Pineal melatonin acts as a circadian zeitgeber and growth factor in chick astrocytes

Abstract:  Melatonin is rhythmically synthesized and released by the avian pineal gland and retina during the night, targeting an array of tissues and affecting a variety of physiological and behavioral processes. Among these targets, astrocytes express two melatonin receptor subtypes in vitro, the Mel_1A and Mel_1C receptors, which play a role in regulating metabolic activity and calcium homeostasis in these cells. Molecular characterization of chick astrocytes has revealed the expression of orthologs of the mammalian clock genes including clock, cry1, cry2, per2, and per3 . To test the hypothesis that pineal melatonin entrains molecular clockworks in downstream cells, we asked whether coculturing astrocytes with pinealocytes or administration of exogenous melatonin cycles would entrain metabolic rhythms of 2-deoxy [14C]-glucose (2DG] uptake and/or clock gene expression in cultured astrocytes. Rhythmic secretion of melatonin from light-entrained pinealocytes in coculture as well as cyclic administration of exogenous melatonin entrained rhythms of 2DG uptake and expression of Gallus per2 ( gper2 ) and/or gper3 , but not of gcry1 mRNA. Surprisingly, melatonin also caused a dose-dependent increase in mitotic activity of astrocytes, both in coculture and when administered exogenously. The observation that melatonin stimulates mitotic activity in diencephalic astrocytes suggests a trophic role of the hormone in brain development. The data suggest a dual role for melatonin in avian astrocytes: synchronization of rhythmic processes in these cells and regulation of growth and differentiation. These two processes may or may not be mutually exclusive.     

Permissive role of thrombopoietin and granulocyte colony-stimulating factor receptors in hematopoietic cell fate decisions in vivo

The question of whether extracellular signals influence hematopoiesis by instructing stem cells to commit to a specific hematopoietic lineage (instructive model) or solely by permitting the survival and proliferation of predetermined progenitors (permissive model) has been controversial since the discovery of lineage-dominant hematopoietic cytokines. To study the potential role of cytokines and their receptors in hematopoietic cell fate decisions, we used homologous recombination to replace the thrombopoietin receptor gene (mpl) with a chimeric construct encoding the extracellular domain of mpl and the cytoplasmic domain of the granulocyte colony-stimulating factor receptor (G-CSFR). This chimeric receptor binds thrombopoietin but signals through the G-CSFR intracellular domain. We found that, despite the absence of a functional mpl signaling domain, homozygous knock-in mice had a normal platelet count, indicating that in vivo the cytoplasmic domain of G-CSFR can functionally replace mpl signaling to support normal megakaryopoiesis and platelet formation. This finding is compatible with the permissive model, according to which cytokine receptors provide a nonspecific survival or proliferation signal, and argues against an instructive role of mpl or G-CSFR in hematopoietic cell fate decisions.     

Specific and rapid induction of the proapoptotic protein Hrk after growth factor withdrawal in hematopoietic progenitor cells

Hrk is a newly described proapoptotic member of the Bcl-2 family that is mainly expressed in hematopoietic tissues and cultured neurons. In this study we have examined the expression and activity of Hrk in hematopoietic progenitors. To address these issues, we used 3 growth factor-dependent murine hematopoietic cell lines, HCD-57, FDCP-Mix, and FL5.12. The expression of Hrk was undetectable in cells cultured with growth factors, but it was rapidly up-regulated on growth factor withdrawal. In contrast, the expression of Bcl-x(L) decreased and that of proapoptotic Bax, Bad, and Bak was unchanged or down-regulated after removal of growth factors. This pattern of expression correlated with the induction of apoptosis. Hrk was also up-regulated in human cell lines and in bone marrow-derived CD34(+) cells cultured in the absence of growth factors. In addition, the levels of Hrk were up-regulated after treatment with the chemotherapeutic drug etoposide. Expression of prosurvival Bcl-x(L) or Bcl-2 proteins blocked the induction of Hrk. Hrk was induced in FDCP-Mix cells treated with ionomicin in the presence of IL-3, suggesting that cytosolic calcium may regulate the expression of this proapoptotic protein. Furthermore, ectopic expression of Hrk induced cell death of hematopoietic progenitors in the presence of IL-3. Thus, Hrk is specifically and rapidly induced in hematopoietic progenitors after growth factor deprivation or treatment with chemotherapeutic drugs, and this may be sufficient to induce apoptosis in these cells. (Blood. 2000;95:2742-2747)     

Differentiation of hematopoietic progenitor cells towards the myeloid and B-lymphoid lineage by hepatocyte growth factor (HGF) and thrombopoietin (TPO) together with early acting cytokines

OBJECTIVES: The effect of stem cell factor (SCF), flt3-ligand (FL), and interleukin (IL)-3 (SF3) in combination with hepatocyte growth factor (HGF), thrombopoietin (TPO), and Hyper-IL-6 on maintenance and differentiation of early human peripheral blood-derived progenitor cells was investigated. METHODS: Single sorted CD34(+) 38(-) cells were cultured with various combinations of these growth factors in order to identify the most effective cytokine combination. Then, lineage-depleted cells were stimulated for 7 d in bulk culture before they were assessed by flow cytometry and in functional assays. RESULTS: The highest number of clones in the single-cell assay was obtained after culture with SF3 + TPO + HGF. Cell expansion with SF3 + TPO + HGF yielded an increase of the total cell number (11-fold), the number of CD34(+) cells (sevenfold), colony forming cells (CFC; 13-fold), granulocytes (CD15/66b(+); 45-fold) and B-cells (CD19/20(+); 55-fold). However, the number of long-term culture initiating cells (LTC-IC) decreased from 779 +/- 338 per 1 x 10(5) CD34(+) cells on day 0 to 253 +/- 115 on day 7. In parallel, the number of pluripotent mouse repopulating cells decreased by the factor 11, and no significant change in the proportion of human myeloid or lymphoid cells found in the mouse bone marrow was noted. CONCLUSION: The observation that mature cells of different lineages are generated and that transplantable multipotent hematopoietic cells are lost during culture suggests the differentiation of early hematopoietic progenitors toward lineage committed cells by the tested cytokines. The detection of cells expressing B-lymphoid markers after culture indicates a possible role in the propagation of B-cells.     

Diminished erythropoietin-induced erythroid growth in patients with renal anemia is restored by recombinant human erythroid differentiation factor

An examination of the in vitro sensitivity of marrow burst-forming units for erythroid (BFU-E) to various concentrations of human recombinant erythropoietin (rEpo) and interleukin-3 (IL-3, 20 ng/mL) in serum-deprived methylcellulose cultures revealed that cells obtained from patients with chronic renal failure showed a defective response to rEpo, particularly at lower concentrations. This poor response was not corrected by the addition of neutralizing antibodies to antitumor necrosis factor-α or antiinterleukin-1 α/β. When purified CD34+ cells from these patients were tested for dose-dependent growth to rEpo, the curve resembled that of normal donors, indicating that there was an intrinsic defect In the patients' progenitor/accessory cell interactions. Using unseparated cells from the patients, we then tested whether the interaction between erythroid differentiation factor (EOF) and rEpo affected BFU-E growth. Although EDF, either alone or in combination wtth IL-3, did not affect the growth of BFU-E in the absence of rEpo, the reduced sensitivity to rEpo in the patients was brought closer to normal limits by the addition of 10 ng/mL EDF to the cultures. The present results may suggest the possibility that, in patients wtth renal anemia, concomitant administration of EDF may increase the therapeutic ratio of rEpo therapy by enhancing the sensitivity of progenitor cells to rEpo, thereby decreasing the therapeutic dose of costly rEpo. © 1994 Wiley-Liss, Inc.     

Hepatocyte growth factor is a synergistic factor for the growth of hematopoietic progenitor cells.

Bone marrow (BM) stromal cells, which include macrophages, fibroblasts, endothelial cells, and adipocytes, have been shown to produce several factors that modulate the growth of BM progenitors. Hepatocyte growth factor (HGF) is a fibroblast-derived factor and has recently been shown to be a ligand for the c-met proto-oncogene, a member of the receptor class of tyrosine kinases. c-met messenger RNA (mRNA) is predominantly expressed in epithelial cells, but has been detected in several murine hematopoietic progenitor cell lines, suggesting that HGF and met might function during hematopoiesis. Here, BM cells were found to express both met mRNA and protein. Moreover, HGF was shown to synergize with interleukin-3 and granulocyte-macrophage colony-stimulating factor to stimulate colony formation of hematopoietic progenitor cells in vitro. These results show that, in addition to its activity on epithelial cells, HGF is a new member of the functionally related group of factors that modulate hematopoiesis.     

Erythropoietin acts as a trophic factor in neonatal rat intestine

BACKGROUND: Erythropoietin (Epo) receptors are present on enterocytes of fetal and neonatal small bowel but the role of Epo in the bowel is not known. AIMS: We tested the following hypotheses: (1) enterally dosed Epo is absorbed from the intestines of neonatal rats, (2) Epo acts as a trophic factor in developing small bowel, and (3) the trophic effects of Epo are dependent on the route of administration. METHODS: The dose dependent effects of enterally dosed recombinant human erythropoietin (rEpo 0--1000 U/kg/day) were studied in artificially raised rat pups and compared with dam raised controls and dam raised pups given rEpo in rat milk. After one week, reticulocyte counts, haematocrits, and plasma Epo concentrations were measured, and calibrated morphometric measurements of villi were performed. The effects of route of rEpo administration (enteral v parenteral) on erythropoiesis, bowel growth, and disaccharidase activity were studied in nursing pups treated for one and two weeks. RESULTS: Serum Epo concentrations ranged from undetectable (<0.6 mU/ml) to 8.4 mU/ml in control and enterally dosed pups (median 1.8 mU/ml), and from 4.9 to 82.3 mU/ml (median 20.4 mU/ml) in parenterally dosed animals. No increase in haematocrit or reticulocyte count was noted in enterally treated pups compared with controls after up to two weeks of treatment. Small bowel length was greater in rEpo treated pups, and a dose dependent increase in villus surface area which was independent of the route of dosing and associated with increased BrdU uptake was found. CONCLUSIONS: rEpo is not enterally absorbed in an intact and functional form from the intestines of neonatal rat pups. Thus enterally dosed rEpo has no erythropoietic effects. However, rEpo acts as a trophic factor in developing rat small bowel whether given enterally or parenterally.     

A role for calmodulin in the growth of human hematopoietic progenitor cells.

A possible role for calmodulin in the colony growth of human hematopoietic progenitor cells was investigated using pharmacologic approaches. We obtained evidence for a dose-dependent inhibition of colony formation of myeloid progenitor cells (CFU-C) stimulated by interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or granulocyte CSF (G-CSF) by three calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide hydrochloride (W-13), and trifluoperazine. Chlorine-deficient analogs of W-7 and W-13, with a lower affinity for calmodulin, did not inhibit the growth of CFU-C colonies. W-7, W-13, and trifluoperazine inhibited the colony formation of immature erythroid progenitor cells (BFU-E) stimulated by IL-3 plus erythropoietin (Ep) or GM-CSF plus Ep, in a dose-dependent manner, while they did not affect the colony formation of mature erythroid progenitor cells (CFU-E) induced by Ep. W-7, W-13, and trifluoperazine also led to a dose-dependent inhibition of GM-CSF-induced colony formation of KG-1 cells. Calmodulin-dependent kinase activity derived from the KG-1 cells was inhibited by these three calmodulin antagonists in a dose-dependent manner. These data suggest that calmodulin may play an important regulatory role via a common process in the growth of hematopoietic progenitor cells stimulated by IL-3, GM-CSF, and G-CSF. Mechanisms related to the growth signal of Ep apparently are not associated with calmodulin-mediated systems.     

Interleukin-11: a multifunctional growth factor derived from the hematopoietic microenvironment

IL-11 is a unique growth factor derived from cells making up the HM. Although cloned based on IL-6-like bioactivity, IL-11 and IL-6 have distinct biologic profiles (Table 1). IL-11, like many recently cloned growth factors, has pleiotropic effects on hematopoietic cells presumably depending on the cytokine and cellular environment into which it is introduced. However, some general findings are consistent (Table 2). In addition, IL-11 has significant effects, either primary or secondary, on nonhematopoietic cells, including neurons, small intestine crypt progenitor/stem cells, and preadipocytes. The institution of human trials with IL-11 will provide important information on the pharmacologic effects of IL-11 on human hematopoietic cells in the context of frequently used chemotherapy protocols. The physiologic role(s) of IL-11 are unknown but will become clear (at least in the mouse) with gene targeting experiments underway in several laboratories.     

Insulin-like growth factor 2 expressed in a novel fetal liver cell population is a growth factor for hematopoietic stem cells

Hematopoietic stem cells (HSCs) undergo dramatic expansion during fetal liver development, but attempts to expand their numbers ex vivo have failed. We hypothesized that unidentified fetal liver cells produce growth factors that support HSC proliferation. Here we describe a novel population of CD3+ and Ter119- day-15 fetal liver cells that support HSC expansion in culture, as determined by limiting dilution mouse reconstitution analyses. DNA array experiments showed that, among other proteins, insulin-like growth factor 2 (IGF-2) is specifically expressed in fetal liver CD3+ cells but not in several cells that do not support HSCs. Treatment of fetal liver CD3+Ter119- cells with anti-IGF-2 abrogated their HSC supportive activity, suggesting that IGF-2 is the key molecule produced by these cells that stimulates HSC expansion. All mouse fetal liver and adult bone marrow HSCs express receptors for IGF-2. Indeed, when combined with other growth factors, IGF-2 supports a 2-fold expansion of day-15 fetal liver Lin-Sca-1+c-Kit+ long-term (LT)-HSC numbers. Thus, fetal liver CD3+Ter119- cells are a novel stromal population that is capable of supporting HSC expansion, and IGF-2, produced by these cells, is an important growth factor for fetal liver and, as we show, adult bone marrow HSCs.     

低氧诱导星形胶质细胞血管内皮生长因子表达

目的探讨低氧环境对体外培养的胎鼠大脑星形胶质细胞血管内皮生长因子(VEGF)表达的影响。方法采用孕16d的SD胎鼠大脑组织培养星形胶质细胞,实验分为正常组(正常培养,5%CO_2,95%空气,37℃,绝对湿度)和低氧组(低氧培养,5%CO_2,2%O_2,93%N_2,37℃、绝对湿度)。MTT实验观察细胞经2、4、6、8、10h低氧培养后细胞增殖情况,免疫荧光染色观察细胞经4、8、12、24、32h低氧培养后VEGF表达的变化。结果低氧组胶质细胞增殖除6h与正常组无差异外,2、4、8、10h较正常组均明显增高,差异有统计学意义(P0.05);低氧组8、12h VEGF表达明显高于正常组,24、32h VFGF表达明显低于正常组(P0.05)。结论低氧培养短期可促进星形胶质细胞增殖,VEGF表达升高,长期低氧可至星形胶质细胞损伤,VEGF表达下降。     

神经元自噬在缺血缺氧性脑损伤中的作用

自噬是广泛存在于真核细胞中通过溶酶体机制降解自身成分的一种代谢途径.自噬不仅可通过激活经典的自噬小体-溶酶体途径,而且还可通过影响凋亡和坏死的发生、发展对细胞死亡进行调控.目前,自噬在急性脑缺血缺氧后神经元损伤方面的作用及其具体机制尚不明确.研究表明,缺血缺氧后的自噬具有神经保护作用,如维持神经元稳态、减少神经元死亡等;但也有研究认为,自噬能通过激活多种通路加重缺血缺氧后神经元损伤,甚至诱导神经元死亡.     

Regulation of adipogenesis and osteogenesis in mesenchymal stem cells by vascular endothelial growth factor A

Understanding the mechanisms by which bone marrow mesenchymal stem cells (BMSCs) differentiate into bone‐forming osteoblasts and marrow adipocytes is crucial to develop strategies for the treatment of several bone diseases. Age‐related bone loss resulting in osteopenia and osteoporosis has been associated with reduced numbers of osteoblasts and increased numbers of adipocytes, likely originating from differentiation defects in BMSCs. Although many factors involved in the complex regulation of osteoblast and adipocyte cell lineages have previously been identified, their functional interactions in the context of BMSC differentiation and maintenance of bone homeostasis during ageing are unknown. Recent discoveries have provided important new insights into the mechanisms by which the nuclear envelope protein lamin A and vascular endothelial growth factor A (VEGF) mutually control BMSC fate. Particularly interesting is the finding that VEGF in this context functions as an intracellular protein, unaffected by neutralizing antibodies, and not as a secreted growth factor. These insights may not only facilitate the identification of new targets for treating bone diseases but also lead to improved design of tissue engineering approaches aimed at stimulating bone regeneration and repair.     

Influence of epidermal growth factor and transforming growth factor beta-1 on patterns of fetal mouse lung branching morphogenesis in organ culture

Transforming growth factor-β (TGF-β), a potent inhibitor of epithelial cell proliferation, and epidermal growth factor (EGF), a mitogenic polypeptide that binds to cell surface receptors, are important regulators of cell differentiation; however, their distinct role(s) in lung development and their mechanisms of action are not well understood. We evaluated the effects of these factors on lung morphogenesis in murine fetal lungs at gestational day 14 (time:zero) and again after 7 days in culture. Baseline controls were cultured after tracheal transection in supplemented BGJb medium, and other tracheally transected lungs were cultured following addition of EGF (10 ng/ml BGJb), TGF-β₁ (2 ng/ml BFJb), or with both in combination added to the medium. The control lungs in culture had poorly developed airways and an absence of defined acinar structures. The addition of EGF resulted in hyperplasia of primary airways with stunted outgrowths, monopodial branching, and absence of distinct acinar structures. Addition of TGF-β₁ alone, led to significant elongation of primary airways, without normal airway branching; however, terminal dipodial branching was seen and the prospective pulmonary acini were well defined. Combination of these growth factors (GF) resulted in a more normal branching pattern and differentiation, suggesting their epigenetic role in lung morphogenesis and mutual interactive mechanisms that regulate lung development. These lungs had more abundant and larger lamellar bodies than those after other treatments. Control lungs remained immature with prominent glycogen aggregates with occasional dense lamellar bodies. The total protein and DNA contents were highest with EGF treatment, followed by combination treatment; these observations were supported by immunohistochemical localization of proliferating cell nuclear antigen, an indication of the proliferative state of tissues. All the surfactant proteins were relatively unaltered and their messages were up-regulated for SP-A, but down-regulated for SP-B and SP-C in the lungs treated with growth factors. In conclusion, we have demonstrated enhanced biochemical and structural development of lungs treated in vitro with GF, and propose that further research in this area may lead to therapeutic uses of GF alone or in combination with other agents for the treatment of newborn respiratory distress due to lung immaturity or hypoplastic lung development. Pediatr Pulmonol. 1998; 25:244–256. © 1998 Wiley-Liss, Inc.     

Sex difference in cell proliferation in developing rat amygdala mediated by endocannabinoids has implications for social behavior

The amygdala is a sexually dimorphic brain region critical for the regulation of social, cognitive, and emotional behaviors, but both the nature and the source of sex differences in the amygdala are largely unknown. We have identified a unique sex difference in the developing rat medial amygdala (MeA) that is regulated by cannabinoids. Newborn females had higher rates of cell proliferation than males. Treatment of neonates with the cannabinoid receptor agonist, WIN 55,212-2 (WIN), reduced cell proliferation in females to that of males and a wide range of WIN doses had no effect on cell proliferation in males. The effect of WIN on cell proliferation in the MeA was prevented by coinfusions of a CB2 but not CB1 receptor antagonist. Females had higher amygdala content of the endocannabinoid degradation enzymes, fatty acid amid hydrolase, and monoacylglycerol lipase than males, and lower amounts of the endocannabinoids 2-arachidonoylglycerol and N-arachidonylethanolamide (anandamide). Inhibition of the degradation of 2-arachidonoylglycerol in females occluded the sex difference in cell proliferation. Analyses of cell fate revealed that females had significantly more newly generated glial cells but not more newly generated neurons than males, and treatment with WIN significantly decreased glial cell genesis in females but not males. Finally, early exposure to cannabinoids masculinized juvenile play behavior in females but did not alter this behavior in males. Collectively, our findings suggest that sex differences in endocannabinoids mediate a sex difference in glial cell genesis in the developing MeA that impacts sex-specific behaviors in adolescence.     

结缔组织生长因子在大鼠肝纤维化形成中的作用

目的 研究结缔组织生长因子（CTGF）在大鼠肝纤维化形成中的表达及作用机制。方法 雄性SD大鼠32只,体重250～300g,皮下注射四氯化碳（CCl4）制备大鼠肝纤维化模型,分别于注射后1、4、8周处理动物．采用免疫组化、RT—PCR等方法对肝组织中CTGF的表达进行检测。结果 CCl4注射诱导后,大鼠肝组织中CTGF的表达较正常对照明显增强（P〈0．01）．且注射1、4、8周组肝组织中CTGF的表达强度呈逐级递增的趋势（P〈0．01,〈0．05）。CTGF主要表达于肝星状细胞胞质中．CTGF mRNA的表达与其蛋白质水平的改变相一致。结论 CTGF作为一种致纤维化因子,其过表达促进肝星状细胞的活化增殖及细胞外基质的形成,从而促进了大鼠肝纤维化的发生、发展。     

MplK, a natural variant of the thrombopoietin receptor with a truncated cytoplasmic domain, binds thrombopoietin but does not interfere with thrombopoietin-mediated cell growth

OBJECTIVE: Interaction of thrombopoietin (TPO) with its receptor c-Mpl is responsible for the formation of megakaryocytes and platelets. In humans, there are two major c-mpl molecules, MplP and MplK, which are generated by alternative splicing. In contrast to MplP, MplK has none of the intracellular sequences required for typical signal transduction but instead has a unique 27 amino acid sequence that is coded by intron 10. We tested to determine if MplK exerts a negative effect on TPO Mpl signal transduction by interfering with the normal homodimerization of MplP. MATERIALS AND METHODS: A cassette coding for MplK cDNA was introduced into parental and MplP-expressing BaF3 cells and TPO-mediated cell growth studied. RESULTS: Cells expressing MplK alone did not respond to TPO compared to cells that expressed MplP. When MplK was coexpressed with MplP on the cell surface of BaF3, no modification in cell growth was observed when compared to those expressing MplP alone. To determine if the normal homodimerization process was negatively influenced, two genetically engineered variants of c-Mpl, one lacking the box1 sequence and the other containing only the first nine amino acids of the intracellular domain, were introduced into MplP-expressing cells. In contrast to MplK, these mutants had a dominant negative effect on TPO-mediated cell growth. CONCLUSIONS: MplK does not influence TPO-mediated growth of Mpl-expressing cells. Our data suggest that the absence of a dominant negative effect of MplK most probably is due to the inability of MplK to dimerize with the MplP receptor.