Platelet-derived growth factor receptor expression after neural grafting in a rat model of Parkinson's disease

Overexpression of α-Synuclein Reorganises Growth Factor Profile of Human Astrocytes

Misfolding and accumulation of aberrant α-synuclein in the brain is associated with the distinct class of neurodegenerative diseases known as α-synucleinopathies, which include Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Pathological changes in astrocytes contribute to all neurological disorders, and astrocytes are reported to possess α-synuclein inclusions in the context of α-synucleinopathies. Astrocytes are known to express and secrete numerous growth factors, which are fundamental for neuroprotection, synaptic connectivity and brain metabolism; changes in growth factor secretion may contribute to pathobiology of neurological disorders. Here we analysed the effect of α-synuclein overexpression in cultured human astrocytes on growth factor expression and release. For this purpose, the intracellular and secreted levels of 33 growth factors (GFs) and 8 growth factor receptors (GFRs) were analysed in cultured human astrocytes by chemiluminescence-based western/dot blot. Overexpression of human α-synuclein in cultured foetal human astrocytes significantly changes the profile of GF production and secretion. We found that human astrocytes express and secrete FGF2, FGF6, EGF, IGF1, AREG, IGFBP2, IGFBP4, VEGFD, PDGFs, KITLG, PGF, TGFB3 and NTF4. Overexpression of human α-synuclein significantly modified the profile of GF production and secretion, with particularly strong changes in EGF, PDGF, VEGF and their receptors as well as in IGF-related proteins. Bioinformatics analysis revealed possible interactions between α-synuclein and EGFR and GDNF, as well as with three GF receptors, EGFR, CSF1R and PDGFRB.

Effects of Surgical Anaesthesia on the Viability of Nigral Grafts in the Rat Striatum

Only a small proportion of dopamine neurons in nigral grafts typically survive transplantation into the adult striatum. Since many anaesthetics reduce blood flow and disturb a variety of brain metabolites, surgical anaesthesia may be one of the factors that compromise graft survival. Conversely, the lowered core body temperature induced by some anaesthetics might promote the survival of grafted cells by slowing their metabolism. In an initial screen, the widely-used surgical anaesthetic, equithesin, was found to reduce core temperature, mean arterial blood pressure, and to increase the partial pressure of oxygen in arterial blood without producing any significant alteration in arterial pH or the partial pressure of carbon dioxide. In the main experiment, rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle received dopamine-rich embryonic nigral grafts injected into the deafferented neostriatum via previously implanted guide cannulae, which allowed comparison to be made of graft survival after transplantation into awake and in re-anaesthetised animals. There were no significant differences between groups in either the functional effects of the grafts to compensate amphetamine-induced rotation, or in the survival and growth of the grafts as measured in post mortem histology. We therefore conclude that anaesthesia per se is not a major contributory factor in the relatively poor survival of dopamine neurons following transplantation into the rat striatum.

The roles of PDGF in development and during neurogenesis in the normal and diseased nervous system

The four platelet-derived growth factor (PDGF) ligands and PDGF receptors (PDGFRs), α and β (PDGFRA, PDGFRB), are essential proteins that are expressed during embryonic and mature nervous systems, i.e., in neural progenitors, neurons, astrocytes, oligodendrocytes, and vascular cells. PDGF exerts essential roles from the gastrulation period to adult neuronal maintenance by contributing to the regulation of development of preplacodal progenitors, placodal ectoderm, and neural crest cells to adult neural progenitors, in coordinating with other factors. In adulthood, PDGF plays critical roles for maintenance of many specific cell types in the nervous system together with vascular cells through controlling the blood brain barrier homeostasis. At injury or various stresses, PDGF modulates neuronal excitability through adjusting various ion channels, and affecting synaptic plasticity and function. Furthermore, PDGF stimulates survival signals, majorly PI3-K/Akt pathway but also other ways, rescuing cells from apoptosis. Studies imply an involvement of PDGF in dendrite spine morphology, being critical for memory in the developing brain. Recent studies suggest association of PDGF genes with neuropsychiatric disorders. In this review, we will describe the roles of PDGF in the nervous system, from the discovery to recent findings, in order to understand the broad spectrum of PDGF in the nervous system. Recent development of pharmacological and replacement therapies targeting the PDGF system is discussed.

Reactive oxygen species regulate the levels of dual oxidase (Duox1-2) in human neuroblastoma cells

Dual Oxidases (DUOX) 1 and 2 are efficiently expressed in thyroid, gut, lung and immune system. The function and the regulation of these enzymes in mammals are still largely unknown. We report here that DUOX 1 and 2 are expressed in human neuroblastoma SK-N-BE cells as well as in a human oligodendrocyte cell line (MO3-13) and in rat brain and they are induced by platelet derived growth factor (PDGF). The levels of DUOX 1 and 2 proteins and mRNAs are induced by reactive oxygen species (ROS) produced by the membrane NADPH oxidase. As to the mechanism, we find that PDGF stimulates membrane NADPH oxidase to produce ROS, which stabilize DUOX1 and 2 mRNAs and increases the levels of the proteins. Silencing of gp91^phox (NOX2), or of the other membrane subunit of NADPH oxidase, p22^phox, blocks PDGF induction of DUOX1 and 2. These data unravel a novel mechanism of regulation of DUOX enzymes by ROS and identify a circuitry linking NADPH oxidase activity to DUOX1 and 2 levels in neuroblastoma cells.

Neuroprotective effects of PDGF against oxidative stress and the signaling pathway involved

The neuroprotective effects of platelet-derived growth factor (PDGF) and the major signaling pathways involved in these were examined using primary cultured mouse cortical neurons subjected to H(2)O(2)-induced oxidative stress. The specific function of the PDGF beta-receptor (PDGFR-beta) was examined by the selective deletion of the corresponding gene using the Cre-loxP system in vitro. In wild-type neurons, PDGF-BB enhanced the survival of these neurons and suppressed H(2)O(2)-induced caspase-3 activation. The prosurvival effect of PDGF-AA was less than that of PDGF-BB. PDGF-BB highly activated Akt, extracellular signal-regulated kinase (ERK), c-jun amino-terminal kinase (JNK) and p38. PDGF-AA activated these molecules at lesser extent than PDGF-BB. In particular, PDGF-AA induced activation of Akt was at very low level. The neuroprotective effects of PDGF-BB were antagonized by inhibitors of phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase kinase (MEK), JNK and p38. The PDGFR-beta-depleted neurons showed increased vulnerability to oxidative stress, and less responsiveness to PDGF-BB-induced cytoprotection and signal activation, in which Akt activation was most strongly suppressed. After all, these results demonstrated the neuroprotective effects of PDGF and the signaling pathways involved against oxidative stress. The effects of PDGF-BB were more potent than those of PDGF-AA. This might be due to the activation and additive effects of two PDGFRs after PDGF-BB stimulation. Furthermore, the PI3-K/Akt pathway that was deduced to be preferentially activated by PDGFR-beta may explain the potent effects of PDGF-BB.

Partial purification of a pramipexole-induced trophic activity directed at dopamine neurons in ventral mesencephalic cultures

We previously demonstrated that media conditioned by exposure to ventral mesencephalic (VM) cultures in the presence of pramipexole (PPX) and other drugs with dopamine (DA) D3 properties, increased the growth and survival of DA neurons in recipient VM cultures. This trophic activity was heat-labile and not present in parietal cortex cultures or cultures pretreated with the DA neuron toxin MPP+. In an effort to begin to identify the protein(s) responsible for this trophic effect, we compared the conditioned media from normal VM cultures, VM cultures incubated with PPX, and VM cultures pretreated with MPP+ and treated with PPX. Neutralization studies using anti-GDNF and anti-BDNF failed to reduce the conditioned media transfer effect, and Millipore Ultrafree centrifugation studies placed the mol.wt. of the activity around 30 kDa. SDS separation revealed three potential bands of interest. A 35-kDa band was present in normal cultures, increased in PPX-incubated cultures, and absent in MPP+-pretreated/PPX-incubated cultures. This conforms to the effect the protein concentrates used to produce these gels had on the growth of DA neurons in VM cultures. Since VM cultures grown in neural basal media, which inhibits the growth of glia, still responded to PPX in a dose-dependent fashion, the trophic activity may be a DA autotrophic factor. However, the gels also revealed two bands at approximately 31 and 55 kDa that were reduced by exposure to PPX and present in MPP+-pretreated cultures. The possibility that these are neuroinhibitory factors that are also regulated by PPX therefore cannot be ruled out.

Enhanced synthesis of platelet-derived growth factor following injury induced by 6-hydroxydopamine in rat brain

The kinetics of platelet-derived growth factor messenger RNA synthesis in the substantia nigra and in the striatum, before and after unilateral intranigral 6-hydroxydopamine injection, was studied and compared with that after sham operation by a quantitative reverse transcription-polymerase chain reaction. The kinetics of brain-derived neurotrophic factor messenger RNA was studied as a comparison. Furthermore, the expression of platelet-derived growth factor A- and B-chain proteins was analysed by enzyme-linked immunosorbent assay and immunohistochemistry. In the ipsilateral striatum of 6-hydroxydopamine-lesioned rats, the signal density of messenger RNA for both A- and B-chains had already increased at one day and remained at an elevated level during the observation period of four weeks. In the substantia nigra ipsilateral to the lesion, a strongly increased level of B-chain and, to a lesser extent, of A-chain messenger RNA was already detected at 4h, reaching a maximal level at one day. No significant increase was seen either in sham-operated rats or in the contralateral striatum and substantia nigra. Amounts of platelet-derived growth factor proteins were examined separately by enzyme-linked immunosorbent assay in both sides of the substantia nigra, striatum and cortex. Three days after 6-hydroxydopamine lesions the levels of both platelet-derived growth factor A- and B-chains increased in the ipsilateral striatum, substantia nigra, and cortex. An increase in the A-chain was also observed in the contralateral side of the brain. The signal for brain-derived neurotrophic factor messenger RNA increased in the striatum in the lesioned side and, to a lesser extent, in the contralateral side, as well as in the substantia nigra, where a significant difference was observed when compared with the contralateral side. Semiquantitative immunohistochemical analysis on the substantia nigra confirmed the enhanced platelet-derived growth factor expression, revealing that the majority of the platelet-derived growth factor-producing cells were neurons. In summary, we have shown that platelet-derived growth factor messenger RNA as well as its protein are induced after injury to dopaminergic cells. These data indicate an important role of platelet-derived growth factor in the dopaminergic system.