Emma J. Croager

Oval cell‐mediated liver regeneration: Role of cytokines and growth factors

Abstract   In experimental models, which induce liver damage and simultaneously block hepatocyte proliferation, the recruitment of a hepatic progenitor cell population comprised of oval cells is invariably observed. There is a substantial body of evidence to suggest that oval cells are involved in liver regeneration, as they differentiate into hepatocytes and biliary cells. Recently, bone marrow cells were shown to be a source of a stem cells with the capacity to repopulate the liver. Presently, the relationship between bone marrow cells and oval cells is unclear. Investigations will be greatly assisted by the availability of in vitro models based on a knowledge of cytokines that affect oval cells. While the cytokines, which regulate the different hematopoietic lineages, are well characterized, there is relatively little information regarding those that influence oval cells. This review outlines recent developments in the field of oval cell research and focuses on cytokines and growth factors that have been implicated in regulating oval cell proliferation and differentiation.

Liver inflammation and cytokine production, but not acute phase protein synthesis, accompany the adult liver progenitor (oval) cell response to chronic liver injury

Oval cells are facultative liver progenitor cells, which are invoked during chronic liver injury in order to replenish damaged hepatocytes and bile duct cells. Previous studies have observed inflammation and cytokine production in the liver during chronic injury. Further, it has been proposed that inflammatory growth factors may mediate the proliferation of oval cells during disease progression. We have undertaken a detailed examination of inflammation and cytokine production during a time course of liver injury and repair, invoked by feeding mice a choline‐deficient, ethionine‐supplemented (CDE) diet. We show that immediately following initial liver injury, B220‐expressing leucocytes transiently infiltrate the liver. This inflammatory response occurred immediately before oval cell numbers began to expand in the liver, suggesting that the two events may be linked. Two waves of liver cytokine production were observed during the CDE time course. The first occurred shortly following commencement of the diet, suggesting that it may represent a hepatic acute phase response. However, examination of acute phase marker expression in CDE‐fed mice did not support this hypothesis. The second wave of cytokine expression correlated with the expansion of oval cell numbers in the liver, suggesting that these factors may mediate oval cell proliferation. No inflammatory signalling was detected following withdrawal of the injury stimulus. In summary, our results document a close correlation between inflammation, cytokine production and the expansion of oval cells in the liver during experimental chronic injury.

Involvement of Sp1 and Microsatellite Repressor Sequences in the Transcriptional Control of the Human CD30 Gene

CD30, as a member of the tumor necrosis factor (TNF) receptor family, is expressed on the surface of activated lymphoid cells. CD30 overexpression is a characteristic of lymphoproliferative diseases such as Hodgkins/non-Hodgkins lymphomas, embryonal carcinoma, and a number of Th2-associated diseases. The CD30 gene has been mapped to a region of the murine genome that is involved in susceptibility to systemic lupus erythematosus. Functionally, CD30 may play a role in the deletion of autoreactive T cells. We were interested in determining the molecular nature of CD30 overexpression. Sequence comparison has revealed significant identity between the TATA-less human and murine CD30 promoters; they share a number of common consensus binding motifs. Transfection assays identified three regions of transcriptional importance; the region between position -1.2 kb and -336 bp, containing a CCAT microsatellite sequence, a conserved Sp1 site at positions -43 to -38, and a downstream promoter element (DPE) at positions +24 to +29. EMSA and DNase I footprinting showed specific DNA-protein interactions of the CD30 promoter with the Sp1 site and the CCAT repeat region. The DPE element was shown to be essential for start site selection. We conclude that the conserved Sp1 site at -43 to -38 is associated with maximum reporter gene activity, the DPE element is required for start site selection, and the CCAT tetranucleotide repeats act to repress transcription. We also have shown that the microsatellite is multiallelic, when we screened a random healthy population. Further studies are required to determine whether microsatellite instability in the repressor predisposes susceptible individuals to CD30 overexpression.

Upregulation of lymphotoxin β expression in liver progenitor (oval) cells in chronic hepatitis C

Background: Bipotent liver progenitor (oval) cells with the ability to differentiate into hepatocytes and biliary epithelium have recently been identified in human subjects with hepatitis C. Animal studies suggest that members of the tumour necrosis factor family, including lymphotoxin β (LT-β), regulate oval cell proliferation in liver disease, but its role in human liver disease is unclear. Aims: This study seeks to establish a role for LT-β in hepatitis C related liver injury and to provide evidence that its increased expression is related to the presence of oval cells. Methods: Liver biopsy specimens were obtained from patients with chronic hepatitis C virus (HCV) infection (n=20). Control liver samples (n=5) were obtained from liver resection or transplant surgery. LT-β expression in liver biopsy specimens was studied using quantitative real time polymerase chain reaction and immunohistochemistry. Results: LT-β mRNA levels were similar in control and HCV liver in the absence of fibrosis. In subjects with portal fibrosis, LT-β mRNA levels were elevated 2.2-fold over control liver levels (p=0.04). In subjects with bridging fibrosis, LT-β mRNA levels increased 4.4-fold over control liver levels (p=0.02). LT-β mRNA levels in subjects with established cirrhosis were increased 3.3-fold compared with controls and 2.6-fold compared with mild liver damage (p=0.02). Immunohistochemical analysis established that LT-β was expressed by oval cells, inflammatory cells, and small portal hepatocytes. Conclusions: In chronic HCV infection, LT-β expression is observed in multiple hepatic cell types, including oval cells. LT-β expression is significantly increased when fibrosis or cirrhosis is present, suggesting a role for LT-β in the pathogenesis of chronic hepatitis C and a possible role in oval cell mediated liver regeneration.

Mapping of a candidate region for susceptibility to inclusion body myositis in the human major histocompatibility complex

Abstract Inclusion body myositis (IBM) is a form of idiopathic inflammatory myopathy of unknown aetiology. A strong association with HLA class II (HLA-DR3) suggested a role for genes in the human major histocompatibility complex (MHC) in the predisposition to this disease. In this study, we have taken advantage of the ancestral haplotype (AH) concept and historical recombinations to map for a possible susceptibility gene(s) in the MHC. We performed detailed typing of three MHC-related HSP70 genes and defined allelic combinations in the context of MHC AH. We also modified existing methods to give a simple and accurate method for typing two TNF microsatellites. Using the HSP70 and TNF markers and HLA-DR, –B, and C4 typing of our patients with IBM, we defined a potential site for the MHC-associated susceptibility gene(s) in the region between HLA-DR and C4.