Additivity of the proliferative effects of HGF/SF and EGF on hepatocytes

Norepinephrine modulates the zonally different hepatocyte proliferation through the regulation of transglutaminase activity

A neurotransmitter, norepinephrine (NE), amplifies the mitogenic effect of epidermal growth factor (EGF) in the liver by acting on the alpha(1)-adrenergic receptor coupled with G protein, Galpha(h). However, the molecular mechanism is not well understood. Galpha(h) is known as a transglutaminase 2 (TG2), a cross-linking enzyme implicated in hepatocyte proliferation. We investigated the effect of NE on EGF-induced cell proliferation and TG2 activity using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in proliferative capacity. Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) were isolated by the digitonin-collagenase perfusion technique. EGF or NE receptor binding was analyzed by Scatchard analysis. Changes in NE-induced DNA synthesis, EGF receptor (EGFR) dimerization and phosphorylation, and TG2 activity were measured. NE enhanced EGF-induced DNA synthesis, EGF-induced EGFR dimerization, and its phosphorylation in PVH but not in PPH. [(3)H]NE binding studies indicated that PVH was found to have a greater affinity and number of receptors than PPH. Furthermore, NE treatment decreased TG2 activity and increased phospholipase C activity in PVH although TG2 level showed no change. These results suggest that NE-induced amplification of EGF-induced DNA synthesis especially in PVH is caused by upregulation of EGFR activation through the switching of function from TG2 to Galpha(h).

Effect of aging on EGF-induced proliferative response in primary cultured periportal and perivenous hepatocytes

BACKGROUND/AIMS

Aging relates to declined proliferative capacity of the liver, but the molecular mechanism is not well understood. We examined whether functional changes of epidermal growth factor (EGF) receptor (EGFR) are involved in age-related decline in EGF-induced DNA synthesis using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in the proliferative capacity.

METHODS

Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) in 7-, 30-, and 90-week-old rats were isolated using the digitonin/collagenase perfusion technique. DNA synthesis was assessed by [methyl-(3)H]thymidine incorporation. EGFR binding affinity to EGF was analyzed by Scatchard analysis using [(125)I]EGF. EGFR dimerization and phosphorylation were determined by Western blot analysis.

RESULTS

EGF-induced DNA synthesis was greater in PPH than in PVH from rats of 7 weeks, but the zonal difference disappeared with aging. [(125)I]EGF binding studies indicated that high-affinity EGFR in both subpopulations also disappeared with aging. Furthermore, EGF-induced dimerization in both subpopulations was down-regulated with aging, and the pattern of EGFR phosphorylation was parallel to that of dimerization.

CONCLUSIONS

These data suggest that age-related decline in EGF-induced DNA synthesis of PPH and PVH is caused by down-regulation of EGFR dimerization through the decrease of high-affinity EGFR.

Tissue assembly guided via substrate biophysics: applications to hepatocellular engineering

The biophysical nature of the cellular microenvironment, in combination with its biochemical properties, can critically modulate the outcome of three-dimensional (3-D) multicellular morphogenesis. This phenomenon is particularly relevant for the design of materials suitable for supporting hepatocellular cultures, where cellular morphology is known to be intimately linked to the functional output of the cells. This review summarizes recent work describing biophysical regulation of hepatocellular morphogenesis and function and focuses on the manner by which biochemical cues can concomitantly augment this responsiveness. In particular, two distinct design parameters of the substrate biophysics are examined--microtopography and mechanical compliance. Substrate microtopography, introduced in the form of increasing pore size on collagen sponges and poly(glycolic acid) (PGLA) foams, was demonstrated to restrict the evolution of cellular morphogenesis to two dimensions (subcellular and cellular void sizes) or induce 3-D cellular assembly (supercellular void size). These patterns of morphogenesis were additionally governed by the biochemical nature of the substrate and were highly correlated to resultant levels of cell function. Substrate mechanical compliance, introduced via increased chemical crosslinking of the basement membrane, Matrigel, and polyacrylamide gel substrates, also was shown to be able to induce active two-dimensional (2-D, rigid substrates) or 3-D (malleable substrates) cellular reorganization. The extent of morphogenesis and the ensuing levels of cell function were highly dependent on the biochemical nature of the cellular microenvironment, including the presence of increasing extracellular matrix (ECM) ligand and growth-factor concentrations. Collectively, these studies highlight not only the ability of substrate biophysics to control hepatocellular morphogenesis but also the ability of biochemical cues to further enhance these effects. In particular, results of these studies reveal novel means by which hepatocellular morphogenesis and assembly can be rationally manipulated leading to the strategic control of the expression of liver-specific functions for hepatic tissue-engineering applications.

Effect of interferon alpha2b plus ribavirin treatment on selected growth factors in respect to inflammation and fibrosis in chronic hepatitis C

AIM: Growth factors (GF) that participate in regeneration and apoptosis have an important role in chronic liver diseases. We analyzed serum GF concentration during antiviral treatment and correlated it with morphological liver failure in chronic hepatitis C.

METHODS: The levels of GF were determined in sera by ELISA method in 0, 16, 32 and 48 wk of therapy in 40 patients treated with IFNα2b (9 MU sc/wk) and RBV (1.2 g/d) and in 25 healthy subjects. Blind liver biopsies were done before treatment with histological grading and staging examination.

RESULTS: The hepatocyte growth factor (HGF) and epidermal growth factor (EGF) were markedly elevated prior the treatment and decreased during the therapy, although they did not reach the normal level. In non-responding (NR) patients, HGF and EGF were higher than that in responders (R), however differences were not significant. Before the treatment thrombopoietin (TPO) level was significantly lower in R than in NR (P<0.03). Platelet-derived growth factor (PDGF) concentration was lower in chronic hepatitis C than in healthy subjects and decreased during the treatment. A significant positive correlation was observed between inflammatory activity in the liver tissue and the concentration of HGF (in R: r = 0.4, in NR: r = 0.5), TPO (R: r = 0.6), and a significant negative correlation between this activity and EGF (R: r = -0.6) and PDGF (R: r = -0.5). Serum HGF concentration was higher in more advanced fibrosis (R: r = 0.5, P<0.05; NR: r = 0.4, P<0.03).

CONCLUSION: The decrease in PDGF can be an effective prognostic marker of the treatment and HCV elimination. Decreasing HGF, EGF, and PDGF can influence the inhibition of inflammatory and fibrotic processes in the liver during the antiviral treatment.

Zonal Differences in DNA Synthesis and in Transglutaminase Activity between Perivenous versus Periportal Regions of Regenerating Rat Liver

We investigated a relationship within zonal differences in DNA synthesis and in transglutaminase (TGase) activity between perivenous versus periportal regions of regenerating rat liver. Using the digitonin/collagenase perfusion technique, hepatocyte subpopulations were isolated from each region at various time points after partial hepatectomy. The amounts of DNA synthesis as well as the levels of TGase mRNA and activity in each subpopulation were measured. Although increased DNA synthesis was observed in both subpopulations with a peak at 24 h after partial hepatectomy, the amount of DNA synthesis in periportal hepatocytes (PPH) was twice as much as that in perivenous hepatocytes (PVH). In PVH, TGase activity peaked at 24 h after partial hepatectomy with a preceding increase in its mRNA expression at 12 h, whereas TGase activity in PPH at 24 h was one-half of that in PVH. As TGase is known to have a growth-arresting activity, our data indicate that relatively higher TGase activity in PVH at 24 h after partial hepatectomy might correlate with relatively lower DNA synthesis in this region compared to periportal region.