receptor 2 (PAR₂) mediates oral cancer pain. Patients with metastatic (N + ) cancers report greater pain. PAR₂ is activated by N-terminal proteolytic cleavage. Here we show that proteases encoded by genes overexpressed in N+ cancers from patients with pain (matrix metallopeptidase 1, MMP1 and serine protease 23, PRSS23) elicit protease-specific receptor redistribution (trafficking) and signaling that differs from that promoted by proteases encoded by genes not differentially expressed (transmembrane serine protease matriptase, ST14 and cathepsin S, CTSS). Mixtures of the proteases prepared to model the oral cancer microenvironment revealed that ST14-mediated PAR₂ activation predominated at low protease concentrations. At high concentrations, MMP1 and PRSS23 prevailed over the greater potency of ST14. We propose that PAR₂ activation in oral N+ cancers from patients with pain is driven by high levels of MMP1 and PRSS23. Our study informs design of signaling and location-specific antagonists to provide more efficacious analgesia.