Astroglial expression of the P-glycoprotein is controlled by intracellular CNTF

BACKGROUND: The P-glycoprotein (P-gp), an ATP binding cassette transmembrane transporter, is expressed by astrocytes in the adult brain, and is positively modulated during astrogliosis. In a search for factors involved in this modulation, P-gp overexpression was studied in long-term in vitro astroglial cultures. RESULTS: Surprisingly, most factors that are known to induce astroglial activation in astroglial cultures failed to increase P-gp expression. The only effective proteins were IFNγ and those belonging to the IL-6 family of cytokines (IL-6, LIF, CT-1 and CNTF). As well as P-gp expression, the IL-6 type cytokines - but not IFNγ - stimulated the expression of endogenous CNTF in astrocytes. In order to see whether an increased intracellular level of CNTF was necessary for induction of P-gp overexpression by IL-6 type cytokines, by the same cytokines analysis was carried out on astrocytes obtained from CNTF knockout mice. In these conditions, IFNγ produced increased P-gp expression, but no overexpression of P-gp was observed with either IL-6, LIF or CT-1, pointing to a role of CNTF in the intracellular signalling pathway leading to P-gp overexpression. In agreement with this suggestion, application of exogenous CNTF -which is internalised with its receptor - produced an overexpression of P-gp in CNTF-deficient astrocytes. CONCLUSIONS: These results reveal two different pathways regulating P-gp expression and activity in reactive astrocytes, one of which depends upon the intracellular concentration of CNTF. This regulation of P-gp may be one of the long searched for physiological roles of CNTF

Efeitos in vitro do ácido retinóico em células de glioblastoma.

Malignant gliomas are highly invasive, rapidly proliferating tumors and present a poor prognosis. In this study, we investigated the potential effects of the retinoic acid (RA) on a high proliferative glioblastoma cell line, GL-15. The exposure to a single dose of t-RA reduces the cell growth, induces a transitory stage of the cell differentiation, and it finally leads to the apoptotic cell death depending on the RA concentration range and the time of exposure. We found that the GL-15 cells express constitutively the RARs isotypes a, b and g, and that RARa1/2, RARb2, and RARg2 expressions are induced by t-RA. These results suggest that the ratio of RAR isoforms may be a crucial element for inducing either efficient differentiaton or apoptotic effects in those cells. Furthermore, they suggest that the use of ligands specific to each receptor isotype might be relevant for further glioma therapies.Os gliomas malignos são tumores muito infiltrantes, cujas células proliferam rapidamente, e apresentam um prognóstico muito reservado. Neste estudo, investigamos o efeito em potencial do ácido retinóico (AR) sobre a linhagem de células de glioblastoma multiforme humano GL-15. A exposição a uma única dose de AR (1-10 mM) inibiu a proliferação celular, induziu uma diferenciação transitória e, finalmente, conduziu estas células à apoptose. Observamos que as células GL-15 expressam os isotipos dos RARs a, b e g, e que as isoformas RARa1/2, RARb2 e RARg2 são induzidas pelo AR. Estes resultados sugerem que a relação entre a expressão das diferentes isoformas de RARs pode ser um elemento fundamental para a indução seja de uma diferenciação completa, seja de apoptose das células de glioblastoma, e que o uso de ligantes específicos a cada isotipo de receptor pode vir a ser um elemento importante para terapias futuras de gliomas

A Role for Transforming Growth Factor α as an Inducer of Astrogliosis

International audienceTGFalpha is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR). Synthesis of TGFalpha and EGFR in reactive astrocytes developing after CNS insults is associated with the differentiative and mitogenic effects of TGFalpha on cultured astrocytes. This suggests a role for TGFalpha in the development of astrogliosis. We evaluated this hypothesis using transgenic mice bearing the human TGFalpha cDNA under the control of the zinc-inducible metallothionein promoter. Expression levels of glial fibrillary acidic protein (GFAP) and vimentin and morphological features of astrocytes were used as indices of astroglial reactivity in adult transgenic versus wild-type mice provided with ZnCl2 in their water for 3 weeks. In the striatum, the hippocampus, and the cervical spinal cord, the three CNS areas monitored, transgenic mice displayed enhanced GFAP mRNA and protein levels and elevated vimentin protein levels. GFAP-immunoreactive astrocytes exhibited numerous thick processes and hypertrophied somata, which are characteristic aspects of reactive astrocytes. Their number increased additionally in the striatum and the spinal cord, but no astrocytic proliferation was observed using bromodeoxyuridine immunohistochemistry. Neither the morphology nor the number of microglial cells appeared modified. A twofold increase in phosphorylated EGFR was detected in the striatum and was associated with the immunohistochemical detection of numerous GFAP-positive astrocytes bearing the EGFR, suggesting a direct action of TGFalpha on astrocytes. Altogether, these results demonstrate that enhanced TGFalpha synthesis is sufficient to trigger astrogliosis throughout the CNS, whereas microglial metabolism is unaffected

A role for transforming growth factor α as an inducer of astrogliosis

International audienceTGFalpha is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR). Synthesis of TGFalpha and EGFR in reactive astrocytes developing after CNS insults is associated with the differentiative and mitogenic effects of TGFalpha on cultured astrocytes. This suggests a role for TGFalpha in the development of astrogliosis. We evaluated this hypothesis using transgenic mice bearing the human TGFalpha cDNA under the control of the zinc-inducible metallothionein promoter. Expression levels of glial fibrillary acidic protein (GFAP) and vimentin and morphological features of astrocytes were used as indices of astroglial reactivity in adult transgenic versus wild-type mice provided with ZnCl2 in their water for 3 weeks. In the striatum, the hippocampus, and the cervical spinal cord, the three CNS areas monitored, transgenic mice displayed enhanced GFAP mRNA and protein levels and elevated vimentin protein levels. GFAP-immunoreactive astrocytes exhibited numerous thick processes and hypertrophied somata, which are characteristic aspects of reactive astrocytes. Their number increased additionally in the striatum and the spinal cord, but no astrocytic proliferation was observed using bromodeoxyuridine immunohistochemistry. Neither the morphology nor the number of microglial cells appeared modified. A twofold increase in phosphorylated EGFR was detected in the striatum and was associated with the immunohistochemical detection of numerous GFAP-positive astrocytes bearing the EGFR, suggesting a direct action of TGFalpha on astrocytes. Altogether, these results demonstrate that enhanced TGFalpha synthesis is sufficient to trigger astrogliosis throughout the CNS, whereas microglial metabolism is unaffected