Hepatic lipase overexpression lowers remnant and LDL levels by a noncatalytic mechanism in LDL receptor-deficient mice.

To address the role of the noncatalytic ligand function of hepatic lipase (HL) in low density lipoprotein (LDL) receptor-mediated lipoprotein metabolism, we characterized transgenic mice lacking the LDL receptor (LDLR) that express either catalytically active (Ldlr(-/-)HL) or inactive (Ldlr(-/-)HL(S145G)) human HL on both chow and high fat diets and compared them with nontransgenic Ldlr(-/-) mice. In mice fed a chow diet, apolipoprotein (apo)B-containing lipoprotein levels were 40-60% lower in Ldlr(-/-)HL and Ldlr(-/-)HL(S145G) mice than in Ldlr(-/-) mice. This decrease was mainly reflected by decreased apoB-48 levels in the Ldlr(-/-)HL mice and by decreased apoB-100 levels in Ldlr(-/-) HL(S145G) mice. These findings indicate that HL can reduce apoB-100-containing lipoproteins through a noncatalytic ligand activity that is independent of the LDLR. Cholesterol enrichment of the apoB-containing lipoproteins induced by feeding Ldlr(-/-)HL and Ldlr(-/-)HL(S145G) mice a cholesterol-enriched high fat (Western) diet resulted in parallel decreases in both apoB-100 and apoB-48 levels, indicating that HL is particularly efficient at reducing cholesterol-enriched apoB-containing lipoproteins through both catalytic and noncatalytic mechanisms. These data suggest that the noncatalytic function of HL provides an alternate clearance pathway for apoB-100- and apoB-48-containing lipoproteins that is independent of the LDLR and that contributes to the clearance of high density lipoproteins.

Cloning of a unique lipase from endothelial cells extends the lipase gene family.

A new lipoprotein lipase-like gene has been cloned from endothelial cells through a subtraction methodology aimed at characterizing genes that are expressed with in vitro differentiation of this cell type. The conceptual endothelial cell-derived lipase protein contains 500 amino acids, including an 18-amino acid hydrophobic signal sequence, and is 44% identical to lipoprotein lipase and 41% identical to hepatic lipase. Comparison of primary sequence to that of lipoprotein and hepatic lipase reveals conservation of the serine, aspartic acid, and histidine catalytic residues as well as the 10 cysteine residues involved in disulfide bond formation. Expression was identified in cultured human umbilical vein endothelial cells, human coronary artery endothelial cells, and murine endothelial-like yolk sac cells by Northern blot. In addition, Northern blot and in situ hybridization analysis revealed expression of the endothelial-derived lipase in placenta, liver, lung, ovary, thyroid gland, and testis. A c-Myc-tagged protein secreted from transfected COS7 cells had phospholipase A1 activity but no triglyceride lipase activity. Its tissue-restricted pattern of expression and its ability to be expressed by endothelial cells, suggests that endothelial cell-derived lipase may have unique functions in lipoprotein metabolism and in vascular disease.

Overexpression of hepatic lipase in transgenic mice decreases apolipoprotein B-containing and high density lipoproteins. Evidence that hepatic lipase acts as a ligand for lipoprotein uptake.

To determine the mechanisms by which human hepatic lipase (HL) contributes to the metabolism of apolipoprotein (apo) B-containing lipoproteins and high density lipoproteins (HDL) in vivo, we developed and characterized HL transgenic mice. HL was localized by immunohistochemistry to the liver and to the adrenal cortex. In hemizygous (hHLTg+/0) and homozygous (hHLTg+/+) mice, postheparin plasma HL activity increased by 25- and 50-fold and plasma cholesterol levels decreased by 80% and 85%, respectively. In mice fed a high fat, high cholesterol diet to increase endogenous apoB-containing lipoproteins, plasma cholesterol decreased 33% (hHLTg+/0) and 75% (hHLTg+/+). Both apoB-containing remnant lipoproteins and HDL were reduced. To extend this observation, the HL transgene was expressed in human apoB transgenic (huBTg) and apoE-deficient (apoE-/-) mice, both of which have high plasma levels of apoB-containing lipoproteins. (Note that the huBTg mice that were used in these studies were all hemizygous for the human apoB gene.) In both the huBTg,hHLTg+/0 mice and the apoE-/-,hHLTg+/0 mice, plasma cholesterol decreased by 50%. This decrease was reflected in both the apoB-containing and the HDL fractions. To determine if HL catalytic activity is required for these decreases, we expressed catalytically inactive HL (HL-CAT) in apoE-/- mice. The postheparin plasma HL activities were similar in the apoE-/- and the apoE-/-,HL-CAT+/0 mice, reflecting the activity of the endogenous mouse HL and confirming that the HL-CAT was catalytically inactive. However, the postheparin plasma HL activity was 20-fold higher in the apoE-/-,hHLTg+/0 mice, indicating expression of the active human HL. Immunoblotting demonstrated high levels of human HL in postheparin plasma of both apoE-/-,hHLTg+/0 and apoE-/-,HL-CAT+/0 mice. Plasma cholesterol and apoB-containing lipoprotein levels were approximately 60% lower in apoE-/-,HL-CAT+/0 mice than in apoE-/- mice. However, the HDL were only minimally reduced. Thus, the catalytic activity of HL is critical for its effects on HDL but not for its effects on apoB-containing lipoproteins. These results provide evidence that HL can act as a ligand to remove apoB-containing lipoproteins from plasma.

Heparan sulfate proteoglycans participate in hepatic lipaseand apolipoprotein E-mediated binding and uptake of plasma lipoproteins, including high density lipoproteins.

High density lipoprotein (HDL) particles and HDL cholesteryl esters are taken up by both receptor-mediated and non-receptor-mediated pathways. Here we show that cell surface heparan sulfate proteoglycans (HSPG) participate in hepatic lipase (HL)- and apolipoprotein (apo) E-mediated binding and uptake of mouse and human HDL by cultured hepatocytes. The HL secreted by HL-transfected McA-RH7777 cells enhanced both HDL binding at 4 degrees C (approximately 2-4-fold) and HDL uptake at 37 degrees C (approximately 2-5-fold). The enhanced binding and uptake of HDL were partially inhibited by the 39-kDa protein, an inhibitor of low density lipoprotein receptor-related protein (LRP), but were almost totally blocked by heparinase, which removes the sulfated glycosaminoglycan chains from HSPG. Therefore, HL may mediate the uptake of HDL by two pathways: an HSPG-dependent LRP pathway and an HSPG-dependent but LRP-independent pathway. The HL-mediated binding and uptake of HDL were only minimally reduced when catalytically inactive HL or LRP binding-defective HL was substituted for wild-type HL, indicating that much of the HDL uptake required neither HL binding to the LRP nor lipolytic processing. To study the role of HL in facilitating the selective uptake of cholesteryl esters, we used HDL into which radiolabeled cholesteryl ether had been incorporated. HL increased the selective uptake of HDL cholesteryl ether; this enhanced uptake was reduced by more than 80% by heparinase but was unaffected by the 39-kDa protein. Like HL, apoE enhanced the binding and uptake of HDL (approximately 2-fold) but had little effect on the selective uptake of HDL cholesteryl ether. In the presence of HL, apoE did not further increase the uptake of HDL, and at a high concentration apoE impaired or decreased the HL-mediated uptake of HDL. Therefore, HL and apoE may utilize similar (but not identical) binding sites to mediate HDL uptake. Although the relative importance of cell surface HSPG in the overall metabolism of HDL in vivo remains to be determined, cultured hepatocytes clearly displayed an HSPG-dependent pathway that mediates the binding and uptake of HDL. This study also demonstrates the importance of HL in enhancing the binding and uptake of remnant and low density lipoproteins via an HSPG-dependent pathway.

Thyroid hormone concentrations in depressed and nondepressed adolescents: group differences and behavioral relations.

OBJECTIVE: To examine thyroid hormone concentrations and the influence of these hormones on mood and problem behaviors in adolescents with depression. METHOD: The sample included 21 depressed adolescents and 20 matched control adolescents. Blood was drawn to measure thyroid-stimulating hormone (TSH), free thyroxine (FT4), thyroxine (T4), and triiodothyronine (T3). Major depression (MD), attention deficit (AD), and obsessive-compulsive (OC) symptom scores were abstracted from the Diagnostic Interview Schedule for Children. Total behavior problem scores from the Youth Self-Report also were obtained. RESULTS: Paired analysis revealed there were no significant group or gender differences or group by gender interactions for TSH, T4, or T3. For FT4, however, there were significant group differences (p = .008) showing lower concentrations in depressed adolescents than control subjects, suggesting that the former might be functionally hypothyroid. Although there were no significant correlations of TSH with any of the psychological measures obtained, in the depressed group correlations were negative (although not always significant) with FT4 and total behavior problems (r = -.40, p = .09), as well as with symptom scores of MD (r = -.25, p = .288), OC (r = -.56, p = .011), and AD behaviors (r = -.57, p = .008). Higher numbers of symptom scores of OC and AD were related to lower concentrations of FT4. CONCLUSIONS: FT4 concentrations were lower in depressed adolescents. These findings suggest a relationship between negative behaviors and dysfunction of the hypothalamic-pituitary-thyroid axis in adolescents with depression.

Human hepatic and lipoprotein lipase: the loop covering the catalytic site mediates lipase substrate specificity.

Hepatic lipase (HL) and lipoprotein lipase (LPL) are key enzymes that mediate the hydrolysis of triglycerides (TG) and phospholipids (PL) present in circulating plasma lipoproteins. Relative to triacylglycerol hydrolysis, HL displays higher phospholipase activity than LPL. The structural basis for this difference in substrate specificity has not been definitively established. We recently demonstrated that the 22-amino acid loops ("lids") covering the catalytic sites of LPL and HL are critical for the interaction with lipid substrate (Dugi, K.A., Dichek, H.L., Talley, G.D., Brewer, H.B., Jr., and Santamarina-Fojo, S. (1992) J. Biol. Chem. 267, 25086-25091). To determine whether the lipase lid plays a role in conferring the different substrate specificities of HL and LPL, we have generated four chimeric lipases. Characterization of these chimeric enzymes using TG (triolein and tributyrin) or PL (dioleoylphosphatidylcholine (DOPC) vesicles, DOPC proteoliposomes, and DOPC-mixed liposomes) substrates demonstrated marked differences between their relative PL/TG hydrolyzing activities. Chimeric LPL containing the lid of HL had reduced triolein hydrolyzing activity (49% of the wild type), but increased phospholipase activity in DOPC vesicle, DOPC proteoliposome, and DOPC-mixed liposome assay systems (443, 628, and 327% of wild-type LPL, respectively). In contrast, chimeric HL containing the LPL lid was more active against triolein (123% of the wild type) and less active against DOPC (23, 0, and 30%, respectively) than normal HL. Similar results were obtained when the lipase lids were exchanged in chimeric enzymes containing the NH2-terminal end of LPL and the COOH-terminal domain of HL. Exchange of the LPL and HL lids resulted in a reversal of the phospholipase/neutral lipase ratio, establishing the important role of this region in mediating substrate specificity. In summary, the lid covering the catalytic domains in LPL and HL plays a crucial role in determining lipase substrate specificity. The lid of LPL confers preferential triglyceride hydrolysis, whereas the lid of HL augments phospholipase activity. This study provides new insight into the structural basis for the observed in vivo differences in LPL and HL function.

Thyroid function in non-growth hormone-deficient short children during a placebo-controlled double blind trial of recombinant growth hormone therapy.

GH treatment in GH-deficient children has been reported to cause decreases in serum T4 and TSH and an increase in serum T3. We sought to determine whether GH treatment alters thyroid function in non-GH-deficient short children. Twenty children (18 boys) were followed for 12 months while receiving either GH (Humatrope, Eli Lilly; 0.074 mg/kg, sc, 3 times/week; n = 9) or placebo (n = 11). Total T4, free T4, T3, and TSH were measured every 6 months and in 12 children also at 1, 2, 3, and 9 months. A TRH test and measurement of nocturnal TSH surge were performed at baseline and after 6 months of treatment in 19 subjects. There were no significant differences at baseline in the clinical features between the placebo and GH groups. Total T4, free T4, T3, and TSH levels did not significantly differ between the placebo and GH groups at baseline and at 1, 2, 3, 6, 9, and 12 months. There were no significant differences between the two groups in TSH response to TRH or nocturnal TSH surge. Although an early transient effect of GH treatment could not be excluded, we conclude that GH treatment for 12 months does not produce sustained alterations in thyroid function in non-GH-deficient children.

A comparison of the standard high dose dexamethasone suppression test and the overnight 8-mg dexamethasone suppression test for the differential diagnosis of adrenocorticotropin-dependent Cushing's syndrome.

To improve the overnight 8-mg dexamethasone (DEX) suppression test (DST) for differential diagnosis of Cushing's syndrome and to develop optimal criteria for its interpretation, we increased the number of blood samples and measured the suppression of both plasma ACTH and cortisol. Forty-one patients who were subsequently proven at surgery to have Cushing's syndrome were studied (34 Cushing's disease and 7 ectopic ACTH secretion). DEX (8 mg, orally) was administered at 2300 h. Blood samples for ACTH and cortisol measurements were obtained at 0800, 0830, and 0900 h on the day before and at 0700, 0800, 0900, and 1000 h on the morning after DEX treatment. The conventional 6-day DST was also performed, with measurement of both urinary free cortisol and urinary 17-hydroxysteroids as indices of suppression. Optimal criteria for the diagnosis of Cushing's disease were developed for both the overnight 8-mg and the 6-day tests using receiver operating characteristic curves. The results were compared with those using the previously published criteria for diagnosis of Cushing's disease by the overnight 8-mg test (> 50% suppression of plasma cortisol at 0700-0800 h). In our patients, the previously published criterion for the overnight 8-mg test yielded high sensitivity (88%), but low specificity (57%), in making the diagnosis of Cushing's disease. When the time of cortisol measurement and the diagnostic criteria for Cushing's disease were revised to achieve 100% specificity, the sensitivity of the overnight 8-mg test was 71%, which was not significantly different from that of the 6-day test (79%; P = NS). Addition of plasma ACTH levels to the test did not improve diagnostic accuracy compared to that with measurement of plasma cortisol levels alone. When the revised 8-mg overnight dexamethasone suppression test was combined with the 6-day dexamethasone suppression test, sensitivity increased to 91%, with a specificity of 100%, which was significantly better than that of the overnight 8-mg test alone (P < 0.002). We conclude that the overnight 8-mg DST has low specificity for the diagnosis of Cushing's disease when performed as originally described. However, with revised sampling times and diagnostic criteria, the overnight test has sensitivity and specificity similar to those of the conventional 6-day DST. The diagnostic performance of a criterion that combines the results of both tests is better than the diagnostic performance of either test alone.

Functional characterization of a chimeric lipase genetically engineered from human lipoprotein lipase and human hepatic lipase.

Lipoprotein lipase (LPL) and hepatic lipase (HL) mediate the hydrolysis of triglycerides and phospholipids present in circulating lipoprotein particles and are essential for normal lipid metabolism. Both enzymes have a similar primary amino acid structure and share requirements for intact catalytic, lipid binding, and heparin binding domains. However, LPL and HL exhibit different substrate specificities and cofactor requirements. In order to characterize the functional domains necessary for LPL activity, a chimeric lipase consisting of the amino-terminal 314 amino acids of human LPL and the carboxyl-terminal 146 amino acids of human HL was synthesized by joining the cDNA of both lipases at the 5'-end of exon 7. Northern blot hybridization and Western blot analyses revealed the size of the chimera mRNA and protein to be approximately 1.5 kb and 55 kDa, respectively. The chimeric enzyme hydrolyzed both long chain and short chain fatty acid triacylglycerols and had catalytic properties that were similar to lipoprotein lipase. Thus, apolipoprotein (apo)C-II was required for maximal lipase activity, and high salt concentration abolished the ability of the chimera to hydrolyze triolein even in the presence of apoC-II. A monospecific anti-HL polyclonal antibody interacting with the C-terminal HL-derived domain of the chimeric enzyme abolished the enzyme's ability to hydrolyze triglyceride emulsion but not tributyrin substrates. Analysis of the heparin binding properties of the chimeric enzyme using heparin-Sepharose affinity chromatography revealed an elution pattern which was intermediate between that of lipoprotein and hepatic lipase. In summary, we have characterized the functional properties of an LPL-HL chimeric enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of triglyceride accumulation in lipoprotein lipase-deficient human monocyte-macrophages incubated with human very low density lipoprotein.

Lipoprotein lipase, a lipolytic enzyme essential for normal hydrolysis of triglycerides in very low density lipoprotein (VLDL) and chylomicrons, is found in several cell types, including macrophages. The role of lipoprotein lipase in mediating the uptake of normal VLDL triglycerides into human cultured monocyte-derived macrophages was studied using macrophage cells from a functionally lipoprotein lipase-deficient patient and macrophages of cells from a normal subject. After incubation with VLDL, massive accumulation of phase refractile (lipid) inclusions were noted by phase contrast microscopy within the normal, but not within the lipoprotein lipase-deficient, macrophages. Chemical determinations of intracellular lipid confirmed massive triglyceride accumulation within normal macrophages, but not in lipoprotein lipase-deficient macrophages. VLDL-derived cholesterol did not accumulate in either cell. These results confirm an additional role of lipoprotein lipase, that of mediating triglyceride accumulation into macrophages from normal human VLDL. Human monocyte-macrophages genetically deficient in a functional lipoprotein lipase will be useful to determine the role of lipoprotein lipase in macrophage accumulation of lipid from other forms of triglyceride-carrying lipoproteins, including hypertriglyceridemic VLDL, beta-VLDL, and chylomicrons.

Human lipoprotein lipase: the loop covering the catalytic site is essential for interaction with lipid substrates.

Lipoprotein lipase (LPL), a key enzyme which initiates the hydrolysis of triglycerides present in chylomicrons and very low density lipoproteins, consists of multiple functional domains which are necessary for normal activity. The catalytic domain of LPL mediates the esterase function of the enzyme but separate lipid binding sites have been proposed to be involved in the interaction of LPL with emulsified lipid substrates at the water-lipid interface. Like pancreatic lipase (PL), LPL contains a surface loop covering the catalytic pocket that may modulate access of the substrate to the active site of the enzyme. Secondary structural analysis of this loop reveals a helix-turn-helix motif with two short amphipathic helices that have hydrophobic moments of 0.64 and 0.68. In order to investigate the role of the loop in the initial interaction of LPL with its substrate, we utilized site-directed mutagenesis to generate eight constructs in which the amphipathic properties of the loop were altered and expressed them in human embryonal kidney-293 cells. Reducing the amphiphilicity without changing the predicted secondary structure of the loop abolished the ability of the lipase to hydrolyze emulsified, long chain fatty acid triglycerides (triolein) but not the water soluble substrate tributyrin. Replacing the loop of LPL with the loop of hepatic lipase, which differs in 15 of 22 amino acids but is also amphiphilic, led to the expression of an enzyme that retained both triolein and tributyrin hydrolyzing activity. Substitution of the LPL loop by a short four amino acid peptide, which may allow more direct access to the active site than the 22 amino acid loop, enhanced hydrolysis of short chain fatty acid triglycerides by more than 2-fold, while the ability to hydrolyze emulsified substrates was abolished. Thus, disruption of the amphipathic structure of the LPL loop selectively decreases the hydrolysis of emulsified lipid substrate without affecting the esterase or catalytic function of the enzyme. These studies establish that the loop with its two amphipathic helices is essential for hydrolysis of long chain fatty acid substrate by LPL providing new insight into the role of the LPL loop in lipid-substrate interactions. We propose that the interaction between the lipoprotein substrates and the amphipathic helices within this loop may in part determine lipase substrate specificity.

Mitotane enhances cytotoxicity of chemotherapy in cell lines expressing a multidrug resistance gene (mdr-1/P-glycoprotein) which is also expressed by adrenocortical carcinomas.

P-Glycoprotein (Pgp), product of the mdr-1 gene, is a 130- to 180-kDa plasma membrane phosphoglycoprotein which mediates multidrug resistance in cell culture by increasing efflux of the natural product chemotherapeutic agents. High levels of expression of mdr-1/Pgp are found in both the normal adrenal and adrenocortical cancers. By RNA in situ hybridization the expression in adrenocortical cancer is shown to be widely distributed. The present study demonstrates that decreased drug accumulation mediated by mdr-1/Pgp can be overcome by clinically achievable concentrations of mitotane (o,p'-DDD). The increase in drug accumulation with the addition of mitotane is due at least in part to a decrease in drug efflux and results in an increase in cytotoxicity when agents of the natural product class are used. This effect is observed in cells with a broad range of mdr-1/Pgp expression, including levels comparable to those found in most adrenocortical cancers. Similar increases in drug accumulation can be demonstrated in an unselected adrenocortical cancer cell line that expresses mdr-1/Pgp. The finding that multidrug resistance mediated by mdr-1/Pgp can be reversed by mitotane provides a rational basis for exploring the use of mitotane in combination with natural product chemotherapeutic agents in adrenocortical cancer.

Partial primary sequence of a human endometrial epithelial progesterone dependent protein secreted in vitro.

We have recently identified a uterine progesterone-dependent 25 kD protein (protein #27) secreted by endometrial epithelial cells but not stroma. Protein #27 was originally isolated from human luteal phase uterine fluids and partially purified by two-dimensional gel-electrophoresis and electroelution. It could not be detected in serum. We here report the further purification and amino terminal sequence of this protein, obtained from in vitro luteal phase endometrial tissue incubation media. Protein #27 was purified by a one-step method using reverse-phase high performance liquid chromatography. Amino acid compositional analysis confirms a high content of nonpolar and hydrophobic residues (40 mol%) and reveals a preponderance of acidic amino acids, consistent with its isoelectric point (5.9-6.3 pH). The amino terminal sequence obtained from a single individual reveals 85% homology with that of pregnancy-associated alpha 2-globulin from pooled cytosolic fractions from pregnancy endometria. We propose that protein #27, secreted by the endometrial epithelium, is an excellent candidate for a marker to be used to study pathological processes of the endometrium such as endometriosis and invasive carcinoma.

Identification of two separate allelic mutations in the lipoprotein lipase gene of a patient with the familial hyperchylomicronemia syndrome.

The molecular defects resulting in a deficiency of lipoprotein lipase activity in a patient with the familial hyperchylomicronemia syndrome have been identified. Increased lipoprotein lipase mass but undetectable lipoprotein lipase activity in the patient's post-heparin plasma indicate the presence of an inactive enzyme. No major gene rearrangements were identified by Southern blot analysis of the patient's lipoprotein lipase gene and Northern blot hybridization revealed an lipoprotein lipase mRNA of normal size. Sequence analysis of polymerase chain reaction-amplified lipoprotein lipase cDNA identified two separate allelic mutations. A T to C transition at nucleotide 836 results in the substitution of Ile194, located near the putative interfacial recognition site of lipoprotein lipase, to a Thr. A G to A mutation at base 983 leads to the substitution of a His for Arg243 and the loss of a HhaI restriction enzyme site. Arg243 is near His241, which has been postulated to be part of the catalytic triad of lipoprotein lipase. Direct sequencing of amplified cDNA and digestion with HhaI established that the proband is a compound heterozygote for each base substitution. Transient expression of each of the mutant lipoprotein lipase cDNAs in human embryonal kidney-293 cells resulted in the synthesis of enzymically inactive proteins, establishing the functional significance of the mutations. We conclude that the Ile194 to Thr194 and Arg243 to His243 substitutions occur in lipoprotein lipase regions essential for normal enzyme activity and each mutation results in the expression of a nonfunctional enzyme leading to the hyperchylomicronemia syndrome manifested in the proband.

Stimulation of gonadotropin secretion in prepubertal monkeys after hypothalamic excitation with aspartate and glutamate.

To test the hypothesis that aspartate (Asp) and glutamate (Glu) can be used to probe the functional integrity of the GnRH neuron, the dose-response relationships between i.v. administered, endogenously occurring amino acids (Asp and Glu) and GnRH release were determined in the prepubertal male monkey. GnRH release was assessed indirectly by monitoring the LH response by the pituitary, the sensitivity of which had been heightened by prior exposure to pulsatile GnRH. Four of these animals received an i.v. bolus of 0, 1.5, 4.8, 15, 48 and 150 mg/kg BW of each of the amino acids. Plasma gonadotropin and amino acid concentrations were measured immediately before and for 3 hours after administration of Asp and Glu. The 150 mg/kg dose of both amino acids resulted in a dramatic rise in plasma LH concentrations that peaked at 10 min after injection. At this dose plasma Asp and Glu levels increased 200-fold and 50-fold, respectively. No significant LH release was seen with any of the lower doses. These results indicate that i.v. administration of these acidic amino acids in prepubertal monkeys stimulates GnRH release. Based upon this observation, we hypothesize that Asp or Glu could be used to develop a clinical test of GnRH neuronal function.

In vitro protein production by the human endometrium.

Protein secretion by the human endometrium was studied in vitro in medium after incubation of tissue minces (n = 10) or glands isolated by collagenase digestion (n = 4) from tissues obtained at the time of curettage from normal women. Samples were incubated in a serum-free medium for 24 h at 38 degrees C in the presence of radiolabeled methionine. Dialyzed medium from each sample was subjected to two-dimensional gel separation, and detected by protein staining. Although 5 of the 27 proteins were considered to be present in the labeling experiments by only one of the three observers, there was agreement about the presence of the 22 others. In addition, the observers categorized the proteins into three groups for purposes of analysis: a) those associated with the follicular phase of the cycle; b) those associated with the luteal phase; and c) those not cycle-related. One protein triplet, labeled #27, showed a significant relation to the luteal phase (p less than 0.01). A complete lack of similarity between the pattern of labeled proteins obtained from the medium and labeled proteins obtained from lysates of cells incubated in the same experiments makes it unlikely that cellular lysis, as opposed to secretion, contributed to the pattern of proteins studied in these experiments.