Transdifferentiation of pancreas to liver

Focal Hepatocellular Carcinoma in Pancreas

A 67-year-old man was found to have a pancreatic head mass on abdominal ultrasound. He had compensated liver cirrhosis due to hepatitis C. The fine-needle aspiration (FNA) biopsy of the mass reported an adenocarcinoma of the pancreas, while the subsequent histopathology report of the supraclavicular lymph node showed features of hepatocellular carcinoma (HCC). A second read and additional stains on the FNA specimen confirmed a hepatoid (hepatocellular) carcinoma of the pancreas. He received atezolizumab and bevacizumab and had a good response. Tumors with features of HCC outside of the liver rarely occur and even more rarely in pancreas, with less than 50 cases reported so far. Pure HCC-like morphology is the most common histological form among four subtypes and has a relatively better prognosis. Surgical resection is considered the treatment of choice if amenable and variable outcomes are reported with different chemotherapies. Challenges exist in the diagnosis and the management of this rare and intriguing entity, and the potential misdiagnosis can have grave consequences as the management is completely different for a pancreatic adenocarcinoma and hepatoid carcinoma. We report a case with a challenging diagnosis of metastatic pancreatic hepatoid carcinoma which was treated as unresectable HCC with immunotherapy and the patient had a good response.

Hepatic insulin synthesis increases in rat models of diabetes mellitus type 1 and 2 differently

Insulin-positive (+) cells (IPCs), detected in multiple organs, are of great interest as a probable alternative to ameliorate pancreatic beta-cells dysfunction and insulin deficiency in diabetes. Liver is a potential source of IPCs due to it common embryological origin with pancreas. We previously demonstrated the presence of IPCs in the liver of healthy and diabetic rats, but detailed description and analysis of the factors, which potentially can induced ectopic hepatic expression of insulin in type 1 (T1D) and type 2 diabetes (T2D), were not performed. In present study we evaluate mass of hepatic IPCs in the rat models of T1D and T2D and discuss factors, which may stimulate it generation: glycaemia, organ injury, involving of hepatic stem/progenitor cell compartment, expression of transcription factors and inflammation. Quantity of IPCs in the liver was up by 1.7-fold in rats with T1D and 10-fold in T2D compared to non-diabetic (ND) rats. We concluded that ectopic hepatic expression of insulin gene is activated by combined action of a number of factors, with inflammation playing a decision role.

Acinar cells and the development of pancreatic fibrosis

Pancreatic fibrosis is caused by excessive deposition of extracellular matrixes of collagen and fibronectin in the pancreatic tissue as a result of repeated injury often seen in patients with chronic pancreatic diseases. The most common causative conditions include inborn errors of metabolism, chemical toxicity and autoimmune disorders. Its pathophysiology is highly complex, including acinar cell injury, acinar stress response, duct dysfunction, pancreatic stellate cell activation, and persistent inflammatory response. However, the specific mechanism remains to be fully clarified. Although the current therapeutic strategies targeting pancreatic stellate cells show good efficacy in cell culture and animal models, they are not satisfactory in the clinic. Without effective intervention, pancreatic fibrosis can promote the transformation from pancreatitis to pancreatic cancer, one of the most lethal malignancies. In the normal pancreas, the acinar component accounts for 82% of the exocrine tissue. Abnormal acinar cells may activate pancreatic stellate cells directly as cellular source of fibrosis or indirectly via releasing various substances and initiate pancreatic fibrosis. A comprehensive understanding of the role of acinar cells in pancreatic fibrosis is critical for designing effective intervention strategies. In this review, we focus on the role of and mechanisms underlying pancreatic acinar injury in pancreatic fibrosis and their potential clinical significance.

Somatic Lineage Reprogramming

Embryonic development and cell specification have been viewed as an epigenetically rigid process. Through accumulation of irreversible epigenetic marks, the differentiation process has been considered unidirectional, and once completed cell specification would be permanent and stable. However, somatic cell nuclear transfer that involved the implantation of a somatic nucleus into a previously enucleated oocyte accomplished in amphibians in the 1950s and in mammals in the late 1990s-resulting in the birth of "Dolly the sheep"-clearly showed that "terminal" differentiation is reversible. In parallel, work on lineage-determining factors like MyoD revealed surprising potential to modulate lineage identity in somatic cells. This work culminated in the discovery that a set of four defined factors can reprogram fibroblasts into induced pluripotent stem (iPS) cells, which were shown to be molecularly and functionally equivalent to blastocyst-derived embryonic stem (ES) cells, thus essentially showing that defined factors can induce authentic reprogramming without the need of oocytes. This concept was further extended when it was shown that fibroblasts can be directly converted into neurons, showing induced lineage conversion is possible even between cells representing two different germ layers. These findings suggest that "everything is possible" (i.e., once key lineage reprogramming factors are identified, cells should be able to convert into any desired lineage).

Regenerated hair cells in the neonatal cochlea are innervated and the majority co-express markers of both inner and outer hair cells

After a damaging insult, hair cells can spontaneously regenerate from cochlear supporting cells within the first week of life. While the regenerated cells express several markers of immature hair cells and have stereocilia bundles, their capacity to differentiate into inner or outer hair cells, and ability to form new synaptic connections has not been well-described. In addition, while multiple supporting cell subtypes have been implicated as the source of the regenerated hair cells, it is unclear if certain subtypes have a greater propensity to form one hair cell type over another. To investigate this, we used two CreER mouse models to fate-map either the supporting cells located near the inner hair cells (inner phalangeal and border cells) or outer hair cells (Deiters’, inner pillar, and outer pillar cells) along with immunostaining for markers that specify the two hair cell types. We found that supporting cells fate-mapped by both CreER lines responded early to hair cell damage by expressing Atoh1, and are capable of producing regenerated hair cells that express terminal differentiation markers of both inner and outer hair cells. The majority of regenerated hair cells were innervated by neuronal fibers and contained synapses. Unexpectedly, we also found that the majority of the laterally positioned regenerated hair cells aberrantly expressed both the outer hair cell gene, oncomodulin, and the inner hair cell gene, vesicular glutamate transporter 3 (VGlut3). While this work demonstrates that regenerated cells can express markers of both inner and outer hair cells after damage, VGlut3 expression appears to lack the tight control present during embryogenesis, which leads to its inappropriate expression in regenerated cells.

Epithelial Cell-Derived Extracellular Vesicles Trigger the Differentiation of Two Epithelial Cell Lines

Extracellular vesicles (EVs), specifically exosomes, carry a cell-type dependent cargo that is transported to the recipient cell and translated in the presence of a required machinery. Differences in the cargo carried by the corneal and conjunctival-derived EVs could be the agent that triggers the transdifferentiation of these two cell populations. Therefore, this study investigates the role of EVs in triggering the plasticity of corneal and conjunctival epithelial cells and identifies prospective miRNA and genes responsible for maintaining ocular surface homeostasis. The EVs were extracted from the conditioned media (after starving) of corneal epithelial (hTCEpi) and conjunctival (HCjE-Gi) cell lines using ultracentrifugation. HCjE-Gi cells were cultured with hTCEpi-derived EVs and vice-versa. The EVs were characterized as exosomes using Nanosight and Flow cytometry. KRT3 and KRT12 were used as associated corneal markers, whereas KRT7 and KRT13 were used as associated conjunctival markers with ΔNp63 as a differentiation marker. Shift of these markers was an indication of transdifferentiation. The cargo of the extracted exosomes from both the cell types was explored using next-generation sequencing. The hTCEpi-derived EVs induced conjunctival epithelial cells to express the corneal-associated markers KRT3 and KRT12, losing their conjunctival phenotype at both the mRNA and protein level. Simultaneously, HCjE-Gi-derived EVs induced corneal epithelial cells to express the conjunctival associated markers KRT7 and KRT13, losing their corneal phenotype. This process of differentiation was accompanied by an intermediate step of cell de-differentiation showed by up-regulation in the expression of epithelial stem cell marker ΔNp63, also shown on the ex vivo human cadaveric donor corneas. miRNA molecules (total of 11 including precursor and mature) with significant differences in their relative abundance between the two populations (p < 0.05) were found and investigated. miR-9-5p expression was higher in HCjE-Gi cells and HCjE-Gi-derived EVs when compared to hTCEpi cells and hTCEPi-derived EVs (p < 0.001). The results suggest that EVs released by the two cell types have the ability to influence the transdifferentiation of human conjunctival and corneal epithelial cells. miR-9-5p could have a role in stem cell homeostasis and cell differentiation via HES-1 gene.

Molecular mechanisms of transcription factor mediated cell reprogramming: conversion of liver to pancreas

Transdifferentiation is a type of cellular reprogramming involving the conversion of one differentiated cell type to another. This remarkable phenomenon holds enormous promise for the field of regenerative medicine. Over the last 20 years techniques used to reprogram cells to alternative identities have advanced dramatically. Cellular identity is determined by the transcriptional profile which comprises the subset of mRNAs, and therefore proteins, being expressed by a cell at a given point in time. A better understanding of the levers governing transcription factor activity benefits our ability to generate therapeutic cell types at will. One well-established example of transdifferentiation is the conversion of hepatocytes to pancreatic β-cells. This cell type conversion potentially represents a novel therapy in T1D treatment. The identification of key master regulator transcription factors (which distinguish one body part from another) during embryonic development has been central in developing transdifferentiation protocols. Pdx1 is one such example of a master regulator. Ectopic expression of vector-delivered transcription factors (particularly the triumvirate of Pdx1, Ngn3 and MafA) induces reprogramming through broad transcriptional remodelling. Increasingly, complimentary cell culture techniques, which recapitulate the developmental microenvironment, are employed to coax cells to adopt new identities by indirectly regulating transcription factor activity via intracellular signalling pathways. Both transcription factor-based reprogramming and directed differentiation approaches ultimately exploit transcription factors to influence cellular identity. Here, we explore the evolution of reprogramming and directed differentiation approaches within the context of hepatocyte to β-cell transdifferentiation focussing on how the introduction of new techniques has improved our ability to generate β-cells.

Direct Lineage Reprogramming: Harnessing Cell Plasticity between Liver and Pancreas

Direct lineage reprogramming of abundant and accessible cells into therapeutically useful cell types holds tremendous potential in regenerative medicine. To date, a number of different cell types have been generated by lineage reprogramming methods, including cells from the neural, cardiac, hepatic, and pancreatic lineages. The success of this strategy relies on developmental biology and the knowledge of cell-fate-defining transcriptional networks. Hepatocytes represent a prime target for β cell conversion for numerous reasons, including close developmental origin, accessibility, and regenerative potential. We present here an overview of pancreatic and hepatic development, with a particular focus on the mechanisms underlying the divergence between the two cell lineages. Additionally, we discuss to what extent this lineage relationship can be exploited in efforts to reprogram one cell type into the other and whether such an approach may provide a suitable strategy for regenerative therapies of diabetes.

Hepatoid carcinoma of the pancreas: A case report and review of the literature

BACKGROUND

Hepatoid carcinoma (HC) is an extremely rare neoplasm that is morphologically similar to hepatocellular carcinoma. HC has been described in various organs; however, HC of the pancreas is extremely rare. To our knowledge, only 38 cases have been reported. We present a case of HC of the pancreas in a 36-year-old male patient.

CASE SUMMARY

A 36-year-old cachexic man with no significant past medical history was transferred to our hospital with a history of painless jaundice, elevated blood glucose and significant weight loss. Lab tests showed elevated serum transaminases, bilirubin and alpha-fetoprotein levels. Magnetic resonance imaging of the upper abdomen showed a diffusely enlarged pancreas, appearing “sausage-shaped”. Magnetic resonance cholangiopancreatography showed upstream ductal dilation secondary to stricture of the main pancreatic duct and the common bile duct, which were not visible. Immunohistochemistry of biopsied tissue from a percutaneous pancreatic biopsy showed tumor cell positivity for HepPar1, polyclonal carcinoembryonic antigen and CK19, suggestive of HC of the pancreas. The characteristics of 39 patients with HC of the pancreas were reviewed.

CONCLUSION

HC of the pancreas is more prevalent in males, and patients have a median age of 57 years. It is most commonly asymptomatic or presents as abdominal back pain, and the pancreatic tail is the most common location. At the time of diagnosis, liver metastasis is often present.

Direct cell reprogramming for tissue engineering and regenerative medicine

Direct cell reprogramming, also called transdifferentiation, allows for the reprogramming of one somatic cell type directly into another, without the need to transition through an induced pluripotent state. Thus, it is an attractive approach to develop novel tissue engineering applications to treat diseases and injuries where there is a shortage of proliferating cells for tissue repair. In certain tissue damage, terminally differentiated somatic cells lose their ability to proliferate, as a result, damaged tissues cannot heal by themselves. Examples of these scenarios include myocardial infarctions, neurodegenerative diseases, and cartilage injuries. Transdifferentiation is capable of reprogramming cells that are abundant in the body into desired cell phenotypes that are able to restore tissue function in damaged areas. Therefore, direct cell reprogramming is a promising direction in the cell and tissue engineering and regenerative medicine fields.

In recent years, several methods for transdifferentiation have been developed, ranging from the overexpression of transcription factors via viral vectors, to small molecules, to clustered regularly interspaced short palindromic repeats (CRISPR) and its associated protein (Cas9) for both genetic and epigenetic reprogramming. Overexpressing transcription factors by use of a lentivirus is currently the most prevalent technique, however it lacks high reprogramming efficiencies and can pose problems when transitioning to human subjects and clinical trials. CRISPR/Cas9, fused with proteins that modulate transcription, has been shown to improve efficiencies greatly. Transdifferentiation has successfully generated many cell phenotypes, including endothelial cells, skeletal myocytes, neuronal cells, and more. These cells have been shown to emulate mature adult cells such that they are able to mimic major functions, and some are capable of promoting regeneration of damaged tissue in vivo. While transdifferentiated cells have not yet seen clinical use, they have had promise in mice models, showing success in treating liver disease and several brain-related diseases, while also being utilized as a cell source for tissue engineered vascular grafts to treat damaged blood vessels. Recently, localized transdifferentiated cells have been generated in situ, allowing for treatments without invasive surgeries and more complete transdifferentiation. In this review, we summarized the recent development in various cell reprogramming techniques, their applications in converting various somatic cells, their uses in tissue regeneration, and the challenges of transitioning to a clinical setting, accompanied with potential solutions.

Primary Hepatoid Carcinoma of the Pancreas: A Clinicopathological Study of 3 Cases With Review of Additional 31 Cases in the Literature

Primary pancreatic hepatoid carcinoma (PHC) is very rare. Here, we reported 3 such cases with review of additional 31 cases in the literature. Our 3 patients were male (83, 72, and 54 years old, respectively). Serum α-fetoprotein (AFP) was elevated in 1 patient (case 3, 8338 ng/mL) and not measured in the other two. The PHC in patient 1 (pathological stage pT2N0M0) and patient 2 (pT3N0M0) showed pure hepatocellular carcinoma (HCC)-like morphology, whereas in case 3 it was a PHC with true glandular differentiation (pT4N0M0). The diagnosis of PHC was confirmed with positive immunohistochemical staining in the tumor cells for AFP (2/3), Hep Par 1 (3/3), glypican-3 (2/3), arginase-1 (2/3), and Sal-like protein 4 (1/3). CD10 and polyclonal carcinoembryonic antigen stains show focal canalicular pattern in 2/3 tumors. Patient 1 did not receive further treatment after resection and was alive with no evidence of disease at 107 months. Patient 2 died of postoperative complications, whereas patient 3 received postsurgical chemoradiation and died of disease at 29 months. Our findings and literature review indicate that PHCs can be divided into 4 histological subtypes: with pure HCC-like morphology (n = 22), with neuroendocrine differentiation (n = 8), with true glandular differentiation (n = 3), and with acinar cell differentiation (n = 1). On univariate analysis, pure HCC-like morphology was associated with better disease-specific survival (DSS; P = .04), whereas lymph node and distant metastases were associated with worse DSS ( P = .002 for both). Age, gender, presenting symptoms, serum AFP level, and T stage were not associated with DSS. On multivariate analysis, none of these parameters was significantly associated with DSS.

Conversion of Fibroblasts to Hepatocytes In Vitro

Primary hepatocytes are widely used in regenerative medicine, drug metabolism analysis, and in vitro drug screens. To overcome the shortage of liver donors, several strategies, such as differentiation of pluripotent stem cells and transdifferentiation from somatic cells, were developed to generate hepatocytes from alternative sources. Here, we describe in detail lenti-virus-based procedure for direct conversion of human fibroblasts to hepatocytes (hiHep cells) in vitro. A detailed protocol for preparation of human fibroblasts from scar tissues is also provided. Based on this protocol, FOXA3, HNF1A, and HNF4A are introduced into SV40-large-T-antigen-expressing human scar fibroblasts by lenti-virus. It usually takes about 5-7 days to get epithelial hiHep colonies. SV40-large-T-antigen-expressing hiHep (hiHep^LT) cells are proliferative and can be expanded to a large number for potential uses.

Increased serum levels of betatrophin in pancreatic cancer-associated diabetes

Long-standing diabetes or glucose intolerance is recognized as a crucial event in the process of pancreatic cancer. Betatrophin, a novel liver-derived hormone, promotes β-cell proliferation and improves glucose intolerance. However, the relationship between betatrophin and PDAC-associated diabetes is not fully understood. To evaluate the serum betatrophin levels in PDAC-associated diabetes, a total 105 Taiwanese subjects including 15 healthy subjects, and 12 patients having PDAC with normal glucose tolerance (PDAC-NGT), 12 patients having PC with impaired glucose tolerance (PDAC-IGT), and 66 patients having PC with diabetes mellitus (PDAC-DM) were enrolled for this study. Serum betatrophin and carbohydrate antigen 19-9 (CA19-9) levels were analyzed by enzyme-linked immunosorbent assay (ELISA). Compared to healthy subjects, PDAC patients had higher levels of betatrophin and CA19-9. Consistently, betatrophin protein was significantly expressed in pancreatic ductal of PDAC-associated DM patients using immunohistochemistry (IHC) method. Furthermore, multivariate regression analysis showed the betatrophin was significantly and positively independent with T category (β= 0.605, P=0.010), serum albumin (β= 0. 423, P=0.021), lipase (β= 0.292, P=0.039), and blood urea nitrogen (BUN) (β= 0.303, P=0.040). Further, the betatrophin was three folds of having PDAC-associated diabetes with the highest odds ratio [OR=3.39; 95% CI (1.20–9.57); P=0.021) and receiver operating characteristic (ROC) curve analysis showed that AUC value of betarophin was 0.853 which is slightly larger than AUC value of CA19-9 (0.792) in PDAC-DM patients. Interestingly, AUC value of betarophin plus CA19-9 was 0.988 in PDAC-DM patients. Therefore, betatrophin combined CA19-9 may serve as a potential biomarker for PDAC-associated diabetes.

Pancreatic β Cell Regeneration as a Possible Therapy for Diabetes

Diabetes is the result of having inadequate supply of functional insulin-producing β cells. Two possible approaches for replenishing the β cells are: (1) replacement by transplanting cadaveric islets or β cells derived from human embryonic stem cells/induced pluripotent stem cells and (2) induction of endogenous regeneration. This review focuses on endogenous regeneration, which can follow two pathways: enhanced replication of existing β cells and formation of new β cells from cells not expressing insulin, either by conversion from a differentiated cell type (transdifferentiation) or differentiation from progenitors (neogenesis). Exciting progress on both pathways suggest that regeneration may have therapeutic promise.

From organoids to organs: Bioengineering liver grafts from hepatic stem cells and matrix

Due to the complex function and structure of the liver, resourceful solutions for treating end-stage liver disease are required. Currently, liver transplantation is the only curative therapeutic option. However, due to a worldwide donor shortage, researchers have been looking in other fields for alternative sources of transplantable liver tissue. Recent advances in our understanding of liver physiology, stem cell and matrix biology, have accelerated tissue engineering research. Most notable is the discovery of a culture system to grow liver-like organoids from human hepatic stem cells. The extensive expansion capacity of these stem cells has contributed greatly to the availability of hepatocyte-like cells for tissue engineering. In addition, new techniques are explored to obtain biological liver scaffolds from full size donor organs. This review summarizes these state-of-art techniques which may lay the groundwork towards re-creating transplantable tissue from autologous or allogenic stem cells in the coming decade.

Abdominal hamartoma with pancreatic and hepatic differentiation in a sow

A 7-year-old Duroc sow exhibited emaciation, loss of appetite and rapid breathing, and was euthanized. Histopathological examination revealed mild to moderate fibrosis of the heart, cystic kidneys and ulcerative enteritis associated with Balantidium infection. Additionally, a small nodule was incidentally found in the peripancreatic fat tissue. The nodule consisted of disarranged cellular components: pancreatic islet cells (either insulin-, glucagon- or somatostatin-positive), pancreatic acinar cells, hepatocytes (human hepatocyte-positive) and ductal cells (cytokeratin 19-positive). Some of the human hepatocyte-positive cells were also positive for chromogranin A and cytokeratin 7, indicating that they were hepatic progenitor cells. The nodule was therefore diagnosed as hamartoma, probably originating from a fragment of the caudal verge of the liver bud, which contains hepatic and pancreatic progenitors.

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.

In vitro reprogramming of pancreatic alpha cells towards a beta cell phenotype following ectopic HNF4α expression

There is currently a shortage of organ donors available for pancreatic beta cell transplantation into diabetic patients. An alternative source of beta cells is pre-existing pancreatic cells. While we know that beta cells can arise directly from alpha cells during pancreatic regeneration we do not understand the molecular basis for the switch in phenotype. The aim of the present study was to investigate if hepatocyte nuclear factor 4 alpha (HNF4α), a transcription factor essential for a normal beta cell phenotype, could induce the reprogramming of alpha cells towards potential beta cells. We utilised an in vitro model of pancreatic alpha cells, the murine αTC1-9 cell line. We initially characterised the αTC1-9 cell line before and following adenovirus-mediated ectopic expression of HNF4α. We analysed the phenotype at transcript and protein level and assessed its glucose-responsiveness. Ectopic HNF4α expression in the αTC1-9 cell line induced a change in morphology (1.7-fold increase in size), suppressed glucagon expression, induced key beta cell-specific markers (insulin, C-peptide, glucokinase, GLUT2 and Pax4) and pancreatic polypeptide (PP) and enabled the cells to secrete insulin in a glucose-regulated manner. In conclusion, HNF4α reprograms alpha cells to beta-like cells.

Transdifferentiation of chondrocytes into neuron-like cells induced by neuronal lineage specifying growth factors

We previously reported that neural-crest-derived stromal cells from adult human and rat corneas can differentiate into neuron-like cells when treated with neuronal lineage specifying growth factors. However, it remains unclear whether this level of cell plasticity is unique to the corneal stromal cell population present in the eye. In this study, non-neural-crest-derived chondrocytes from the xiphosternum of adult rats were subjected to the same differentiation protocol. Cells of the adult rat xiphosternum can also differentiate into neuron-like cells when treated with neurogenic differentiation specifying growth factors. After 1 week in neurogenic differentiation culture conditions, the chondrocytes changed from a round to a stellate morphology and started to express neuron-specific protein neurofilament-200 (NF-200), microtubule associated protein-2 (Map-2), and β-III tubulin. Lineage-specifying growth factors can affect changes in morphology and protein expression of adult cells in culture, findings that challenge the notion of a restricted differentiation potential of adult cell populations and questions the stability of the differentiated state of cells.

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.

Model on cell movement, growth, differentiation and de-differentiation: reaction-diffusion equation and wave propagation

We construct a model for cell proliferation with differentiation into different cell types, allowing backward de-differentiation and cell movement. With different cell types labeled by state variables, the model can be formulated in terms of the associated transition probabilities between various states. The cell population densities can be described by coupled reaction-diffusion partial differential equations, allowing steady wavefront propagation solutions. The wavefront profile is calculated analytically for the simple pure growth case (2-states), and analytic expressions for the steady wavefront propagating speeds and population growth rates are obtained for the simpler cases of 2-, 3- and 4-states systems. These analytic results are verified by direct numerical solutions of the reaction-diffusion PDEs. Furthermore, in the absence of de-differentiation, it is found that, as the mobility and/or self-proliferation rate of the down-lineage descendant cells become sufficiently large, the propagation dynamics can switch from a steady propagating wavefront to the interesting situation of propagation of a faster wavefront with a slower waveback. For the case of a non-vanishing de-differentiation probability, the cell growth rate and wavefront propagation speed are both enhanced, and the wavefront speeds can be obtained analytically and confirmed by numerical solution of the reaction-diffusion equations.

3D co-culturing model of primary pancreatic islets and hepatocytes in hybrid spheroid to overcome pancreatic cell shortage

Here, a spheroidal 3D co-culture model of primary (rat) pancreatic islets and hepatocytes with uniform size and shape was developed using hemispheric concave microwell arrays. We conducted morphological and functional analyses of hybrid spheroids versus mono-cultures of islets or hepatocytes (controls). For the establishment of a 3D hybrid model, a broad range of cell ratios - 1:1, 1:3, 1:5, 1:7, 3:1, 5:1 and 7:1 mixture - of hepatocytes and pancreatic islets were used. As control, each hepatocyte and pancreatic islet were mono-cultured forming 3D spheroids. The transient morphology of spheroid formation in 9 culture models was observed using optical microscopy. Cell viability under these culture environments was assessed, and the morphologies of the outer and inner porous cell-spheroid structures were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and imaging of stained spheroid sections. The pancreatic islet-specific function of hybrid spheroids was evaluated by measuring insulin secretion and in vivo test by xenotransplantation of encapsulated spheroids in microfibers with a consistent maintenance of normal blood glucose levels over 4 weeks, while liver-specific functions were measured in terms of albumin secretion, urea secretion and cytochrome P450 activity. These diverse observations and evaluations validated the positive and bidirectional effects of co-cultured 3D spheroids. The proposed 3D co-culture model demonstrated that both cells appeared to support each other's functions strongly in spheroids, even though smaller proportions of each cell type was evaluated compared to mono-culture models, suggesting that the proposed model could help overcome the problem of cell shortages in clinical applications.

Dedifferentiated follicular granulosa cells derived from pig ovary can transdifferentiate into osteoblasts

Transdifferentiation is the conversion of cells from one differentiated cell type into another. How functionally differentiated cells already committed to a specific cell lineage can transdifferentiate into other cell types is a key question in cell biology and regenerative medicine. In the present study we show that porcine ovarian follicular GCs (granulosa cells) can transdifferentiate into osteoblasts in vitro and in vivo. Pure GCs isolated and cultured in Dulbecco's modified Eagle's medium supplemented with 20% FBS (fetal bovine serum) proliferated and dedifferentiated into fibroblast-like cells. We referred to these cells as DFOG (dedifferentiated follicular granulosa) cells. Microarray analysis showed that DFOG cells lost expression of GC-specific marker genes, but gained the expression of osteogenic marker genes during dedifferentiation. After osteogenic induction, DFOG cells underwent terminal osteoblast differentiation and matrix mineralization in vitro. Furthermore, when DFOG cells were transplanted subcutaneously into SCID mice, these cells formed ectopic osteoid tissue. These results indicate that DFOG cells derived from GCs can differentiate into osteoblasts in vitro and in vivo. We suggest that GCs provide a useful model for studying the mechanisms of transdifferentiation into other cell lineages in functionally differentiated cells.

Cellular reprogramming--lowering gravity on Waddington's epigenetic landscape

During development, cell fate is specified precisely through programming by multiple complex elements and processes, including chromatin modifications that result in epigenetic marks. Once determined, cell fate is specified further only through maturation processes, which include differentiation and senescence. However, recent studies have shown that it is possible to influence cell fate through artificial manipulation. For example, the exogenous expression of a set of transcription factors can result in the reprogramming of differentiated skin fibroblasts to a pluripotent state. In addition, recent reports have demonstrated the directed reprogramming of one type of differentiated somatic cell to another type of differentiated somatic cell, without rejuvenation to a pluripotent state. Reprogramming factors blur the boundaries between different cell fates, which can never meet, as if the hierarchy were flattened by 'lowering gravity'. Although attempts to use direct reprogramming to generate certain cell types, such as those found in the kidneys and the lungs, have remained unsuccessful, recent advances suggest that we are nearing the identification of determinants that allow cells to be directly reprogrammed into cell types from all organs in the not too distant future. This Commentary summarises our current knowledge on cellular reprogramming, and more specifically, recent advances in direct reprogramming to generate a variety of cell types.

Modulating zymogen granule formation in pancreatic AR42J cells

Zymogen granules (ZG) are specialized organelles in the exocrine pancreas which allow digestive enzyme storage and regulated secretion. To investigate ZG biogenesis, cargo sorting and packaging, suitable cellular model systems are required. Here, we demonstrate that granule formation in pancreatic AR42J cells, an acinar model system, can be modulated by altering the growth conditions in cell culture. We find that cultivation of AR42J cells in Panserin™ 401, a serum-free medium, enhances the induction of granule formation in the presence or absence of dexamethasone when compared to standard conditions including serum. Biochemical and morphological studies revealed an increase in ZG markers on the mRNA and protein level, as well as in granule size compared to standard conditions. Our data indicate that this effect is related to pronounced differentiation of AR42J cells. To address if enhanced expression of ZG proteins promotes granule formation, we expressed several zymogens and ZG membrane proteins in unstimulated AR42J cells and in constitutively secreting COS-7 cells. Neither single expression nor co-expression was sufficient to initiate granule formation in AR42J cells or the formation of granule-like structures in COS-7 cells as described for neuroendocrine cargo proteins. The importance of our findings for granule formation in exocrine cells is discussed.

Cdx function is required for maintenance of intestinal identity in the adult

The homeodomain transcription factors Cdx1 and Cdx2 are expressed in the intestinal epithelium from early development, with expression persisting throughout the life of the animal. While our understanding of the function of Cdx members in intestinal development has advanced significantly, their roles in the adult intestine is relatively poorly understood. In the present study, we found that ablation of Cdx2 in the adult small intestine severely impacted villus morphology, proliferation and intestinal gene expression patterns, resulting in the demise of the animal. Long-term loss of Cdx2 in a chimeric model resulted in loss of all differentiated intestinal cell types and partial conversion of the mucosa to a gastric-like epithelium. Concomitant loss of Cdx1 did not exacerbate any of these phenotypes. Loss of Cdx2 in the colon was associated with a shift to a cecum-like epithelial morphology and gain of cecum-associated genes which was more pronounced with subsequent loss of Cdx1. These findings suggest that Cdx2 is essential for differentiation of the small intestinal epithelium, and that both Cdx1 and Cdx2 contribute to homeostasis of the colon.

In vitro transdifferentiation of HepG2 cells to pancreatic-like cells by CCl₄, D-galactosamine, and ZnCl₂

OBJECTIVE

The objective of the study was to induce transdifferentiation of human hepatoma HepG2 cells into pancreatic-like cells without direct genetic intervention.

METHODS

HepG2 cells were transfected with plasmids for the hepatocyte marker protein green fluorescent protein (albumin-GFP) and the pancreatic cell marker Discosoma spp red fluorescent protein (elastase-DsRed) to create FAE-HepG2 cells. Fluorescent marker expression was used to monitor in vitro transdifferentiation stimulated 100 mM CCl₄, 2 mM D-galactosamine, or 200 μM ZnCl₂. Concentrations were selected for optimal cell survival rate. Transdifferentiation was also characterized by immunohistochemical detection of amylase, glucagon, and insulin and by polymerase change reaction analysis of amylase and insulin mRNA production.

RESULTS

Control cells expressed albumin-GFP but no elastase-DsRed. By 30 days of culture, all 3 agents induced expression of pancreatic-like cell marker elastase-DsRed. ZnCl₂ was the most effective as most cells expressed elastase-DsRed in the absence of simultaneous expression of albumin-GFP. For CCl₄ and D-galactosamine, elastase-DsRed was expressed in the same cells as albumin-GFP. Cells treated by each agent also expressed amylase, insulin, and glucagon proteins and mRNAs.

CONCLUSIONS

Without direct genetic intervention, select low small molecules can induce in vitro transformation of hepatoma cells into pancreatic-like cells.

Signals from pancreatic mesoderm influence the expression of a pancreatic phenotype in hepatic stem-like cell line PHeSC-A2 in vitro: a preliminary study

The ex vivo generation of pancreatic cells from adult hepatic stem cells for subsequent transplantation has been proposed as a novel treatment for Diabetes mellitus. The pancreas and liver, closely related developmentally, may retain a shared (hepatopancreatic) stem cell whose plasticity could be exploited to differentiate into either lineage, dependent on environmental signals. This novel study investigated whether signals from pancreatic mesoderm could induce the differentiation of adult hepatic stem cell-like cells into pancreatic endocrine cells in vitro. A porcine hepatic stem-like cell line, designated PHeSC-A2, was co-cultured with quail pancreatic mesoderm in a Growth Factor Reduced Matrigel-Ham's F12.ITS culture system. Immunocytochemical studies revealed insulin- and glucagon-producing cells. Assessment of nuclear morphology indicated that these endocrine cells were PHeSC-A2-derived. It is thus proposed that the PHeSC-A2 cell line has a higher level of plasticity than previously indicated. These preliminary results and assessment of published data have led to the following postulations: (a) permissive signaling from pancreatic mesoderm suffices to induce hepatic stem cells to assume a pancreatic lineage, (b) the pancreatic phenotype assumed by hepatic stem cells is a default state, (c) the differentiation capacity embodied by these cells indicates the existence of a hepatopancreatic stem cell lineage.

Transdifferentiation of pancreatic cells to hepatocytes

Hepatocytes maintained in culture provide an attractive model system for the study of liver function. Furthermore, hepatocyte transplantation offers an alternative cellular therapy to orthotopic liver transplantation for the treatment of hepatic failure and hereditary liver disease. To overcome the problem of organ shortage, additional source of hepatocytes must be found. Here, we present a strategy and protocol to transdifferentiate (or convert) developmentally related pancreatic cells into hepatocytes based on the addition of the synthetic glucocorticoid dexamethasone.

A robust and highly efficient immune cell reprogramming system

Here we describe a lineage reprogramming system consisting of a B cell line with an estradiol-inducible form of C/EBPalpha where cells can be converted into macrophage-like cells at 100% efficiency within 2 to 3 days. The reprogrammed cells are larger, contain altered organelle and cytoskeletal structures, are phagocytic, and exhibit an inflammatory response. Time-lapse experiments showed that the cells acquire a macrophage morphology and increased migratory activity as early as 10 hr. During induction, thousands of genes become up- or downregulated, including several dozen transcription and chromatin-remodeling factors. Time-limited exposure of cells to the inducer showed that the reprogrammed cells become transgene independent within 1 to 2 days. The reprogramming can be inhibited, at least partially, by perturbation experiments with B cell and macrophage transcription factors. The tightness, robustness, and speed of the system described make it a versatile tool to study biochemical and biological aspects of lineage reprogramming.

Methodological aspects of attempts to trans-differentiate adult stem cells into embryonic-like cells in vitro

AIMS

The aim of this research was to set up an in vitro system to trans-differentiate haematopoietic stem cells (HSCs) into embryo-like stem cells in order to de-differentiate them. In this more naive state they should be cultivated more easily in order to augment them for consecutive differentiation and autologous transplantation for use in clinical practice.

METHODS

Using the principle of the methodology of blastocyst injection, HSCs were co-cultivated with mouse embryonic stem cells (mES) with and without cell to cell contact. After co-cultivation HSCs were analyzed by flow-cytometry using haematopoietic markers (CD34, CD45, CD133) and embryonic stem cell markers (SSEA-4, Tra-1-60, Tra-1-81).

RESULTS

No ES cell markers were detected on the former HSCs. A decrease in HSC marker intensity was the only finding. This implies that no de-differentiation took place.

CONCLUSIONS

We hypothesize that the unnatural situation of a mixture of two cell types originating in different species may have led to this outcome. To achieve our goal of in vitro de-differentiation we need to use a purely human culture system without animal additives.

Developmental biology of the pancreas: a comprehensive review

Pancreatic development represents a fascinating process in which two morphologically distinct tissue types must derive from one simple epithelium. These two tissue types, exocrine (including acinar cells, centro-acinar cells, and ducts) and endocrine cells serve disparate functions, and have entirely different morphology. In addition, the endocrine tissue must become disconnected from the epithelial lining during its development. The pancreatic development field has exploded in recent years, and numerous published reviews have dealt specifically with only recent findings, or specifically with certain aspects of pancreatic development. Here I wish to present a more comprehensive review of all aspects of pancreatic development, though still there is not a room for discussion of stem cell differentiation to pancreas, nor for discussion of post-natal regeneration phenomena, two important fields closely related to pancreatic development.

Potential role of glucocorticoid signaling in the formation of pancreatic islets in the human fetus

Glucocorticoids have been suggested to play a role in programming late adult disorders like diabetes during fetal life. Recent work in rodents showed their role in pancreas development by modulating the expression of transcription factors. The aim of this work was to investigate their possible implication in human pancreas development. The ontogenesis of glucocorticoid receptor (GR) and several pancreatic transcription factors was studied by immunohistochemistry and RT-PCR on human fetal pancreatic specimens. At 6 wk of development (wd) insulin promoting factor 1 (IPF1) was expressed in the majority of epithelial cells forming tubular structures while GR was present in the mesenchyme, suggesting an early role of glucocorticoids, before endocrine and exocrine differentiation. Only GR alpha (active form) mRNA was expressed from 6 wk onwards while GR beta (inactive form) was never observed. The first insulin cells did not express IPF1 or GR. Islet formation occurred from 10 wd as IPF1-positive cells started to express simultaneously insulin and GR. This coexpression in beta cells persisted until adulthood. The mRNA expression profiles confirmed immunohistochemistry and showed the early expression of crucial transcription factors. In conclusion, the presence of the active GR isoform around islet formation supports the novel idea that glucocorticoids could modulate human pancreas development.

Diabetes mellitus: an opportunity for therapy with stem cells?

In both Type 1 and 2 diabetes, insufficient numbers of insulin-producing beta-cells are a major cause of defective control of blood glucose and its complications. Restoration of damaged beta-cells by endocrine pancreas regeneration would be an ideal therapeutic option. The possibility of generating insulin-secreting cells with adult pancreatic stem or progenitor cells has been investigated extensively. The conversion of differentiated cells such as hepatocytes into beta-cells is being attempted using molecular insights into the transcriptional make-up of beta-cells. Additionally, the enhanced proliferation of beta-cells in vivo or in vitro is being pursued as a strategy for regenerative medicine for diabetes. Advances have also been made in directing the differentiation of embryonic stem cells into beta-cells. Although progress is encouraging, major gaps in our understanding of developmental biology of the pancreas and adult beta-cell dynamics remain to be bridged before a therapeutic application is made possible.

Conversion of immortal liver progenitor cells into pancreatic endocrine progenitor cells by persistent expression of Pdx-1

The conversion of expandable liver progenitor cells into pancreatic beta cells would provide a renewable cell source for diabetes cell therapy. Previously, we reported the establishment of liver epithelial progenitor cells (LEPCs). In this work, LEPCs were modified into EGFP/Pdx-1 LEPCs, cells with stable expression of both Pdx-1 and EGFP. Unlike previous work, with persistent expression of Pdx-1, EGFP/Pdx-1 LEPCs acquired the phenotype of pancreatic endocrine progenitor cells rather than giving rise to insulin-producing cells directly. EGFP/Pdx-1 LEPCs proliferated vigorously and expressed the crucial transcription factors involved in beta cell development, including Ngn3, NeuroD, Nkx2.2, Nkx6.1, Pax4, Pax6, Isl1, MafA and endogenous Pdx-1, but did not secrete insulin. When cultured in high glucose/low serum medium supplemented with cytokines, EGFP/Pdx-1 LEPCs stopped proliferating and gave rise to functional beta cells without any evidence of exocrine or other islet cell lineage differentiation. When transplanted into diabetic SCID mice, EGFP/Pdx-1 LEPCs ameliorated hyperglycemia by secreting insulin in a glucose regulated manner. Considering the limited availability of beta cells, we propose that our experiments will provide a framework for utilizing the immortal liver progenitor cells as a renewable cell source for the generation of functional pancreatic beta cells.

Pancreatic and duodenal homeobox gene 1 induces hepatic dedifferentiation by suppressing the expression of CCAAT/enhancer-binding protein beta

It is believed that adult tissues in mammals lack the plasticity needed to assume new developmental fates because of the absence of efficient pathways of dedifferentiation. However, the well-documented ability of the transcription factor pancreatic and duodenal homeobox gene 1 (PDX-1) to activate pancreatic lineage development and insulin production following ectopic expression in liver suggests a surprising degree of residual plasticity in adult liver cells. This study seeks a mechanistic explanation for the capacity of PDX-1 to endow liver cells with pancreatic characteristics and function. We demonstrate that PDX-1, previously shown to play an essential role in normal pancreatic organogenesis and pancreatic beta-cell function and to possess the potential to activate multiple pancreatic markers in liver, can also direct hepatic dedifferentiation. PDX-1 represses the adult hepatic repertoire of gene expression and activates the expression of the immature hepatic marker alpha-fetoprotein. We present evidence indicating that PDX-1 triggers hepatic dedifferentiation by repressing the key hepatic transcription factor CCAAT/enhancer-binding protein beta. Hepatic dedifferentiation is necessary though not sufficient for the activation of the mature pancreatic repertoire in liver.

CONCLUSION

Our study suggests a dual role for PDX-1 in liver: inducing hepatic dedifferentiation and activating the pancreatic lineage. The identification of dedifferentiation signals may promote the capacity to endow mature tissues in mammals with the plasticity needed for acquiring novel developmental fates and functions to be implemented in the field of regenerative medicine.

The transdifferentiation of bone-marrow-derived cells in colonic mucosal regeneration after dextran-sulfate-sodium-induced colitis in mice

Bone-marrow-derived cells (BMDCs) transdifferentiate into various types of gastrointestinal cells. The precise transdifferentiation of BMDCs in gut regeneration, however, is controversial. In this study, we examined the transdifferentiation of BMDCs in the regeneration of damaged colonic epithelia. Lethally irradiated wild-type female mice (C57BL/6) were rescued by bone marrow transplantation from male green fluorescent protein transgenic mouse donors. Chronic colitis was induced by administering 3% dextran sulfate sodium (DSS) in the drinking water for 5 days on day 28 after the bone marrow transplantation. The mice were killed on day 25 after DSS administration. BMDC phenotypes were examined by confocal microscopy and fluorescence immunohistochemistry. BMDCs were frequently observed in the vimentin-positive colonic interstitial cells, which also expressed alpha-smooth muscle actin and had a spindle-like morphology, but did not express leukocyte common antigen. Green-fluorescent-protein-positive cells were rarely or less frequently found in Ki-67-positive proliferating cells, cytokeratin-positive epithelial cells, or CD31-positive endothelial cells. BMDCs frequently transdifferentiated into subepithelial myofibroblasts and fibroblasts, and often continued to reside in the colonic subepithelia after the experimental colitis had healed. In conclusion, our data indicate the fate of BMDCs, which might be involved in the healing process of the colon after DSS-induced colitis. Our data show that BMDCs contribute to colonic interstitial cells after the colitis has healed. Understanding the fate of BMDCs may be important for stem cell therapy by BMDCs.

All-trans retinoic acid suppresses exocrine differentiation and branching morphogenesis in the embryonic pancreas

Recent evidence has shown that retinoic acid (RA) signalling is required for early pancreatic development in zebrafish and frog but its role in later development in mammals is less clear cut. In the present study, we determined the effects of RA on the differentiation of the mouse embryonic pancreas. Addition of all-trans retinoic acid (atRA) to embryonic pancreatic cultures induced a number of changes. Branching morphogenesis and exocrine differentiation were suppressed and there was premature formation of endocrine cell clusters (although the total area of β cells was not different in control and atRA-treated buds). We investigated the mechanism of these changes and found that the premature formation of β cells was associated with the early expression of high-level Pdx1 in the endocrine cell clusters. In contrast, the suppressive effect of RA on exocrine differentiation may be due to a combination of two mechanisms (i) up-regulation of the extracellular matrix component laminin and (ii) enhancement of apoptosis. We also demonstrate that addition of fibroblast growth factor (FGF)-10 is able to partially prevent apoptosis and rescue exocrine differentiation and branching morphogenesis in atRA-treated cultures but not in mice lacking the FGF receptor 2-IIIb, suggesting the effects of FGF-10 are mediated through this receptor.

Cellular pathways to beta-cell replacement

In the twenty-first century, diabetic patients are likely to be one of the major beneficiaries from the advancement of regenerative medicine through cellular therapies. Though the existence of a specific self-renewing stem cell within the pancreas is still far from clear, a surprising variety of cells within the pancreas can differentiate towards a beta-cell phenotype: ductular cells, periductular mesenchymal cells and beta-cells themselves can all give rise to new beta-cells. Extra-pancreatic adult somatic stem cells, in particular, those originating from bone marrow may also be capable of differentiating to beta-cells, though equally well the beneficial effects of bone marrow cells may reside in their contribution to the damaged islet vasculature. Forced expression of the beta-cell-specific transcription factor Pdx1 in hepatocytes also holds promise as a therapeutic strategy to increase insulin levels in diabetic individuals. Embryonic stem (ES) cells are clearly another possible source for generating beta-cells, but ES cells are beyond the scope of this review, which focuses on adult stem and progenitor cells capable of producing beta-cells. Despite considerable endeavour, we still have much to learn in the field of pancreatic regeneration prior to any clinically applicable therapy based upon adult stem cells.

Pancreatitis associated with hyperlipoproteinaemia type I in mink (Mustela vison): earliest detectable changes occur in mitochondria of exocrine cells

Pancreatic tissue from young mink homozygous for a mutation in the lipoprotein lipase gene was studied by light and electron microscopy, with the aim of describing the earliest detectable changes in a process which rapidly progresses into overt pancreatitis. The mutation leads to hyperlipoproteinaemia, corresponding to hyperlipoproteinaemia type I in man. Assessment of relevant hepatic and pancreatic enzymes were included in the investigation. The earliest detectable changes consisted of widespread swelling and vacuolation of exocrine cells, arising mainly from swollen mitochondria. To a lesser extent, vesiculation of endoplasmic reticulum occurred. Mitochondria exhibited various changes, including cavitation and dilution of the matrix, with shortened and disorganized cristae displaced towards the periphery. Lamellar figures that developed within mitochondria were numerous. Acinar lumina were somewhat dilated, while plasma membranes were relatively well preserved and secretory granules seemed unchanged. Exfoliative processes progressively occurred, resulting in total necrosis of groups of parenchymal cells, while intercalated ducts were spared. The necrosis was rapidly followed by inflammatory reactions. The activity of the mitochondrial enzyme carnitine O-palmitoyltransferase, essential for the transport of fatty acids into the mitochondria, was lower in the pancreas than in the liver. The activity of the peroxisomal fatty acid beta-oxidation was high in the liver and low in the pancreas of both lipoprotein lipase-deficient and control mink. It is concluded that pancreatic lesions associated with hyperlipoproteinaemia start in exocrine cells, and are most probably the result of a metabolic disturbance, possibly a toxic effect of an excess of free fatty acids.

Cellular reprogramming

The concept of reprogramming a cell is very intriguing and has immense therapeutic potential. Examples from physiology and developmental biology suggest that it may well be possible. Experimental approaches are beginning to suggest this also, in particular the initially astonishing accomplishment of somatic cell nuclear transfer and cloning. This chapter reviews current strategies and describes emerging methods for the proposition of reprogramming cells with cell extracts.

Pancreatic acinar cell: its role in acute pancreatitis

The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes. Under normal physiological conditions, digestive enzymes are activated only once they have reached the duodenum. Premature activation of these enzymes within pancreatic acinar cells leads to the onset of acute pancreatitis; it is the major clinical disorder associated with pancreatic acinar cells. Although there have been major advances in our understanding of the pathogenesis of this disease in recent years, available treatment options are still limited to traditional nonspecific and palliative interventions. Novel therapeutic strategies have been suggested based on ongoing research in the physiology and pathophysiology of the disease; these include the administration of systemic antibiotics, antioxidants, cytokine antagonists, and more recently, inhibition of the renin-angiotensin system. Notwithstanding this promising development, most of these potential therapies are still in an experimental stage or clinical trial. Further investigation is needed to prove the efficacy of these novel treatment modalities.

Liver stem cell-derived beta-cell surrogates for treatment of type 1 diabetes

Consistent with the common embryonic origin of liver and pancreas as well the similar glucose-sensing systems in hepatocytes and pancreatic beta-cells, it should not be surprising that liver stem cells/hepatocytes can transdifferentiate into insulin-producing cells under high-glucose culture conditions or by genetic reprogramming. Persistent expression of the pancreatic duodenal homeobox-1 (Pdx1) transcription factor or its super-active form Pdx1-VP16 fusion protein in hepatic cells reprograms these cells into pancreatic beta-cell precursors. In vitro culture at elevated glucose concentrations or in vivo exposure to a hyperglycemia are required for further differentiation and maturation of liver-derived pancreatic beta-cell precursor into functional insulin-producing pancreatic beta-like cells. Under appropriate conditions, multiple pancreatic transcription factors can work in concert to reprogram liver stem/adult liver cells into functional insulin-producing cells. If such autologous liver-derived insulin-producing cells can be made to escape the type 1 diabetes-associated autoimmunity, they may serve as a valuable cell source for future cell replacement therapy without the need for life-long immunosuppression.