The thymus-brain connection: interactions between thymosin and the neuroendocrine system.
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Animals↗
Biomedical subjects
A L Goldstein
Publications and source records attributed to A L Goldstein.
Circadian rhythm of thymosin-alpha 1 in normal and thymectomized mice.
Studies by many investigators have demonstrated that the immune system is subject to regular circadian fluctuation. Some rhythms that have been reported include circadian changes in components of the immune system, e.g., lymphocytes, and circadian variation in primary and secondary immune responsiveness. The observation that many of these rhythms are inversely correlated to the glucocorticoid rhythm has led to the suggestion that fluctuations in the immune system may be a result of the glucocorticoid circadian rhythm. This study was designed to see if thymosin-alpha 1 (Tsn-alpha 1), a 28-amino acid polypeptide isolated from bovine thymus that has been reported to influence thymocyte differentiation, might follow a circadian rhythm, and thus play a role in the periodicity of the immune system. In these experiments, groups of 10 C57BL/6 or Swiss Webster mice were sacrificed at 4- or 6-hr intervals over a 24-hr period. Serum Tsn-alpha 1 and corticosterone levels were determined by radioimmunoassay. Results from the first experiment showed that Tsn-alpha 1 undergoes a circadian rhythm (p less than 0.001) with an acrophase (time of peak levels) 1.5 hr after the onset of light, and an amplitude (amount of maximum variation from the 24-hr mean) of 0.493 ng/ml Tsn-alpha 1-like immunoreactivity. These results were confirmed in an experiment in which the animals were placed on a reversed light cycle. In a separate experiment, the Tsn-alpha 1 circadian rhythm persisted in mice thymectomized 6 mo. earlier. In this latter experiment, a significant increase in the amplitude of the corticosterone rhythm in the thymectomized relative to sham-operated controls was also observed. Although these experiments do not imply casuality, it is interesting that the time of peak Tsn-alpha 1 levels can be correlated with the time of optimal immune function.
Animals↗
New role for 15-hydroxyeicosatetraenoic acid. Activator of leukotriene biosynthesis in PT-18 mast/basophil cells.
Leukotrienes are vasoactive arachidonic acid metabolites which are released by mast cells during hypersensitivity reactions. The mechanisms for regulating leukotriene biosynthesis are not well understood. A murine mast/basophil cell line (PT-18) was used to investigate this problem. Exogenously supplied [14C]arachidonic acid is not appreciably converted to leukotrienes by untreated PT-18 cells. However, when the cells were preincubated with the lymphocyte product 15-hydroxyeicosatetraenoic acid (15-HETE), addition of [14C]arachidonic acid consistently resulted in a dose-dependent synthesis of large amounts of both [14C]leukotriene B4 and [14C]5-HETE. These metabolites were isolated by high pressure liquid chromatography, converted to the methyl ester trimethylsilyl ether derivatives, and the structures confirmed by gas chromatography-mass spectrometry. These findings indicate that 15-HETE induces a direct activation of a cryptic 5-lipoxygenase in these cells. The closely related 12-HETE was ineffective. The activation phenomenon occurs rapidly and is reversible. Furthermore, the activation appears to be highly cell- and enzyme-specific, since lipoxygenases in three primary cell types including one that contains a 5-lipoxygenase and six other cell lines did not show this specific induction of leukotriene biosynthesis by 15-HETE. This report is the first evidence that 15-HETE, a major arachidonate metabolite in lymphocytes, can act as a signal to activate leukotriene production by susceptible mast cells.
Animals↗
Chemical characterization of thymosin beta 4.
As part of our ongoing investigations on the endocrine thymus, we have isolated and purified to homogeneity a hormone-like peptide which we have termed thymosin beta 4. Thymosin beta 4 has Mr = 4982 and an isoelectric point of 5.1. The complete amino acid sequence of this polypeptide has been established by automated Edman degradation as well as by manual sequence analysis. Thymosin beta 4 is composed of 43 amino acid residues with acetylserine at the NH2 terminus. This molecule induces expression of terminal deoxynucleotidyl transferase in transferase-negative murine thymocytes in vivo and in vitro. It also exhibits ability to inhibit the migration of macrophages. Comparison of the sequence of thymosin beta 4 to other thymic hormones or other published protein sequences does not reveal any statistically significant relationship. Two helical regions were identified in the structure using data for prediction of protein conformation. It is proposed that thymosin beta 4 is one of the biologically active peptides present in thymosin fractions 5 and 5A which participate in the regulation, differentiation, and function of thymus-derived lymphocytes and may also act directly or indirectly on macrophages and perhaps other cells involved in cell-mediated immunity.
Amino Acid Sequence↗
Primary culture of adipoblasts from obese and lean Zucker rat adipose tissue.
Adipocyte precursors derived from the epididymal fat pads of young adult lean (FaFa) and obese (fafa) Zucker rats were established in primary culture. The two types of culture were used to assess intrinsic cellular differences in proliferative capacity, lipoprotein lipase (LPL) activity and triglyceride (TG) accumulation related to genotype. Proliferative capacity was similar over seven days in vitro in lean- and obese-derived cultures. Heparin-releasable LPL activity was significantly greater in lean- than in obese-derived cultures grown in media supplemented with penicillin and streptomycin (pen-strep). However, when grown in media supplemented with cephalothin, heparin-releasable and total LPL activity increased significantly in obese-derived cultures and equalled LPL activity in lean-derived cultures. Substantial LPL activity was measurable in both types of culture at confluence, before exposure to media that promoted lipid-filling. TG accumulation was significantly greater in lean-than in obese-derived cultures in the presence of pen-strep but was similar in both culture types grown in cephalothin. These data support our hypothesis that the fa gene may affect mechanisms of protein turnover regulation, since pen-strep, but not cephalothin, has inhibitory effects on mammalian protein synthesis and degradation. The substantial LPL activity present in confluent, but unconverted cultures, suggests that some percentage of cells in the confluent monolayers are adipoblasts.
Adipose Tissue↗
Ataxia-Telangiectasia: a multiparameter analysis of eight families.
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Adolescent↗
Effects of 6-hydroxydopamine upon primary and secondary thymus dependent immune responses.
Adult male mice were treated with various doses of 6-hydroxydopamine in order to assess the effects of this drug upon thymic dependent immunity. A consistent decrease in primary antibody titers to sheep erythrocytes was observed following treatment with this drug. Serum levels of thymosin alpha 1 were increased by day three after 6-OHDA with a return to normal by day five. Thymocyte terminal deoxynucleotidyl transferase changes were biphasic with an initial decrease after 6-OHDA followed by an increase. Changes in mitogen responsiveness were observed but were not consistently reproducible. Involvement of both catecholamines and corticosteroids in bringing about these observed changes was discussed.
Adrenalectomy↗
Age-related changes in localization of thymosin in the human thymus.
Using an indirect fluorescent antibody technique, localization of thymosin alpha 1, thymosin beta 3 and thymosin fraction 6 was studied in human thymus glands ranging in age from newborn to 62 yr old. Thymosin alpha 1 was detected specifically in thymic epithelial cells of the medulla and in cells covering the cortical surface. Thymosin beta 3 was detected almost exclusively in cells covering the cortical surface. Epithelial cells in the medulla, which were positive for thymosin alpha 1, decreased in number progressively with age, beginning at around 13 yr of age. Epithelial cells positive for thymosin alpha 1 and covering the cortical surface were observed in thymus tissue from all ages, although the absolute number decreased. Several of the peptide components of thymosin fraction 6 were found in thymic epithelial cells as well as in macrophages in the thymus and spleen.
Adolescent↗
Decrease of tumor growth in mice after intravenous thymosin-treated bone marrow cell injection.
The effect of iv injection in C57BL/6 mice of 3X10(7) bone marrow cells preincubated in either thymosin fraction V or thymosin alpha-1 was evaluated on the growth of a 3-methylcholanthrene-induced transplantable tumor in a syngeneic system. The effect was then compared to that elicited by theophylline or levamisole, which both demonstrated thymosin-like action in vitro. The results showed significantly retarded tumor growth (P less than 0.001) and prolonged survival time (P less than 0.001) when thymosin fraction V was used. The same results were obtained with thymosin alpha-1 with use of the same protocol but only one-twentieth of the concentration of fraction V. Theophylline and levamisole demonstrated no antitumor effect.
Animals↗
Immunochemical studies on thymosin: radioimmunoassay of thymosin alpha 1.
A sensitive and specific radioimmunoassay (RIA) has been developed to measure thymosin alpha 1 in human blood and tissue extracts. Thymosin alpha 1, originally isolated from bovine thymosin fraction 5, has an identical primary structure in bovine and human species. Antiserum to synthetic thymosin alpha 1 was prepared in rabbits. A synthetic analogue, N-Ac-(Tyr1)thymosin alpha 1 was radioiodinated by utilizing Na125I and soluble lactoperoxidase. The RIA is capable of detecting as small an amount as 40 pg thymosin alpha 1 in serum/plasma and does not significantly cross-react with other putative thymic hormones or other purified blood proteins that have been assayed. Proteolytic degradation of thymosin alpha 1 does not occur during the collection, storage, or assay of serum or plasma. The concentration of thymosin alpha 1 in the blood is highest in utero, decreases sharply after birth, and appears to remain fairly constant during the first 15 yr of life. Maternal blood levels of thymosin alpha 1 appear to be above normal during pregnancy.
Absorption↗
Modulation of terminal deoxynucleotidyl transferase activity by thymosin.
Thymosin fraction 5, a family of acidic polypeptides isolated from bovine thymus, contains several hormonal-like factors which have been shown to influence the maturation, differentiation and functions of T-cells. Some of these peptides have been chemically defined. Two of them, thymosin alpha 1 (M.W. 3108) and thymosin beta 4 (M.W. 4982) have been sequenced. In murine systems, terminal deoxynucleotidyl transferase (TdT) has been shown to be T-cell specific and to be present primarily in the cortisone sensitive immature T-cell populations. The daily injection of thymosin fraction 5 and two of its components, thymosin beta 3 and beta 4, significantly increases TdT activity in immune suppressed mice as compared to control groups. This study indicates that thymosin can act on prothymocytes and influence the early stages of T-cell differentiation. In an in vivo system, thymosin fraction 5 and the purified peptide, thymosin alpha 1, have high activities in decreasing TdT in normal murine thymocytes after a 22-h incubation. This effect suggests that thymosin can also act on thymocytes and regulate the later biochemical processes during T-cell differentiation.
Animals↗
Thymosin stimulates secretion of luteinizing hormone-releasing factor.
Partially purified thymosin fraction 5 and one of its synthetic peptide components, thymosin beta 4, but not thymosin alpha 1, stimulated secretion of luteinizing hormone--releasing factor from superfused medial basal hypothalami from random cycling female rats. In addition, luteinizing hormone was released from pituitary glands superfused in sequence with hypothalami. No release of luteinizing hormone in response to thymosin was observed from pituitaries superfused alone. These data provide the first evidence of a direct effect of the endocrine thymus on the hypothalamus and suggest a potentially important role for thymic peptides in reproductive function.
Animals↗
Primary cultures of fetal hepatocytes from the genetically obese Zucker rat: protein synthesis.
Primary fetal hepatocytes derived from Zucker rats with expected fa gene frequencies of 0.0 and 0.75 have been established and can be used to detect early effects of the fa gene on hepatocellular metabolism. Paired incubation experiments demonstrate that protein synthesis in 0.75 fa gene cultures is significantly less than in 0.0 fa gene cultures under basal conditions. Insulin stimulates protein synthesis in 0.0 fa gene cultures but has no effect on 0.75 fa gene cultures. Cycloheximide inhibits protein synthesis in both types of culture. NH4Cl inhibits protein synthesis in 0.0 but not in 0.75 fa gene cultures. These data suggest that fetal hepatocytes bearing the fa gene have in vitro a generally sluggish anabolic capacity and a blunted capacity to respond to insulin compared to fetal hepatocytes without the fa gene. These diminished capacities may be expression of a genetic error in lysosomal function.
Ammonium Chloride↗
Immunocytochemical localization of thymosin-alpha 1 in thymic epithelial cells of normal and myasthenia gravis patients and in thymic cultures.
Thymosin alpha 1 (alpha 1) is a potent thymic polypeptide hormone. With antibodies against synthetic thymosin alpha 1, indirect immunofluorescence was applied to human normal thymus and to hyperplastic, thymomatous or "involuted" thymus of myasthenia gravis (MG) patients. Alpha 1 was localized only in the epithelial cells, lying singly, grouped, in Hassall's corpuscles or proliferated in thymomas. In contrast to normal thymus, which had fewer and more weakly stained cells, MG hyperplastic thymus had many strongly positive epithelial cells: this was markedly evident in thymomas. "Involuted" MG thymus had a few but brightly stained cells lying within the fatty tissue. In tissue cultures of human thymus, anti-alpha 1 stained the epithelial cells, but not fibroblasts. These findings: (a) demonstrate the origin of the thymic hormone alpha 1 to be the thymic epithelial cell; (b) raise the possibility that excess alpha 1 may act pathologically to facilitate and perpetuate the dysimmune mechanism in MG; (c) may partially explain the beneficial effect of thymectomy in MG patients of any age; and (d) suggest that epithelial cells may be autonomous for the production of alpha 1 as evidenced by their positivity in tissue culture.
Adolescent↗
Current status of thymosin and other hormones of the thymus gland.
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Adolescent↗
Complete amino acid sequence of bovine thymosin beta 4: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations.
The amino acid sequence of thymosin beta 4, a polypeptide isolated from calf thymus, was determined. Thymosin beta 4 is composed of 43 amino acid residues and has a molecular weight of 4982 and an isoelectric point of 5.1. The NH2 terminus of the peptide is blocked by an acetyl group. This molecule induces expression of terminal deoxynucleotidyl transferase (DNA nucleotidylexotransferase, EC 2.7.7.31) in transferase-negative murine thymocytes in vivo and in citro. Thus, it appears that thymosin beta 4 acts on lymphoid stem cells and may control the early stages of the maturation process of thymus-dependent lymphocytes. This peptide is one of several present in thymosin fraction 5 that participates in the regulation, differentiation, and function of thymus-dependent thymocytes.
Amino Acid Sequence↗
Induction of terminal deoxynucleotidyl transferase and Lyt antigens with thymosin: identification of multiple subsets of prothymocytes in mouse bone marrow and spleen.
Thymosin (fraction 5 and synthetic alpha 1 peptide) induced prothymocytes in mouse bone marrow and spleen to express terminal deoxynucleotidyl transferase (TdT; DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) or Lyt-1+, 2+, 3+ alloantigens (or both) after brief incubation in vitro. Three antigenic phenotypes were generated: (i) TdT+ Lyt+, (ii) TdT- Lyt+, and (iii) TdT+ Lyt-. The TdT+ Lyt+ phenotype was expressed by 80% of prothymocytes in bone marrow and 30% of prothymocytes in spleen from normal mice. The TdT- Lyt+ phenotype was expressed by 81% of prothymocytes in bone marrow from athymic mice. More than 80% of TdT+ bone marrow cells from normal and athymic mice expressed Lyt antigens after thymosin treatment. We interpret these observations as suggesting that (i) most TdT+ hemopoietic cells in normal and athymic mice are thymocyte progenitors; (ii) two independent lineages of prothymocytes exist, one that expresses TdT and another that does not, (iii) commitment of prothymocytes to the TdT+ cell pathway is partially regulated by a thymic feedback mechanism; and (iv) the bone marrow preferentially produces TdT+ prothymocytes, whereas the spleen may serve as a repository for TdT- prothymocytes. A model of T-cell development is presented in which the thymus functions as a compound organ to process TdT+ and TdT- thymocytes progenitors and to generate two lines of T cells.
Animals↗
Thymosin treatment modulates production of interferon.
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Animals↗