Biology subjects

Conant, K.

Publications and source records attributed to Conant, K..

13 recordsLinked to original sources

bioRxiv2026

4-methylumbelliferone attenuates amyloid pathology and learning deficits in the APP/PS1 mouse model

4-Methylumbelliferone (4-MU) inhibits hyaluronic acid (HA) synthesis and is currently approved in Europe for biliary spasm. 4-MU administration reduces perineuronal nets (PNNs), and enzymatic degradation of PNNs in mouse models of Alzheimers disease (AD) attenuates memory impairment. Although 4-MU has therapeutic efficacy in rodent models of fibrosis and cancer, it has not been examined in an Alzheimers model. Here, we evaluated the impact of long-term 4-MU treatment in the APP/PS1 amyloid mouse model. From three months of age, mice were on either a vehicle or 4-MU-supplemented diet for 70 days or 52 weeks. Short and long-term 4-MU treatment decreased the soluble parenchymal A{beta}1-42/A{beta}1-40 ratio. Reductions in insoluble amyloid plaque were observed following 52 weeks of treatment. Extended 4-MU administration also reduced PNN intensity and ameliorated spatial memory deficits in APP/PS1 mice. These findings provide support for targeting brain extracellular matrix (ECM) as a therapeutic strategy for AD.

neuroscience↗

bioRxiv2025

Varied monoamine reuptake inhibitors reduce parvalbumin expression; implications for pyramidal cell disinhibition and enhanced neuroplasticity

First-line antidepressants are effective in a significant percent of individuals but a full understanding of how these therapeutics target specific endpoints is lacking. Prior work has shown that depression is associated with hippocampal atrophy and that antidepressants can increase neurotrophin levels to increase hippocampal neurogenesis as well as hippocampal pyramidal cell (PC) spine density and arbor. These effects likely contribute to amelioration of symptoms. A less well-explored possibility is that antidepressants concomitantly disinhibit hippocampal PC activity, which could also facilitate increased PC arbor, spinogenesis and/or activity. In accordance, previous studies have shown antidepressants can attenuate stress-induced upregulation of perineuronal nets (PNNs). PNNs are predominantly localized to parvalbumin (PV) expressing GABAergic interneurons and increase PV expression and neuronal activity. Though specific antidepressants have been explored for effects on regional PNN expression, the question of whether hippocampal PNN/ECM remodeling is a shared feature of varied antidepressant drugs and more importantly, of whether it is associated with significant hippocampal PV inhibition, has not been well-addressed. Herein we examine three monoamine reuptake inhibitors, fluoxetine, venlafaxine and viloxazine, in animal models for effects on PNN remodeling and PV expression, a proxy for PV activity. We observe shared effects of these therapeutics including the ability to increase PNN degrading effectors that can downregulate PV activity. Consistent with this, we observe shared effects of these drugs in terms of their ability to significantly reduce PV levels. These findings highlight the possibility that ECM remodeling and associated hippocampal PC disinhibition represent a shared feature of varied antidepressant medications.

neuroscience↗

bioRxiv2025

Increased levels of HAPLN2, which anchors dense extracellular matrix, in the hippocampus of APOE4 targeted replacement mice

Hyaluronan and proteoglycan link protein 2 (HAPLN2) / Brain link protein-1 (Bral1) is important for the binding of chondroitin sulfate proteoglycans (CSPGs) to hyaluronan and thus for the formation of specific types of brain extracellular matrix (ECM). It is also significantly increased with aging. Moreover, machine learning has identified it as a brain-derived protein most predictive of Alzheimers disease (AD). HAPLN2 binds to CSPGs that may sequester aggregation-prone proteins and also restrict neuronal plasticity. Because the apolipoprotein 4 (APOE4) allele increases AD risk, in the present study we have examined hippocampal lysates from APOE3 and APOE4 targeted replacement (TR) mice using unbiased proteomics, Western blot and hippocampal immunostaining. With proteomics, we observe that HAPLN2 is among the most significantly upregulated proteins in APOE4 mice. Prior work suggests HAPLN2 is particularly important to the assembly of perinodal matrix, and herein we show that it also co-localizes with Wisteria floribunda agglutinin (WFA) positive perineuronal nets (PNNs). PNNs represent a dense form of ECM that can increase GABAergic neurotransmission to alter overall excitatory/inhibitory (E/I) balance and neuronal oscillations important to mood and memory. Proteomics also detected elevated levels of high temperature requirement peptidase-1 (HTRA1), which accumulates in cerebral blood vessels harboring amyloid, in APOE4 mice. In Western blot studies, lysates from APOE4 mice also showed significantly reduced levels chondroitin-6 sulfated proteoglycans, which makes PNNs more susceptible to proteolysis and less inhibitory. In addition, immunostaining studies showed that levels of the PNN component aggrecan were increased in the hippocampus of APOE4 animals. Overall, these findings contribute to an emerging body of literature suggesting that brain extracellular matrix may be altered with aging and other risk factors for AD, and suggest that future studies should assess PNNs, peri-nodal structure and axonal conduction in the background of APOE4.

neuroscience↗

bioRxiv2025

CCL5/CCR5 signaling modulates depression-relevant behavior, neuronal oscillations, and long-term depression of synaptic activity.

Major depressive disorder (MDD) is a debilitating disorder, often associated with perseverative thinking and anxiety. Localized reductions in pyramidal cell activity may contribute to associated symptoms, and effective antidepressant treatments typically enhance overall neuronal excitation. CCL5 is a chemokine that has been shown to reduce excitatory-neuronal activity, and is also increased with MDD and conditions that increase MDD risk. Here, we investigate the CCL5/CCR5 axis for its ability to modulate depression-relevant endpoints that are diminished in MDD, including neuronal oscillations, as well as biochemical and behavioral correlates of the disorder. In comparison to wildtype mice, CCR5 knockouts had increased gamma and theta power, and stronger theta/high-gamma phase amplitude coupling during dark-cycle EEG recordings. Compared to strain-matched wildtype mice, CCR5 knockouts also demonstrated reduced anxiety, increased sucrose preference, and improved associative memory. Proteomic analysis of the hippocampus showed that CCR5 knockouts had reduced levels of the GABA receptor alpha-4 subunit, which mediates tonic inhibition and restricts pyramidal cell plasticity. In complementary primary neuronal culture studies, CCL5 diminished GSK-3{beta} activity and impaired NMDA-dependent long-term depression (LTD), a form of plasticity that promotes cognitive flexibility. In addition, CCL5 signaling increased parvalbumin expression in GABAergic neurons through a CCR5-dependent manner. In combination with the ability of CCR5 to restrain gamma oscillation power and LTD, our data raise the possibility that CCL5/CCR5 signaling inhibits neuronal excitation through increased PV+ interneuron activity. Moreover, data are consistent with the possibility that CCR5 antagonists might share the ability of established antidepressants to both increase PC excitation and reduce PC inhibition. Significance StatementMajor depressive disorder (MDD) is a global leading cause of disability, and is associated with increased chemokine activation and inflammation. In this study, we investigate how the CCR5/CCL5 chemokine axis regulates behavioral and cognitive endpoints associated with MDD. This study aims to provide insight to how chemokine signaling underlies mood and behavioral symptoms of neuropsychiatric disorders. We hope this research supports further investigation of CCR5 antagonists for MDD and related mood and anxiety disorders.

neuroscience↗

bioRxiv2025

MMP-2/9 inhibition modulates sharp wave abundance, inhibitory proteoglycan sulfation, and fear memory in juvenile zebrafish: relevance to affective disorders

Sharp wave ripple (SWR) events, present in diverse species, spontaneously occur in the hippocampus during quiescent restfulness and slow-wave sleep. SWRs comprise a negative deflection, the sharp wave (SW) event with an often-superimposed ripple (R) and are the neural correlates of memory consolidation and recall. The Anterodorsolateral lobe (ADL) (zebrafish hippocampal homologue) exhibits SW and SWR events, and since SWs initiate SWRs, their abundance typically shows the same directionality. In previous work, we observed matrix metalloproteinase-9 (MMP-9)-dependent effects on depression-relevant behaviors, perineuronal net (PNN) levels, and SWR abundance in the adult rodent hippocampus. Here, we investigate MMP-2/9-dependent effects on biochemical, behavioral, and neurophysiological endpoints in juvenile zebrafish and zebrafish at the transition from the late juvenile period to early adulthood. With MMP-2/9 inhibition, juvenile zebrafish showed reduced SW amplitude and abundance together with increased fear memory retention and reduced sociability. Juvenile zebrafish also showed an increased percentage of longer-duration SW events. Except for a reduction in SW amplitude, these changes were not observed at the transition from late juvenile to early adulthood. These changes were accompanied by increased levels of chondroitin sulfate (CS) proteoglycan 4-O-sulfation, which modulates PNNs and excitatory-to-inhibitory (E/I) balance. Discontinuation of MMP-2/9 inhibition in juvenile zebrafish normalized deficits in ADL SW abundance and sociability. Together, these findings show that MMP-2/9 significantly influences E/I balance and learning and memory during the highly plastic juvenile period in zebrafish. Findings also have relevance to an emerging appreciation of PNN changes that may contribute to altered neuronal oscillations and mood or cognition.

neuroscience↗

bioRxiv2023

Radial glia control microglial differentiation via integrin avb8-dependent trans-activation of TGFB1

Microglia diversity emerges from interactions between intrinsic genetic programs and environment-derived signals, but how these processes unfold and interact in the developing brain remains unclear. Here, we show that radial glia-expressed integrin beta 8 (ITGB8) expressed in radial glia progenitors activates microglia-expressed TGF{beta}1, permitting microglial development. Domain-restricted deletion of Itgb8 in these progenitors establishes complementary regions with developmentally arrested "dysmature" microglia that persist into adulthood. In the absence of autocrine TGF{beta}1 signaling, we find that microglia adopt a similar dysmature phenotype, leading to neuromotor symptoms almost identical to Itgb8 mutant mice. In contrast, microglia lacking the TGF{beta} signal transducers Smad2 and Smad3 have a less polarized dysmature phenotype and correspondingly less severe neuromotor dysfunction. Finally, we show that non-canonical (Smad-independent) signaling partially suppresses disease and development associated gene expression, providing compelling evidence for the adoption of microglial developmental signaling pathways in the context of injury or disease.

immunology↗

bioRxiv2023

Sharp wave ripple coupling in zebrafish hippocampus and basolateral amygdala

The mammalian hippocampus exhibits sharp wave events (1-30 Hz) with an often-present superimposed fast ripple oscillation (120-200 Hz) forming a sharp wave ripple (SWR) complex. During slow wave sleep or consummatory behaviors, SWRs result from the sequential spiking of hippocampal cell assemblies initially activated during imagined or learned experiences. SWRs occur in tandem with cortical/subcortical assemblies critical to the long-term storage of specific memory types. Leveraging juvenile zebrafish, we show that SWR events in their hippocampal homologue, the anterodorsolateral lobe (ADL), in ex vivo whole-brains are locally generated and maintained. SWR events were also recorded in the basolateral amygdala (BLA). Concomitant single cell calcium imaging and local field potential (LFP) recordings showed that BLA SWs couple to ADL SWs. Calcium imaging recordings of whole-brains demonstrated that ADL and BLA SWRs are endogenously and spontaneously silenced by the activation of a more caudal population of putative cholinergic cells. Electrical stimulation of this caudal region silenced ADL SWs. Our results suggest that the SWR-generating circuit is evolutionarily conserved through shared acetylcholine modulating mechanisms. These findings further our understanding of neuronal population dynamics in the zebrafish brain and highlights their advantage for simultaneously recording SW/SWRs and single cell activity in diverse brain regions.

neuroscience↗

bioRxiv2022

CCR5 deficiency normalizes TIMP levels, working memory, and gamma oscillation power in APOE4 targeted replacement mice

The APOE4 allele increases the risk for Alzheimers disease (AD) in a dose-dependent manner and is also associated with cognitive decline in non-demented elderly controls. In mice with targeted gene replacement (TR) of murine APOE with human APOE3 or APOE4, the latter show reduced neuronal dendritic complexity and impaired learning. APOE4 TR mice also show reduced gamma oscillation power and sharp wave ripple (SWR) abundance, neuronal population activities important to learning and memory. Published work has shown that brain extracellular matrix (ECM) can reduce neuroplasticity as well as gamma power and SWR abundance, while attenuation of ECM can instead enhance these endpoints. In the present study we examine human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 individuals and brain lysates from APOE3 and APOE4 TR mice for levels of ECM effectors that can increase matrix deposition and restrict neuroplasticity. We find that CCL5, a molecule linked to ECM deposition in liver and kidney, is increased in CSF samples from APOE4 individuals. Levels of tissue inhibitor of metalloproteinases (TIMPs), which inhibit the activity of ECM-degrading enzymes, are also increased in APOE4 CSF as well as protein lysates from APOE4 TR mice. Importantly, as compared to wildtype/APOE4 heterozygotes, CCR5 knockout/APOE4 heterozygotes show reduced TIMP levels and enhanced EEG gamma power. The latter also show improved learning and memory, suggesting that the CCR5/CCL5 axis could represent a therapeutic target for APOE4 individuals.

neuroscience↗

bioRxiv2020

Inhibitory parvalbumin basket cells are selectively impaired during hippocampal sharp wave ripples in a mouse model of familial Alzheimer's disease

Memory disruption in mild cognitive impairment (MCI) and Alzheimers disease (AD) is poorly understood, particularly at early stages preceding neurodegeneration. In mouse models of AD, there are disruptions to sharp wave ripples (SWRs), hippocampal population events with a critical role in memory consolidation. However, the micro-circuitry underlying these disruptions is under-explored. We tested if a selective reduction in parvalbumin-expressing (PV) inhibitory interneuron activity underlies hyperactivity and SWR disruption. We employed the 5xFAD model of familial AD crossed with mouse lines labeling excitatory pyramidal cells (PCs) and inhibitory PV cells. We observed a 33% increase in frequency, 58% increase in amplitude, and 8% decrease in duration of SWRs in ex vivo slices from male and female 3-month 5xFAD mice versus littermate controls. 5xFAD mice of the same age were impaired in a hippocampal-dependent memory task. Concurrent with SWR recordings, we performed calcium imaging, cell-attached, and whole-cell recordings of PC and PV cells within the CA1 region. PCs in 5xFAD mice participated in enlarged ensembles, with superficial PCs having a higher probability of spiking during SWRs. Both deep and superficial PCs displayed an increased synaptic E/I ratio, suggesting a disinhibitory mechanism. In contrast, we observed a 46% spike rate reduction during SWRs in PV basket cells (PVBCs), while PV bistratified and axo-axonic cells were unimpaired. Excitatory synaptic drive to PVBCs was selectively reduced by 50%, resulting in decreased E/I ratio. Considering prior studies of intrinsic PV cell dysfunction in AD, these findings suggest alterations to the PC-PVBC micro-circuit also contribute to impairment. Significance StatementWe demonstrate that a specific sub-type of inhibitory neuron, parvalbumin-expressing basket cells, have selectively reduced activity in a model of Alzheimers disease during activity critical for the consolidation of memory. These results identify a potential cellular target for therapeutic intervention to restore aberrant network activity in early amyloid pathology. While parvalbumin cells have previously been identified as a potential therapeutic target, this study for the first time recognizes that other parvalbumin neuronal sub-types, including bistratified and axo-axonic cells, are spared. These experiments are the first to record synaptic and spiking activity during sharp wave ripple events in early amyloid pathology and reveal that a selective decrease in excitatory synaptic drive to parvalbumin basket cells likely underlies reduced function.

neuroscience↗

bioRxiv2019

Venlafaxine stimulates an MMP-9-dependent increase in excitatory/inhibitory balance in a stress model of depression

Emerging evidence suggests that there is a reduction in overall cortical excitatory to inhibitory balance in major depressive disorder (MDD), which afflicts approximately 14-20% of individuals. Reduced pyramidal cell arborization occurs with stress and MDD, and may diminish excitatory neurotransmission. Enhanced deposition of perineuronal net (PNN) components also occurs with stress. Since parvalbumin-expressing interneurons are the predominant cell population that is enveloped by PNNs, which enhance their ability to release GABA, excess PNN deposition likely increases pyramidal cell inhibition. In the present study we investigate the potential for matrix metalloprotease-9 (MMP-9), an endopeptidase secreted in response to neuronal activity, to contribute to the antidepressant efficacy of venlafaxine, a serotonin/norepinephrine reuptake inhibitor. Chronic venlafaxine increases MMP-9 levels in murine cortex, and increases both pyramidal cell arborization and PSD-95 expression in the cortex of wild-type but not MMP-9 null mice. We have previously shown that venlafaxine reduces PNN deposition and increases the power of ex vivo gamma oscillations in conventionally-housed mice. Gamma power is increased with pyramidal cell disinhibition and with remission from MDD. Herein we observe that PNN expression is increased in a corticosterone-induced stress model of disease and reduced by venlafaxine. As compared to mice that receive concurrent venlafaxine, corticosterone treated mice also display reduced ex vivo gamma power and impaired working memory. Autopsy-derived prefrontal cortex samples show elevated MMP-9 levels in anti-depressant treated MDD patients as compared to controls. These preclinical and postmortem findings highlight a link between extracellular matrix regulation and MDD.

neuroscience↗

bioRxiv2019

A New Role for Telomerase in Promoting Meiotic Homolog Pairing Fidelity

We report a role for telomerase, beyond its known function of telomeric DNA end extension, in maintaining normal chromosome dynamics during meiosis in Saccharomyces cerevisiae. When telomerase at telomeres was reduced by various genetic means, increased frequencies of crossover and noncrossover recombination events occurred. To investigate the mechanism of this increased meiotic recombination, we examined the kinetics of meiosis events, and tracked the movement of chromosomes in live cells during meiotic prophase. Cytoskeletal forces acting on telomeres during meiosis have been shown to promote active chromosome motion needed to pair homologous chromosomes. Here we show that changes in telomerase interaction with telomeres using a tlc1-11 mutant result in altered meiotic motion. Specifically, reduction in telomerase at telomeres leads to a decreased frequency of high velocity chromosome pulls. In the tlc1-11 mutant, we see earlier synapsis and increased genome-wide recombination for the majority of the cells and lower gamete viability. Notably, homologous pairing is not delayed unlike other telomere binding mutants. Although synapsis initiates earlier, the overall timing of synapsis remains the same, except for a subset of cells that do not exit meiosis I. Together, these results suggest that the strong pulling component of the active chromosome motion promotes homolog pairing fidelity, likely by pulling apart improperly associated regions. Our combined observations are consistent with a model in which telomerase-mediated telomeric anchoring to the nuclear envelope helps engage and properly transmit cytoskeletal forces to chromosomes. Thus, telomerase contributes to efficient chromosome movements leading to normal gamete viability.

cell biology↗

bioRxiv2018

Venlafaxine stimulates PNN proteolysis and MMP-9 dependent enhancement of gamma power; relevance to antidepressant efficacy

Drugs that target monoaminergic transmission represent a first-line treatment for major depression. Though a full understanding of the mechanisms that underlie antidepressant efficacy is lacking, evidence supports a role for enhanced excitatory transmission. This can occur through two non-mutually exclusive mechanisms. The first involves increased function of excitatory neurons through relatively direct mechanisms such as enhanced dendritic arborization. Another mechanism involves reduced inhibitory function, which occurs with the rapid antidepressant ketamine. Consistent with this, GABAergic interneuron-mediated cortical inhibition is linked to reduced gamma oscillatory power, a rhythm also diminished in depression. Remission of depressive symptoms correlates with restoration of gamma power.\n\nDue to strong excitatory input, reliable GABA release and fast firing, PV neurons represent critical pacemakers for synchronous oscillations. PV neurons also represent the predominant GABAergic population enveloped by perineuronal nets (PNNs), lattice-like structures that localize glutamatergic input. Disruption of PNNs enhances lateral diffusion of glutamate receptors, reduces PV excitability, and enhances gamma activity.\n\nStudies suggest that monoamine reuptake inhibitors reduce integrity of the PNN. Mechanisms by which these inhibitors reduce PNN integrity, however, remain largely unexplored. A better understanding of these issues might encourage development of therapeutics that best upregulate PNN modulating proteases.\n\nWe observe that the serotonin/norepinephrine reuptake inhibitor venlafaxine reduces PNN integrity in murine brain. Moreover, venlafaxine treated mice (30 mg/kg/day) show an increase in carbachol-induced gamma power in hippocampal slices. Studies with mice deficient in matrix metalloproteinase-9 (MMP-9), a protease linked to PNN disruption in other settings, suggest that MMP-9 contributes to venlafaxine-enhanced gamma activity.

neuroscience↗

bioRxiv2017

Disruption of perineuronal nets increases the frequency of sharp wave ripples

Hippocampal sharp wave ripples (SWRs) represent irregularly occurring synchronous neuronal population events that are observed during phases of rest and slow wave sleep. SWR activity that follows learning involves sequential replay of training-associated neuronal assemblies and is critical for systems level memory consolidation. SWRs are initiated by CA2 or CA3 pyramidal cells and require initial excitation of CA1 pyramidal cells as well as subsequent participation of parvalbumin (PV) expressing fast spiking (FS) inhibitory interneurons. These interneurons are relatively unique in that they represent the major neuronal cell type known to be surrounded by perineuronal nets (PNNs), lattice like structures composed of a hyaluronin backbone that surround the cell soma and proximal dendrites. Though the function of the PNN is not completely understood, previous studies suggest it may serve to localize glutamatergic input to synaptic contacts and thus influence the activity of ensheathed cells. Noting that FS PV interneurons impact the activity of pyramidal cells thought to initiate SWRs, and that their activity is critical to ripple expression, we examine the effects of PNN integrity on SWR activity in the hippocampus. Extracellular recordings from the stratum radiatum of 490 micron horizontal murine hippocampal hemisections demonstrate SWRs that occur spontaneously in CA1. As compared to vehicle, pretreatment (120 min) of paired hemislices with hyaluronidase, which cleaves the hyaluronin backbone of the PNN, decreases PNN integrity and increases SWR frequency. Pretreatment with chondroitinase, which cleaves PNN side chains, also increases SWR frequency. Together, these data contribute to an emerging appreciation of extracellular matrix as a regulator of neuronal plasticity and suggest that one function of mature perineuronal nets could be to modulate the frequency of SWR events.

neuroscience↗