Norihisa Ichinohe

Sry HMG Box Protein 9-positive (Sox9+) Epithelial Cell Adhesion Molecule-negative (EpCAM−) Biphenotypic Cells Derived from Hepatocytes Are Involved in Mouse Liver Regeneration

Background: Biphenotypic hepatocytes expressing Sox9 emerge upon liver injuries associated with ductular reaction. Results: Sox9+ biphenotypic hepatocytes are derived from mature hepatocytes (MHs). Some of them are incorporated into ductular structures, whereas they efficiently differentiate to functional hepatocytes. Conclusion: Biphenotypic hepatocytes not only terminally convert to cholangiocytes but also differentiate back to MHs. Significance: Mature epithelial cells can show plasticity upon severe injuries and contribute to regeneration. It has been shown that mature hepatocytes compensate tissue damages not only by proliferation and/or hypertrophy but also by conversion into cholangiocyte-like cells. We found that Sry HMG box protein 9-positive (Sox9+) epithelial cell adhesion molecule-negative (EpCAM−) hepatocyte nuclear factor 4α-positive (HNF4α+) biphenotypic cells showing hepatocytic morphology appeared near EpCAM+ ductular structures in the livers of mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet. When Mx1-Cre:ROSA mice, which were injected with poly(I:C) to label mature hepatocytes, were fed with the DDC diet, we found LacZ+Sox9+ cells near ductular structures. Although Sox9+EpCAM− cells adjacent to expanding ducts likely further converted into ductular cells, the incidence was rare. To know the cellular characteristics of Sox9+EpCAM− cells, we isolated them as GFP+EpCAM− cells from DDC-injured livers of Sox9-EGFP mice. Sox9+EpCAM− cells proliferated and could differentiate to functional hepatocytes in vitro. In addition, Sox9+EpCAM− cells formed cysts with a small central lumen in collagen gels containing Matrigel® without expressing EpCAM. These results suggest that Sox9+EpCAM− cells maintaining biphenotypic status can establish cholangiocyte-type polarity. Interestingly, we found that some of the Sox9+ cells surrounded luminal spaces in DDC-injured liver while they expressed HNF4α. Taken together, we consider that in addition to converting to cholangiocyte-like cells, Sox9+EpCAM− cells provide luminal space near expanded ductular structures to prevent deterioration of the injuries and potentially supply new hepatocytes to repair damaged tissues.

Bone Regeneration Using Titanium Nonwoven Fabrics Combined with FGF-2 Release from Gelatin Hydrogel Microspheres in Rabbit Skull Defects

The objective of this study was to modify titanium nonwoven fabrics (Ti) with a hydroxyapatite (HA)-like coating and fibroblast growth factor (FGF)-2 combination, and evaluate the bone regeneration potential of the modified Ti. Biodegradable gelatin hydrogel microspheres (GM) were prepared as a carrier matrix for the controlled release of FGF-2. Ti, HA-coated Ti (Ti-HA), and Ti-HA incorporating GM (Ti-HA-GM) infused FGF-2 were applied to skull defects of rabbits. Then osteointegration in the Ti was evaluated by alkaline phosphatase activity, Ca(2+) content, and histological observation, and the hemoglobin content was assessed for angiogenic measurement. Ti-HA-GM promoted bone regeneration to a significantly greater extent than Ti, Ti-HA, or mixed Ti-HA and free FGF-2 6 weeks after application, and it also enhanced the hemoglobin content. It is concluded that the combination of HA-like coating and FGF-2 release promotes Ti induction of bone regeneration.

Thy1-Positive Cells Have Bipotential Ability to Differentiate into Hepatocytes and Biliary Epithelial Cells in Galactosamine-Induced Rat Liver Regeneration

In galactosamine (GalN)-induced rat liver injury, hepatic stem/progenitor cells, small hepatocytes (SHs) and oval cells, transiently appear in the initial period of liver regeneration. To clarify the relationship between SHs and oval cells, CD44(+) and Thy1(+) cells were sorted from GalN-treated livers and used as candidates for SHs and oval cells, respectively. Some Thy1(+) cells isolated 3 days after GalN-treatment (GalN-D3) formed CD44(+) cell colonies, but those from GalN-D2 could form few. GeneChip (Affymetrix, Inc, Santa Clara, CA) analysis of the sorted cells and cultured Thy1(+) cells suggested that hepatocytic differentiation progressed in the order Thy1(+) (GalN-D3), Thy1(+) cell colony (Thy1-C), and CD44(+) (GalN-D4) cells. When Thy1(+), Thy1-C, and CD44(+) cells were transplanted into retrorsine/PH rat livers, they could proliferate to form hepatocytic foci. At 30 days after transplantation most cells forming the foci derived from CD44(+) cells possessed C/EBPalpha(+) nuclei, whereas only a few cells derived from Thy1-C showed this positivity. When Thy1(+) (GalN-D3) cells were cultured between collagen gels in medium with hepatocyte growth factor(+)/dexamethasone(-)/dimethyl sulfoxide(-), ducts/cysts consisting of biliary epithelial cells appeared, whereas with CD44(+) and Thy1(+) (GalN-D2) cells they did not. Taken together, these results indicate that the commitment of Thy1(+) cells to differentiate into hepatocytes or biliary epithelial cells may occur between Day 2 and Day 3. Furthermore, some Thy1(+) cells may differentiate into hepatocytes via CD44(+) SHs.

Downregulation of miR122 by grainyhead-like 2 restricts the hepatocytic differentiation potential of adult liver progenitor cells

Late fetal and adult livers are reported to contain bipotential liver stem/progenitor cells (LPCs), which share surface markers, including epithelial cell adhesion molecule (EpCAM), with cholangiocytes and differentiate into both hepatocytes and cholangiocytes. However, recent results do not necessarily support the idea that LPCs contribute significantly to cellular turnover and regeneration by supplying new hepatocytes. Here, we examined the colony-forming capability of EpCAM+ cells isolated from mouse livers between E17 and 11 weeks of age. We found that the number of bipotential colonies was greatly reduced between 1 and 6 weeks, indicating that the number of LPCs decreases during postnatal development. Moreover, bipotential colonies derived from adult LPCs contained substantially fewer albumin+ cells than those from neonatal LPCs. We further examined the differentiation potential of neonatal and adult LPCs by transplantation and found that neonatal cells differentiated into mature hepatocytes in recipient livers more frequently than adult LPCs. Since we previously reported that the transcription factor grainyhead-like 2 (GRHL2) expressed in EpCAM+ cells inhibits hepatocytic differentiation, we examined whether targets of GRHL2 might block hepatocytic differentiation. DNA and microRNA microarrays revealed that miR122, the expression of which correlates with hepatocytic differentiation, was greatly reduced in adult as compared with neonatal EpCAM+ cells. Indeed, GRHL2 negatively regulates the promoter/enhancer activity of the Mir122 gene. Our results indicate that neonatal but not adult EpCAM+ LPCs have great potential to produce albumin+ hepatocytes. GRHL2 suppresses transcription of miR122 and thereby restricts the differentiation potential of adult LPCs.

Proliferation, Osteogenic Differentiation, and Distribution of Rat Bone Marrow Stromal Cells in Nonwoven Fabrics by Different Culture Methods

The proliferation, osteogenic differentiation, and distribution patterns of stromal cells from rat bone marrow were investigated in a three-dimensional nonwoven fabric of polyethylene terephthalate fiber by the static, agitated, and stirred culture methods; stirring speeds were 10, 50, and 100 rpm in the stirred culture method. The culture method affected the time profile of proliferation and osteogenic differentiation of cells or their distribution in the fabric. The extent of cell proliferation and osteogenic differentiation became higher in order of the stirred at 100 rpm = the stirred at 50 rpm > the stirred at 10 rpm > the agitated > the static methods. In addition, the cells were more uniformly proliferated in the fabric by the stirred culture method with time than they were proliferated in the fabric by other methods. The alkaline phosphatase (ALP) activity and calcium content were higher for cells cultured by the stirred culture method than those cultured by other methods. The total ALP activity, calcium content, and bone mineral density were higher for every stirred method than those for other methods. However, the distribution uniformity of cells differentiated was low irrespective of the culture method. It is concluded that the extent of proliferation and differentiation of cells or their distribution uniformity in the nonwoven fabrics was influenced by the culture method.

Differentiation capacity of hepatic stem/progenitor cells isolated from D-galactosamine-treated rat livers.

Oval cells and small hepatocytes (SHs) are known to be hepatic stem and progenitor cells. Although oval cells are believed to differentiate into mature hepatocytes (MHs) through SHs, the details of their differentiation process are not well understood. Furthermore, it is not certain whether the induced cells possess fully mature functions as MHs. In the present experiment, we used Thy1 and CD44 to isolate oval and progenitor cells, respectively, from D‐galactosamine‐treated rat livers. Epidermal growth factor, basic fibroblast growth factor, or hepatocyte growth factor could trigger the hepatocytic differentiation of sorted Thy1+ cells to form epithelial cell colonies, and the combination of the factors stimulated the emergence and expansion of the colonies. Cells in the Thy1+‐derived colonies grew more slowly than those in the CD44+‐derived ones in vitro and in vivo and the degree of their hepatocytic differentiation increased with CD44 expression. Although the induced hepatocytes derived from Thy1+ and CD44+ cells showed similar morphology to MHs and formed organoids from the colonies similar to those from SHs, many hepatic differentiated functions of the induced hepatocytes were less well performed than those of mature SHs derived from the healthy liver. The gene expression of cytochrome P450 1A2, tryptophan 2,3‐dioxygenase, and carbamoylphosphate synthetase I was lower in the induced hepatocytes than in mature SHs. In addition, the protein expression of CCAAT/enhancer‐binding protein alpha and bile canalicular formation could not reach the levels of production of mature SHs. Conclusion: The results suggest that, although Thy1+ and CD44+ cells are able to differentiate into hepatocytes, the degree of maturation of the induced hepatocytes may not be equal to that of healthy resident hepatocytes. (HEPATOLOGY 2013)

Growth Ability and Repopulation Efficiency of Transplanted Hepatic Stem Cells, Progenitor Cells, and Mature Hepatocytes in Retrorsine-Treated Rat Livers:

Cell-based therapies as an alternative to liver transplantation have been anticipated for the treatment of potentially fatal liver diseases. Not only mature hepatocytes (MHs) but also hepatic stem/progenitor cells are considered as candidate cell sources. However, whether the stem/progenitor cells have an advantage to engraft and repopulate the recipient liver compared with MHs has not been comprehensively assessed. Therefore, we used Thy1+ (oval) and CD44+ (small hepatocytes) cells isolated from GalN-treated rat livers as hepatic stem and progenitor cells, respectively. Cells from dipeptidylpeptidase IV (DPPIV)+ rat livers were transplanted into DPPIV” livers treated with retrorsine following partial hepatectomy. Both stem and progenitor cells could differentiate into hepatocytes in host livers. In addition, the growth of the progenitor cells was faster than that of MHs until days 14. However, their repopulation efficiency in the long term was very low, since the survival period of the progenitor cells was much shorter than that of MHs. Most foci derived from Thy1+ cells disappeared within 2 months. Many cells expressed senescence-associated β-galactosidase in 33% of CD44-derived foci at day 60, whereas the expression was observed in 13% of MH-derived ones. The short life of the cells may be due to their cellular senescence. On the other hand, the incorporation of sinusoidal endothelial cells into foci and sinusoid formation, which might be correlated to hepatic maturation, was completed faster in MH-derived foci than in CD44-derived ones. The survival of donor cells may have a close relation to not only early integration into hepatic plates but also the differentiated state of the cells at the time of transplantation.

Intrahepatic bile ducts are developed through formation of homogeneous continuous luminal network and its dynamic rearrangement in mice

The intrahepatic bile duct (IHBD) is a highly organized tubular structure consisting of cholangiocytes, biliary epithelial cells, which drains bile produced by hepatocytes into the duodenum. Although several models have been proposed, it remains unclear how the three‐dimensional (3D) IHBD network develops during liver organogenesis. Using 3D imaging techniques, we demonstrate that the continuous luminal network of IHBDs is established by 1 week after birth. Beyond this stage, the IHBD network consists of large ducts running along portal veins (PVs) and small ductules forming a mesh‐like network around PVs. By analyzing embryonic and neonatal livers, we found that newly differentiated cholangiocytes progressively form a continuous and homogeneous luminal network. Elongation of this continuous network toward the liver periphery was attenuated by a potent Notch‐signaling inhibitor N‐[N‐(3,5‐difluorophenacetyl)‐L‐alanyl]‐S‐phenylglycine t‐butyl ester. Subsequent to this first step, the fine homogenous network is reorganized into the mature hierarchical network consisting of large ducts and small ductules. Between E17 and E18, when the homogenous network is radically reorganized into the mature hierarchical network, bile canaliculi rapidly extend and bile flow into IHBDs may increase. When formation of bile canaliculi was blocked between E16 and E18 by a multidrug resistance protein 2 inhibitor (benzbromarone), the structural rearrangement of IHBDs was significantly suppressed. Conclusion: Establishment of the mature IHBD network consists of two sequential events: (1) formation of the continuous luminal network regulated by the Notch‐signaling pathway and (2) dynamic rearrangement of the homogeneous network into the hierarchical network induced by increased bile flow resulting from the establishment of hepatobiliary connections. (Hepatology 2016;64:175–188)

Proliferation of rat small hepatocytes requires follistatin expression.

Small hepatocytes (SHs) are a subpopulation of hepatocytes that have high growth potential in culture and can differentiate into mature hepatocytes (MHs). The activin (Act)/follistatin (Fst) system critically contributes to homeostasis of cell growth in the normal liver. ActA and ActB consist of two disulfide‐linked Inhibin (Inh)β subunits, InhβA and InhβB, respectively. Fst binds to Act and blocks its bioactivity. In the present study we carried out the experiments to clarify how Fst regulates the proliferation of SHs. The gene expression was analyzed using DNA microarray analysis, reverse transcription‐polymerase chain reaction (RT‐PCR) and real‐time PCR, and protein expression was examined by western blots, immunocytochemistry, and enzyme‐linked immunosorbent assay. RT‐PCR showed that Fst expression was high in SHs and low in MHs. Although the ActA expression was opposite to that of Fst, ActB expression was high in SHs and low in MHs and increased with time in culture. Fst protein was detected in the cytoplasm of SHs and secreted into the culture medium. ActB protein was also secreted into the medium. Although the exogenous administration of ActA and ActB apparently suppressed the proliferation of SHs, apoptosis of SHs was not induced by treatment with ActA or ActB. On the other hand, Fst treatment did not affect the colony formation of SHs but prevented the inhibitory effect of ActA. Neutralization by the anti‐Fst antibody resulted in the suppression of DNA synthesis in SHs, and small hairpin RNA against Fst suppressed the expansion of SH colonies. In conclusion, Fst expression is necessary for the proliferation of SHs. J. Cell. Physiol. 227: 2363–2370, 2012.

Liver Progenitors Isolated from Adult Healthy Mouse Liver Efficiently Differentiate to Functional Hepatocytes In Vitro and Repopulate Liver Tissue

It has been proposed that tissue stem cells supply multiple epithelial cells in mature tissues and organs. However, it is unclear whether tissue stem cells generally contribute to cellular turnover in normal healthy organs. Here, we show that liver progenitors distinct from bipotent liver stem/progenitor cells (LPCs) persistently exist in mouse livers and potentially contribute to tissue maintenance. We found that, in addition to LPCs isolated as EpCAM+ cells, liver progenitors were enriched in CD45−TER119−CD31−EpCAM−ICAM‐1+ fraction isolated from late‐fetal and postnatal livers. ICAM‐1+ liver progenitors were abundant by 4 weeks (4W) after birth. Although their number decreased with age, ICAM‐1+ liver progenitors existed in livers beyond that stage. We established liver progenitor clones derived from ICAM‐1+ cells between 1 and 20W and found that those clones efficiently differentiated into mature hepatocytes (MHs), which secreted albumin, eliminated ammonium ion, stored glycogen, and showed cytochrome P450 activity. Even after long‐term culture, those clones kept potential to differentiate to MHs. When ICAM‐1+ clones were transplanted into nude mice after retrorsine treatment and 70% partial hepatectomy, donor cells were incorporated into liver plates and expressed hepatocyte nuclear factor 4α, CCAAT/enhancer binding protein α, and carbamoylphosphate synthetase I. Moreover, after short‐term treatment with oncostatin M, ICAM‐1+ clones could efficiently repopulate the recipient liver tissues. Our results indicate that liver progenitors that can efficiently differentiate to MHs exist in normal adult livers. Those liver progenitors could be an important source of new MHs for tissue maintenance and repair in vivo, and for regenerative medicine ex vivo. Stem Cells 2016;34:2889–2901