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Cell-based drug delivery systems (DDSs) have been increasingly exploited because cells can be utilized as a continuous drug delivering system to produce therapeutic molecules over a more extended period compared to the simple drug carriers. Although hydrogels have many advantages for this application, their mechanical properties are generally not desirable to structurally protect implanted cells. Here, we present a three-dimensional (3D) hybrid scaffold with a combination of a 3D framework and a hydrogel to enhance the mechanical properties without chemically altering the transport properties of the hydrogel. Based on the 3D Ormocomp scaffold (framework) fabricated by projection-based microstereolithography with defined parameters, we developed a 3D hybrid scaffold by injection of the mixture of cells and the alginate gel into the internal space of the framework. This hybrid scaffold showed the improved mechanical strength and the framework in the scaffold played the role of an adhesion site for the encapsulated cells during the culture period. Additionally, we confirmed its protection of exogenous human cells from acute immune rejection in a mouse model. Eventually, we demonstrated the feasibility of applying this hybrid scaffold to the treatment of Parkinson's disease as a cell-based DDS. Dopamine released from the 3D hybrid scaffolds encapsulating dopamine-secreting cells for 8weeks suggested its clinical applicability. Further study on its long-term efficacy is necessary for the clinical applicability of this 3D hybrid scaffold for the treatment of Parkinson's disease., (Copyright © 2013 Elsevier B.V. All rights reserved.)

There are two causes of Parkinson's disease (PD): environmental insults and genetic mutations of PD-associated genes. Environmental insults and genetic mutations lead to mitochondrial dysfunction, and a combination of mitochondrial dysfunction and increased oxidative stress in dopaminergic neurons is thought to contribute to the pathogenesis of PD. Among the PD-associated genes, DJ-1 acts as a redox sensor for oxidative stress and has been also proposed to maintain mitochondrial complex I activity. To understand molecular functions of DJ-1 in the cell, we have generated DJ-1 null cells from the DJ-1(-/-) mouse embryos. Using these null cells, we investigated the susceptibility to an environmental toxin, paraquat, which is known to inhibit mitochondrial complex I. Interestingly, we found that DJ-1 null cells showed a resistance to paraquat-induced apoptosis, including reduced poly (ADP-ribose) polymerase and procaspase-3. Also DJ-1 null cells generated less superoxide than SN4741 cells by paraquat treatment. Consistent with the reduced paraquat sensitivity, DJ-1 null cells showed reduced complex I activity, which was partially rescued by ectopic DJ-I expression. In summary, our results suggest that DJ-1 is critical to maintain mitochondrial complex I and complex I could be a key target in interaction of paraquat toxicity and DJ-1 for giving rise to PD., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Our previous microarray analysis identified a neuroprotective protein Oxi-alpha, that was down-regulated during oxidative stress (OS)-induced cell death in dopamine neurons [Neurochem. Res. (2004) vol. 29, pp. 1223]. Here we find that the phylogenetically conserved Oxi-alpha protects against OS by a novel mechanism: activation of the mammalian target of rapamycin (mTOR) kinase and subsequent repression of autophagic vacuole accumulation and cell death. To the best of our knowledge, Oxi-alpha is the first molecule discovered in dopamine neurons, which activates mTOR kinase. Indeed, the down-regulation of Oxi-alpha by OS suppresses the activation of mTOR kinase. The pathogenic effect of down-regulated Oxi-alpha was confirmed by gene-specific knockdown experiment, which resulted in not only the repression of mTOR kinase and the subsequent phosphorylation of p70 S6 kinase and 4E-BP1, but also enhanced susceptibility to OS. In accordance with these observations, treatment with rapamycin, an mTOR inhibitor and autophagy inducer, potentiated OS-induced cell death, while similar treatment with an autophagy inhibitor, 3-methyladenine protected the dopamine cells. Our findings present evidence for the presence of a novel class of molecule involved in autophagic cell death triggered by OS in dopamine neurons.

Septin 5, a parkin substrate, is a vesicle- and membrane-associated protein that plays a significant role in inhibiting exocytosis. The regulatory function of Septin 5 in dopaminergic (DAergic) neurons of substantia nigra (SN), maintained at relatively low levels, has not yet been delineated. As loss of function mutations of parkin are the principal cause of a familial Parkinson's disease, a prevailing hypothesis is that the loss of parkin activity results in accumulation of Septin 5 which confers neuron-specific toxicity in SN-DAergic neurons. In vitro and in vivo models were used to support this hypothesis. In our well-characterized DAergic SN4741 cell model, acute accumulation of elevated levels of Septin 5, but not synphilin-1 (another parkin substrate), resulted in cytotoxic cell death that was markedly reduced by parkin co-transfection. A transgenic mouse model expressing a dominant negative parkin mutant accumulated moderate levels of Septin 5 in SN-DAergic neurons. These mice acquired a progressive l-DOPA responsive motor dysfunction that developed despite a 25% higher than normal level of striatal dopamine (DA) and no apparent loss of DAergic neurons. The phenotype of this animal, increased striatal dopamine and reduced motor function, was similar to that observed in parkin knockout animals, suggesting a common DAergic alteration. These data suggest that a threshold level of Septin 5 accumulation is required for DAergic cell loss and that l-DOPA-responsive motor deficits can occur even in the presence of elevated DA.

We investigated the transcriptional events and signaling pathways involved in the induction of heme oxygenase-1 (HO-1) by dieldrin, an environmental risk factor of Parkinson's disease, in a dopaminergic neuronal cells (SN4741). Dieldrin exposure caused dose-dependent and time-dependent induction of heme oxygenase activity and HO-1 protein expression. Deletional and mutational analyses showed that the 5' distal enhancers, E1 and E2, mediate dieldrin-induced HO-1 gene transcription, and the AP-1 DNA binding sites in the E2 enhancer are critical for E2-mediated HO-1 gene activation. Furthermore, both the p38 and JNK mitogen-activated protein kinase pathways are utilized for HO-1 transcriptional activation by dieldrin. HO-1 inhibitor, ZnPP IX reduced the expression of HO-1 but enhanced the cytotoxicity induced by dieldrin.

Neuropathological evidence from both human and experimental models of Parkinson's disease (PD) firmly supports a significant role for oxidative stress (OS) in the death of dopaminergic (DA) neurons in substantia nigra. Largely unknown are the genes underlying selective susceptibility of nigral DA neuron to OS and how they effect nigral DA cell death. The major barriers to high-throughput identification of candidate genes are the paucity of nigral DA neurons as well as the dilution effect of non-DA cells both in primary cultures and brain tissues. To overcome these barriers, we have developed a DA cell line model, SN4741, appropriate for cDNA microarray analysis. Candidate genes were selected from both the microarray analysis and the molecular implication of their pathological mechanisms (i.e., decreased mitochondrial complex I activity and proteasomal dysfunction) of PD. Subsequent secondary validation tests were devised to characterize genes including clone #45 that may underlie selective vulnerability of nigral DA neuron to OS.

Oxidative stress (OS) is a primary pathogenic mechanism of nigral dopaminergic (DA) cell death in Parkinson's disease (PD). Oxidative damage, Lewy body formation and decreased mitochondrial complex I activity are the consistent pathological findings in PD. In nigral DA neurons, however, it is unknown whether any gene expressional changes induced by OS contribute to the typical PD pathology. Here, using microarray analysis, we identified several groups of genes in the nigral DA cell line, SN4741 [J. Neurosci. 19 (1999) 10; J. Neurochem. 76 (2001) 1010], that were regulated by OS. Approximately 36 significantly regulated genes that encode functional molecules of nuclear subunits of mitochondrial complex I, exocytosis and membrane trafficking proteins, markers for OS and oxidoreductases, regulatory molecules of apoptosis and unidentified EST clones were further analysed. OS modulated the expression of specific genes, of which physiological dysfunctions have been implicated in PD. For instance, the expression of the nuclear-encoded subunits of mitochondrial complex I, B8 and B17, were significantly down-regulated by OS, possibly contributing to selective defect in mitochondrial complex I activity in PD. Furthermore, syntaxin 8 and heme oxygenase-1 (HO-1) are most dramatically up-regulated by OS in DA cells. Syntaxin 8 is a SNARE protein, regulating lipid vesicle docking and fusion as well as early endosome membrane recycling. Lipid membranes are significantly oxidative-damaged in PD. HO-1 is an important cytoplasmic constituent of Lewy bodies, a pathological hallmark of idiopathic PD. Thus, our findings provide novel molecular probes that may be useful in unraveling the molecular mechanism(s) of OS-induced pathogenesis in PD. Further functional characterization of the affected genes including ESTs can help elucidate the underlying molecular pathology as well as develop biomarkers for monitoring degenerating DA neurons in PD.

Glial cell line-derived neurotrophic factor (GDNF) shows potent neuroprotective as well as neurorestorative actions on the adult neurons impacted in animal models of Parkinson's disease (PD). Long-term pharmaco-physiological effects of GDNF on developing dopaminergic (DA) neurons have not yet been explored because of technical difficulties in producing prolonged cell type-specific delivery of this neurotrophic factor in mammalian embryonic brain. The current studies used our previously characterized 9.0-kb tyrosine hydroxylase promoter to produce transgenic mice with neuronal cell type-specific expression of GDNF in substantia nigra pars compacta (SNc) and locus coeruleus (LC). These mice were used to test the parsimonious hypothesis that increased developmental expression of GDNF in SNc and LC would significantly enhance the number of postmitotic adult neurons. To our surprise, adult transgenic mice carrying the TH9.0kb-GDNF hybrid gene showed dramatic reductions in both the numbers and the volumes of SNc-DA and LC-noradrenergic (NA) neurons by quantitative morphometric analysis. The decrease in the number of DA neurons was apparent as early as postnatal day 2, the period before the major naturally occurring apoptotic cell death in midbrain. Aged transgenic mice exhibited no further significant deficits in motor behaviors. These data suggest that continuous, early developmental GDNF expression exerts physiological effects on newly differentiated, immature dopamine neurons that differ from those observed on more mature and adult DA neurons. Further elucidation of the mechanisms underlying differential GDNF actions will greatly improve the pharmacological efficacy of GDNF in fetal neural transplantation as well as adult neuronal gene therapy in PD patients., (©2002 Elsevier Science (USA).)

Our previous microarray analysis identified a neuroprotective protein Oxi-α, that was down-regulated during oxidative stress (OS)-induced cell death in dopamine neurons [Neurochem. Res. (2004) vol. 29, pp. 1223]. Here we find that the phylogenetically conserved Oxi-α protects against OS by a novel mechanism: activation of the mammalian target of rapamycin (mTOR) kinase and subsequent repression of autophagic vacuole accumulation and cell death. To the best of our knowledge, Oxi-α is the first molecule discovered in dopamine neurons, which activates mTOR kinase. Indeed, the down-regulation of Oxi-α by OS suppresses the activation of mTOR kinase. The pathogenic effect of down-regulated Oxi-α was confirmed by gene-specific knockdown experiment, which resulted in not only the repression of mTOR kinase and the subsequent phosphorylation of p70 S6 kinase and 4E-BP1, but also enhanced susceptibility to OS. In accordance with these observations, treatment with rapamycin, an mTOR inhibitor and autophagy inducer, potentiated OS-induced cell death, while similar treatment with an autophagy inhibitor, 3-methyladenine protected the dopamine cells. Our findings present evidence for the presence of a novel class of molecule involved in autophagic cell death triggered by OS in dopamine neurons. [ABSTRACT FROM AUTHOR]