Type I collagen structure regulates cell morphology and EGF signaling in primary rat hepatocytes through cAMP-dependent protein kinase A

The Pathophysiology of Portal Hypertension

This article reviews the pathophysiology of portal hypertension that includes multiple mechanisms internal and external to the liver. This article starts with a review of literature describing the cellular and molecular mechanisms of portal hypertension, microvascular thrombosis, sinusoidal venous congestion, portal angiogenesis, vascular hypocontractility, and hyperdynamic circulation. Mechanotransduction and the gut-liver axis, which are newer areas of research, are reviewed. Dysfunction of this axis contributes to chronic liver injury, inflammation, fibrosis, and portal hypertension. Sequelae of portal hypertension are discussed in subsequent studies.

Extracellular Matrices as Bioactive Materials for In Situ Tissue Regeneration

Bioactive materials based on a nature-derived extracellular matrix (NECM) represent a category of biomedical devices with versatile therapeutic applications in the realms of tissue repair and engineering. With advancements in decellularization technique, the inherent bioactive molecules and the innate nano-structural and mechanical properties are preserved in three-dimensional scaffolds mainly composed of collagens. Techniques such as electrospinning, three-dimensional printing, and the intricate fabrication of hydrogels are developed to mimic the physical structures, biosignalling and mechanical cues of ECM. Until now, there has been no approach that can fully account for the multifaceted properties and diverse applications of NECM. In this review, we introduce the main proteins composing NECMs and explicate the importance of them when used as therapeutic devices in tissue repair. Nano-structural features of NECM and their applications regarding tissue repair are summarized. The origins, degradability, and mechanical property of and immune responses to NECM are also introduced. Furthermore, we review their applications, and clinical features thereof, in the repair of acute and chronic wounds, abdominal hernia, breast deformity, etc. Some typical marketed devices based on NECM, their indications, and clinical relevance are summarized.

Effect of Phytic Acid Addition on the Structure of Collagen-Hyaluronic Acid Composite Gel

Composite collagen gels with hyaluronic acid are developed tissue-engineered structures for filling and regeneration of defects in various organs and tissues. For the first time, phytic acid was used to increase the stability and improve the mechanical properties of collagen gels with hyaluronic acid. Phytic acid is a promising cross-linker for collagen hydrogels and is a plant-derived antioxidant found in rich sources of beans, grains, and oilseeds. Phytic acid has several benefits due to its antioxidant, anticancer, and antitumor properties. In this work, studies were carried out on the kinetics of the self-assembly of collagen molecules in the presence of phytic and hyaluronic acids. It was shown that both of these acids do not lead to collagen self-assembly. Scanning electron microscopy showed that in the presence of phytic and hyaluronic acids, the collagen fibrils had a native structure, and the FTIR method confirmed the chemical cross-links between the collagen fibrils. DSC and rheological studies demonstrated that adding the phytic acid improved the stability and modulus of elasticity of the collagen gel. The presence of hyaluronic acid in the collagen gel slightly reduced the effect of phytic acid. The presence of phytic acid in the collagen gel improved the stability of the scaffold, but, after 1 week of cultivation, slightly reduced the viability of mesenchymal stromal cells cultured in the gel. The collagen type I gel with hyaluronic and phytic acids can be used to replace tissue defects, especially after the removal of cancerous tumors.

A review on regulation of cell cycle by extracellular matrix

The extracellular matrix (ECM) is a network of structural proteins, glycoproteins and proteoglycans that assists independent cells in aggregating and forming highly organized functional structures. ECM serves numerous purposes and is an essential component of tissue structure and functions. Initially, the role of ECM was considered to be confined to passive functions like providing mechanical strength and structural identity to tissues, serving as barriers and platforms for cells. The doors to understanding ECM's proper role in tissue functioning opened with the discovery of cellular receptors, integrins to which ECM components binds and influences cellular activities. Understanding and utilizing ECM's potential to control cellular function has become a topic of much interest in recent decades, providing different outlooks to study processes involved in developmental programs, wound healing and tumour progression. On another front, the regulatory mechanisms operating to prevent errors in the cell cycle have been topics of a titanic amount of studies. This is expected as many diseases, most infamously cancer, are associated with defects in their functioning. This review focuses on how ECM, through different methods, influences the progression of the somatic cell cycle and provides deeper insights into molecular mechanisms of functional communication between adhesion complex, signalling pathways and cell cycle machinery.

Significance of the p38MAPK-CRP2 axis in myofibroblastic phenotypic transition

We have recently demonstrated that a LIM domain protein, cysteine and glycine-rich protein 2 (CSRP2 [CRP2]), plays a vital role in the functional expression of myofibroblasts and cancer-associated fibroblasts. CRP2 binds directly to myocardin-related transcription factors (MRTF [MRTF-A or MRTF-B]) and serum response factor (SRF) to stabilize the MRTF/SRF/CArG-box complex, leading to the expression of smooth muscle cell (SMC) genes such as α-smooth muscle actin (α-SMA) and collagens. These are the marker genes for myofibroblasts. Here, we show that the adhesion of cultured human skin fibroblasts (HSFs) to collagen reduces the myofibroblastic features. HSF adhesion to collagen suppresses the expression of CRP2 and CSRP2-binding protein (CSRP2BP [CRP2BP]) and reduces the expression of SMC genes. Although CRP2BP is known as an epigenetic factor, we find that CRP2BP also acts as an adaptor protein to enhance the function of CRP2 mentioned above. This CRP2BP function does not depend on its histone acetyltransferase activity. We also addressed the molecular mechanism of the reduced myofibroblastic features of HSFs on collagen. HSF adhesion to collagen inhibits the p38MAPK-mediated pathway, and reducing the p38MAPK activity decreases the expression of CRP2 and SMC genes. Thus, the activation of p38MAPK is critical for the myofibroblastic features. We also show evidence that CRP2 plays a role in the myofibroblastic transition of retinal pigment epithelial cells (RPEs). Like HSFs, such phenotypic modulation of RPEs depends on the p38MAPK pathway.Key words: CRP2, p38MAPK, MRTF, myofibroblasts, retinal pigment epithelial cells.

Correlations on the Structure and Properties of Collagen Hydrogels Produced by E-Beam Crosslinking

In this study, a collagen hydrogel using collagen exclusively produced in Romania, was obtained by electron beam (e-beam) crosslinking. The purpose of our study is to obtain new experimental data on the crosslinking of collagen and to predict as faithfully as possible, its behavior at high irradiation doses and energies. To pursue this, the correlations between macromolecular structure and properties of collagen hydrogels were determined by rheological analysis, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Differential Scanning Calorimetry (DSC), respectively. The gel fraction, swelling degree, and network parameters of the collagen hydrogels were also investigated at different irradiation doses. Through experimental exploration, we concluded that irradiation with e-beam up to 25 kGy induces crosslinking processes in collagen structure without producing advanced degradation processes. E-beam technology is a great method to develop new materials for medical applications without adding other chemical reagents harmful to human health. The future aim is to develop new wound dressings for rapid healing based on collagen, through irradiation technologies.

Isolation, culture, and characterisation of bovine ovarian fetal fibroblasts and gonadal ridge epithelial-like cells and comparison to their adult counterparts

During ovarian development, gonadal ridge epithelial-like (GREL) cells arise from the epithelial cells of the ventral surface of the mesonephros. They ultimately develop into follicular granulosa cells or into ovarian surface epithelial cells. Stromal fibroblasts arise from the mesonephros and penetrate the ovary. We developed methods for isolating and culturing fetal ovarian GREL cells and ovarian fibroblasts by expansion of colonies without passage. In culture, these two cell types were morphologically different. We examined the expression profile of 34 genes by qRT-PCR, of which 24 genes had previously been studied in whole fetal ovaries. Expression of nine of the 10 newly-examined genes in fetal ovaries correlated with gestational age (MUC1, PKP2, CCNE1 and CCNE2 negatively; STAR, COL4A1, GJA1, LAMB2 and HSD17B1 positively). Comparison between GREL cells and fetal fibroblasts revealed higher expression of KRT19, PKP2, OCLN, MUC1, ESR1 and LGR5 and lower expression of GJA1, FOXL2, NR2F2, FBN1, COL1A1, NR5A1, CCND2, CCNE1 and ALDH1A1. Expression of CCND2, CCNE1, CCNE2, ESR2 and TGFBR1 was higher in the fetal fibroblasts than in adult fibroblasts; FBN1 was lower. Expression of OCLN, MUC1, LAMB2, NR5A1, ESR1, ESR2, and TGFBR3 was lower in GREL cells than ovarian surface epithelial cells. Expression of KRT19, DSG2, PKP2, OCLN, MUC1, FBN1, COL1A1, COL3A1, STAR and TGFBR2 was higher and GJA1, CTNNB1, LAMB2, NR5A1, CYP11A1, HSD3B1, CYP19A1, HSD17B1, FOXL2, ESR1, ESR2, TGFBR3 and CCND2 was lower in GREL cells compared to granulosa cells. TGFβ1 altered the expression of COL1A1, COL3A1 and FBN1 in fetal fibroblasts and epidermal growth factor altered the expression of FBN1 and COL1A1. In summary, the two major somatic cell types of the developing ovary have distinct gene expression profiles. They, especially GREL cells, also differ from the cells they ultimately differentiate in to. The regulation of cell fate determination, particularly of the bi-potential GREL cells, remains to be elucidated.

Phosphatidic acid-PKA signaling regulates p38 and ERK1/2 functions in ligand-independent EGFR endocytosis

Ligand-independent epidermal growth factor receptor (EGFR) endocytosis is inducible by a variety of stress conditions converging upon p38 kinase. A less known pathway involves phosphatidic acid (PA) signaling toward the activation of type 4 phosphodiesterases (PDE4) that decrease cAMP levels and protein kinase A (PKA) activity. This PA/PDE4/PKA pathway is triggered with propranolol used to inhibit PA hydrolysis and induces clathrin-dependent and clathrin-independent endocytosis, followed by reversible accumulation of EGFR in recycling endosomes. Here we give further evidence of this signaling pathway using biosensors of PA, cAMP, and PKA in live cells and then show that it activates p38 and ERK1/2 downstream the PKA inhibition. Clathrin-silencing and IN/SUR experiments involved the activity of p38 in the clathrin-dependent route, while ERK1/2 mediates clathrin-independent EGFR endocytosis. The PA/PDE4/PKA pathway selectively increases the EGFR endocytic rate without affecting LDLR and TfR constitute endocytosis. This selectiveness is probably because of EGFR phosphorylation, as detected in Th1046/1047 and Ser669 residues. The EGFR accumulates at perinuclear recycling endosomes colocalizing with TfR, fluorescent transferrin, and Rab11, while a small proportion distributes to Alix-endosomes. A non-selective recycling arrest includes LDLR and TfR in a reversible manner. The PA/PDE4/PKA pathway involving both p38 and ERK1/2 expands the possibilities of EGFR transmodulation and interference in cancer.

Exploring Interactions between Primary Hepatocytes and Non-Parenchymal Cells on Physiological and Pathological Liver Stiffness

Simple Summary

Chronic liver disease is characterized by progressive hepatic fibrosis leading to the formation of cirrhosis irrespective of the etiology with no effective treatment currently available. Liver stiffness (LS) is currently the best clinical predictor of this fibrosis progression irrespective of the cause of the disease. However, it is not well understood how does LS regulate the critical hepatocytes–non parenchymal cell interactions. We here present, to the best of our knowledge, the first analyses of the impact of physiological and pathological stiffness on hepatocytes–non parenchymal cell interaction. Our findings indicate the role of stiffness in regulating the hepatocytes interactions with NPCs necessary for maintenance of hepatocytes function.

Abstract

Chronic liver disease is characterized by progressive hepatic fibrosis leading to the formation of cirrhosis irrespective of the etiology with no effective treatment currently available. Liver stiffness (LS) is currently the best clinical predictor of this fibrosis progression irrespective of the etiology. LS and hepatocytes-nonparenchymal cells (NPC) interactions are two variables known to be important in regulating hepatic function during liver fibrosis, but little is known about the interplay of these cues. Here, we use polydimethyl siloxane (PDMS) based substrates with tunable mechanical properties to study how cell–cell interaction and stiffness regulates hepatocytes function. Specifically, primary rat hepatocytes were cocultured with NIH-3T3 fibroblasts on soft (2 kPa) and stiff substrates that recreates physiologic (2 kPa) and cirrhotic liver stiffness (55 kPa). Urea synthesis by primary hepatocytes depended on the presence of fibroblast and was independent of the substrate stiffness. However, albumin synthesis and Cytochrome P450 enzyme activity increased in hepatocytes on soft substrates and when in coculture with a fibroblast. Western blot analysis of hepatic markers, E-cadherin, confirmed that hepatocytes on soft substrates in coculture promoted better maintenance of the hepatic phenotype. These findings indicate the role of stiffness in regulating the hepatocytes interactions with NPCs necessary for maintenance of hepatocytes function.

Protein kinase inhibitor-based cancer therapies: Considering the potential of nitric oxide (NO) to improve cancer treatment

The deregulation of a wide variety of protein kinases is associated with cancer cell initiation and tumor progression. Owing to their indispensable function in signaling pathways driving malignant cell features, protein kinases constitute major therapeutic targets in cancer. Over the past two decades, intense efforts in drug development have been dedicated to this field. The development of protein kinase inhibitors (PKIs) have been a real breakthrough in targeted cancer therapy. Despite obvious successes across patients with different types of cancer, the development of PKI resistance still prevails. Combination therapies are part of a comprehensive approach to address the problem of drug resistance. The therapeutic use of nitric oxide (NO) donors to bypass PKI resistance in cancer has never been tested in clinic yet but several arguments suggest that the combination of PKIs and NO donors may exert a potential anticancer effect. The present review summarized the current state of knowledge on common targets to both PKIs and NO. Herein, we attempt to provide the rationale underlying a potential combination of PKIs and NO donors for future directions and design of new combination therapies in cancer.

The role of stem cells in liver injury and repair

Introduction: Liver disease is an increasing cause of worldwide mortality, and currently the only curative treatment for end-stage liver disease is whole organ allograft transplantation. Whilst this is an effective treatment, there is a shortage of suitable grafts and consequently some patients die whilst on the waiting list. Cell therapy provides an alternative treatment to increase liver function and potentially ameliorate fibrosis. Areas covered: In this review, we discuss the different cellular sources for therapy investigated to date in humans including mature hepatocytes, hematopoietic stem cells, mesenchymal stromal cells and hepatic progenitor cells. Cells investigated in animals include embryonic stem cells, induced pluripotent stem cells and directly reprogrammed cells. We then appraise the experience and evidence base underlying each cell type. Expert opinion: We discuss how this field may evolve in the years to come focusing on opportunities to enhance the intrinsic regenerative response with therapeutic targets and cell therapies. Growing expertise in tissue engineering will likely lead to increasingly complex bio-reactors and bio-artificial livers, which open a further avenue to restore liver function and delay or prevent the need for transplantation.

Hepatocyte-like cells derived from human amniotic epithelial, bone marrow, and adipose stromal cells display enhanced functionality when cultured on decellularized liver substrate

Transplantation of primary hepatocytes has been used in treatments for various liver pathologies and end-stage liver disease. However, shortage of donor tissue and the inability of hepatocyte proliferation in vitro have lead to alternative methods such as stem cell-derived hepatocyte-like cells (HLCs). Mesenchymal stromal/stem cells, and amniotic epithelial cells were isolated from human bone marrow (BM-MSCs), lipoaspirates (ASCs), and amniotic tissue (AECs) respectively. All cells were differentiated into HLCs on plates coated with Type I collagen or Porcine Liver Extracellular Matrix (PLECM-AA) matrix. Flow cytometry of BM-MSCs and ASCs, and AECs showed high expression of MSC-specific and embryonic stem cell markers respectively. All cell types differentiated into osteocytes, chondrocytes, and adipocytes. All cell type-derived HLCs presented the typical cuboidal primary hepatocyte morphology on PLECM-AA and fewer vacuoles (AECs) compared to HLCs cultured on type I collagen. Gene analysis of all cell type-derived HLCs cultured on PLECM-AA revealed higher upregulation of genes involved in drug transportation and metabolism compared to HLCs cultured on type I collagen. Although, HLCs cultured on PLECM-AA displayed some hepatocyte-related function and bioactivity, overall gene expression was lower compared to that of primary hepatocytes suggesting that caution should be taken when considering using HLCs to replace total hepatocyte functionality.

Lupin seed hydrolysate promotes G-protein-coupled receptor, intracellular Ca2+ and enhanced glycolytic metabolism-mediated insulin secretion from BRIN-BD11 pancreatic beta cells

Lupin seed proteins have been reported to exhibit hypoglycaemic effects in animals and humans following oral administration, however little is known about its mechanism of action. This study investigated the signalling pathway(s) responsible for the insulinotropic effect of the hydrolysate obtained from lupin (Lupinus angustifolius L.) seed extracts utilizing BRIN-BD11 β-cells. The extract was treated with digestive enzymes to give a hydrolysate rich in biomolecules ≤7 kDa. Cells exhibited hydrolysate induced dose-dependent stimulation of insulin secretion and enhanced intracellular Ca²⁺ and glucose metabolism. The stimulatory effect of the hydrolysate was potentiated by depolarizing concentrations of KCl and was blocked by inhibitors of the ATP sensitive K⁺ channel, Gα_q protein, phospholipase C (PLC) and protein kinase C (PKC). These findings reveal a novel mechanism for lupin hydrolysate stimulated insulin secretion via Gα_q mediated signal transduction (Gα_q/PLC/PKC) in the β-cells. Thus, lupin hydrolysates may have potential for nutraceutical treatment in type 2 diabetes.

Decellularization and Solubilization of Porcine Liver for Use as a Substrate for Porcine Hepatocyte Culture: Method Optimization and Comparison

Biologic substrates, prepared by decellularizing and solubilizing tissues, have been of great interest in the tissue engineering field because of the preservation of complex biochemical constituents found in the native extracellular matrix (ECM). The integrity of the ECM is critical for cell behavior, adhesion, migration, differentiation, and proliferation that in turn affect homeostasis and tissue regeneration. Previous studies have shown that various processing methods have a distinctive way of affecting the composition of the decellularized ECM. In this study, we developed a bioactive substrate for hepatocytes in vitro, made of decellularized and solubilized liver tissue. The present work is a comparative approach of 2 different methods. First, we decellularized porcine liver tissue with ammonium hydroxide versus a sodium deoxycholate method, then characterized the decellularized tissue using various methods including double stranded DNA (dsDNA) content, DNA size, immunogenicity, and mass spectrometry. Second, we solubilized the decellularized porcine liver with hydrochloric acid versus acetic acid (AA) and characterized the resultant solubilized tissues using relevant methodologies including protein yield, immunogenicity, and bioactivity. Finally, we isolated primary porcine hepatocytes, cultured, and evaluated their bioactivity on the optimized decellularized–solubilized liver substrate. The decellularized porcine liver ECM processed by the ammonium hydroxide method and solubilized with AA displayed higher ECM integrity, low dsDNA, no evidence of intact nuclei, low human monocyte chemoattraction, and the presence of key molecules typically found in the native liver, a very important element for normal cell function. In addition, primary porcine hepatocytes showed enhanced functionality including albumin and urea production and bile canaliculi formation when cultured on the developed liver substrate compared to type I collagen.

Extracellular matrix with defective collagen cross-linking affects the differentiation of bone cells

Fibrillar type I collagen, the predominant organic component in bone, is stabilized by lysyl oxidase (LOX)-initiated covalent intermolecular cross-linking, an important determinant of bone quality. However, the impact of collagen cross-linking on the activity of bone cells and subsequent tissue remodeling is not well understood. In this study, we investigated the effect of collagen cross-linking on bone cellular activities employing a loss-of-function approach, using a potent LOX inhibitor, β-aminopropionitrile (BAPN). Osteoblastic cells (MC3T3-E1) were cultured for 2 weeks in the presence of 0–2 mM BAPN to obtain low cross-linked collagen matrices. The addition of BAPN to the cultures diminished collagen cross-links in a dose-dependent manner and, at 1 mM level, none of the major cross-links were detected without affecting collagen production. After the removal of cellular components from these cultures, MC3T3-E1, osteoclasts (RAW264.7), or mouse primary bone marrow-derived stromal cells (BMSCs) were seeded. MC3T3-E1 cells grown on low cross-link matrices showed increased alkaline phosphatase (ALP) activity. The number of multinucleate tartrate-resistant acid phosphatase (TRAP)-positive cells increased in RAW264.7 cells. Initial adhesion, proliferation, and ALP activity of BMSCs also increased. In the animal experiments, 4-week-old C57BL/6 mice were fed with BAPN-containing diet for 8 weeks. At this point, biochemical analysis of bone demonstrated that collagen cross-links decreased without affecting collagen content. Then, the diet was changed to a control diet to minimize the direct effect of BAPN. At 2 and 4 weeks after the change, histological samples were prepared. Histological examination of femur samples at 4 weeks showed a significant increase in the number of bone surface osteoblasts, while the bone volume and surface osteoclast numbers were not significantly affected. These results clearly demonstrated that the extent of collagen cross-linking of bone matrix affected the differentiation of bone cells, underscoring the importance of collagen cross-linking in the regulation of cell behaviors and tissue remodeling in bone. Characterization of collagen cross-linking in bone may be beneficial to obtain insight into not only bone mechanical property, but also bone cellular activities.

Bioinspired liver scaffold design criteria

Maintaining hepatic functional characteristics in-vitro is considered one of the main challenges in engineering liver tissue. As hepatocytes cultured ex-vivo are deprived of their native extracellular matrix (ECM) milieu, developing scaffolds that mimic the biomechanical and physicochemical properties of the native ECM is thought to be a promising approach for successful tissue engineering and regenerative medicine applications. On the basis that the decellularized liver matrix represents the ideal design template for engineering bioinspired hepatic scaffolds, to derive quantitative descriptors of liver ECM architecture, we characterised decellularised liver matrices in terms of their biochemical, viscoelastic and structural features along with porosity, permeability and wettability. Together, these data provide a unique set of quantitative design criteria which can be used to generate guidelines for fabricating biomaterial scaffolds for liver tissue engineering. As proof-of-concept, we investigated hepatic cell response to substrate viscoelasticity. On collagen hydrogels mimicking decellularised liver mechanics, cells showed superior morphology, higher viability and albumin secretion than on stiffer and less viscous substrates. Although scaffold properties are generally inspired by those of native tissues, our results indicate significant differences between the mechano-structural characteristics of untreated and decellularised hepatic tissue. Therefore, we suggest that design rules - such as mechanical properties and swelling behaviour - for engineering biomimetic scaffolds be re-examined through further studies on substrates matching the features of decellularized liver matrices.

Monocyte Adhesion, Migration, and Extracellular Matrix Breakdown Are Regulated by Integrin αVβ3 in Mycobacterium tuberculosis Infection

In tuberculosis (TB), the innate inflammatory immune response drives tissue destruction, morbidity, and mortality. Monocytes secrete matrix metalloproteinases (MMPs), which have key roles in local tissue destruction and cavitation. We hypothesized that integrin signaling might regulate monocyte MMP secretion in pulmonary TB during cell adhesion to the extracellular matrix (ECM). Adhesion to type I collagen and fibronectin by Mycobacterium tuberculosis-stimulated monocytes increased MMP-1 gene expression by 2.6-fold and 4.3-fold respectively, and secretion by 60% (from 1208.1 ± 186 to 1934.4 ± 135 pg/ml; p < 0.0001) and 63% (1970.3 ± 95 pg/ml; p < 0.001). MMP-10 secretion increased by 90% with binding to type I collagen and 55% with fibronectin, whereas MMP-7 increased 57% with collagen. The ECM did not affect the secretion of tissue inhibitors of metalloproteinases-1 or -2. Integrin αVβ3 surface expression was specifically upregulated in stimulated monocytes and was further increased after adhesion to type I collagen. Binding of either β3 or αV integrin subunits increased MMP-1/10 secretion in M. tuberculosis-stimulated monocytes. In a cohort of TB patients, significantly increased integrin β3 mRNA accumulation in induced sputum was detected, to our knowledge, for the first time, compared with control subjects (p < 0.05). Integrin αVβ3 colocalized with areas of increased and functionally active MMP-1 on infected monocytes, and αVβ3 blockade markedly decreased type I collagen breakdown, and impaired both monocyte adhesion and leukocyte migration in a transwell system (p < 0.0001). In summary, our data demonstrate that M. tuberculosis stimulation upregulates integrin αVβ3 expression on monocytes, which upregulates secretion of MMP-1 and -10 on adhesion to the ECM. This leads to increased monocyte recruitment and collagenase activity, which will drive inflammatory tissue damage.

Sample, testing and analysis variables affecting liver mechanical properties: A review

Given the critical role of liver mechanics in regulating cell response and directing the development of tissue fibrosis, accurately characterising its mechanical behaviour is of relevance for both diagnostic purposes as well as for tissue engineering and for the development of in-vitro models. Determining and quantifying the mechanical behaviour of soft biological tissues is, however, highly challenging due to their intrinsic labile nature. Indeed, a unique set of values of liver mechanical properties is still lacking to date; testing conditions can significantly affect sample status and hence the measured behaviour and reported results are strongly dependent on the adopted testing method and configuration as well as sample type and status. This review aims at summarising the bulk mechanical properties of liver described in the literature, discussing the possible sources of variation and their implications on the reported results. We distinguish between the intrinsic mechanical behaviour of hepatic tissue, which depends on sample variables, and the measured mechanical properties which also depend on the testing and analysis methods. Finally, the review provides guidelines on tissue preparation and testing conditions for generating reproducible data which can be meaningfully compared across laboratories.

STATEMENT OF SIGNIFICANCE

Soft tissue mechanics is widely investigated, but poorly understood. This review identifies and discusses sample and testing variables which can influence the mechanical behaviour of hepatic tissue and consequently the measured mechanical properties. To encourage the biomaterial community towards more standardized testing of soft tissues and enable comparisons between data from different laboratories, we have established new testing methods and experimental recommendations for sample preparation and testing. The review could be of wide interest to scientists involved in biomaterials research because it addresses and proposes guidelines for several issues related to the mechanical testing of soft tissues whose implications have not been considered together before.

Role of the prostaglandin E2 receptor agonists in TGF-β1-induced mesangial cell damage

PGE₂ exerts its biological effect through binding to various EP receptors that result inactivation of various signal transduction pathways. It also plays an important role in mice glomerular mesangial cells (MCs) damage induced by transforming growth factor-β1 (TGF-β1); however, the molecular mechanisms remain unknown. In the present study, we tested the efficacy of four selective agonists of PGE₂ receptor, EP₁A (17-phenyl trinor prostaglandin E₂ ethyl amid), EP₂A (butaprost), EP₃A (sulprostone) and EP₄A (cay10580), on mice MCs. Compared with the cAMP produced by TGF-β1, additional pretreatment of EP₃A decreased the cAMP level. MCs treated with EP₁A and EP₃A augmented PGE₂, cyclooxygenase-2 (COX-2), membrane-bound PGE synthase 1 (mPGES1), laminin (LN), connective tissue growth factor (CTGF) and cyclin D1 expression stimulated by TGFβ1. EP₁A and EP₃A increased the number of cells in S+G2/M phase and reduced cells in G0/G1 phase. EP₁ and EP₃ agonists also strengthened TGFβ1-induced mitogen-activated protein kinase (p38MAPK) and extracellular-signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Whereas MCs treated with EP₂A and EP₄A weakened PGE₂, COX-2, mPGES1, LN, CTGF and cyclin D1 expression stimulated by TGFβ1. EP₂A and EP₄A decreased the number of cells in S+G2/M phase and increased cells in G0/G1 phase. EP₂ and EP₄ agonists weakened TGFβ1-induced p38MAPK and ERK1/2 phosphorylation. These findings suggest that PGE₂ has an important role in the progression of kidney disease via the EP₁/EP₃ receptor, whereas EP₂ and EP₄ receptors are equally important in preserving the progression of chronic kidney failure. Thus, agonists of EP₂ and EP₄ receptors may provide a basis for treating kidney damage induced by TGF-β1.

Physiological ranges of matrix rigidity modulate primary mouse hepatocyte function in part through hepatocyte nuclear factor 4 alpha

Matrix rigidity has important effects on cell behavior and is increased during liver fibrosis; however, its effect on primary hepatocyte function is unknown. We hypothesized that increased matrix rigidity in fibrotic livers would activate mechanotransduction in hepatocytes and lead to inhibition of liver-specific functions. To determine the physiologically relevant ranges of matrix stiffness at the cellular level, we performed detailed atomic force microscopy analysis across liver lobules from normal and fibrotic livers. We determined that normal liver matrix stiffness was around 150 Pa and increased to 1-6 kPa in areas near fibrillar collagen deposition in fibrotic livers. In vitro culture of primary hepatocytes on collagen matrix of tunable rigidity demonstrated that fibrotic levels of matrix stiffness had profound effects on cytoskeletal tension and significantly inhibited hepatocyte-specific functions. Normal liver stiffness maintained functional gene regulation by hepatocyte nuclear factor 4 alpha (HNF4α), whereas fibrotic matrix stiffness inhibited the HNF4α transcriptional network. Fibrotic levels of matrix stiffness activated mechanotransduction in primary hepatocytes through focal adhesion kinase. In addition, blockade of the Rho/Rho-associated protein kinase pathway rescued HNF4α expression from hepatocytes cultured on stiff matrix.

CONCLUSION

Fibrotic levels of matrix stiffness significantly inhibit hepatocyte-specific functions in part by inhibiting the HNF4α transcriptional network mediated through the Rho/Rho-associated protein kinase pathway. Increased appreciation of the role of matrix rigidity in modulating hepatocyte function will advance our understanding of the mechanisms of hepatocyte dysfunction in liver cirrhosis and spur development of novel treatments for chronic liver disease. (Hepatology 2016;64:261-275).

Differentiation of Murine Bone Marrow-Derived Smooth Muscle Progenitor Cells Is Regulated by PDGF-BB and Collagen

Smooth muscle cells (SMCs) are key regulators of vascular disease and circulating smooth muscle progenitor cells may play important roles in vascular repair or remodelling. We developed enhanced protocols to derive smooth muscle progenitors from murine bone marrow and tested whether factors that are increased in atherosclerotic plaques, namely platelet-derived growth factor-BB (PDGF-BB) and monomeric collagen, can influence the smooth muscle specific differentiation, proliferation, and survival of mouse bone marrow-derived progenitor cells. During a 21 day period of culture, bone marrow cells underwent a marked increase in expression of the SMC markers α-SMA (1.93 ± 0.15 vs. 0.0008 ± 0.0003 (ng/ng GAPDH) at 0 d), SM22-α (1.50 ± 0.27 vs. 0.005 ± 0.001 (ng/ng GAPDH) at 0 d) and SM-MHC (0.017 ± 0.004 vs. 0.001 ± 0.001 (ng/ng GAPDH) at 0 d). Bromodeoxyuridine (BrdU) incorporation experiments showed that in early culture, the smooth muscle progenitor subpopulation could be identified by high proliferative rates prior to the expression of smooth muscle specific markers. Culture of fresh bone marrow or smooth muscle progenitor cells with PDGF-BB suppressed the expression of α-SMA and SM22-α, in a rapidly reversible manner requiring PDGF receptor kinase activity. Progenitors cultured on polymerized collagen gels demonstrated expression of SMC markers, rates of proliferation and apoptosis similar to that of cells on tissue culture plastic; in contrast, cells grown on monomeric collagen gels displayed lower SMC marker expression, lower growth rates (319 ± 36 vs. 635 ± 97 cells/mm2), and increased apoptosis (5.3 ± 1.6% vs. 1.0 ± 0.5% (Annexin 5 staining)). Our data shows that the differentiation and survival of smooth muscle progenitors are critically affected by PDGF-BB and as well as the substrate collagen structure.

Cellular modulation by the elasticity of biomaterials

The elasticity of the extracellular matrix has been increasingly recognized as a dominating factor of cell fate and activities. This review provides an overview of the general principles and recent advances in the field of matrix elasticity-dependent regulation of a variety of cellular activities and functions, the underlying biomechanical and molecular mechanisms, as well as the pathophysiological implications.

Atomic force microscopy investigation of the interaction of low-level laser irradiation of collagen thin films in correlation with fibroblast response

Low-level red laser (LLRL)-tissue interactions have a wide range of medical applications and are garnering increased attention. Although the positive effects of low-level laser therapy (LLLT) have frequently been reported and enhanced collagen accumulation has been identified as one of the most important mechanisms involved, little is known about LLRL-collagen interactions. In this study, we aimed to investigate the influence of LLRL irradiation on collagen, in correlation with fibroblast response. Atomic force microscopy (AFM) and fluorescence spectroscopy were used to characterize surfaces and identify conformational changes in collagen before and after LLRL irradiation. Irradiated and non-irradiated collagen thin films were used as culturing substrates to investigate fibroblast response with fluorescence microscopy. The results demonstrated that LLRL induced small alterations in fluorescence emission and had a negligible effect on the topography of collagen thin films. However, fibroblasts cultured on LLRL-irradiated collagen thin films responded to LRLL. The results of this study show for the first time the effect of LLRL irradiation on pure collagen. Although irradiation did not affect the nanotopography of collagen, it influenced cell behavior. The role of collagen appears to be crucial in the LLLT mechanism, and our results demonstrated that LLRL directly affects collagen and indirectly affects cell behavior.

Substrate stiffness regulates primary hepatocyte functions

Liver fibrosis occurs as a consequence of chronic injuries from viral infections, metabolic disorders, and alcohol abuse. Fibrotic liver microenvironment (LME) is characterized by excessive deposition and aberrant turnover of extracellular matrix proteins, which leads to increased tissue stiffness. Liver stiffness acts as a vital cue in the regulation of hepatic responses in both healthy and diseased states; however, the effect of varying stiffness on liver cells is not well understood. There is a critical need to engineer in vitro models that mimic the liver stiffness corresponding to various stages of disease progression in order to elucidate the role of individual cellular responses. Here we employed polydimethyl siloxane (PDMS) based substrates with tunable mechanical properties to investigate the effect of substrate stiffness on the behavior of primary rat hepatocytes. To recreate physiologically relevant stiffness, we designed soft substrates (2 kPa) to represent the healthy liver and stiff substrates (55 kPa) to represent the diseased liver. Tissue culture plate surface (TCPS) served as the control substrate. We observed that hepatocytes cultured on soft substrates displayed a more differentiated and functional phenotype for a longer duration as compared to stiff substrates and TCPS. We demonstrated that hepatocytes on soft substrates exhibited higher urea and albumin synthesis. Cytochrome P450 (CYP) activity, another critical marker of hepatocytes, displayed a strong dependence on substrate stiffness, wherein hepatocytes on soft substrates retained 2.7 fold higher CYP activity on day 7 in culture, as compared to TCPS. We further observed that an increase in stiffness induced downregulation of key drug transporter genes (NTCP, UGT1A1, and GSTM-2). In addition, we observed that the epithelial cell phenotype was better maintained on soft substrates as indicated by higher expression of hepatocyte nuclear factor 4α, cytokeratin 18, and connexin 32. These results indicate that the substrate stiffness plays a significant role in modulating hepatocyte behavior. Our PDMS based liver model can be utilized to investigate the signaling pathways mediating the hepatocyte-LME communication to understand the progression of liver diseases.

Increasing 3D Matrix Rigidity Strengthens Proliferation and Spheroid Development of Human Liver Cells in a Constant Growth Factor Environment

Mechanical forces influence the growth and shape of virtually all tissues and organs. Recent studies show that increased cell contractibility, growth and differentiation might be normalized by modulating cell tensions. Particularly, the role of these tensions applied by the extracellular matrix during liver fibrosis could influence the hepatocarcinogenesis process. The objective of this study is to determine if 3D stiffness could influence growth and phenotype of normal and transformed hepatocytes and to integrate extracellular matrix (ECM) stiffness to tensional homeostasis. We have developed an appropriate 3D culture model: hepatic cells within three-dimensional collagen matrices with varying rigidity. Our results demonstrate that the rigidity influenced the cell phenotype and induced spheroid clusters development whereas in soft matrices, Huh7 transformed cells were less proliferative, well-spread and flattened. We confirmed that ERK1 played a predominant role over ERK2 in cisplatin-induced death, whereas ERK2 mainly controlled proliferation. As compared to 2D culture, 3D cultures are associated with epithelial markers expression. Interestingly, proliferation of normal hepatocytes was also induced in rigid gels. Furthermore, biotransformation activities are increased in 3D gels, where CYP1A2 enzyme can be highly induced/activated in primary culture of human hepatocytes embedded in the matrix. In conclusion, we demonstrated that increasing 3D rigidity could promote proliferation and spheroid developments of liver cells demonstrating that 3D collagen gels are an attractive tool for studying rigidity-dependent homeostasis of the liver cells embedded in the matrix and should be privileged for both chronic toxicological and pharmacological drug screening.

Photopatterning of hydrogel scaffolds coupled to filter materials using stereolithography for perfused 3D culture of hepatocytes

In vitro models that recapitulate the liver's structural and functional complexity could prolong hepatocellular viability and function to improve platforms for drug toxicity studies and understanding liver pathophysiology. Here, stereolithography (SLA) was employed to fabricate hydrogel scaffolds with open channels designed for post-seeding and perfused culture of primary hepatocytes that form 3D structures in a bioreactor. Photopolymerizable polyethylene glycol-based hydrogels were fabricated coupled to chemically activated, commercially available filters (polycarbonate and polyvinylidene fluoride) using a chemistry that permitted cell viability, and was robust enough to withstand perfused culture of up to 1 µL/s for at least 7 days. SLA energy dose, photoinitiator concentrations, and pretreatment conditions were screened to determine conditions that maximized cell viability and hydrogel bonding to the filter. Multiple open channel geometries were readily achieved, and included ellipses and rectangles. Rectangular open channels employed for subsequent studies had final dimensions on the order of 350 µm by 850 µm. Cell seeding densities and flow rates that promoted cell viability were determined. Perfused culture of primary hepatocytes in hydrogel scaffolds in the presence of soluble epidermal growth factor (EGF) prolonged the maintenance of albumin production throughout the 7-day culture relative to 2D controls. This technique of bonding hydrogel scaffolds can be employed to fabricate soft scaffolds for a number of bioreactor configurations and applications.

Liver bioengineering: from the stage of liver decellularized matrix to the multiple cellular actors and bioreactor special effects

Liver bioengineering has been a field of intense research and popular excitement in the past decades. It experiences great interest since the introduction of whole liver acellular scaffolds generated by perfusion decellularization (1-3). Nevertheless, the different strategies developed so far have failed to generate hepatic tissue in vitro bioequivalent to native liver tissue. Even notable novel strategies that rely on iPSC-derived liver progenitor cells potential to self-organize in association with endothelial cells in hepatic organoids are lacking critical components of the native tissue (e.g., bile ducts, functional vascular network, hepatic microarchitecture, etc) (4). Hence, it is vital to understand the strengths and short comes of our current strategies in this quest to re-create liver organogenesis in vitro. To shed some light into these issues, this review describes the different actors that play crucial roles in liver organogenesis and highlights the steps still missing to successfully generate whole livers and hepatic organoids in vitro for multiple applications.

Novel use for polyvinylpyrrolidone as a macromolecular crowder for enhanced extracellular matrix deposition and cell proliferation

Macromolecular crowding (MMC) is a biophysical effect that governs biochemical processes inside and outside of cells. Since standard cell culture media lack this effect, the physiological performance of differentiated and progenitor cells, including extracellular matrix (ECM) deposition, is impaired in vitro. To bring back physiological crowdedness to in vitro systems, we have previously introduced carbohydrate-based macromolecules to culture media and have achieved marked improvements with mixed MMC in terms of ECM deposition and differentiation of mesenchymal stem cells (MSCs). We show here that although this system is successful, it is limited, due to viscosity, to only 33% of the fractional volume occupancy (FVO) of full serum, which we calculated to have an FVO of approximately 54% v/v. We show here that full-serum FVO can be achieved using polyvinylpyrrolidone (PVP) 360 kDa. Under these conditions, ECM deposition in human fibroblasts and MSCs is on par, if not stronger than, with original MMC protocols using carbohydrates, but with a viscosity that is not significantly changed. In addition, we have found that the proliferation rate for bone marrow-derived MSCs and fibroblasts increases slightly in the presence of PVP360, similar to that observed with carbohydrate-based crowders. A palette of MMC compounds is now emerging that enables us to tune the crowdedness of culture media seamlessly from interstitial fluid (9% FVO), in which the majority of tissue cells might be based, to serum environments mimicking intravascular conditions. Despite identical FVO's, individual crowder size effects play a role and different cell types appear to have preferences in terms of FVO and the crowder that this is achieved with. However, in the quest of crowders that we have predicted to have a smoother regulatory approval path, PVP is a highly interesting compound, as it has been widely used in the medical and food industries and shows a novel promising use in cell culture and tissue engineering.

Characterizing the effects of heparin gel stiffness on function of primary hepatocytes

In the liver, hepatocytes are exposed to a large array of stimuli that shape hepatic phenotype. This in vivo microenvironment is lost when hepatocytes are cultured in standard cell cultureware, making it challenging to maintain hepatocyte function in vitro. Our article focused on one of the least studied inducers of the hepatic phenotype-the mechanical properties of the underlying substrate. Gel layers comprised of thiolated heparin (Hep-SH) and diacrylated poly(ethylene glycol) (PEG-DA) were formed on glass substrates via a radical mediated thiol-ene coupling reaction. The substrate stiffness varied from 10 to 110 kPa by changing the concentration of the precursor solution. ELISA analysis revealed that after 5 days, hepatocytes cultured on a softer heparin gel were synthesizing five times higher levels of albumin compared to those on a stiffer heparin gel. Immunofluorescent staining for hepatic markers, albumin and E-cadherin, confirmed that softer gels promoted better maintenance of the hepatic phenotype. Our findings point to the importance of substrate mechanical properties on hepatocyte function.

Extracellular matrix collagen alters cell proliferation and cell cycle progression of human uterine leiomyoma smooth muscle cells

Uterine leiomyomas (ULs) are benign tumors occurring in the majority of reproductive aged women. Despite the high prevalence of these tumors, little is known about their etiology. A hallmark of ULs is the excessive deposition of extracellular matrix (ECM), primarily collagens. Collagens are known to modulate cell behavior and function singularly or through interactions with integrins and growth factor-mediated mitogenic pathways. To better understand the pathogenesis of ULs and the role of ECM collagens in their growth, we investigated the interaction of leiomyoma smooth muscle cells (LSMCs) with two different forms of collagen, non-polymerized collagen (monomeric) and polymerized collagen (fibrillar), in the absence or presence of platelet-derived growth factor (PDGF), an abundant growth factor in ULs. Primary cultures of human LSMCS from symptomatic patients were grown on these two different collagen matrices and their morphology, cytoskeletal organization, cellular proliferation, and signaling pathways were evaluated. Our results showed that LSMCs had distinct morphologies on the different collagen matrices and their basal as well as PDGF-stimulated proliferation varied on these matrices. These differences in proliferation were accompanied by changes in cell cycle progression and p21, an inhibitory cell cycle protein. In addition we found alterations in the phosphorylation of focal adhesion kinase, cytoskeletal reorganization, and activation of the mitogen activated protein kinase (MAPK) signaling pathway. In conclusion, our results demonstrate a direct effect of ECM on the proliferation of LSMCs through interplay between the collagen matrix and the PDGF-stimulated MAPK pathway. In addition, these findings will pave the way for identifying novel therapeutic approaches for ULs that target ECM proteins and their signaling pathways in ULs.

Cellular functions regulated by phosphorylation of EGFR on Tyr845

The Src gene product (Src) and the epidermal growth factor receptor (EGFR) are prototypes of oncogene products and function primarily as a cytoplasmic non-receptor tyrosine kinase and a transmembrane receptor tyrosine kinase, respectively. The identification of Src and EGFR, and the subsequent extensive investigations of these proteins have long provided cutting edge research in cancer and other molecular and cellular biological studies. In 1995, we reported that the human epidermoid carcinoma cells, A431, contain a small fraction of Src and EGFR in which these two kinase were in physical association with each other, and that Src phosphorylates EGFR on tyrosine 845 (Y845) in the Src-EGFR complex. Y845 of EGFR is located in the activation segment of the kinase domain, where many protein kinases contain kinase-activating autophosphorylation sites (e.g., cAMP-dependent protein kinase, Src family kinases, transmembrane receptor type tyrosine kinases) or trans-phosphorylation sites (e.g., cyclin-dependent protein kinase, mitogen-activated protein kinase, Akt protein kinase). A number of studies have demonstrated that Y845 phosphorylation serves an important role in cancer as well as normal cells. Here we compile the experimental facts involving Src phosphorylation of EGFR on Y845, by which cell proliferation, cell cycle control, mitochondrial regulation of cell metabolism, gamete activation and other cellular functions are regulated. We also discuss the physiological relevance, as well as structural insights of the Y845 phosphorylation.

In vivo tracking and comparison of the therapeutic effects of MSCs and HSCs for liver injury

Background

Mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) have been studied for damaged liver repair; however, the conclusions drawn regarding their homing capacity to the injured liver are conflicting. Besides, the relative utility and synergistic effects of these two cell types on the injured liver remain unclear.

Methodology/Principal Findings

MSCs, HSCs and the combination of both cells were obtained from the bone marrow of male mice expressing enhanced green fluorescent protein(EGFP)and injected into the female mice with or without liver fibrosis. The distribution of the stem cells, survival rates, liver function, hepatocyte regeneration, growth factors and cytokines of the recipient mice were analyzed. We found that the liver content of the EGFP-donor cells was significantly higher in the MSCs group than in the HSCs or MSCs+HSCs group. The survival rate for the MSCs group was significantly higher than that of the HSCs or MSCs+HSCs group; all surpassed the control group. After MSC-transplantation, the injured livers were maximally restored, with less collagen than the controls. The fibrotic areas had decreased to a lesser extent in the mice transplanted with HSCs or MSCs+HSCs. Compared with mice in the HSCs group, the mice that received MSCs had better improved liver function. MSCs exhibited more remarkable paracrine effects and immunomodulatory properties on hepatic stellate cells and native hepatocytes in the treatment of the liver pathology. Synergistic actions of MSCs and HSCs were most likely not observed because the stem cells in liver were detected mostly as single cells, and single MSCs are insufficient to provide a beneficial niche for HSCs.

Conclusions/Significance

MSCs exhibited a greater homing capability for the injured liver and modulated fibrosis and inflammation more effectively than did HSCs. Synergistic effects of MSCs and HSCs were not observed in liver injury.

Helix versus coil polypeptide macromers: gel networks with decoupled stiffness and permeability

As a platform for investigating the individual effects of substrate stiffness, permeability, and ligand density on cellular behavior, we developed a set of hydrogels with stiffness tuned by polymer backbone rigidity, independent of cross-link density and concentration. Previous studies report that poly(propargyl-L-glutamate) (PPLG), synthesized by ring-opening polymerization of the N-carboxy anhydride of γ-propargyl-L-glutamate (γpLglu), adopts a rigid a-helix conformation: we hypothesized that a random copolymer (PPDLG) with equal amounts of γpLglu and γ-propargyl-D-glutamate (γpDglu) monomers would exhibit a more flexible random coil conformation. The resulting macromers exhibited narrow molecular weight distributions (PDI = 1.15) and were grafted with ethylene glycol groups using a highly efficient "click" azide/alkyne cycloaddition reaction with average grafting efficiency of 97% for PPLG and 85% for PPDLG. The polypeptide secondary structure, characterized via circular dichroism spectroscopy, FTIR spectroscopy, and dynamic light scattering, is indeed dependent upon monomer chirality: PPLG exhibits an α-helix conformation while PPDLG adopts a random coil conformation. Hydrogel networks produced by cross-linking either helical or random coil polypeptides with poly(ethylene glycol) (PEG) were analyzed for amount of swelling, gelation efficiency, and permeability to a model protein. In addition, the elastic modulus of helical and coil polypeptide gels was determined by AFM indentation in fluid. Importantly, we found that helical and coil polypeptide gels exhibited similar swelling and permeability but different stiffnesses, which correspond to predictions from the theory of semi-flexible chains.

Autocrine-controlled formation and function of tissue-like aggregates by primary hepatocytes in micropatterned hydrogel arrays

The liver carries out a variety of essential functions regulated in part by autocrine signaling, including hepatocyte-produced growth factors and extracellular matrix (ECM). The local concentrations of autocrine factors are governed by a balance between receptor-mediated binding at the cell surface and diffusion into the local matrix and are thus expected to be influenced by the dimensionality of the cell culture environment. To investigate the role of growth factor and ECM-modulated autocrine signaling in maintaining appropriate primary hepatocyte survival, metabolic functions, and polarity, we created three-dimensional cultures of defined geometry using micropatterned semisynthetic polyethylene glycol-fibrinogen hydrogels to provide a mechanically compliant, nonadhesive material platform that could be modified by cell-secreted factors. We found that in the absence of exogenous peptide growth factors or ECM, hepatocytes retain the epidermal growth factor (EGF) receptor ligands (EGF and transforming growth factor-α) and the proto-oncogenic mesenchymal epithelial transition factor (c-MET) ligand hepatocyte growth factor (HGF), along with fibronectin. Further, hepatocytes cultured in this three-dimensional microenvironment maintained high levels of liver-specific functions over the 10-day culture period. Function-blocking inhibitors of α5β1 or EGF receptor dramatically reduced cell viability and function, suggesting that signaling by both these receptors is needed for in vitro survival and function of hepatocytes in the absence of other exogenous signals.

Unique Properties of Hepatocarcinogenesis-Resistant DRH Rat Hepatocytes Linked or Not Linked to the Drh1 Locus on Rat Chromosome 1

Hepatocarcinogenesis-resistant DRH rats exhibit few and small preneoplastic hepatocytic lesions during hepatocarcinogenesis, of which traits have been assigned to two major chromosomal regions, Drh1 and Drh2. In this study, hepatocytes from DRH.F344-Drh1, a congenic strain in which the Drh1 chromosomal region was replaced with that of F344 rats, were compared to hepatocytes from Donryu (original strain), DRH, and F344 rats. Although DRH hepatocytes exhibited low proliferation and p38 dephosphorylation after lead nitrate (LN) treatment despite cytokine and Cox2 activation, DRH.F344-Drh1 hepatocytes exhibited high responses, as did Donryu and F344 hepatocytes. Moreover, although DRH hepatocytes were resistant to hepatotoxins, DRH.F344-Drh1 hepatocytes were as sensitive to hepatotoxins as Donryu and F344 hepatocytes. However, DRH.F344-Drh1 hepatocytes like DRH hepatocytes proliferated at lower rates in vitro and contained smaller nuclei than Donryu and F344 hepatocytes. Thus, low responses to LN and resistance to hepatotoxins in DRH hepatocytes were linked to the Drh1 locus, while low proliferation in vitro and small nuclear size were not linked to the Drh1 locus.

Heparin-based hydrogel as a matrix for encapsulation and cultivation of primary hepatocytes

Primary hepatocytes are commonly used as liver surrogates in toxicology and tissue engineering fields, therefore, maintenance of functional hepatocytes in vitro is an important topic of investigation. This paper sought to characterize heparin-based hydrogel as a three-dimensional scaffold for hepatocyte culture. The primary rat hepatocytes were mixed with a prepolymer solution comprised of thiolated heparin and acrylated poly(ethylene glycol) (PEG). Raising the temperature from 25 degrees to 37 degrees C initiated Michael addition reaction between the thiol and acrylated moieties and resulted in formation of hydrogel with entrapped cells. Analysis of liver-specific products, albumin and urea, revealed that the heparin hydrogel was non-cytotoxic to cells and, in fact, promoted hepatic function. Hepatocytes entrapped in the heparin-based hydrogel maintained high levels of albumin and urea synthesis after three weeks in culture. Because heparin is known to bind growth factors, we incorporated hepatocyte growth factor (HGF)-an important liver signaling molecule - into the hydrogel. HGF release from heparin hydrogel matrix was analyzed using enzyme linked immunoassay (ELISA) and was shown to occur in a controlled manner with only 40% of GF molecules released after 30 days in culture. Importantly, hepatocytes cultured within HGF-containing hydrogels exhibited significantly higher levels of albumin and urea synthesis compared to cells cultured in the hydrogel alone. Overall, heparin-based hydrogel showed to be a promising matrix for encapsulation and maintenance of difficult-to-culture primary hepatocytes. In the future, we envision employing heparin-based hyrogels as matrices for in vitro differentiation of hepatocytes or stem cells and as vehicles for transplantation of these cells.

Synergistic effects of tethered growth factors and adhesion ligands on DNA synthesis and function of primary hepatocytes cultured on soft synthetic hydrogels

The composition, presentation, and spatial orientation of extracellular matrix molecules and growth factors are key regulators of cell behavior. Here, we used self-assembling peptide nanofiber gels as a modular scaffold to investigate how fibronectin-derived adhesion ligands and different modes of epidermal growth factor (EGF) presentation synergistically regulate multiple facets of primary rat hepatocyte behavior in the context of a soft gel. In the presence of soluble EGF, inclusion of dimeric RGD and the heparin binding domain from fibronectin (HB) increased hepatocyte aggregation, spreading, and metabolic function compared to unmodified gels or gels modified with a single motif, but unlike rigid substrates, gels failed to induce DNA synthesis. Tethered EGF dramatically stimulated cell aggregation and spreading under all adhesive ligand conditions and also preserved metabolic function. Surprisingly, tethered EGF elicited DNA synthesis on gels with RGD and HB. Phenotypic differences between soluble and tethered EGF stimulation of cells on peptide gels are correlated with differences in expression and phosphorylation the EGF receptor and its heterodimerization partner ErbB2, and activation of the downstream signaling node ERK1/2. These modular matrices reveal new facets of hepatocellular biology in culture and may be more broadly useful in culture of other soft tissues.

Effect of a hepatocyte growth factor/heparin-immobilized collagen system on albumin synthesis and spheroid formation by hepatocytes

A hepatocyte growth factor (HGF)/heparin-immobilized collagen system was used as a synthetic extracellular matrix for hepatocyte culture. The albumin synthesis, nucleus numbers and morphology of the hepatocytes were determined separately to evaluate the hepatocyte number and hepatocyte-specific function under this system. The benefits of the HGF/heparin-immobilized collagen system for hepatocyte culture were confirmed by three types of culture methods in vitro, namely 2D film cultures, 2D gel cultures and 3D gel cultures. In 2D collagen film cultures, hepatocytes exhibited the highest albumin synthesis (1.42 microg/well/day) in HGF/heparin-immobilized collagen films at 7 days of culture. Heparin inhibited hepatocyte adhesion while HGF promoted hepatocyte migration, and spheroid formation was easily detected in HGF/heparin-immobilized collagen films. In 2D collagen gel cultures, albumin synthesis of around 15 microg/well/day was detected and maintained for more than 18 days on HGF/heparin-immobilized collagen gels. Similar findings were obtained in 3D HGF/heparin-immobilized collagen gel cultures, which exhibited albumin synthesis of up to 30 microg/well/day. The albumin synthesis by hepatocytes was two-fold higher in 3D gel cultures compared with 2D gel cultures, and was maintained for over 2 weeks compared with 2D film cultures using the HGF/heparin-immobilized collagen system. Taken together, the HGF/heparin-immobilized collagen system was effective for albumin synthesis by hepatocytes in both 2D film cultures and 3D gel cultures, and therefore shows good potential for tissue engineering use.

Entrapped collagen type 1 promotes differentiation of embryonic pancreatic precursor cells into glucose-responsive beta-cells when cultured in three-dimensional PEG hydrogels

Development of an alternative source of functional, transplantable beta-cells to replace or supplement cadaveric tissue is critical to the future success of islet cell transplantation therapy. Embryonic pancreatic precursor cells are desirable as a renewable source of beta-cells as they are both proliferative and inherently capable of pancreatic cell differentiation. We have previously shown that precursor cells undergo selective beta-cell differentiation when dissociated and photoencapsulated in a polyethylene glycol (PEG) hydrogel network; however, these cells remained immature and were not glucose responsive. Collagen type 1 supports mature cell viability and function in many cell types and we hypothesized that incorporating it within our gels may support differentiating beta-cells and facilitate beta-cell maturation. For these studies, collagen-1 was entrapped with dissociated pancreatic precursor cells in a PEG hydrogel matrix (PEGCol) with the following key findings: (1) mature, glucose-responsive, islet-like structures differentiated from spontaneously forming precursor cell clusters in PEGCol, but not unmodified PEG, hydrogels; (2) a balance existed between providing sufficient collagen-1 signaling to support precursor cell development and providing an overabundance of adhesive sites allowing contaminating mesenchymal cells to thrive' and (3) mechanical stability provided by the PEG hydrogel platform is important for successful precursor cell culture, as PEGCol hydrogels encourage glucose responsiveness and high-insulin gene expression, while pure collagen gel cultures, with the same collagen concentration, have negligible insulin gene expression. These results indicate that PEGCol hydrogels are a useful culture platform to promote differentiation of a glucose-responsive beta-cell population from dissociated precursor cells.

Collagen Structural Hierarchy and Susceptibility to Degradation by Ultraviolet Radiation

Collagen type I is the most abundant extracellular matrix protein in the human body, providing the basis for tissue structure and directing cellular functions. Collagen has complex structural hierarchy, organized at different length scales, including the characteristic triple helical feature. In the present study, the relationship between collagen structure (native vs. denatured) and sensitivity to UV radiation was assessed, with a focus on changes in primary structure, changes in conformation, microstructure and material properties. A brief review of free radical reactions involved in collagen degradation is also provided as a mechanistic basis for the changes observed in the study. Structural and functional changes in the collagens were related to the initial conformation (native vs. denatured) and the energy of irradiation. These changes were tracked using SDS-PAGE to assess molecular weight, Fourier transform infrared (FTIR) spectroscopy to study changes in the secondary structure, and atomic force microscopy (AFM) to characterize changes in mechanical properties. The results correlate differences in sensitivity to irradiation with initial collagen structural state: collagen in native conformation vs. heat-treated (denatured) collagen. Changes in collagen were found at all levels of the hierarchical structural organization. In general, the native collagen triple helix is most sensitive to UV-254nm radiation. The triple helix delays single chain degradation. The loss of the triple helix in collagen is accompanied by hydrogen abstraction through free radical mechanisms. The results received suggest that the effects of electromagnetic radiation on biologically relevant extracellular matrices (collagen in the present study) are important to assess in the context of the state of collagen structure. The results have implications in tissue remodeling, wound repair and disease progression.

Critical review of clinical trials of bone marrow stem cells in liver disease

Morbidity and mortality from cirrhosis is increasing rapidly in the Western world. Currently the only effective treatment is liver transplantation, an increasingly limited and expensive resource. Consequently, there has been great hope that stem cells may offer new therapeutic approaches in the management of liver disease. In this review we critically appraise the 11 published clinical studies of bone marrow stem cells in liver disease, and focus on the unresolved issues regarding their role. We outline the different mechanisms by which stem cells may impact on liver disease, as well as highlight the importance of the type of stem cell chosen. There are multiple different stem cell populations that have, in rodent studies, been shown to have differing effects on liver regeneration and fibrogenesis/degradation. Thus, choice of cell should reflect the desired or expected mechanism of action. The importance, and methods, of studying the fate of stem cells infused in clinical studies is emphasized as we seek to translate observations in rodents into the clinical setting. Finally, we discuss which cohorts of patients with liver disease would benefit from stem cell therapy, as well as establish minimum criteria for future clinical trials of stem cells.

The role of matrix stiffness in regulating cell behavior

Matrix stiffness (resistance to deformation), one of the many mechanical forces acting on cells, is increasingly appreciated as an important mediator of cell behavior. It regulates cell signaling broadly, with effects on growth, survival, and motility. Although the stiffness optima for different kinds of adherent cells vary widely, it is generally true that cell proliferation and differentiation increase with the stiffness of the matrix. This review summarizes recent data exploring the nature of matrix stiffness, mechanotransducers, and the many effects of changes in stiffness on cell function. Particular mention is made of data suggesting that cells of the liver are mechanosensitive, highlighting the potential importance of these findings in understanding the biology of normal and diseased liver.

Epidermal growth factor potentiates in vitro metastatic behaviour of human prostate cancer PC-3M cells: involvement of voltage-gated sodium channel

Background

Although a high level of functional voltage-gated sodium channel (VGSC) expression has been found in strongly metastatic human and rat prostate cancer (PCa) cells, the mechanism(s) responsible for the upregulation is unknown. The concentration of epidermal growth factor (EGF), a modulator of ion channels, in the body is highest in prostatic fluid. Thus, EGF could be involved in the VGSC upregulation in PCa. The effects of EGF on VGSC expression in the highly metastatic human PCa PC-3M cell line, which was shown previously to express both functional VGSCs and EGF receptors, were investigated. A quantitative approach, from gene level to cell behaviour, was used. mRNA levels were determined by real-time PCR. Protein expression was studied by Western blots and immunocytochemistry and digital image analysis. Functional assays involved measurements of transverse migration, endocytic membrane activity and Matrigel invasion.

Results

Exogenous EGF enhanced the cells' in vitro metastatic behaviours (migration, endocytosis and invasion). Endogenous EGF had a similar involvement. EGF increased VGSC Nav1.7 (predominant isoform in PCa) mRNA and protein expressions. Co-application of the highly specific VGSC blocker tetrodotoxin (TTX) suppressed the effect of EGF on all three metastatic cell behaviours studied.

Conclusion

1) EGF has a major involvement in the upregulation of functional VGSC expression in human PCa PC-3M cells. (2) VGSC activity has a significant intermediary role in potentiating effect of EGF in human PCa.