Regulation of nerve growth factor synthesis in mouse submaxillary glands by testosterone

Genetic and endocrine control of renin activity in the submaxillary gland of the mouse

Basal activity of submaxillary gland (SMG) renin is high in female mice that carry the Rnrs allele and is induced to higher levels by treatment with dihydrotestosterone (DHT). To determine whether the difference in basal activity between high (Rnrs/Rnrs) and low (Rnrb/Rnrb) strains is due to enhanced sensitivity of Rnrs/Rnrs strains to endogenous androgen, we first studied the effect of several types of endocrine ablation on SMG renin in young female mice, and second, we removed normal androgen receptor protein by introducing the X-linked Tfm gene. Adrenalectomy with or without castration had no effect on basal SMG renin; hypophysectomy decreased basal renin activity 400-fold but did not abolish responsiveness to DHT. Loss of androgen receptor did not affect basal renin activity but did prevent enhancement by DHT. Basal and induced renin activities in L.AKR(Alll)/Cy, a congenic strain homozygous for Rnrs introduced from AKR/J into the background of C57L/J, an Rnrb/Rnrb type strain, are intermediate between levels observed in the original strains. We conclude that (1) the basal level of SMG renin is regulated directly or indirectly by some pituitary hormone(s) but not by androgen, (2) androgen induction of renin activity requires a normal androgen receptor, and (3) major gene(s) that regulate basal as well as induced SMG renin are in a circumscribed region of chromosome 1.

Submandibular glands in mice with muscular dystrophy: studies with nerve growth factor

Experiments have been carried out to examine the submandibular glands in mice with hereditary muscular dystrophy. Radioimmunoassay data confirm biological studies which show that submandibular glands in mice with muscular dystrophy contain less nerve growth factor (NGF) than glands of normal animals. Male dystrophics have half as much submandibular NGF as unafflicted mice, while females have only 10% of control levels. Gel filtration and electrophoretic studies detect no differences in the molecular properties of NGF in gland extracts from normal and dystrophic mice. Furthermore, NGF from both sources show equal activity in the sensory ganglion bioassay. Together, these results suggest that NGF deficits in submandibular glands of dystrophic mice are not due to measurement artifacts arising from alterations in the structure of the molecule. Morphological studies have uncovered a cytological basis for chemical deficits within submandibular glands of dystrophic mice. Stereological analysis of light and electron microscopic sections revealed that growth factor containing granular tubule cells (GTC) take up a smaller portion of the total gland volume, are smaller in size, and contain fewer secretory granules than comparable cells in glands from controls. Furthermore, the ultrastructure of GTC in dystrophic animals suggests that the cells are less active in producing secretory protein than GTC in glands from normal animals. These results are consistent with the idea that growth factor deficits arise from cellular abnormalities in the granular tubule segment of the gland.

Factors in the rat submaxillary gland that stimulate growth of cultured glioma cells: identification and partial characterization

The effect of rat submaxillary extract on the growth of rat C6 glioma cells in serum-free culture has been examined. Extracts (10-15 microgram/ml) of submaxillary glands from both male and female rats markedly enhanced the growth of serum-deprived C6 cells and, in combination with insulin, transferrin, and NIH-LH (a source of fibroblast growth factor), were able to stimulate C6 cell growth to an extent comparable to that achieved with an optimal amount of fetal calf serum. The mitogenic activity of rat submaxillary extracts was found to be heat-labile, acid-stable, and partially inactivated by protease and 2-mercaptoethanol. Under our assay conditions, biologically active preparations of purified mouse submaxillary gland epidermal growth factor (EGF) or nerve growth factor (NGF) were not mitogenic for C6 cells, nor was the mitogenic activity of rat submaxillary extracts inhibited by antiserum to these mouse submaxillary gland growth factors. These results suggest that the active component(s) of rat submaxillary extracts is unrelated to either EGF or NGF. The growth-enhancing effect also appears unrelated to esteropeptidase activity present in these extracts since the mitogenic activity was unaffected by several protease inhibitors. Moreover, two purified mouse submaxillary gland arginylesteropeptidases, EGF-binding protein and gamma-subunit of 7 S NGF, were unable to elicit a comparable growth response even when added to cell culture medium at unreasonably high concentrations. The C6 cell mitogenic activity of crude submaxillary extracts could be separated into two biologically similar components by either gel filtration on Sephadex G-100, preparative isoelectric focusing in a pH gradient of 3-10, or adsorption to DEAE-cellulose followed by elution with a sodium chloride gradient. One of the active components was acidic in nature and had an apparent molecular weight of 40,000, while the other was near neutral in charge and possessed a molecular weight of approximately 20,000. The relationship between these two C6 cell mitogenic components and the rat submaxillary gland component responsible for stimulating Balb/c-3T3 cell growth in serum-free, factor supplemented medium (McClure et al., 1979, J. Cell Biol. 83:96a) is also discussed.

Radioimmunoassay for mouse nerve growth factor (NGF). Effects of thyroxine administration on tissue NGF levels

A sensitive and specific radioimmunoassay (RIA) has been developed for beta-nerve growth factor (NGF) purified from the submaxillary gland of the adult male mouse. The RIA is sensitive to 13 pg/assay tube with an intra-assay coefficient of variation of 7% and an interassay coefficient of variation of 11.8%. Of the substances tested for immunological cross-reactivity in the RIA, only mouse epidermal growth factor caused significant displacement of the radiolabeled ligand; 11% at a dose of 10 microgram/ml. Mouse tissue extracts diluted out parallel to the standard curve. The effects of altered thyroid function on tissue NGF concentration in adult male mice were studied using the RIA. Thyroxine administration (25 microgram T4 i.p. daily for 12 days) caused significant increases in submaxilllary gland and liver NGF content and concentration (P less than 0.001) compared to controls but had no significant effect on heart and kidney NGF levels. Propylthiouracil treatment (0.05% PTU in the drinking water for 21 days) led to a marked increase in thyroid gland weight (550% of control) but had no significant effect on NGF concentration in any of the organs studied with the exception of kidney where a 75% reduction in NGF concentration was observed. These studies indicate that thyroid hormones increase NGF content and concentration in the submaxillary gland and liver of adult male mice and are suggestive of increased NGF synthesis. Thyroid hormones may therefore play an important regulatory role in NGF metabolism in peripheral tissues of the adult mouse.

Growth-promoting actions of extracts from mouse submaxillary glands on human endothelial cells in culture

Extracts of submaxillary glands from two different strains of inbred mice were mitogenic for human endothelial cells in culture. The mitogenic activity of extracts from glands of males of the SWR/J and C57BL/10J strains were equivalent, and the growth stimulating effect was unrelated to renin or esteroproteolytic activity. Mitogenic activity in extracts from SWR/J females was less than that from males, and extracts from C57BL/10J females were inactive. The polypeptide growth factors, epidermal (EGF) and fibroblast (FGF) growth factors, also stimulated replication of endothelial cells. Cells from either umbilical arteries or veins responded to submaxillary extracts, EGF, or FGF with a similar increase in cell number, increase in protein and enhanced uptake of 3H-thymidine. The proliferative response was associated with decreased activity of angiotensin I converting enzyme which is localized on the endothelial surface. Nerve growth factor (NGF) was not mitogenic for endothelial cells. Extracts of submaxillary glands from male mice of either strain contained approximately 20 times more EGF than extracts from females, as determined by immunodiffusion. Mitogenic activity of the extracts was completely inhibited by antiserum to EGF, suggesting that the active component of these preparations is EGF.

Thyroxine increases nerve growth factor concentration in adult mouse brain

The effects of thyroxine and propylthiouracil on nerve growth factor concentrations in cerebral cortex, cerebellum, and brainstem of adult male mice were assessed by using a sensitive radioimmunoassay for the beta-subunit of mouse nerve growth factor. Thyroxine administration significantly increased the concentration of nerve growth factor in all three brain areas compared to control values, whereas propylthiouracil was without effect. These results suggest that thyroid hormones stimulate nerve growth factor synthesis in the mature central nervous system, and raise the possibility that the influence of thyroid hormones on central nervous system development might be mediated or influenced by nerve growth factor.

A serological assay for the detection of cell surface receptors of nerve growth factor

When single-cell suspensions prepared from embryonic day 8 (E8) chick sensory ganglia are incubated with nerve growth factor (NGF), anti-NGF antiserum, and complement, an NGF-dependent cytotoxic kill of 20 (+/- 3)% of the ganglia cells is observed. This percentage is increased by a factor of two when only the neuronal cells are tested. No kill is observed on the nonneuronal cell population representing 50% of the ganglia dissociate. When E8 sensory ganglia cells are cultured in the presence of NGF following cytotoxic kill, the large, phase-bright NGF-reponsive neurons are missing from the culture. These results indicate that the cells recognized in the cytotoxicity assay have to carry NGF-binding sites of type I, which is the one with the higher affinity of the two types of NGF-binding sites (I and II) present on sensory ganglia cells. This conclusion is further supported by the following data: a) half maximal cytotoxicity is reached already at a concentration of NGF which is below the KD of binding site I; b) a washing step which removes all NGF bound to type II receptors while leaving a high percentage of type I receptors occupied has no effect on the percentage of ganglia cells killed. Using the cytotoxicity assay the presence of high-affinity binding sites of type I can be demonstrated on sensory ganglia cells from E8 chick embryos but not from E4 embryos and not on liver and heart cells from E8 embryos. Further, type I receptor-bearing cells were detectable in the brain using this assay. At E8, NGF receptors could be detected on cells of the forebrain and the tectum but not on brain stem cells. Cytotoxic kill of forebrain cells was found to be especially high at E8 and E9, and decreased by E10.

Genetic control of renin activity in the submaxillary gland of the mouse

Administration of androgen to female mice is known to increase the level of several proteins in the submaxillary gland, including nerve growth factor, epidermal growth factor, esteroproteolytic activity, and renin. In the present study, renin activity has been assessed in extracts of submaxillary gland of female mice from two inbred strains (SWR/J and C57BL/10J), from F1 and F2 hybrids, and from backcrosses between F1 and parental strains. In both uninduced and induced mice, renin activity of submaxillary gland was more than 100-fold greater in SWR/J than in C57BL/10J mice as measured by either an enzymatic assay or an immunodiffusion method. This difference was not due to differences in plasma testosterone levels between the strains, and the enzymes from the two strains had similar pH optima, substrate specificities, heat stabilities, and apparent Michaelis constants. In the submaxillary gland the difference was relatively specific for renin because increases in esteroproteolytic activity, nerve growth factor, and epidermal growth factor after androgen treatment appeared to be similar in both strains. Studies with the various hybrids indicate that the difference in renin activity between the two strains is apparently due to a single regulatory gene.