Insulin sensitization via partial agonism of PPARγ and glucose uptake through translocation and activation of GLUT4 in PI3K/p-Akt signaling pathway by embelin in type 2 diabetic rats

Background

The present study was aimed at isolating an antidiabetic molecule from a herbal source and assessing its mechanism of action.

Methods

Embelin, isolated from Embelia ribes Burm. (Myrsinaceae) fruit, was evaluated for its potential to regulate insulin resistance, alter β-cell dysfunction and modulate key markers involved in insulin sensitivity and glucose transport using high-fat diet (HFD) fed-streptozotocin (STZ) (40 mg/kg)-induced type 2 diabetic rats. Molecular-dockings were performed to investigate the binding modes of embelin into PPARγ, PI3K, p-Akt and GLUT4 active sites.

Results

Embelin (50 mg/kg b wt.) reduced body weight gain, blood glucose and plasma insulin in treated diabetic rats. It further modulated the altered lipid profiles and antioxidant enzymes with cytoprotective action on β-cell. Embelin significantly increased the PPARγ expression in epididymal adipose tissue compared to diabetic control group; it also inhibited adipogenic activity; it mildly activated PPARγ levels in the liver and skeletal muscle. It also regulated insulin mediated glucose uptake in epididymal adipose tissue through translocation and activation of GLUT4 in PI3K/p-Akt signaling cascade. Embelin bound to PPARγ; it disclosed stable binding affinities to the active sites of PI3K, p-Akt and GLUT4.

Conclusions

These findings show that embelin could improve adipose tissue insulin sensitivity without increasing weight gain, enhance glycemic control, protect β-cell from damage and maintain glucose homeostasis in adipose tissue.

General significance

Embelin can be used in the prevention and treatment of type 2 diabetes mellitus caused due to obesity.     

Cloning,characterization, and expression of glucose transporter 2 in the freeze-tolerant wood frog, Rana sylvatica

Background

The essential role of glucose transporter 2 (GLUT2) in glucose homeostasis has been extensively studied in mammals; however, little is known about this important protein in lower vertebrates. The freeze-tolerant wood frog (Rana sylvatica), which copiously mobilizes glucose in response to freezing, represents an excellent system for the study of glucose transport in amphibians.

Methods

GLUT2 was sequenced from northern and southern phenotypes of R. sylvatica, as well as the freeze-intolerant Rana pipiens. These proteins were expressed and functionally characterized in Xenopus oocytes. Abundance of GLUT2 in tissues was analyzed using immunoblotting techniques.

Results

GLUT2s cloned from these anurans encoded proteins with high sequence homologies to known vertebrate GLUT2s and had similar transport properties, although, notably, transport of the glucose analog 3-O-methyl-d-glucose (3-OMG) was strongly inhibited by 150 mM urea. Proteins from all study subjects had similar affinity constants (~ 12 mM) and other kinetic properties; however, GLUT2 abundance in liver was 3.5-fold greater in northern R. sylvatica than in the southern conspecific and R. pipiens.

Conclusion

Our results indicate that amphibian GLUT2s are structurally and functionally similar to their homologs in other vertebrates, attesting to the conserved nature of this transport protein. The greater abundance of this protein in the northern phenotype of R. sylvatica suggests that these transporters contribute importantly to freezing survival.

General significance

This study provides the first functional characterization of any GLUT isoform from an anuran amphibian and novel insights into the role of these proteins in glucose homeostasis and cryoprotectant mobilization in freeze-tolerant vertebrates.     

Roles of mitochondrial fragmentation and reactive oxygen species in mitochondrial dysfunction and myocardial insulin resistance

Purpose

Evidence suggests an association between aberrant mitochondrial dynamics and cardiac diseases. Because myocardial metabolic deficiency caused by insulin resistance plays a crucial role in heart disease, we investigated the role of dynamin-related protein-1 (DRP1; a mitochondrial fission protein) in the pathogenesis of myocardial insulin resistance.

Methods and Results

DRP1-expressing H9c2 myocytes, which had fragmented mitochondria with mitochondrial membrane potential (ΔΨ_m) depolarization, exhibited attenuated insulin signaling and 2-deoxy-d-glucose (2-DG) uptake, indicating insulin resistance. Treatment of the DRP1-expressing myocytes with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP) significantly improved insulin resistance and mitochondrial dysfunction. When myocytes were exposed to hydrogen peroxide (H₂O₂), they increased DRP1 expression and mitochondrial fragmentation, resulting in ΔΨ_m depolarization and insulin resistance. When DRP1 was suppressed by siRNA, H₂O₂-induced mitochondrial dysfunction and insulin resistance were restored. Our results suggest that a mutual enhancement between DRP1 and reactive oxygen species could induce mitochondrial dysfunction and myocardial insulin resistance. In palmitate-induced insulin-resistant myocytes, neither DRP1-suppression nor TMPyP restored the ΔΨ_m depolarization and impaired 2-DG uptake, however they improved insulin signaling.

Conclusions

A mutual enhancement between DRP1 and ROS could promote mitochondrial dysfunction and inhibition of insulin signal transduction. However, other mechanisms, including lipid metabolite-induced mitochondrial dysfunction, may be involved in palmitate-induced insulin resistance.     

The AMPK-SIRT signaling network regulates glucose tolerance under calorie restriction conditions

Aims

SIRT1 and AMP-activated protein kinase (AMPK) share common activators, actions and target molecules. Previous studies have suggested that a putative SIRT1-AMPK regulatory network could act as the prime initial sensor for calorie restriction-induced adaptations in skeletal muscle—the major site of insulin-stimulated glucose disposal. Our study aimed to investigate whether a feedback loop exists between AMPK and SIRT1 in skeletal muscle and how this may be involved glucose tolerance.

Main methods

To investigate this, we used skeletal muscle-specific AMPKα1/2 knockout mice (AMPKα1/2^−/−) fed ad libitum (AL) or a 30% calorie restricted (CR) diet and L6 rat myoblasts incubated with SIRT1 inhibitor (EX527).

Key findings

CR-AMPKα1/2^−/− displayed impaired glucose tolerance (*p < 0.05), in association with down-regulated SIRT1 and PGC-1α expression (< 300% vs. CR-WT, ^±±p < 0.01). Moreover, AMPK activity was decreased following SIRT1 inhibition in L6 cells (~ 0.5-fold vs. control, *p < 0.05).

Significance

This study demonstrates that skeletal muscle-specific AMPK deficiency impairs the beneficial effects of CR on glucose tolerance and that these effects may be dependent on reduced SIRT1 levels.     

3β-taraxerol of Mangifera indica, a PI3K dependent dual activator of glucose transport and glycogen synthesis in 3T3-L1 adipocytes

Background

The present study focuses on identifying and developing an anti-diabetic molecule from plant sources that would effectively combat insulin resistance through proper channeling of glucose metabolism involving glucose transport and storage.

Methods

Insulin-stimulated glucose uptake formed the basis for isolation of a bioactive molecule through column chromatography followed by its characterization using NMR and mass spectroscopic analysis. Mechanism of glucose transport and storage was evaluated based on the expression profiling of signaling molecules involved in the process.

Results

The study reports (i) the isolation of a bioactive compound 3β-taraxerol from the ethyl acetate extract (EAE) of the leaves of Mangifera indica (ii) the bioactive compound exhibited insulin-stimulated glucose uptake through translocation and activation of the glucose transporter (GLUT4) in an IRTK and PI3K dependent fashion. (iii) the fate of glucose following insulin-stimulated glucose uptake was ascertained through glycogen synthesis assay that involved the activation of PKB and suppression of GSK3β.

General significance

This study demonstrates the dual activity of 3β-taraxerol and the ethyl acetate extract of Mangifera indica as a glucose transport activator and stimulator of glycogen synthesis. 3β-taraxerol can be validated as a potent candidate for managing the hyperglycemic state.     

Involvement of MAPK signaling pathway in the osteogenic gene expressions of Cervi Pantotrichum Cornu in MG-63 human osteoblast-like cells

Aims

The purposes of this study were to determine whether Cervi Pantotrichum Cornu (CPC) has osteogenic activities in human osteoblastic MG-63 cells and to investigate the underlying molecular mechanism.

Main methods

The effects of CPC on alkaline phosphatase activity, collagen synthesis, and calcium deposits were measured. The COL1A1, ALPL, BGLAP, and SPP1 expressions were measured by real-time PCR. Phosphorylated MAP kinases (ERK1/2, JNK1/2, p38, ELK1, and cJUN) were studied by western blot analysis. The involvement of MAPK pathway in osteogenic gene expressions was determined by using each selective MAPK inhibitor (PD98059, SP600125, and SB203580).

Key findings

CPC increased alkaline phosphatase activity, collagen synthesis, and calcium deposits. CPC activated ERK1/2, JNK1/2, p38, and ELK1 phosphorylation except cJUN. CPC increased the COL1A1, ALPL, BGLAP, and SPP1 gene expressions. The elevated COL1A1 and BGLAP expressions were inhibited by PD98059, SP600125 or SB203580. The elevated ALPL expression was blocked by SB203580. The elevated SPP1 expression was inhibited by SP600125 or SB203580. CPC increased COL1A1 and BGLAP expressions via ERK1/2, JNK1/2, and p38 MAPKs pathways and SPP1 expression via JNK1/2 and p38 pathways. p38 pathway is needed for ALPL expression.

Significance

These results imply that MAPK signaling pathway is an indispensable factor for bone matrix genes expression of CPC in MG-63 human osteoblast-like cells.     

GLUT4 and UBC9 protein expression is reduced in muscle from type 2 diabetic patients with severe insulin resistance

Aims

Subgroups of patients with type 2 diabetes mellitus demand large insulin doses to maintain euglycemia. These patients are characterized by severe skeletal muscle insulin resistance and the underlying pathology remains unclear. The purpose of this study was to examine protein expression of the principal glucose transporter, GLUT4, and associated proteins in skeletal muscle from type 2 diabetic patients characterized by severe insulin resistance.

Methods

Seven type 2 diabetic patients with severe insulin resistance (mean insulin dose 195 IU/day) were compared with seven age matched type 2 diabetic patients who did not require insulin treatment, and with an age matched healthy control group. Protein expression of GLUT4 and associated proteins was assessed in muscle and fat biopsies using standard western blotting techniques.

Results

GLUT4 protein expression was significantly reduced by ∼30 pct in skeletal muscle tissue from severely insulin resistant type 2 diabetic subjects, compared with both healthy controls and type 2 diabetic subjects that did not require insulin treatment. In fat tissue, GLUT4 protein expression was reduced in both diabetic groups. In skeletal muscle, the reduced GLUT4 expression in severe insulin resistance was associated with decreased ubiquitin-conjugating enzyme 9 (UBC9) expression while expression of GLUT1, TBC1D1 and AS160 was not significantly different among type 2 diabetic patients and matched controls.

Conclusions

Type 2 diabetic patients with severe insulin resistance have reduced expression of GLUT4 in skeletal muscle compared to patients treated with oral antidiabetic drugs alone. GLUT4 protein levels may therefore play a role in the pathology behind type 2 diabetes mellitus among subgroups of patients, and this may explain the heterogeneous response to insulin treatment. This new finding contributes to the understanding of the underlying mechanisms for the development of extreme insulin resistance.     

Intracellular cholesterol transporters and modulation of hepatic lipid metabolism: Implications for diabetic dyslipidaemia and steatosis

Aims/hypotheses

To examine hepatic expression of cholesterol-trafficking proteins, mitochondrial StarD1 and endosomal StarD3, and their relationship with dyslipidaemia and steatosis in Zucker (fa/fa) genetically obese rats, and to explore their functional role in lipid metabolism in rat McArdle RH-7777 hepatoma cells.

Methods

Expression of StarD1 and StarD3 in rat liver and hepatoma samples were determined by Q-PCR and/or immunoblotting; lipid mass by colorimetric assays; radiolabelled precursors were utilised to measure lipid synthesis and secretion, and lipidation of exogenous apolipoprotein A-I.

Results

Hepatic expression of StarD3 protein was repressed by genetic obesity in (fa/fa) Zucker rats, compared with lean (Fa/?) controls, suggesting a link with storage or export of lipids from the liver. Overexpression of StarD1 and StarD3, and knockdown of StarD3, in rat hepatoma cells, revealed differential effects on lipid metabolism. Overexpression of StarD1 increased utilisation of exogenous (preformed) fatty acids for triacylglycerol synthesis and secretion, but impacted minimally on cholesterol homeostasis. By contrast, overexpression of StarD3 increased lipidation of exogenous apoA-I, and facilitated de novo biosynthetic pathways for neutral lipids, potentiating triacylglycerol accumulation but possibly offering protection against lipotoxicity. Finally, StarD3 overexpression altered expression of genes which impact variously on hepatic insulin resistance, inducing Ppargcla, Cyp2e1, Nr1h4, G6pc and Irs1, and repressing expression of Scl2a1, Igfbp1, Casp3 and Serpine 1.

Conclusions/interpretation

Targeting StarD3 may increase circulating levels of HDL and protect the liver against lipotoxicity; loss of hepatic expression of this protein, induced by genetic obesity, may contribute to the pathogenesis of dyslipidaemia and steatosis.     

Up-regulation of cyclinD1 and Bcl2A1 by insulin is involved in osteoclast proliferation

Aims

Insulin receptor signaling in osteoblasts has been well established, but the effects of insulin on osteoclast proliferation are poorly explored. The objective of this study was to investigate the roles and the mechanisms of insulin on osteoclast proliferation.

Main methods

After insulin treatment to primary osteoclast precursors, BrdU incorporation assay was performed and the expression of cell cycle- and apoptosis-related genes was determined by real-time PCR and immunoblotting. Apoptosis was analyzed using a FACScan flow cytometer.

Key findings

Insulin activated insulin receptor and promoted the proliferation of osteoclast precursors in time- and dose-dependent manners. However, the expression of insulin receptor was not changed by it during that time. Insulin remarkably induced the expression of cyclinD1, a cell cycle marker, and Bcl2A1, an anti-apoptotic oncogene, whereas cdk1 and cdk4 were not affected by it. The expression of Bcl2l11 and Bax, both apoptotic markers, was reduced or not changed in osteoclast precursors. Bcl2A1/Bax ratio was also increased in protein levels. Treatment with obatoclax, a Bcl2 family inhibitor, significantly induced the apoptosis of osteoclast precursors in the presence of insulin. These results demonstrate that insulin promotes osteoclast proliferation by increasing cell cycle and suppressing apoptosis through specific gene regulation.

Significance

These data provide a basis for understanding and ultimately treating several bone-related metabolic diseases.     

Autocrine GM-CSF transcription in the leukemic progenitor cell line KG1a is mediated by the transcription factor ETS1 and is negatively regulated through SECTM1 mediated ligation of CD7

Background

CD7 expression is found on ~ 30% of acute myeloblastic leukemias (AML). The leukemic progenitor cell line KG1a (CD7 +) constitutively expresses GM-CSF while the parental KG1 (CD7-) cell line does not. This study focuses on the molecular basis of CD7 mediated GM-CSF regulation.

Methods

KG1a cells were treated with recombinant SECTM1-Fc protein, the PI3K kinase inhibitors wortmannin, LY292004, or PI4K activator spermine. Stable KG1-CD7 +, KG1a-shCD7, KG1a-shETS1 as well as KG1a-GFP, KG1a-PKCβII-GFP cell lines were generated and the levels of CD7, GM-CSF and ETS-1 mRNA and protein were compared by real-time-PCR, western blotting, flow cytometry and ELISA.

Results

SECTM1 is expressed in Human Bone Marrow Endothelial Cells (HBMEC) and its expression can be upregulated by both IFN-γ. KG1a cells demonstrated high expression levels of CD7 and ETS-1 allowing a constitutative signaling through the PI3K/Atk pathway to promote GM-CSF expression, while KG1 cells with low expression of CD7 and ETS-1 showed low GM-CSF expression. On KG1a cells GM-CSF expression could be negatively regulated by PI3K inhibitors or by recombinant SECTM1-Fc. Overexpression of CD7 in KG1 cells was insufficient to promote GM-CSF expression, while silencing of CD7 or ETS-1 resulted in reduced GM-CSF expression levels. Differentiation capable KG1a cells overexpressing PKCβII illustrated complete loss of CD7, but maintained normal levels of both ETS-1 and GM-CSF expression.

Conclusion

These findings add an additional layer to the previously described autocrine/paracrine signaling between leukemic progenitor cells and the bone marrow microenvironment and highlight a role for SECTM1 in both normal and malignant hematopoiesis.

General Significance

This work shows that SECTM1 secreted from bone marrow stromal cells may interact with CD7 to influence GM-CSF expression in leukemic cells.     

Hyperoxia reverses glucotoxicity-induced inhibition of insulin secretion in rat INS-1 β cells

Chronic hyperglycemia has deleterious effects on pancreatic β-cell function, a process known as glucotoxicity. This study examined whether chronic high glucose (CHG) induces cellular hypoxia in rat INS-1 β cells, and whether hyperoxia (35% O₂) can reverse glucotoxicity-induced inhibition of insulin secretion. CHG (33.3?mm, 96?h) reduced insulin secretion, and down-regulated insulin and pancreatic duodenal homeobox factor 1 gene expression. CHG also increased intracellular pimonidazole-protein adducts, a marker for hypoxia. CHG also enhanced hypoxia-inducible factor 1α (HIF-1α) protein expression and its DNA-binding activity, which was accompanied by a decrease in mRNA expression of glucose transporter 2 (GLUT2), glucokinase and uncoupling protein-2 and an increase in mRNA expression of GLUT1 and pyruvate dehydrogenase kinase 1. Hyperoxia restored the decrease in insulin secretion and the gene expression except for GLUT2, and suppressed intracellular hypoxia and HIF-1α activation. These results suggest that glucotoxicity may cause β-cell hypoxia. Hyperoxia might prevent glucotoxicity-induced β-cell dysfunction and improve insulin secretion.     

Expression of the hypoxia-inducible monocarboxylate transporter MCT4 is increased in triple negative breast cancer and correlates independently with clinical outcome

Background

¹⁸Fluor-deoxy-glucose PET-scanning of glycolytic metabolism is being used for staging in many tumors however its impact on prognosis has never been studied in breast cancer.

Methods

Glycolytic and hypoxic markers: glucose transporter (GLUT1), carbonic anhydrase IX (CAIX), monocarboxylate transporter 1 and 4 (MCT1, 4), MCT accessory protein basigin and lactate-dehydrogenase A (LDH-A) were assessed by immunohistochemistry in two cohorts of breast cancer comprising 643 node-negative and 127 triple negative breast cancers (TNBC) respectively.

Results

In the 643 node-negative breast tumor cohort with a median follow-up of 124 months, TNBC were the most glycolytic (≈70%), followed by Her-2 (≈50%) and RH-positive cancers (≈30%). Tumoral MCT4 staining (without stromal staining) was a strong independent prognostic factor for metastasis-free survival (HR = 0.47, P = 0.02) and overall-survival (HR = 0.38, P = 0.002). These results were confirmed in the independent cohort of 127 cancer patients.

Conclusion

Glycolytic markers are expressed in all breast tumors with highest expression occurring in TNBC. MCT4, the hypoxia-inducible lactate/H⁺ symporter demonstrated the strongest deleterious impact on survival. We propose that MCT4 serves as a new prognostic factor in node-negative breast cancer and can perhaps act soon as a theranostic factor considering the current pharmacological development of MCT4 inhibitors.     

Osthole activates glucose uptake but blocks full activation in L929 fibroblast cells,and inhibits uptake in HCLE cells

Aims

Osthole, a coumarin derivative, has been used in Chinese medicine and studies have suggested a potential use in treatment of diabetes and cancers. Therefore, we investigated the effects of osthole and other coumarins on GLUT1 activity in two cell lines that exclusively express GLUT1.

Main methods

We measured the magnitude and time frame of the effects of osthole and related coumarins on glucose uptake in two cells lines; L929 fibroblast cells which have low GLUT1 expression levels and low basal glucose uptake and HCLE cells which have high GLUT1 concentrations and high basal uptake. We also explored the effects of these coumarins in combination with other GLUT1 activators.

Key findings

Osthole activates glucose uptake in L929 cells with a modest maximum 1.7-fold activation achieved by 50 μM with both activation and recovery occurring within minutes. However, osthole blocks full acute activation of glucose uptake by other, more robust activators. This behavior mimics the effects of other thiol reactive compounds and suggests that osthole is interacting with cysteine residues, possibly within GLUT1 itself. Coumarin, 7-hydroxycoumarin, and 7-methoxycoumarin, do not affect glucose uptake, which is consistent with the notion that the isoprenoid structure in osthole may be important to gain membrane access to GLUT1. In contrast to its effects in L929 cells, osthole inhibits basal glucose uptake in the more active HCLE cells.

Significance

The differential effects of osthole in L929 and HCLE cells indicated that regulation of GLUT1 varies, likely depending on its membrane concentration.     

Synthetic peptides derived from the C-terminal 6 kDa region of Plasmodium falciparum SERA5 inhibit the enzyme activity and malaria parasite development

Background

Plasmodium falciparum serine repeat antigen 5 (PfSERA5) is an abundant blood stage protein that plays an essential role in merozoite egress and invasion. The native protein undergoes extensive proteolytic cleavage that appears to be tightly regulated. PfSERA5 N-terminal fragment is being developed as vaccine candidate antigen. Although PfSERA5 belongs to papain-like cysteine protease family, its catalytic domain has a serine in place of cysteine at the active site.

Methods

In the present study, we synthesized a number of peptides from the N- and C-terminal regions of PfSERA5 active domain and evaluated their inhibitory potential.

Results

The final proteolytic step of PfSERA5 involves removal of a C-terminal ~ 6 kDa fragment that results in the generation of a catalytically active ~ 50 kDa enzyme. In the present study, we demonstrate that two of the peptides derived from the C-terminal ~ 6 kDa region inhibit the parasite growth and also cause a delay in the parasite development. These peptides reduced the enzyme activity of the recombinant protein and co-localized with the PfSERA5 protein within the parasite, thereby indicating the specific inhibition of PfSERA5 activity. Molecular docking studies revealed that the inhibitory peptides interact with the active site of the protein. Interestingly, the peptides did not have an effect on the processing of PfSERA5.

Conclusions

Our observations indicate the temporal regulation of the final proteolytic cleavage step that occurs just prior to egress.

General significance

These results reinforce the role of PfSERA5 for the intra-erythrocytic development of malaria parasite and show the role of carboxy terminal ~ 6 kDa fragments in the regulation of PfSERA5 activity. The results also suggest that final cleavage step of PfSERA5 can be targeted for the development of new anti-malarials.     

The insulin-mimetic effect of Morin: A promising molecule in diabetes treatment

Background

Type-2 diabetes is a worldwidely diffuse disease characterized by insulin resistance that arises from alterations of receptor and/or post-receptor events of insulin signalling. Studies performed with PTP1B-deficent mice demonstrated that PTP1B is the main negative regulator of insulin signalling. Inhibition or down regulation of this enzyme causes enhanced insulin sensitivity. Hence this enzyme represents the most attractive target for development of innovative anti-diabetic drugs.

Methods

Selection of new PTP1B inhibitors among an in house library of polyphenolic compounds was carried out screening their activity. The inhibition mechanism of Morin was determined by kinetic analyses. The cellular action of Morin was assayed on HepG2 cells. Analyses of the insulin signalling pathways was carried out by Western blot methods, glycogen synthesis was estimated by measuring the incorporation of [³H]-glucose, gluconeogenesis rate was assayed by measuring the glucose release in the cell medium. Cell growth was estimated by cell count. Docking analysis was conducted with SwissDock program.

Results

We demonstrated that Morin: i) is a non-competitive inhibitor of PTP1B displaying a K_i in the μM range; ii) increases the phosphorylation of the insulin receptor and Akt; iii) inhibits gluconeogenesis and enhances glycogen synthesis. Morin does not enhance cell growth.

Conclusions

We have identified Morin as a new small molecular non-competitive inhibitor of PTP1B, which behaves as an activator and sensitizer of the insulin receptor stimulating the metabolic pathways only.

General significance

Our study suggests that Morin is a useful lead for development of new low Mr compounds potentially active as antidiabetic drugs.     

The physiological effects of deleting the mouse SLC30A8 gene encoding zinc transporter-8 are influenced by gender and genetic background

Objective

The SLC30A8 gene encodes the islet-specific transporter ZnT-8, which is hypothesized to provide zinc for insulin-crystal formation. A polymorphic variant in SLC30A8 is associated with altered susceptibility to type 2 diabetes. Several groups have examined the effect of global Slc30a8 gene deletion but the results have been highly variable, perhaps due to the mixed 129SvEv/C57BL/6J genetic background of the mice studied. We therefore sought to remove the conflicting effect of 129SvEv-specific modifier genes.

Methods

The impact of Slc30a8 deletion was examined in the context of the pure C57BL/6J genetic background.

Results

Male C57BL/6J Slc30a8 knockout (KO) mice had normal fasting insulin levels and no change in glucose-stimulated insulin secretion (GSIS) from isolated islets in marked contrast to the ∼50% and ∼35% decrease, respectively, in both parameters observed in male mixed genetic background Slc30a8 KO mice. This observation suggests that 129SvEv-specific modifier genes modulate the impact of Slc30a8 deletion. In contrast, female C57BL/6J Slc30a8 KO mice had reduced (∼20%) fasting insulin levels, though this was not associated with a change in fasting blood glucose (FBG), or GSIS from isolated islets. This observation indicates that gender also modulates the impact of Slc30a8 deletion, though the physiological explanation as to why impaired insulin secretion is not accompanied by elevated FBG is unclear. Neither male nor female C57BL/6J Slc30a8 KO mice showed impaired glucose tolerance.

Conclusions

Our data suggest that, despite a marked reduction in islet zinc content, the absence of ZnT-8 does not have a substantial impact on mouse physiology.