Characterization of Zinc Influx Transporters (ZIPs) in pancreatic beta cells: roles in regulating cytosolic zinc homeostasis and insulin secretion

Zinc plays an essential role in the regulation of pancreatic beta cell function, affecting important processes including proinsulin biosynthesis, glucose-stimulated insulin secretion, and cell viability. Mutations in zinc efflux transport protein ZnT8, have been linked with both type 1 and type 2 diabetes, further supporting an important role for zinc in glucose homeostasis. However, very little is known about how cytosolic zinc is controlled by zinc influx proteins (ZIPs). In the current study, we have examined the beta cell and islet ZIP transcriptome and show consistent high expression of ZIP6 (Slc39a6) and ZIP7 (Slc39a7) genes across human, mouse islets and MIN6 beta cells. Modulation of ZIP6 and ZIP7 expression significantly altered cytosolic zinc influx in pancreatic beta cells, indicating an important role for ZIP6 and ZIP7 in regulating cellular zinc homeostasis. Functionally, this deregulated cytosolic zinc homeostasis led to impaired insulin exocytosis and insulin secretion. In parallel studies, we identified both ZIP6 and ZIP7 as potential interacting proteins with GLP-1R by a membrane yeast-two-hybrid (MYTH) assay. Knock-down of ZIP6 but not ZIP7 in MIN6 beta cells impaired the protective effects of GLP-1 on fatty acid-induced cell death possibly via reduced p-ERK pathway. Thus, our data suggests that ZIP6 and ZIP7 function as two important zinc influx transporters to regulate cytosolic zinc concentrations and insulin secretion in beta cells. In particular, ZIP6 is also capable of directly interacting with GLP-1R to facilitate the protective effect of GLP-1 on beta cell survival

GDF15 promotes weight loss by enhancing energy expenditure in muscle

Funding Information: We thank R. Seeley for sharing GFRAL-null mice; B. Lowell for sharing β-less mice; and J. Wu for shipping β-less mice to us. G.R.S. was supported by a Diabetes Canada Investigator Award (DI-5-17-5302-GS), a Canadian Institutes of Health Research Foundation Grant (201709FDN-CEBA-116200), a Tier 1 Canada Research Chair in Metabolic Diseases and a J. Bruce Duncan Endowed Chair in Metabolic Diseases; D.W. by Fellowship Grants from the McMaster Institute for Research on Aging (MIRA) at McMaster University; S.R. by a postdoctoral fellowship supported by MITACS and Novo Nordisk; L.K.T. by a CIHR Post-Doctoral Fellowship Award and Michael DeGroote Fellowship Award in Basic Biomedical Science; E.M.D. by a Vanier Canada Graduate Scholarship; G.P.H. by the Natural Sciences and Engineering Research Council of Canada (NSERC: 400362); G.J.D. and S.M.F. by NSERC-CGSM scholarships; L.D. by the Fonds de Recherche du Québec-Santé doctoral training award; D.P.B. by the GSK Chair in Diabetes of Université de Sherbrooke and a FRQS J1 salary award. The Genotype-Tissue Expression (GTEx) Project was supported by the Common Fund of the Office of the Director of the National Institutes of Health, and by the NCI, NHGRI, NHLBI, NIDA, NIMH and NINDS. Funding Information: S.B.J. and R.E.K. are employees of Novo Nordisk, a pharmaceutical company producing and selling medicine for the treatment of diabetes and obesity. G.R.S. is a co-founder and shareholder of Espervita Therapeutics. McMaster University has received funding from Espervita Therapeutics, Esperion Therapeutics, Poxel Pharmaceuticals and Nestle for research conducted in the laboratory of G.R.S. S.R. is supported by a MITACS postdoctoral fellowship sponsored by Novo Nordisk. H.C.G. holds the McMaster-Sanofi Population Health Institute Chair in Diabetes Research and Care. G.R.S., G.P. and H.C.G. are inventors listed on a patent for identifying GDF15 as a biomarker for metformin. G.R.S. has received consulting/speaking fees from Astra Zeneca, Eli Lilly, Esperion Therapeutics, Merck, Poxel Pharmaceuticals and Cambrian Biosciences. The other authors declare no competing interests. Publisher Copyright: © 2023, The Author(s).Peer reviewedPublisher PD

Critical metals in porphyry copper deposits

The ability to yield glucose-responsive pancreatic beta-cells from human pluripotent stem cells in vitro will facilitate the development of the cell replacement therapies for the treatment of Type 1 Diabetes. Here, through the sequential in vitro targeting of selected signaling pathways, we have developed an abbreviated five-stage protocol (25-30 days) to generate human Embryonic Stem Cell-Derived Beta-like Cells (ES-DBCs). We showed that Geltrex, as an extracellular matrix, could support the generation of ES-DBCs more efficiently than that of the previously described culture systems. The activation of FGF and Retinoic Acid along with the inhibition of BMP, SHH and TGF-beta led to the generation of 75% NKX6.1+/NGN3+ Endocrine Progenitors. The inhibition of Notch and tyrosine kinase receptor AXL, and the treatment with Exendin-4 and T3 in the final stage resulted in 35% mono-hormonal insulin positive cells, 1% insulin and glucagon positive cells and 30% insulin and NKX6.1 co-expressing cells. Functionally, ES-DBCs were responsive to high glucose in static incubation and perifusion studies, and could secrete insulin in response to successive glucose stimulations. Mitochondrial metabolic flux analyses using Seahorse demonstrated that the ES-DBCs could efficiently metabolize glucose and generate intracellular signals to trigger insulin secretion. In conclusion, targeting selected signaling pathways for 25-30 days was sufficient to generate ES-DBCs in vitro. The ability of ES-DBCs to secrete insulin in response to glucose renders them a promising model for the in vitro screening of drugs, small molecules or genes that may have potential to influence beta-cell function

RGS4-Deficiency Alters Intracellular Calcium and PKA-Mediated Control of Insulin Secretion in Glucose-Stimulated Beta Islets

A number of diverse G-protein signaling pathways have been shown to regulate insulin secretion from pancreatic β-cells. Accordingly, regulator of G-protein signaling (RGS) proteins have also been implicated in coordinating this process. One such protein, RGS4, is reported to show both positive and negative effects on insulin secretion from β-cells depending on the physiologic context under which it was studied. We here use an RGS4-deficient mouse model to characterize previously unknown G-protein signaling pathways that are regulated by RGS4 during glucose-stimulated insulin secretion from the pancreatic islets. Our data show that loss of RGS4 results in a marked deficiency in glucose-stimulated insulin secretion during both phase I and phase II of insulin release in intact mice and isolated islets. These deficiencies are associated with lower cAMP/PKA activity and a loss of normal calcium surge (phase I) and oscillatory (phase II) kinetics behavior in the RGS4-deficient β-cells, suggesting RGS4 may be important for regulation of both Gαi and Gαq signaling control during glucose-stimulated insulin secretion. Together, these studies add to the known list of G-protein coupled signaling events that are controlled by RGS4 during glucose-stimulated insulin secretion and highlight the importance of maintaining normal levels of RGS4 function in healthy pancreatic tissues

Short protocol outline.

<p>(A) Schematic overview of the 25 to 30-day protocol to generate human H1 ES-derived beta-like cells (DBCs). Below, images of the differentiated H1 cells and the control cells (Non-Treated ES cell) at each stage are shown. The arrow symbol identifies tube-like structure in the differentiated cells in the stage 2. The star symbol identifies detached dead cells as spheres in the Non-Treated cells in stage 4. Scale bar = 100μm for all cell images. The <i>red font</i> indicates modifications to molecules or timing in comparison to the protocol described by Rezania et al [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164457#pone.0164457.ref009" target="_blank">9</a>]. (B) Expression analyses of <i>SOX17</i>, <i>FOXA2</i> and <i>Gooscoid</i> as Definitive Endoderm (DE), <i>Sox1</i> as ectoderm, and <i>Brachyury</i> as mesoderm-specific markers in the H1 ES cells differentiated on MEF, Mouse Embryonic Fibroblast; as EB (Embryoid Bodies) or on Geltrex, analyzed by quantitative RT-PCR. (* <i>p< 0</i>.<i>05</i>, **<i>p< 0</i>.<i>01</i>, p***<<i>0</i>.<i>001</i>, significant differences between the treated and control cells in each condition, unpaired two-tailed <i>t</i>-test, n = 3).</p

Prevention of Lipotoxicity in Pancreatic Islets with Gammahydroxybutyrate

Oxidative stress caused by the exposure of pancreatic &szlig;-cells to high levels of fatty acids impairs insulin secretion. This lipotoxicity is thought to play an important role in &szlig;-cell failure in type 2 diabetes and can be prevented by antioxidants. Gamma-hydroxybutyrate (GHB), an endogenous antioxidant and energy source, has previously been shown to protect mice from streptozotocin and alloxan-induced diabetes; both compounds are generators of oxidative stress and yield models of type-1 diabetes. We sought to determine whether GHB could protect mouse islets from lipotoxicity caused by palmitate, a model relevant to type 2 diabetes. We found that GHB prevented the generation of palmitate-induced reactive oxygen species and the associated lipotoxic inhibition of glucose-stimulated insulin secretion while increasing the NADPH/NADP+ ratio. GHB may owe its antioxidant and insulin secretory effects to the formation of NADPH

Comparison of gene expression in human H1 ES-DBCs and mature beta-cells.

<p>Expression of the top-ten most significantly enriched mRNAs in either adult mature or fetal beta-cells as described by <i>Hrvatin et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164457#pone.0164457.ref026" target="_blank">26</a>]</i> were examined in ES-DBCs vs. the human adult islets via real time RT-PCR assay. (*<i>p< 0</i>.<i>05</i>, **<i>p< 0</i>.<i>01</i>, p***<<i>0</i>.<i>001</i>, unpaired two-tailed <i>t</i>-test, n = 3).</p

The mRNA expression analysis of pancreatic islet, beta-cell and related genes in the differentiated human H1 ES-DBCs.

<p>(A) Exact copy number of insulin mRNA molecules in the ES-DBCs and human islets by digital droplet RT-PCR (GAPDH was used for normalization). Quantitative real time RT-PCR analysis for (B) endocrine hormones, (C) Chromogranin A, (D) pancreatic transcription factors, Ca⁺² and K⁺ channels genes, (E) Glucose transporters (<i>GLUT1 and 2</i>) and <i>PCSK2</i> as the enzyme required for pro-insulin processing and in the ES-DBCs compared to human islets. (*<i>p< 0</i>.<i>05</i>, **<i>p< 0</i>.<i>01</i>, p***<<i>0</i>.<i>001</i>, unpaired two-tailed <i>t</i>-test, n = 3).</p