Hepatocyte-conditioned medium potentiates insulin-like growth factor (IGF) 1 and 2 stimulated DNA synthesis of cultured fat storing cells

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Homogeneous differentiation of hepatocyte-like cells from embryonic stem cells: applications for the treatment of liver failure

One of the major hurdles of cellular therapies for the treatment of liver failure is the low availability of functional human hepatocytes. While embryonic stem (ES) cells represent a potential cell source for therapy, current methods for differentiation result in mixed cell populations or low yields of the cells of interest. Here we describe a rapid, direct differentiation method that yields a homogeneous population of endoderm-like cells with 95% purity. Mouse ES cells cultured on top of collagen-sandwiched hepatocytes differentiated and proliferated into a uniform and homogeneous cell population of endoderm-like cells. The endoderm-like cell population was positive for Foxa2, Sox17, and AFP and could be further differentiated into hepatocyte-like cells, demonstrating hepatic morphology, functionality, and gene and protein expression. Incorporating the hepatocyte-like cells into a bioartificial liver device to treat fulminant hepatic failure improved animal survival, thereby underscoring the therapeutic potential of these cells.

Oxygen uptake rates and liver-specific functions of hepatocyte and 3T3 fibroblast co-cultures

Bioartificial liver (BAL) devices have been developed to treat patients undergoing acute liver failure. One of the most important parameters to consider in designing these devices is the oxygen consumption rate of the seeded hepatocytes which are known to have oxygen consumption rates 10 times higher than most other cell types. Hepatocytes in various culture configurations have been tested in BAL devices including those formats that involve co-culture of hepatocytes with other cell types. In this study, we investigated, for the first time, oxygen uptake rates (OUR)s of hepatocytes co-cultured with 3T3-J2 fibroblasts at various hepatocyte to fibroblast seeding ratios. OURs were determined by measuring the rate of oxygen disappearance using a ruthenium-coated optical probe after closing and sealing the culture dish. Albumin and urea production rates were measured to assess hepatocyte function. Lower hepatocyte density co-cultures demonstrated significantly higher OURs (2 to 3.5-fold) and liver- specific functions (1.6-fold for albumin and 4.5-fold for urea production) on a per cell basis than those seeded at higher densities. Increases in OUR correlated well with increased liver-specific functions. OURs (V(m)) were modeled by fitting Michaelis-Menten kinetics and the model predictions closely correlated with the experimental data. This study provides useful information for predicting BAL design parameters that will avoid oxygen limitations, as well as maximize metabolic functions.

Coordinate activation of intracellular signaling pathways by insulin-like growth factor-1 and platelet-derived growth factor in rat hepatic stellate cells

Proliferation of activated hepatic stellate cells (HSC) is an important event in the development of hepatic fibrosis. Insulin-like growth factor-1 (IGF-1) has been shown to be mitogenic for HSC, but the intracellular signaling pathways involved have not been fully characterized. Thus, the aims of the current study were to examine the roles of the extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3-K) and p70-S6 kinase (p70-S6-K) signaling pathways in IGF-1- and platelet-derived growth factor (PDGF)-induced mitogenic signaling of HSC and to examine the potential crosstalk between these pathways. Both IGF-1 and PDGF increased ERK, PI3-K and p70-S6-K activity. When evaluating potential crosstalk between these signaling pathways, we observed that PI3-K is required for p70-S6-K activation by IGF-1 and PDGF, and is partially responsible for PDGF-induced ERK activation. PDGF and IGF-1 also increased the levels of cyclin D1 and phospho-glycogen synthase kinase-3beta. Coordinate activation of ERK, PI3-K and p70-S6-K is important for perpetuating the activated state of HSC during fibrogenesis.

Suppression of transforming growth factor-beta results in upregulation of transcription of regeneration factors after chronic liver injury

BACKGROUND/AIMS

To determine the effects of dominant-negative TGF-beta receptor expression during liver regeneration in rats with dimethylnitrosamine (DMN)-induced liver injury.

METHODS

Rats were first treated with DMN for 3 weeks, and then intravenously injected once with AdTbeta-TR, AdLacZ, or saline. Serial changes in hepatocyte proliferation and apoptosis were evaluated by immunohistochemistry using anti-Ki67 antibody, and TUNEL staining, respectively. The mRNA expression of regeneration factors (HGF, TGF-alpha, EGF, and IGF-I) and IL-6 were evaluated by real-time PCR and northern blotting.

RESULTS

Anti-TGF-beta molecular intervention up-regulated hepatocyte proliferation and inhibited apoptosis. In the AdTbeta-TR-treated rats, EGF and IGF-I mRNA expression levels were significantly increased at day 1 and remained high for 3 days after gene transfer; TGF-alpha mRNA expression levels were significantly increased at 2 to 5 days after gene transfer; HGF mRNA expression levels were significantly up-regulated at day 2 only after gene transfer; while IL-6 mRNA expression level tended to increase at day 1, but decreased thereafter.

CONCLUSIONS

In rats with DMN-induced liver injury, anti-TGF-beta molecular intervention therapy stimulates proliferation and reduces apoptosis of hepatocytes, and also up-regulates the transcription of various growth factors.

IGF-I induces DNA synthesis and apoptosis in rat liver hepatic stellate cells (HSC) but DNA synthesis and proliferation in rat liver myofibroblasts (rMF)

Several lines of evidence suggest a role of insulin-like growth factor I (IGF-I) in the regulation of apoptosis. Up to now its impact on many specific cells is unknown. We therefore studied the effect of IGF-I on two similar mesenchymal matrix-producing cell types of the liver, the hepatic stellate cells (HSC) and the myofibroblasts (rMF). The present study aimed to reveal the influence of IGF-I on cell cycle and apoptosis of HSC and rMF and to elucidate responsible signaling. While IGF-I significantly increased DNA synthesis in HSC, cell number decreased and apoptosis increased. In rMF IGF-I also increased DNA synthesis, which is, however, followed by proliferation. Blocking extracellular signal regulating kinase (ERK) revealed that in HSC, bcl-2 upregulation and bax downregulation are effected downstream of ERK, whereas downregulation of NFkappaB and consecutive of bcl-xL is mediated upstream. In the rMF upregulation of both, the antiapoptotic bcl-2 and bcl-xL is mediated upstream of ERK. The expression of the proapoptotic bax is not regulated by IGF-I in rMF. The studies demonstrate a completely different effect and signaling of IGF-I in two morphologically and functionally similar matrix-producing cells of the liver.

Insulin-like growth factor (IGF)-binding protein-1 is highly induced during acute carbon tetrachloride liver injury and potentiates the IGF-I-stimulated activation of rat hepatic stellate cells

Hepatic stellate cells (HSC) play a pivotal role in hepatic tissue repair and fibrogenesis. IGF-I has been considered a mitogenic signal for activation and proliferation of HSC in vitro. In the present study IGF-I and IGF-binding protein (IGFBP) gene expression was studied in a model of acute liver injury induced by a single intragastric dose of carbon tetrachloride (CCl(4)) in adult rats. Northern blot analysis revealed a marked increase in IGFBP-1 mRNA levels, with a maximum between 3 and 9 h after CCl(4) application, whereas steady state mRNA levels of IGF-I were only moderately altered. In situ hybridization experiments demonstrated that this increase in IGFBP-1 mRNA was due to a strong expression of IGFBP-1 in the perivenous region 6-12 h after CCl(4) application, extending to the midzonal region of the acinus within 24-48 h. Consequently, a prominent immunostaining for IGFBP-1 was observed in perivenous areas, with a maximum 24-48 h after intoxication. Preincubation of early cultured HSC with a nonphosphorylated IGFBP-1 from human amniotic fluid resulted in a 3.4-fold increase in IGF-I-induced DNA synthesis. The mitogenic effect of IGF-I was also potentiated when HSC were cocultivated with IGFBP-1-overexpressing BHK-21 cells compared with nontransfected cells. These data suggest that IGFBP-1 released during the early steps of liver tissue damage and repair may interact with HSC and potentiate the sensitivity of IGF-I to mitogenic signals.

Antifibrogenic effect in vivo of low doses of insulin-like growth factor-I in cirrhotic rats

Insulin-like growth factor-I (IGF-I) is produced mainly in the liver and it induces beneficial effects on the nutritional status, the liver function and oxidative hepatic damage in cirrhotic rats. The aim of this work was to analyze the effect of IGF-I on mechanisms of fibrogenesis in cirrhotic rats. Liver cirrhosis was induced by CCl(4) inhalation and phenobarbital in Wistar rats. Ten days after stopping CCl(4) administration (day 0), rats received either IGF-I (2 microg/100 g bw/day) (CI+IGF) or saline (CI) subcutaneously during 14 days. Animals were sacrificed on day 15. As control groups were used: healthy rats (CO) and healthy rats treated with IGF-I (CO+IGF). Liver histopathology, hydroxyproline content, prolyl hydroxylase activity, collagen I and III mRNA expression and the evolution of transformed Ito cells into myofibroblasts were assessed. Among the two control groups (CO+IGF), no differences were found in hydroxyproline content and these levels were lower than those found in the two cirrhotic groups. Compared with untreated cirrhotic rats, the CI+IGF-I animals showed a significant reduction in hydroxyproline content, prolyl hydroxylase activity and collagen alpha 1(I) and alpha1(III) mRNA expression. A higher number of transformed Ito cells (alpha-actin +) was observed in untreated cirrhotic animals as compared to CO and CI+IGF groups. In summary, treatment with IGF-I reduced all of the studied parameters of fibrogenesis. In conclusion, low doses of IGF-I induce in vivo an antifibrogenic effect in cirrhotic rats.

Increased insulin-like growth factor binding protein-4 expression after partial hepatectomy in the rat

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are important regulators of cell growth produced by different tissues. The IGFBPs regulate cell growth by modulating the activity and bioavailability of IGFs. The evidence that IGFBP-1 is a liver-specific immediate-early gene highly induced after 70% partial hepatectomy (PHx) suggests a role for the IGF-IGFBP system in hepatic regeneration. In this work we analyzed the effect of PHx on the expression of IGFBP-4, which is highly produced by the liver and very abundant in rat serum. Our results show a marked increase in hepatic IGFBP-4 mRNA levels 6-12 h after PHx and no significant change in sham-operated control animals. A parallel rise in IGFBP-4 transcript abundance was observed in the kidneys of PHx rats but not in sham-operated animals. Moreover, ligand blot analysis demonstrated that serum IGFBP-4 levels began to increase 12-24 h after surgery, consistent with the rise in the corresponding mRNA. This enhancement in IGFBP-4 production after PHx could be part of a fine regulatory mechanism to modulate IGF activity during liver regeneration.

Characterization of the IGF axis components in isolated rat hepatic stellate cells

The insulin-like growth factors I and II (IGF-I, -II) are circulating peptides known to participate in the regulation of metabolism, growth, and cellular differentiation. In the present study, "early cultured" (days 2-3 of culture) and "culture-activated" (days 6-7 of culture) rat hepatic stellate cells (HSCs) were analyzed for expression of individual components of the IGF axis. Northern blot analysis of IGF-I messenger RNA (mRNA) revealed transcripts of 7.5, 4, 2, and 1.0 to 1.5 kb in culture-activated HSCs, while early cultured HSCs did not express IGF-I mRNA. In culture-activated HSCs, an IGF-I secretion of 8.3+/-2.5 ng/10(6) cells per 24 hours was determined radioimmunologically. In media from early cultured HSCs, IGF-I was not detectable. The IGF-I receptor (IGF-I-R) mRNA expression was three-fold higher in early cultured HSCs than in culture-activated HSCs. By immunohistochemistry, a decrease of IGF-I-R expression of HSCs in vivo following CCl4-induced liver damage was noted as well. IGF binding proteins (IGFBPs) were detected in conditioned media from HSCs by 125I-IGF-I ligand blotting at apparent molecular masses of 24 and 41 to 45 kd that were immunologically identified as IGFBP-4 and -3, respectively. Synthesis of these IGFBPs increased with time of culture. At neutral pH, no IGFBP proteolysis was observed in conditioned media of early cultured and culture-activated HSCs, whereas at acidic pH, protease activities against IGFBP-3 and -4 were detectable. IGFBP protease activities were completely abolished by inhibitors of aspartyl and cysteine proteases. Addition of 100 nmol/L IGF-I stimulated cell proliferation of early cultured HSCs 5.6+/-1.1- and 4.6+/-0.2-fold as measured by [3H]thymidine and 5-bromo-2'-deoxyuridine incorporation, respectively. In culture-activated HSCs, proliferation was increased 1.2+/-0.1-fold in the presence of 100 nmol/L IGF-I in both proliferation assays. It can be concluded that due to a higher expression of the IGF-I-R and lower levels of IGFBPs, early cultured HSCs are more susceptible to the mitogenic actions of IGFs than the culture-activated HSCs. The present data suggest a role for the IGF axis components in the initiation rather than the perpetuation of HSC proliferation during hepatic fibrogenesis.

Insulin-like growth factors stimulate expression of hepatocyte growth factor but not transforming growth factor beta1 in cultured hepatic stellate cells

Hepatic stellate cells (HSC) are located adjacent to hepatocytes and produce hepatocyte growth factor (HGF) in the normal liver, whereas transformed HSC in fibrotic livers produce transforming growth factor beta1 (TGFbeta1), an inhibitor ofhepatocyte proliferation. In addition to the endocrine actions of hepatic insulin-like growth factor-I (IGF-I), it also stimulates the proliferation of HSC. In this study we found that addition of IGF-1 (20-500 ng/ml) for 48 h to 2- to 7-day-old primary cultures of rat HSC resulted in a time- and dose-dependent increase by 50-190% of the concentrations of immunoreactive HGF in the medium. The levels of HGF as well as DNA synthesis measured as thymidine incorporation were also enhanced by IGF-II and des(1-3)IGF-I, which has reduced binding to IGF binding proteins. There was no consistent effect of the IGFs on the levels of immunoreactive TGFbeta1 or on the total DNA content of the cultures. There was no effect of human GH on medium levels of HGF or TGFbeta1, thymidine incorporation, or total DNA content. IGF-I increased the abundance of HGF messenger RNA, as measured by the RNase protection/solution hybridization technique, whereas there was no effect on TGFbeta1 or glyceraldehyde phosphate dehydrogenase messenger RNA. The results suggest that IGFs stimulate the production of HGF but not TGFbeta1 by HSC in vitro.

The hepatic stellate (Ito) cell: its role in human liver disease

The hepatic stellate (Ito) cell lies within the space of Disse and has a variety of functions. Stellate cells store vitamin A in characteristic lipid droplets. In the normal human liver, the cells can be identified by the presence of these lipid droplets; in addition, many stellate cells in the normal liver express alpha-smooth muscle actin. In acute liver injury, there is an expansion of the stellate cell population with increased alpha-smooth muscle actin expression; stellate cells appear to play a role in extracellular matrix remodelling after recovery from injury. In chronic liver injury, the stellate cell differentiates into a myofibroblast-like cell with marked expression of alpha-smooth muscle actin and occasional expression of desmin. Myofibroblast-like cells have a high fibrogenic capacity in the chronically diseased liver and are also involved in matrix degradation. In vitamin A intoxication, hypertrophy and proliferation of the stellate and myofibroblast-like cells may lead to non-cirrhotic portal hypertension, fibrosis and cirrhosis. In liver tumours, myofibroblast-like cells are involved in the capsule formation around the tumour and in the production of extracellular matrix within it. The transition of stellate cells into myofibroblast-like cells is regulated by an intricate network of intercellular communication between stellate cells and activated Kupffer cells, damaged hepatocytes, platelets, endothelial and inflammatory cells, involving cytokines and nonpeptide mediators such as reactive oxygen species, eicosanoids and acetaldehyde. The findings suggest that the stellate cell plays an active role in a number of human liver diseases, with a particular reactivity pattern in fibrotic liver disorders.

Characterization of insulin-like growth factor (IGF)-I-receptor binding sites during in vitro transformation of rat hepatic stellate cells to myofibroblasts

Insulin-like growth factors are growth-promoting peptides structurally related to insulin which possess autocrine and paracrine activities. IGF-I is mainly synthesized in hepatocytes, but little is known about its paracrine action on hepatocyte-adjacent perisinusoidal hepatic stellate cells, the principal matrix producing precursor cell type in the liver. IGF-I might stimulate proliferation and phenotypical transformation of hepatic stellate cells into myofibroblasts, the cell type responsible for the excessive production of connective tissue elements during fibrogenesis. In this study we investigated the expression and function of the IGF-I receptor during transformation of isolated and cultured hepatic stellate cells. The respective stages of transformation of hepatic stellate cells were defined by determination of cellular smooth muscle iso-alpha-actin and retinyl-palmitate content, respectively. IGF-I receptor protein decreased stage-dependently down to 0.5 at the 4th day and about 0.17 at the 8th day. The number of IGF-I receptors was determined to be initially 1.3 x 10(5)/cell. Their quantity decreased to 0.8 x 10(5) sites/cell (4th day) down to 0.5 x 10(5) sites/cell at the 7th day and remained constant thereafter at 0.7 x 10(5) sites/cell. Dissociation constants (KD) for IGF-I range from 0.32-0.57 nmol/l showing constantly high receptor affinity. Northern blot analyses revealed distinct upregulation of IGF-I receptor mRNA level during culture. It is concluded that hepatocyte-generated IGF-I and/or IGF-I binding proteins are candidate mediators of hepatic stellate cell activation during the initial period of transformation to myofibroblasts. After completion of transformation the cell becomes relatively refractory to the action of IGF-I as judged from receptor density.