Molecular mechanisms involved in the actions of apotransferrin upon the central nervous system: Role of the cytoskeleton and of second messengers

Abstract

Apotransferrin (aTf), intracranially administered into newborn rats, produces increased myelination with marked increases in the levels of myelin basic protein (MBP), phospholipids and galactolipids, and mRNAs of MBP and 2', 3' cyclic nucleotide 3'-phosphohydrolase (CNPase). Cytoskeletal proteins such as tubulin, actin, and microtubule-associated proteins are also increased after aTf injection. In contrast, almost no changes are observed in myelin proteolipid protein (PLP) or in its mRNA or cholesterol. In the present study, we used brain-tissue slices and cell cultures highly enriched for oligodendroglia to investigate signaling pathways involved in the action of aTf, and to find out whether cytoskeletal integrity and dynamics were essential for its action upon the neural expression of certain genes. Treatment of brain-tissue slices with aTf produced a marked increase in the expression of MBP, CNPase, and tubulin mRNAs. Colchicine, cytochalasin, and taxol severely reduced the effect of aTf. Addition to cultures of an antibody against transferrin receptor (TfR), protein kinase inhibitors, or a cyclic AMP (cAMP) analogue showed that a functionally intact TfR was necessary, and that tyrosine kinase, protein kinase C and A, as well as calcium-calmodulin-dependent kinase (Ca-CaMK) activities appeared to mediate aTf actions upon the expression of the above mentioned genes. Changes in the levels of phosphoinositides and cAMP induced by aTf in oligodendroglial cell (OLGc) cultures correlated with these results and coincide with an activation of the cyclic response element binding protein (CREB) and of mitogen activated protein kinases. The increased expression of certain myelin genes produced by aTf appear to be mediated by interaction of this glycoprotein with its receptor, by the cytoskeleton of the OLGc, and by a complex activation of protein kinases which lead to CREB phosphorylation.

Exosome Release Is Regulated by a Calcium-dependent Mechanism in K562 Cells

“…Furthermore, the Tf-stimulated exosome release was also inhibited by 2-APB, suggesting that IP 3 -sensitive Ca 2ϩ channels participate in this process. This is in agreement with a recent observation that the addition of apotransferrin to cultured oligodendroglial cells increased the levels of IP 3 (41).…”

“…Therefore, Tf, by increasing intracellular Ca 2ϩ , may modulate some critical components of the transport/fusion machinery. Interestingly, in a recent paper it has been shown that the binding of apotransferrin to its receptor increased, via a calcium-calmodulin-dependent kinase, the levels of tubulin and actin, proteins known to be involved in vesicular trafficking (41). In conclusion, the TfR seems to function as a signal transduction molecule that modulates not only its own recycling but also its shedding via the exosome pathway, and Ca 2ϩ is one of the components of this signaling pathway triggered by Tf binding.…”

Cellular iron status influences the functional relationship between microglia and oligodendrocytes

“…Our results showing ferritin release from microglia, taken in context of the published results on ferritin binding, identify H-ferritin as a potential major trophic factor for oligodendrocytes. Traditionally, transferrin, the iron mobilization protein, has been considered critical for developing oligodendrocytes (Eccleston and Silberberg, 1984), but the ability of transferrin to impact mature oligodendrocytes is limited (Marta et al, 2002(Marta et al, , 2003 and transferrin binding is not seen in adult white matter (Hill et al, 1985;. Our data suggest that ferritin may be the primary iron delivery protein to mature oligodendrocytes.…”

Overexpression of human transferrin in two oligodendroglial cell lines enhances their differentiation

“…Tf, an early differentiation marker of OLGcs (Espinosa de los Monteros et al, 1988) was postulated as having a role in the myelination process (Escobar Cabrera et al, 1994;Espinosa de los Monteros et al, 1999;EspinosaJeffrey et al, 2002;Marta et al, 2002). In the present work we have studied the effects of Tf overexpression in N19 and N20.1 cells, two OLGc lines obtained from mouse primary cultures .…”