Visualizing the expression of a human growth hormone (hGH) transgene in the liver: intrahepatic regional and intracellular differences of expression are associated with morphological alterations and hepatocellular proliferation

Expression levels of mRNA for insulin-like growth factors 1 and 2, IGF receptors and IGF binding proteins in in vivo and in vitro grown bovine follicles

This study investigated mRNA levels for insulin-like growth factors (IGFs) IGF1 (IGF-I) and IGF2 (IGF-II), IGF receptors (IGF1R and IGF2R), and binding proteins (IGFBP-1, IGFBP-2. IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6) in bovine follicles of 0.2, 0.5 or 1.0 mm in diameter. mRNA expression levels in in vitro cultured follicles that reached approximately 0.5 mm were compared with that of in vivo grown follicles. IGF1R and IGF2R expression levels in 0.5 mm in vivo follicles were higher than in 1.0 or 0.2 mm follicles, respectively. IGFBP-1, IGFBP-2. IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6 showed variable expression in the follicular size classes analyzed. In vitro grown follicles had significantly reduced expression levels for IGF1, IGF1R, IGFBP-3, IGFBP-5 and IGFBP-6 mRNA when compared with 0.2 mm follicles, but, when compared with in vivo grown follicles (0.5 mm), only IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-6 showed a reduction in their expression. In conclusion, IGFs, their receptors and IGFBPs showed variable expression of mRNA levels in the follicular size classes analyzed.

Efeito da suplementação de L-arginina sobre a secreção de hormônio do crescimento e fator de crescimento semelhante à insulina em adultos

Baseado nos pressupostos de que a infusão de aminoácidos pode aumentar a secreção de hormônio de crescimento (GH), e que o metabolismo deste hormônio está relacionado com a secreção do fator de crescimento semelhante à insulina (IGF-I), o objetivo deste estudo foi verificar o efeito da suplementação de L-arginina sobre o GH e IGF-I em adultos. Participaram do estudo 17 indivíduos do sexo masculino, que foram randomizados para receber L-arginina (n= 10) ou placebo (n= 7), sete gramas ao dia, durante um período de sete dias. Antes e após o período de suplementação, os voluntários realizaram coleta de sangue em jejum para verificação dos níveis séricos de GH e IGF-I, bem como coleta de urina para verificação da excreção de uréia. Ao final do período experimental, verificamos que o grupo que recebeu L-arginina aumentou a excreção de uréia na urina (de 2684,1 ± 475,2 mg/dl para 2967,2 ± 409,7 mg/dl, p= 0,002), entretanto não modificou significativamente a secreção dos hormônios avaliados. O grupo que recebeu placebo não alterou significativamente nenhum parâmetro avaliado. A suplementação de L-arginina durante sete dias mostrou-se ineficaz para aumentar a secreção de GH e IGF-I em indivíduos adultos do sexo masculino.

Hepatocellular kinetics and the expression of growth hormone (GH) in the livers and liver tumours of GH-transgenic mice

Although it is well known that transgenic mice that overexpress growth hormone (GH) frequently develop liver tumours, the precise nature of the relationship between the overexpression of GH and hepatocarcinogenesis is not clear. The current study was designed to investigate the relationship between the expression of the GH transgene and changes in hepatocyte morphology and kinetics, prior to and during hepatocarcinogenesis in GH-transgenic mice. In young mice (1-month-old) prior to tumour development, GH protein, as detected by immunohistochemistry, was observed in the cytoplasm of essentially all hepatocytes. In liver tissues of older animals, apoptotic cells and hypertrophic hepatocytes did not express immunoreactive GH, even though GH was expressed strongly in the smaller hepatocytes. A relatively high proportion of large dysplastic hepatocytes (>50 microm) were apoptotic (TUNEL positive), whereas smaller hepatocytes featured more prominently in the proliferative phase, as measured by BrdU incorporation. GH expression in tumour tissue, as detected by immunohistochemistry, was often variable and generally decreased with tumour development. Northern blot analysis showed that equivalent levels of GH mRNA were present in tumour tissue and adjacent liver. However, there was no clear trend when the levels of GH mRNA extracted from adenoma, and hepatocellular carcinoma, were compared. These observations help clarify some of the mechanisms by which GH promotes hepatocarcinogenesis in GH-transgenic mice.

High, persistent hepatocellular proliferation and apoptosis precede hepatocarcinogenesis in growth hormone transgenic mice

AIMS/BACKGROUND

Growth hormone (GH) transgenic mice are known to develop hepatocellular adenomas and carcinomas. In order to understand more about hepatocarcinogenesis in the GH-transgenic mouse model we quantitated the rates of hepatocellular proliferation and apoptosis in these mice.

METHODS

Two lines of GH-transgenic mice and non-transgenic control mice were generated and sacrificed at regular intervals between one and nine months. Hepatocellular replication was measured by in vivo incorporation of bromodeoxyuridine (BrdU) and counting BrdU-positive nuclei in histological liver sections. Serial sections taken from these mouse livers were also assessed for rates of hepatocellular apoptosis using the in situ end-labelling of fragmented DNA (TUNEL) method.

RESULTS

High levels of hepatocellular replication were sustained life-long in this model. Increased rates of hepatocellular proliferation preceded the onset of hepatic inflammation, a prominent feature in the liver pathology of GH-transgenic mice. In tumour tissue, cellular proliferation was up to 17-fold greater than in surrounding non-tumour tissue. Apoptosis rates were also elevated in non-tumour regions of GH-transgenic mouse livers compared to controls. Interestingly, large dysplastic hepatocytes were common in the fraction of cells undergoing apoptosis, especially in older mice with inflamed livers. The increase in the rate of hepatocellular apoptosis in GH-transgenic animals largely balanced the augmented levels of proliferation seen in these mice. In tumour tissue, however, the profound increase in the number of proliferating tumour cells outstripped the increase in apoptosis.

CONCLUSION

Relatively high and enduring levels of hepatocellular replication and apoptosis precede hepatocarcinogenesis in GH-transgenic mice. Increased cellular proliferation and resistance to apoptosis were evident in tumour growth in older animals.