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J Törnell

Publications and source records attributed to J Törnell.

At least 37 records · Page 2Linked to original sources
PubMed1997

Mode of the autocrine/paracrine mechanism of growth hormone action.

GH is synthesized at multiple extrapituitary sites suggestive of an autocrine/paracrine mechanism of action. We have investigated a possible autocrine/paracrine mechanism of GH action, compared the cellular response to exogenous versus endogenously produced GH, and determined the nature of the interaction between external stimuli and endogenously produced GH. BRL cells expressing the GH receptor were transiently transfected with expression plasmids containing either the hGH or the bGH gene and the response of the cell was measured by CAT reporter plasmids requiring either STATs 1 and 3 or STAT5 for their response. Transient transfection of the hGH gene resulted in hGH accumulation in the cell and secretion into the media. The functional response through STATs 1 and 3 and STAT5 obtained with endogenously produced hGH was comparable or greater in magnitude to that obtained with the maximal stimulatory dose of exogenous hGH. Similar results were obtained with an expression plasmid containing the bGH gene. Endogenously produced hGH interacted in an additive manner when combined with submaximal doses of both exogenous hGH and serum. Such results were also observed in a more physiologically relevant mammary carcinoma cell line (MCF-7). The nonreceptor-dimerizing hGH antagonist, hGH-G120R, used in cells expressing the homologous receptor extracellular domain was able to only partially inhibit the response of the cell to endogenously produced hGH, in contrast to full inhibition of exogenous hGH. We therefore conclude that GH can function in an autocrine/paracrine manner, additive in effect to external stimuli.

Animals↗
PubMed1997

Effects of chronically elevated growth hormone levels on polyamine metabolism in elderly transgenic mice.

The polyamines are ubiquitous, multifunctional aliphatic amines with roles in cell growth, proliferation, differentiation, and malignant development. After growth stimulation, rapid and transient changes occur in polyamine regulatory enzymes. In this respect, acute effects of growth hormone (GH) injection on polyamine metabolic enzymes have earlier been shown. The present investigation comprises studies of the effects on polyamine metabolism of constitutively elevated levels of circulating GH in elderly transgenic (tg+) mice, overexpressing bovine GH. Polyamine levels were found to be constitutively altered in the liver and kidney of tg+ mice. Less changes were found in the spleen and none in the brain. The cellular uptake of polyamines in the liver from tg+ mice showed an increase and considerable changes were observed in the activity of ornithine decarboxylase (ODC) in the liver and kidney and S-adenosylmethionine decarboxylase (AdoMetDC) in the liver. A conspicuous finding was the distribution pattern of ODC protein in the liver and both tg- and tg+ animals. The results show that the effects of chronically elevated GH levels are organ-dependent and complex, and differ from acute GH effects. Despite high ODC activity and polyamine levels in liver, these mice did not display any malignant transformation even at an advanced age, indicating that high ODC activity is not sufficient to induce tumorigenesis in vivo.

Adenosylmethionine Decarboxylase↗
PubMed1997

Transgenic mice overexpressing the prolactin gene develop dramatic enlargement of the prostate gland.

An altered endocrine status of elderly men has been hypothesized to be important for development of prostate hyperplasia. The present study addresses the question whether increased PRL expression is of importance for development of prostate hyperplasia in mice. Three lines of PRL transgenic mice were generated having serum levels of PRL of approximately 15 ng/ml, 100 ng/ml, and 250 ng/ml, respectively. These mice developed dramatic enlargement of the prostate gland, approximately 20 times the normal prostate weight and they had a 4- to 5-fold increased DNA content. Histologically, the prostate glands in the transgenic mice were distended from secretion, and the amount of interstitial tissue was increased. The levels oftestosterone and IGF-I were increased in the PRL transgenic animals. In mice overexpressing the bovine GH gene, displaying elevated IGF-I levels, the prostate gland was slightly larger compared with normal mice, indicating that the effect of PRL was not primarily mediated through elevated plasma IGF-I levels. The present study suggests that PRL is an important factor in the development of prostate hyperplasia acting directly on the prostate gland or via increased plasma levels of testosterone.

Animals↗
PubMed1997

Improved long-term bone-implant integration. Experiments in transgenic mice overexpressing bovine growth hormone.

Several recent studies have investigated the effects of growth hormone (GH) on the healing of fractures and bone ingrowth, but with conflicting results. The negative results may be due to antibody formation against injected GH or because some experimental models are able to prove only positive GH effects. In this study, we wanted to investigate the effect of GH on implant integration in bone. To avoid potential formation of antibodies against injected GH, we used a model with transgenic mice overexpressing bovine GH (bGH). Titanium implants were inserted in the forehead of the mice. 4 months after insertion, the implants were cut out en bloc with the surrounding bone. The calcified specimens were cut and ground to a thickness of approximately 10 microns. Histomorphometry demonstrated significantly more direct bone-to-metal contact in the transgenic mice than in the nontransgenic littermates. Our findings indicate that systemic administration of GH in humans may improve implant integration in bone.

Animals↗
PubMed1996

PDGF-A signaling is a critical event in lung alveolar myofibroblast development and alveogenesis.

A mouse platelet-derived growth factor A chain (PDGF-A) null allele is shown to be homozygous lethal, with two distinct restriction points, one prenatally before E10 and one postnatally. Postnatally surviving PDGF-A-deficient mice develop lung emphysema secondary to the failure of alveolar septation. This is apparently caused by the loss of alveolar myofibroblasts and associated elastin fiber deposits. PDGF alpha receptor-positive cells in the lung having the location of putative alveolar myofibroblast progenitors were specifically absent in PDGF-A null mutants. We conclude that PDGF-A is crucial for alveolar myofibroblast ontogeny. We have previously shown that PDGF-B is required in the ontogeny of kidney mesangial cells. The PDGFs therefore appear to regulate the generation of specific populations of myofibroblasts during mammalian development. The two PDGF null phenotypes also reveal analogous morphogenetic functions for myofibroblast-type cells in lung and kidney organogenesis.

Actins↗
PubMed1996

Expression of Epstein-Barr nuclear antigen 2 in kidney tubule cells induce tumors in transgenic mice.

The effect of EBNA2 in normal cells in vivo has not as yet been explored. The experiments described here were initiated to follow the consequences of the expression of EBNA2 in different tissues in transgenic mice. EBNA2 transgenic strains were generated using a vector containing EBNA2 encoding sequences under the control of the simian virus 40 (SV 40) early enhancer/promoter fused to the endogenous EBNA2 Wp promoter. Control mice carrying a transgene with the same sequence but lacking the EBV DNA part remained healthy during observation periods of up to 15 months. The SV-EBNA2 transgenic animals, however, over time developed abdominal masses that on necropsy showed to be due to kidney tumors. Histological examination revealed the presence of tumors with the morphology of kidney adenocarcinoma with a solid growth pattern. At the age of 20 weeks the kidneys of all animals investigated showed disseminated islands of tubular hyperplasia but no true malignant neoplasms. At about 50 weeks of age multiple foci of microscopic tubular adenocarcinomas were found in both kidneys. Eventually, tumors could be diagnosed in about 90% of the SV-EBNA2 transgenic mice. EBNA2-encoding RNA was expressed in both non-malignant kidney tissue and in tumors as shown by cDNA/PCR analysis. Immunoprecipitation and immunoblot analysis showed that the tumor cells contained a polypeptide of the same size as EBNA2 in B95-8 cells that reacted with a monoclonal anti-EBNA2 antibody. Immunohistochemistry demonstrated nuclear expression of EBNA2 in hyperplastic tubules and in tumor tissue.

Adenocarcinoma↗
PubMed1996

Recombinant human bile salt-stimulated lipase: an example of defective O-glycosylation of a protein produced in milk of transgenic mice.

The expression of recombinant human bile salt-stimulated lipase (bssl) was targeted to the lactating mammary gland of transgenic mice. Expression of recombinant genes comprising bsslcDNA, or alternatively genomic bssl DNA, under control of regulatory elements derived from the murine whey acidic protein (wap) gene was achieved and evaluated. Constructs containing genomic bssl sequences mediated high levels (0.5-1 mg ml-1) of recombinant human BSSL in the milk. The recombinant BSSL produced was purified, biochemically characterized and compared to native BSSL and recombinant BSSL produced in mouse C127 and hamster CHO cells. Recombinant BSSL derived from transgenic mice showed a different migration and distribution after SDS-PAGE electrophoresis, lower apparent molecular mass on size-exclusion chromatography and no detectable interactions with a panel of lectins. These results indicate a significantly lower degree of O-glycosylation of recombinant BSSL in milk from transgenic mice than was found for the native enzyme or recombinant CHO- or C127 cell-produced BSSL. Despite these differences, mouse-milk-derived recombinant BSSL exhibited similar lipase activity, the same stability to low pH and similar sensitivity to elevated temperatures as the native enzyme. The observation that mouse-C127-cell-produced recombinant BSSL is heavily O-glycosylated makes species-related restrictions less attractive as an explanation for the reduced O-glycosylation.

Animals↗
PubMed1996

Elevated levels of growth hormone increase bone mineral content in normal young mice, but not in ovariectomized mice.

Both estrogens and GH are necessary for normal bone remodeling. This study investigates the effect of elevated GH levels on the amount and density of bone in young female mice and its dependence on intact ovarian function. Metallothionein promoter-GH-transgenic mice were either sham operated or ovariectomized at 25-29 days of age, and the bone measurements were made at about 90 days of age. A 6-mm high cylinder containing only cortical bone was cut from the right tibia, and lumbar vertebrae 6 was measured as a bone with predominantly cancellous bone. The amounts of tibial and vertebral bone, measured by dry weight, mineral weight, organic weight, bone mineral content (measured by dual energy x-ray analysis), and volume, were increased in GH-transgenic animals compared to those in normal littermates. This stimulatory effect of elevated GH levels was not seen in ovariectomized mice. The real density of the tibial bone were slightly decreased in GH-transgenic animals compared to normal littermates. In conclusion, elevated levels of GH increase the amounts of vertebral (predominantly cancellous) bone and tibial (cortical) bone in young mice. Intact ovaries are a prerequisite for the stimulatory effect of elevated levels of GH. The fact that ovariectomy decreases the stimulatory effect of elevated GH levels suggests that the effect of elevated GH levels in bone is dependent upon the presence of basic sex steroid secretion.

Absorptiometry, Photon↗
PubMed1995

Effect of recombinant human gonadotrophins on oocyte meiosis and steroidogenesis in isolated pre-ovulatory rat follicles.

In order to study the effects of recombinant human luteinizing hormone (LH) and recombinant follicle stimulating hormone (FSH) on the pre-ovulatory follicle, immature pregnant mare's serum gonadotrophin-treated rats were used. Follicles were isolated by dissection and incubated for 4 h in medium 199 containing different concentrations of the gonadotrophins. In control medium the follicle-enclosed oocytes remained arrested in prophase I, but in the presence of recombinant human LH or recombinant human FSH, a concentration-dependent increase in the proportion of oocytes which underwent germinal vesicle breakdown (GVB) was seen. The lowest effective concentration of recombinant human LH was 10-50 ng/ml, and at 1000 ng/ml 97% of the oocytes underwent GVB. Recombinant human FSH was also effective, albeit slightly less so than recombinant human LH. Follicular oestradiol accumulation was stimulated up to 5-fold, both gonadotrophins showing similar effectiveness. Follicular progesterone and testosterone accumulation was markedly stimulated by recombinant human LH, giving a maximal 20-fold and 15-fold increase respectively. A 5-fold stimulation of progesterone production was found with recombinant human FSH. When submaximal concentrations of recombinant human LH and recombinant human FSH were combined, an additive effect was found on oocyte meiosis and on oestradiol and progesterone accumulation. The results are in agreement with previous studies using pituitary gonadotrophin and show that both recombinant human LH and recombinant human FSH have intrinsic effects on oocyte meiosis and steroidogenesis. It is likely that in the physiological situation in vivo, both gonadotrophins contribute to regulate these events in the peri-ovulatory period.

Animals↗
PubMed1994

Expression and characterization of biologically active human extracellular superoxide dismutase in milk of transgenic mice.

We have targeted the expression of recombinant human extracellular superoxide dismutase, a glycosylated tetrameric metalloprotein, to the mammary gland of transgenic mice. This was achieved by using regulatory elements from either the murine whey acidic protein gene or the ovine beta-lactoglobulin gene to control expression of human extracellular superoxide dismutase cDNA. Whey acidic protein regulatory sequences directed high level mammary gland-specific expression of the recombinant gene and secretion of biologically active extracellular superoxide dismutase into the milk. The produced recombinant protein was fully active, it was in tetrameric form, it showed heparin affinity, and its mass was similar to that of the native enzyme. In addition, the in vivo plasma clearance in a rabbit model was similar to the previously studied native and recombinant forms. To our knowledge, this is the first example of efficient production of a tetrameric, protease-susceptible metalloprotein in milk of transgenic animals. Production at equivalent levels in transgenic farm animals would yield sufficient extracellular superoxide dismutase for therapeutic purposes.

Animals↗
PubMed1994

Disproportional bone growth and reduced weight gain in gonadectomized male bovine growth hormone transgenic and normal mice.

Sex steroids have been shown to influence longitudinal bone growth during sexual maturation, partially by increased GH secretion. Mice transgenic for metallothionein promoter bovine GH were developed by pronuclear injection as a model with sex steroid-independent GH secretion. Prepubertal normal and transgenic, male and female mice were either gonadectomized or sham operated. The growth was divided into two segments: peripubertal growth from 30-60 days of age and adult growth from 60-90 days of age. Orchidectomy resulted in a decreased growth rate of the lumbar spine and a decreased weight gain during the peripubertal growth, whereas tibia growth was unaffected. The alteration in proportions between the lumbar spine and the tibia was apparent for both normal and bovine GH transgenic mice, suggesting that the effect was not mediated via decreased GH secretion. Orchidectomy resulted in increased adult tibial growth, whereas weight gain and lumbar growth were unaffected. In female mice, gonadectomy did not influence these parameters during either time period studied. In summary, we present data indicating that the male gonads in a GH secretion-independent manner stimulate pubertal growth of the spine and inhibit the tibial growth of adult animals.

Animals↗
PubMed1993

Effect of cyclic AMP on the isolated human oocyte--cumulus complex.

Cyclic AMP (cAMP) is one of the key regulators of the resumption of oocyte meiosis (oocyte maturation) in several mammalian species. In this study we have examined the role for cAMP in regulation of spontaneous maturation of human oocytes. Oocytes were obtained in connection with gynaecological operations and cultured for 24 or 48 h. A significantly larger proportion (77%) of oocytes cultured in the presence of 1 mM dibuturyl-cAMP (dbcAMP) for 24 h were arrested in meiosis compared to oocytes cultured in control medium (25%). In addition, dbcAMP stimulated progesterone accumulation during 48 h of incubation and inhibited monolayer formation of the cumulus cells attached to the oocyte. The data presented in this study demonstrate that dbcAMP delayed the spontaneous maturation of human oocytes and stimulated progesterone production by the cumulus cells. These results indicate that cAMP may be important also for regulation of meiosis in human oocytes and confirm results obtained in other species.

Adult↗
PubMed1993

Expression of insulin-like growth factor-I (IGF-I) in the rat fallopian tube: possible autocrine and paracrine action of fallopian tube-derived IGF-I on the fallopian tube and on the preimplantation embryo.

Recent studies have indicated that growth factors such as insulin-like growth factors (IGFs) increase the growth rate of cultured preimplantation embryos. We therefore hypothesized that the fallopian tube may produce IGFs which in turn participate in the regulation of preimplantation embryo development in vivo. In the present study we examined the expression of IGF-I in the fallopian tube. We demonstrated that IGF-I transcripts (7.0, 1.7, and 1.2-0.8 kilobases) were abundant in the fallopian tube. Immunoreactive IGF-I was most abundant in the epithelial cells in the fallopian tube, and IGF-I messenger RNA (mRNA) was detected in the luminal region of the fallopian tube. A solution hybridization assay was used to examine the regulation of IGF-I mRNA. The abundance of IGF-I transcripts changed markedly during the 4-day estrous cycle with the highest levels on the day of proestrus. The increase in IGF-I mRNA between the day of diestrus II and the day of proestrus was 4-fold (P < 0.01). The pattern of IGF-I mRNA expression in the fallopian tube resembled the pattern of ovarian estrogen production during the estrous cycle. The level of IGF-I mRNA decreased after hypophysectomy. The expression of IGF-I mRNA in the fallopian tube was dose-dependently regulated by estradiol, and a single sc injection of estradiol [5 micrograms/100 g body wt (BW)] increased the IGF-I mRNA in a time-dependent manner with a significant increase after 3 h (P < 0.01). The lowest estradiol dose tested (0.1 microgram/100 g BW) increased the expression after 6 h, whereas progesterone (5 micrograms/100 g BW) was ineffective. The presence of embryos in the fallopian tube did not statistically significantly influence the abundance of IGF-I transcripts as measured with a solution hybridization assay on RNA extracted from whole fallopian tubes. In order to determine possible targets for fallopian tube-derived IGF-I we examined the expression of IGF-I receptor mRNA. Northern blot analysis revealed that an 11-kilobase IGF-I receptor transcript was expressed in the fallopian tube. Using a reverse transcriptase-polymerase chain reaction, IGF-I receptor mRNA was also detected in the eight-cell but not two-cell preimplantation embryo. The present study demonstrates that IGF-I is produced in the fallopian tube and its expression is regulated by estradiol. Both the fallopian tube and the eight-cell preimplantation embryo express IGF-I receptors and are therefore potential target tissues.

Animals↗
PubMed1993

Embryonic stem cells express growth hormone receptors: regulation by retinoic acid.

Embryonic and fetal growth are generally considered to be independent of pituitary GH. However, it has been demonstrated recently that 18-day-old rat embryos and rat fetuses express GH receptors, suggesting that GH could play a role in early development. The aim of the present investigation was to determine whether preimplantation embryos also express GH receptors. Germ line competent mouse embryonic stem (ES) cells and cultured mouse preimplantation embryos were examined with Northern blot analysis, RNAse-protection solution-hybridization assays, reverse transcription/polymerase chain reaction assays and immunohistochemistry for the detection of GH receptors. Northern blot analysis of ES cells using a probe corresponding to the extracellular domain of the GH receptor demonstrated the presence of two transcripts (1.2 and 4.5 kilobases). The RNAse-protection solution-hybridization assay revealed that ES cells express approximately one sixth of the GH-receptor messenger RNA (mRNA) levels expressed in liver from pregnant mice. Treatment of cultured ES cells with retinoic acid (100 nM) for 6 days increased GH-receptor mRNA levels (P < 0.01). GH-receptor mRNA was further identified in ES cells, preimplantation embryos, muscle, liver, and placenta by a reverse transcription/polymerase chain reaction assay. In humans it has previously been shown that exon 3 of the GH-receptor is deleted in the placenta. However, none of the studied mouse tissues had a deletion of the GH-receptor mRNA corresponding to exon 3 of the human GH receptor. GH-receptor immunoreactivity was identified on the cultured ES-cells by immunohistochemistry. In conclusion, we have in the present study shown that germline competent ES cells and preimplantation mouse embryos express the GH receptor transcript and that this transcription is increased by retinoic acid in ES cells. Furthermore, the presence of GH-receptor immunoreactivity on the ES cells indicates that the GH-receptor transcript is translated.

Animals↗
PubMed1992

High frequency of mammary adenocarcinomas in metallothionein promoter-human growth hormone transgenic mice created from two different strains of mice.

Transgenic mice were developed by injecting a mouse metallothionein promoter-human growth hormone (Mt-hGH) gene fragment into the pronucleus of C57Bl x DBA/2J-f2 or C57Bl x CBA-f2 one cell embryos. Six founder animals with the C57Bl x DBA genetic background grew 1.3-2.2 times larger than littermate controls and had higher levels of hGH in plasma (4.6-279 mU/l). Three of the four female transgenic founders developed malignant papillar adenocarcinomas of mammary origin at 27-43 weeks of age. One male transgenic founder was successfully mated and two of three female transgenic offsprings developed mammary tumors. To examine if the tumor induction was dependent on the strain of mice used the experiments were repeated using animals with different genetic background. Fourteen female hGH transgenic mice from five founder animals were generated using C57Bl x CBA-f2 mice. Thirteen of the animals had elevated levels of hGH in plasma (7-1960 mU/l) and grew larger than control animals. Nine of the animals developed mammary adenocarcinomas. Four of the hGH expressing animals did not demonstrate macroscopic tumor formation but have not yet been analyzed histologically. The present study suggests that markedly elevated endogenous levels of GH cause mammary carcinoma in hGH transgenic mice. The present animal model might prove useful for studying molecular mechanisms involved in the development of hormonally induced mammary tumors.

Adenocarcinoma, Papillary↗
PubMed1991

Induction of mammary adenocarcinomas in metallothionein promoter-human growth hormone transgenic mice.

To develop transgenic mice, a mouse metallothionein promoter-human growth hormone (Mt-hGH) gene fragment was injected into the pronucleus of C57BI x DBA/2J F2 one-cell embryos. Six founder animals grew larger (1.3-2.2 times) than littermate controls and had higher levels of hGH in plasma (4.6-279 mU/l). At 27-43 weeks of age, 3 of the 4 female transgenic founders developed malignant papillary adenocarcinomas of mammary origin. One of the male transgenic founders was successfully mated and 2 of 3 female transgenic offspring developed mammary tumors. Forty-two female mice with the same genetic background as the transgenic animals and older than 43 weeks served as controls. No palpable tumor was found in this group. Five of the control animals were killed and examined histologically, revealing only normal mammary tissue. Earlier studies have shown that GH is important for growth and development of the mammary gland. Our study suggests that markedly elevated endogenous levels of GH cause mammary carcinoma in a specific strain of transgenic mice. The present animal model might be useful for studying molecular mechanisms that are involved in the development of hormonally induced mammary tumors.

Adenocarcinoma↗