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Biomedical subjects

J Breu

Publications and source records attributed to J Breu.

13 recordsLinked to original sources
PubMed2004

Preservation of neuroendocrine control of reproductive function despite severe undernutrition.

Anorexia nervosa (AN) is characterized by low weight and self-imposed caloric restriction and leads to severe bone loss. Although amenorrhea due to acquired GnRH deficiency is nearly universal in AN, a subset of patients maintains menses despite low weight. The mechanisms underlying continued GnRH secretion despite low weight in these patients and the impact of gonadal hormone secretion on bone mineral density (BMD) in such eumenorrheic, low-weight patients remain unknown. We hypothesized that 1) eumenorrheic women with AN would have higher body fat and levels of nutritionally dependent hormones, including leptin and IGF-I, than amenorrheic women with AN and comparable body mass index; and 2) BMD would be higher in these women. We also investigated whether the severity of eating disorder symptomatology differed between the groups. We studied 116 women: 1) 42 low-weight women who fulfilled all Diagnostic and Statistical Manual of Mental Disorders (fourth edition) diagnostic criteria for AN, except for amenorrhea; and 2) 74 women with AN and amenorrhea for at least 3 months. The two groups were similar in body mass index (17.1 +/- 0.2 vs. 16.8 +/- 0.2 kg/m(2)), percent ideal body weight (78.2 +/- 0.8% vs. 76.7 +/- 0.8%), duration of eating disorder (70 +/- 13 vs. 59 +/- 9 months), age of menarche (13.2 +/- 0.3 vs. 13.5 +/- 0.2 yr), and exercise (4.5 +/- 1.0 vs. 4.2 +/- 0.5 h/wk). As expected, eumenorrheic patients had a higher mean estradiol level (186.6 +/- 19.0 vs. 59.4 +/- 2.5 nmol/liter; P < 0.0001) than amenorrheic subjects. Mean percent body fat, total body fat mass, and truncal fat were higher in eumenorrheic than amenorrheic patients [20.9 +/- 0.9% vs. 16.7 +/- 0.6% (P = 0.0001); 9.8 +/- 0.5 vs. 7.8 +/- 0.3 kg (P = 0.0009); 3.4 +/- 0.2 vs. 2.7 +/- 0.1 kg (P = 0.006)]. The mean leptin level was higher in the eumenorrheic compared with the amenorrheic group (3.7 +/- 0.3 vs. 2.8 +/- 0.2 ng/ml; P = 0.04). Serum IGF-I levels were also higher in the eumenorrheic than in the amenorrheic group (41.8 +/- 3.7 vs. 30.8 +/- 2.3 nmol/liter; P = 0.02). There were only minor differences in severity of eating disorder symptomatology, as measured by the Eating Disorders Inventory, and where differences were observed, eumenorrheic subjects manifested more severe symptomatology than amenorrheic subjects. Mean BMD at the posterior-anterior and lateral spine were low in both groups, but were higher in patients with eumenorrhea than in those with amenorrhea [posterior-anterior spine T-score, -0.9 +/- 0.1 vs. -1.9 +/- 0.1 (P < 0.0001); lateral spine T-score, -1.2 +/- 0.1 vs. -2.3 +/- 0.2 (P < 0.0001)]. In contrast, preservation of menstrual function was not protective at the total hip (total hip T-score, -0.9 +/- 0.1 vs. -1.1 +/- 0.1; P = 0.27), trochanter, or femoral neck. In summary, patients with eumenorrhea had more body fat and higher serum leptin levels than their amenorrheic counterparts of similar weight. Moreover, reduced bone density was observed in both groups, but was less severe at the spine, but not the hip, in women with undernutrition and preserved menstrual function than in amenorrheic women of similar weight. Therefore, fat mass may be important for preservation of normal menstrual function in severely undernourished women, and this may be in part mediated through leptin secretion. In addition, nutritional intake and normal hormonal function may be independent contributors to maintenance of trabecular bone mass in low-weight women.

Adult↗
PubMed1997

Rapid stimulation of amyloid precursor protein release by epidermal growth factor: role of protein kinase C.

The amyloid precursor protein (APP) of Alzheimer's disease is a transmembrane protein that is cleaved by an uncharacterized enzyme known as alpha-secretase within its extracellular/intraluminal domain after the activation of guanine nucleotide-binding protein-coupled receptors linked to phosphoinositide hydrolysis. The secretory process results in the release of large soluble derivatives of APP (APPs), and, when elicited by muscarinic receptor activation, exhibits both protein kinase C (PKC)-dependent and tyrosine phosphorylation-dependent components [Slack, Breu, Petryniak, Srivastava and Wurtman (1995) J. Biol. Chem. 270, 8337-8344]. In this report we examine the regulation of the release of APPs by epidermal growth factor (EGF) receptors, which possess intrinsic tyrosine kinase activity, and are coupled to a variety of effectors including phosphoinositide-specific phospholipase Cgamma. In A431 cells, EGF caused time-dependent and dose-dependent increases in the formation of inositol phosphates in cultures prelabelled with myo--3H-inositol, and in the release of APPs into the culture medium; the two responses exhibited similar time courses and EC50 values for EGF. Concomitant with these effects, there were concentration-dependent (3-300 ng/ml) increases in the phosphorylation of tyrosine residues in several proteins, including the EGF receptor itself. The specific PKC antagonist GF 109203X decreased the effect of EGF by approx. 35% at a concentration that abolished the stimulation of the release of APPs by the PKC activator PMA. Tyrphostin AG 1478, an inhibitor of EGF receptor tyrosine kinase, abolished the EGF-induced release of APPs. These results demonstrate that in A431 cells, activation of the EGF receptor stimulates alpha-secretase activity by a mechanism that is partly dependent on PKC activity.

Amyloid Precursor Protein Secretases↗
PubMed1995

Tyrosine phosphorylation-dependent stimulation of amyloid precursor protein secretion by the m3 muscarinic acetylcholine receptor.

Stimulation of m1 and m3 muscarinic acetylcholine receptors, which are coupled to phosphoinositide hydrolysis and protein kinase C activation, has been shown to increase the release of soluble amyloid precursor protein derivatives (APPs). The effect is mimicked by phorbol esters, which directly activate protein kinase C. Using human embryonic kidney cells expressing individual muscarinic receptor subtypes, we found that stimulation of APPs release by the muscarinic agonist carbachol was only partially reduced by a specific inhibitor of protein kinase C (the bisindolylmaleimide GF 109203X), while the response to phorbol 12-myristate 13-acetate (PMA) was abolished. The increase in APPs release elicited by carbachol and PMA was accompanied by elevated tyrosine phosphorylation of several proteins and reduced by tyrosine kinase inhibitors; GF 109203X significantly reduced the stimulation of tyrosine phosphorylation by carbachol and PMA. Inhibition of protein tyrosine phosphatases by vanadyl hydroperoxide markedly increased cellular tyrosine phosphorylation and enhanced APPs release as effectively as PMA and carbachol. Direct phosphorylation of amyloid precursor protein on tyrosine residues following treatment with carbachol, PMA, or vanadyl hydroperoxide was not observed. The results implicate both tyrosine phosphorylation and protein kinase C-dependent mechanisms in the regulation of APPs release by G protein-coupled receptors, and suggest that carbachol and PMA increase APPs release from human embryonic kidney cells expressing m3 muscarinic receptors via partially divergent pathways that converge at a tyrosine phosphorylation-dependent step.

Alkaloids↗
PubMed1995

Phorbol ester stimulates choline uptake in Swiss 3T3 fibroblasts following introduction of the gene encoding protein kinase C alpha.

Phorbol 12-myristate 13-acetate (PMA) stimulated radiolabelled choline uptake and incorporation into phosphatidylcholine (PtdCho) in a time- and concentration-dependent manner in wild-type NIH 3T3 fibroblasts. The accumulation of labelled choline induced by PMA was paralled by an increase in choline mass. The results implicate protein kinase C (PKC) in the regulation of choline uptake. In order to address the PKC-subtype specificity of this response, a study was undertaken in Swiss 3T3 fibroblast cells, which normally express very low levels of PKC alpha. A retroviral expression system was used to introduce the genes for PKC alpha and neomycin resistance (used for selection) into the cells. Two resulting lines expressed PKC alpha at levels that were 20-fold higher than those found in the control (neomycin-resistant) line, or in the wild-type cells. In control Swiss 3T3 fibroblasts, 1 microM PMA elevated choline levels by only 30%, whereas, in Swiss 3T3 cell lines that stably over-expressed PKC alpha, PMA caused a 5-fold enhancement in [14C]choline accumulation. This concentration of PMA significantly increased [14C]PtdCho levels in both control and PKC alpha-over-expressing lines, although the effect in the latter was significantly greater. The effects of PMA were inhibited by the PKC antagonist sphingosine. These results implicate PKC alpha in the regulation of choline accumulation and phospholipid synthesis in fibroblasts. Although additional PKC subtypes appear to participate in the control of PtdCho synthesis in these cells, PMA-stimulated choline uptake in Swiss 3T3 fibroblasts is almost entirely dependent on the presence of PKC alpha.

3T3 Cells↗
PubMed1993

Regulation by phorbol esters of amyloid precursor protein release from Swiss 3T3 fibroblasts overexpressing protein kinase C alpha.

Release of large soluble NH2-terminal fragments of the amyloid precursor protein (APP) of Alzheimer's disease was measured in two Swiss 3T3 fibroblast cell lines (designated SF1.4 and SF3.2), overexpressing the alpha subtype of protein kinase C, and in two control cell lines (SC1 and SC2) (Eldar, H., Zisman, Y., Ullrich, A., and Livneh, E. (1990) J. Biol. Chem. 265, 13290-13296). Basal release of APP was significantly increased in SF1.4 cells, but not in SF3.2 cells, relative to controls. Phorbol 12-myristate 13-acetate, an activator of protein kinase C, elicited a concentration-dependent increase in APP release in all four cell lines. However, the estimated EC50 for this effect was lower in the two cell lines overexpressing protein kinase C-alpha (7 and 6 nM, in SF1.4 and SF3.2 cells, respectively) than in control SC1 and SC2 cells (56 and 22 nM, respectively). The absolute amount of APP released by maximal concentrations of phorbol ester was not altered by overexpression of protein kinase C alpha. The protein kinase C inhibitor H-7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride) significantly reduced the response to phorbol esters in control (SC1) cells but not in cells (SF1.4) that overexpress protein kinase C alpha. Levels of cell-associated APP were slightly elevated, and rates of APP turnover were unchanged, in SF1.4 cells relative to controls. However, cell-associated APP levels were lower in SF3.2 cells than in controls. The results demonstrate that protein kinase C alpha regulates APP release in Swiss 3T3 fibroblasts, and perhaps in other tissues, including brain, and may be the isozyme that mediates receptor-evoked release of APP.

3T3 Cells↗
PubMed1991

Production of diacylglycerol by exogenous phospholipase C stimulates CTP:phosphocholine cytidylyltransferase activity and phosphatidylcholine synthesis in human neuroblastoma cells.

The involvement of endogenous diacylglycerol production in the stimulation of phosphatidylcholine synthesis by exogenous phospholipase C was examined using a neuroblastoma (LA-N-2) cell line. Phospholipase C treatment (0.1 unit/ml) of intact cells stimulated CTP:phosphocholine cytidylyltransferase activity significantly more effectively than did maximally effective concentrations of the synthetic diacylglycerol sn-1,2-dioctanoylglycerol (1 mM). When added to cells together with phospholipase C, oleic acid, but not dioctanoylglycerol, further increased cytidylyltransferase activity with respect to phospholipase C treatment alone, indicating that the enzyme was not maximally activated by the lipase. This suggests that the lack of additivity of diacylglycerol and phospholipase C reflects a common mechanism of action. The time course of activation of cytidylyltransferase by phospholipase C paralleled that of [3H]diacylglycerol production in cells prelabeled for 24 h with [3H]oleic acid. Diacylglycerol mass was similarly increased. Significant elevations of [3H]oleic acid and total fatty acids occurred later than did the increases in cytidylyltransferase activity and diacylglycerol levels. No significant reduction in total or [3H]phosphatidylcholine was elicited by this concentration of phospholipase C, but higher concentrations (0.5 unit/ml) significantly reduced phosphatidylcholine content. The stimulation of cytidylyltransferase activity by phospholipase C or dioctanoylglycerol was also associated with enhanced incorporation of [methyl-14C]choline into phosphatidylcholine. Dioctanoylglycerol was more effective than phospholipase C at stimulating the formation of [14C]phosphatidylcholine, and the effects of the two treatments were additive. However, further analysis revealed that dioctanoylglycerol served as a precursor for [14C]dioctanoylphosphatidylcholine as well as an activator of cytidylyltransferase; and when corrections were made for this effect, the apparent additivity disappeared. The results indicate that the generation of diacylglycerol by exogenous phospholipase C (and possibly the subsequent production of fatty acids via diacylglycerol metabolism) activates cytidylyltransferase activity in neuronal cells under conditions in which membrane phosphatidylcholine content is not measurably reduced.

Choline-Phosphate Cytidylyltransferase↗