Differential effects of hypoxia on untreated and NGF treated PC12 cells

Polybutylcyanoacrylate nanoparticles for delivering hormone response element-conjugated neurotrophin-3 to the brain of intracerebral hemorrhagic rats

Hypertensive intracerebral hemorrhage (ICH) is a rapidly evolutional pathology, inducing necrotic cell death followed by apoptosis, and alters gene expression levels in surrounding tissue of an injured brain. For ICH therapy by controlled gene release, the development of intravenously administrable delivery vectors to promote the penetration across the blood-brain barrier (BBB) is a critical challenge. To enhance transfer efficiency of genetic materials under hypoxic conditions, polybutylcyanoacrylate (PBCA) nanoparticles (NPs) were used to mediate the intracellular transport of plasmid neurotrophin-3 (NT-3) containing hormone response element (HRE) with a cytomegalovirus (cmv) promoter and to differentiate induced pluripotent stem cells (iPSCs). The differentiation ability of iPSCs to neurons was justified by various immunological stains for protein fluorescence. The effect of PBCA NP/cmvNT-3-HRE complexes on treating ICH rats was studied by immunostaining, western blotting and Nissl staining. We found that the treatments with PBCA NP/cmvNT-3-HRE complexes increased the capability of differentiating iPSCs to express NT-3, TrkC and MAP-2. Moreover, PBCA NPs could protect cmvNT-3-HRE against degradation with EcoRI/PstI and DNase I in vitro and raise the delivery across the BBB in vivo. The administration of PBCA NP/cmvNT-3-HRE complexes increased the expression of NT-3, inhibited the expression of apoptosis-inducing factor, cleaved caspase-3 and DNA fragmentation, and reduced the cell death rate after ICH in vivo. PBCA NPs are demonstrated as an appropriate delivery system for carrying cmvNT-3-HRE to the brain for ICH therapy.

The influence of oxygen supply on metabolism of neural cells cultured on a gas-permeable PTFE foil

The influence of oxygen on neural stem cell proliferation, differentiation, and apoptosis is of great interest for regenerative therapies in neurodegenerative disorders, such as Parkinson's disease. These oxygen depending mechanisms have to been considered for the optimization of neural cell culture conditions. In this study, we used a cell culture system with an oxygen-permeable polytetrafluorethylene (PTFE) foil to investigate the effect of oxygen on metabolism and survival of neural cell lines in vitro. Human glial astrocytoma-derived cells (GOS-3) and rat pheochromacytoma cells (PC12) were cultured on the gas-permeable PTFE foil as well as a conventional non oxygen-permeable cell culture substrate at various oxygen concentrations. Analyses of metabolic activity, gene expression of apoptotic grade, and dopamine synthesis were performed. Under low oxygen partial pressure (2%, 5%) the anaerobic metabolism and apoptotic rate of cultured cells is diminished on PTFE foil when compared with the conventional culture dishes. In contrast, under higher oxygen atmosphere (21%) the number of apoptotic cells on the PTFE foil was enhanced. This culture model demonstrates a suitable model for the improvement of oxygen dependent metabolism under low oxygen conditions as well as for induction of oxidative stress by high oxygen atmosphere without supplementation of neurotoxins.

Dynamic production of hypoxia-inducible factor-1alpha in early transplanted islets

More than half of transplanted beta-cells undergo apoptotic cell death triggered by nonimmunological factors within a few days after transplantation. To investigate the dynamic hypoxic responses in early transplanted islets, syngeneic islets were transplanted under the kidney capsule of balb/c mice. Hypoxia-inducible factor-1alpha (HIF-1alpha) was strongly expressed at post-transplant day (POD) 1, increased on POD 3, and gradually diminished on POD 14. Insulin secretion decreased on POD 3 in association with a significant increase of HIF-1alpha-related beta-cell death, which can be suppressed by short-term hyperbaric oxygen therapy. On POD 7, apoptosis was not further activated by continually produced HIF-1alpha. In contrast, improvement of nerve growth factor and duodenal homeobox factor-1 (PDx-1) production resulted in islet graft recovery and remodeling. In addition, significant activation of vascular endothelial growth factor in islet grafts on POD 7 correlated with development of massive newly formed microvessels, whose maturation is advanced on POD 14 with gradual diminution of HIF-1alpha. We conclude that (1) transplanted islets strongly express HIF-1alpha in association with beta-cell death and decreased insulin production until adequate revascularization is established and (2) early suppression of HIF-1alpha results in less beta-cell death thereby minimizing early graft failure.

Neuronal differentiation of PC12 cells abolishes the expression of membrane androgen receptors

Sex steroids affect adrenal chromaffin cell function. In the present work, we have examined the expression and functional significance of membrane androgen receptor sites in normal rat adrenal chromaffin cells and in the PC12 rat pheochromocytoma cell line which can differentiate to either a neuronal or to an epithelial phenotype and expresses membrane estrogen receptor sites. Our data are as follows: (a) no cytosolic androgen receptors were found in both normal chromaffin and PC12 cells; (b) both types of chromaffin cells expressed high affinity membrane testosterone binding sites; (c) activation of these sites increased cytosolic Ca(2+), decreased catecholamine secretion and induced apoptosis; (d) NGF-induced neuronal differentiation of PC12 cells resulted in the suppression of the number of membrane testosterone sites. In conclusion, our data provide evidence for the existence of specific membrane testosterone receptors on adrenal chromaffin cells via which androgens, (some of them originating in the cortex) modulate their function. Neuronal differentiation of chromaffin cells results in a significant attenuation of these effects, via suppression of the expression of membrane androgen receptors suggesting, that the latter are specific for epithelioid chromaffin cells.

Gene regulation by hypoxia and the neurodevelopmental origin of schizophrenia

Neurodevelopmental changes may underlie the brain dysfunction seen in schizophrenia. While advances have been made in our understanding of the genetics of schizophrenia, little is known about how non-genetic factors interact with genes for schizophrenia. The present analysis of genes potentially associated with schizophrenia is based on the observation that hypoxia prevails in the embryonic and fetal brain, and that interactions between neuronal genes, molecular regulators of hypoxia, such as hypoxia-inducible factor 1 (HIF-1), and intrinsic hypoxia occur in the developing brain and may create the conditions for complex changes in neurodevelopment. Consequently, we searched the literature for currently hypothesized candidate genes for susceptibility to schizophrenia that may be subject to ischemia-hypoxia regulation and/or associated with vascular expression. Genes were considered when at least two independent reports of a significant association with schizophrenia had appeared in the literature. The analysis showed that more than 50% of these genes, particularly AKT1, BDNF, CAPON, CCKAR, CHRNA7, CNR1, COMT, DNTBP1, GAD1, GRM3, IL10, MLC1, NOTCH4, NRG1, NR4A2/NURR1, PRODH, RELN, RGS4, RTN4/NOGO and TNF, are subject to regulation by hypoxia and/or are expressed in the vasculature. Future studies of genes proposed as candidates for susceptibility to schizophrenia should include their possible regulation by physiological or pathological hypoxia during development as well as their potential role in cerebral vascular function.

The transcriptional response to hypoxic insult controlled by FRA-2

FRA-2 is involved in cellular differentiation and is also upregulated in response to ischemic injury to the brain. To shed light on the function of this transcription factor, a novel microarray analysis was utilized to identify FRA-2-dependent gene expression increased in the hypoxic response. Genes were identified that were upregulated by exposure of neuronally differentiated PC12 cells to hypoxia. Using a dominant negative construct to block FRA-2, a second subset of genes that were FRA-2 dependent was found. Cross comparison then allowed isolation of a list of genes that were induced in response to hypoxia in a FRA-2-dependent manner. These data suggest that FRA-2 is involved in the transcriptional control of neuroprotective genes and in the switch from aerobic to anaerobic metabolism.

Down-regulation of hypoxia-inducible factor-2 in PC12 cells by nerve growth factor stimulation

Cellular responses to low oxygen tension are mediated, at least in part, by the activation of the hypoxia-inducible factors (HIFs). In the presence of oxygen, specific HIF residues become hydroxylated by the action of a recently described group of dioxygenases. These post-translational modifications target HIF for proteosomal degradation and prevent its transcriptional activity. Despite these detailed studies, little is known about the regulation of HIF by stimuli other than hypoxia. Here we report that, in rat pheochromocytoma PC12 cells, nerve growth factor (NGF) stimulation results in a decrease of both basal and hypoxia-induced levels of HIF-2 alpha protein. NGF treatment did not increase HIF-hydroxylase gene expression or activity, and the reduction of the HIF-2 alpha protein level upon stimulation was observed even in the presence of HIF-hydroxylase inhibitors such as deferoxamine or dimethyloxoglutarate. Thus, in contrast to the response to hypoxia, the effect of NGF on HIF-2 alpha protein levels is not mediated by the HIF hydroxilases. Quantitative real time (RT)-PCR showed that NGF stimulation results in a decrease of the HIF-2 alpha mRNA level similar to that found at the protein level. Interestingly, NGF effect was specific for HIF-2 alpha mRNA because it did not affect HIF-1 alpha mRNA levels. NGF treatment reduced HIF-2 alpha mRNA levels even in the presence of actinomycin D, suggesting an effect on mRNA stability. Finally, the effect of NGF on HIF2 alpha correlates with reduction of both basal and hypoxia-induced vascular endothelial growth factor mRNA levels. Reporter assays suggest that the reduced expression of hypoxia-inducible genes upon NGF treatment is related, at least in part, to the reduction of HIF-2 alpha protein. Hence, in PC12 cells the level of HIF-2 alpha protein and its effect on gene expression can be down-regulated by stimuli other than oxygen.