Biology subjects

Smith, B. N.

Publications and source records attributed to Smith, B. N..

6 recordsLinked to original sources

bioRxiv2026

Lack of tau expression modifies epileptogenesis associated neuroplasticity in the ventral dentate gyrus in a mouse model of temporal lobe epilepsy

Deletion of the microtubule-associated protein, tau reduces seizure burden in rodent models of genetic epilepsies and suppresses evoked seizures. In the intrahippocampal kainate (IHK) model of acquired temporal lobe epilepsy (TLE), mice lacking tau expression develop spontaneous seizures, but at a lower rate than controls. Mechanisms by which tau deletion modifies the development of acquired TLE are not well understood, but a modification of the synaptic reorganization that accompanies epileptogenesis may contribute to modified seizure expression. Increased inhibitory synaptic input to dorsal dentate granule cells (DGCs) contralateral to the focal kainate injection results after development of TLE in tau-/- mice, but inhibitory synaptic reorganization distal to the kainate lesion is undefined in this model. We therefore investigated how development of TLE modifies excitability and synaptic transmission in DGCs of the ventral dentate gyrus, distant from the kainate lesion. Our results show that development of TLE increases evoked action potential firing of ventral DGCs (vDGCs) in mice that develop TLE, demonstrating an effect of TLE development on excitability of DGCs distant from the focal injury. After development of TLE, DGCs from tau-/- mice received increased inhibitory synaptic input bilaterally, suggesting that tau expression suppresses inhibitory synaptic reorganization in DGCs. Optogenetic stimulation of interneurons in tau-/- mice revealed increased inhibitory synaptic input to vDGCs and an increase in inhibitory convergence onto vDGCs once epileptogenesis occurred. Therefore, tau deletion modifies spontaneous seizure expression after epileptogenesis in mice, potentially involving increased synaptic inhibition of DGCs throughout the dentate gyrus.

neuroscience↗

bioRxiv2024

Activation of hypoactive parvalbumin-positive fast-spiking interneuron restores dentate inhibition to prevent epileptiform activity in the mouse intrahippocampal kainate model of temporal lobe epilepsy

Parvalbumin-positive (PV+) GABAergic interneurons in the dentate gyrus provide powerful perisomatic inhibition of dentate granule cells (DGCs) to prevent overexcitation and maintain the stability of dentate gyrus circuits. Most dentate PV+ interneurons survive status epilepticus, but surviving PV+ interneuron mediated inhibition is compromised in the dentate gyrus shortly after status epilepticus, contributing to epileptogenesis in temporal lobe epilepsy. It is uncertain whether the impaired activity of dentate PV+ interneurons recovers at later times or if it continues for months following status epilepticus. The development of compensatory modifications related to PV+ interneuron circuits in the months following status epilepticus is unknown, although reduced dentate GABAergic inhibition persists long after status epilepticus. We employed PV immunostaining and whole-cell patch-clamp recordings from dentate PV+ interneurons and DGCs in slices from male and female sham controls and intrahippocampal kainate (IHK) treated mice that developed spontaneous seizures months after status epilepticus to study epilepsy-associated changes in dentate PV+ interneuron circuits. We found that the number of dentate PV+ cells was reduced in IHK treated mice. Electrical recordings showed that: 1) Action potential firing rates of dentate PV+ interneurons were reduced in IHK treated mice up to four months after status epilepticus; 2) Spontaneous inhibitory postsynaptic currents (sIPSCs) in DGCs exhibited reduced frequency but increased amplitude in IHK treated mice; and 3) The amplitude of evoked IPSCs in DGCs by optogenetic activation of dentate PV+ cells was upregulated without changes in short-term plasticity. Video-EEG recordings revealed that IHK treated mice showed spontaneous epileptiform activity in the dentate gyrus and that chemogenetic activation of PV+ interneurons abolished the epileptiform activity. Our results suggest not only that the compensatory changes in PV+ interneuron circuits develop after IHK treatment, but also that increased PV+ interneuron mediated inhibition in the dentate gyrus may compensate for cell loss and reduced intrinsic excitability of dentate PV+ interneurons to stop seizures in temporal lobe epilepsy. HighlightsO_LIReduced number of dentate PV+ interneurons in TLE mice C_LIO_LIPersistently reduced action potential firing rates of dentate PV+ interneurons in TLE mice C_LIO_LIEnhanced amplitude but decreased frequency of spontaneous IPSCs in the dentate gyrus in TLE mice C_LIO_LIIncreased amplitude of evoked IPSCs mediated by dentate PV+ interneurons in TLE mice C_LIO_LIChemogenetic activation of PV+ interneurons prevents epileptiform activity in TLE mice C_LI

neuroscience↗

bioRxiv2023

Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the "WIN" site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small molecule WIN site inhibitors, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anti-cancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anti-cancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

cancer biology↗

bioRxiv2022

In Situ Microwave Fixation to Define the Terminal Rodent Brain Metabolome

The brain metabolome directly connects to brain physiology and neuronal function. Brain glucose metabolism is highly heterogeneous among brain regions and continues postmortem. Therefore, challenges remain to capture an accurate snapshot of the physiological brain metabolome in healthy and diseased rodent models. To overcome this barrier, we employ a high-power focused microwave for the simultaneous euthanasia and fixation of mouse brain tissue to preserve metabolite pools prior to surgical removal and dissection of brain regions. We demonstrate exhaustion of glycogen and glucose and increase in lactate production during conventional rapid brain resection prior to preservation by liquid nitrogen that is not observed with microwave fixation. Next, microwave fixation was employed to define the impact of brain glucose metabolism in the mouse model of streptozotocin-induced type 1 diabetes. Using both total pool and isotope tracing analyses, we identified global glucose hypometabolism in multiple regions of the mouse brain, evidenced by reduced 13C enrichment into glycogen, glycolysis, and the TCA cycle. Reduced glucose metabolism correlated with a marked decrease in GLUT2 expression and several metabolic enzymes in unique brain regions. In conclusion, our study supports the incorporation of microwave fixation to study terminal brain metabolism in rodent models.

biochemistry↗

bioRxiv2021

Fast A-type currents shape a rapidly adapting form of delayed short latency firing of excitatory superficial dorsal horn neurons that express the NPY Y1 receptor

Neuroanatomical and behavioral evidence indicates that neuropeptide Y Y1 receptor-expressing interneurons (Y1-INs) in the superficial dorsal horn (SDH) are predominantly excitatory and contribute to chronic pain. Using an adult ex vivo spinal cord slice preparation from Y1eGFP reporter mice, we characterized firing patterns in response to steady state depolarizing current injection of GFP-positive cells in lamina II, the great majority of which expressed Y1 mRNA (88%). Randomly sampled and Y1eGFP neurons exhibited five firing patterns: tonic (TF), initial burst (IBF), phasic (PF), delayed short-latency <180 ms (DSLF), and delayed long-latency >180 ms (DLLF). When studied at resting membrane potential, most RS neurons exhibited delayed firing, while most Y1eGFP neurons exhibited phasic firing and not delayed firing. A preconditioning membrane hyperpolarization produced only subtle changes in the firing patterns of randomly sampled neurons, but dramatically shifted Y1eGFP neurons to DSLF (46%) and DLLF (24%). In contrast to randomly sampled DSLF neurons which rarely exhibited spike frequency adaptation, Y1eGFP DSLF neurons were almost always rapidly adapting, a characteristic of nociceptive-responsive SDH neurons. Rebound spiking was more prevalent in Y1eGFP neurons (6% RS vs 32% Y1eGFP), indicating enrichment of T-type calcium currents. Y1eGFP DSLF neurons exhibited fast A-type potassium currents that are known to delay or limit action potential firing, and these were of smaller current density as compared to randomly sampled DSLF neurons. Our results inspire future studies to determine whether tissue or nerve injury downregulates channels that contribute to A-currents, thus potentially unmasking T-type calcium channel activity and membrane hyperexcitability in Y1-INs, leading to persistent pain. KEYPOINTSO_LINeuropeptide Y Y1 receptor-expressing neurons in the dorsal horn of the spinal cord contribute to chronic pain. C_LIO_LIFor the first time, we characterized the firing patterns of Y1-expressing neurons in Y1eGFP reporter mice. C_LIO_LIUnder hyperpolarized conditions, most Y1eGFP neurons exhibited fast A-type potassium currents and delayed, short-latency firing (DSLF). C_LIO_LIY1eGFP DSLF neurons were almost always rapidly adapting and often exhibited rebound spiking, characteristics of spinal pain neurons under the control of T-type calcium channels. C_LIO_LIThese results inspire future studies to determine whether tissue or nerve injury downregulates the channels that underlie A-currents, thus unmasking membrane hyperexcitability in Y1- expressing dorsal horn neurons, leading to persistent pain C_LI

neuroscience↗

bioRxiv2020

MCL1 dependence across MDS subtypes and dual inhibition of MCL1 and BCL2 in MISTRG6 mice

Treatment for myelodysplastic syndromes (MDS) remains insufficient due to clonal heterogeneity and clinical complexity. Dysregulation of apoptosis is observed across MDS subtypes regardless of mutations and represents an attractive therapeutic opportunity. Venetoclax (VEN), a selective inhibitor of anti-apoptotic protein B-cell lymphoma-2 (BCL2), has yielded impressive responses in older patients with acute myeloid leukemia (AML). BCL2 family anti-apoptotic proteins BCL-XL and induced myeloid cell leukemia 1 (MCL1) are implicated in leukemia survival, and upregulation of MCL1 is seen in VEN-resistant AML and MDS. Here, we determined the in vitro sensitivity of MDS patient samples to selective inhibitors of BCL2, BCL-XL and MCL1. While VEN response positively correlated with increasing blast counts, all MDS subtypes responded to the MCL1 inhibitor, S63845. Treatment with combined VEN+S63845 was synergistic in all MDS subtypes and reduced MDS engraftment in MISTRG6 mice supporting the pursuit of clinical trials with combined BCL2+MCL1 inhibition in MDS.

cancer biology↗