Bottom-up signaling from HGF-containing surfaces promotes hepatic differentiation of mesenchymal stem cells

In Vitro Generated Equine Hepatic-Like Progenitor Cells as a Novel Potent Cell Pool for Equine Metabolic Syndrome (EMS) Treatment

Equine metabolic syndrome (EMS) is recognized as one of the leading cause of health threatening in veterinary medicine worldwide. Recently, PTP1B inhibition has been proposed as an interesting strategy for liver insulin resistance reversion in both equines and humans, however as being a multifactorial disease, proper management of EMS horses further necessities additional interventional approaches aiming at repairing and restoring liver functions. In this study, we hypothesized that in vitro induction of Eq_ASCs hepatogenic differentiation will generate a specialized liver progenitor-like cell population exhibiting similar phenotypic characteristics and regenerative potential as native hepatic progenitor cells. Our obtained data demonstrated that Eq_ASCs-derived liver progenitor cells (Eq_HPCs) displayed typical flattened polygonal morphology with packed fragmented mitochondrial net, lowered mesenchymal CD105 and CD90 surface markers expression, and significant high expression levels of specific hepatic lineage genes including PECAM-1, ALB, AFP and HNF4A. therewith, generated Eq_HPCs exhibited potentiated stemness and pluripotency markers expression (NANOG, SOX-2 and OCT-4). Hence, in vitro generation of hepatic progenitor-like cells retaining high differentiation capacity represents a promising new approach for the establishment of cell-based targeted therapies for the restoration of proper liver functions in EMS affected horses.

Immobilization of modular peptides on graphene cocktail for differentiation of human mesenchymal stem cells to hepatic-like cells

In this study, two novel biomimetic modular peptide motifs based on the alpha-2 subunit of type IV collagen (CO4A2) were designed and immobilized on a graphene platform to imitate integrin and heparan sulfate- (HS-) binding proteins. The in silico study was used to design 9-mer K[KGDRGD]AG and 10-mer KK[SGDRGD]AG for testing designed Integrin-Binding Peptide (dIBP) and HS-Binding Peptide (dHBP). The virtual docking technique was used to optimize the peptide motifs and their relevant receptors. Molecular dynamic (MD) simulation was used to evaluate the stability of peptide-receptor complexes. The effect of the platform on the differentiation of human mesenchymal stem cells (hMSCs) to hepatic-like cells (HLCs) was evaluated. After differentiation, some hepatic cells’ molecular markers such as albumin, AFP, CK-18, and CK-19 were successfully followed. Graphene-heparan sulfate binding peptide (G-HSBP) enhances the mature hepatic markers’ expression instead of control (p ≤ 0.05). The pathological study showed that the designed platform is safe, and no adverse effects were seen till 21 days after implantation.

ATSC transplantation contributes to liver regeneration following paracetamol-induced acute liver injury through differentiation into hepatic-like cells

INTRODUCTION

Drug-induced liver injury (DILI) is a leading cause of acute liver injury (ALI). Acetaminophen (also termed paracetamol), can often be found in drugs that may be abused (i.e., prescription for pain relief). Animal experiments have shown that mesenchymal stem cell transplantation can ameliorate or even reverse hepatic injury.

MATERIAL AND METHODS

ALI was induced in Wistar rats using paracetamol. ATSCs were transplanted via the intravenous, portal vein, or intrahepatic route directly onto the liver parenchyma. Histological evaluation was conducted to assess drug-induced injury following transplantation. Fluorescence in situ hybridization (FISH) was used to verify the location of stem cells on the liver parenchyma. The effect of those cells on liver regeneration was tested by immunohistochemistry for hepatic growth factor (HGF). In addition, reverse transcription-quantitative PCR (qRT-PCR) was used to assess hepatic growth factor (HGF), hepatic nuclear factor 4α (HNF4α), cytochrome P450 1A2 (CYP1A2) and α-fetoprotein (AFP) mRNA expression.

RESULTS

Immunohistochemical staining for HGF was stronger in the transplanted groups than that in the control group (P<0.001). HNF4α and HGF mRNA levels were increased on day 7 following transplantation (P<0.001 and P=0.009, respectively). CYP1A2 mRNA levels were also increased (P=0.013) in the intravenous groups, while AFP levels were higher in the intrahepatic groups (P=0.006). ATSC transplantation attenuates ALI injury and promotes liver regeneration. Furthermore, expression of specific hepatic enzymes points to ATSC hepatic differentiation.

CONCLUSION

The study showed the positive effects of transplanted adipose tissue stem cells (ATSCs) on liver regeneration (LG) through hepatotrophic factors. Furthermore, increased expression of hepatic specific proteins was recorded in ATSC transplanted groups that indicate stem cells differentiation into hepatic cells.

Amniotic mesenchymal stem cells derived hepatocyte-like cells attenuated liver fibrosis more efficiently by mixed-cell transplantation

BACKGROUND

Cell transplantation is a promising treatment for the patients with end-stage liver diseases. Stem cells derived hepatocyte-like cells (HLCs) attenuated liver injury upon transplantation in animal models for liver fibrosis. However, only a small portion of the transplanted cells propagated in the recipient liver.

AIM

We hypothesized that the efficiency of cell therapy could be improved by transplanting amniotic mesenchymal stem cells (AMSCs) derived HLCs along with human umbilical vein endothelial cells (HUVECs) and undifferentiated AMSCs.

METHODS

Briefly, we used a two-step protocol to generate induced HLCs. We confirmed organoids formation of HLCs in 3D collagen scaffolds with HUVECs and AMSCs. To determine whether the HLCs can migrate into the liver tissue and perform in vivo function, we transplanted the cells to mice with liver fibrosis.

RESULTS

Co-culture of HLCs with HUVECs and AMSCs demonstrated improved function of HLCs within the organoids. Furthermore, transplantation using non-homogeneous cells, i.e. HLCs mixed with HUVECs and AMSCs, exhibited better graft survival in the host animals with liver fibrosis. Our experiment results suggested that compared to mock transplantation or HLCs transplantation groups, liver fibrosis was reduced significantly in mixed-cell groups. The AST levels in the plasma of transplanted mice were markedly decreased only in the mixed-cell transplantation group. The engraftment of HLCs in mice liver was better in mixed-cell transplantation group, compared with HLCs-only transplantation group.

CONCLUSIONS

The HLCs attenuated liver fibrosis more efficiently when transplanted along with HUVECs and AMSCs, and this suggested that we could improve the efficiency of cell therapy by transplanting functional cells partially along with stromal cells.

Current understanding of adipose-derived mesenchymal stem cell-based therapies in liver diseases

The liver, the largest organ with multiple synthetic and secretory functions in mammals, consists of hepatocytes, cholangiocytes, hepatic stellate cells (HSCs), sinusoidal endothelial cells, Kupffer cells (KCs), and immune cells, among others. Various causative factors, including viral infection, toxins, autoimmune defects, and genetic disorders, can impair liver function and result in chronic liver disease or acute liver failure. Mesenchymal stem cells (MSCs) from various tissues have emerged as a potential candidate for cell transplantation to promote liver regeneration. Adipose-derived MSCs (ADMSCs) with high multi-lineage potential and self-renewal capacity have attracted great attention as a promising means of liver regeneration. The abundance source and minimally invasive procedure required to obtain ADMSCs makes them superior to bone marrow-derived MSCs (BMMSCs). In this review, we comprehensively analyze landmark studies that address the isolation, proliferation, and hepatogenic differentiation of ADMSCs and summarize the therapeutic effects of ADMSCs in animal models of liver diseases. We also discuss key points related to improving the hepatic differentiation of ADMSCs via exposure of the cells to cytokines and growth factors (GFs), extracellular matrix (ECM), and various physical parameters in in vitro culture. The optimization of culturing methods and of the transplantation route will contribute to the further application of ADMSCs in liver regeneration and help improve the survival rate of patients with liver diseases. To this end, ADMSCs provide a potential strategy in the field of liver regeneration for treating acute or chronic liver injury, thus ensuring the availability of ADMSCs for research, trial, and clinical applications in various liver diseases in the future.

Construction of 3D Cellular Composites with Stem Cells Derived from Adipose Tissue and Endothelial Cells by Use of Optical Tweezers in a Natural Polymer Solution

To better understand the regulation and function of cellular interactions, three-dimensional (3D) assemblies of single cells and subsequent functional analysis are gaining popularity in many research fields. While we have developed strategies to build stable cellular structures using optical tweezers in a minimally invasive state, methods for manipulating a wide range of cell types have yet to be established. To mimic organ-like structures, the construction of 3D cellular assemblies with variety of cell types is essential. Our recent studies have shown that the presence of nonspecific soluble polymers in aqueous solution is the key to creating stable 3D cellular assemblies efficiently. The present study further expands on the construction of 3D single cell assemblies using two different cell types. We have successfully generated 3D cellular assemblies, using GFP-labeled adipose tissue-derived stem cells and endothelial cells by using optical tweezers. Our findings will support the development of future applications to further characterize cellular interactions in tissue regeneration.

Human umbilical cord mesenchymal stem cells alleviate cyclophosphamide-induced liver injury in rats

AIM

To assess the effect of human umbilical cord mesenchymal stem cells (UC-MSCs) on cyclophosphamide (CTX)-induced liver injury.

METHODS

UC-MSCs were isolated from the human umbilical cord. Male SD rats were randomly divided into three groups: control group, CTX group, and CTX + UC-MSC group. The CTX group and CTX + UC-MSC group were intraperitoneally injected with CTX. After that, the control group and CTX group were injected with water via the tail vein, and the CTX + UC-MSC group was injected with MSCs via the tail vein. Six rats of each group were selected randomly and sacrificed at different time points. Blood samples were taken to measure serum alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and total bilirubin (TBIL). Liver tissues were collected for biochemical assays of malondialdehyde (MDA), lipid peroxide (LPO), NO, glutathione (GSH), glutathione peroxidase (GSH-PX), and total superoxide dismutase (T-SOD). qPCR was used to test the expression of Bcl-2, Bax, and vascular endothelial growth factor (VEGF) A. Histological examination (HE straining) and immunohistochemical staining for α-smooth muscle actin (α-SMA) and Ki-67 were also performed.

RESULTS

Compared with the control group, the levels of ALT, AST, ALP, and TBIL were significantly higher, the SOD, GSH, and GSH-PX contents were significantly lower, MDA, LPO, and NO were significantly higher, cell apoptosis significantly increased, and the expression of VEGFA significantly decreased in the CTX group. Compared with the CTX group, the ALT, AST, ALP, and TBIL were significantly lower, the SOD, GSH, and GSH-PX contents were significantly higher, and MDA, LPO, and NO were significantly lower in the CTX + UC-MSC group (P < 0.05). The expression of Bax was lower and Bcl-2 and VEGFA expression was higher in the CTX + UC-MSC group than in the CTX group (P < 0.05). Pathological analysis showed that liver status was better in the CTX + UC-MSC group than in the CTX group. The α-SMA⁺ cells in the CTX + UC-MSC group were less than and Ki-67⁺ cells were more than those in the CTX group (P < 0.05).

CONCLUSION

UC-MSCs injected via the tail vein could alleviate CTX-induced hepatotoxicity in rats.

A decade of progress in liver regenerative medicine

Liver diseases can be caused by viral infection, metabolic disorder, alcohol consumption, carcinoma or injury, chronically progressing to end-stage liver disease or rapidly resulting in acute liver failure. In either situation, liver transplantation is most often sought for life saving, which is, however, significantly limited by severe shortage of organ donors. Until now, tremendous multi-disciplinary efforts have been dedicated to liver regenerative medicine, aiming at providing transplantable cells, microtissues, or bioengineered whole liver via tissue engineering, or maintaining partial liver functions via extracorporeal support. In both directions, new compatible biomaterials, stem cell sources, and bioengineering approaches have fast-forwarded liver regenerative medicine towards potential clinical applications. Another important progress in this field is the development of liver-on-a-chip technologies, which enable tissue engineering, disease modeling, and drug testing under biomimetic extracellular conditions. In this review, we aim to highlight the last decade's progress in liver regenerative medicine from liver tissue engineering, bioartificial liver devices (BAL), to liver-on-a-chip platforms, and then to present challenges ahead for further advancement.

Living Cell Microarrays: An Overview of Concepts

Living cell microarrays are a highly efficient cellular screening system. Due to the low number of cells required per spot, cell microarrays enable the use of primary and stem cells and provide resolution close to the single-cell level. Apart from a variety of conventional static designs, microfluidic microarray systems have also been established. An alternative format is a microarray consisting of three-dimensional cell constructs ranging from cell spheroids to cells encapsulated in hydrogel. These systems provide an in vivo-like microenvironment and are preferably used for the investigation of cellular physiology, cytotoxicity, and drug screening. Thus, many different high-tech microarray platforms are currently available. Disadvantages of many systems include their high cost, the requirement of specialized equipment for their manufacture, and the poor comparability of results between different platforms. In this article, we provide an overview of static, microfluidic, and 3D cell microarrays. In addition, we describe a simple method for the printing of living cell microarrays on modified microscope glass slides using standard DNA microarray equipment available in most laboratories. Applications in research and diagnostics are discussed, e.g., the selective and sensitive detection of biomarkers. Finally, we highlight current limitations and the future prospects of living cell microarrays.

Liver-derived human mesenchymal stem cells: a novel therapeutic source for liver diseases

Mesenchymal stem cells (MSCs) represent an attractive cell type for research and therapy due to their ability to proliferate, differentiate, modulate immune reactions, and secrete trophic factors. MSCs exist in a multitude of tissues, including bone marrow, umbilical cord, and adipose tissues. Moreover, MSCs have recently been isolated from the liver. Compared with other MSC types, liver-derived human MSCs (LHMSCs) possess general morphologies, immune functions, and differentiation capacities. Interestingly, LHMCSs produce higher levels of pro-angiogenic, anti-inflammatory, and anti-apoptotic cytokines than those of bone marrow-derived MSCs. Thus, these cells may be a promising therapeutic source for liver diseases. This paper summarizes the biological characteristics of LHMSCs and their potential benefits and risks for the treatment of liver diseases.

Effects of mesenchymal stem cells and VEGF on liver regeneration following major resection

PURPOSE

The study aims to determine the effects of mesenchymal stem cell (MSC) therapy and a combination therapy of MSCs transfected with vascular endothelial growth factor (VEGF) for liver regeneration after major resection.

METHODS

Thirty-eight rats were divided into four groups: group 1: control (sham operation); group 2: control (70 % hepatic resection); group 3: 70 % hepatic resection + systemically transplanted MSCs; and group 4: 70 % hepatic resection + systemically transplanted MSCs transfected with the VEGF gene. MSCs were injected via the portal vein route in study groups 3 and 4. Expression levels of VEGF, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), transforming growth factor (TGF), hepatocyte growth factor (HGF), and augmenter of liver regeneration (ALR) were analyzed in the remnant liver tissue. We investigated the levels of angiogenic factors, VEGF-receptor, angiopoietin-1 (Angpt1) and Angpt2. Biochemical parameters of liver function in blood samples were measured and a histologic assessment of the livers was performed. The postoperative liver weight and volume of each rat were measured 14 days after surgery.

RESULTS

The expression levels of all measured growth factors were significantly increased in groups 3 and 4 compared to the control groups. The levels of Angpt1 and Angpt2 correlated with levels of VEGF and thus were also significantly higher in the study groups. There were significant differences between the estimated liver weights and volumes of group 4 and the resected controls in group 2. With the exception of portal inflammation, levels of all histological parameters were observed to be higher in MSC-treated groups when compared with the resected controls in group 2.

CONCLUSIONS

Transplanted stem cells and MSCs transfected with VEGF significantly accelerated many parameters of the healing process following major hepatic resection. After the injection of MSCs and VEGF-transfected MSCs into the portal vein following liver resection, they were engrafted in the liver. They increased bile duct and liver hepatocyte proliferation, and secreted many growth factors including HGF, TGFβ, VEGF, PDGF, EGF, and FGF via paracrine effects. These effects support liver function, regeneration, and liver volume/weight.

Microfluidic fabrication of bioactive microgels for rapid formation and enhanced differentiation of stem cell spheroids

A major challenge in tissue engineering is to develop robust protocols for differentiating ES and iPS cells to functional adult tissues at a clinically relevant scale. The goal of this study is to develop a high throughput platform for generating bioactive, stem cell-laden microgels to direct differentiation in a well-defined microenvironment. We describe a droplet microfluidics system for fabricating microgels composed of polyethylene glycol and heparin, with tunable geometric, mechanical, and chemical properties, at kHz rates. Heparin-containing hydrogel particles sequestered growth factors Nodal and FGF-2, which are implicated in specifying pluripotent cells to definitive endoderm. Mouse ESCs were encapsulated into heparin microgels with a single dose of Nodal and FGF-2, and expressed high levels of endoderm markers Sox17 and FoxA2 after 5 days. These results highlight the use of microencapsulation for tailoring the stem cell microenvironment to promote directed differentiation, and may provide a straightforward path to large scale bioprocessing in the future.

STATEMENT OF SIGNIFICANCE

Multicellular spheroids and microtissues are valuable for tissue engineering, but fabrication approaches typically sacrifice either precision or throughput. Microfluidic encapsulation in polymeric biomaterials is a promising technique for rapidly generating cell aggregates with excellent control of microenvironmental parameters. Here we describe the microfluidic fabrication of bioactive, heparin-based microgels, and demonstrate the adsorption of heparin-binding growth factors for enhancing directed differentiation of embryonic stem cells toward endoderm. This approach also facilitated a ∼90-fold decrease in consumption of exogenous growth factors compared to conventional differentiation protocols.

Synergistic influence of collagen I and BMP 2 drives osteogenic differentiation of mesenchymal stem cells: A cell microarray analysis

Cell microarrays are a novel platform for the high throughput discovery of new biomaterials. By re-creating a multitude of cell microenvironments on a single slide, this approach can identify the optimal surface composition to drive a desired cell response. To systematically study the effects of molecular microenvironments on stem cell fate, we designed a cell microarray based on parallel exposure of mesenchymal stem cells (MSCs) to surface-immobilised collagen I (Coll I) and bone morphogenetic protein 2 (BMP 2). This was achieved by means of a reactive coating on a slide surface, enabling the covalent anchoring of Coll I and BMP 2 as microscale spots printed by a robotic contact printer. The surface between the printed protein spots was passivated using poly (ethylene glycol) bisamine 10,000Da (A-PEG). MSCs were then captured and cultured on array spots composed of binary mixtures of Coll I and BMP 2, followed by automated image acquisition and quantitative, multi-parameter analysis of cellular responses. Surface compositions that gave the highest osteogenic differentiation were determined using Runx2 expression and calcium deposition. Quantitative single cell analysis revealed subtle concentration-dependent effects of surface-immobilised proteins on the extent of osteogenic differentiation obscured using conventional analysis. In particular, the synergistic interaction of Coll I and BMP 2 in supporting osteogenic differentiation was confirmed. Our studies demonstrate the value of cell microarray platforms to decipher the combinatorial interactions at play in stem cell niche microenvironments.

Role of Stem Cells Transplantation in Tissue Regeneration After Acute or Chronic Acetaminophen Induced Liver Injury

PURPOSE

Acetaminophen-induced liver injury (APAP) is recognized as a frequent etiologic factor responsible for hepatic damage in the developed world. Management remains still elusive as treatment options are limited and their results are inconclusive. Consequently new strategies are explored at the experimental level. Mesenchymal stem cells (MSCs) present a promising modality as they can promote liver regeneration (LG) and compensate acute liver injury (ALI).

MATERIALS AND METHODS

Our research was focused on articles related to drug-induced liver injury, mechanisms of liver regeneration (LG) after Acute Liver Injury (ALI) and recent experimental protocols of Mesenchymal Stem Cells (MSCs) transplantation after chemical insult. All these studies are cited on Pubmed and MedLine.

RESULTS

This review has three distinct sections. First recent developments in ALI pathogenesis are presented. The second section covers cellular pathways and histological findings relevant to liver regeneration. The final chapter analyzes MSCs transplantation protocols after ALI and interrelation between liver regeneration and hepatic differentiation of MSCs.

CONCLUSION

Adipose tissue stem cells (ADSCs) and (MSCs) transplantation represents a promising modality in severe ALI management although many aspects remain to be clarified.

In Vitro and In Vivo Hepatic Differentiation of Adult Somatic Stem Cells and Extraembryonic Stem Cells for Treating End Stage Liver Diseases

The shortage of liver donors is a major handicap that prevents most patients from receiving liver transplantation and places them on a waiting list for donated liver tissue. Then, primary hepatocyte transplantation and bioartificial livers have emerged as two alternative treatments for these often fatal diseases. However, another problem has emerged. Functional hepatocytes for liver regeneration are in short supply, and they will dedifferentiate immediately in vitro after they are isolated from liver tissue. Alternative stem-cell-based therapeutic strategies, including hepatic stem cells (HSCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs), are more promising, and more attention has been devoted to these approaches because of the high potency and proliferation ability of the cells. This review will focus on the general characteristics and the progress in hepatic differentiation of adult somatic stem cells and extraembryonic stem cells in vitro and in vivo for the treatment of end stage liver diseases. The hepatic differentiation of stem cells would offer an ideal and promising source for cell therapy and tissue engineering for treating liver diseases.

Three-dimensional, soft neotissue arrays as high throughput platforms for the interrogation of engineered tissue environments

Local signals from tissue-specific extracellular matrix (ECM) microenvironments, including matrix adhesive ligand, mechanical elasticity and micro-scale geometry, are known to instruct a variety of stem cell differentiation processes. Likewise, these signals converge to provide multifaceted, mechanochemical cues for highly-specific tissue morphogenesis or regeneration. Despite accumulated knowledge about the individual and combined roles of various mechanochemical ECM signals in stem cell activities on 2-dimensional matrices, the understandings of morphogenetic or regenerative 3-dimenstional tissue microenvironments remain very limited. To that end, we established high-throughput platforms based on soft, fibrous matrices with various combinatorial ECM proteins meanwhile highly-tunable in elasticity and 3-dimensional geometry. To demonstrate the utility of our platform, we evaluated 64 unique combinations of 6 ECM proteins (collagen I, collagen III, collagen IV, laminin, fibronectin, and elastin) on the adhesion, spreading and fate commitment of mesenchymal stem cell (MSCs) under two substrate stiffness (4.6 kPa, 20 kPa). Using this technique, we identified several neotissue microenvironments supporting MSC adhesion, spreading and differentiation toward early vascular lineages. Manipulation of the matrix properties, such as elasticity and geometry, in concert with ECM proteins will permit the investigation of multiple and distinct MSC environments. This paper demonstrates the practical application of high through-put technology to facilitate the screening of a variety of engineered microenvironments with the aim to instruct stem cell differentiation.

In vitro culture of isolated primary hepatocytes and stem cell-derived hepatocyte-like cells for liver regeneration

Various liver diseases result in terminal hepatic failure, and liver transplantation, cell transplantation and artificial liver support systems are emerging as effective therapies for severe hepatic disease. However, all of these treatments are limited by organ or cell resources, so developing a sufficient number of functional hepatocytes for liver regeneration is a priority. Liver regeneration is a complex process regulated by growth factors (GFs), cytokines, transcription factors (TFs), hormones, oxidative stress products, metabolic networks, and microRNA. It is well-known that the function of isolated primary hepatocytes is hard to maintain; when cultured in vitro, these cells readily undergo dedifferentiation, causing them to lose hepatocyte function. For this reason, most studies focus on inducing stem cells, such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), hepatic progenitor cells (HPCs), and mesenchymal stem cells (MSCs), to differentiate into hepatocyte-like cells (HLCs) in vitro. In this review, we mainly focus on the nature of the liver regeneration process and discuss how to maintain and enhance in vitro hepatic function of isolated primary hepatocytes or stem cell-derived HLCs for liver regeneration. In this way, hepatocytes or HLCs may be applied for clinical use for the treatment of terminal liver diseases and may prolong the survival time of patients in the near future.

Signalling pathways involved in the process of mesenchymal stem cells differentiating into hepatocytes

End‐stage liver disease can be the termination of acute or chronic liver diseases, with manifestations of liver failure; transplantation is currently an effective treatment for these. However, transplantation is severely limited due to the serious lack of donors, expense, graft rejection and requirement of long‐term immunosuppression. Mesenchymal stem cells (MSCs) have attracted considerable attention as therapeutic tools as they can be obtained with relative ease and expanded in culture, along with features of self‐renewal and multidirectional differentiation. Many scientific groups have sought to use MSCs differentiating into functional hepatocytes to be used in cell transplantation with liver tissue engineering to repair diseased organs. In most of the literature, hepatocyte differentiation refers to use of various additional growth factors and cytokines, such as hepatocyte growth factor (HGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), oncostatin M (OSM) and more, and most are involved in signalling pathway regulation and cell–cell/cell–matrix interactions. Signalling pathways have been shown to play critical roles in embryonic development, tumourigenesis, tumour progression, apoptosis and cell‐fate determination. However, mechanisms of MSCs differentiating into hepatocytes, particularly signalling pathways involved, have not as yet been completely illustrated. In this review, we have focused on progress of signalling pathways associated with mesenchymal stem cells differentiating into hepatocytes along with the stepwise differentiation procedure.

Local control of hepatic phenotype with growth factor-encoded surfaces

The goal of the present study was to modulate the phenotype expression of hepatocytes in vitro on surfaces imprinted with growth factors (GFs). Hepatocyte growth factor (HGF) or transforming-growth factor-β1 (TGF-β1) were mixed with collagen (I) and robotically printed onto standard glass slides to create arrays of 300 μm or 500 μm diameter spots. Primary rat hepatocytes were seeded on top of the arrays, forming clusters corresponding in size to the underlying protein spots. The TGF-β1 spots appeared to downregulate markers of hepatic (epithelial) phenotype while upregulating expression of mesenchymal markers. Conversely, hepatocytes cultured on HGF spots maintained high level of epithelial markers. When hepatocytes were seeded onto alternating spots of HGF and TGF-β1, their phenotype was found to depend on center-to-center distance between the spots. At shorter distances cross-expression of epithelial and mesenchymal markers was observed while at distances exceeding 1.25 mm divergence of phenotypes, epithelial on HGF and mesenchymal on TGF-β was seen. Overall, our results demonstrate that GF-encoded surfaces can modulate phenotype within groups of cells cultured on the same surface. Given the importance of phenotype switching in development, fibrosis and cancer, this platform may be used to gain useful insights into the mechanisms of processes such as epithelial-to-mesenchymal transition or stem cell fate selections.

Generation of insulin-producing cells from rat mesenchymal stem cells using an aminopyrrole derivative XW4.4

Type 1 diabetes mellitus (T1DM), a multisystem disease with both biochemical and anatomical/structural consequences, is a major health concern worldwide. Pancreatic islet transplantation provides a promising treatment for T1DM. However, the limited availability of islet tissue or new sources of insulin producing cells (IPCs) that are responsive to glucose hinder this promising approach. Though slow, the development of pancreatic beta-cell lines from rodent or human origin has been steadily progressing. Bone marrow-derived mesenchymal stem cells (MSCs) are multipotent, culture-expanded, non-hematopoietic cells that are currently being investigated as a novel cellular therapy. The in vitro differentiation potential of IPCs has raised hopes for a treatment of clinical diseases associated with autoimmunity. We screened for small molecules that induce pancreatic differentiation of IPCs. There are some compounds which showed positive effects on the DTZ staining. The aminopyrrole derivative compound XW4.4 which shows the best activity among them was found to induce pancreatic differentiation of rat MSCs (rMSCs). The in vitro studies indicated that treatment of rMSCs with compound XW4.4 resulted in differentiated cells with characteristics of IPCs including islet-like clusters, spherical, grape-like morphology, insulin secretion, positive for dithizone, glucose stimulation and expression of pancreatic endocrine cell marker genes. The data has also suggested that hepatocyte nuclear factor 3β (HNF 3β) may be involved in pancreatic differentiation of rMSCs when treated with XW4.4. Results indicate that XW4.4 induced rMSCs support the efforts to derive functional IPCs and serve as a means to alleviate limitations surrounding islet cell transplantation in the treatment of T1DM.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Arrayed cellular environments for stem cells and regenerative medicine

The behavior and composition of both multipotent and pluripotent stem cell populations are exquisitely controlled by a complex, spatiotemporally variable interplay of physico-chemical, extracellular matrix, cell-cell interaction, and soluble factor cues that collectively define the stem cell niche. The push for stem cell-based regenerative medicine models and therapies has fuelled demands for increasingly accurate cellular environmental control and enhanced experimental throughput, driving an evolution of cell culture platforms away from conventional culture formats toward integrated systems. Arrayed cellular environments typically provide a set of discrete experimental elements with variation of one or several classes of stimuli across elements of the array. These are based on high-content/high-throughput detection, small sample volumes, and multiplexing of environments to increase experimental parameter space, and can be used to address a range of biological processes at the cell population, single-cell, or subcellular level. Arrayed cellular environments have the capability to provide an unprecedented understanding of the molecular and cellular events that underlie expansion and specification of stem cell and therapeutic cell populations, and thus generate successful regenerative medicine outcomes. This review focuses on recent key developments of arrayed cellular environments and their contribution and potential in stem cells and regenerative medicine.