Biology subjects

Campbell, S. A.

Publications and source records attributed to Campbell, S. A..

11 recordsLinked to original sources

bioRxiv2026

The regulator of G protein signaling RGS9 supports insulin secretion in male mouse islets

Objectives Regulators of G protein signaling (RGS) proteins terminate G protein-coupled receptor signaling and regulate multiple aspects of pancreatic islet function. Although RGS9 is highly enriched in human and rodent islets, its cellular localization and physiological role remain largely unknown. Here, we investigated the expression of Rgs9 in mouse islets and its contribution to insulin secretion. Methods Rgs9 expression was characterized by RNA in situ hybridization and fluorescence-activated cell sorting coupled with quantitative PCR. Rgs9 function was investigated by shRNA-mediated knockdown in wild-type and Dishevelled, Egl-10 and Pleckstrin (DEP) domain-deficient Rgs9 mutant (Rgs9{Delta}DEP/{Delta}DEP) mouse pseudo-islets. Results Rgs9 was detected throughout the endocrine pancreas but was enriched in {beta} and {delta}cells, with the Rgs9-1 isoform representing the predominant splice variant in mouse islets. Rgs9 knockdown in mouse pseudo-islets impaired glucose- and KCl-stimulated insulin secretion without affecting insulin content. In contrast, Rgs9{Delta}DEP/{Delta}DEP mouse islets failed to reproduce this phenotype. Further characterization of the mutant mice revealed persistent expression of Rgs9 transcripts, which when knocked down impaired both glucose- and KCl-stimulated insulin secretion. Conclusions These data indicate that RGS9 supports glucose-stimulated insulin secretion. Given that RGS9 acts exclusively on Gi/o, our results further suggest that RGS9 in {beta} cells dampens inhibitory signaling to promote insulin secretion. Finally, the Rgs9{Delta}DEP/{Delta}DEP mutant does not represent a complete loss-of-function in islets likely due to the retention of the GTPase-activating protein (GAP) activity in the absence of the DEP domain.

cell biology↗

bioRxiv2026

Targeting Microbial Bile Salt Hydrolase Reprograms Bile Acid Metabolism and Ameliorates Metabolic Dysfunction-Associated Steatohepatitis in Mice

Microbial bile salt hydrolase (BSH) plays a central role in shaping bile acid composition and gut-liver metabolic signaling, yet its therapeutic potential in metabolic dysfunction-associated steatohepatitis (MASH) remains incompletely defined. Here, we evaluated the efficacy of the non-absorbable BSH inhibitor GR-7 in a diet induced mouse model of steatohepatitis using early and late intervention strategies with different dosing regimens. GR-7 reduced food intake and exerted stage- and dose-dependent therapeutic effects, with early intervention robustly suppressing hepatic fibrosis even at low dose, whereas late-stage administration of high-dose GR-7 markedly reduced hepatic steatosis and inflammation, as evidenced by decreased liver weight, hepatic triglyceride and cholesterol levels, and plasma ALT. Although late intervention did not result in statistically significant histological reversal of fibrosis, a trend toward improvement was observed, together with suppression of fibrogenic gene expression, suggesting that prolonged treatment may further enhance antifibrotic efficacy. Mechanistically, GR-7 effectively inhibited microbial BSH activity in vivo, leading to reduced cecal unconjugated primary and secondary bile acids--including deoxycholic acid and lithocholic acid, which was associated with improved gut barrier integrity and reduced hepatic inflammation. In parallel, BSH inhibition reprogrammed hepatic bile acid metabolism toward activation of the alternative CYP27A1-mediated synthesis pathway, accompanied by reduced food intake, thereby contributing to improved hepatic lipid accumulation. Furthermore, late-stage high-dose treatment selectively remodeled the hepatic immune landscape rather than fully restoring homeostasis, highlighting immune recalibration as a key component of therapeutic response. Together, these findings identify microbial BSH inhibition as a promising microbiome-targeted therapeutic strategy for MASH. HighlightsO_LIThe non-absorbable BSH inhibitor GR-7 improves steatosis, inflammation, and fibrosis in of Western diet-induced steatohepatitis model in mice in a dose-dependent manner. C_LIO_LIGR-7 reduces food intake and body weight gain. C_LIO_LIGR-7 reduces cytotoxic secondary bile acids, including DCA and LCA. C_LIO_LIGR-7 reprograms hepatic bile acid metabolism and immune responses. C_LI

pharmacology and toxicology↗

bioRxiv2025

Computational Modelling of Resistance to Hormone-Mediated Remission in Childhood Absence Epilepsy

Childhood absence epilepsy (CAE) often resolves during adolescence, a period marked by hormonal and neurosteroid changes associated with puberty. However, remission does not occur in all individuals. To investigate this clinical heterogeneity, we developed a simplified thalamocortical model with a layered cortical structure, using deep-layer intrinsically bursting (IB) neurons to represent frontal cortex and regular spiking (RS) neurons modelling the parietal cortex. By simulating two cortical configurations, we explored how variations in neuronal composition and frontocortical connectivity influence seizure dynamics and the effectiveness of allopregnanolone (ALLO) in resolving pathological spike-wave discharges (SWDs) associated with CAE. While both models exhibited similar physiological and pathological oscillations, only the parietal-dominant network (with a higher proportion of regular spiking neurons in layer 5) recovered from SWDs under increased frontocortical connectivity following ALLO administration. These findings suggest that neuronal composition critically modulates ALLO-mediated resolution of SWDs, providing a mechanistic link between structural connectivity and clinical outcomes in CAE, and highlighting the potential for personalized treatment strategies based on underlying network architecture.

neuroscience↗

bioRxiv2025

Experimental wildflower additions increase pollination in urban agroecosystems

O_LIThe addition of nectar-rich flower patches in human-modified ecosystems is a common practice to mitigate pollinator declines and boost pollination. However, the benefits of these additions for pollinator communities and pollination services are rarely tested, especially in urban environments. C_LIO_LIIn a city-scale experiment we added floral resources to urban allotments and monitored the effects on bees, hoverflies and moths, and tested for improved seed set in a model crop (tomato, Solanum lycopersicum). C_LIO_LIThe addition of wildflowers did not benefit all insect communities. Only social bee abundance (Bombus and Apis) benefitted from increasing floral resource area whereas other insect taxa showed no changes in abundance potentially due to the divergence in foraging patterns of moths, hoverflies, social bees and solitary bees. The addition of wildflower patches enhanced pollination by supporting a 25.3% increase in tomato seed set, providing evidence that wildflower interventions can improve urban pollination. Seed set was higher in more urban sites, suggesting an "oasis effect" where pollinating insects are concentrated into limited greenspaces. This highlights the precarity of pollination services in highly urban areas. C_LIO_LIOur results suggest that the practice of planting wildflower patches can positively affect pollination services in urban areas. The continued promotion of flower patch addition is likely to benefit some key insect taxa, however, the common wildflower species in seed mixes may not benefit hoverflies and moths compared to bees. The taxon-specific foraging patterns we observed should inform the design and development of pollinator-friendly wildflower seed mixes. C_LI Societal impact statementEnhancing urban greenspaces for pollinator communities by planting wildflower patches is increasingly common, but their efficacy for different groups of insects (bees, hoverflies and moths) is unclear. Our city-scale experiment demonstrated that wildflower patches benefitted the abundance of social bees, but did not increase other groups. Wildflower addition increased pollination services, with an increase in seed-set in our model crop, particularly in more urban areas. Wildflower patches do benefit pollinator communities and in turn humans, through the pollination services, but the species mix may not benefit some insect groups. This suggests there is potential to improve the benefit provided by wildflower patches by redesigning pollinator-friendly seed mixes.

ecology↗

bioRxiv2024

Supplementing floral resources does not mitigate the negative effects of urbanisation on cavity-nesting bees and wasps.

O_LICavity-nesting bees and wasps provide essential ecosystem services such as pollination and pest control. Within urban environments, it is likely that cavity-nesting insects are using greenspaces to forage for food and nesting resources, and thus may benefit from urban greenspace management interventions, such as the addition of flower patches and "bee hotels" (trap nests). C_LIO_LIIn contrast to the relatively large body of work demonstrating the effects of wildflower provisioning on bees in an agricultural context, there have been few studies testing the benefits of floral provisioning, or the relative importance of nest site and food constraints on urban cavity-nesting bees and wasps. Consequently, we lack an empirical evidence base for optimising and informing conservation interventions for these taxa. C_LIO_LITo understand how the addition of floral resources influences cavity-nesting insect communities, we conducted a 2-year study in urban greenspaces used for horticulture (allotments). We manipulated floral and nesting resources by adding nectar-rich flower patches and artificial trap nests, and compared nest colonisation by cavity-nesting bees and wasps in sites with floral additions and where no additions were made. Our sites were configured along an urbanisation gradient, allowing us to examine how surrounding urbanisation influenced these patterns. C_LIO_LIContrary to our predictions, we found no significant difference in trap nest uptake in sites where floral resources were added, compared to control sites. However, cavity-nesting insect abundance showed a 6-fold decrease over our urbanisation gradient. The addition of floral resources did not mitigate the negative effects of urbanisation on cavity-nesting insects. C_LI Synthesis and Applications: Although enhancing floral resources in urban systems is a recognised strategy for conserving key pollinators such as social bees, our findings suggest that this approach alone does not address the challenges faced by cavity-nesting bees or wasps in urban landscapes. Our results suggest that accounting for the diversity of resource requirements and incorporating landscape-scale analysis is essential to ensure local conservation interventions will benefit a diversity of insect communities.

ecology↗

bioRxiv2023

Modelling the Effect of Allopregnanolone on the Resolution of Spike-Wave Discharges

ObjectiveChildhood absence epilepsy (CAE) is a paediatric generalized epilepsy disorder with a confounding feature of resolving in adolescence in a majority of cases. In this study, we modelled how the small-scale (synapse-level) effect of progesterone metabolite allopregnanolone induces a large-scale (network-level) effect on a thalamocortical circuit associated with this disorder. In particular, our goal was to understand the role of sex steroid hormones in the spontaneous remission of CAE. MethodsThe conductance-based computational model consisted of single-compartment cortical pyramidal, cortical interneurons, thalamic reticular and thalamocortical relay neurons, each described by a set of ordinary differential equations. Excitatory and inhibitory synapses were mediated by AMPA, GABAa and GABAb receptors. The model was implemented using the NetPyne modelling tool and the NEURON simulator. ResultsThe action of allopregnanolone on individual GABAa-receptor mediated synapses has an ameliorating effect on spike-wave discharges (SWDs) associated with absence seizures. This effect is region-specific and most significant in the thalamus, particularly the synapses between thalamic reticular neurons. SignificanceThe remedying effect of allopregnanolone on SWDs may possibly be true only for individuals that are predisposed to remission due to intrinsic connectivity differences or differences in tonic inhibition. These results are a useful first-step and prescribe directions for further investigation into the role of ALLO together with these differences to distinguish between models for CAE-remitting and non-remitting individuals.

neuroscience↗

bioRxiv2021

14-3-3ζ constrains insulin secretion in pancreatic β-cells by regulating mitochondrial function

While critical for neurotransmitter synthesis in the brain, members of the 14-3-3 protein family are often assumed to have redundant, over-lapping roles due to their high sequence homology and ubiquitous expression. Despite this assumption, various mammalian 14-3-3 isoforms have now been implicated in regulating cellular and organismal metabolism; however, these functions were primarily observed in cell lines or from systemic knockout mouse models. To date, we have begun to define the contributions of 14-3-3{zeta} in adipocytes, but whether 14-3-3{zeta} has additional metabolic roles in other cell types, such as the pancreatic {beta}-cell, is unclear. We previously documented a pro-survival role of 14-3-3{zeta} in MIN6 insulinoma cells, as depletion of 14-3-3{zeta} induced cell death, but paradoxically, whole-body deletion of 14-3-3{zeta} in mice resulted in significantly enlarged {beta}-cell area with no effects on insulin secretion. To better understand the role of 14-3-3{zeta} in {beta}-cells, we generated {beta}-cell-specific 14-3-3{zeta} knockout ({beta}14-3-3{zeta}KO) mice, and while no differences in {beta}-cell mass were observed, {beta}14-3-3{zeta}KO mice displayed potentiated insulin secretion due to enhanced mitochondrial function and ATP synthesis. Deletion of 14-3-3{zeta} led to profound changes to the {beta}-cell transcriptome, where pathways associated with mitochondrial respiration and oxidative phosphorylation were upregulated. Acute treatment of mouse islets and human islets with pan-14-3-3 inhibitors recapitulated the potentiation in glucose-stimulated insulin secretion (GSIS) and mitochondrial function, suggesting that 14-3-3{zeta} is a critical isoform in {beta}-cells that regulates GSIS. In dysfunctional db/db islets and islets from type 2 diabetic donors, expression of Ywhaz/YWHAZ, the gene encoding 14-3-3{zeta}, was inversely associated with insulin secretory capacity, and pan-14-3-3 protein inhibition was capable of enhancing GSIS and mitochondrial function. Taken together, this study demonstrates important regulatory functions of 14-3-3{zeta} and its related isoforms in insulin secretion and mitochondrial function in {beta}-cells. A deeper understanding of how 14-3-3{zeta} influences {beta}-cell function will further advance our knowledge of how insulin secretion from {beta}-cells is regulated.

physiology↗

bioRxiv2021

Myofilament Glycation in Diabetes Reduces Contractility by Inhibiting Tropomyosin Movement, is Rescued by cMyBPC Domains

Diabetes doubles the risk of developing heart failure (HF). As the prevalence of diabetes grows, so will HF unless the mechanisms connecting these diseases can be identified. Methylglyoxal (MG) is a glycolysis by-product that forms irreversible modifications on lysine and arginine, called glycation. We previously found that myofilament MG glycation causes sarcomere contractile dysfunction and is increased in patients with diabetes and HF. The aim of this study was to discover the molecular mechanisms by which MG glycation of myofilament proteins cause sarcomere dysfunction and to identify therapeutic avenues to compensate. In humans with type 2 diabetes without HF, we found increased glycation of sarcomeric actin compared to non-diabetics and it correlated with decreased calcium sensitivity. Depressed calcium sensitivity is pathogenic for HF, therefore myofilament glycation represents a promising therapeutic target to inhibit the development of HF in diabetics. To identify possible therapeutic targets, we further defined the molecular actions of myofilament glycation. Skinned myocytes exposed to 100 M MG exhibited decreased calcium sensitivity, maximal calcium-activated force, and crossbridge kinetics. Replicating MGs functional affects using a computer simulation of sarcomere function predicted simultaneous decreases in tropomyosins blocked-to-closed rate transition and crossbridge duty cycle were consistent with all experimental findings. Stopped-flow experiments and ATPase activity confirmed MG decreased the blocked-to-closed transition rate. Currently, no therapeutics target tropomyosin, so as proof-of-principal, we used a n-terminal peptide of myosin-binding protein C, previously shown to alter tropomyosins position on actin. C0C2 completely rescued MG-induced calcium desensitization, suggesting a possible treatment for diabetic HF.

biophysics↗

bioRxiv2020

H3K4 trimethylation is required for postnatal pancreatic endocrine cell functional maturation

During pancreas development, endocrine progenitors differentiate into the islet-cell subtypes, which undergo further functional maturation in postnatal islet development. In islet {beta}-cells, genes involved in glucose-stimulated insulin secretion are activated and glucose exposure increases the insulin response as {beta}-cells mature. Here, we investigated the role of H3K4 trimethylation in endocrine cell differentiation and functional maturation by disrupting TrxG complex histone methyltransferase activity in mouse endocrine progenitors. In the embryo, genetic inactivation of TrxG component Dpy30 in NEUROG3+ cells did not affect the number of endocrine progenitors or endocrine cell differentiation. H3K4 trimethylation was progressively lost in postnatal islets and the mice displayed elevated random and fasting glycemia, as well as impaired glucose tolerance by postnatal day 24. Although postnatal endocrine cell proportions were equivalent to controls, islet RNA-sequencing revealed a downregulation of genes involved in glucose-stimulated insulin secretion and an upregulation of immature {beta}-cell genes. Comparison of histone modification enrichment profiles in NEUROG3+ endocrine progenitors and mature islets suggested that genes downregulated by loss of H3K4 trimethylation more frequently acquire active histone modifications during maturation. Taken together, these findings suggest that H3K4 trimethylation is required for the activation of genes involved in the functional maturation of pancreatic islet endocrine cells.

developmental biology↗

bioRxiv2020

Effect of time delay on the synchronization of excitatory-inhibitory neural networks

We study a model for a network of synaptically coupled, excitable neurons to identify the role of coupling delays in generating different network behaviors. The network consists of two distinct populations, each of which contains one excitatory-inhibitory neuron pair. The two pairs are coupled via delayed synaptic coupling between the excitatory neurons, while each inhibitory neuron is connected only to the corresponding excitatory neuron in the same population. We show that multiple equilibria can exist depending on the strength of the excitatory coupling between the populations. We conduct linear stability analysis of the equilibria and derive necessary conditions for delay-induced Hopf bifurcation. We show that these can induce two qualitatively different phase-locked behaviors, with the type of behavior determined by the sizes of the coupling delays. Numerical bifurcation analysis and simulations supplement and confirm our analytical results. Our work shows that the resting equilibrium point is unaffected by the coupling, thus the network exhibits bistability between a rest state and an oscillatory state. This may help understand how rhythms spontaneously arise neuronal networks.

neuroscience↗

bioRxiv2020

Spatially localized cluster solutions in inhibitory neural networks

Neurons in the inhibitory network of the striatum display cell assembly firing patterns which recent results suggest may consist of spatially compact neural clusters. Previous computational modeling of striatal neural networks has indicated that non-monotonic, distance-dependent coupling may promote spatially localized cluster firing. Here, we identify conditions for the existence and stability of cluster firing solutions in which clusters consist of spatially adjacent neurons in inhibitory neural networks. We consider simple non-monotonic, distance-dependent connectivity schemes in weakly coupled 1-D networks where cells make strong connections with their kth nearest neighbors on each side. Using the phase model reduction of the network system, we prove the existence of cluster solutions where neurons that are spatially close together are also synchronized in the same cluster, and find stability conditions for these solutions. Our analysis predicts the long-term behavior for networks of neurons, and we confirm our results by numerical simulations of biophysical neuron network models. Additionally, we add weaker coupling between closer neighbors as a perturbation to our network connectivity. We analyze the existence and stability of cluster solutions of the perturbed network and validate our results with numerical simulations. Our results demonstrate that an inhibitory network with non-monotonic, distance-dependent connectivity can exhibit cluster solutions where adjacent cells fire together.

neuroscience↗