Platelet-derived growth factor receptor-β in myocyte was upregulated by angiotensin Ⅱ

To observe the regulation of platelet-derived growth factor (PDGF) receptor-βin myocyte stimulated by angiotensin II (AngII) at both integrated and cellular levels and reveal the signal transduction mechanism in cell, two kidneys, one clip (2K1C) renal hypertension were performed by placing a sliver clip around the left renal artery. Blood pressure and the ratio of left ventricular weight to body weight were measured at 4 and 8 weeks after operation. The content of AngII in heart was detected by radioimmunology assay; the protein level of PDGF receptor-βin heart was measured by Western blot analysis. The alteration of PDGF receptor-βstimulated by AngII and several inhibitors was observed on cultured neonatal rat ventricular myocyte (NRVM). The content of AngII in heart of 2K1C renal hypertensive rat at 4 and 8 weeks after operation was increased. Compared with sham group, 4 and 8 weeks after operation, PDGF receptor-βin heart of 2K1C group was upregulated by 100.3% and 127.1% (P < 0.05), respectively. This upregulation could be inhibited by captopril. For cultured myocyte, PDGF receptor-βwas increased by 47.1% after being stimulated by AngII and this upregulation could be inhibited by losartan which was an inhibitor of AT1 receptor. PLC inhibitor (U73122) and MEK inhibitor (PD98059) could partly inhibit PDGF receptor-βupregulation induced by AngII. These results suggested that AngII could upregulate PDGF receptor-βin myocyte by its AT1 receptor and this effect was at least partly dependent on PLC and extracellular signal-regulated kinase (ERK).     

Platelet-derived growth factor from astrocytes drives the clock that times oligodendrocyte development in culture

The various cell types in a multicellular animal differentiate on a predictable schedule but the mechanisms responsible for timing cell differentiation are largely unknown. We have studied a population of bipotential glial (O-2A) progenitor cells in the developing rat optic nerve that gives rise to oligodendrocytes beginning at birth and to type-2 astrocytes beginning in the second postnatal week. Whereas, in vivo, these O-2A progenitor cells proliferate and give rise to postimitotic oligodendrocytes over several weeks, in serum-free (or low-serum) culture they stop dividing prematurely and differentiate into oligodendrocytes within two or three days. The normal timing of oligodendrocyte development can be restored if embryonic optic-nerve cells are cultured in medium conditioned by type-1 astrocytes, the first glial cells to differentiate in the nerve: in this case the progenitor cells continue to proliferate, the first oligodendrocytes appear on the equivalent of the day of birth, and new oligodendrocytes continue to develop over several weeks, just as in vivo. Here we show that platelet-derived growth factor (PDGF) can replace type-1-astrocyte-conditioned medium in restoring the normal timing of oligodendrocyte differentiation in vitro and that anti-PDGF antibodies inhibit this property of the appropriately conditioned medium. We also show that PDGF is present in the developing optic nerve. These findings suggest that type-1-astrocyte-derived PDGF drives the clock that times oligodendrocyte development.     

Basic fibroblast growth factor prevents death of lesioned cholinergic neurons in vivo

Cutting the axons of the cholinergic neurons that project to the hippocampal formation results in death of most of these cells. Previous studies have shown that administration of nerve growth factor before or at the same time as the lesion will prevent this cell death. Here we demonstrate that basic fibroblast growth factor (FGF) administered into the brain reduces the death of cholinergic neurons in the medial septum and diagonal band of Broca after transection of their axons, in both young adult and aged rats. Moreover, FGF can partially protect against death of cholinergic neurons even when administered two days after axonal transection. These results indicate a possible function for FGF in the normal support of basal forebrain cholinergic neurons, but its range of activity could be wider, for FGF also supports noncholinergic neurons in vitro, it is localized in many of the central nervous system neurons, and it is found in relatively high concentrations in the brain.     

Parthenolide inhibits proliferation of vascular smooth muscle cells through induction of G0/G1 phase cell cycle arrest

Objective: This study is to determine the effect of the natural product parthenolide, a sesquiterpene lactone isolated from extracts of the herb Tanacetum parthenium, on the proliferation of vascular smooth muscle cells (VSMCs). Methods: Rat aortic VSMCs were isolated and cultured in vitro, and treated with different concentrations of parthenolide (10, 20 and 30 μmol/L). [³H]thymidine incorporation was used as an index of cell proliferation. Cell cycle progression and distribution were determined by flow cytometric analysis. Furthermore, the expression of several regulatory proteins relevant to VSMC proliferation including IκBα, cyclooxygenase-2 (Cox-2), p21, and p27 was examined to investigate the potential molecular mechanism. Results: Treatment with parthenolide significantly decreased the [³H]thymidine incorporation into DNA by 30%~56% relative to control values in a dose-dependent manner (P<0.05). Addition of parthenolide also increased cell population at G₀/G₁ phase by 19.2%~65.7% (P<0.05) and decreased cell population at S phase by 50.7%~84.8% (P<0.05), which is consistent with its stimulatory effects on p21 and p27. In addition, parthenolide also increased IκBα expression and reduced Cox-2 expression in a time-dependent manner. Conclusion: Our results show that parthenolide significantly inhibits the VSMC proliferation by inducing G₀/G₁ cell cycle arrest. IκBα and Cox-2 are likely involved in such inhibitory effect of parthenolide on VSMC proliferation. These findings warrant further investigation on potential therapeutic implications of parthenolide on VSMC proliferation in vivo.     

Platelet-derived growth factor is structurally related to the putative transforming protein p28sis of simian sarcoma virus

A partial amino acid sequence of human platelet-derived growth factor, the major mitogen in serum for cells of mesenchymal origin, has been determined. A region of 104 contiguous amino acids shows virtual identity with the predicted sequence of p28sis, the putative transforming protein of simian sarcoma virus (SSV). This similarity suggests a mechanism for transformation by SSV and other agents, involving expression of growth factors.     

Platelet-derived growth factor promotes division and motility and inhibits premature differentiation of the oligodendrocyte/type-2 astrocyte progenitor cell

The mitogens which modulate cell-cell interactions during development of the central nervous system are unknown. One of the few interactions sufficiently well understood to allow identification of such molecules involves the two glial lineages which make up the rat optic nerve. One population of glial cells in this tissue, the type-1 astrocytes, secrete a soluble factor(s) which promotes division of a second population of bipotential oligodendrocyte/type-2 astrocyte (O-2A) progenitor cells; these progenitors give rise to oligodendrocytes, which myelinate large axons in the CNS, and type-2 astrocytes, which enwrap bare axons at nodes of Ranvier. Type-1 astrocytes also promote progenitor motility, and inhibit the premature differentiation of progenitors into oligodendrocytes which occur when these cells are grown in the absence of type-1 astrocytes. We have now found that platelet-derived growth factor mimics the effects of type-1 astrocytes on O-2A progenitor cells, and antibodies to PDGF block the effects of type-1 astrocytes.     

Platelet-derived growth factor stimulates synthesis of PtdIns(3,4,5)P3 by activating a PtdIns(4,5)P2 3-OH kinase.

Although the hormone-stimulated synthesis of 3-phosphorylated inositol lipids is known to form an intracellular signalling system, there is no consensus on the crucial receptor-regulated event in this pathway and it is still not clear which of the intermediates represent potential output signals. We show here that the key step in the synthesis of 3-phosphorylated inositol lipids in 3T3 cells stimulated by platelet-derived growth factor is the activation of a phosphatidylinositol(4,5)-bisphosphate (3)-hydroxy (PtdIns(4,5)P2 3-OH) kinase. A similar conclusion has been applied to explain the actions of formyl-Met-Leu-Phe on neutrophils, and it may be that receptors that couple through intrinsic tyrosine kinases or through G proteins stimulate the same step in 3-phosphorylated inositol lipid metabolism. The close parallel between these two mechanisms for the activation of PtdIns(4,5)P2 3-OH kinase and those described for the activation of another key signalling enzyme, phospholipase C (ref. 7), focuses attention on the product of the PtdIns(4,5)P2 3-OH kinase, PtdIns(3,4,5)P3, as a possible new second messenger.     

G0 is a major growth cone protein subject to regulation by GAP-43

G0, a GTP-binding protein that transduces information from transmembrane receptors, has been found to be a major component of the neuronal growth cone membrane. GAP-43, an intracellular growth cone protein closely associated with neuronal growth, stimulates GTP-gamma-S binding to G0. It does so through an amino-terminal domain homologous to G-linked transmembrane receptors. Thus, G0 in the growth cone may be regulated by intracellular as well as extracellular signals.     

Platelet-derived growth factor-alpha receptor activation is required for human cytomegalovirus infection

Human cytomegalovirus (HCMV) is a ubiquitous human herpesvirus that can cause life-threatening disease in the fetus and the immunocompromised host. Upon attachment to the cell, the virus induces robust inflammatory, interferon- and growth-factor-like signalling. The mechanisms facilitating viral entry and gene expression are not clearly understood. Here we show that platelet-derived growth factor-alpha receptor (PDGFR-alpha) is specifically phosphorylated by both laboratory and clinical isolates of HCMV in various human cell types, resulting in activation of the phosphoinositide-3-kinase (PI(3)K) signalling pathway. Upon stimulation by HCMV, tyrosine-phosphorylated PDGFR-alpha associated with the p85 regulatory subunit of PI(3)K and induced protein kinase B (also known as Akt) phosphorylation, similar to the genuine ligand, PDGF-AA. Cells in which PDGFR-alpha was genetically deleted or functionally blocked were non-permissive to HCMV entry, viral gene expression or infectious virus production. Re-introducing human PDGFRA gene into knockout cells restored susceptibility to viral entry and essential viral gene expression. Blockade of receptor function with a humanized PDGFR-alpha blocking antibody (IMC-3G3) or targeted inhibition of its kinase activity with a small molecule (Gleevec) completely inhibited HCMV viral internalization and gene expression in human epithelial, endothelial and fibroblast cells. Viral entry in cells harbouring endogenous PDGFR-alpha was competitively inhibited by pretreatment with PDGF-AA. We further demonstrate that HCMV glycoprotein B directly interacts with PDGFR-alpha, resulting in receptor tyrosine phosphorylation, and that glycoprotein B neutralizing antibodies inhibit HCMV-induced PDGFR-alpha phosphorylation. Taken together, these data indicate that PDGFR-alpha is a critical receptor required for HCMV infection, and thus a target for novel anti-viral therapies.     

A microbial symbiosis factor prevents intestinal inflammatory disease

Humans are colonized by multitudes of commensal organisms representing members of five of the six kingdoms of life; however, our gastrointestinal tract provides residence to both beneficial and potentially pathogenic microorganisms. Imbalances in the composition of the bacterial microbiota, known as dysbiosis, are postulated to be a major factor in human disorders such as inflammatory bowel disease. We report here that the prominent human symbiont Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus, a commensal bacterium with pathogenic potential. This beneficial activity requires a single microbial molecule (polysaccharide A, PSA). In animals harbouring B. fragilis not expressing PSA, H. hepaticus colonization leads to disease and pro-inflammatory cytokine production in colonic tissues. Purified PSA administered to animals is required to suppress pro-inflammatory interleukin-17 production by intestinal immune cells and also inhibits in vitro reactions in cell cultures. Furthermore, PSA protects from inflammatory disease through a functional requirement for interleukin-10-producing CD4+ T cells. These results show that molecules of the bacterial microbiota can mediate the critical balance between health and disease. Harnessing the immunomodulatory capacity of symbiosis factors such as PSA might potentially provide therapeutics for human inflammatory disorders on the basis of entirely novel biological principles.     

Brain-derived neurotrophic factor prevents neuronal death in vivo

Developing vertebrate neurons are thought to depend for their survival on specific neurotrophic proteins present in their target fields. The limited availability of these proteins does not allow the survival of all neurons initially innervating a target, resulting in the widely observed phenomenon of naturally occurring neuronal death. Although a variety of proteins have been reported to promote the survival of neurons in tissue culture, the demonstration that these proteins increase neuronal numbers and/or decrease neuronal death in vivo has only been possible with nerve growth factor (NGF). The generalization of the concept that neurotrophic proteins regulate neuronal survival during normal development critically depends on the demonstration that the survival of neurons in vivo can be increased by the administration of a neurotrophic protein different from NGF. We report here that this is the case with brain-derived neurotrophic factor, a protein of extremely low abundance purified from the central nervous system.     

Brain-derived neurotrophic factor prevents the death of motoneurons in newborn rats after nerve section.

Motoneurons innervating the skeletal musculature were among the first neurons shown to require the presence of their target cells to develop appropriately. But the characterization of molecules allowing motoneuron survival has been difficult. Ciliary neurotrophic factor prevents the death of motoneurons, but its gene is not expressed during development. Although the presence of a neurotrophin receptor on developing motoneurons has suggested a role for neurotrophins, none could be shown to promote motoneuron survival in vitro. We report here that brain-derived neurotrophic factor can prevent the death of axotomized motoneurons in newborn rats, suggesting a role for this neurotrophin for motoneuron survival in vivo.     

Ciliary neurotrophic factor prevents degeneration of motor neurons in mouse mutant progressive motor neuronopathy.

Ciliary neurotrophic factor (CNTF) supports the survival of embryonic motor neurons in vitro and in vivo, and prevents lesion-mediated degeneration of rat motor neurons during early post-natal stages. Here we report that CNTF greatly reduces all the functional and morphological changes in pmn/pmn mice, an autosomal recessive mutant leading to progressive caudo-cranial motor neuron degeneration. The first manifestations of progressive motor neuronopathy in homozygous pmn/pmn mice become apparent in the hind limbs at the end of the third post-natal week, and all the mice die up to 6 or 7 weeks after birth from respiratory paralysis. Treatment with CNTF prolongs survival and greatly improves motor function of these mice. Moreover, morphological manifestations, such as loss of motor axons in the phrenic nerve and degeneration of facial motor neurons, were greatly reduced by CNTF, although the treatment did not start until the first symptoms of the disease had already become apparent and substantial degenerative changes were already present. The protective and restorative effects of CNTF in this mouse mutant give new perspectives for the treatment of human degenerative motor neuron diseases with CNTF.