Engineering islets from stem cells for advanced therapies of diabetes.

Diabetes mellitus is a metabolic disorder that affects more than 460 million people worldwide. Type 1 diabetes (T1D) is caused by autoimmune destruction of ß-cells, whereas type 2 diabetes (T2D) is caused by a hostile metabolic environment that leads to ß-cell exhaustion and dysfunction. Currently, first-line medications treat the symptomatic insulin resistance and hyperglycaemia, but do not prevent the progressive decline of ß-cell mass and function. Thus, advanced therapies need to be developed that either protect or regenerate endogenous ß-cell mass early in disease progression or replace lost ß-cells with stem cell-derived ß-like cells or engineered islet-like clusters. In this Review, we discuss the state of the art of stem cell differentiation and islet engineering, reflect on current and future challenges in the area and highlight the potential for cell replacement therapies, disease modelling and drug development using these cells. These efforts in stem cell and regenerative medicine will lay the foundations for future biomedical breakthroughs and potentially curative treatments for diabetes.

Increasing Gene Editing Efficiency for CRISPR-Cas9 by Small RNAs in Pluripotent Stem Cells.

Gene manipulations of human induced pluripotent stem cells (iPSCs) by CRISPR-Cas9 genome engineering are widely used for disease modeling and regenerative medicine applications. There are two competing pathways, non-homologous end joining (NHEJ) and homology directed repair (HDR) that correct the double-strand break generated by CRISPR-Cas9. Here, we improved gene editing efficiency of gene knock-in (KI) in iPSCs with minimum components by manipulating the Cas9 expression vector. Either we inserted short hairpin RNA expression cassettes to downregulate DNAPK and XRCC4, two main players of the NHEJ pathway, or we increased cell survival by inserting an anti-apoptotic expression cassette of miRNA-21 into the Cas9 vector. For an easy readout, the pluripotency gene SOX2 was targeted with a T2A-tdTomato reporter construct. In vitro downregulating DNAPK and XRCC4 increased the targeting efficiency of SOX2 KI by around twofold. Furthermore, co-expression of miRNA-21 and Cas9 improved the efficiency of SOX2 KI by around threefold. Altogether, our strategies provide a simple and valuable approach for efficient CRISPR-Cas9 gene editing in iPSCs.

Inceptor counteracts insulin signalling in ß-cells to control glycaemia.

Resistance to insulin and insulin-like growth factor 1 (IGF1) in pancreatic ß-cells causes overt diabetes in mice; thus, therapies that sensitize ß-cells to insulin may protect patients with diabetes against ß-cell failure1-3. Here we identify an inhibitor of insulin receptor (INSR) and IGF1 receptor (IGF1R) signalling in mouse ß-cells, which we name the insulin inhibitory receptor (inceptor; encoded by the gene Iir). Inceptor contains an extracellular cysteine-rich domain with similarities to INSR and IGF1R4, and a mannose 6-phosphate receptor domain that is also found in the IGF2 receptor (IGF2R)5. Knockout mice that lack inceptor (Iir-/-) exhibit signs of hyperinsulinaemia and hypoglycaemia, and die within a few hours of birth. Molecular and cellular analyses of embryonic and postnatal pancreases from Iir-/- mice showed an increase in the activation of INSR-IGF1R in Iir-/- pancreatic tissue, resulting in an increase in the proliferation and mass of ß-cells. Similarly, inducible ß-cell-specific Iir-/- knockout in adult mice and in ex vivo islets led to an increase in the activation of INSR-IGF1R and increased proliferation of ß-cells, resulting in improved glucose tolerance in vivo. Mechanistically, inceptor interacts with INSR-IGF1R to facilitate clathrin-mediated endocytosis for receptor desensitization. Blocking this physical interaction using monoclonal antibodies against the extracellular domain of inceptor resulted in the retention of inceptor and INSR at the plasma membrane to sustain the activation of INSR-IGF1R in ß-cells. Together, our findings show that inceptor shields insulin-producing ß-cells from constitutive pathway activation, and identify inceptor as a potential molecular target for INSR-IGF1R sensitization and diabetes therapy.

Generation of a heterozygous C-peptide-mCherry reporter human iPSC line (HMGUi001-A-8).

The peptide hormone insulin produced by pancreatic ß-cells undergoes post-transcriptional processing before secretion. In particular, C-peptide is cleaved from pro-insulin to generate mature insulin. Here, we introduce a C-peptide-mCherry human iPSC line (HMGUi001-A-8). The line was generated by CRISPR/Cas9 mediated heterozygous insertion of the mCherry sequence into exon 3 of the insulin locus. We demonstrate that the line is pluripotent and efficiently differentiates towards pancreatic ß-like cells, which localize a red fluorescent C-peptide-mCherry fusion protein in insulin containing granules. Hence, the HMGUi001-A-8 line is a valuable resource to purify derived ß-like cells and follow insulin-containing granules in real time.

Generation of a human iPSC line harboring a biallelic large deletion at the INK4 locus (HMGUi001-A-5).

The INK4 locus is considered as a hot-spot region for the complex genetic disorders, including cancer, type 2 diabetes (T2D) and coronary artery disease (CAD). By CRISPR/Cas9 gene editing, we generated a human induced pluripotent stem cell (hiPSC) line (HMGUi001-A-5) deleting an 8 kb genomic DNA encompassing six T2D-associated SNPs at the INK4 locus. The resulting hiPSC line revealed a normal karyotype, preserved pluripotency and was able to differentiate towards germ layers, endoderm, mesoderm and ectoderm. Thus, the HMGUi001-A-5 line could provide a valuable cellular model to explore the molecular mechanisms linking these SNPs to T2D and other genetic disorders.

Generation of an INSULIN-H2B-Cherry reporter human iPSC line.

Differentiating human induced pluripotent stem cells (hiPSCs) into insulin (INS)-producing ß-like cells has potential for diabetes research and therapy. Here, we generated a heterozygous fluorescent hiPSC reporter, labeling INS-producing ß-like cells. We used CRISPR/Cas9 technology to knock-in a T2A-H2B-Cherry cassette to replace the translational INS stop codon, enabling co-transcription and T2A-peptide mediated co-translational cleavage of INS-T2A and H2B-Cherry. The hiPSC-INS-T2A-H2B-Cherry reporter cells were pluripotent and showed multi-lineage differentiation potential. Cells expressing the ß-cell specific hormone INS are identified by nuclear localized H2B-Cherry reporter upon pancreatic endocrine differentiation. Thus, the generated reporter hiPSCs enable live identification of INS hormone-producing ß-like cells.

Pharmacological Targeting of the Actin Cytoskeleton to Drive Endocrinogenesis.

In vitro generation of insulin-secreting beta cells from human pluripotent stem cells (hPSCs) opens new avenues for treating and modeling diabetes. Hogrebe and colleaguesestablished a new 2D differentiation protocol where they targeted the cytoskeleton pharmacologically for controlled endocrine induction and generation of hPSC-derived beta cells with improved function.

Generation of a human induced pluripotent stem cell line (HMGUi002-A) from a healthy male individual.

Induced pluripotent stem cells (iPSCs) can be used to generate different somatic cell types in vitro, including insulin-producing pancreatic ß-cells. Here, we have generated iPSCs from a healthy male individual using an episomal reprogramming method. The resulting iPSCs are integration-free, have a normal karyotype and are pluripotent in vitro and in vivo. Furthermore, we show that this iPSC line can be differentiated into pancreatic lineage cells. Taken together, this iPSC line will be useful to test differentiation protocols towards ß-cell as well as other cell types and will also serve as a control for drug development and disease modelling studies.

Point mutations in the PDX1 transactivation domain impair human ß-cell development and function.

OBJECTIVE: Hundreds of missense mutations in the coding region of PDX1 exist; however, if these mutations predispose to diabetes mellitus is unknown. METHODS: In this study, we screened a large cohort of subjects with increased risk for diabetes and identified two subjects with impaired glucose tolerance carrying common, heterozygous, missense mutations in the PDX1 coding region leading to single amino acid exchanges (P33T, C18R) in its transactivation domain. We generated iPSCs from patients with heterozygous PDX1P33T/+, PDX1C18R/+ mutations and engineered isogenic cell lines carrying homozygous PDX1P33T/P33T, PDX1C18R/C18R mutations and a heterozygous PDX1 loss-of-function mutation (PDX1+/-). RESULTS: Using an in vitro ß-cell differentiation protocol, we demonstrated that both, heterozygous PDX1P33T/+, PDX1C18R/+ and homozygous PDX1P33T/P33T, PDX1C18R/C18R mutations impair ß-cell differentiation and function. Furthermore, PDX1+/- and PDX1P33T/P33T mutations reduced differentiation efficiency of pancreatic progenitors (PPs), due to downregulation of PDX1-bound genes, including transcription factors MNX1 and PDX1 as well as insulin resistance gene CES1. Additionally, both PDX1P33T/+ and PDX1P33T/P33T mutations in PPs reduced the expression of PDX1-bound genes including the long-noncoding RNA, MEG3 and the imprinted gene NNAT, both involved in insulin synthesis and secretion. CONCLUSIONS: Our results reveal mechanistic details of how common coding mutations in PDX1 impair human pancreatic endocrine lineage formation and ß-cell function and contribute to the predisposition for diabetes.