Biology subjects

Huising, M. O.

Publications and source records attributed to Huising, M. O..

10 recordsLinked to original sources

bioRxiv2025

Somatostatin Receptors Shape Insulin and Glucagon Output within the Pancreatic Islet through Direct and Paracrine Effects

Aims/HypothesisPancreatic delta cells secrete somatostatin (SST), which can inhibit both alpha and beta cells of the pancreatic islet. By controlling insulin and glucagon release, delta cells play an important role in maintaining nutrient homeostasis. However, the mechanism by which a single inhibitory hormone inhibits both alpha and beta cells, which are often considered as functional antagonists in the counterregulatory control of blood glucose, has been a physiological riddle. Here, we solve this riddle through assessment of the contributions of alpha and beta cell specific somatostatin receptors to cell intrinsic behaviors and hormone release. MethodsIslets from mice constitutively expressing fluorescent sensors reporting on cyclic AMP and Ca2+ in both alpha and beta cells were imaged using stimuli to mimic the post-prandial state of a meal consisting of glucose and amino acids. This approach was coupled with cell specific somatostatin receptor antagonists to identify how somatostatin inhibits alpha and beta cell hormone output through modulation of cAMP and Ca2+ secondary messengers and paracrine interactions. ResultsOur results support and extend prior observation that somatostatin receptor 2 (SSTR2) is the only somatostatin receptor expressed by alpha cells, while somatostatin receptor 3 (SSTR3) is the only receptor expressed by mouse beta cells. Interestingly, SSTR2 and SSTR3 regulate downstream cAMP and Ca2+ signaling cascades differently within alpha and beta cells of intact islets. Stimulation of somatostatin receptors robustly inhibits cyclic AMP in alpha or beta cells. In contrast, stimulation of SSTR2 inhibits alpha cell Ca2+ with significantly greater potency compared to inhibition of beta cell Ca2+ via SSTR3. Despite the absence of SSTR2 on beta cells, blocking alpha cell SSTR2 during nutrient stimulation resulted in a significant increase in insulin release downstream of local release of glucagon. Conclusions/InterpretationOur observations address the physiological riddle of the delta cells role during the post-prandial phase where we demonstrate that somatostatin primarily inhibits alpha cell cAMP and Ca2+ via SSTR2, preventing glucagon release. Blocking SSTR2 resulted in an increase in locally released glucagon, which coupled with muted ability for SSTR3 to inhibit beta cell calcium under strong nutrient stimulation, results in potentiation of glucose stimulated insulin secretion from the beta cell. We conclude that the role of delta cells under nutrient stimulation is to modulate the volume of insulin release by tuning the strength of intra-islet paracrine potentiation of insulin secretion by glucagon, mediated via beta cell GLP1R. Research in ContextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LISomatostatin released by delta cells can attenuate glucagon release from the alpha cells and insulin release from the beta cells of the islet through inhibitory somatostatin receptors. C_LIO_LISomatostatin receptor 2 is a major receptor expressed on the mouse alpha cell surface, while mouse beta cells express SSTR3 on their primary cilia. C_LIO_LIParacrine signaling by alpha cell glucagon potentiates insulin release through the engagement of stimulatory glucagon-like peptide 1 receptors on beta cells. C_LI What are the key questions?O_LIHow do the cell specific somatostatin receptors of the alpha cell (SSTR2) and beta cell (SSTR3) differentially regulate cell-intrinsic Ca2+ and cAMP signaling and the indirect paracrine pathways that shape insulin secretion in the post-prandial state? C_LI What are the new findings?O_LIAlpha cells of the mouse islet express exclusively SSTR2 and not SSTR3. C_LIO_LISomatostatin is a more potent inhibitor of cytosolic calcium activity via alpha cell SSTR2 compared to beta cell SSTR3. C_LIO_LIPreventing somatostatin inhibition of the alpha cell in the presence of elevated glucose and amino acids potentiates insulin release through the engagement of glucagon-like peptide 1 receptors on the beta cell by glucagon. C_LI How might this impact on clinical practice in the foreseeable future?O_LIOur findings indicate that local feedback inhibition of beta cells is accomplished by tuning the strength of the paracrine potentiation of locally released glucagon. This is relevant in the context of developing treatments for hypoglycemia with alpha cell specific SSTR2-specific antagonists that could potentiate insulin release and potentially exacerbate hypoglycemic episodes. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/688371v1_ufig1.gif" ALT="Figure 1"> View larger version (71K): org.highwire.dtl.DTLVardef@1138ddaorg.highwire.dtl.DTLVardef@c613f9org.highwire.dtl.DTLVardef@49806eorg.highwire.dtl.DTLVardef@18ece86_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2025

Free fatty acid receptor 4 agonists stimulate insulin secretion via different mechanisms in mouse versus human islets

The free fatty acid receptor FFAR4 is expressed in pancreatic islets, and its activation potentiates insulin and inhibits somatostatin (SST) secretion. We investigated the mechanisms of action of FFAR4 on hormone secretion in mouse and human islets. The effects of the FFAR4 agonist Compound A (Cpd A) on insulin and SST secretion were investigated in islets from mice following ablation of {delta} cells, deletion of SST and deletion of the G protein Gz (Gnaz-/-), in purified mouse {beta} and {delta} cells, in human EndoC-{beta}H5 cells, and in human islets. Ca++ dynamics in response to Cpd A were measured in {delta} cells from Gnaz-/- mouse islets and in human islets. The insulinotropic effect of Cpd A was lost in {delta} cell-ablated and SST-deficient mouse islets and was absent in purified mouse {beta} cells. Gz deletion prevented Cpd A inhibition of SST secretion but not the potentiation of insulin release. Cpd A diminished Ca++ transients in mouse {delta} cells, an effect that was lost in Gz deficient islets. In human islets, FFAR4 activation increased insulin secretion and intracellular Ca++ transient independent of SST secretion. Consistent with a direct effect on {beta} cells, Cpd A potentiated insulin secretion in human EndoC-{beta}H5 cells. We conclude that FFAR4 activation stimulates insulin secretion from mouse islets indirectly via Gz-coupled inhibition of SST secretion from {delta} cells, while in human islets, it stimulates insulin release via a direct effect on {beta} cells. These key species-related differences are to be taken into account as FFAR4 is considered a potential therapeutic target for metabolic diseases. STRUCTURED ABSTRACTO_ST_ABSObjectivesC_ST_ABSThe free fatty acid receptor FFAR4 (GPR120) is expressed in the murine islet where its activation promotes insulin and glucagon and inhibits somatostatin (SST) secretion. However, its precise mechanism of action in different islet cells is still unknown, and potential species-related differences have not been explored. This study was aimed to address three questions: 1-What is the relative importance of {delta} cells and SST in the insulinotropic effect of FFAR4 in mouse islets? 2-Which G protein does FFAR4 couple to in mouse {delta} cells? 3-Does FFAR4 stimulate insulin secretion by similar mechanisms in mouse and human islets? MethodsThe effects of the FFAR4 agonist Compound A (Cpd A) on insulin and SST secretion were investigated in islets from mice following ablation of {delta} cells, deletion of SST and deletion of the G protein Gz (Gnaz-/-), in purified mouse {beta} and {delta} cells, in human EndoC-{beta}H5 cells, and in human islets. Ca++ dynamics in response to Cpd A were measured in {delta} cells from Gnaz-/- mouse islets and in human islets using adenovirally-transduced Ca++ reporters. ResultsThe insulinotropic effect of Cpd A was lost in {delta} cell-ablated and SST-deficient mouse islets and was absent in purified mouse {beta} cells. Gz deletion diminished Ca++ transients in mouse {delta} cells, prevented Cpd A inhibition of SST secretion but did not inhibit the potentiation of insulin release. In human islets, FFAR4 activation increased insulin secretion and intracellular Ca++ transient without affecting SST secretion. Consistent with a direct effect on {beta} cells, Cpd A potentiated insulin secretion in human EndoC-{beta}H5 cells. ConclusionFFAR4 activation stimulates insulin secretion from mouse islets indirectly via Gz-coupled inhibition of SST secretion from {delta} cells, while in human islets, it stimulates insulin release via a direct effect on {beta} cells. These key species-related differences are to be taken into account as FFAR4 is considered a potential therapeutic target for metabolic diseases.

cell biology↗

bioRxiv2024

Sex-dependent additive effects of dorzagliatin and incretin on insulin secretion in a novel mouse model of GCK-MODY

Glucokinase (GK) catalyses the key regulatory step in glucose-stimulated insulin secretion. Correspondingly, hetero- and homozygous mutations in human GCK cause maturity-onset diabetes of the young (GCK-MODY) and permanent neonatal diabetes (PNDM), respectively. To explore the possible utility of glucokinase activators (GKA) and of glucagon-like receptor-1 (GLP-1) agonists in these diseases, we have developed a novel hypomorphic Gck allele in mice encoding an aberrantly spliced mRNA deleted for exons 2 and 3. In islets from homozygous knock-in (GckKI/KI) mice, GK immunoreactivity was reduced by >85%, and glucose-stimulated insulin secretion eliminated. Homozygous GckKI/KI mice were smaller than wildtype littermates and displayed frank diabetes (fasting blood glucose >18 mmol/L; HbA1c [~]12%), ketosis and nephropathy. Heterozygous GckKI/+ mice were glucose intolerant (HbA1c [~]5.5%). Abnormal glucose-stimulated Ca2+ dynamics and beta cell-beta cell connectivity in GckKI/+ islets were completely reversed by the recently-developed GKA, dorzagliatin, which was largely inactive in homozygous GckKI/KI mouse islets. The GLP-1 receptor agonist exendin-4 improved glucose tolerance in male GckKI/+ mice, an action potentiated by dorzagliatin, in male but not female mice. Sex-dependent additive effects of these agents were also observed on insulin secretion in vitro. Combined treatment with GKA and incretin may thus be useful in GCK-MODY or GCK-PNDM. Article Highlightsa. Glucokinase deficiency can drive maturity-onset diabetes of the young (GCK-MODY; heterozygotes) and permanent neonatal diabetes (GCK-PNDM; homozygotes) b. We describe a hypomorphic Gck allele where aberrant splicing in islets lowers GK activity to by [~]85%. We use these mice to explore the effects of the glucokinase activator, dorzagliatin, and incretin on insulin secretion c. Whereas heterozygous mutant mice are mildly hyperglycemic, homozygotes have frank diabetes but survive to adulthood. Dorzagliatin potentiates the effects of GLP-1 receptor activation sex-dependently in heterozygotes d. Combined use of these drugs may be useful in some forms of GCK diabetes

physiology↗

bioRxiv2024

G protein-Coupled Receptor Associated Sorting ProteinGASP1 mediated trafficking of the Glucagon Like Peptide-1Receptor contributes to the development of tolerance toincretin drugs

Incretin mimetic drugs are in widespread use for the treatment of type 2 diabetes and obesity and more recently have been prescribed for weight loss in otherwise healthy individuals. These drugs are all agonists of the glucagon-like peptide 1 receptor (GLP-1R) and function by supplementing effects produced by the endogenous hormone agonist glucagon-like peptide 1 (GLP-1). The therapeutic benefits of these medications, including improved glucose control and weight loss, require continued usage and wane with time. The molecular mechanisms underlying this loss of effect to incretin drugs remain unknown. Following activation by agonist and signaling to G protein, the GLP-1R engages arrestins and is endocytosed. Here we investigated the role of G protein-coupled receptor associated sorting protein 1 (GASP1), a critical regulator of the post-endocytic trafficking of GLP-1R, on tolerance to GLP-1R agonist drug. We found that tolerance to incretin drug was prevented at the cellular, tissue and whole animal level in mice with a selective disruption of the GASP1 protein in beta cells of the pancreatic islet. These studies implicate post-endocytic sorting of the GLP-1R in the loss of effectiveness of incretin therapeutics with prolonged use. These findings also suggest a novel strategy to prevent tolerance by biasing incretin drugs for G protein and away from arrestin engagement.

cell biology↗

bioRxiv2022

Species-specific roles for the MAFA and MAFB transcription factors in regulatingislet β cell identity

Type 2 diabetes (T2D) is associated with compromised identity of insulin-producing pancreatic islet beta ({beta}) cells, characterized by inappropriate production of other islet cell-enriched hormones. Here we examined how hormone misexpression was influenced by the MAFA and MAFB transcription factors, closely related proteins that maintain islet cell function. Mice specifically lacking MafA in {beta} cells demonstrated broad, population-wide changes in hormone gene expression with an overall gene signature closely resembling islet gastrin (Gast)-positive cells generated under conditions of chronic hyperglycemia and obesity. A human {beta} cell line deficient in MAFB, but not one lacking MAFA, also produced a gastrin (GAST)-positive gene expression pattern. In addition, GAST was detected in human T2D {beta} cells with low levels of MAFB. Moreover, evidence is provided that human MAFB can directly repress GAST gene transcription. These results support a novel, species-specific role for MafA and MAFB in maintaining adult mouse and human {beta} cell identity, respectively, by repressing expression of Gast/GAST and other non-{beta} cell hormones.

cell biology↗

bioRxiv2022

Paracrine signaling by pancreatic delta cells determines the glycemic set point in mice

Pancreatic islets contain several endocrine cell types that coordinate to maintain blood glucose homeostasis. While {beta} and cells are thought to be the main drivers of glucose homeostasis through insulin and glucagon secretion respectively, the contribution of {delta} cells and somatostatin (SST) secretion to establishing the glycemic set point remains unresolved. Here we remove local SST signaling from {delta} cells within the pancreatic islet to investigate their contribution to the glycemic set point. Our data demonstrate that ablating {delta} cells or SST leads to a sustained decrease in the glycemic set point. This coincides with a decreased glucose threshold for insulin response from {beta} cells, leading to increased insulin secretion to the same glucose challenge. In contrast, cell ablation had no effect on glycemic set point. Collectively, these data establish the physiological role of {delta} cells in determining the glycemic set point through their interaction with {beta} cells.

physiology↗

bioRxiv2021

Chromatin accessibility differences between alpha, beta, and delta cells identifies common and cell type-specific enhancers

High throughput sequencing has enabled the interrogation of the transcriptomic landscape of glucagon-secreting alpha cells, insulin-secreting beta cells, and somatostatin-secreting delta cells. These approaches have furthered our understanding of expression patterns that define healthy or diseased islet cell types and helped explicate some of the intricacies between major islet cell crosstalk and glucose regulation. All three endocrine cell types derive from a common pancreatic progenitor, yet alpha and beta cells have partially opposing functions, and delta cells modulate and control insulin and glucagon release. While gene signatures that define and maintain cellular identity have been widely explored, the underlying epigenetic components are incompletely characterized and understood. Chromatin accessibility and remodeling is a dynamic attribute that plays a critical role to determine and maintain cellular identity. Here, we compare and contrast the chromatin landscape between mouse alpha, beta, and delta cells using ATAC-Seq to evaluate the significant differences in chromatin accessibility. The similarities and differences in chromatin accessibility between these related islet endocrine cells help define their fate in support of their distinct functional roles. We identify patterns that suggest that both alpha and delta cells are poised, but repressed, from becoming beta-like. We also identify patterns in differentially enriched chromatin that have transcription factor motifs preferentially associated with different regions of the genome. Finally, we identify and visualize both novel and previously discovered common endocrine- and cell specific- enhancer regions across differentially enriched chromatin.

genomics↗

bioRxiv2021

epiRomics: a multi-omics R package to identify and visualize enhancers

SummaryepiRomics is an R package designed to integrate multi-omics data in order to identify and visualize enhancer regions alongside gene expression and other epigenomic modifications. Regulatory network analysis can be done using combinatory approaches to infer regions of significance such as enhancers, when combining ChIP and histone data. Downstream analysis can identify co-occurrence of these regions of interest with other user-supplied data, such as chromatin availability or gene expression. Finally, this package allows for results to be visualized at high resolution in a stand-alone browser. Availability and ImplementationepiRomics is released under Artistic-2.0 License. The source code and documents are freely available through Github (https://github.com/Huising-Lab/epiRomics). Contactammawla@ucdavis.edu or mhuising@ucdavis.edu Supplementary informationSupplementary data, and methods are available online on biorxiv or Github.

bioinformatics↗

bioRxiv2020

Free-fatty acid receptor 4 inhibitory signaling in delta cells regulates islet hormone secretion in mice

ObjectiveMaintenance of glucose homeostasis requires the precise regulation of hormone secretion from the endocrine pancreas. Free fatty-acid receptor 4 (FFAR4/GPR120) is a G protein-coupled receptor whose activation in islets of Langerhans promotes insulin and glucagon secretion and inhibits somatostatin secretion. However, the contribution of individual islet cell types (, {beta}, and {delta} cells) to the insulinotropic and glucagonotropic effects of GPR120 remains unclear. As gpr120 mRNA is enriched in somatostatin-secreting {delta} cells, we hypothesized that GPR120 activation stimulates insulin and glucagon secretion via inhibition of somatostatin release. MethodsGlucose tolerance tests were performed in mice after administration of the selective GPR120 agonist Compound A. Insulin, glucagon and somatostatin secretion were measured in static incubations of isolated mouse islets in response to endogenous ({omega}-3 polyunsaturated fatty acids) and/or pharmacological (Compound A and AZ-13581837) GPR120 agonists. The effect of Compound A on hormone secretion was tested further in islets isolated from mice with global or somatostatin cell-specific knockout of gpr120. Gpr120 expression was assessed in pancreatic sections by RNA in situ hybridization. Cyclic AMP (cAMP) and calcium dynamics in response to pharmacological GPR120 agonists were measured specifically in , {beta} and {delta} cells in intact islets using cAMPER and GCaMP6 reporter mice, respectively. ResultsAcute exposure to Compound A increased glucose tolerance and circulating insulin and glucagon levels in vivo. Endogenous and/or pharmacological and GPR120 agonists reduced somatostatin secretion in isolated islets and concomitantly demonstrated dose-dependent potentiation of glucose-stimulated insulin secretion and arginine-stimulated glucagon secretion. Gpr120 was enriched in {delta} cells. Pharmacological GPR120 agonists reduced cAMP and calcium levels in {delta} cells but increased these signals in and {beta} cells. Compound A-mediated inhibition of somatostatin secretion was insensitive to pertussis toxin. The effect of Compound A on hormone secretion was completely absent in islets from mice with either global or somatostatin cell-specific deletion of gpr120 and was partially reduced upon blockade of somatostatin receptor signaling by cyclosomatostatin. ConclusionsInhibitory GPR120 signaling in {delta} cells contributes to both insulin and glucagon secretion in part via mitigating somatostatin release.

physiology↗

bioRxiv2019

Nutrient regulation of the islet epigenome controls adaptive insulin secretion

Adaptation of the islet {beta}-cell insulin secretory response to changing insulin demand is critical for blood glucose homeostasis, yet the mechanisms underlying this adaptation are unknown. Here, we show that nutrient-stimulated histone acetylation plays a key role in adapting insulin secretion through regulation of genes involved in {beta}-cell nutrient sensing and metabolism. Nutrient regulation of the epigenome occurs at sites occupied by the chromatin-modifying enzyme Lsd1 in islets. We demonstrate that {beta}-cell-specific deletion of Lsd1 leads to insulin hypersecretion, aberrant expression of nutrient response genes, and histone hyperacetylation. Islets from mice adapted to chronically increased insulin demand exhibited similar epigenetic and transcriptional changes. Moreover, genetic variants associated with fasting glucose and type 2 diabetes are enriched at LSD1-bound sites in human islets, suggesting that interpretation of nutrient signals is genetically determined. Our findings reveal that adaptive insulin secretion involves Lsd1-mediated coupling of nutrient state to regulation of the islet epigenome.

physiology↗