Normal Liver Growth Research Articles

Abstract LB-015: Yap reprograms de novo lipogenesis to fuel liver cancer

Abstract Hepatocellular carcinoma (HCC) is the most common form of liver cancer, originating from liver cells known as hepatocytes. At the molecular level, HCC is driven by transcription factors which are able to reprogram metabolism to support tumorigenesis that are still poorly understood. The Yes-associated protein (Yap) is the nuclear effector of the Hippo pathway, responsible in regulating organ size control and metabolism. Metabolic reprogramming has recently emerged as a fundamental hallmark of cancer. In our previous studies, we found that Yap integrates the anabolic demands of tumour growth by reprogramming glutamine and glucose metabolism to support nucleotide biosynthesis. The central aim of this study was to determine the role that Yap plays in regulating lipid metabolism in the context of liver cancer. We took advantage of a larval zebrafish model in which a hyperactivated form of Yap is specifically expressed in hepatocytes (lf:YapS87A;lf:NLS-mcherry). We found that the expression of Yap was sufficient to stimulate de novo lipogenesis (DNL) and induce lipid droplet formation in hepatocytes (steatosis). To determine whether the stimulation of DNL was required for oncogenic growth, we exposed larvae to pharmacological inhibitors of DNL and examined the impact on growth at the cellular level by multiphoton microscopy. Strikingly, we identified that fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD) inhibitors suppressed Yap-driven growth. To complement these studies, we took a genetic approach using CRISPR to generate FAS and SCD KO zebrafish larvae and we found that Yap-driven growth required both FAS and SCD. Importantly both chemical and genetic suppression of FAS and SCD activity had no effect on normal liver growth. Together, these findings suggest that oncogenic Yap-driven growth is conditionally dependent upon the stimulation of DNL. Consequently, these studies provide a rationale for examining the clinical efficacy of DNL inhibitors to combat liver cancer. Citation Format: Talhah M. Salmi, Srimayee Vaidyanathan, Malcolm J. McConville, Kristin K. Brown, Andrew G. Cox. Yap reprograms de novo lipogenesis to fuel liver cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-015.

Hepatic Hippo signaling inhibits protumoural microenvironment to suppress hepatocellular carcinoma

ObjectiveHippo signalling is a recently identified major oncosuppressive pathway that plays critical roles in inhibiting hepatocyte proliferation, survival and hepatocellular carcinoma (HCC) formation. Hippo kinase (Mst1 and Mst2) inhibits HCC...

한방차 조성물의 세포활성과 혈관이완 효과에 대한 융합적 연구

본 연구는 혈관 활성에 도움이 되는 한방차를 개발하고, 섭취효능에 대한 동 서 융합적인 접근 필요성에 대한 기초자료로 사용하고자 하였다. 이에 따라 기미론에 따라 혈관 활성을 가질 수 있는 포공영(Taraxaci Herba), 치자(Gardeniae Fructus), 감국(Chrysanthemum indicum) 및 금은화(Lonicerae Flos)를 선정하여 조성물을 만들고 각각 재료와 조성물의 영양성분, 조성물이 세포활성에 미치는 영향 및 수축혈관에 대한 이완정도를 분석하였다. 기미론적 원리에 따른 한방차 조성물은 체내 열을 제거하고 혈액순환을 촉진할 수 있는 효능을 가지고 있음을 알 수 있었다. 네 가지를 재료를 배합한 조성물은 세포활성에 유익한 영향을 미치고 있음을 확인하였다. 또한 조성물은 수축혈관에 대해 이완효과를 가지고 있었고 조성물의 농도가 높을수록 수축된 혈관의 이완효과가 큰 것으로 관찰되어 이 조성물이 혈관 활성에 긍정적 영향을 주고 있음을 확인하였다. 본 연구는 한방차 조성물의 기미 특성과 현대 영양학의 특성이 융합된 섭취효능을 제시하였다고 사료된다. This study was aimed to secure the basis for developing the hangbang-tea may help promote healthy blood vessels by natural herbal ingredients formulated in accordance with the basic principles of oriental medicinal theory. We investigated the vessels contracted by concentrations and safety assessment carried out by the cell viability of Taraxaci Herba, Gardeniae Fructus, Chrysanthemum indicum and Lonicerae Flos composition and concentration. We found cell survival were higher than the control group show a beneficial trend in the growth of normal liver and kidney cells. As a results of this study will be the basis to develop the hangbang-tea differentiated in the future oriental medicine resources. Medicinal resources will be hangbang-tea based on clinical trials utilizing herbal western and oriental medicine convergence principle and vascular relaxation mechanism.

Tissue Remodelling following Resection of Porcine Liver.

Aim. To study genes regulating the extracellular matrix (ECM) and investigate the tissue remodelling following liver resection in porcine. Methods. Four pigs with 60% partial hepatectomy- (PHx-) induced liver regeneration were studied over six weeks. Four pigs underwent sham surgery and another four pigs were used as controls of the normal liver growth. Liver biopsies were taken upon laparotomy, after three and six weeks. Gene expression profiles were obtained using porcine-specific oligonucleotide microarrays. Immunohistochemical staining was performed and a proliferative index was assessed. Results. More differentially expressed genes were associated with the regulation of ECM in the resection group compared to the sham and control groups. Secreted protein acidic and rich in cysteine (SPARC) and collagen 1, alpha 2 (COL1A2) were both upregulated in the early phase of liver regeneration, validated by immunopositive cells during the remodelling phase of liver regeneration. A broadened connective tissue was demonstrated by Masson's Trichrome staining, and an immunohistochemical staining against pan-Cytokeratin (pan-CK) demonstrated a distinct pattern of migrating cells, followed by proliferating cell nuclear antigen (PCNA) positive nuclei. Conclusions. The present study demonstrates both a distinct pattern of PCNA positive nuclei and a deposition of ECM proteins in the remodelling phase of liver regeneration.

Prolactin promotes normal liver growth, survival, and regeneration in rodents: effects on hepatic IL-6, suppressor of cytokine signaling-3, and angiogenesis

Prolactin (PRL) is a potent liver mitogen and proangiogenic hormone. Here, we used hyperprolactinemic rats and PRL receptor-null mice (PRLR(-/-)) to study the effect of PRL on liver growth and angiogenesis before and after partial hepatectomy (PH). Liver-to-body weight ratio (LBW), hepatocyte and sinusoidal endothelial cell (SEC) proliferation, and hepatic expression of VEGF were measured before and after PH in hyperprolactinemic rats, generated by placing two anterior pituitary glands (AP) under the kidney capsule. Also, LBW and hepatic expression of IL-6, as well as suppressor of cytokine signaling-3 (SOCS-3), were evaluated in wild-type and PRLR(-/-) mice before and after PH. Hyperprolactinemia increased the LBW, the proliferation of hepatocytes and SECs, and VEGF hepatic expression. Also, liver regeneration was increased in AP-grafted rats and was accompanied by elevated hepatocyte and SEC proliferation, and VEGF expression compared with nongrafted controls. Lowering circulating PRL levels with CB-154, an inhibitor of AP PRL secretion, prevented AP-induced stimulation of liver growth. Relative to wild-type animals, PRLR(-/-) mice had smaller livers, and soon after PH, they displayed an approximately twofold increased mortality and elevated and reduced hepatic IL-6 and SOCS-3 expression, respectively. However, liver regeneration was improved in surviving PRLR(-/-) mice. PRL stimulates normal liver growth, promotes survival, and regulates liver regeneration by mechanisms that may include hepatic downregulation of IL-6 and upregulation of SOCS-3, increased hepatocyte proliferation, and angiogenesis. PRL contributes to physiological liver growth and has potential clinical utility for ensuring survival and regulating liver mass in diseases, injuries, or surgery of the liver.

Morphology and morphometry of fetal liver at 16–26 weeks of gestation by magnetic resonance imaging: Comparison with embryonic liver at Carnegie stage 23

Normal liver growth was described morphologically and morphometrically using magnetic resonance imaging (MRI) data of human fetuses, and compared with embryonic liver to establish a normal reference chart for clinical use. MRI images from 21 fetuses at 16-26 weeks of gestation and eight embryos at Carnegie stage (CS)23 were investigated in the present study. Using the image data, the morphology of the liver as well as its adjacent organs was extracted and reconstructed three-dimensionally. Morphometry of fetal liver growth was performed using simple regression analysis. The fundamental morphology was similar in all cases of the fetal livers examined. The liver tended to grow along the transversal axis. The four lobes were clearly recognizable in the fetal liver but not in the embryonic liver. The length of the liver along the three axes, liver volume and four lobes correlated with the bodyweight (BW). The morphogenesis of the fetal liver on the dorsal and caudal sides was affected by the growth of the abdominal organs, such as the stomach, duodenum and spleen, and retroperitoneal organs, such as the right adrenal gland and right kidney. The main blood vessels such as inferior vena cava, portal vein and umbilical vein made a groove on the surface of the liver. Morphology of the fetal liver was different from that of the embryonic liver at CS23. The present data will be useful for evaluating the development of the fetal liver and the adjacent organs that affect its morphology.

Genetic and pharmacological disruption of the TEAD–YAP complex suppresses the oncogenic activity of YAP

The Drosophila TEAD ortholog Scalloped is required for Yki-mediated overgrowth but is largely dispensable for normal tissue growth, suggesting that its mammalian counterpart may be exploited for selective inhibition of oncogenic growth driven by YAP hyperactivation. Here we test this hypothesis genetically and pharmacologically. We show that a dominant-negative TEAD molecule does not perturb normal liver growth but potently suppresses hepatomegaly/tumorigenesis resulting from YAP overexpression or Neurofibromin 2 (NF2)/Merlin inactivation. We further identify verteporfin as a small molecule that inhibits TEAD-YAP association and YAP-induced liver overgrowth. These findings provide proof of principle that inhibiting TEAD-YAP interactions is a pharmacologically viable strategy against the YAP oncoprotein.

Postnatal liver growth and regeneration are independent of c-myc in a mouse model of conditional hepatic c-myc deletion

BackgroundThe transcription factor c-myc regulates genes involved in hepatocyte growth, proliferation, metabolism, and differentiation. It has also been assigned roles in liver development and regeneration. In previous studies, we made the unexpected observation that c-Myc protein levels were similar in proliferating fetal liver and quiescent adult liver with c-Myc displaying nucleolar localization in the latter. In order to investigate the functional role of c-Myc in adult liver, we have developed a hepatocyte-specific c-myc knockout mouse, c-mycfl/fl;Alb-Cre.ResultsLiver weight to body weight ratios were similar in control and c-myc deficient mice. Liver architecture was unaffected. Conditional c-myc deletion did not result in compensatory induction of other myc family members or in c-Myc's binding partner Max. Floxed c-myc did have a negative effect on Alb-Cre expression at 4 weeks of age. To explore this relationship further, we used the Rosa26 reporter line to assay Cre activity in the c-myc floxed mice. No significant difference in Alb-Cre activity was found between control and c-mycfl/fl mice. c-myc deficient mice were studied in a nonproliferative model of liver growth, fasting for 48 hr followed by a 24 hr refeeding period. Fasting resulted in a decrease in liver mass and liver protein, both of which recovered upon 24 h of refeeding in the c-mycfl/fl;Alb-Cre animals. There was also no effect of reducing c-myc on recovery of liver mass following 2/3 partial hepatectomy.Conclusionsc-Myc appears to be dispensable for normal liver growth during the postnatal period, restoration of liver mass following partial hepatectomy and recovery from fasting.

Beta‐Catenin Expression in Pediatric Malignancies

Wnt/β‐catenin signaling is important in normal liver growth and development where it dictates processes of proliferation, zonation and metabolism. Here we examined pediatric hepatoblastoma (HB), hepatocellular cancer (HCC) and tyrosinemias for expression of β‐catenin, its target Glutamine synthetase (GS) and upstream effector glypican‐3 (GPC3) by immunohistochemistry (IHC). Normal livers displayed membranous β‐catenin, cytoplasmic GS in a single layer of pericentral hepatocytes and no GPC3 expression. 2/9 HCC showed cytoplasmic/nuclear localization, which coincided with increased GS and GPC3. All 10 HB showed strong nuclear and cytoplasmic β‐catenin and increased GPC3, but only 7/10 showed diffuse GS staining. 5/6 livers with tyrosinemia (including 2 with dysplasia and 1 with HCC) showed cytoplasmic β‐catenin, which correlated with diffuse GS and increased GPC3 immunoreactivity. We conclude that significant numbers of HCC, HB and tyrosinemias show aberrant β‐catenin activation, which could be due to increased GPC3, which is known to activate Wnt pathway.

Conditional Deletion of β-Catenin Reveals Its Role in Liver Growth and Regeneration

The Wnt/beta-catenin pathway plays a role in liver growth and development. To address this conclusively, we used a conditional knockout approach to delete beta-catenin in the liver. Floxed beta-catenin (exons 2-6) mice were intercrossed with Albumin-Cre recombinase transgenic mice; considerable beta-catenin deletion was evident 15 days after birth by Western blot and immunohistochemistry analyses. Although these mice were viable, there was a significant decrease in their liver weight/body weight ratio by 14% at 1 month and 28%-35% by 2-6 months of age, which was sustained throughout their normal life span. There was an accompanying decrease in basal hepatocyte proliferation showed by Ki-67 staining. Additional analysis revealed several known and novel genes to be down-regulated in these mice that play a role in normal liver homeostasis. When subjected to two-thirds partial hepatectomy, the Ctnnb1(loxp/loxp); Alb-Cre(+/-) mice were sick and lethargic, especially during the first 2-3 days only. These mice display a 2-fold decrease in the number of Ki-67- or PCNA-positive cells at the time of peak hepatocyte proliferation at 40 hours, which coincided with decreased cyclin A, D, and E expression. However, a rebound increase in hepatocyte proliferation was evident in the knockout mice at 3 days. Also, increased apoptosis was observed in the knockout livers during regeneration at all stages. Thus, beta-catenin is essential for normal liver growth and development. Also, although regeneration is delayed in the absence of beta-catenin, it does occur suboptimally, showing its redundancy in the liver.

β‐Catenin is essential in normal liver growth, regeneration and function

Wnt/β-catenin pathway has shown to be important in embryogenesis and carcinogenesis. In liver, it has been shown to play a role in development, growth and regeneration. The aim of the present study was to conditionally knockout β-catenin, a key component of the Wnt pathway. Floxed β-catenin mice (Ex2–6) were intercrossed with Albumin-Cre recombinase transgenic mice to knockout β-catenin in hepatocytes, which was obvious at 15-30 days after birth by western blot analysis and immunohistochemistry (IHC). While these mice were viable, there was a significant decrease in liver weight/body weight (LW/BW) ratio by 14% at 1 month and 28–35% by 2–6 months of age. There was an accompanying decrease in basal hepatocyte proliferation exhibited by Ki-67 staining. Additional analysis revealed several genes to be downregulated in these mice that play a role in normal liver homeostasis such as those involved in urea cycle, xenobiotic metabolism such as cytochrome P450 and glutathione transferases. When subjected to two-third partial hepatectomy, the Ctnnb1loxp/loxp; Alb-Cre+/− mice appeared lethargic and sicker especially during the first few days. These mice at 40 hours displayed a 3-fold decrease in the number of Ki-67-positive cells and PCNA at the time of peak hepatocyte proliferation in the wild-type mice. This was secondary to decreased expression of various cyclins including A, B, D, E, K and T, demonstrating a compromise in cell cycle. At 14 days after hepatectomy there was still double the number of Ki-67 positive hepatocytes in the knockout mice as compared to the wild-type indicating some continued regeneration. Thus β-catenin plays an important role in normal liver growth and development. In addition, loss of β-catenin blunts and compromises normal liver regeneration. (Supported by RSG-03-141-CNE and NIH-1RO1DK62277 to SPSM)

Therapeutic neonatal hepatic gene therapy in mucopolysaccharidosis VII dogs.

Dogs with mucopolysaccharidosis VII (MPS VII) were injected intravenously at 2-3 days of age with a retroviral vector (RV) expressing canine beta-glucuronidase (cGUSB). Five animals received RV alone, and two dogs received hepatocyte growth factor (HGF) before RV in an attempt to increase transduction efficiency. Transduced hepatocytes expanded clonally during normal liver growth and secreted enzyme with mannose 6-phosphate. Serum GUSB activity was stable for up to 14 months at normal levels for the RV-treated dogs, and for 17 months at 67-fold normal for the HGF/RV-treated dog. GUSB activity in other organs was 1.5-60% of normal at 6 months for two RV-treated dogs, which was likely because of uptake of enzyme from blood by the mannose 6-phosphate receptor. The body weights of untreated MPS VII dogs are 50% of normal at 6 months. MPS VII dogs cannot walk or stand after 6 months, and progressively develop eye and heart disease. RV- and HGF/RV-treated MPS VII dogs achieved 87% and 84% of normal body weight, respectively. Treated animals could run at all times of evaluation for 6-17 months because of improvements in bone and joint abnormalities, and had little or no corneal clouding and no mitral valve thickening. Despite higher GUSB expression, the clinical improvements in the HGF/RV-treated dog were similar to those in the RV-treated animals. This is the first successful application of gene therapy in preventing the clinical manifestations of a lysosomal storage disease in a large animal.

Reduction in normal liver growth in interleukin-6-deficientmice

Reduction in normal liver growth in interleukin-6-deficientmice

Characterization of a murine Ahr null allele: involvement of the Ah receptor in hepatic growth and development.

The Ah receptor (AHR) is a ligand-activated transcription factor that mediates a pleiotropic response to environmental contaminants such as benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin. In an effort to gain insight into the physiological role of the AHR and to develop models useful in risk assessment, gene targeting was used to inactivate the murine Ahr gene by homologous recombination. Ahr-/- mice are viable and fertile but show a spectrum of hepatic defects that indicate a role for the AHR in normal liver growth and development. The Ahr-/- phenotype is most severe between 0-3 weeks of age and involves slowed early growth and hepatic defects, including reduced liver weight, transient microvesicular fatty metamorphosis, prolonged extramedullary hematopoiesis, and portal hypercellularity with thickening and fibrosis.

Liver Regeneration in Children after Major Hepatectomy for Malignancy—Evaluation Using a Computer-Aided Technique of Volume Measurement

Purpose: The time course of hepatic volume regeneration and return of excretory and synthetic function was studied in eight children undergoing lobar or extended lobar liver resections for hepatoblastoma (n= 5), hepatoma (n= 1), and recurrent nephroblastoma (n= 2). Five patients received preoperative and all were administered postoperative chemotherapy. Whole-liver irradiation was administered to one patient. One additional patient who underwent an extended hepatic resection for benign disease and did not receive chemotherapy was included for comparison. Methods: A previously validated technique of computer-aided volume measurement was used to measure liver volumes from serial CT scans obtained after hepatic surgery. Normal liver volume as a function of age was determined from the literature and the time course of regeneration was compared to normal liver growth. Postoperative serum albumin, total bilirubin, serum glutamic oxaloacetic transaminase, and alkaline phosphatase levels were recorded and correlated with volume regeneration. Results: In six patients hepatic regeneration had progressed to normal volume by 90 days after resection (normal volume for age was achieved by 50 days in three patients). There was an initial rapid rate of regeneration (>10 cc/day) which declined to a normal rate of less than 0.5 cc/day at 90 days after surgery. Two children with failure to thrive displayed the same pattern of rapid regeneration, attaining a volume appropriate for weight but less than that expected for age. The shape of the liver volume regeneration curve was similar in one additional patient undergoing an extended left lobectomy for benign disease. A brief rise in bilirubin occurred during the first week and a transient fall in serum albumin was followed by resumption of normal synthetic capacity within 6 weeks in all but two patients. Conclusions: Liver regeneration in children is a rapid process occurring despite the administration of cytotoxic agents and hepatic irradiation.

The gene encoding rat insulinlike growth factor-binding protein 1 is rapidly and highly induced in regenerating liver.

The liver is an epithelioid organ that can regenerate following partial hepatectomy. Although it is composed mainly of hepatocytes, it has a complex, multicellular architecture, implying that intercellular communications must exist during regeneration. As in other mitogen-stimulated cells, immediate-early growth response genes induced in the absence of prior protein synthesis are likely to play an important regulatory role in the regenerative process. Through differential screening of regenerating liver cDNA libraries, we found that one of the most highly expressed immediate-early genes in liver regeneration encodes the rat homolog of the low-molecular-weight insulinlike growth factor (IGF)-binding protein (IGFBP-1). This protein has been implicated in enhancing the mitogenic effect of IGF on tissues. IGFBP-1 gene induction is transcriptionally mediated and specific to regenerating liver, as the gene is not expressed in mitogen-stimulated fibroblasts. IGFBP-1 expression has been shown to increase under low-insulin conditions such as diabetes, and the complex regulation of expression is indicated by our finding that insulin treatment of H35 rat hepatoma cells, which induces proliferation, also causes a rapid decrease in transcription and expression of the IGFBP-1 gene. Of note, IGFBP-1 mRNA is abundant in fetal rat liver, implying that it participates in normal liver growth and development. Although regenerating liver cells continue to produce IGF-I, we did not detect IGF-I receptor mRNA during the first 24 h after hepatectomy. However, some IGFBPs may act to enhance the activity of IGF-I independently of IGF-I receptors. Thus, IGF-1 and IGFBPs may interact with hepatocytes or nonparenchymal liver cells, through either IGF-I or novel receptors. In this way, IGFBP-I and IGF-I could act in a paracrine and/or autocrine fashion in maintaining normal liver architecture during regeneration.

The Gene Encoding Rat Insulinlike Growth Factor-Binding Protein 1 Is Rapidly and Highly Induced in Regenerating Liver

The liver is an epithelioid organ that can regenerate following partial hepatectomy. Although it is composed mainly of hepatocytes, it has a complex, multicellular architecture, implying that intercellular communications must exist during regeneration. As in other mitogen-stimulated cells, immediate-early growth response genes induced in the absence of prior protein synthesis are likely to play an important regulatory role in the regenerative process. Through differential screening of regenerating liver cDNA libraries, we found that one of the most highly expressed immediate-early genes in liver regeneration encodes the rat homolog of the low-molecular-weight insulinlike growth factor (IGF)-binding protein (IGFBP-1). This protein has been implicated in enhancing the mitogenic effect of IGF on tissues. IGFBP-1 gene induction is transcriptionally mediated and specific to regenerating liver, as the gene is not expressed in mitogen-stimulated fibroblasts. IGFBP-1 expression has been shown to increase under low-insulin conditions such as diabetes, and the complex regulation of expression is indicated by our finding that insulin treatment of H35 rat hepatoma cells, which induces proliferation, also causes a rapid decrease in transcription and expression of the IGFBP-1 gene. Of note, IGFBP-1 mRNA is abundant in fetal rat liver, implying that it participates in normal liver growth and development. Although regenerating liver cells continue to produce IGF-I, we did not detect IGF-I receptor mRNA during the first 24 h after hepatectomy. However, some IGFBPs may act to enhance the activity of IGF-I independently of IGF-I receptors. Thus, IGF-1 and IGFBPs may interact with hepatocytes or nonparenchymal liver cells, through either IGF-I or novel receptors. In this way, IGFBP-I and IGF-I could act in a paracrine and/or autocrine fashion in maintaining normal liver architecture during regeneration.

Insulin-like growth factor receptors in chicken liver membranes: binding properties, specificity, developmental pattern and evidence for a single receptor type

Two distinct receptors for the insulin-like growth factors (IGF-I and IGF-II) have been identified in mammalian tissues, but so far only a receptor structurally related to the type I receptor has been identified in chicken embryonic tissues. This study was designed to characterize binding sites for IGF peptides in chicken liver microsomal membranes prepared from hatch to 10 weeks of age which is the period of most rapid growth. Binding of both human (h) IGF-I and hIGF-II was displaceable by either peptide and exhibited similar pH, time and temperature dependency. Human IGF-II was more potent than hIGF-I in competing for the binding of the iodinated ligands with half-maximum effective concentrations of 3-5 micrograms/l and 7-13 micrograms/l respectively. Porcine insulin was also a potent competitor. Affinity cross-linking studies, followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing conditions demonstrated that both IGF peptides were linked to a protein with a molecular weight of about 130,000 Da characteristic of the alpha-subunit of the type I receptor. There was no evidence for the presence of a type II receptor similar to that found in mammals. Specific binding of both peptides was low on the day of hatch, increased about threefold by day 3 of age and remained high for the first 3 weeks of life before returning to a lower steady state level up to 10 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Type beta transforming growth factor reversibly inhibits the early proliferative response to partial hepatectomy in the rat.

Type beta transforming growth factor (TGF-beta), a factor produced by many cell types, is a potent inhibitor of hepatocyte DNA synthesis in vitro. To determine whether TGF-beta can influence hepatocyte proliferation in vivo, its effects were examined on the regenerative response of liver to partial hepatectomy (PH) in the rat. Porcine platelet-derived TGF-beta 1 (0.5 micrograms), administered intravenously at the time of PH and 11 hr later, reduced the fraction of hepatocytes engaged in DNA synthesis 22 hr after PH by 67% and inhibited the rate of hepatic [3H]thymidine incorporation by 50%. TGF-beta 2 produced a similar effect. A single dose of 0.5 micrograms of TGF-beta 1 given 11 hr after PH reduced liver [3H]thymidine incorporation by 32%; 4.5 micrograms of TGF-beta 1 or TGF-beta 2 inhibited DNA synthesis by 88% and the labeling index by 86%. Although sensitive to TGF-beta administered 11 hr after PH, late in the G1 phase of the cell cycle, a single dose of 0.5 micrograms given at the time of PH did not significantly influence DNA synthesis 22 hr after PH. The inhibitory effects of TGF-beta were transient; rats treated with two 0.5-microgram doses of TGF-beta at 0 and 11 hr had completely restored their original liver DNA mass 8 days after PH. Administration of 0.5 microgram of either TGF-beta 1 or TGF-beta 2 every 12 hr for 5 days failed to suppress the recovery of hepatic DNA mass. However, the nuclear labeling index of the TGF-beta-treated animals was significantly higher than that of the controls. There was no evidence of cytotoxicity from TGF-beta, as determined by liver histology and plasma concentrations of glucose, insulin-like growth factor I, and two hepatic enzymes. Thus, TGF-beta 1 and TGF-beta 2 reversibly inhibit the proliferative response of liver to PH and may be important in the modulation of normal liver growth and repair.

The role of growth of normal and preneoplastic cell populations for tumor promotion in rat liver.

A number of different compounds, including phenobarbital, hypolipidemic drugs such as clofibrate and nafenopin, the sex steroids progesterone, cyproterone acetate, estradiol and mestranol, chlorinated hydrocarbons such as DDT, hexachlorocyclohexane, and TCDD and the antioxidant butylhydroxytoluene, appears to promote the development of liver tumors from previously induced initiated cells. The mechanisms of tumor promotion by several representative prototypes of these compounds were studied in rat liver in vivo. All liver tumor promoters mentioned above stimulate growth of normal liver. The growth response is due to cellular hypertrophy and/or increased rate of DNA (and cell) replication and/or decreased rate of cell death. Hepatocytes in foci or islands of altered cells (putatively preneoplastic) show higher rates of replication than normal liver cells; various different liver tumor promoters cause a further increase of proliferation of focal cells. The increased proliferative activity is found in different island phenotypes and thus seems to be a useful marker of the putative preneoplastic state. The focal cells respond to several factors limiting proliferation in normal liver, suggesting that they are not autonomous with respect to growth control. Early preneoplastic foci grow slowly without promotion, despite the relatively high rates of cell replication. Thus their cells seem to have a much shorter life-time than normal hepatocytes or to undergo reversion to the normal phenotype. Promoters seem to accelerate island enlargement by increasing cell replication and delaying cell death or remodeling. Thus, tumor promoters enhance the manifestation of the proliferation advantage of the putative initiated cell population. In addition, promoters cause increases in the number of detectable islands. This can partially be explained by enlargement of existing islands, but phenotypic changes that would enhance the probability of detection of remodelling islands and growth of dormant initiated cells, probably contribute to the apparent increase of island number. Putative preneoplastic foci of unknown origin are frequent in the liver of aged Wistar rats. They are morphologically and functionally very similar to those induced by carcinogens and are responsive to the mitogenic effect of tumor promoters. Promotion of these "spontaneous" foci may explain tumor appearance after long-term application of promoters.The findings may provide a basis for improved identification of initiated hepatocytes (and of initiating hepatocarcinogens) and for detection of tumor promoters. All suspected liver tumor promoters tested so far induced enhanced preneoplastic cell proliferation after single doses. The long-term carcinogenicity bioassay as currently performed does not discriminate between initiating and promoting properties of a test compound if the animals used develop spontaneous preneoplastic lesions in the organ affected.