In vitro reprogramming of adult hepatocytes into insulin-producing cells without viral vectors

Cellular Reprogramming and Immortality: Expression Profiling Reveals Putative Genes Involved in Turritopsis dohrnii's Life Cycle Reversal

To gather insight on the genetic network of cell reprogramming and reverse development in a nonmodel cnidarian system, we produced and annotated a transcriptome of the hydrozoan Turritopsis dohrnii, whose medusae respond to damage or senescence by metamorphosing into a juvenile stage (the polyp), briefly passing through an intermediate and uncharacterized stage (the cyst), where cellular transdifferentiation occurs. We conducted sequential and pairwise differential gene expression (DGE) analyses of the major life cycle stages involved in the ontogenetic reversal of T. dohrnii. Our DGE analyses of sequential stages of T. dohrnii's life cycle stages show that novel and characterized genes associated with aging/lifespan, regulation of transposable elements, DNA repair, and damage response, and Ubiquitin-related processes, among others, were enriched in the cyst stage. Our pairwise DGE analyses show that, when compared with the colonial polyp, the medusa is enriched with genes involved in membrane transport, the nervous system, components of the mesoglea, and muscle contraction, whereas genes involved in chitin metabolism and the formation of the primary germ layers are suppressed. The colonial polyp and reversed polyp (from cyst) show significant differences in gene expression. The reversed polyp is enriched with genes involved in processes such as chromatin remodeling and organization, matrix metalloproteinases, and embryonic development whereas suppressing genes involved in RAC G-protein signaling pathways. In summary, we identify genetic networks potentially involved in the reverse development of T. dohrnii and produce a transcriptome profile of all its life cycle stages, and paving the way for its use as a system for research on cell reprogramming.

Soluble expression, purification, and secondary structure determination of human PDX1 transcription factor

The transcription factor PDX1 is a master regulator essential for proper development of the pancreas, duodenum and antrum. Furthermore, it is an indispensable reprogramming factor for the derivation of human β-cells, and recently, it has been identified as a tumor suppressor protein in gastric cancer. Here, we report the soluble expression and purification of the full-length human PDX1 protein from a heterologous system. To achieve this, the 849 bp coding sequence of the PDX1 gene was first codon-optimized for expression in Escherichia coli (E. coli). This codon-optimized gene sequence was fused to a protein transduction domain, a nuclear localization sequence, and a His-tag, and this insert was cloned into the protein expression vector for expression in E. coli strain BL21(DE3). Next, screening and identification of the suitable gene construct and optimal expression conditions to obtain this recombinant fusion protein in a soluble form was performed. Further, we have purified this recombinant fusion protein to homogeneity under native conditions. Importantly, the secondary structure of the protein was retained after purification. Further, this recombinant PDX1 fusion protein was applied to human cells and showed the ability to enter the cells as well as translocate to the nucleus. This recombinant tool can be used as a safe tool and can potentially replace its genetic and viral forms in the reprogramming process to induce a β-cell-specific transcriptional profile in an integration-free manner. Additionally, it can also be used to elucidate its role in cellular processes and for structural and biochemical studies.

Antifibrotic effects of specific siRNA targeting connective tissue growth factor delivered by polyethyleneimine‑functionalized magnetic iron oxide nanoparticles on LX‑2 cells

Connective tissue growth factor (CTGF) is a possible key determinant of progressive fibrosis. Nanotechnology has been considered as a potential tool for developing novel drug delivery systems for various diseases, including liver fibrosis. The present study aimed to investigate the potential antifibrotic activity of CTGF small interfering RNA (siRNA) mediated by polyethyleneimine (PEI)-functionalized magnetic iron oxide (Fe₃O₄) nanoparticles (NPs) in LX-2 cells. PEI-Fe₃O₄/siRNA complexes were synthesized to facilitate siRNA delivery and were transfected into LX-2 cells. Laser confocal microscopy was employed to investigate the cell uptake of PEI-Fe₃O₄/siRNA complexes. Reverse transcription-quantitative PCR (RT-qPCR) and western blotting were used to verify the effect of gene silencing. The results showed that siRNA-loaded PEI-Fe₃O₄ exhibited low cytotoxicity. The transfection efficiency of PEI-Fe₃O₄/siRNA reached 73.8%, and RT-qPCR and western blotting demonstrated effective gene silencing. These results indicated that CTGF siRNA delivered by PEI-Fe₃O₄ NPs significantly reduces CTGF expression and collagen production in activated LX-2 cells, providing a basis for future in vivo studies.

Epigenetic and Transcriptome Profiling Identifies a Population of Visceral Adipose-Derived Progenitor Cells with the Potential to Differentiate into an Endocrine Pancreatic Lineage

Type 1 diabetes (T1D) is characterized by the loss of insulin-producing β-cells in the pancreas. T1D can be treated using cadaveric islet transplantation, but this therapy is severely limited by a lack of pancreas donors. To develop an alternative cell source for transplantation therapy, we carried out the epigenetic characterization in nine different adult mouse tissues and identified visceral adipose-derived progenitors as a candidate cell population. Chromatin conformation, assessed using chromatin immunoprecipitation (ChIP) sequencing and validated by ChIP-polymerase chain reaction (PCR) at key endocrine pancreatic gene promoters, revealed similarities between visceral fat and endocrine pancreas. Multiple techniques involving quantitative PCR, in-situ PCR, confocal microscopy, and flow cytometry confirmed the presence of measurable (2-1000-fold over detectable limits) pancreatic gene transcripts and mesenchymal progenitor cell markers (CD73, CD90 and CD105; >98%) in visceral adipose tissue-derived mesenchymal cells (AMCs). The differentiation potential of AMCs was explored in transgenic reporter mice expressing green fluorescent protein (GFP) under the regulation of the Pdx1 (pancreatic and duodenal homeobox-1) gene promoter. GFP expression was measured as an index of Pdx1 promoter activity to optimize culture conditions for endocrine pancreatic differentiation. Differentiated AMCs demonstrated their capacity to induce pancreatic endocrine genes as evidenced by increased GFP expression and validated using TaqMan real-time PCR (at least 2-200-fold relative to undifferentiated AMCs). Human AMCs differentiated using optimized protocols continued to produce insulin following transplantation in NOD/SCID mice. Our studies provide a systematic analysis of potential islet progenitor populations using genome-wide profiling studies and characterize visceral adipose-derived cells for replacement therapy in diabetes.

Treatment with specific soluble factors promotes the functional maturation of transcription factor-mediated, pancreatic transdifferentiated cells

Pancreatic lineage-specific transcription factors (TFs) display instructive roles in converting adult cells to endocrine pancreatic cells through a process known as transdifferentiation. However, little is known about potential factors capable of accelerating transdifferentiation following transduction to achieve the functional maturation of transdifferentiated cells. In this study, we demonstrated, using adult liver-derived progenitor cells, that soluble factors utilized in pancreatic differentiation protocols of pluripotent stem cells promote functional maturation of TFs-mediated transdifferentiated cells. Treatment with an N2 supplement in combination with three soluble factors (glucagon-like peptide-1 [GLP-1] receptor agonist, notch inhibitor, and transforming growth factor-β [TGF-β] inhibitor) enhanced liver-to-pancreas transdifferentiation based on the following findings: i) the incidence of c-peptide-positive cells increased by approximately 1.2-fold after the aforementioned treatment; ii) the c-peptide expression level in the treated cells increased by approximately 12-fold as compared with the level in the untreated cells; iii) the treated cells secreted insulin in a glucose-dependent manner, whereas the untreated cells did not; and iv) transplantation of treated-transdifferentiated cells into streptozotocin-induced immunodeficient diabetic mice led to the amelioration of hyperglycemia. These results suggest that treatment with specific soluble factors promotes the functional maturation of transdifferentiated cells. Our findings could facilitate the development of new modalities for cell-replacement therapy for patients with diabetes.

Reprogramming of liver cells into insulin-producing cells

Tissue replacement is a promising direction for the treatment of diabetes, which will become widely available only when islets or insulin-producing cells that will not be rejected by the diabetic recipients are available in unlimited amounts. The present review addresses the research in the field of generating functional insulin-producing cells by transdifferentiation of adult liver cells both in vitro and in vivo. It presents recent knowledge of the mechanisms which underlie the process and assesses the challenges which should be addressed for its efficient implementation as a cell based replacement therapy for diabetics.

A small-molecule inducer of PDX1 expression identified by high-throughput screening

Pancreatic and duodenal homeobox 1 (PDX1), a member of the homeodomain-containing transcription factor family, is a key transcription factor important for both pancreas development and mature β cell function. The ectopic overexpression of Pdx1, Neurog3, and MafA in mice reprograms acinar cells to insulin-producing cells. We developed a quantitative PCR-based gene expression assay to screen more than 60,000 compounds for expression of each of these genes in the human PANC-1 ductal carcinoma cell line. We identified BRD7552, which upregulated PDX1 expression in both primary human islets and ductal cells, and induced epigenetic changes in the PDX1 promoter consistent with transcriptional activation. Prolonged compound treatment induced both insulin mRNA and protein and also enhanced insulin expression induced by the three-gene combination. These results provide a proof of principle for identifying small molecules that induce expression of transcription factors to control cellular reprogramming.

Beta cell dynamics: beta cell replenishment, beta cell compensation and diabetes

Type 2 diabetes, characterized by persistent hyperglycemia, arises mostly from beta cell dysfunction and insulin resistance and remains a highly complex metabolic disease due to various stages in its pathogenesis. Glucose homeostasis is primarily regulated by insulin secretion from the beta cells in response to prevailing glycemia. Beta cell populations are dynamic as they respond to fluctuating insulin demand. Beta cell replenishment and death primarily regulate beta cell populations. Beta cells, pancreatic cells, and extra-pancreatic cells represent the three tiers for replenishing beta cells. In rodents, beta cell self-replenishment appears to be the dominant source for new beta cells supported by pancreatic cells (non-beta islet cells, acinar cells, and duct cells) and extra-pancreatic cells (liver, neural, and stem/progenitor cells). In humans, beta cell neogenesis from non-beta cells appears to be the dominant source of beta cell replenishment as limited beta cell self-replenishment occurs particularly in adulthood. Metabolic states of increased insulin demand trigger increased insulin synthesis and secretion from beta cells. Beta cells, therefore, adapt to support their physiology. Maintaining physiological beta cell populations is a strategy for targeting metabolic states of persistently increased insulin demand as in diabetes.

Hacking cell differentiation: transcriptional rerouting in reprogramming, lineage infidelity and metaplasia

Initiating neoplastic cell transformation events are of paramount importance for the comprehension of regeneration and vanguard oncogenic processes but are difficult to characterize and frequently clinically overlooked. In epithelia, pre-neoplastic transformation stages are often distinguished by the appearance of phenotypic features of another differentiated tissue, termed metaplasia. In haemato/lymphopoietic malignancies, cell lineage ambiguity is increasingly recorded. Both, metaplasia and biphenotypic leukaemia/lymphoma represent examples of dysregulated cell differentiation that reflect a history of trans-differentiation and/or epigenetic reprogramming. Here we compare the similarity between molecular events of experimental cell trans-differentiation as an emerging therapeutic concept, with lineage confusion, as in metaplasia and dysplasia forecasting tumour development.

Generation of islet-like cells from mouse gall bladder by direct ex vivo reprogramming

Cell replacement is an emerging therapy for type 1 diabetes. Pluripotent stem cells have received a lot of attention as a potential source of transplantable β-cells, but their ability to form teratomas poses significant risks. Here, we evaluated the potential of primary mouse gall bladder epithelial cells (GBCs) as targets for ex vivo genetic reprogramming to the β-cell fate. Conditions for robust expansion and genetic transduction of primary GBCs by adenoviral vectors were developed. Using a GFP reporter for insulin, conditions for reprogramming were then optimized. Global expression analysis by RNA-sequencing was used to quantitatively compare reprogrammed GBCs (rGBCs) to true β-cells, revealing both similarities and differences. Adenoviral-mediated expression of NEUROG3, Pdx1, and MafA in GBCs resulted in robust induction of pancreatic endocrine genes, including Ins1, Ins2, Neurod1, Nkx2-2 and Isl1. Furthermore, expression of GBC-specific genes was repressed, including Sox17 and Hes1. Reprogramming was also enhanced by addition of retinoic acid and inhibition of Notch signaling. Importantly, rGBCs were able to engraft long term in vivo and remained insulin-positive for 15weeks. We conclude that GBCs are a viable source for autologous cell replacement in diabetes, but that complete reprogramming will require further manipulations.

Physical non-viral gene delivery methods for tissue engineering

The integration of gene therapy into tissue engineering to control differentiation and direct tissue formation is not a new concept; however, successful delivery of nucleic acids into primary cells, progenitor cells, and stem cells has proven exceptionally challenging. Viral vectors are generally highly effective at delivering nucleic acids to a variety of cell populations, both dividing and non-dividing, yet these viral vectors are marred by significant safety concerns. Non-viral vectors are preferred for gene therapy, despite lower transfection efficiencies, and possess many customizable attributes that are desirable for tissue engineering applications. However, there is no single non-viral gene delivery strategy that "fits-all" cell types and tissues. Thus, there is a compelling opportunity to examine different non-viral vectors, especially physical vectors, and compare their relative degrees of success. This review examines the advantages and disadvantages of physical non-viral methods (i.e., microinjection, ballistic gene delivery, electroporation, sonoporation, laser irradiation, magnetofection, and electric field-induced molecular vibration), with particular attention given to electroporation because of its versatility, with further special emphasis on Nucleofection™. In addition, attributes of cellular character that can be used to improve differentiation strategies are examined for tissue engineering applications. Ultimately, electroporation exhibits a high transfection efficiency in many cell types, which is highly desirable for tissue engineering applications, but electroporation and other physical non-viral gene delivery methods are still limited by poor cell viability. Overcoming the challenge of poor cell viability in highly efficient physical non-viral techniques is the key to using gene delivery to enhance tissue engineering applications.

New method to differentiate human peripheral blood monocytes into insulin producing cells: Human hematosphere culture

Strategy to differentiate stem cells into insulin producing cells (IPCs) in vitro has been a promising one to get cell source of β-cell replacement therapy for diabetes. It has been suggested that islets and neurons share features and nestin-positive cells could differentiate into IPCs. We have recently developed a three-dimensional culture system using human peripheral blood cells named as blood-born hematosphere (BBHS). Here we showed that most of BBHS were composed of nestin-positive cells. Under the four-stage differentiation protocol for IPCs, we plated nestin-positive BBHS onto fibronectin-coated dish. These cells form islet-like clusters and most of them expressed insulin. Pancreatic specific genes were turned on, such as transcription factors (Pdx-1, Ngn3 and Nkx6.1), genes related to endocrine function (Glut-2 and PC2) or β cell function (Kir6.2, SUR1). Furthermore islet differentiation was confirmed by dithizone (DTZ) staining to detect zinc ion which binds insulin protein within the cells. Finally, IPCs derived from BBHS showed capability to secrete insulin in response to glucose stimulation. Taken together, our novel protocol successfully induced islet-like human insulin producing cells out of BBHS. This strategy of ex vivo expansion of IPCs using BBHS provides an autologous therapeutic cell source for the treatment of diabetes.

Concise Review: Alchemy of Biology: Generating Desired Cell Types from Abundant and Accessible Cells

A major goal of regenerative medicine is to produce cells to participate in the generation, maintenance, and repair of tissues that are damaged by disease, aging, or trauma, such that function is restored. The establishment of induced pluripotent stem cells, followed by directed differentiation, offers a powerful strategy for producing patient-specific therapies. Given how laborious and lengthy this process can be, the conversion of somatic cells into lineage-specific stem/progenitor cells in one step, without going back to, or through, a pluripotent stage, has opened up tremendous opportunities for regenerative medicine. However, there are a number of obstacles to overcome before these cells can be widely considered for clinical applications. Here, we focus on induced transdifferentiation strategies to convert mature somatic cells to other mature cell types or progenitors, and we summarize the challenges that need to be met if the potential applications of transdifferentiation technology are to be achieved.

Dedifferentiation of human primary thyrocytes into multilineage progenitor cells without gene introduction

While identification and isolation of adult stem cells have potentially important implications, recent reports regarding dedifferentiation/reprogramming from differentiated cells have provided another clue to gain insight into source of tissue stem/progenitor cells. In this study, we developed a novel culture system to obtain dedifferentiated progenitor cells from normal human thyroid tissues. After enzymatic digestion, primary thyrocytes, expressing thyroglobulin, vimentin and cytokeratin-18, were cultured in a serum-free medium called SAGM. Although the vast majority of cells died, a small proportion (∼0.5%) survived and proliferated. During initial cell expansion, thyroglobulin/cytokeratin-18 expression was gradually declined in the proliferating cells. Moreover, sorted cells expressing thyroid peroxidase gave rise to proliferating clones in SAGM. These data suggest that those cells are derived from thyroid follicular cells or at least thyroid-committed cells. The SAGM-grown cells did not express any thyroid-specific genes. However, after four-week incubation with FBS and TSH, cytokeratin-18, thyroglobulin, TSH receptor, PAX8 and TTF1 expressions re-emerged. Moreover, surprisingly, the cells were capable of differentiating into neuronal or adipogenic lineage depending on differentiating conditions. In summary, we have developed a novel system to generate multilineage progenitor cells from normal human thyroid tissues. This seems to be achieved by dedifferentiation of thyroid follicular cells. The presently described culture system may be useful for regenerative medicine, but the primary importance will be as a tool to elucidate the mechanisms of thyroid diseases.

Induced pluripotent stem cells: a new era for hepatology

Stem cell transplantation has been proposed as an attractive alternative approach to restore liver mass and function. Recent progress has been reported on the generation of induced pluripotent stem (iPS) cells from somatic cells. Human-iPS cells can be differentiated towards the hepatic lineage which presents possibilities for improving research on diseases, drug development, tissue engineering, the development of bio-artificial livers, and a foundation for producing autologous cell therapies that would avoid immune rejection and enable correction of gene defects prior to cell transplantation. This focused review will discuss how human iPS cell advances are likely to have an impact on hepatology.