Pathogen inactivation of human serum facilitates its clinical use for islet cell culture and subsequent transplantation

Principal Criteria for Evaluating the Quality, Safety and Efficacy of hMSC-Based Products in Clinical Practice: Current Approaches and Challenges

Human Mesenchymal Stem Cells (hMSCs) play an important role as new therapeutic alternatives in advanced therapies and regenerative medicine thanks to their regenerative and immunomodulatory properties, and ability to migrate to the exact area of injury. These properties have made hMSCs one of the more promising cellular active substances at present, particularly in terms of the development of new and innovative hMSC-based products. Currently, numerous clinical trials are being conducted to evaluate the therapeutic activity of hMSC-based products on specific targets. Given the rapidly growing number of hMSC clinical trials in recent years and the complexity of these products due to their cellular component characteristics and medicinal product status, there is a greater need to define more stringent, specific, and harmonized requirements to characterize the quality of the hMSCs and enhance the analysis of their safety and efficacy in final products to be administered to patients. These requirements should be implemented throughout the manufacturing process to guarantee the function and integrity of hMSCs and to ensure that the hMSC-based final product consistently meets its specifications across batches. This paper describes the principal phases involved in the design of the manufacturing process and updates the specific technical requirements needed to address the appropriate clinical use of hMSC-based products. The challenges and limitations to evaluating the safety, efficacy, and quality of hMSCs have been also reviewed and discussed.

Interleukin-22 reverses human islet dysfunction and apoptosis triggered by hyperglycemia and LIGHT

Interleukin (IL)-22 has recently been suggested as an anti-inflammatory cytokine that could protect the islet cells from inflammation- and glucose-induced toxicity. We have previously shown that the tumor necrosis factor family member, LIGHT, can impair human islet function at least partly via pro-apoptotic effects. Herein, we aimed to investigate the protective role of IL-22 on human islets exposed to the combination of hyperglycemia and LIGHT. First, we found upregulation of LIGHT receptors (LTβR and HVEM) in engrafted human islets exposed to hyperglycemia (>11 mM) for 17 days post transplantation by using a double islet transplantation mouse model as well as in human islets cultured with high glucose (HG) (20 mM glucose) + LIGHT in vitro, and this latter effect was attenuated by IL-22. The effect of HG + LIGHT impairing glucose-stimulated insulin secretion was reversed by IL-22. The harmful effect of HG + LIGHT on human islet function seemed to involve enhanced endoplasmic reticulum stress evidenced by upregulation of p-IRE1α and BiP, elevated secretion of pro-inflammatory cytokines (IL-6, IL-8, IP-10 and MCP-1) and the pro-coagulant mediator tissue factor (TF) release and apoptosis in human islets, whereas all these effects were at least partly reversed by IL-22. Our findings suggest that IL-22 could counteract the harmful effects of LIGHT/hyperglycemia on human islet cells and potentially support the strong protective effect of IL-22 on impaired islet function and survival.

Reflections on Dry Eye Syndrome Treatment: Therapeutic Role of Blood Products

Dry eye syndrome (DES) is a multifactorial, frequent, pathology characterized by deficient tear production or increased evaporation of tears and associated with ocular surface alteration and inflammation. It mostly affects, but not exclusively, older individuals and leads to varying degrees of discomfort and decreased quality of life. Although the typical treatments of DES rely on using artificial tears, polyunsaturated fatty acids, integrin antagonists, anti-inflammatory agents, or on performing punctal occlusion, recently, standardized blood-derived serum eye drops (SED) are generating much interest as a new physiological treatment option. The scientific rationale in using SED for treating or releasing the symptoms of DES is thought to lie in its composition in multiple factors that resembles that of tears and contributes to the healing and protection of the ocular surface. This manuscript seeks to provide relevant background information on the management of DES, and on the increasing role that various types of SED or platelet lysates, from autologous or allogeneic origins, are playing in the improved therapeutic management of this pathology. The increasing role played by blood establishments in producing better-standardized SED is also addressed.

Glucose-Induced Changes in Gene Expression in Human Pancreatic Islets: Causes or Consequences of Chronic Hyperglycemia

Dysregulation of gene expression in islets from patients with type 2 diabetes (T2D) might be causally involved in the development of hyperglycemia, or it could develop as a consequence of hyperglycemia (i.e., glucotoxicity). To separate the genes that could be causally involved in pathogenesis from those likely to be secondary to hyperglycemia, we exposed islets from human donors to normal or high glucose concentrations for 24 h and analyzed gene expression. We compared these findings with gene expression in islets from donors with normal glucose tolerance and hyperglycemia (including T2D). The genes whose expression changed in the same direction after short-term glucose exposure, as in T2D, were considered most likely to be a consequence of hyperglycemia. Genes whose expression changed in hyperglycemia but not after short-term glucose exposure, particularly those that also correlated with insulin secretion, were considered the strongest candidates for causal involvement in T2D. For example, ERO1LB, DOCK10, IGSF11, and PRR14L were downregulated in donors with hyperglycemia and correlated positively with insulin secretion, suggesting a protective role, whereas TMEM132C was upregulated in hyperglycemia and correlated negatively with insulin secretion, suggesting a potential pathogenic role. This study provides a catalog of gene expression changes in human pancreatic islets after exposure to glucose.

Glial cell-line derived neurotrophic factor protects human islets from nutrient deprivation and endoplasmic reticulum stress induced apoptosis

One of the key limitations to successful human islet transplantation is loss of islets due to stress responses pre- and post-transplantation. Nutrient deprivation and ER stress have been identified as important mechanisms leading to apoptosis. Glial Cell-line Derived Neurotrophic Factor (GDNF) has recently been found to promote islet survival after isolation. However, whether GDNF could rescue human islets from nutrient deprivation and ER stress-mediated apoptosis is unknown. Herein, by mimicking those conditions in vitro, we have shown that GDNF significantly improved glucose stimulated insulin secretion, reduced apoptosis and proinsulin:insulin ratio in nutrient deprived human islets. Furthermore, GDNF alleviated thapsigargin-induced ER stress evidenced by reduced expressions of IRE1α and BiP and consequently apoptosis. Importantly, this was associated with an increase in phosphorylation of PI3K/AKT and GSK3B signaling pathway. Transplantation of ER stressed human islets pre-treated with GDNF under kidney capsule of diabetic mice resulted in reduced expressions of IRE1α and BiP in human islet grafts with improved grafts function shown by higher levels of human C-peptide post-transplantation. We suggest that GDNF has protective and anti-apoptotic effects on nutrient deprived and ER stress activated human islets and could play a significant role in rescuing human islets from stress responses.

Blood-based biomarkers of age-associated epigenetic changes in human islets associate with insulin secretion and diabetes

Aging associates with impaired pancreatic islet function and increased type 2 diabetes (T2D) risk. Here we examine whether age-related epigenetic changes affect human islet function and if blood-based epigenetic biomarkers reflect these changes and associate with future T2D. We analyse DNA methylation genome-wide in islets from 87 non-diabetic donors, aged 26-74 years. Aging associates with increased DNA methylation of 241 sites. These sites cover loci previously associated with T2D, for example, KLF14. Blood-based epigenetic biomarkers reflect age-related methylation changes in 83 genes identified in human islets (for example, KLF14, FHL2, ZNF518B and FAM123C) and some associate with insulin secretion and T2D. DNA methylation correlates with islet expression of multiple genes, including FHL2, ZNF518B, GNPNAT1 and HLTF. Silencing these genes in β-cells alter insulin secretion. Together, we demonstrate that blood-based epigenetic biomarkers reflect age-related DNA methylation changes in human islets, and associate with insulin secretion in vivo and T2D.

Improving the anti-inflammatory effect of serum eye drops using allogeneic serum permissive for regulatory T cell induction

PURPOSE

To investigate the cytokine composition and anti-inflammatory effects of allogeneic serum preparations for improved use as serum eye drops.

METHODS

Serum of 15 healthy blood donors was extensively screened for cytokines, including IL-1β, IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-12p70, IL-13, IL-15, 1L-17A, E and F, IL-21, IL-22, IL-23, IL-27, IL-28A, IL-31, IL-33, granulocyte macrophage colony-stimulating factor (GM-CSF), chemokine ligand 20 (CCL20), tumour necrosis factor (TNF)-α and TNF-β, interferon (IFN)-γ and transforming growth factor (TGF)-β. The levels of cytokines were assessed before and after heat-induced inactivation. Individual serum preparations were tested for their anti-inflammatory effect using an in vitro test to differentiate effector T lymphocytes into anti-inflammatory regulatory T cells.

RESULTS

The anti-inflammatory cytokine TGF-β was readily detected in the serum of all blood donors and was only modestly affected by heat-induced inactivation. Serum containing high amounts of TGF-β was more effective at inducing anti-inflammatory regulatory T cells. The serum of one healthy blood donor displayed high levels of inflammatory cytokines.

CONCLUSION

We propose that serum used as eye drops is screened for its cytokine content, making it possible to correlate the composition to the clinical outcome. Based on the findings in this study, tailored serum eye drops produced from allogeneic donors may provide increased anti-inflammatory effects. This may be superior to autologous serum eye drops, which in many cases are retrieved from patients with inflammatory diseases.

Human platelet lysate: Replacing fetal bovine serum as a gold standard for human cell propagation?

The essential physiological role of platelets in wound healing and tissue repair builds the rationale for the use of human platelet derivatives in regenerative medicine. Abundant growth factors and cytokines stored in platelet granules can be naturally released by thrombin activation and clotting or artificially by freeze/thaw-mediated platelet lysis, sonication or chemical treatment. Human platelet lysate prepared by the various release strategies has been established as a suitable alternative to fetal bovine serum as culture medium supplement, enabling efficient propagation of human cells under animal serum-free conditions for a multiplicity of applications in advanced somatic cell therapy and tissue engineering. The rapidly increasing number of studies using platelet derived products for inducing human cell proliferation and differentiation has also uncovered a considerable variability of human platelet lysate preparations which limits comparability of results. The main variations discussed herein encompass aspects of donor selection, preparation of the starting material, the possibility for pooling in plasma or additive solution, the implementation of pathogen inactivation and consideration of ABO blood groups, all of which can influence applicability. This review outlines the current knowledge about human platelet lysate as a powerful additive for human cell propagation and highlights its role as a prevailing supplement for human cell culture capable to replace animal serum in a growing spectrum of applications.

Mesenchymal stromal cells support endothelial cell interactions in an intramuscular islet transplantation model

Background

Mesenchymal stromal cells (MSC) have been under investigation for a number of therapies and have lately been in focus as immunosuppressive actors in the field of transplantation. Herein we have extended our previously published in vitro model of MSC-islets in an experimental setting of islet transplantation to the abdominal muscle.

Human islets coated with luciferase-GFP transduced human MSC were transplanted to the abdomen muscle tissue of NOD-scid ILR2γ^null mice and cellular interactions were investigated by confocal microscopy.

Results

The MSC reduced fibrotic encapsulation and facilitated endothelial cell interactions. In particular, we show a decreased fraction of αSMA expressing fibrotic tissue surrounding the graft in presence of MSC-islets compared to islets solely distributed into the muscle tissue. Also, in the presence of MSC, human islet endothelial cells migrated from the center of the graft out into the surrounding tissue forming chimeric blood vessels with recipient endothelial cells. Further, in the graft periphery, MSC were seen interacting with infiltrating macrophages.

Conclusions

Here, in our experimental in vivo model of composite human islets and luciferase-GFP-transduced human MSC, we enable the visualization of close interactions between the MSC and the surrounding tissue. In this model of transplantation the MSC contribute to reduced fibrosis and increased islet endothelial cell migration. Furthermore, the MSC interact with the recipient vasculature and infiltrating macrophages.

Electronic supplementary material

The online version of this article (doi:10.1186/s40340-015-0010-9) contains supplementary material, which is available to authorized users.

Characterization of Innate Immunity in an Extended Whole Blood Model of Human Islet Allotransplantation

The instant blood-mediated inflammatory reaction (IBMIR) has been studied in whole blood models of human allo-islet transplantation for short periods (<6 h). Beyond this time frame the innate response to intraportally transplanted islets is less well described. A novel whole blood model was applied to study blood-islet-graft interactions up to 48 h. Heparinized polyvinyl chloride tubing was sealed into small bags containing venous blood together with allogeneic human islets and exocrine tissue, respectively. The bags were attached to a rotating wheel (37°C). Concentrated glucose and sodium hydrogen carbonate were added every 12 h to maintain physiological limits for sustained immune cell functions. Plasma was collected at repeated time points for analyses of coagulation/complement activation and chemokine/cytokine production. Immune cell infiltration was analyzed using immunohistochemistry. Coagulation and platelet activation markers, thrombin-antithrombin complex (TAT) and soluble CD40 ligand (sCD40L) showed early high concentrations (at 6-12 h). sC5b-9 steadily increased over 48 h. At 6 h neutrophils and monocytes surrounded the clotted cellular grafts with a following massive infiltration of neutrophils. High and increasing concentrations of CXCR1/2 ligands [IL-8 and growth-regulated oncogene α/β/γ (Gro-α/β/γ)] and IL-6 were produced in response to human islets and exocrine tissue. The CCR2 ligand monocyte chemoattractant protein 1 (MCP-1) exhibited increasing concentrations in response to exocrine tissue. The CXCR3 ligand interferon-inducible T cell α chemoattractant (I-TAC) was produced in response to both human islets and exocrine tissue from 6 h. Monokine induced by γ interferon (Mig) and interferon γ-induced protein 10 (IP-10) showed a later response, preferentially to exocrine tissue and with larger variations among preparations. An extended blood model of clinical islet transplantation allowed characterization of early immune activation in response to human islets and exocrine tissue. Increased production of chemokines targeting CXCR1/2, CCR2, and CXCR3 was observed, accompanied by massive intraislet neutrophil infiltration over 48 h. The model proved to be useful in exploring early blood-mediated reactions to cellular transplants and has relevance for evaluation of pharmacological interventions to prevent graft loss.

A novel model for studies of blood-mediated long-term responses to cellular transplants

AIMS

Interaction between blood and bio-surfaces is important in many medical fields. With the aim of studying blood-mediated reactions to cellular transplants, we developed a whole-blood model for incubation of small volumes for up to 48 h.

METHODS

Heparinized polyvinyl chloride tubing was cut in suitable lengths and sealed to create small bags. Multiple bags, with fresh venous blood, were incubated attached to a rotating wheel at 37°C. Physiological variables in blood were monitored: glucose, blood gases, mono- and divalent cations and chloride ions, osmolality, coagulation (platelet consumption, thrombin-antithrombin complexes (TAT)), and complement activation (C3a and SC5b-9), haemolysis, and leukocyte viability.

RESULTS

Basic glucose consumption was high. Glucose depletion resulted in successive elevation of extracellular potassium, while sodium and calcium ions decreased due to inhibition of energy-requiring ion pumps. Addition of glucose improved ion balance but led to metabolic acidosis. To maintain a balanced physiological environment beyond 6 h, glucose and sodium hydrogen carbonate were added regularly based on analyses of glucose, pH, ions, and osmotic pressure. With these additives haemolysis was prevented for up to 72 h and leukocyte viability better preserved. Despite using non-heparinized blood, coagulation and complement activation were lower during long-term incubations compared with addition of thromboplastin and collagen.

CONCLUSION

A novel whole-blood model for studies of blood-mediated responses to a cellular transplant is presented allowing extended observations for up to 48 h and highlights the importance of stringent evaluations and adjustment of physiological conditions.

Sex differences in the genome-wide DNA methylation pattern and impact on gene expression, microRNA levels and insulin secretion in human pancreatic islets

Background

Epigenetic factors regulate tissue-specific expression and X-chromosome inactivation. Previous studies have identified epigenetic differences between sexes in some human tissues. However, it is unclear whether epigenetic modifications contribute to sex-specific differences in insulin secretion and metabolism. Here, we investigate the impact of sex on the genome-wide DNA methylation pattern in human pancreatic islets from 53 males and 34 females, and relate the methylome to changes in expression and insulin secretion.

Results

Glucose-stimulated insulin secretion is higher in female versus male islets. Genome-wide DNA methylation data in human islets clusters based on sex. While the chromosome-wide DNA methylation level on the X-chromosome is higher in female versus male islets, the autosomes do not display a global methylation difference between sexes. Methylation of 8,140 individual X-chromosome sites and 470 autosomal sites shows sex-specific differences in human islets. These include sites in/near AR, DUSP9, HNF4A, BCL11A and CDKN2B. 61 X-chromosome genes and 18 autosomal genes display sex-specific differences in both DNA methylation and expression. These include NKAP, SPESP1 and APLN, which exhibited lower expression in females. Functional analyses demonstrate that methylation of NKAP and SPESP1 promoters in vitro suppresses their transcriptional activity. Silencing of Nkap or Apln in clonal beta-cells results in increased insulin secretion. Differential methylation between sexes is associated with altered levels of microRNAs miR-660 and miR-532 and related target genes.

Conclusions

Chromosome-wide and gene-specific sex differences in DNA methylation associate with altered expression and insulin secretion in human islets. Our data demonstrate that epigenetics contribute to sex-specific metabolic phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0522-z) contains supplementary material, which is available to authorized users.

Genome-wide associations between genetic and epigenetic variation influence mRNA expression and insulin secretion in human pancreatic islets

Genetic and epigenetic mechanisms may interact and together affect biological processes and disease development. However, most previous studies have investigated genetic and epigenetic mechanisms independently, and studies examining their interactions throughout the human genome are lacking. To identify genetic loci that interact with the epigenome, we performed the first genome-wide DNA methylation quantitative trait locus (mQTL) analysis in human pancreatic islets. We related 574,553 single nucleotide polymorphisms (SNPs) with genome-wide DNA methylation data of 468,787 CpG sites targeting 99% of RefSeq genes in islets from 89 donors. We identified 67,438 SNP-CpG pairs in cis, corresponding to 36,783 SNPs (6.4% of tested SNPs) and 11,735 CpG sites (2.5% of tested CpGs), and 2,562 significant SNP-CpG pairs in trans, corresponding to 1,465 SNPs (0.3% of tested SNPs) and 383 CpG sites (0.08% of tested CpGs), showing significant associations after correction for multiple testing. These include reported diabetes loci, e.g. ADCY5, KCNJ11, HLA-DQA1, INS, PDX1 and GRB10. CpGs of significant cis-mQTLs were overrepresented in the gene body and outside of CpG islands. Follow-up analyses further identified mQTLs associated with gene expression and insulin secretion in human islets. Causal inference test (CIT) identified SNP-CpG pairs where DNA methylation in human islets is the potential mediator of the genetic association with gene expression or insulin secretion. Functional analyses further demonstrated that identified candidate genes (GPX7, GSTT1 and SNX19) directly affect key biological processes such as proliferation and apoptosis in pancreatic β-cells. Finally, we found direct correlations between DNA methylation of 22,773 (4.9%) CpGs with mRNA expression of 4,876 genes, where 90% of the correlations were negative when CpGs were located in the region surrounding transcription start site. Our study demonstrates for the first time how genome-wide genetic and epigenetic variation interacts to influence gene expression, islet function and potential diabetes risk in humans.

Inter-individual variation in genetics and epigenetics affects biological processes and disease susceptibility. However, most studies have investigated genetic and epigenetic mechanisms independently and to uncover novel mechanisms affecting disease susceptibility there is a highlighted need to study interactions between these factors on a genome-wide scale. To identify novel loci affecting islet function and potentially diabetes, we performed the first genome-wide methylation quantitative trait locus (mQTL) analysis in human pancreatic islets including DNA methylation of 468,787 CpG sites located throughout the genome. Our results showed that DNA methylation of 11,735 CpGs in 4,504 unique genes is regulated by genetic factors located in cis (67,438 SNP-CpG pairs). Furthermore, significant mQTLs cover previously reported diabetes loci including KCNJ11, INS, HLA, PDX1 and GRB10. We also found mQTLs associated with gene expression and insulin secretion in human islets. By performing causality inference tests (CIT), we identified CpGs where DNA methylation potentially mediates the genetic impact on gene expression and insulin secretion. Our functional follow-up experiments further demonstrated that identified mQTLs/genes (GPX7, GSTT1 and SNX19) directly affect pancreatic β-cell function. Together, our study provides a detailed map of genome-wide associations between genetic and epigenetic variation, which affect gene expression and insulin secretion in human pancreatic islets.

Multifaceted regenerative lives of expired platelets in the second decade of the 21st century

A traditional concept in transfusion medicine is the expiration of platelet concentrates 5-7 days after collection due to storage conditions that favor the risks of bacterial contamination and may lead to a gradual alteration of platelet hemostatic power. Newer findings are strongly suggesting that, after their supposed expiration date, platelet concentrates still contain multiple functional growth factors and cytokines and actually have unaltered power for application in regenerative medicine and cell therapy. Expired platelets can be a valuable source of growth factors to promote the healing of wounds, and can be used for ex vivo expansion of stem cells. There is also preliminary evidence that infusible platelet membrane (IPM) from outdated platelet concentrates and thrombosomes have potential clinical applications as hemostatic products. Experimental work is certainly needed to further validate and standardize the clinical potential of "expired" platelet blood products in human clinical medicine. However, strong evidence accumulates toward a potential for further manufacturing avenues of expired platelet concentrates into valuable therapeutic and clinically relevant products.

Preparation, quality criteria, and properties of human blood platelet lysate supplements for ex vivo stem cell expansion

Most clinical applications of human multipotent mesenchymal stromal cells (MSCs) for cell therapy, tissue engineering, regenerative medicine, and treatment of immune and inflammatory diseases require a phase of isolation and ex vivo expansion allowing a clinically meaningful cell number to be reached. Conditions used for cell isolation and expansion should meet strict quality and safety requirements. This is particularly true for the growth medium used for MSC isolation and expansion. Basal growth media used for MSC expansion are supplemented with multiple nutrients and growth factors. Fetal bovine serum (FBS) has long been the gold standard medium supplement for laboratory-scale MSC culture. However, FBS has a poorly characterized composition and poses risk factors, as it may be a source of xenogenic antigens and zoonotic infections. FBS has therefore become undesirable as a growth medium supplement for isolating and expanding MSCs for human therapy protocols. In recent years, human blood materials, and most particularly lysates and releasates of platelet concentrates have emerged as efficient medium supplements for isolating and expanding MSCs from various origins. This review analyzes the advantages and limits of using human platelet materials as medium supplements for MSC isolation and expansion. We present the modes of production of allogeneic and autologous platelet concentrates, measures taken to ensure optimal pathogen safety profiles, and methods of preparing PLs for MSC expansion. We also discuss the supply of such blood preparations. Produced under optimal conditions of standardization and safety, human platelet materials can become the future 'gold standard' supplement for ex vivo production of MSCs for translational medicine and cell therapy applications.

DNA methylation of the glucagon-like peptide 1 receptor (GLP1R) in human pancreatic islets

BACKGROUND

Insulin secretion is enhanced upon the binding of Glucagon-like peptide-1 (GLP-1) to its receptor (GLP1R) in pancreatic β cells. Although a reduced expression of GLP1R in pancreatic islets from type 2 diabetic patients and hyperglycaemic rats has been established, it is still unknown if this is caused by differential DNA methylation of GLP1R in pancreatic islets of type 2 diabetic patients.

METHODS

In this study, DNA methylation levels of 12 CpG sites close to the transcription start site of GLP1R were analysed in pancreatic islets from 55 non-diabetic and 10 type 2 diabetic human donors as well as in β and α cells isolated from human pancreatic islets. DNA methylation of GLP1R was related to GLP1R expression, HbA1c levels and BMI. Moreover, mRNA expression of MECP2, DNMT1, DNMT3A and DNMT3B was analysed in pancreatic islets of the non-diabetic and type 2 diabetic donors.

RESULTS

One CpG unit, at position +199 and +205 bp from the transcription start site, showed a small increase in DNA methylation in islets from donors with type 2 diabetes compared to non-diabetic donors (0.53%, p=0.02). Furthermore, DNA methylation levels of one CpG site located 376 bp upstream of the transcription start site of GLP1R correlated negatively with GLP1R expression (rho=-0.34, p=0.008) but positively with BMI and HbA1c (rho=0.30, p=0.02 and rho=0.30, p=0.03, respectively). This specific CpG site is located in an area with known SP1 and SP3 transcription factor binding sites. Moreover, when we compared the DNA methylation of the GLP1R promoter in isolated human β and α cells, we found that it was higher in α- compared with β-cells (p=0.009). Finally, there was a trend towards decreased DNMT3A expression (p=0.056) in type 2 diabetic compared with non-diabetic islets.

CONCLUSIONS

Together, our study shows that while BMI and HbA1c are positively associated with DNA methylation levels of GLP1R, its expression is negatively associated with DNA methylation of GLP1R in human pancreatic islets.

Identification of CpG-SNPs associated with type 2 diabetes and differential DNA methylation in human pancreatic islets

AIMS/HYPOTHESIS

To date, the molecular function of most of the reported type 2 diabetes-associated loci remains unknown. The introduction or removal of cytosine-phosphate-guanine (CpG) dinucleotides, which are possible sites of DNA methylation, has been suggested as a potential mechanism through which single-nucleotide polymorphisms (SNPs) can affect gene function via epigenetics. The aim of this study was to examine if any of 40 SNPs previously associated with type 2 diabetes introduce or remove a CpG site and if these CpG-SNPs are associated with differential DNA methylation in pancreatic islets of 84 human donors.

METHODS

DNA methylation was analysed using pyrosequencing.

RESULTS

We found that 19 of 40 (48%) type 2 diabetes-associated SNPs introduce or remove a CpG site. Successful DNA methylation data were generated for 16 of these 19 CpG-SNP loci, representing the candidate genes TCF7L2, KCNQ1, PPARG, HHEX, CDKN2A, SLC30A8, DUSP9, CDKAL1, ADCY5, SRR, WFS1, IRS1, DUSP8, HMGA2, TSPAN8 and CHCHD9. All analysed CpG-SNPs were associated with differential DNA methylation of the CpG-SNP site in human islets. Moreover, six CpG-SNPs, representing TCF7L2, KCNQ1, CDKN2A, ADCY5, WFS1 and HMGA2, were also associated with DNA methylation of surrounding CpG sites. Some of the type 2 diabetes CpG-SNP sites that exhibit differential DNA methylation were further associated with gene expression, alternative splicing events determined by splice index, and hormone secretion in the human islets. The 19 type 2 diabetes-associated CpG-SNPs are in strong linkage disequilibrium (r² > 0.8) with a total of 295 SNPs, including 91 CpG-SNPs.

CONCLUSIONS/INTERPRETATION

Our results suggest that the introduction or removal of a CpG site may be a molecular mechanism through which some of the type 2 diabetes SNPs affect gene function via differential DNA methylation and consequently contributes to the phenotype of the disease.

Supplements in human islet culture: human serum albumin is inferior to fetal bovine serum

Culture of human islets before clinical transplantation or distribution for research purposes is standard practice. At the time the Edmonton protocol was introduced, clinical islet manufacturing did not include culture, and human serum albumin (HSA), instead of fetal bovine serum (FBS), was used during other steps of the process to avoid the introduction of xenogeneic material. When culture was subsequently introduced, HSA was also used for medium supplementation instead of FBS, which was typically used for research islet culture. The use of HSA as culture supplement was not evaluated before this implementation. We performed a retrospective analysis of 103 high-purity islet preparations (76 research preparations, all with FBS culture supplementation, and 27 clinical preparations, all with HSA supplementation) for oxygen consumption rate per DNA content (OCR/DNA; a measure of viability) and diabetes reversal rate in diabetic nude mice (a measure of potency). After 2-day culture, research preparations exhibited an average OCR/DNA 51% higher (p < 0.001) and an average diabetes reversal rate 54% higher (p < 0.05) than clinical preparations, despite 87% of the research islet preparations having been derived from research-grade pancreata that are considered of lower quality. In a prospective paired study on islets from eight research preparations, OCR/DNA was, on average, 27% higher with FBS supplementation than that with HSA supplementation (p < 0.05). We conclude that the quality of clinical islet preparations can be improved when culture is performed in media supplemented with serum instead of albumin.