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

DNA synthesis in periportal and perivenous hepatocytes of intact and hepatectomized young mice

DNA synthesis of hepatocytes in two areas of Intact and Hepatectomized young mice liver along a circadian period was studied. DNA synthesis was significantly different at all analyzed time points in Intact and Hepatectomized animals. Differences between periportal and perivenous hepatocytes were found in hepatectomized animals at 04/42 and 08/46 hr of day/hour post-hepatectomy. DNAs peak in periportal hepatocytes regenerating liver occurs 4 hr earlier than in perivenous hepatocytes, probably reflecting their shorter G1 phase. Besides, daily mean values of regenerating livers were higher than those observed in Intact animals, as a consequence of surgical removal.

Effect of aging on norepinephrine-related proliferative response in primary cultured periportal and perivenous hepatocytes

Norepinephrine (NE) amplifies the mitogenic effect of EGF in a rat liver through the adrenergic receptor coupled with G protein, Ghα. Ghα is also known as a transglutaminase 2 (TG2), whose cross-linking activity is implicated in hepatocyte growth. Recently, we found that NE-induced amplification of EGF-induced DNA synthesis in hepatocytes obtained from perivenous regions of liver is caused by inhibiting the downregulation of EGF receptor (EGFR) by TG2. In the present study, we investigated the effect of aging on NE-related proliferative response. Hepatocytes were obtained from the liver of 7- and 90-wk-old rats. To examine this in detail, periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) were isolated using the digitonin/collagenase perfusion technique. EGF or NE receptor binding was analyzed by Scatchard analysis. Changes in NE-induced DNA synthesis, G protein activity, and TG2 activity were measured. NE slightly potentiated [125I]EGF binding to EGFR, and EGF-induced DNA synthesis in PVH but not in PPH. [3H]NE binding studies indicated that PVH have a greater number of receptors than PPH, and that the number of receptors in both subpopulations increased with aging. NE-induced changes in G protein activity and TG2 activity in 90-wk-old rats were slight compared with 7-wk-old rats. These results suggest that NE results in a slight recovery effect on the age-related decline in EGF-induced DNA synthesis because of incomplete switching of the function from TG2 to Ghα.

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).

X-radiation-induced down-regulation of the EGF receptor in primary cultured rat hepatocytes

Exposure to X radiation is associated with a decline in the proliferative activity of the liver, but the molecular mechanism(s) is not well understood. We investigated whether exposure to X radiation is involved in functional changes in the epidermal growth factor (EGF) receptor (EGFR), thereby causing a reduction of EGF-induced DNA synthesis using periportal hepatocytes (PPH) and perivenous hepatocytes (PVH), which differ in their proliferative activity. X radiation dose-dependently decreased DNA synthesis in both subpopulations. The rate of decline in the DNA synthesis was greater in PPH than in PVH, but the zonal difference disappeared after exposure to 10 Gy X radiation. [(125)I]EGF binding studies indicated that high-affinity EGFRs in both subpopulations were down-regulated after X irradiation. Furthermore, EGF-induced EGFR dimerization and phosphorylation at Y1173 in both subpopulations were down-regulated after X irradiation, and the rate of decline was greater in PPH than in PVH. In contrast, phosphorylation at Y845 after EGF treatment was dose-dependently up-regulated after X irradiation in both subpopulations. These results suggest that the X-radiation-related decline in EGF-induced DNA synthesis is caused at least partly by the modification of EGFR function.

Transglutaminase down-regulates the dimerization of epidermal growth factor receptor in rat perivenous and periportal hepatocytes

OBJECTIVE

Recently, we found that transglutaminase 2 (TG2) might be involved in the difference in proliferative capacities between periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) through down-regulation of high-affinity epidermal growth factor receptor (EGFR). However, it is uncertain whether this high-affinity EGFR contributes to the hepatocyte growth signalling pathway. Here, we have investigated the influence of TG2 on EGF-induced EGFR dimerization and its phosphorylation, which are important steps in the hepatocyte proliferative/growth signalling pathway, in PPH and PVH.

MATERIALS AND METHODS

PPH and PVH were isolated using the digitonin/collagenase perfusion technique. Amounts of TG2, EGFR dimerization and its phosphorylation were determined by Western blot analysis.

RESULTS

Pretreatment with monodansylcadaverine, an inhibitor of TG2, greatly increased EGF-induced EGFR dimerization and its phosphorylation in PVH compared with PPH. Conversely, treatment with retinoic acid, an inducer of TG2, significantly decreased EGF-induced EGFR dimerization and its phosphorylation with a significant increase in TG2 expression and its catalysed products, isopeptide bonds, in both subpopulations. It was found that EGFR served as a substrate for TG2.

CONCLUSION

The present data showed good correlation with our previous data on EGF-induced DNA synthesis and EGFR-binding affinity to EGF. These results suggest that zonal difference in cell growth between PPH and PVH may be caused by down-regulation of EGFR dimerization and subsequent autophosphorylation through TG2-mediated cross-linking of EGFR.

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.

The Uptake Mechanism of Gallium-67 into Hepatocytes Treated with Carbon Tetrachloride

We have recently reported that transferrin (Tf)-unbound gallium-67 (67Ga) may be taken up into the liver of carbon tetrachloride (CCl4)-treated rats. In the present study, we attempted to clarify detailed mechanism of Tf-unbound 67Ga uptake by hepatocytes treated with CCl4 using in vitro experimental system. Hepatotoxic damages by CCl4 are mostly attributed to radical formed by an action of cytochrome P450. P450 isozymes have a higher expression in the perivenous hepatocytes (PVH) more than periportal hepatocytes (PPH). Therefore, we thought that the uptake of 67Ga which had been used for the detection of liver damage might have a zonal difference. The results of ALT activities showed that the CCl4 exposure for 4 h strongly impaired PVH more than PPH. The uptake of 67Ga by PVH treated with CCl4 was also higher than that by PPH. Moreover, the uptake of 45Ca by PVH was higher than that by PPH. In order to investigate whether 67Ga passed through calcium channel of hepatocytes, we made use of calcium channel blocker and activator. The Ca2+-channel blocker, verapamil, significantly decreased the uptakes of 45Ca and 67Ga by PPH and PVH pretreated with CCl4. The addition of the Ca2+-channel activator, Bay K8644, significantly increased the uptake both of 45Ca and 67Ga by PPH pretreated with CCl4. In the present study, it was demonstrated that the uptake of Tf-unbound 67Ga preferentially occurred in CCl4-damaged PVH and 67Ga was taken up into the hepatocytes in part through calcium channel.

Involvement of retinoic acid-induced transglutaminase activity in zonal differences of hepatocyte proliferation after partial hepatectomy

BACKGROUND

The authors have recently demonstrated that there is inverse correlation between transglutaminase (TGase) activity and DNA synthesis in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) at 1 day after partial hepatectomy in rats. In order to ensure the involvement of TGase in the differential growth capacities between periportal and perivenous regions of regenerating liver, the aim of this study was to investigate the effect of retinoic acid, an inducer of TGase expression, on zonal differences of hepatocyte proliferation between PPH and PVH isolated from regenerating rat liver.

METHODS

Regenerating liver was prepared by 70% partial hepatectomy. PPH and PVH subpopulations were isolated by the digitonin/collagenase perfusion technique. Cell cycle was evaluated for incorporation of BrdU into hepatocytes and detected by flow cytometric analysis. TGase activity was determined by incorporation of 14C-putrescine into dimethylcasein.

RESULTS

When retinoic acid was injected immediately after partial hepatectomy, TGase activity greatly increased in both PPH and PVH at 1 day after partial hepatectomy, and activity was higher in PPH than in PVH. DNA synthesis in both subpopulations did not increase 1 day after partial hepatectomy, with peaks of DNA synthesis shifting to 2 days, and synthesis was higher in PVH than in PPH.

CONCLUSION

These results suggest that TGase might be involved in differential growth capacities between periportal and perivenous regions of regenerating rat liver after partial hepatectomy.

Alteraciones hepáticas en la enfermedad celíaca del adulto. Caracterización clínico-patológica y evolución

BACKGROUND AND AIM

The clinical manifestations of adult celiac disease are highly varied and may include liver disease. The present study aimed to characterize liver abnormalities and outcome after a gluten-free diet in patients with celiac disease diagnosed in a hepatology clinic.

MATERIAL AND METHOD

The clinical records of patients diagnosed with celiac disease during a 7-year period were reviewed.

RESULTS

Of 1916 patients attending a first consultation at the clinic, 10 were finally diagnosed with celiac disease. All patients had been referred for evaluation of persistent elevation of liver enzyme levels. All patients were young (mean age 30 years, range 21-39 years) and there were more women than men (eight women, 80%). Six patients (60%) had additional manifestations attributable to undiagnosed celiac disease, sometimes since childhood. In all patients, elevation of liver enzyme levels was moderate and overall liver function was preserved. Liver biopsy was performed in five patients and all showed chronic periportal infiltrate. Immunohistochemical studies revealed that the infiltrate was mainly composed of CD8-positive T lymphocytes. In all patients, a gluten-free diet was followed by normalization of liver enzyme levels.

CONCLUSIONS

Although celiac disease is not highly frequent, it should be considered in the differential diagnosis of patients with persistent abnormalities of liver markers. The most conspicuous histopathological change is periportal T-cell infiltrate. Liver abnormalities in celiac disease are generally mild and improve after a gluten-free diet.

Transglutaminase differentially regulates growth signalling in rat perivenous and periportal hepatocytes

The influence of transglutaminase 2 (TG2) activity on the proliferative effect of epidermal growth factor (EGF) and on EGF receptor affinity in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) has been investigated using a primary culture system. PPH and PVH subpopulations have been isolated using the digitonin/collagenase perfusion technique. DNA synthesis was assessed by [3H] thymidine incorporation into hepatocytes. The assay for binding of [125I] EGF to cultured hepatocytes was analysed by Scatchard plot analysis. Pretreatment with the TG2 inhibitor monodansylcadaverine (MDC) greatly increased EGF-induced DNA synthesis in both PPH and PVH. Furthermore, [125I] EGF binding studies in PVH treated with MDC indicated that high-affinity EGF receptor expression was markedly up-regulated, whereas in PPH, there was no significant effect. Treatment with retinoic acid (RA), an inducer of TG2 expression, significantly decreased EGF-induced DNA synthesis in both PPH and PVH. Binding studies in the presence of RA revealed that the high-affinity EGF receptor was down-regulated and completely absent in both PPH and PVH. These results suggest that TG2 was involved in the differential growth capacities of PPH and PVH through down-regulation of high-affinity EGF receptors.

The Involvement of Polyamines as Substrates of Transglutaminase in Zonal Different Hepatocyte Proliferation after Partial Hepatectomy

We have recently demonstrated the inverse correlation between transglutaminase (TGase) activity and DNA synthesis in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) at 1 d after partial hepatectomy. In order to elucidate a role of polyamines as substrates of TGase in the differential growth capacities between PPH and PVH from regenerating liver, we investigated the zonal differences in alteration of ornithine decarboxylase (ODC) activity and polyamines. In two subpopulations, the inverse correlation between DNA synthesis and epsilon-(gamma-glutamyl) lysine (Gln-Lys) cross-linking catalyzed by TGase was demonstrated at 1 d after partial hepatectomy. ODC activity in PPH significantly increased with a peak at 1 d after partial hepatectomy, whereas did not in PVH. Protein-binding SPD in PPH also transiently increased with a peak at 1 d after partial hepatectomy, but did not in PVH. These results suggest that at 1 d after partial hepatectomy, in PPH, the inhibition of Gln-Lys cross-linking by the formation of N-gamma-glutamyl SPD leads to the increase of DNA synthesis, whereas in PVH, enhanced formation of Gln-Lys cross-linking leads to the lower DNA synthesis.