Self-Assembly and Anti-Amyloid Cytotoxicity Activity of Amyloid beta Peptide Derivatives

The self-assembly of two derivatives of KLVFF, a fragment Aβ(16-20) of the amyloid beta (Aβ) peptide, is investigated and recovery of viability of neuroblastoma cells exposed to Aβ (1-42) is observed at sub-stoichiometric peptide concentrations. Fluorescence assays show that NH2-KLVFF-CONH2 undergoes hydrophobic collapse and amyloid formation at the same critical aggregation concentration (cac). In contrast, NH2-K(Boc)LVFF-CONH2 undergoes hydrophobic collapse at a low concentration, followed by amyloid formation at a higher cac. These findings are supported by the β-sheet features observed by FTIR. Electrospray ionization mass spectrometry indicates that NH2-K(Boc)LVFF-CONH2 forms a significant population of oligomeric species above the cac. Cryo-TEM, used together with SAXS to determine fibril dimensions, shows that the length and degree of twisting of peptide fibrils seem to be influenced by the net peptide charge. Grazing incidence X-ray scattering from thin peptide films shows features of β-sheet ordering for both peptides, along with evidence for lamellar ordering of NH2-KLVFF-CONH2. This work provides a comprehensive picture of the aggregation properties of these two KLVFF derivatives and shows their utility, in unaggregated form, in restoring the viability of neuroblastoma cells against Aβ-induced toxicity.

Combined effects of transferrin and thyroid hormone during oligodendrogenesis In vitro

Thyroid hormones (THs) and transferrin (Tf) are factors capable of favoring myelination due to their positive effects on oligodendroglial cell (OLG) differentiation. The first notion of a combined effect of apotransferrin (aTf) and TH emerged from experiments conducted in young hyperthyroid animals, which showed a seven-fold increase in the expression of Tf mRNA and precocious myelination when compared with control animals. The mechanism underlying this phenomenon in young hyperthyroid rats could consist of an increase in Tf synthesis, which in the CNS is almost exclusively produced by OLG. Overall, our results show that, during the initial stages of OLG differentiation, Tf synthesis triggers thyroid hormone receptor alpha 1 (TRα1) expression in the subventricular zone (SVZ) and promotes proliferating cells to become responsive to this trophic factor. Exposure to TH could then regulate Tf expression through TRα1 and promote the induction of thyroid hormone receptor beta (TRβ) expression, which mediates TH effects on myelination through the activation of final OLG differentiation. This regulation of the combined effects of Tf and THs implies that both factors are fundamental actors during oligodendrogenesis. GLIA 2016;64:1879-1891.

Transferrin and thyroid hormone converge in the control of myelinogenesis

Myelination is a concerted mechanism tightly regulated in the brain. Although several factors are known to participate during this process, the complete sequence of events is far from being fully elucidated. Separate effects of apotransferrin (aTf) and thyroid hormone (TH) are well documented on rat myelin formation. TH promotes the maturation of oligodendrocyte progenitors (OPCs) into myelinating oligodendrocytes (OLGs), while aTf is able to induce the commitment of neural stem cells (NSCs) toward the oligodendroglial linage and favors OLG maturation. We have also demonstrated that Tf mRNA exhibited a seven-fold increase in hyperthyroid animals. These observations have led us to hypothesize that both factors may interplay during oligodendrogenesis. To assess the combined effects of aTf and TH on proper myelination in the rat brain, Tf expression and oligodendroglial maturation were evaluated at postnatal days 10 (P10) and 20 (P20) in several experimental groups. At P10, an up-regulation of both Tf mRNA and protein, as well as myelination, was found in hyperthyroid animals, while a decrease in Tf mRNA levels and myelin formation was detected in the hypothyroid group. At P20, no differences were found either in Tf mRNA or protein levels between hyperthyroid and control (Ctrol) rats, although differences in OLG differentiation remained. Also at P20, hypothyroid animals showed decreased Tf mRNA and protein levels accompanied with a less mature myelinating phenotype. Moreover, TH and aTf differentially regulate the expression of KLF9 transcription factor as well as TRα and TRβ at P10 and P20. Our results suggest that TH is necessary early in OLG development for aTf action, as exogenous aTf administration was unable to counteract the effect of low TH levels in the hypothyroid state in all the time points analyzed. Furthermore, the fact that hyperthyroidism induced an increase in Tf expression and aTf-dependent regulation of TRα strongly suggests that Tf could be involved in some of TH later effects on OLG maturation. Here we describe the possible relationship between TH and aTf and its implication in oligodendrogenesis.

Apotransferrin decreases the response of oligodendrocyte progenitors to PDGF and inhibits the progression of the cell cycle

In the CNS, transferrin (Tf) is expressed by the oligodendroglial cells (OLGcs) and is essential for their development. We have previously shown that apotransferrin (aTf) accelerates maturation of OLGcs in vivo as well as in vitro. The mechanisms involved in this action appear to be complex and have not been completely elucidated. The aim of this study was to investigate if Tf participates in the regulation of the cell cycle of oligodendroglial progenitor cells (OPcs). Primary cultures of OPcs were treated with aTf and/or with different combinations of mitogenic factors. Cell cycle progression was studied by BrdU incorporation, flow cytometry and by the expression of cell cycle regulatory proteins. Apotransferrin decreased the number of BrdU+ cells, increasing the cell cycle time and decreasing the number of cells in S phase. The cell cycle inhibitors p27kip1, p21cip1 and p53 were increased, and in agreement with these results, the activity of the complexes involved in G1-S progression (cyclin D/CDK4, cyclin E/CDK2), was dramatically decreased. Apotransferrin also inhibited the mitogenic effects of PDGF and PDGF/IGF on OPcs, but did not affect their proliferation rate in the presence of bFGF, bFGF/PDGF or bFGF/IGF. Our results indicate that inhibition of the progression of the cell cycle of OPcs by aTf, even in the presence of PDGF, leads to an early beginning of the differentiation program, evaluated by different maturation markers (O4, GC and MBP) and by morphological criteria. The modulation by aTf of the response of OPcs to PDGF supports the idea that this glycoprotein might act as a key regulator of the OLGc lineage progression.

Oligodendroglial cell differentiation in rat brain is accelerated by the intracranial injection of apotransferrin

In the present paper we first studied the brain distribution and the time and dose dependent effects of apotransferrin, after its intracranial injection into young rats and at different post-natal ages. Its action upon the transferrin receptor (TfR) and upon the expression of brain transferrin, as well as its effect on the proliferation and differentiation of oligodendroglial cells (OLGc) was one of the main objectives of our investigation. Total DNA and BrdU labeling, as an index of cellularity and proliferation, respectively, were the same in the control and experimental groups of rats. A significant increase in the MBP+ and CA II+ OLGc, and a decrease in the more immature (A2B5+) OLGc were found in the aTf injected rats. At 10 and 17 days of age, Tf-mRNA decreased to around 20% of the amount present in control animals. The TfR-mRNA in the animals receiving a single dose of aTf at 3 days of age showed an increase in its expression at 10 and 17 days of age, coincident with a higher immunoreactivity of the TfR itself of neurons, choroid plexus and brain capillaries in different brain areas. Although TfR+ OLGc were present up to 7 days of age in controls and in the Tf injected rats, no positive cells were observed at 17 days of age, even in the aTf injected rats. Our results give support to the hypothesis that aTf is an important factor necessary for the maturation of the OLGc, and that the effects that it produces in the OLGc-myelin unit after its intracranial injection in young rats are not due to an increase in proliferation, but to an accelerated differentiation of Tf-sensitive OLGc.

Effect of neonatal capsaicin treatment on neurogenic pulmonary edema from fluid-percussion brain injury in the adult rat

The frequent occurrence of acute death from pulmonary failure in experimental head injury studies on Sprague-Dawley rats prompted an investigation into the manner in which acute neurogenic pulmonary edema develops in these animals as a result of an applied fluid pressure pulse to the cerebral hemispheres. Studies were performed in adult animals using histamine H1 and H2 blocking agents, or in adult animals treated as neonates with capsaicin to destroy unmyelinated C-fibers. Recordings were made of either the pulmonary arterial or the right ventricular pressure, and the left atrial and femoral arterial pressures before, during, and after injury to provide a record of the hemodynamic response throughout the development of neurogenic pulmonary edema. Head injury triggered the almost immediate development of pressure transients with and without neurogenic pulmonary edema. All rats, regardless of treatment, reacted with nearly identical systemic arterial pressure responses; however, the pulmonary responses followed a time course that was independent of systemic arterial pressure changes. Acute neurogenic pulmonary edema was always associated with a substantial increase in pulmonary arterial and left atrial pressures; conversely, pressure increases of similar magnitude were not always associated with edema. Histamine H1 and H2 blockers significantly reduced the pulmonary pressure surges only in rats free of neurogenic pulmonary edema. All capsaicin-treated rats showed suppressed pulmonary pressure responses, normal lung water content, elevated lung surface tension, and significantly reduced levels of immunoreactive substance P in the spinal cord and vagus nerve. While the pressures cannot clarify how edema influences the observed hemodynamics, they do not support the view that edema is the direct consequence of pulmonary hypertension. It is proposed that neurogenic pulmonary edema is a functional disturbance provoked by adverse stimuli from outside the lungs and that in the rat the primary afferent fiber is essential to the production of this entity.