Hepatocyte transplantation: studies in preclinical models

ROCK inhibition enhanced hepatocyte liver engraftment by retaining membrane CD59 and attenuating complement activation

Hepatocyte transplantation can be an effective treatment for patients with certain liver-based metabolic disorders and liver injuries. Hepatocytes are usually infused into the portal vein, from which hepatocytes migrate into the liver and integrate into the liver parenchyma. However, early cell loss and poor liver engraftment represent major hurdles to sustaining the recovery of diseased livers after transplantation. In the present study, we found that ROCK (Rho-associated kinase) inhibitors significantly enhanced in vivo hepatocyte engraftment. Mechanistic studies suggested that the isolation of hepatocytes caused substantial degradation of cell membrane proteins, including the complement inhibitor CD59, probably due to shear stress-induced endocytosis. ROCK inhibition by ripasudil, a clinically used ROCK inhibitor, can protect transplanted hepatocytes by retaining cell membrane CD59 and blocking the formation of the membrane attack complex. Knockdown of CD59 in hepatocytes eliminates ROCK inhibition-enhanced hepatocyte engraftment. Ripasudil can accelerate liver repopulation of fumarylacetoacetate hydrolase-deficient mice. Our work reveals a mechanism underlying hepatocyte loss after transplantation and provides immediate strategies to enhance hepatocyte engraftment by inhibiting ROCK.

C/EBPβ Coupled with E2F2 Promoted the Proliferation of hESC-Derived Hepatocytes through Direct Binding to the Promoter Regions of Cell-Cycle-Related Genes

Human embryonic stem cells (hESCs) hold the potential to solve the problem of the shortage of functional hepatocytes in clinical applications and drug development. However, a large number of usable hepatocytes derived from hESCs cannot be effectively obtained due to the limited proliferation capacity. In this study, we found that enhancement of liver transcription factor C/EBPβ during hepatic differentiation could not only significantly promote the expression of hepatic genes, such as albumin, alpha fetoprotein, and alpha-1 antitrypsin, but also dramatically reinforce proliferation-related phenotypes, including increasing the expression of proliferative genes, such as CDC25C, CDC45L, and PCNA, and the activation of cell cycle and DNA replication pathways. In addition, the analysis of CUT&Tag sequencing further revealed that C/EBPβ is directly bound to the promoter region of proliferating genes to promote cell proliferation; this interaction between C/EBPβ and DNA sequences of the promoters was verified by luciferase assay. On the contrary, the knockdown of C/EBPβ could significantly inhibit the expression of the aforementioned proliferative genes. RNA transcriptome analysis and GSEA enrichment indicated that the E2F family was enriched, and the expression of E2F2 was changed with the overexpression or knockdown of C/EBPβ. Moreover, the results of CUT&Tag sequencing showed that C/EBPβ also directly bound the promoter of E2F2, regulating E2F2 expression. Interestingly, Co-IP analysis exhibited a direct binding between C/EBPβ and E2F2 proteins, and this interaction between these two proteins was also verified in the LO2 cell line, a hepatic progenitor cell line. Thus, our results demonstrated that C/EBPβ first initiated E2F2 expression and then coupled with E2F2 to regulate the expression of proliferative genes in hepatocytes during the differentiation of hESCs. Therefore, our findings open a new avenue to provide an in vitro efficient approach to generate proliferative hepatocytes to potentially meet the demands for use in cell-based therapeutics as well as for pharmaceutical and toxicological studies.

Successful Derivation of Hepatoblasts, Cholangiocytes and Hepatocytes from Simian Induced Pluripotent Stem Cells

The use of primary cells in human liver therapy is limited by a lack of cells. Induced pluripotent stem cells (iPSCs) represent an alternative to primary cells as they are infinitely expandable and can be differentiated into different liver cell types. The aim of our work was to demonstrate that simian iPSCs (siPSCs) could be used as a new source of liver cells to be used as a large animal model for preclinical studies. We first differentiated siPSCs into a homogenous population of hepatoblasts (siHBs). We then separately differentiated them into hepatocytes (siHeps) and cholangiocytes (siChols) expressing respective specific markers and displaying epithelial polarity. Moreover, we showed that polarized siChols can self-organize into 3D structures. These results should facilitate the deciphering of liver development and open the way to exploring co-culture systems that could be assessed during preclinical studies, including in autologous monkey donors, for regenerative medicine purposes.

In vitro recovery of FIX clotting activity as a marker of highly functional hepatocytes in a hemophilia B iPSC model

BACKGROUND AND AIMS

Pluripotent stem cell-derived hepatocytes differentiated in monolayer culture are known to have more fetal than adult hepatocyte characteristics. If numerous studies tend to show that this immature phenotype might not necessarily be an obstacle to their use in transplantation, other applications such as drug screening, toxicological studies, or bioartificial livers are reliant on hepatocyte functionality and require full differentiation of hepatocytes. New technologies have been used to improve the differentiation process in recent years, usually evaluated by measuring the albumin production and CYP450 activity. Here we used the complex production and most importantly the activity of the coagulation factor IX (FIX) produced by mature hepatocytes to assess the differentiation of hemophilia B (HB) patient's induced pluripotent stem cells (iPSCs) in both monolayer culture and organoids.

APPROACH AND RESULTS

Indeed, HB is an X-linked monogenic disease due to an impaired activity of FIX synthesized by hepatocytes in the liver. We have developed an in vitro model of HB hepatocytes using iPSCs generated from fibroblasts of a severe HB patient. We used CRISPR/Cas9 technology to target the genomic insertion of a coagulation factor 9 minigene bearing the Padua mutation to enhance FIX activity. Noncorrected and corrected iPSCs were differentiated into hepatocytes under both two-dimensional and three-dimensional differentiation protocols and deciphered the production of active FIX in vitro. Finally, we assessed the therapeutic efficacy of this approach in vivo using a mouse model of HB.

CONCLUSIONS

Functional FIX, whose post-translational modifications only occur in fully mature hepatocytes, was only produced in corrected iPSCs differentiated in organoids. Immunohistochemistry analyses of mouse livers indicated a good cell engraftment, and the FIX activity detected in the plasma of transplanted animals confirmed rescue of the bleeding phenotype.

Maintenance of Primary Hepatocyte Functions In Vitro by Inhibiting Mechanical Tension-Induced YAP Activation

Hepatocytes are the primary functional cells of the liver, performing its metabolic, detoxification, and endocrine functions. Functional hepatocytes are extremely valuable in drug discovery and evaluation, as well as in cell therapy for liver diseases. However, it has been a long-standing challenge to maintain the functions of hepatocytes in vitro. Even freshly isolated hepatocytes lose essential functions after short-term culture for reasons that are still not well understood. In the present study, we find that mechanical tension-induced yes-associated protein activation triggers hepatocyte dedifferentiation. Alleviation of mechanical tension by confining cell spreading is sufficient to inhibit hepatocyte dedifferentiation. Based on this finding, we identify a small molecular cocktail through reiterative chemical screening that can maintain hepatocyte functions over the long term and in vivo repopulation capacity by targeting actin polymerization and actomyosin contraction. Our work reveals the mechanisms underlying hepatocyte dedifferentiation and establishes feasible approaches to maintain hepatocyte functions.

Transplantation speed offers early hepatocyte engraftment in acute liver injured rats: A translational study with clinical implications

The impact of the rate of intraportal hepatocyte transplantation on early engraftment and repopulation is unclear. The aim of this study was to address this and to improve the engraftment and repopulation efficiencies of hepatocyte transplantation for the treatment of a rat model of acute liver failure in a clinically useful way without preconditioning. Acute hepatic injury was induced into Sprague-Dawley rats with D-galactosamine. Hepatocytes were infused intraportally over a period of 30, 70, or 100 seconds to study early engraftment (2 days) and repopulation (7 days). Three groups had significant differences in hepatocyte engraftment (P = 0.018) and repopulation efficiencies (P = 0.037), and an infusion over a period of 70 seconds produced superior outcomes. After the 70-second infusion, the transplanted cells immediately transmigrated the sinusoidal endothelial layer and rarely accumulated in the portal venules, with liver function improving significantly. The mean first peak pressures, without significant differences, were 14.8 ± 6.5, 17.7 ± 3.7, and 13.6 ± 3.0 mm Hg in the 30-, 70-, and 100-second groups, respectively. Differential hepatocyte transfusion rates contributed to accelerated early engraftment and repopulation in rats with acute liver injury. These proof-of-concept findings are of clinical significance because they are easy to translate into practice.

Three-dimensional culture in a microgravity bioreactor improves the engraftment efficiency of hepatic tissue constructs in mice

Tissue-engineered liver using primary hepatocytes has been considered a valuable new therapeutic modality as an alternative to whole organ liver transplantation for different liver diseases. The development of clinically feasible liver tissue engineering approaches, however, has been hampered by the poor engraftment efficiency of hepatocytes. We developed a three-dimensional (3D) culture system using a microgravity bioreactor (MB), biodegradable scaffolds and growth-factor-reduced Matrigel to construct a tissue-engineered liver for transplantation into the peritoneal cavity of non-obese diabetic severe combined immunodeficient mice. The number of viable cells in the hepatic tissue constructs was stably maintained in the 3D MB culture system. Hematoxylin-eosin staining and zonula occludens-1 expression revealed that neonatal mouse liver cells were reorganized to form tissue-like structures during MB culture. Significantly upregulated hepatic functions (albumin secretion, urea production and cytochrome P450 activity) were observed in the MB culture group. Post-transplantation analysis indicated that the engraftment efficiency of the hepatic tissue constructs prepared in MB cultures was higher than that of those prepared in the static cultures. Higher level of hepatic function in the implants was confirmed by the expression of albumin. These findings suggest that 3D MB culture systems may offer an improved method for creating tissue-engineered liver because of the higher engraftment efficiency and the reduction of the initial cell function loss.

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.

The future of cell transplant therapies: a need for tissue grafting

Current methodologies of solid organ-derived cell transplant therapies introduce donor cells into hosts through a vascular route, a strategy modeled after hematopoietic therapies. These strategies fail because of inefficient engraftment, poor survival of the cells, and propensity for formation of life-threatening emboli. Transplant success necessitates grafting methods, requiring a mixture of appropriate cell sources embedded into or onto precise mixes of extracellular matrix components and then localized to the diseased or dysfunctional tissue, promoting necessary proliferation, engraftment, and vascularization. Grafting technologies are rapidly translatable to therapeutic uses in patients and provide alternative treatments for regenerative medicine.

Pluripotent plasticity of stem cells and liver repopulation

Different types of stem cells have a role in liver regeneration or fibrous repair during and after several liver diseases. Otherwise, the origin of hepatic and/or extra-hepatic stem cells in reactive liver repopulation is under controversy. The ability of the human body to self-repair and replace the cells and tissues of some organs is often evident. It has been estimated that complete renewal of liver tissue takes place in about a year. Replacement of lost liver tissues is accomplished by proliferation of mature hepatocytes, hepatic oval stem cells differentiation, and sinusoidal cells as support. Hepatic oval cells display a distinct phenotype and have been shown to be a bipotential progenitor of two types of epithelial cells found in the liver, hepatocytes, and bile ductular cells. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy, and acute or chronic hepatopaties. In the future, pluripotent plasticity of stem cells will open a variety of clinical application strategies for the treatment of tissue injuries, degenerated organs. The promise of liver stem cells lie in their potential to provide a continuous and readily available source of liver cells that can be used for gene therapy, cell transplant, bio-artificial liver-assisted devices, drug toxicology testing, and use as an in vitro model to understand the developmental biology of the liver.

Hepatocyte transplantation techniques: large animal models

The poor hepatocyte engraftment efficiency and the low level of their expansion in the host liver are a major limitation to cell therapy for the treatment of life-threatening liver diseases. Many rodent models have shown that liver repopulation via transplanted hepatocytes occurs only when liver growth capacity is impaired for an extended period of time. However, these models are not transposable to the clinics and to date there is no safe method to achieve this result in a clinical setting.Therefore, it is necessary to define on large animal models strategies that provide to transplanted hepatocytes sufficient proliferation stimuli to induce their division and that could permit a direct extrapolation to humans. Such procedures should be transposable to patients. We have defined a protocol of liver partial portal branch embolisation and shown that it induces the proliferation of transplanted hepatocytes in non-human primates (Macaca mulatta). This animal model is also appropriate to evaluate the lentiviral-mediated ex vivo gene therapy approach, since simian hepatocytes are efficiently transduced by HIV-1-derived lentivirus vectors.

Proliferation of Hepatocyte Progenitor Cells Isolated from Adult Human Livers in Serum-Free Medium

Rat small hepatocytes (SHs) are committed progenitor cells that can differentiate into mature hepatocytes and can selectively proliferate in serum-free medium when they are cultured on hyaluronic acid (HA)-coated dishes. In this study we examined the separation of human SHs from adult human livers. We obtained liver tissues from the resected liver of 16 patients who underwent hepatic resections. Extracted liver specimens were clearly separate from the tumor regions with sufficient margins. Hepatic cells were isolated using the modified method of two-step collagenase perfusion. A low-speed centrifugation was performed and cells in the supernatant were finally cultured on HA-coated dishes in serum-free DMEM/F12 medium including nicotinamide, EGF, and HGF. Small-sized hepatocytes selectively proliferated to form colonies and many colonies continued growing for more than 3 weeks. The average number of cells in a colony was 38.6 ± 18.0, 79.0 ± 54.0, and 101.5 ± 115.7 at day 7, 14, and 21, respectively. About 0.04% of plated cells could form an SH colony. Immunocytochemistry showed that the cells forming a colony were positive for albumin, transferrin, keratin 8, and CD44. The results of RT-PCR showed that colony-forming cells expressed albumin, transferrin, α1-antitrypsin, fibrinogen, glutamine synthetase, many cytochrome P450s, and liver-enriched transcription factors (HNF3α, HNF4α, C/EBPα, and C/EBPβ). Furthermore, the cells expressed not only the genes of hepatic differentiated functions but also those of both hepatic stem cell marker (Thy1.1, EpCAM, AFP) and SH marker (CD44, D6.1A, BRI3). Albumin secretion into culture medium was also observed. Our results demonstrate the existence of hepatocyte progenitor cells in human adult livers, and the cells can grow in a serum-free medium on HA-coated dishes. Human SHs may be a useful source for cell transplantation as well as pharmaceutical and toxicological investigations.

Liver regeneration and recanalization time course following reversible portal vein embolization

BACKGROUND/AIMS

Permanent portal vein embolization (PVE) is a widely practised technique. The use of an absorbable material would be safer in clinical situations in which the embolized liver is not resected. We evaluated the efficiency of reversible PVE in terms of liver regeneration and analyzed the precise time course of portal recanalization.

METHODS

Nine monkeys underwent PVE of the left and right anterior portal branches using powdered absorbable material. Repeated portograms were carried out until complete revascularization of the embolized liver. Hepatocyte proliferation rates were assessed by BrdU incorporation. Liver segment volumes were determined by CT scans performed before embolization, then 1 month and 1 year after embolization.

RESULTS

Reversible PVE induced significant hepatocyte proliferation in the non-embolized segments (13.5+/-1.0%, 10.5+/-0.8% and 9.1+/-2.0% of cells on days 3, 5 and 7, respectively). One month after the embolization, the non-embolized liver volume had increased from 38.4+/-1.3% to 54.8+/-0.5% of total liver volume. Proximal and complete revascularization occurred 6-8 and 12-16 days, respectively.

CONCLUSIONS

Reversible PVE efficiently induces liver regeneration. The use of absorbable material avoids long-term liver scarring. Such material may be suitable for several clinical indications, including cell transplantation.