Biology subjects

Shamardani, K.

Publications and source records attributed to Shamardani, K..

6 recordsLinked to original sources

bioRxiv2025

Dysregulated Microglial Synaptic Engulfment in Diffuse Midline Glioma

Diffuse midline glioma (DMG) is a near-universally lethal form of pediatric high-grade glioma, driven by neuronal activity-regulated paracrine signaling and synaptic integration of malignant cells into neural circuits. In turn, DMG increases neuronal excitability, augmenting neuron-to-glioma signaling. In the healthy brain, microglia, the resident immune cells of the central nervous system (CNS), regulate neuronal excitability and synaptic connectivity. However, the role of microglia in promoting tumor-associated hyperexcitable neural networks in glioma remains unknown. Here, we investigate the activity-regulated engulfment of neuronal synapses by microglia in both healthy and glioma-bearing mice, and further explore how glioma cells alter microglia-mediated circuit refinement, contributing to pathogenic neuronal hyperexcitability. Microglia-mediated circuit refinement in the glioma microenvironment was characterized through synaptic engulfment analysis of both excitatory and inhibitory synapses by microglia in healthy mice and patient-derived DMG xenograft models, paired with optogenetic stimulation in the neocortex. We found that glutamatergic neuronal activity in the healthy brain increased excitatory synaptic engulfment by microglia in a previously unappreciated negative feedback mechanism that may guard against hyperexcitability. In contrast, this activity-regulated increase in excitatory synaptic engulfment was abrogated in DMG-infiltrated brains. Instead, inhibitory synaptic engulfment was significantly increased in DMG in response to glutamatergic neuronal activity. Together, these dysregulated synaptic engulfment mechanisms may create imbalance in the excitatory to inhibitory (E:I) synapse ratio predicted to increase neuronal excitability. Complementary single-nuclei sequencing studies revealed concordant tumor-specific, activity-regulated changes in microglia-neuron signaling showing reduced expression of excitatory synaptic refinement gene programs in microglia, potentially mediating the aberrant synaptic engulfment observed in DMG. These findings reveal novel cancer-neuron-immune interactions in DMG and provide an opportunity to potentially modulate tumor-associated neuronal hyperexcitability by targeting aberrant microglial synaptic engulfment. HIGHLIGHTSO_LIExcitatory synaptic engulfment by microglia increases in a glutamatergic neuronal activity-dependent manner in the healthy brain. C_LIO_LIIn the glioma-infiltrated brain, this feedback regulatory mechanism is inverted, with loss of activity-regulated excitatory synaptic engulfment and aberrant increased inhibitory synaptic engulfment. C_LIO_LITranscriptomic changes in glioma-associated microglia contribute to differential excitatory and inhibitory synaptic engulfment, with reduced excitatory synaptic refinement gene programs in tumor-associated microglia. C_LIO_LIActivity-regulated soluble factors drive this imbalanced excitatory-inhibitory postsynaptic engulfment by glioma-associated microglia. C_LI

neuroscience↗

bioRxiv2025

Serotonergic neuron-glioma interactions drive high-grade glioma pathophysiology

High-grade gliomas are lethal brain cancers that are powerfully regulated by glutamatergic neurons through activity-dependent paracrine factors and functional neuron-to-glioma synapses. Here, we report that serotonergic neurons promote the proliferation of high-grade gliomas throughout the brain. Serotonergic neuronal activity drives circuit-specific increases in high-grade glioma proliferation, calcium transients, and reduced survival. This growth-promoting effect is chiefly mediated by activation of the serotonin (5-hydroxytryptamine; 5HT) receptor 5HT2A on glioma cells. Knock out or pharmacological blockade of 5HT2A receptors in glioma abrogated the glioma growth-promoting effects of serotonergic neuronal activity, while serotonergic psychedelic drugs robustly promote malignant cell proliferation. Gliomas alter serotonergic neuronal activity patterns, resulting in elevated serotonin release into the tumor microenvironment. Together, these findings uncover pathogenic, feed-forward interactions between serotonergic neurons and glioma cells.

neuroscience↗

bioRxiv2024

Cholinergic Neuronal Activity Promotes Diffuse Midline Glioma Growth through Muscarinic Signaling

Neuronal activity promotes the proliferation of healthy oligodendrocyte precursor cells (OPC) and their malignant counterparts, gliomas. Many gliomas arise from and closely resemble oligodendroglial lineage precursors, including diffuse midline glioma (DMG), a cancer affecting midline structures such as the thalamus, brainstem and spinal cord. In DMG, glutamatergic and GABAergic neuronal activity promotes progression through both paracrine signaling and through bona-fide neuron-to-glioma synapses. However, the putative roles of other neuronal subpopulations - especially neuromodulatory neurons located in the brainstem that project to long-range target sites in midline anatomical locations where DMGs arise - remain largely unexplored. Here, we demonstrate that the activity of cholinergic midbrain neurons modulates both healthy OPC and malignant DMG proliferation in a circuit-specific manner at sites of long-range cholinergic projections. Optogenetic stimulation of the cholinergic pedunculopontine nucleus (PPN) promotes glioma growth in pons, while stimulation of the laterodorsal tegmentum nucleus (LDT) facilitates proliferation in thalamus, consistent with the predominant projection patterns of each cholinergic midbrain nucleus. Reciprocal signaling was evident, as increased activity of cholinergic neurons in the PPN and LDT was observed in pontine DMG-bearing mice. In co-culture, hiPSC-derived cholinergic neurons form neuron-to-glioma networks with DMG cells and robustly promote proliferation. Single-cell RNA sequencing analyses revealed prominent expression of the muscarinic receptor genes CHRM1 and CHRM3 in primary patient DMG samples, particularly enriched in the OPC-like tumor subpopulation. Acetylcholine, the neurotransmitter cholinergic neurons release, exerts a direct effect on DMG tumor cells, promoting increased proliferation and invasion through muscarinic receptors. Pharmacological blockade of M1 and M3 acetylcholine receptors abolished the activity-regulated increase in DMG proliferation in cholinergic neuron-glioma co-culture and in vivo. Taken together, these findings demonstrate that midbrain cholinergic neuron long-range projections to midline structures promote activity-dependent DMG growth through M1 and M3 cholinergic receptors, mirroring a parallel proliferative effect on healthy OPCs. HIGHLIGHTSO_LIActivity of midbrain cholinergic neuron long-range projections increases proliferation of both healthy oligodendrocyte precursor cells (OPC) and malignant diffuse midline glioma (DMG) cells. C_LIO_LIOptogenetic stimulation of cholinergic midbrain nuclei promotes growth in thalamic and pontine glioma in a circuit-dependent manner. C_LIO_LIReciprocally, DMG cells increase cholinergic neuronal activity in cholinergic midbrain nuclei. C_LIO_LIThe muscarinic receptors CHRM1 and CHRM3 are identified as therapeutic targets in DMG. C_LI

neuroscience↗

bioRxiv2024

Immunotherapy-related cognitive impairment after CAR T cell therapy in mice

Persistent central nervous system (CNS) immune dysregulation and consequent dysfunction of multiple neural cell types is central to the neurobiological underpinnings of a cognitive impairment syndrome that can occur following traditional cancer therapies or certain infections. Immunotherapies have revolutionized cancer care for many tumor types, but the potential long-term cognitive sequelae are incompletely understood. Here, we demonstrate in mouse models that chimeric antigen receptor (CAR) T cell therapy for both CNS and non-CNS cancers can impair cognitive function and induce a persistent CNS immune response characterized by white matter microglial reactivity and elevated cerebrospinal fluid (CSF) cytokines and chemokines. Consequently, oligodendroglial homeostasis and hippocampal neurogenesis are disrupted. Microglial depletion rescues oligodendroglial deficits and cognitive performance in a behavioral test of attention and short-term memory function. Taken together, these findings illustrate similar mechanisms underlying immunotherapy-related cognitive impairment (IRCI) and cognitive impairment following traditional cancer therapies and other immune challenges.

neuroscience↗

bioRxiv2022

GABAergic neuron-to-glioma synapses in diffuse midline gliomas

Pediatric high-grade gliomas are the leading cause of brain cancer-related death in children. High-grade gliomas include clinically and molecularly distinct subtypes that stratify by anatomical location into diffuse midline gliomas (DMG) such as diffuse intrinsic pontine glioma (DIPG) and hemispheric high-grade gliomas. Neuronal activity drives high-grade glioma progression both through paracrine signaling1,2 and direct neuron-to-glioma synapses3-5. Glutamatergic, AMPA receptor-dependent synapses between neurons and malignant glioma cells have been demonstrated in both pediatric3 and adult high-grade gliomas4, but neuron-to-glioma synapses mediated by other neurotransmitters remain largely unexplored. Using whole-cell patch clamp electrophysiology, in vivo optogenetics and patient-derived glioma xenograft models, we have now identified functional, tumor-promoting GABAergic neuron-to-glioma synapses mediated by GABAA receptors in DMGs. GABAergic input has a depolarizing effect on DMG cells due to NKCC1 expression and consequently elevated intracellular chloride concentration in DMG tumor cells. As membrane depolarization increases glioma proliferation3, we find that the activity of GABAergic interneurons promotes DMG proliferation in vivo. Increasing GABA signaling with the benzodiazepine lorazepam - a positive allosteric modulator of GABAA receptors commonly administered to children with DMG for nausea or anxiety - increases GABAA receptor conductance and increases glioma proliferation in orthotopic xenograft models of DMG. Conversely, levetiracetam, an anti-epileptic drug that attenuates GABAergic neuron-to-glioma synaptic currents, reduces glioma proliferation in patient-derived DMG xenografts and extends survival of mice bearing DMG xenografts. Concordant with gene expression patterns of GABAA receptor subunit genes across subtypes of glioma, depolarizing GABAergic currents were not found in hemispheric high-grade gliomas. Accordingly, neither lorazepam nor levetiracetam influenced the growth rate of hemispheric high-grade glioma patient-derived xenograft models. Retrospective real-world clinical data are consistent with these conclusions and should be replicated in future prospective clinical studies. Taken together, these findings uncover GABAergic synaptic communication between GABAergic interneurons and diffuse midline glioma cells, underscoring a tumor subtype-specific mechanism of brain cancer neurophysiology with important potential implications for commonly used drugs in this disease context.

neuroscience↗

bioRxiv2022

The logic of recurrent circuits in the primary visual cortex

Recurrent cortical activity sculpts visual perception by refining, amplifying, or suppressing incoming visual signals. Despite the importance of recurrent circuits for cortical processing, the basic rules that govern how nearby cortical neurons influence each other remains enigmatic. We used two-photon holographic optogenetics to activate ensembles of neurons in Layer 2/3 of the primary visual cortex (V1) in the absence of external stimuli to isolate the impact of local recurrence from external inputs. We find that the spatial arrangement and the stimulus feature preference of both the stimulated and the target ensemble jointly determine the net effect of recurrent activity, defining the cortical activity patterns that drive competition versus facilitation in L2/3 circuits. Computational modeling suggests that a combination of highly local recurrent excitatory connectivity and selective convergence onto inhibitory neurons give rise to these principles of recurrent activity. Our data and modeling reveal that recurrent activity can have varied impact, but a logic emerges through an understanding of the precise spatial distribution and feature preference of the multicellular pattern of activity.

neuroscience↗