Hepatic thrombopoietin mRNA is increased in acute inflammation

The plasma concentration of thrombopoietin (TPO) in general is inversely related to the mass of platelets and megakaryocytes. However, reactive thrombocytosis of inflammatory disease is accompanied by elevated TPO levels. To investigate whether the rate of TPO mRNA expression is altered during acute inflammation, rats were injected with bacterial lipopolysaccharide (LPS). After 6 h, total RNA from liver and kidney was reverse transcribed and analyzed by competitive PCR for TPO and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). LPS-treated rats showed a significant increase in hepatic TPO mRNA concentration. The ratio of TPO to GAPDH mRNA was 3.5 +/- 0.6% in the livers of control rats and 8.3 +/- 2.0% in the livers of LPS-treated rats (mean +/- SD). Thus, reactive thrombocytosis of inflammatory disease might result from an increase in hepatic TPO production. Since platelets are involved in the immune reaction, reactive thrombocytosis may be a mechanism of host defense.

Vascular endothelial growth factor mRNA in eutopic and ectopic endometrium

OBJECTIVE

To evaluate changes in expression levels of vascular endothelial growth factor (VEGF) mRNA in human endometrial explants in a chicken chorioallantoic membrane model of endometriosis.

DESIGN

Experimental prospective study.

SETTING

University hospital.

PATIENT(S)

Endometrial biopsy samples were obtained from healthy, ovulating women undergoing elective surgery.

INTERVENTION(S)

Endometrial fragments were placed on the chicken chorioallantoic membrane and removed for analysis after 0, 24, 48, and 72 hours.

MAIN OUTCOME MEASURE(S)

Expression of different VEGF mRNA splice variants was tested. Expression of VEGF(165) mRNA was assessed by using competitive polymerase chain reaction and normalized to expression of the housekeeping gene human glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA.

RESULT(S)

After 0, 24, 48, and 72 hours of incubation, all grafts expressed VEGF(121), VEGF(145), VEGF(165), and VEGF(189) mRNA. Expression of VEGF(165) mRNA increased up to 10-fold at 24 to 72 hours compared with precultivation values.

CONCLUSION(S)

Levels of VEGF(165) mRNA in endometrial grafts increase after implantation on chicken chorioallantoic membrane. Hypoxic induction of VEGF mRNA expression in endometrial cell cultures has been reported previously. Induction of VEGF expression might indicate relative hypoxia of the specimen due to insufficient vascularization. Expression of VEGF may assist in vascularization of endometrial explants after retrograde menstruation.

Hypoxia and interleukin-1beta stimulate vascular endothelial growth factor production in human proximal tubular cells

BACKGROUND

Vascular endothelial growth factor (VEGF) promotes angiogenesis and inflammatory reactions. VEGF mRNA is detectable in the proximal tubules of inflamed kidneys but not in normals. In other organs VEGF gene expression is induced by hypoxia and cytokines such as interleukin 1 (IL-1). To identify the cellular mechanisms in control of tubular VEGF production, we studied effects of hypoxia and IL-1beta in VEGF mRNA levels, VEGF secretion, and activity of the hypoxia-inducible dimeric transcription factor 1 (HIF-1alpha/beta) in human proximal tubular epithelial cells (PTECs) in primary culture.

METHODS

PTECs were grown in monolayers from human kidneys. Hypoxia was induced by incubation at 3% O2. VEGF mRNA was quantitated by competitive polymerase chain reaction following reverse transcription. VEGF was measured by enzyme-linked immunoassay. HIF-1alpha was demonstrated by Western blot analysis and HIF-1 DNA binding by gel shift assay.

RESULTS

Significant amounts of VEGF mRNA and VEGF protein were measured in PTEC extracts and culture media, respectively. Stimulation of VEGF synthesis at low O2 tension and following IL-1beta treatment was detectable at the protein level only. Nuclear HIF-1alpha protein levels and HIF-1 binding to DNA were also increased under these conditions.

CONCLUSIONS

PTECs in culture produce VEGF. One mechanism of induction appears to be increased DNA binding of HIF-1 to hypoxia-responsive elements in the VEGF gene promoter. In inflammatory diseases of the kidney, tubular cell-derived VEGF may contribute to microvascular leakage and monocyte extravasation.

Interleukin-6 increases thrombopoietin production in human hepatoma cells HepG2 and Hep3B

The concentration of circulating thrombopoietin (TPO) is relatively high in patients with thrombocytosis reactive to inflammatory diseases. We investigated whether immunomodulatory cytokines stimulate TPO synthesis in cultured human hepatoma cells (lines HepG2 and Hep3B), renal proximal tubular cells, and bone marrow fibroblasts. The effects of interleukins (IL) IL-1beta, IL-6, and IL-11 and of tumor necrosis factor-a (TNF-alpha) on the rate of TPO secretion were measured by ELISA. TPO mRNA levels were quantitated by competitive reverse transcription PCR. HepG2 and Hep3B cells produced significant amounts of TPO mRNA and TPO protein. Renal tubular cells synthesized less TPO, and in bone marrow fibroblasts, neither TPO mRNA nor TPO protein was detected. Only IL-6 affected TPO protein secretion, causing a 1.5-fold stimulation in HepG2 and Hep3B cells in 24-h incubation periods. The TPO mRNA content in these cells was doubled by IL-6 after 2, 6, or 24 h of stimulation. Thus, IL-6 could cause thrombocytosis in inflammatory disease partly by increasing hepatic TPO production.

Expression of the thrombopoietin gene in human fetal and neonatal tissues

Thrombopoietin (TPO) regulates megakaryopoiesis and platelet production. In the adult, TPO is mainly produced by the liver and the kidneys. This study focuses on fetal and neonatal TPO mRNA expression. In 26 human fetuses and preterm neonates, samples from liver, kidney, spleen, lung, and bone marrow were extracted for total RNA. We measured platelet counts, TPO serum concentrations by enzyme-linked immunosorbent assay, and TPO mRNA contents by reverse transcription/competitive polymerase chain reaction. TPO mRNA concentrations per microgram total RNA were similar in liver, spleen, and bone marrow, slightly lower in kidney, and significantly lower in lung. When related to gram tissue, TPO mRNA levels were highest in the liver. Considering the total amount of TPO mRNA produced in liver, kidney, and spleen, the liver accounted for 95.3%. No correlations between TPO mRNA expression and serum TPO concentration, blood platelet count, or gestational age were observed. In conclusion, the liver is the primary site of TPO gene expression in human fetuses and neonates. The spleen may contribute to TPO production during fetal life. Like in the adult, TPO mRNA is expressed in fetal bone marrow.

Hepatic thrombopoietin mRNA levels in acute and chronic liver failure of childhood

The liver is the main production site of the hormone thrombopoietin (TPO), the major regulator of megakaryopoiesis. To investigate the role of an impaired TPO gene expression in the pathogenesis of thrombocytopenia in pediatric patients suffering from liver failure, we measured hepatic TPO mRNA in children with acute or chronic end-stage liver disease undergoing orthotopic liver transplantation. Tissue samples for RNA extraction were obtained from 12 children with compensated cirrhosis (CC), 22 children with decompensated cirrhosis (DC), and 9 children with acute liver failure (ALF). TPO mRNA was quantitated by competitive polymerase chain reaction (PCR), following reverse transcription (RT). Furthermore, in 9 children with ALF, serum TPO levels were measured by enzyme-linked immunosorbent assay before and 10 to 14 days after liver transplantation. The hepatic TPO mRNA concentration was highest in children with CC (median, 50.9 amol/micrograms RNA). This value was significantly reduced in children with DC (30.2 amol/micrograms RNA) or ALF (13.8 amol/micrograms RNA). Children with ALF (139 cells/nL) or DC (200 cells/nL) had lower platelet counts than children with CC (368 cells/nL). The serum TPO concentration increased from a median of 156 pg/mL in patients with ALF to 547 pg/mL after liver transplantation. These results show that the thrombocytopenia in children with liver failure is associated with reduced hepatic TPO mRNA levels. It remains to be investigated whether the serum TPO level and platelet counts are markers for the severity of liver damage that may serve as a prognostic indicator.