Biology subjects

MacDonald, P. E.

Publications and source records attributed to MacDonald, P. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Spatial and functional mapping of the human pancreas reveals endocrine and exocrine cell states in health and metabolic disease

The human pancreas contains diverse endocrine and exocrine cell populations whose spatial organization is essential for tissue physiology. While single-cell and spatial transcriptomics revealed molecular heterogeneity across pancreatic cell types, linking these states to physiological activity in situ has remained challenging. Here, we combined single-nucleus RNA sequencing, spatial transcriptomics, and functional calcium imaging across pancreatic samples in health and metabolic disease. We identified heterogeneous endocrine and exocrine cell states associated with obesity and diabetes, including inflammatory remodeling of acinar and ductal populations. To directly couple tissue physiology with molecular state, we developed Slice-seq, which integrates calcium imaging with spatial transcriptomics in acute pancreatic slices. Slice-seq linked local endocrine composition and transcriptional programs with {beta} cell activity and identified extra-islet {beta} cells with reduced glucose responsiveness and mitochondrial oxidative metabolism. Together, our study provides a framework for linking pancreatic cell states to tissue organization and physiological activity in health and disease.

genomics↗

bioRxiv2026

Multi-modal comparison of primary and stem cell-derived β-cells nominates targets for maturation

Stem-cell-derived {beta}-like-cells (SC{beta}-cells) provide a promising platform for diabetes modelling and cell replacement therapy, but their incomplete functional maturation remains a challenge. Here, we compared immature SC{beta}-cells to human primary {beta}-cells utilizing a multi-omic, single-cell framework integrating patch-clamp electrophysiology with scRNA sequencing (patch-seq), regulatory network inference, and functional phenotyping. Despite low insulin secretion and reduced insulin content, SC{beta}-cells displayed larger Na+ and Ca2+ currents and depolarization-induced exocytosis. Ultrastructural and metabolic profiling revealed immature insulin granules, altered mitochondrial morphology, elevated basal respiration and proton leak, and diminished spare respiratory capacity and glucose-responsive metabolism. Patch-seq linked exocytotic activity in SC{beta}-cells to oxidative phosphorylation and MYC target programs, consistent with incomplete terminal differentiation, whereas SC{beta}-cells expressing higher levels of mature identity markers showed reduced ion channel hyperactivity. Multi-omics profiling showed that electrophysiological features in SC{beta}-cells were embedded in transcriptional programs distinct from those of primary {beta}-cells and other endocrine cells. Network control theory nominated SREBP1, an endoplasmic reticulum tethered transcription factor regulating cholesterol and lipid homeostasis, as a promising candidate involved in this immature state. Inhibition of cholesterol trafficking increased SREBF1 expression and shifted metabolic and transcriptional features towards a more mature {beta}-like state. These data identify potential targets and pathways that can be leveraged to improve SC{beta}-cell maturation and validate cholesterol and lipid homeostasis through the SREBP1 axis as one such candidate.

cell biology↗

bioRxiv2025

Linking molecular pathways and islet cell dysfunction in human type 1 diabetes

Type 1 diabetes (T1D) is characterized by the autoimmune destruction of most insulin-producing {beta}-cells, along with dysregulated glucagon secretion from pancreatic -cells. We conducted an integrated analysis that combines electrophysiological and transcriptomic profiling, along with machine learning, of islet cells from T1D donors to investigate the mechanisms underlying their dysfunction. Surviving {beta}-cells exhibit altered electrophysiological properties and transcriptomic signatures indicative of increased antigen presentation, metabolic reprogramming, and impaired protein translation. In -cells, we observed hyper-responsiveness and increased exocytosis, which are associated with upregulated immune signaling, disrupted transcription factor localization and lysosome homeostasis, as well as dysregulation of mTORC1 complex signaling. Notably, key genetic risk signals for T1D were enriched in transcripts related to -cell dysfunction, including MHC class I which were closely linked with -cell dysfunction. Our data provide novel insights into the molecular underpinnings of islet cell dysfunction in T1D, highlighting pathways that may be leveraged to preserve residual {beta}-cell function and modulate -cell activity. These findings underscore the complex interplay between immune signaling, metabolic stress, and cellular identity in shaping islet cell phenotypes in T1D. HighlightsO_LISurviving {beta}-cells in T1D show disrupted electrical function linked to metabolic reprogramming and immune stress. C_LIO_LITranscripts associated with -cell dysfunction are enriched in genetic risk alleles for T1D. C_LIO_LIUpregulated MHC class I and impaired nuclear localization of key transcription factors associate with -cell dysfunction in T1D. C_LIO_LIT1D -cells exhibit increased hyper-activity, lysosomal imbalance and impaired mTORC1 signaling, which promotes dysregulated glucagon secretion. C_LI

cell biology↗

bioRxiv2024

TMEM55A-mediated PI5P signaling regulates α-cell actin depolymerization and glucagon secretion

Diabetes is associated with the dysfunction of glucagon-producing pancreatic islet -cells, although the underlying mechanisms regulating glucagon secretion and -cell dysfunction remain unclear. While insulin secretion from pancreatic {beta}-cells has long been known to be partly controlled by intracellular phospholipid signaling, very little is known about the role of phospholipids in glucagon secretion. Here we show that TMEM55A, a lipid phosphatase that dephosphorylates phosphatidylinositol-4,5-bisphosphate (PIP2) to phosphatidylinositol-5-phosphate (PI5P), regulates -cell exocytosis and glucagon secretion. TMEM55A knockdown in both human and mouse -cells reduces exocytosis at low glucose, and this is rescued by the direct reintroduction of PI5P. This does not occur through an effect on Ca2+ channel activity, but through a re-modelling of cortical F-actin dependent upon TMEM55A lipid phosphatase activity which occurs in response to oxidative stress. In summary, we reveal a novel pathway by which TMEM55A regulates -cell exocytosis by manipulating intracellular PI5P level and the F-actin network.

cell biology↗

bioRxiv2024

Molecular Correlates of Glycine Receptor Activity in Human β Cells

ObjectivesGlycine acts in an autocrine positive feedback loop in human {beta} cells through its ionotropic receptors (GlyRs). In type 2 diabetes (T2D), islet GlyR activity is impaired by unknown mechanisms. We sought to investigate if the GlyR dysfunction in T2D is replicated by hyperglycemia per se, and to further characterize its action in {beta} cells and islets. MethodsGlyR-mediated currents were measured using whole-cell patch-clamp in human {beta} cells from donors with or without T2D, or after high glucose (15 mM) culture. We also correlated glycine-induced current amplitude with transcript expression levels through patch-seq. The expression of the GlyR 1, 3, and {beta} subunit mRNA splice variants was compared between islets from donors with and without T2D, and after high glucose culture. Insulin secretion from human islets was measured in the presence or absence of the GlyR antagonist strychnine. ResultsAlthough gene expression of GlyRs was decreased in T2D islets, and {beta} cell GlyR-mediated currents were smaller, we found no evidence for a shift in GlyR subunit splicing. Glycine-induced currents are also reduced after 48 hours culture of islets from donors without diabetes in high glucose, where we also find the reduction of the 1 subunit expression, but an increase in the 3 subunit. We discovered that glycine-evoked currents are highly heterogeneous amongst {beta} cells, inversely correlate with donor HbA1c, and are significantly correlated to the expression of 92 different transcripts and gene regulatory networks (GRNs) that include CREB3(+), RREB1(+) and ZNF697(+). Finally, glucose-stimulated insulin secretion is decreased in the presence of the GlyR antagonist strychnine. ConclusionsWe demonstrate that glucose can modulate GlyR expression, and that the current decrease in T2D is likely due to the receptor gene expression downregulation, and not a change in transcript splicing. Moreover, we define a previously unknown set of genes and regulons that are correlated to GlyR-mediated currents and could be involved in GlyR downregulation in T2D. HighlightsO_LIGlycine-evoked currents in {beta} cells are lower in T2D and after high glucose culture C_LIO_LIGlyR gene expression is reduced in T2D, with no shift in splice variant expression C_LIO_LIGlyR inhibition with strychnine decreases insulin secretion C_LIO_LIWe define transcripts and gene regulatory networks correlated to glycine-induced currents C_LI

cell biology↗

bioRxiv2024

HumanIslets: An integrated platform for human islet data access and analysis

Comprehensive molecular and cellular phenotyping of human islets can enable deep mechanistic insights for diabetes research. We established the Human Islet Data Analysis and Sharing (HI-DAS) consortium to advance goals in accessibility, usability, and integration of data from human islets isolated from donors with and without diabetes at the Alberta Diabetes Institute (ADI) IsletCore. Here we introduce HumanIslets.com, an open resource for the research community. This platform, which presently includes data on 547 human islet donors, allows users to access linked datasets describing molecular profiles, islet function and donor phenotypes, and to perform various statistical and functional analyses at the donor, islet and single-cell levels. As an example of the analytic capacity of this resource we show a dissociation between cell culture effects on transcript and protein expression, and an approach to correct for exocrine contamination found in hand-picked islets. Finally, we provide an example workflow and visualization that highlights links between type 2 diabetes status, SERCA3b Ca2+-ATPase levels at the transcript and protein level, insulin secretion and islet cell phenotypes. HumanIslets.com provides a growing and adaptable set of resources and tools to support the metabolism and diabetes research community.

systems biology↗

bioRxiv2024

Human research islet cell culture outcomes at the Alberta Diabetes Institute IsletCore

Human islets from deceased organ donors have made important contributions to our understanding of pancreatic endocrine function and continue to be an important resource for research studies aimed at understanding, treating, and preventing diabetes. Understanding the impacts of isolation and culture upon the yield of human islets for research is important for planning research studies and islet distribution to distant laboratories. Here we examine islet isolation and cell culture outcomes at the Alberta Diabetes Institute (ADI) IsletCore (n=197). Research-focused isolations typically have a lower yield of islet equivalents (IEQ), with a median of 252,876 IEQ, but a higher purity (median 85%) than clinically-focused isolations before culture. The median recovery of IEQs after culture was 75%, suggesting some loss. This was associated with a shift towards smaller islet particles, indicating possible islet fragmentation, and occurred within 24 hours with no further loss after longer periods of culture (up to 136 hours). No overall change in stimulation index as a measure of islet function was seen with culture time. These findings were replicated in a representative cohort of clinical islet preparations from the Clinical Islet Transplant Program at the University of Alberta. Thus, loss of islets occurs within 24 hours of isolation and there is no further impact of extended culture prior to islet distribution for research.

cell biology↗

bioRxiv2023

Caloric restriction promotes beta cell longevity and delays aging and senescence by enhancing cell identity and homeostasis mechanisms.

Caloric restriction (CR) extends organismal lifespan and health span by improving glucose homeostasis mechanisms. How CR affects organellar structure and function of pancreatic beta cells over the lifetime of the animal remains unknown. Here, we used single nucleus transcriptomics to show that CR increases the expression of genes for beta cell identity, protein processing, and organelle homeostasis. Gene regulatory network analysis link this transcriptional phenotype to transcription factors involved in beta cell identity (Mafa) and homeostasis (Atf6). Imaging metabolomics further demonstrates that CR beta cells are more energetically competent. In fact, high-resolution light and electron microscopy indicates that CR reduces beta cell mitophagy and increases mitochondria mass, increasing mitochondrial ATP generation. Finally, we show that long-term CR delays the onset of beta cell aging and senescence to promote longevity by reducing beta cell turnover. Therefore, CR could be a feasible approach to preserve compromised beta cells during aging and diabetes.

cell biology↗

bioRxiv2022

Deletion of carboxypeptidase E in beta cells disrupts proinsulin processing and alters beta cell identity in mice

Carboxypeptidase E (CPE) facilitates the conversion of prohormones into mature hormones and is highly expressed in multiple neuroendocrine tissues. Carriers of CPE mutations have elevated plasma proinsulin and develop severe obesity and hyperglycemia. We aimed to determine whether loss of Cpe in pancreatic beta cells disrupts proinsulin processing and accelerates development of diabetes and obesity in mice. Pancreatic beta cell-specific Cpe knockout mice ({beta}CpeKO; Cpefl/fl x Ins1Cre/+) lack mature insulin granules and have elevated proinsulin in plasma; however, glucose-and KCl-stimulated insulin secretion in {beta}CpeKO islets remained intact. High fat diet-fed {beta}CpeKO mice showed comparable weight gain and glucose tolerance compared to Wt littermates. Notably, beta-cell area was increased in chow-fed {beta}CpeKO mice and beta-cell replication was elevated in {beta}CpeKO islets. Transcriptomic analysis of {beta}CpeKO beta cells revealed elevated glycolysis and Hif1-target gene expression. Upon high glucose challenge, beta cells from {beta}CpeKO mice showed reduced mitochondrial membrane potential, increased reactive oxygen species, reduced MafA, and elevated Aldh1a3 transcript levels. Following multiple low-dose streptozotocin treatment, {beta}CpeKO mice had accelerated hyperglycemia with reduced beta-cell insulin and Glut2 expression. These findings suggest that Cpe and proper proinsulin processing are critical in maintaining beta cell function during the development of diabetes.

physiology↗

bioRxiv2022

Loss of RREB1 in pancreatic beta cells reduces cellular insulin content and affects endocrine cell gene expression

Aims/hypothesisGenome-wide studies have uncovered multiple independent signals at the RREB1 locus associated with altered type 2 diabetes risk and related glycemic traits. However, little is known about the function of the zinc finger transcription factor RREB1 in glucose homeostasis or how changes in its expression and/or function influence diabetes risk. MethodsA zebrafish model lacking rreb1a and rreb1b was used to study the effect of RREB1 loss in vivo. Using transcriptomic and cellular phenotyping of a human beta cell model (EndoC-{beta}H1) and human induced pluripotent stem cell (hiPSC)-derived beta-like cells, we investigated how loss of RREB1 expression and activity affects pancreatic endocrine cell development and function. Ex vivo measurements of human islet function were performed in donor islets from carriers of RREB1 T2D-risk alleles. ResultsCRISPR-Cas9-mediated loss of rreb1a and rreb1b function in zebrafish supports an in vivo role for the transcription factor in beta cell mass, beta cell insulin expression, and glucose levels. Loss of RREB1 reduced insulin gene expression and cellular insulin content in EndoC-{beta}H1 cells, and impaired insulin secretion under prolonged stimulation. Transcriptomic analysis of RREB1 knockdown and knockout EndoC-{beta}H1 cells supports RREB1 as a novel regulator of genes involved in insulin secretion. In vitro differentiation of RREB1KO/KO hiPSCs revealed a dysregulation of pro-endocrine cell genes, including RFX family members, suggesting that RREB1 also regulates genes involved in endocrine cell development. Human donor islets from carriers of T2D-risk alleles in RREB1 have altered glucose-stimulated insulin secretion ex vivo, consistent with RREB1 regulating islet cell function. Conclusions/interpretationTogether, our results indicate that RREB1 regulates beta cell function by transcriptionally regulating the expression of genes involved in beta cell development and function. Research in contextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIHuman genetic variation in RREB1 is associated with altered diabetes risk, variation in glycemic, and anthropometric traits C_LIO_LIRREB1 is a transcription factor that binds to Ras-responsive elements and is expressed in multiple diabetes relevant tissues, including pancreatic islets C_LI What is the key question?O_LIHow does altered expression or function of RREB1 influence diabetes risk? C_LI What are the new findings?O_LIKnockdown and knockout of RREB1 in mature human EndoC-{beta}H1 cells reduces expression of insulin transcript and cellular content, as well as insulin secretion under prolonged stress C_LIO_LICarriers of the T2D-risk RREB1 coding allele trend towards reduced insulin content, but have improved glucose-stimulated insulin secretion C_LIO_LIA loss-of-function zebrafish model suggests that RREB1 is required for insulin expression C_LI How might this impact on clinical practice in the foreseeable future?O_LIRREB1 controls beta cell function and whole-body glucose homeostasis by transcriptionally regulating the development and function of pancreatic beta cells C_LI

physiology↗

bioRxiv2022

Zmiz1 is required for mature β-cell function and mass expansion upon high fat feeding

Genome-wide association studies have identified hundreds of signals for type 2 diabetes (T2D), most of which confer risk through effects on gene expression. We previously identified the transcription factor ZMIZ1 as a probable effector transcript in human islets, but how altered ZMIZ1 expression impacts T2D risk is unknown. We now show that islets from carriers of the T2D-risk alleles have reduced islet insulin content and glucose-stimulated insulin secretion. To elucidate the mechanism for islet-cell dysfunction, we generated {beta}-cell-specific Zmiz1 knockout (Zmiz1{beta}KO) mice. Male and female Zmiz1{beta}KO mice were glucose intolerant with impaired insulin secretion, compared with control littermates. Transcriptomic profiling of Zmiz1{beta}KO islets identified over 500 differentially expressed genes including those involved in {beta}-cell function and maturity which we confirmed at the protein level. After high fat feeding, Zmiz1{beta}KO mice fail to expand {beta}-cell mass and become severely diabetic. Thus, Zmiz1 is required for normal glucose homeostasis and may contribute to T2D risk by maintaining a mature {beta}-cell state and allowing islet mass expansion upon metabolic stress.

physiology↗

bioRxiv2022

Redox sensing by SENP1 augments insulin secretion early after high-fat feeding in mice

Pancreatic {beta}-cells respond to metabolic stress by upregulating insulin secretion, however the underlying mechanisms remain unclear. In {beta}-cells from overweight humans without diabetes, and mice fed a high-fat diet for 2 days, insulin exocytosis and secretion are enhanced without increased Ca2+ influx. {beta}-cell RNA-seq suggests altered metabolic pathways early following HFD, where we find increased basal oxygen consumption, proton leak, but a more reduced cytosolic redox state. Increased {beta}-cell exocytosis after 2-day HFD is dependent on this reduced intracellular redox and requires the sentrin-specific SUMO-protease-1 (SENP1). Mice with either pancreas- or {beta}-cell-specific SENP1 deletion fail to up-regulate exocytosis and become rapidly glucose intolerant after 2-day HFD. Mechanistically, redox-sensing by SENP1 requires a thiol group at C535 which together with Zn+-binding suppresses basal protease activity and unrestrained {beta}-cell exocytosis and increases SENP1 sensitivity to regulation by redox signals.

cell biology↗

bioRxiv2021

Impacts of the COVID-19 Pandemic on a Human Research Islet Program

Designated a pandemic in March 2020, the spread of severe acute respiratory syndrome virus 2 (SARS-CoV2), the virus responsible for coronavirus disease 2019 (COVID-19), led to new guidelines and restrictions being implemented for individuals, businesses, and societies in efforts to limit the impacts of COVID-19 on personal health and healthcare systems. Here we report the impacts of the COVID-19 pandemic on pancreas processing and islet isolation/distribution outcomes at the Alberta Diabetes Institute IsletCore, a facility specialising in the processing and distribution of human pancreatic islets for research. While the number of organs processed was significantly reduced, organ quality and the function of cellular outputs were minimally impacted during the pandemic when compared to an equivalent period immediately prior. Despite the maintained quality of isolated islets, recipient groups reported poorer feedback regarding the samples. Our findings suggest this is likely due to disrupted distribution which led to increased transit times to recipient labs, particularly those overseas. Thus, to improve overall outcomes in a climate of limited research islet supply, prioritization of tissue recipients based on likely tissue transit times may be needed.

physiology↗

bioRxiv2021

Heterogenous impairment of α-cell function in type 2 diabetes is linked to cell maturation state

In diabetes, glucagon secretion from pancreatic -cells is dysregulated. We examined -cells from human donors and mice using combined electrophysiological, transcriptomic, and computational approaches. Rising glucose suppresses -cell exocytosis by reducing P/Q-type Ca2+ channel activity, and this is disrupted in type 2 diabetes (T2D). Upon high-fat-feeding of mice, -cells shift towards a {beta}-cell-like electrophysiologic profile in concert with an up-regulation of the {beta}-cell Na+ channel isoform Scn9a and indications of impaired -cell identity. In human -cells we identify links between cell membrane properties and cell surface signalling receptors, mitochondrial respiratory complex assembly, and cell maturation. Cell type classification using machine learning of electrophysiology data demonstrates a heterogenous loss of electrophysiologic identity in -cells from donors with T2D. Indeed, a sub-set of -cells with impaired exocytosis is defined by an enrichment in progenitor markers suggesting important links between -cell maturation state and dysfunction in T2D. Key findingsO_LI-cell exocytosis is suppressed by glucose-dependent inhibition of P/Q-type Ca2+ currents C_LIO_LIDysfunction of -cells in type 2 diabetes is associated with a {beta}-cell-like electrophysiologic signature C_LIO_LIPatch-seq links maturation state, the mitochondrial respiratory chain, and cell surface receptor expression to -cell function C_LIO_LI-cell dysfunction occurs preferentially in cells enriched in endocrine lineage markers C_LI

cell biology↗

bioRxiv2021

Combinatorial transcription factor profiles predict mature and functional human islet α and β cells

Islet-enriched transcription factors (TFs) exert broad control over cellular processes in pancreatic and {beta} cells and changes in their expression are associated with developmental state and diabetes. However, the implications of heterogeneity in TF expression across islet cell populations are not well understood. To define this TF heterogeneity and its consequences for cellular function, we profiled >40,000 cells from normal human islets by scRNA-seq and stratified and {beta} cells based on combinatorial TF expression. Subpopulations of islet cells co-expressing ARX/MAFB ( cells) and MAFA/MAFB ({beta} cells) exhibited greater expression of key genes related to glucose sensing and hormone secretion relative to subpopulations expressing only one or neither TF. Moreover, all subpopulations were identified in native pancreatic tissue from multiple donors. By Patch-seq, MAFA/MAFB co-expressing {beta} cells showed enhanced electrophysiological activity. Thus, these results indicate combinatorial TF expression in islet and {beta} cells predicts highly functional, mature subpopulations.

genomics↗

bioRxiv2020

The type 1 diabetes at-risk allele at rs3842753 increases beta cell INS mRNA expression and variance in a meta-analysis of single cell RNA sequencing data

Type 1 diabetes is characterized by the autoimmune destruction of insulin secreting {beta} cells. Genetic variations upstream at the insulin (INS) locus contribute to ~10% of type 1 diabetes heritable risk. Multiple studies showed an association between rs3842753 C/C genotype and type 1 diabetes susceptibility, but the molecular mechanisms remain unclear. To date, no large-scale studies have looked at the effect of genetic variation at rs3842753 on INS mRNA at the single cell level. We aligned all human islet single cell RNA sequencing datasets available to us in 2020 to the reference genome GRCh38.98 and genotyped rs3842753, integrating 2315 {beta} cells and 1223 {beta}-like cells from 13 A/A protected donors, 23 A/C heterozygous donors, and 35 C/C at-risk donors, including adults without diabetes and with type 2 diabetes. INS expression mean and variance were significantly higher in single {beta} cells from females compared with males. Comparing across {beta} cells and {beta}-like cells, we found that rs3842753 C containing cells (either homozygous or heterozygous) had the highest INS expression. We also found that {beta} cells with the rs3842753 C allele had significantly higher ER stress marker gene expression compared to the A/A homozygous genotype. These findings support the emerging concept that inherited risk of type 1 diabetes may be associated with inborn, persistent elevated insulin production which may lead to {beta} cell ER stress and fragility.

cell biology↗

bioRxiv2020

β-cell SENP1 facilitates responsiveness to incretins and limits oral glucose intolerance in high fat fed mice

SUMOylation reduces oxidative stress and preserves islet mass; but this happens at the expense of robust insulin secretion. To investigate a role for the deSUMOylating enzyme sentrin-specific protease 1 (SENP1) in glycemia following metabolic stress, we put pancreas/gut-specific SENP1 knockout mice (pSENP1-KO) on an 8-10-week high fat diet (HFD). Male pSENP1-KO mice were more glucose intolerant following HFD than littermate controls, but this was only obvious in response to oral glucose, and a similar but milder phenotype was observed in females. Plasma incretin responses were identical, and glucose-dependent insulinotropic polypeptide (GIP) was equally upregulated after HFD, in pSENP1-KO and - WT littermates. Islet mass was not different, but insulin secretion and {beta}-cell exocytotic responses to Exendin4 (Ex4) and GIP were impaired in islets lacking SENP1. Glucagon secretion from pSENP1-KO islets was also reduced, consistent with the expected SENP1 knockout in all islet cells, so we generated {beta}-cell-specific SENP1 knockout mice ({beta}SENP1-KO). These phenocopied the pSENP1-KO mice with selective impairment in oral glucose tolerance following HFD, preserved islet mass expansion, and impaired {beta}-cell exocytosis and insulin secretion to Ex4 and GIP. Thus, {beta}-cell SENP1 limits glucose intolerance following HFD by ensuring a robust facilitation of insulin secretion by incretins such as GIP.

physiology↗

bioRxiv2020

Beta-cell specific insulin resistance promotes glucose-stimulated insulin hypersecretion

Abstract Insulin receptor (Insr) protein can be found at higher levels in pancreatic {beta}-cells than in most other tissues, but the consequences of {beta}-cell insulin resistance remain enigmatic. Ins1cre allele was used to delete Insr specifically in {beta}-cells of both female and male mice. Experimental mice were compared to Ins1cre-containing littermate controls at multiple ages and on multiple diets. RNA-seq of purified recombined {beta}-cells revealed transcriptomic consequences of Insr loss, which differed between female and male mice. Action potential and calcium oscillation frequencies were increased in Insr knockout {beta}- cells from female, but not male mice, whereas only male {beta}InsrKO mice had reduced ATP-coupled oxygen consumption rate and reduced expression of genes involved in ATP synthesis. Female {beta}InsrKO and {beta}InsrHET mice exhibited elevated insulin release in perifusion experiments, during hyperglycemic clamps, and following i.p. glucose challenge. Deletion of Insr did not alter {beta}-cell area up to 9 months of age, nor did it impair hyperglycemia-induced proliferation. Based on our data, we adapted a mathematical model to include {beta}-cell insulin resistance, which predicted that {beta}-cell Insr knockout would improve glucose tolerance depending on the degree of whole-body insulin resistance. Indeed, glucose tolerance was significantly improved in female {beta}InsrKO and {beta}InsrHET mice when compared to controls at 9, 21 and 39 weeks, and also in insulin-sensitive 4-week old males. We did not observe improved glucose tolerance in older male mice or in high fat diet-fed mice, corroborating the prediction that global insulin resistance obscures the effects of {beta}-cell specific insulin resistance. The propensity for hyperinsulinemia was associated with mildly reduced fasting glucose and increased body weight. We further validated our main in vivo findings using the Ins1-CreERT transgenic line and found that male mice had improved glucose tolerance 4 weeks after tamoxifen-mediated Insr deletion. Collectively, our data show that loss of {beta}-cell Insr contributes to glucose-induced hyperinsulinemia, thereby improving glucose homeostasis in otherwise insulin sensitive dietary and age contexts.

physiology↗