Reprogramming of Pancreatic Exocrine Cells AR42J Into Insulin-producing Cells Using mRNAs for Pdx1, Ngn3, and MafA Transcription Factors

Abstract

Direct reprogramming of pancreatic nonendocrine cells into insulin-producing β-cells represents a promising approach for the treatment of insulin-dependent diabetes. However, its clinical application is limited by the potential for insertional mutagenesis associated with the viral vectors currently used for cell reprogramming. With the aim of developing a nonintegrative reprogramming strategy for derivation of insulin-producing cells, here, we evaluated a new approach utilizing synthetic messenger RNAs encoding reprogramming transcription factors. Administration of synthetic mRNAs encoding three key transcription regulators of β-cell differentiation-Pdx1, Neurogenin3, and MafA-efficiently reprogrammed the pancreatic exocrine cells into insulin-producing cells. In addition to the insulin genes expression, the synthetic mRNAs also induced the expressions of genes important for proper pancreatic β-cell function, including Sur1, Kir6.2, Pcsk1, and Pcsk2. Pretreating cells with the chromatin-modifying agent 5-Aza-2'-deoxycytidine further enhanced reprogramming efficiency, increasing the proportion of insulin-producing cells from 3.5 ± 0.9 to 14.3 ± 1.9% (n = 4). Moreover, 5-Aza-2'-deoxycytidine pretreatment enabled the reprogrammed cells to respond to glucose challenge with increased insulin secretion. In conclusion, our results support that the reprogramming of pancreatic exocrine cells into insulin-producing cells, induced by synthetic mRNAs encoding pancreatic transcription factors, represents a promising approach for cell-based diabetes therapy.

Figure 1

Scheme of DNA template construct production, in vitro transcription, and determination of efficiencies of transfection and expressions of synthetic mRNAs of the transcription factors Pdx1, Neurogenin3, and MafA by the pancreatic exocrine cell line AR42J. (a) Production of DNA template constructs and subsequent mRNA synthesis: (1) homologous recombination of transcription factor cDNA and linearized vector containing the T7 promoter, the 5′UTR (untranslated region) of the rat β-globin gene, and the 3′UTR of the human β-globin gene; (2) PCR amplification of DNA template; (3) in vitro transcription; and (4) polyadenylation of synthetic mRNA. (b, c) Dose-dependent expressions of Pdx1, Neurogenin3, and MafA upon transfection of AR42J cells with synthetic mRNAs at doses of 0, 250, 500, 1,000, and 2,000 ng/ml media as determined by immunofluorescence staining 20 hours post-transfection. Cell nuclei are stained blue with 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride (DNA). Scale bars = 200 µm. Values are shown as mean ± standard deviation (n = 5).

Figure 2

Stability of synthetic mRNAs of the transcription factors Pdx1, Neurogenin3, and MafA. (a) Stability of synthetic mRNAs for Pdx1, Neurogenin3, and MafA upon their transfection into AR42J cells as revealed by quantitative reverse transcription polymerase chain reaction (n = 3). (b, c) Immunofluorescence staining results showing the stability of Pdx1, Neurogenin3, and MafA at 20, 40, and 60 hours after transfection of AR42J cells with the corresponding synthetic mRNAs at a dose of 1 µg mRNA/ml media. Cell nuclei (DNA) are stained blue by 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride. Scale bars = 200 µm. Values are shown as mean ± standard deviation (n = 5).

Figure 3

Transcription factors coexpression. (a, b) Immunofluorescence staining results showing coexpression of the transcription factors Pdx1, Neurogenin3 (Ngn3), and MafA following simultaneous transfection of AR42J cells with all three synthetic mRNAs at a dose of 500 ng of each mRNA/ml media. Double-positive cells are indicated by yellow color in the upper row. Cell nuclei (DNA) are stained blue with 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride. Scale bars = 200 µm. Values are shown as mean ± standard deviation (n = 4).

Figure 4

Scheme of the experimental design and evaluation of reprogramming efficiency. (a) Overview of the reprogramming protocol and subsequent analyses. Cell samples were divided into five groups based on culture conditions and the administration of all three reprogramming transcription factors (Pdx1, Neurogenin3, and MafA) for 10 days in the form of synthetic mRNAs at a dose of 500 ng of each mRNA/ml media. Cells were either cultured in serum-containing medium with mRNA transfection (treatment group A), cultured in serum-free medium with mRNA transfection (treatment group B), or pretreated for 3 days with 5-Aza-2′-deoxycytidine and cultured in serum-free medium with mRNA transfection (treatment group C). The expression profiles were compared with those of non-transfected AR42J cells that were either cultured in serum-containing medium (control group D), or pretreated for 3 days with 5-Aza-2′-deoxycytidine and cultured in serum-free medium (control group E) and of native rat pancreatic islets (control group RI). (b, c) Evaluation of reprogramming efficiency by immunofluorescence staining for the β-cell marker insulin (Ins) and the α-cell marker glucagon (Gcg). Insulin and glucagon expression was compared with non-transfected AR42J cells that were pretreated for 3 days with 5-Aza-2′-deoxycytidine and cultured in serum-free medium (control group E) and native rat pancreatic islet cells (control group RI). Cell nuclei (DNA) are stained blue with 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride. Scale bars = 200 μm. Values are shown as mean ± standard deviation (n = 4). n.d., not detected.

Figure 5

Gene expression profiles of reprogrammed cells were analyzed by quantitative reverse transcription polymerase chain reaction at the end of reprogramming (day 10—blue bars) and at 4 days after the last transfection with synthetic mRNAs (day 14—green bars). AR42J cells were treated with all three synthetic mRNAs (Pdx1, Neurogenin3, and MafA) for 10 days at a dose of 500 ng of each mRNA/ml media. Cells were either cultured in serum-containing medium with mRNA transfection (treatment group A), cultured in serum-free medium with mRNA transfection (treatment group B), or pretreated for 3 days with 5-Aza-2′-deoxycytidine and cultured in serum-free medium with mRNA transfection (treatment group C). The gene expression profiles were compared with those of native rat pancreatic islets (control group RI) and of nontransfected AR42J cells that were either cultured in serum-containing medium (control group D), or pretreated for 3 days with 5-Aza-2′-deoxycytidine and cultured in serum-free medium (control group E). Endogenous expressions of Pdx1, Neurogenin3, and MafA genes were determined using reverse primers specific for the 3′UTR (untranslated region) of each particular gene, which were not specific for synthetic mRNAs. The expression levels are presented relative to gene expression of rat pancreatic islets (normalized to 1). Values are shown as mean ± standard deviation (n = 5). Statistical analysis was performed using a two-tailed unpaired Student's t-test with Holm–Bonferroni correction. Samples were compared with nontransfected AR42J cells cultured in serum-containing medium (control group D). Asterisks indicate statistical significance: *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 6

Reprogramming efficiency and determination of insulin secretion capacity and insulin content. (a) Reprogramming efficiency was evaluated by immunofluorescence staining for the exocrine marker amylase (Amy) and the β-cell marker C-peptide (C-pep). Cell nuclei (DNA) are stained blue with 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride. Scale bars = 200 μm. (b) Glucose-stimulated insulin secretion of cell samples was determined by sequential 60-minute incubations at low (2.5 mmol/l) and high (20 mmol/l) glucose concentrations. The effect of depolarizing agent KCl on insulin secretion was determined by sequential 60-minute incubations at low (2.5 mmol/l) glucose concentration followed by low (2.5 mmol/l) glucose concentration with 30 mmol/l KCl. Insulin content in cell lysates was determined following KCl stimulated insulin secretion capacity test. Values are shown as mean ± standard deviation (n = 5). n.d., not detected. Statistical analysis was performed using a two-tailed unpaired Student's t-test. Asterisks indicate statistical significance: *P < 0.05, **P < 0.01.