An amino-terminal fragment peptide of acidic fibroblast growth factor modulates synaptic transmission in rat hippocampal slices

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.

Effects of acidic fibroblast growth factor fragments on nocturnal feeding in rats by intracerebroventricular and hypodermic injection

AIM: To investigate the active region of aFGF responsible for food intake by calculating nocturnal food consumption to examine the efficacy of peripheral administration of the active fragments.

METHODS: For intracerebroventricular infusion, a guide cannula made of stainless steel tubing was fixed into the third cerebral ventricle one week before the experiments. Under no anesthesia seven synthesized aFGF fragments aFGF-(1-15), [D-Trp⁶]-aFGF-(1-15), [desaminoPhe1.D-Trp⁶]-aFGF-(1-15), [desaminoPhe1.Lys (ε-myristyl)¹⁶]-aFGF-(1-16), [Lys (ε-myristyl)¹⁶]-aFGF-(1-16), [D-Trp6.Lys (ε-myristyl)¹⁶]-aFGF-(1-16) and [Ala16] aFGF-(1-29) were injected into the third ventricle of rats during the period from 18:30 to 19:00. Powdered food in the animal food boxes were weighed at 19:00, 22:00, and 7:00 for calculating food consumption by rats in 3 hours and 12 hours. Then the two active aFGF fragments aFGF-(1-15) and [Ala¹⁶] aFGF-(1-29) were injected into the subcutaneous tissue of rats during the period from 18:30 to 19:00, to calculate nocturnal food consumption.

RESULTS: For intracerebroventricular infusion, aFGF-(1-15) (per rat 200 ng) had no effect on the feeding, while aFGF-(1-15) (per rat 400 ng) suppressed the food intake (3 h: 3.0 ± 0.2 vs 2.1 ± 0.2; 12 h: 18.5 ± 0.5 vs 16.1 ± 0.5, both P < 0.01). As for [Ala¹⁶] aFGF-(1-29), not only per rat 200 ng (3 h: 4.9 ± 0.2 vs 3.4 ± 0.2; 12 h: 19.3 ± 1.2 vs 17.3 ± 1.1, both P < 0.01) but also per rat 400 ng (3 h: 3.6 ± 0.1 vs 1.6 ± 0.2; 12 h: 19.9 ± 0.8 vs 16.4 ± 1.6, both P < 0.01) suppressed the food intake. Other five aFGF fragments had no effect on the feeding in the dose of per rat 200 ng and per rat 400 ng. For hypodermic injection, [Ala¹⁶] aFGF-(1-29) (300 mg/kg) suppressed the food intake (3 h: 3.9 ± 0.2 vs 2.1 ± 0.3; 12 h: 19.8 ± 0.5 vs 11.2 ± 0.8, both P < 0.01), while others had no effect.

CONCLUSION: These findings suggest the amino-terminal portion of aFGF is active in food intake suppression. The replacement of cysteine residue by alanine is important in some amino-terminal aFGF fragments. Other aFGF fragments, in which glycine at position 6 was replaced with D-tryptophane, phenylalanine at position 1 with desaminoPhe, and cysteine at position 16 with Lys (ε-myristyl) has no effect on nocturnal feeding in rats. Peripheral administration of one fragment is also effective on nocturnal feeding in rats.

Modulation of synaptic efficacy and synaptic depression by glial cells at the frog neuromuscular junction

The ability of perisynaptic glial cells to modulate transmitter release and synaptic depression was studied at the frog neuromuscular junction (nmj). Injection of GTPgammaS in perisynaptic Schwann cells (PSCs), glial cells at this synapse, induced a reduction in the amplitude of nerve-evoked synaptic responses but had no effect on the frequency, the amplitude, or the duration of the miniature endplate currents (MEPCs). Also, paired pulse facilitation was not affected. The reduction in transmitter release was mediated by pertussis toxin-(PTX) sensitive and insensitive G proteins. Blockade of G proteins in PSCs with GDPbetaS reduced synaptic depression induced by high frequency trains of stimuli, whereas activation of G proteins occluded it. Hence, the activation by endogenous neurotransmitters of G proteins in PSCs induced a profound depression in neurotransmitter release.

Enhancement of phagocytosis in mouse peritoneal macrophages by fragments of acidic fibroblast growth factor (aFGF)

To characterize the effects of acidic fibroblast growth factor (aFGF) in mouse peritoneal macrophages, the effects of aFGF fragments on phagocytosis were examined. Fragments that were tested included aFGF(1-15), aFGF(1-20), aFGF(1-29), Ala16-aFGF(1-29), aFGF(9-29) and aFGF(114-140). aFGF(1-29) induced an enhancement of phagocytosis in a dose-dependent manner and was more effective than any other fragments tested. Even in Ca2+-and Mg2+-free solutions, phagocytosis was enhanced by aFGF(1-29). However, the enhancement induced by aFGF(1-29) was completely inhibited in the presence of mannan (4 mg/ml). Furthermore, the enhancement of phagocytosis by aFGF(1-29) was suppressed by heparin (100 microg/ml). The results of the present study suggest that the active region of aFGF that is responsible for the enhancement of phagocytosis corresponds to residues 15-29 and that phagocytosis, which is modulated by aFGF, is independent of extracellular Ca2+ and is mediated by mannose receptors.

Chronic intraventricular infusion with NGF improves LTP in old cognitively-impaired rats

Aged (21 months) cognitively-impaired male Sprague-Dawley rats received intraventricular infusion of nerve growth factor (NGF) or cytochrome C (Cit C) for 14 or 28 days using miniosmotic pumps and were evaluated either 1 week or 3 months after treatment. Groups of untreated young, aged-impaired and aged non-impaired rats were also evaluated. Under narcose recording and stimulating electrodes were stereotactically implanted in the dentate gyrus and the perforant path. The stimulation intensity was individually adjusted to obtain a half-maximal population spike (P) for test stimuli and a quarter-maximal for tetanization. The amplitude and latency of P and the slope (S) of the field EPSP were determined before and at 2, 5, 15, 30 and 60 min after tetanization at 400 Hz. Paired stimuli at 30 ms interval were also applied before and after tetanization. Aged, cognitively impaired rats showed an absent S potentiation and a delayed P potentiation, both in amplitude and latency, while non-impaired rats behaved like the young controls. Paired pulse inhibition showed no difference among groups before or after tetanization suggesting that the impaired potentiation is not due to an increased retroactive inhibition. NGF treatment ameliorates LTP deficits to levels equivalent to non-impaired rats, while Cit C controls showed no improvement. No differences appear among NGF treated groups, but evidence suggest that the animals evaluated 3 months after treatment developed a stronger potentiation.

A 10-amino acid sequence of fibroblast growth factor 2 is sufficient for its mitogenic activity on neural progenitor cells

During development of the central nervous system, neurons and glia are generated from immature neural progenitor cells (NPCs). Basic fibroblast growth factor (FGF-2) is a mitogen for these cells both in vitro and in vivo. However, it is not known whether other members of the FGF family have similar mitogenic effects on NPCs. We have found that FGF-4, in addition to FGF-2, is a mitogen for NPCs isolated from fetal and adult central nervous systems. Other family members have no proliferative effects on these cells. FGFs transduce signals to the cytoplasm through a family of transmembrane tyrosine kinase receptors (FGFR-1-4) or their isoforms. The high-affinity receptor binding sites are found in two regions of the FGF-2 molecule. We have examined the involvement of these sites in mitogenic signaling. Synthetic peptides corresponding to sequences in FGF-2 receptor binding sites were examined in [3H]thymidine incorporation assays for their agonist or antagonist activity. A 10-aa sequence present in the first receptor binding domain has been found to act as an antagonist, blocking the mitogenic effects of FGF-2. Chemical crosslinking studies using 125I-labeled FGF-2 showed specific reduction in binding of radiolabeled FGF-2 to its receptors present on the membranes of NPCs. The identification of this sequence will assist in the study of pathways involved in signal transduction for mitogenesis in these cells and elucidate the role of FGF-2 and FGF-4 during normal development and in the pathogenesis of disease.

X-ray structure of native full-length human fibroblast-growth factor at 0.25-nm resolution

Acidic fibroblast-growth factor (aFGF) is one of the typical members of a group of nine polypeptides of relatively similar amino acid sequence known as the fibroblast-growth-factor family of proteins. Widely distributed throughout the organism, fibroblast-growth factors seem to be involved in numerous physiological processes ranging from control of cell proliferation and differentiation to modulation of animal behaviour and arterial blood pressure. This wide assortment of biological activities explains their involvement in numerous pathologies. Instability and low yields of the purified protein have precluded high-resolution structural studies of the physiological form of aFGF. Nevertheless, modifications introduced recently into the synthesis and purification procedures of this protein have allowed preparations of samples that, as shown here, are reliable substrates to obtain crystals suitable for X-ray-diffraction studies. These analyses have allowed us to elucidate the three-dimensional structure of the physiological form of human aFGF by molecular-replacement methods, from the previously reported structure of a shortened form of bovine aFGF that was stabilized by point-directed mutagenesis. The structure was refined at a resolution of 0.25 nm to an R factor of 20.4% for 13,109 reflections between 0.6 nm and 0.25 nm, with rmsd of 1.1 pm and 1.9 degrees from ideal bond lengths and bond angles, respectively. Human aFGF folds according to a beta-trefoil topology. This fold consist of six beta-strand pairs. Three of them form a six-stranded beta-barrel structure that is capped at one end by the other three pairs arranged in a triangular array. The N-terminus of aFGF up to residue Pro19 appears flexible in the structure and does not specifically interact with the rest of the molecule.