Biology subjects

Rice, H. C.

Publications and source records attributed to Rice, H. C..

7 recordsLinked to original sources

bioRxiv2025

sAPPalpha inhibits neurite outgrowth in primary mouse neurons via GABA B Receptor subunit 1a

Neurite outgrowth is essential for neural circuit formation and is tightly regulated by secreted factors and their receptors. The secreted extracellular domain of the amyloid precursor protein (sAPP) has been shown to modulate neurite outgrowth. Recently, the gamma amino butyric acid receptor type-B subunit 1a (GABABR1a) was identified as an sAPP binding partner that mediates its effects on synaptic transmission. Here, we investigated whether this interaction also regulates neurite outgrowth. In primary hippocampal neurons, the GABABR agonist baclofen reduced axon length; whereas, its antagonist CGP54626 increased axon length in primary hippocampal neurons. Moreover, GABABR1a knockout increased axon length and abolished the effect of baclofen. Application of sAPP reduced axon length, an effect that required the presence of both GABABR1a and the extension domain of sAPP, which mediates its binding to GABABR1a. Similarly, the APP 17mer peptide, which is sufficient to bind GABABR1a and mimic the effects of sAPP on synaptic transmission, reduced axon outgrowth in wildtype but not in GABABR1a-deficient neurons. Together, these findings indicate that the 1a isoform contributes to GABABR-dependent suppression of neurite outgrowth and mediates the inhibitory effect of sAPP on neurite outgrowth. Statement of SignificanceAmyloid precursor protein (APP) plays a central role in Alzheimers disease, yet its normal functions are not fully understood. In this study, we uncover a previously unrecognized role of the GABA B Receptor in mediating the inhibitory effects of sAPP on neurite outgrowth. These findings provide mechanistic insight into how disruptions in APP signaling could influence both normal brain development and pathological processes in neurodevelopmental disorders and Alzheimers disease.

neuroscience↗

bioRxiv2025

Modeling presynaptic inhibition by the amyloid precursor protein demonstrates one potential mechanism for preventing runaway synaptic modification in Alzheimers disease

INTRODUCTIONPrevious simulations of Hebbian associative memory models inspired the malignant synaptic growth hypothesis of Alzheimers disease (AD), which suggests that cognitive impairments arise due to runaway synaptic modification resulting from poor separation between encoding and retrieval. METHODSWe computationally model presynaptic inhibition by the recently identified interaction of soluble amyloid precursor protein (sAPP) with the {gamma}-aminobutyric acid type B receptor (GABABR) as one potential biological mechanism which can enhance separation between encoding and retrieval. RESULTSSimulations predict that the dual effect of sAPP on long-term potentiation and presynaptic inhibition of glutamatergic synapses maintains effective associative memory function and prevents runaway synaptic modification. Moreover, computational modeling predicts that sAPP, which interacts with the 1a isoform of GABABR, is more effective at stabilizing associative memory than the GABABR agonist Baclofen. DISCUSSIONMolecular mechanisms that enhance presynaptic inhibition, such as sAPP-GABABR1a signaling, are potential therapeutic targets for preventing cognitive impairments in AD.

neuroscience↗

bioRxiv2025

Protocol to isolate oligodendrocytes, microglia, endothelial cells, astrocytes, and neurons from a single mouse brain using magnetic-activated cell sorting

The isolation of specific cell types of the brain is essential to study cell-type-specific differences in complex neurological diseases such as Alzheimers disease. This protocol isolates oligodendrocytes, microglia, endothelial cells, astrocytes, and neurons from a single mouse brain. The process involves gentle tissue homogenization, debris removal, and sequential sorting of five distinct cell types. We validate cell purity and viability using flow cytometry and RT-qPCR. This protocol is well-suited for a range of downstream applications, including genomics, transcriptomics, and proteomics. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/666877v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@1426b97org.highwire.dtl.DTLVardef@1a5bb77org.highwire.dtl.DTLVardef@1b69f32org.highwire.dtl.DTLVardef@8da416_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Tau conveys intrinsic hyperactivity of VTA dopamine neurons but an inability to sustain burst firing

INTRODUCTIONVentral tegmental area (VTA) dopamine has been implicated in neuropsychiatric symptoms observed in Alzheimers disease (AD) patients. Dopaminergic dysfunction and aberrant firing are observed in mouse AD models, but the specific roles of A{beta} and tau have not been determined. METHODSWe performed electrophysiological recordings of single VTA dopamine neuron firing in the 3xTg-AD model, followed by recordings in amyloid (APPNL-G-F)- and human tau (hTau)-based models to determine the pathological triggers of impaired firing. RESULTSIn vivo dopamine neuron recordings showed fewer spikes in defined bursts in 3xTg-AD mice versus controls. Ex vivo studies showed an impaired ability to sustain firing during depolarization, which was mimicked with depolarized current in wild type neurons. Dopamine neurons transduced with hTau reflected firing aberrations and impaired bursting, but the effects were not recapitulated in the APPNL-G-F model, DISCUSSIONThese results suggest that hTau specifically induces hyperexcitable states within individual dopamine neurons, disrupting burst firing. This dopaminergic dysfunction could compromise reward learning and contribute to the psychiatric symptoms observed in AD.

neuroscience↗

bioRxiv2023

17α-estradiol Alleviates High-Fat Diet-Induced Inflammatory and Metabolic Dysfunction in Skeletal Muscle of Male and Female Mice

Skeletal muscle has a central role in maintaining metabolic homeostasis. 17-estradiol (17-E2), a naturally-occurring non-feminizing diastereomer of 17{beta}-estradiol that demonstrates efficacy for improving metabolic outcomes in male, but not female, mice. Despite several lines of evidence showing that 17-E2 treatment improves metabolic parameters in middle-aged obese and old male mice through effects in brain, liver, and white adipose tissue little is known about how 17-E2 alters skeletal muscle metabolism, and what role this may play in mitigating metabolic declines. Therefore, this study aimed to determine if 17-E2 treatment improves metabolic outcomes in skeletal muscle from obese male and female mice following chronic high fat diet (HFD) administration. We hypothesized that male, but not female, mice, would benefit from 17-E2 treatment during HFD. To test this hypothesis, we used a multi-omics approach to determine changes in lipotoxic lipid intermediates, metabolites, and proteins related to metabolic homeostasis. In male mice, we show that 17-E2 alleviates HFD-induced metabolic detriments of skeletal muscle by reducing the accumulation of diacylglycerol (DAGs) and ceramides, inflammatory cytokine levels, and reduced the abundance of most of the proteins related to lipolysis and beta-oxidation. In contrast to males, 17-E2 treatment in female mice had little effect on the DAGs and ceramides content, muscle inflammatory cytokine levels, or changes to the relative abundance of proteins involved in beta-oxidation. These data support to the growing evidence that 17-E2 treatment could be beneficial for overall metabolic health in male mammals.

physiology↗

bioRxiv2023

Microglial MHC-I induction with aging and Alzheimer's is conserved in mouse models and humans

Major Histocompatibility Complex I (MHC-I) CNS cellular localization and function is still being determined after previously being thought to be absent from the brain. MHC-I expression has been reported to increase with brain aging in mouse, rat, and human whole tissue analyses but the cellular localization was undetermined. Neuronal MHC-I is proposed to regulate developmental synapse elimination and tau pathology in Alzheimers disease (AD). Here we report that across newly generated and publicly available ribosomal profiling, cell sorting, and single-cell data, microglia are the primary source of classical and non-classical MHC-I in mice and humans. Translating Ribosome Affinity Purification-qPCR analysis of 3-6 and 18-22 month old (m.o.) mice revealed significant age-related microglial induction of MHC-I pathway genes B2m, H2-D1, H2-K1, H2-M3, H2-Q6, and Tap1 but not in astrocytes and neurons. Across a timecourse (12-23 m.o.), microglial MHC-I gradually increased until 21 m.o. and then accelerated. MHC-I protein was enriched in microglia and increased with aging. Microglial expression, and absence in astrocytes and neurons, of MHC-I binding Leukocyte Immunoglobulin-like (Lilrs) and Paired immunoglobin-like type 2 (Pilrs) receptor families could enable cell-autonomous MHC-I signaling and increased with aging in mice and humans. Increased microglial MHC-I, Lilrs, and Pilrs were observed in multiple AD mouse models and human AD data across methods and studies. MHC-I expression correlated with p16INK4A, suggesting an association with cellular senescence. Conserved induction of MHC-I, Lilrs, and Pilrs with aging and AD opens the possibility of cell-autonomous MHC-I signaling to regulate microglial reactivation with aging and neurodegeneration.

neuroscience↗

bioRxiv2022

Hypothalamic melanocortin-4 receptors on astrocytes mediate inflammation and body weight homeostasis

World-wide, nearly 40% of the adult population is classified as clinically obese. Central inflammation is highly correlated with obesity and increases morbidity and deterioration of health. The hypothalamus is a brain region that governs many facets of energy homeostasis, and melanocortins in the hypothalamus both decrease feeding and increase metabolism via melanocortin-4 receptors (MC4Rs). Although MC4Rs are present on neurons and astrocytes (aMC4R) previous work has focused almost exclusively on the neuronal population with the contribution of aMC4R on these processes largely unknown. Our objective was to determine the effects of hypothalamic aMC4R deletion on central and peripheral inflammation, as well as feeding and body weight homeostasis. Adult MC4R fl/fl mice were microinjected with an astrocyte-specific promoter driving Cre-expression (AAV-GFAP-GFP-Cre) or AAV-control (AAV-GFAP-GFP; n=4-7/group/sex) to produce a hypothalamic knock-down of aMC4R (KD). Body weight and composition were monitored throughout the study, and indirect calorimetry was conducted at 1 and 4 weeks after AAV injection. Acquisition of operant self-administration of palatable food was also examined. Mice were euthanized 7-8 weeks post AAV injection and brain and tissue samples were collected. We observed a significant increase in body weight, feeding, and energy balance in the KD group compared to control group. Inflammation was significantly increased centrally in KD mice within the hypothalamus, but not peripherally within serum. Additionally, aMC4R KD mice trended towards an increased reward learning for palatable food. This is the first demonstration that hypothalamic aMC4R, independent of neuronal MC4R, is important in modulating inflammation as well as contributing to energy balance. These results provide an integral understanding of the aMC4R system that will provide the foundation for future studies investigating the role of aMC4R in various disease states.

neuroscience↗