ZnT8 Loss of Function Mutation Increases Resistance of Human Embryonic Stem Cell-Derived Beta Cells to Apoptosis in Low Zinc Condition.

The rare SLC30A8 mutation encoding a truncating p.Arg138* variant (R138X) in zinc transporter 8 (ZnT8) is associated with a 65% reduced risk for type 2 diabetes. To determine whether ZnT8 is required for beta cell development and function, we derived human pluripotent stem cells carrying the R138X mutation and differentiated them into insulin-producing cells. We found that human pluripotent stem cells with homozygous or heterozygous R138X mutation and the null (KO) mutation have normal efficiency of differentiation towards insulin-producing cells, but these cells show diffuse granules that lack crystalline zinc-containing insulin granules. Insulin secretion is not compromised in vitro by KO or R138X mutations in human embryonic stem cell-derived beta cells (sc-beta cells). Likewise, the ability of sc-beta cells to secrete insulin and maintain glucose homeostasis after transplantation into mice was comparable across different genotypes. Interestingly, sc-beta cells with the SLC30A8 KO mutation showed increased cytoplasmic zinc, and cells with either KO or R138X mutation were resistant to apoptosis when extracellular zinc was limiting. These findings are consistent with a protective role of zinc in cell death and with the protective role of zinc in T2D.

Pancreatic ß cell-selective zinc transporter 8 insufficiency accelerates diabetes associated with islet amyloidosis.

GWAS have shown that the common R325W variant of SLC30A8 (ZnT8) increases the risk of type 2 diabetes (T2D). However, ZnT8 haploinsufficiency is protective against T2D in humans, counterintuitive to earlier work in humans and mouse models. Therefore, whether decreasing ZnT8 activity is beneficial or detrimental to ß cell function, especially under conditions of metabolic stress, remains unknown. In order to examine whether the existence of human islet amyloid polypeptide (hIAPP), a coresident of the insulin granule, affects the role of ZnT8 in regulating ß cell function, hIAPP-expressing transgenics were generated with reduced ZnT8 (ZnT8B+/- hIAPP) or null ZnT8 (ZnT8B-/- hIAPP) expression specifically in ß cells. We showed that ZnT8B-/- hIAPP mice on a high-fat diet had intensified amyloid deposition and further impaired glucose tolerance and insulin secretion compared with control, ZnT8B-/-, and hIAPP mice. This can in part be attributed to impaired glucose sensing and islet cell synchronicity. Importantly, ZnT8B+/- hIAPP mice were also glucose intolerant and had reduced insulin secretion and increased amyloid aggregation compared with controls. These data suggest that loss of or reduced ZnT8 activity in ß cells heightened the toxicity induced by hIAPP, leading to impaired ß cell function and glucose homeostasis associated with metabolic stress.

Effects of ZnT8 on epithelial-to-mesenchymal transition and tubulointerstitial fibrosis in diabetic kidney disease.

Zinc transporter 8 (ZnT8) transports zinc ions for crystallization and storage of insulin in pancreatic beta-cells and ZnT8 dysfunction is involved in pathogenesis of diabetes. The current study aimed to investigate whether ZnT8 has effects in pathophysiology of diabetic kidney disease (DKD) by using animal models for diabetes, including STZ-induced diabetic, db/db, ZnT8-KO, ZnT8-KO-STZ and ZnT8-KO-db/db mice. Results demonstrated that urine albumin to creatinine ratio and epithelial-to-mesenchymal transition (EMT) were increased in kidneys of ZnT8-KO-STZ and ZnT8-KO-db/db mice compared with C57BL/6 J and ZnT8-KO mice, while serum TGF-ß1, IL-6, and TNF-α levels were elevated in parallel. In kidneys of mice intercrossed between ZnT8-KO and STZ-induced diabetic or db/db mice, these three inflammatory factors, ACR and EMT were also found to be increased compared with C57BL/6J, db/db and ZnT8-KO mice. Furthermore, ZnT8 up-regulation by hZnT8-EGFP reduced the levels of high glucose (HG)-induced EMT and inflammatory factors in normal rat kidney tubular epithelial cell (NRK-52E cells). Expression of phosphorylated Smad2/Smad3 was up-regulated after HG stimulation and further enhanced by ZnT8 siRNA but down-regulated after hZnT8-EGFP gene transfection. The current study thus provides the first evidence that ZnT8 protects against EMT-tubulointerstitial fibrosis though the restrain of TGF-ß1/Smads signaling activation in DKD.

Childhood thyroid autoimmunity and relation to islet autoantibodies in children at risk for type 1 diabetes in the diabetes prediction in skåne (DiPiS) study.

BACKGROUND: The aim was to determine prevalence and age at seroconversion of thyroid autoimmunity in relation to islet autoantibodies, gender and HLA-DQ genotypes in children with increased risk for type 1 diabetes followed from birth. METHODS: In 10-year-old children (n = 1874), blood samples were analysed for autoantibodies against thyroid peroxidase (TPOAb), thyroglobulin (TGAb), glutamic acid decarboxylase 65 (GADA), Zink transporter 8 (ZnT8R/W/QA), insulinoma-associated protein-2 (IA-2A), insulin (IAA) and HLA-DQ genotypes. Prospectively collected samples from 2 years of age were next analysed for TPOAb, and TGAb and, finally, in confirming samples at 11-16 years of age along with TSH and FT4. Frequencies were tested with Chi-square or Fischer's exact tests, autoantibody levels with Wilcoxon and correlations between autoantibody levels with Spearman's rank correlation test. RESULTS: The prevalence of thyroid autoimmunity was 6.9%, overrepresented in girls (p < .001) also having higher TPOAb levels at 10 years (p = .049). TPOAb was associated with GADA (p = .002), ZnT8R/W/QA (p = .001) and IA-2A (p = .001) while TGAb were associated with ZnT8R/W/QA (p = .021). In boys only, TPOAb were associated with GADA (p = .002), IA-2A (p = .001), ZnT8R/W/QA (p = .001) and IAA (p = .009), and TGAb with GADA (p = .013), IA-2A (p = .005) and ZnT8R/W/QA (p = .003). Levels of IA-2A correlated to both TPOAb (p = .021) and to TGAb (p = .011). In boys only, levels of GADA and TGAb correlated (p = .009 as did levels of IA-2A and TPOAb (p = .013). The frequency and levels of thyroid autoantibodies increased with age. At follow-up, 22.3% had abnormal thyroid function or were treated with thyroxine. CONCLUSIONS: Thyroid autoimmunity and high TPOAb levels were more common in girls. In contrast, in boys only, there was a strong association with as well as correlation between levels of thyroid and islet autoantibodies. It is concluded that while girls may develop autoimmune thyroid disease (AITD) independent of islet autoantibodies, the risk for thyroid disease in boys may be linked to concomitant islet autoimmunity.

Mice harboring the human SLC30A8 R138X loss-of-function mutation have increased insulin secretory capacity.

SLC30A8 encodes a zinc transporter that is primarily expressed in the pancreatic islets of Langerhans. In ß-cells it transports zinc into insulin-containing secretory granules. Loss-of-function (LOF) mutations in SLC30A8 protect against type 2 diabetes in humans. In this study, we generated a knockin mouse model carrying one of the most common human LOF mutations for SLC30A8, R138X. The R138X mice had normal body weight, glucose tolerance, and pancreatic ß-cell mass. Interestingly, in hyperglycemic conditions induced by the insulin receptor antagonist S961, the R138X mice showed a 50% increase in insulin secretion. This effect was not associated with enhanced ß-cell proliferation or mass. Our data suggest that the SLC30A8 R138X LOF mutation may exert beneficial effects on glucose metabolism by increasing the capacity of ß-cells to secrete insulin under hyperglycemic conditions.

Prolonged stimulation of insulin release from MIN6 cells causes zinc depletion and loss of ß-cell markers.

Zinc is integral for the normal function of pancreatic ß-cells in glycaemic control. Large amounts of zinc are secreted from ß-cells following insulin exocytosis and regulated replenishment is required, which is thought to be mediated by the ZIP family of zinc importer proteins. Within Type 2 Diabetic patients, ß-cells are stressed through prolonged stimulation by hyperglycaemia and this is thought to be a major factor contributing to loss of ß-cell identity and mass. However, the consequences for the ß-cell zinc status remain largely unexplored. We used inductively coupled plasma mass spectrometry (ICP-MS) to show that 24 h treatment of MIN6 cells with potassium chloride, mimicking hyperglycaemic stimulation, reduces the total cellular zinc content 2.8-fold, and qPCR to show an increase in mRNA expression for metallothioneins (Mt1 and Mt2) following 4 and 24 h of stimulation, suggestive of an early rise in cytosolic zinc. To determine which ZIP paralogues may be responsible for zinc replenishment, we used immunocytochemistry, Western blot and qPCR to demonstrate initial ZIP1 protein upregulation proceeded by downregulation of mRNA coding for ZIP1, ZIP6, ZIP7 and ZIP14. To assign a biological significance to the decreased total cellular zinc content, we assessed expression of key ß-cell markers to show downregulation of mRNA for MafA, Mnx-1, Nkx2.2 and Pax6. Our data suggest hyperglycaemia-induced zinc depletion may contribute to loss of ß-cell markers and promote ß-cell dedifferentiation through disrupting expression of key transcription factors.

Primary islet autoantibody at initial seroconversion and autoantibodies at diagnosis of type 1 diabetes as markers of disease heterogeneity.

OBJECTIVE: The relationship between patterns of islet autoantibodies at diagnosis and specificity of the first islet autoantibody at the initiation of autoimmunity was analyzed with the aim of identifying patterns informative of the primary autoantibodies. METHODS: Information about a single first autoantibody at seroconversion and autoantibody data at diagnosis were available for 128 children participating in the follow-up cohort of the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) study. Autoantibody data at diagnosis and genotyping results were also obtained from children in the Finnish Pediatric Diabetes Register (FPDR). RESULTS: Insulin autoantibodies (IAA) were the most common primary antibodies (N = 68), followed by those for glutamic acid decarboxylase (GADA; N = 38), IA-2 antigen (IA-2A; N = 13), and zinc transporter 8 (ZnT8A; N = 9), whereas at diagnosis, IA-2A were most frequent (N = 103), followed by IAA (N = 78), ZnT8A (N = 73), and GADA (N = 71). Accordingly, the presence of many specific autoantibodies at diagnosis was due to the secondary antibodies appearing after primary antibodies, and in some cases, the primary autoantibody, most often IAA, had already disappeared at the time of diagnosis. Many of the autoantibody combinations present at diagnosis could be assembled into groups associated with either IAA or GADA as first autoantibodies. These combinations, in children diagnosed below the age of 10 years in the FPDR, were found to be strongly associated with risk genotypes in either INS (IAA first) or IKZF4-ERBB3 (GADA first) genes. CONCLUSIONS: Autoantibody patterns at diagnosis may be informative on primary autoantibodies initiating autoimmunity in young children developing type 1 diabetes.

Prevalence of Positive Diabetes-Associated Autoantibodies among Type 2 Diabetes and Related Metabolic and Inflammatory Differences in a Sample of the Bulgarian Population.

BACKGROUND: The study aimed to estimate the prevalence of unrecognized cases with positive autoantibodies among type 2 diabetes (T2D) in a sample of the Bulgarian population and to compare some metabolic and inflammatory markers to those of patients having negative autoantibodies and subjects with latent autoimmune diabetes (LADA). METHODS: Patients with T2D, patients with LADA, and control participants were enrolled. Antiglutamic acid decarboxylase, anti-insulinoma-associated 2, and antizinc transporter 8 autoantibodies were assayed through ELISA. C-reactive protein and interleukin 6 (IL-6) and tumor necrosis factor alpha were assessed. RESULTS: Ten percent of patients with T2D had positive autoantibodies. They had lower body mass index (p = 0.014), worse glycemic control (HbA1c, p = 0.033), and better HDL cholesterol (p = 0.026) than those in negative autoantibodies cases. Compared to LADA, glycemia and anthropometric data did not differ significantly but metabolic syndrome was more prevalent among newly found cases with positive autoantibodies (p = 0.046). Their level of inflammatory markers was similar to that of patients having negative autoantibodies (p > 0.05), but IL-6 was higher when compared to LADA (p = 0.002). CONCLUSION: Prevalence of patients having positive autoantibodies within T2D in the analyzed sample of the Bulgarian population was 10%. They shared common metabolic features with subjects with LADA, but inflammatory phenotype was closer to that of T2D.

Exploring the Association Between Demographics, SLC30A8 Genotype, and Human Islet Content of Zinc, Cadmium, Copper, Iron, Manganese and Nickel.

A widely prevalent single nucleotide polymorphism, rs13266634 in the SLC30A8 gene encoding the zinc transporter ZnT8, is associated with an increased risk for T2DM. ZnT8 is mostly expressed in pancreatic insulin-producing islets of Langerhans. The effect of this variant on the divalent metal profile in human islets is unknown. Additionally, essential and non-essential divalent metal content of human islets under normal environmental exposure conditions has not been described. We therefore examined the correlation of zinc and other divalent metals in human islets with rs13266634 genotype and demographic characteristics. We found that the diabetes risk genotype C/C at rs13266634 is associated with higher islet Zn concentration (C/C genotype: 16792 ± 1607, n = 22, C/T genotype: 11221 ± 1245, n = 18 T/T genotype: 11543 ± 6054, n = 3, all values expressed as mean nmol/g protein ± standard error of the mean, p = 0.040 by ANOVA). A positive correlation between islet cadmium content and both age (p = 0.048, R2 = 0.09) and female gender (women: 36.88 ± 4.11 vs men: 21.22 ± 3.65 nmol/g protein, p = 0.007) was observed. Our results suggest that the T2DM risk allele C is associated with higher islet zinc levels and support prior evidence of cadmium's higher bioavailability in women and its long tissue half-life.