Role of dopamine in the pathophysiology of Parkinson's disease

A pathological feature of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons and decreased dopamine (DA) content in the substantia nigra pars compacta in PD brains. DA is the neurotransmitter of dopaminergic neurons. Accumulating evidence suggests that DA interacts with environmental and genetic factors to contribute to PD pathophysiology. Disturbances of DA synthesis, storage, transportation and metabolism have been shown to promote neurodegeneration of dopaminergic neurons in various PD models. DA is unstable and can undergo oxidation and metabolism to produce multiple reactive and toxic by-products, including reactive oxygen species, DA quinones, and 3,4-dihydroxyphenylacetaldehyde. Here we summarize and highlight recent discoveries on DA-linked pathophysiologic pathways, and discuss the potential protective and therapeutic strategies to mitigate the complications associated with DA.

F-box protein 7 mutations promote protein aggregation in mitochondria and inhibit mitophagy

The mutations of F-box protein 7 (FBXO7) gene (T22M, R378G and R498X) are associated with a severe form of autosomal recessive juvenile-onset Parkinson's disease (PD) (PARK 15). Here we demonstrated that wild-type (WT) FBXO7 is a stress response protein and it can play both cytoprotective and neurotoxic roles. The WT FBXO7 protein is vital to cell mitophagy and can facilitate mitophagy to protect cells, whereas mutant FBXO7 inhibits mitophagy. Upon stress, the endogenous WT FBXO7 gets up-regulated, concentrates into mitochondria and forms FBXO7 aggregates in mitochondria. However, FBXO7 mutations aggravate deleterious FBXO7 aggregation in mitochondria. The FBXO7 aggregation and toxicity can be alleviated by Proline, glutathione (GSH) and coenzyme Q10, whereas deleterious FBXO7 aggregation in mitochondria can be aggravated by prohibitin 1 (PHB1), a mitochondrial protease inhibitor. The overexpression of WT FBXO7 could lead to FBXO7 protein aggregation and dopamine neuron degeneration in transgenic Drosophila heads. The elevated FBXO7 expression and aggregation were identified in human fibroblast cells from PD patients. FBXO7 can also form aggregates in brains of PD and Alzheimer's disease. Our study provides novel pathophysiologic insights and suggests that FBXO7 may be a potential therapeutic target in FBXO7-linked neuron degeneration in PD.

Cytoplasmic nucleophosmin has elevated T199 phosphorylation upon which G2/M phase progression is dependent

The cytoplasmic mutant of nucleophosmin (NPMc) is found approximately in one-third of acute myeloid leukemia (AML) cases and is highly associated with normal karyotype. Whereas previous studies have focused on wtNPM in centrosome duplication, we further elucidate the role of NPM in the cell cycle by utilizing the increased cytoplasmic load of NPMc. Overexpression of NPMc causes increased phosphorylation of NPM on T199 and, to a lesser degree, S4. T199 phosphorylation is dependent on cdk2 but activators of cdk2 were not elevated. Upon inhibition of cdk2, NPMc-overexpressing cells demonstrate a greater G2/M phase arrest than wtNPM or GFP counterparts. However, the number of cells with 2 centrosomes did not increase concordantly. This suggests that the arrest was caused by a delay in centrosome duplication, most likely due to the inhibition of centrosome duplication caused by unphosphorylated NPMc. Overall, these results suggest that the phosphorylation of T199 is important in the mitotic progression of NPMc-expressing cells. This further supports the hypothesis that NPMc is associated with normal karyotypes in AML because the higher cytoplasmic load of NPM can better suppress centrosome overduplication which would otherwise result in unequal segregation of chromosomes during mitosis, leading to aneuploidy and other genomic instabilities.

Inactivation of dinoflagellate Scripsiella trochoidea in synthetic ballast water by advanced oxidation processes

Ship-borne ballast water contributes significantly to the transfer of non-indigenous species across aquatic environments. To reduce the risk of bio-invasion, ballast water should be treated before discharge. In this study, the efficiencies of several conventional and advanced oxidation processes were investigated for potential ballast water treatment, using a marine dinoflagellate species, Scripsiella trochoidea, as the indicator organism. A stable and consistent culture was obtained and treated by ultraviolet (UV) light, ozone (O3), hydrogen peroxide (H2O2), and their various combinations. UV apparently inactivated the cells after only 10 s of irradiation, but subsequently photo-reactivation of the cells was observed for all methods involving UV. O3 exhibited 100% inactivation efficiency after 5 min treatment, while H2O2 only achieved maximum 80% inactivation in the same duration. Combined methods, e.g. UV/O3 and UV/H2O2, were found to inhibit photo-reactivation and improve treatment efficiency to some degree, indicating the effectiveness of using combined treatment processes. The total residual oxidant (TRO) levels of the methods were determined, and the results indicated that UV and O3 generated the lowest and highest TRO, respectively. The synergic effect of combined processes on TRO generation was found to be insignificant, and thus UV/O3 was recommended as a potentially suitable treatment process for ballast water.

High Mdm4 levels suppress p53 activity and enhance its half-life in acute myeloid leukaemia

Although p53 is found mutated in almost 50% of all cancers, p53 mutations in leukaemia are relatively rare. Acute myeloid leukaemia (AML) cells employ other strategies to inactivate their wild type p53 (WTp53), like the overexpression of the p53 negative regulators Mdm2 and Mdm4. As such, AMLs are excellent candidates for therapeutics involving the reactivation of their WTp53 to restrict and destroy cancer cells, and the Mdm2 antagonist nutlin-3 is one such promising agent. Using AML cell lines with WTp53, we identified stable and high levels of p53 in the OCI/AML-2 cell lines. We demonstrate that this nutlin-3 sensitive cell line overexpressed Mdm4 to sequester, stabilise and inhibit p53 in the cytoplasm. We also show that elevated Mdm4 competed with Mdm2-p53 interaction and therefore extended p53 half-life while preventing p53 transcriptional activity. Our results provide biochemical evidence on the dynamics of the p53-Mdm2-Mdm4 interactions in affecting p53 levels and activity, and unlike previously reported findings derived from genetically manipulated systems, AML cells with naturally high levels of Mdm4 remain sensitive to nutlin treatment.

Mutant PINK1 upregulates tyrosine hydroxylase and dopamine levels, leading to vulnerability of dopaminergic neurons

PINK1 mutations cause autosomal recessive forms of Parkinson disease (PD). Previous studies suggest that the neuroprotective function of wild-type (WT) PINK1 is related to mitochondrial homeostasis. PINK1 can also localize to the cytosol; however, the cytosolic function of PINK1 has not been fully elucidated. In this study we demonstrate that the extramitochondrial PINK1 can regulate tyrosine hydroxylase (TH) expression and dopamine (DA) content in dopaminergic neurons in a PINK1 kinase activity-dependent manner. We demonstrate that overexpression of full-length (FL) WT PINK1 can downregulate TH expression and DA content in dopaminergic neurons. In contrast, overexpression of PD-linked G309D, A339T, and E231G PINK1 mutations upregulates TH and DA levels in dopaminergic neurons and increases their vulnerability to oxidative stress. Furthermore transfection of FL WT PINK1 or PINK1 fragments with the PINK1 kinase domain can inhibit TH expression, whereas kinase-dead (KD) FL PINK1 or KD PINK1 fragments upregulate TH level. Our findings highlight a potential novel function of extramitochondrial PINK1 in dopaminergic neurons. Deregulation of these functions of PINK1 may contribute to PINK1 mutation-induced dopaminergic neuron degeneration. However, deleterious effects caused by PINK1 mutations may be alleviated by iron-chelating agents and antioxidant agents with DA quinone-conjugating capacity.

Wild-type and mutant p53 mediate cisplatin resistance through interaction and inhibition of active caspase-9

The p53 gene has been implicated in many cancers due to its frequent mutations as well as mutations in other genes whose proteins directly affect p53's functions. In addition, high expression of p53 [wild-type (WT) or mutant] has been found in the cytoplasm of many tumor cells, and studies have associated these observations with more aggressive tumors and poor prognosis. Cytoplasmic mis-localization of p53 subsequently reduced its transcriptional activity and this loss-of-function (LOF) was used to explain the lack of response to chemotherapeutic agents. However, this hypothesis seemed inadequate in explaining the apparent selection for tumor cells with high levels of p53 protein, a phenomenon that suggests a gain-of-function (GOF) of these mis-localized p53 proteins. In this study, we explored whether the direct involvement of p53 in the apoptotic response is via regulation of the caspase pathway in the cytoplasm. We demonstrate that p53, when present at high levels in the cytoplasm, has an inhibitory effect on caspase-9. Concurrently, knockdown of endogenous p53 caused an increase in the activity of caspase-9. p53 was found to interact with the p35 fragment of caspase-9, and this interaction inhibits the caspase-9 activity. In a p53-null background, the high-level expression of both exogenous WT and mutant p53 increased the resistance of these cells to cisplatin, and the data showed a correlation between high p53 expression and caspase-9 inhibition. These results suggest the inhibition of caspase-9 as a potential mechanism in evading apoptosis in tumors with high-level p53 expression that is cytoplasmically localized.

Iron species-mediated dopamine oxidation, proteasome inhibition, and dopaminergic cell demise: implications for iron-related dopaminergic neuron degeneration

Iron species have been suggested to be highly involved in the pathogenesis of Parkinson disease. However, the detailed mechanism of iron-induced dopaminergic degeneration is still unclear. In this study, we demonstrate that free iron ions (trivalent or bivalent) and iron ions in stable complex with cyanide ions (K(4)Fe(CN)(6) and K(3)Fe(CN)(6)) can induce dopamine (DA) oxidation with different profiles and subsequently lead to proteasome inhibition and even dopaminergic MN9D cell demise via different mechanisms. The free iron ions could mediate extensive DA oxidation in an iron-DA complex-dependent manner. However, iron ions in stable complex with cyanide ions could not induce, or could induce only brief, DA oxidation. Deferoxamine, a specific iron ion chelator, could disrupt iron-DA complex formation and thus abrogate free iron ion-catalyzed DA oxidation and subsequent cell toxicity. Glutathione could neither disrupt iron-DA complex formation nor influence free iron ion-catalyzed DA oxidation but could protect against iron-mediated toxicity via detoxification of toxic by-products of iron-mediated DA oxidation. The resulting DA oxidation could inhibit chymotrypsin-like, trypsin-like, and caspase-like proteasome activities. However, we demonstrated that oxidative damage was not the major toxic mechanism of MN9D cell degeneration, but it was the DA quinones derived from iron-induced DA oxidation that contributed significantly to proteasome inhibition and even dopaminergic cell demise.

Antiglioma effects of combined use of a baculovirual vector expressing wild-type p53 and sodium butyrate

BACKGROUND

Combination therapy is usually desirable for successful cancer treatment, especially in cancers that are resistant to single forms of therapy.

METHODS

To achieve an optimal therapeutic effect against glioblastoma, we tested a strategy that combines baculovirus-mediated transfer of the p53 tumor suppressor gene with the use of sodium butyrate, a histone deacetylase inhibitor. This strategy was designed based on the findings that the transduction efficiency of baculovirus in mammalian cells can be markedly enhanced by the addition of histone deacetylase inhibitors and that these inhibitors are effective in inducing cell cycle arrest, differentiation, or apoptosis in tumor cells.

RESULTS

We observed a synergistic effect of the combination of the two treatments in provoking apoptosis in glioblastoma cells with mutant p53. In a mouse glioma xenograft model, the tumor inhibitory effect of baculovirus-expressed p53 was significantly enhanced by co-administration of sodium butyrate.

CONCLUSIONS

These findings suggest a new approach to treat glioblastoma using baculovirus-mediated gene transfer in combination with administration of histone deacetylase inhibitor.

The Drosophila female germline stem cell lineage acts to spatially restrict DPP function within the niche

Maintenance of stem cells requires spatially restricted, niche-associated signals. In the Drosophila female germline stem cell (GSC) niche, Decapentaplegic (DPP) is the primary niche-associated factor and functions over a short range to promote GSC self-renewal rather than differentiation. Here, we show that the GSC lineage and, more specifically, the stem cells themselves participate in the spatial restriction of DPP function by activating epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) signaling in the surrounding somatic cells. EGFR-MAPK signaling in somatic cells repressed the expression of dally, which encodes a glypican required for DPP movement and stability. Consequently, only GSCs close to the DPP source (the somatic cells in the niche) showed high signal activation and were maintained as stem cells, whereas cystoblasts outside the niche showed low signal activation and initiated differentiation. Thus, our data reveal that the reciprocal crosstalk between the GSCs and the somatic cells defines the spatial limits of DPP action and therefore the extent of the GSC niche.

Dopamine (DA) induced irreversible proteasome inhibition via DA derived quinones

This study demonstrated that DA and its oxidative metabolites: H2O2 and aminochrome (AM), cyclized DA quinones, could all directly inhibit proteasome activity. DA and AM, especially AM, could induce intensive and irreversible proteasome inhibition, whereas proteasome inhibition induced by H2O2 was weaker and GSH reversible. It was concluded that DA induced irreversible proteasome inhibition via DA-derived quinones, rather than through small molecular weight ROS. The AM was also more toxic than H2O2 to dopaminergic MN9D cells. Furthermore the cytotoxicity and proteasome inhibition induced by DA, AM and H2O2 could be abrogated by GSH, ascorbic acid (AA), Vitamin E, SOD (superoxidase dismutase) or CAT (catalase) with different profiles. Only GSH was potent to abrogate DA, AM or H2O2-induced cell toxicity and proteasome inhibition, as well as to reverse H2O2-induced proteosome inhibition. Therefore, therapeutic strategies to increase GSH level or to use GSH substitutes should function to control PD onset and development.

Dopamine auto-oxidation aggravates non-apoptotic cell death induced by over-expression of human A53T mutant alpha-synuclein in dopaminergic PC12 cells

In this study, we demonstrated that transient transfection and over-expression of human mutant A53T alpha-synuclein (alpha-syn) could induce expression level- and time-dependent, non-apoptotic cell death in PC12 cells, while wild-type and mutant A30P alpha-syn could not. The non-apoptotic cell death induced by over-expression of A53T alpha-syn in PC12 cells was found to be dopamine (DA) related. It could be alleviated by nerve growth factor but not by chemicals that abrogate endoplasmic reticulum stress. Furthermore, PC12 cell death could be alleviated by N-acetyl-cysteine (NAC) as well as by L-cysteine; but not by cell permeable tyrosinase inhibitors. NAC could prevent DA auto-oxidation and tyrosinase-catalyzed DA oxidation, whereas L-cysteine could potently abrogate DA auto-oxidation but could not prevent tyrosinase-catalyzed DA oxidation. Both NAC and L-cysteine could increase the reduced and total GSH levels, and concurrently decrease the oxidized GSH level in PC12 cells. On the other hand, over-expression of human mutant A53T alpha-syn could decrease the reduced and total GSH levels, and increase the oxidized GSH level in the cells. Taken together, we concluded that auto-oxidation of endogenous DA aggravates non-apoptotic cell death induced by over-expression of human mutant A53T alpha-syn in PC12 cells.

Silicon-based microfilters for whole blood cell separation

This paper reports on the comparison analysis of four main types of silicon-based microfilter for isolation of white blood cells (WBCs) from red blood cells (RBCs) in a given whole blood. The microfilter designs, namely, weir, pillar, crossflow, and membrane, all impose the same cut-off size of 3.5 mum to selectively trap WBCs. Using human whole blood, the microfilters have been characterized and compared for their blood handling capacity, WBCs trapping efficiency and RBCs passing efficiency. Based on the experimental results, the crossflow microfilter is superior and can be integrated with downstream components for on-chip genomic analysis.

Nucleophosmin interacts with HEXIM1 and regulates RNA polymerase II transcription

Hexamethylene bis-acetamide-inducible protein 1 (HEXIM1) was identified earlier as an inhibitor of positive transcription elongation factor b (P-TEFb), which is a key transcriptional regulator of RNA polymerase II (Pol II). Studies show that more than half of P-TEFb in cells is associated with HEXIM1, which results in the inactivation of P-TEFb. Here, we identify a nucleolar protein, nucleophosmin (NPM), as a HEXIM1-binding protein. NPM binds to HEXIM1 in vitro and in vivo, and functions as a negative regulator of HEXIM1. Over-expression of NPM leads to proteasome-mediated degradation of HEXIM1, resulting in activation of P-TEFb-dependent transcription. In contrast, an increase in HEXIM1 protein levels and a decrease in transcription are detected when NPM is knocked down. We show that a cytoplasmic mutant of NPM, NPMc+, associates with and sequesters HEXIM1 in the cytoplasm resulting in higher RNA Pol II transcription. Correspondingly, cytoplasmic localization of endogenous HEXIM1 is detected in an acute myeloid leukemia (AML) cell line containing the NPMc+ mutation, suggesting the physiological importance of HEXIM1-NPMc+ interaction. Over-expression of NPM has been detected in tumors of various histological origins and our results may provide a possible molecular mechanism for the proto-oncogenic function of NPM. Furthermore, considering that 35% of AML patients are diagnosed with NPMc+ mutation, our findings suggest that in some cases of AML, RNA Pol II transcription may be disregulated by the malfunction of NPM and the mislocation of HEXIM1.

Neuronal PAS domain protein 1 regulates tyrosine hydroxylase level in dopaminergic neurons

Catecholamines (dopamine, norepinephrine, and epinephrine) are all synthesized from a common pathway in which tyrosine hydroxylase (TH) is the rate-limiting enzyme. Dopamine is the main neurotransmitter present in dopaminergic neurons of the ventral midbrain, where dysfunction of these neurons can lead to Parkinson's disease and schizophrenia. Neuronal PAS domain protein 1 (NPAS1) was identified as one of the genes up-regulated during dopaminergic MN9D cell differentiation. We found that there was a corresponding decrease in TH level during MN9D differentiation. Overexpression and siRNA experiments revealed that NPAS1, in concert with ARNT, negatively regulates the expression of TH and that this regulation is mediated by a direct binding of NPAS1 on the TH promoter. Expression studies also confirmed a decrease in TH level in the ventral midbrain during mouse development, concomitant with an increase in NPAS1 level. These results suggest that NPAS1 plays a novel and important role in regulating TH level of dopaminergic neurons in the ventral midbrain during development.

Neuronal PAS domain protein 1 is a transcriptional repressor and requires arylhydrocarbon nuclear translocator for its nuclear localization

Neuronal PAS domain protein 1 (NPAS1), a basic helix-loop-helix-PAS transcription factor expressed in the central nervous system, has been suggested to be involved in neuronal differentiation. However, relatively little is known about the molecular mechanism underlying the role of NPAS1 during development. In this study we set out to characterize the different domains within NPAS1. We showed that the nuclear localization of NPAS1 is dependent on the presence of ARNT. In addition, the transcriptional potential of ARNT is not required for this localization. In the absence of ARNT, NPAS1 is excluded from the nucleus, and this exclusion is due to the presence of a nuclear export signal within the N terminus of NPAS1. The interaction between NPAS1 and ARNT is via their N termini. We found no transactivation domain within NPAS1; instead, we mapped out at least three repression domains within NPAS1, suggesting that NPAS1 acts as a repressor. Furthermore, our experiments showed that NPAS1 is able to repress the transactivation functions of ARNT and ARNT2. We suggest that NPAS1 is guided into the nucleus by ARNT via the ARNT nuclear localization signal, and NPAS1 can override the activation function of adjacent transcription factors, providing a mechanism by which NPAS1 may inhibit transcription.

Tissue engineering of a periodontal ligament-alveolar bone graft construct

PURPOSE

This paper reports on a 2-phase study of a novel membrane-scaffold graft construct, its ability to support periodontal ligament fibroblast (PDLF) and alveolar osteoblast (AO) growth in vitro, and its use for tissue engineering a PDL-AO interface in vivo.

MATERIALS AND METHODS

Human PDLFs were seeded onto perforated poly(epsilon-caprolactone) membranes (n=30) at 78,000 cells/cm2; human AOs were seeded on poly(epsilon-caprolactone) scaffolds (n=30) with fibrin glue at 625,000 cells/cm3. Cell attachment, morphology, viability, and metabolic activity were monitored for 3 weeks in vitro. Subsequently, cell-seeded membrane-scaffold constructs (experimental group, n=9) and nonseeded constructs (control group, n=4) assembled with fibrin glue were implanted subcutaneously into 7 athymic mice for 4 weeks.

RESULTS

PDLFs formed confluent layers on membranes, whereas AOs produced mineralized matrices within scaffolds upon osteoinduction in vitro. Well-vascularized tissue formation was observed after implantation. Integration at the membrane-scaffold interface was enhanced in the experimental group. Type I collagen, type III collagen, fibronectin, and vitronectin were found adjacent to membranes and within constructs. Bone sialoprotein expression and bone formation were undetectable.

DISCUSSION

Membrane perforation and scaffold porosity facilitated tissue integration and vascularization at the construct-recipient site. However, the interaction between PDLF and AO could have interfered with osteogenesis at the interface of soft and mineralizing tissues.

CONCLUSIONS

Both matrices supported PDLF and AO attachment and proliferation in vitro. The membrane-scaffold construct facilitated tissue growth and vascularization while providing strength and form in vivo.

Does seeding density affectin vitro mineral nodules formation in novel composite scaffolds?

This study investigated the human alveolar osteoblasts (AOs) proliferation and extracellular matrix formation at seeding density of 0.05, 0.1, 0.2, 0.4, and 0.8 million (M) per 3x4x4 mm3 on medical grade polycaprolactone-tricalcium phosphate (mPCL-TCP) scaffolds designed for bone regeneration. Over 80-90% of the initial seeded cells were retained in the scaffolds after 24 h. AOs bridged over pores at density of 0.2M/scaffold and below, but formed cell balls at density of 0.4M/scaffold and above. At seeding density of 0.2M and below, cell proliferation increased with time having DNA content peaked to 1600 ng/scaffold at day 21 and 28, respectively, whereas at 0.4 and 0.8M, the corresponding DNA content decreased to 1600 ng in 28 days. At day 7, higher alkaline phosphatase (ALP) activity and higher osteocalcin (OCN) secretion were detected at 0.2M/scaffold and below. After 28 days, multilayered cell-sheet formation and collagen fibers were observed at all densities. ALP and OCN in matrix and mineral nodules were found mainly at the border of AOs-scaffold construct. These findings demonstrated that the density of 0.2M and below per 3 x 4 x 4 mm(3) scaffold resulted in better cell proliferation and extracellular matrix synthesis, potentially resulting in better mineralized tissue formation.

Dopamine-related and caspase-independent apoptosis in dopaminergic neurons induced by overexpression of human wild type or mutant α-synuclein

Human wild type (WT) and mutant alpha-synuclein (alpha-syn) genes were overexpressed using a Tet-on expression system in stably transfected dopaminergic MN9D cells. Their overexpression induced caspase-independent and dopamine-related apoptosis not rescued by general caspase inhibitor Z-VAD-FMK. While apoptosis due to overexpression of WT alpha-syn was completely abrogated by a specific tyrosine hydroxylase (TH) inhibitor, alpha-methyl-p-tyrosine (alpha-MT), the inhibitor only partially rescued apoptosis caused by overexpression of alpha-syn mutants. In addition, overexpression of mutants enhanced the toxicity of 1-methyl-4-phenylpyridinium (MPP+) and 6-hydroxyldopamine (6-OHDA) to MN9D cells, whereas overexpression of WT protected MN9D cells against MPP+ toxicity, but not against 6-OHDA. We conclude that WT alpha-syn is beneficial to dopaminergic neurons but its overexpression in the presence of endogenous dopamine makes it a potential threat to the cells. In contrast, mutant alpha-syn not only caused the loss of WT protective function but also the gain-of-toxicity which becomes more serious in the presence of dopamine and neurotoxins.

Low molecular weight polyethylenimines linked by β-cyclodextrin for gene transfer into the nervous system

BACKGROUND

Polyethylenimines (PEIs) with high molecular weights are effective nonviral gene delivery vectors. However, the in vivo use of these PEIs can be hampered by their cellular toxicity. In the present study we developed and tested a new PEI polymer synthesized by linking less toxic, low molecular weight (MW) PEIs with a commonly used, biocompatible drug carrier, beta-cyclodextrin (CyD).

METHODS AND RESULTS

The terminal CyD hydroxyl groups were activated by 1,1'-carbonyldiimidazole. Each activated CyD then linked two branched PEI molecules with MW of 600 Da to form a CyD-containing polymer with MW of 61 kDa, in which CyD served as a part of the backbone. The PEI-CyD polymer developed was soluble in water and biodegradable. In cell viability assays with sensitive neurons, the polymer performed similarly to low-MW PEIs and displayed much lower cellular cytotoxicity compared to PEI 25 kDa. The gene delivery efficiency of the polymer was comparable to, and at higher polymer/DNA ratios even higher than, that offered by PEI 25 kDa in neural cells. Attractively, intrathecal injection of plasmid DNA complexed by the polymer into the rat spinal cord provided levels of gene expression close to that offered by PEI 25 kDa.

CONCLUSIONS

The polymer reported in the current study displayed improved biocompatibility over non-degradable PEI 25 kDa and mediated gene transfection in cultured neurons and in the central nervous system effectively. The new polymer would be worth exploring further as an in vivo delivery system of therapeutic genetic materials for gene therapy of neurological disorders.

Effect of Collagen-I Modified Composites on Proliferation and Differentiation of Human Alveolar Osteoblasts

Collagen modification of scaffolds has been reported to promote matrix mineralization as an effective way to increase osseointegration of implants. The aim of this study was to investigate in vitro proliferation and differentiation of human alveolar osteoblasts (AOs) on medical-grade polycaprolactone–tricalcium phosphate (mPCL-TCP 80:20) scaffolds after collagen modification (mPCL-TCP-c) for 28 days. Collagen modification significantly increased the scaffold’s protein adsorption ability, and improved the initial seeding efficiency and cell attachment at day 1, compared with non-collagen-modified scaffolds. However, the total DNA content of both groups reached similar levels with no significant difference at 28 days’ culture. AOs were observed to spread along the collagen fibres and form extensive collagenous fibres with mineral nodules embedded, while multilayered cell sheets were formed in mPCL-TCP scaffolds. During culture, alkaline phosphatase (ALP) activity increased three- to five-fold in both groups, and collagen modification did not significantly affect either the metabolic rate or ALP activity kinetics of AOs. During osteogenic differentiation, similar gene expression of collagen type-I, osterix, osteopontin, and osteocalcin were detected in both groups. The mPCL-TCP group showed better organized mineralized tissue, but the mPCL-TCP-c showed more scattered and unorganized tissue. These results indicate that collagen modification improved the scaffold’s protein adsorption ability and encouraged initial cell attachment and distribution, but promoted fibrous-like tissue formation rather than mineralized tissue.

Improved neuronal transgene expression from an AAV-2 vector with a hybrid CMV enhancer/PDGF-beta promoter

BACKGROUND

Adeno-associated virus type 2 (AAV-2) vectors are highly promising tools for gene therapy of neurological disorders. After accommodating a cellular promoter, AAV-2 vectors are able to drive sustained expression of transgene in the brain. This study aimed to develop AAV-2 vectors that also facilitate a high level of neuronal expression by enhancing the strength of a neuron-specific promoter, the human platelet-derived growth factor beta-chain (PDGF) promoter.

METHODS AND RESULTS

A hybrid promoter approach was adopted to fuse the enhancer of human cytomegalovirus immediately early (CMV) promoter to the PDGF promoter. In cultured cortex neurons, AAV-2 vectors containing the hybrid promoter augmented transgene expression up to 20-fold over that mediated by titer-matched AAV-2 vectors with the PDGF promoter alone and 4-fold over the CMV enhancer/promoter. Injection of AAV-2 vectors with the hybrid promoter into the rat striatum resulted in neuron-specific transgene expression, the level of which was about 10-fold higher than those provided by the two control AAV-2 expression cassettes at 4 weeks post-injection and maintained for at least 12 weeks. Gene expression in the substantia nigra through possible retrograde transport of the AAV-2 vectors injected into the striatum was not obvious. After direct injection of AAV-2 vectors into the substantia nigra, transgene expression driven by the hybrid promoter was observed specifically in dopaminergic neurons and its level was about 3 and 17 times higher than that provided by the PDGF promoter alone and the CMV enhancer/promoter, respectively.

CONCLUSIONS

Enhanced transgene capacity plus neuron-specificity of the AAV-2 vectors developed in this study might prove valuable for gene therapy of Parkinson's disease.

Pharmacological activity of peroral chitosan-insulin nanoparticles in diabetic rats

The objective of the present study was to evaluate the effects of formulation parameters on the in vivo pharmacological activity of the chitosan-insulin nanoparticles. Chitosan-insulin nanoparticles were prepared by ionotropic gelation at pH 5.3 and 6.1 and denoted as F5.3 np and F6.1 np, respectively. F5.3 np and F6.1 np administered orally at insulin doses of 50 U/kg and/or 100 U/kg were effective at lowering the serum glucose level of streptozotocin-induced diabetic rats. The 100 U/kg-dose F5.3 np sustained the serum glucose at pre-diabetic levels for at least 11 h. In comparison, F6.1 np had a faster onset of action (2h versus 10h) but lower efficiency. The effectiveness of peroral F5.3 np and F6.1 np in lowering the serum glucose level of streptozotocin-induced diabetic rats was ascribed to the local effect of insulin in intestine. Confocal micrographs showed strong interaction between rat intestinal epithelium and chitosan nanoparticles 3h post-oral administration.

Preparation and characterization of aligned carbon nanotube-ruthenium oxide nanocomposites for supercapacitors

A novel type of ruthenium oxide (RuO(2))-modified multi-walled carbon nanotube (MWNT) nanocomposite electrode (RuO(2)/MWNT) for supercapacitors has been prepared. The nanocomposites were formed by depositing Ru by magnetic-sputtering in an Ar/O(2) atmosphere onto MWNTs, which were synthesized on Ta plates by chemical vapor deposition. Cyclic voltammetry, chronopotentiometry, and electrochemical impedance measurements were applied to investigate the performance of the RuO(2)/MWNT nanocomposite electrodes. The capacitance of the MWNT electrodes in 1.0 M H(2)SO(4) is significantly increased from 0.35 to 16.94 mF cm(-2) by modification with RuO(2). The RuO(2) film on the surface of the nanotubes is composed of small crystal grains with tilted bundle-like microstructures, as observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results demonstrate a promising route to prepare RuO(2)/MWNT-based double-layer supercapacitors.

Alterations in the solubility and intracellular localization of parkin by several familial Parkinson's disease-linked point mutations

Mutations in the parkin gene, which encodes a ubiquitin ligase, are currently recognized as the main contributor to familial forms of Parkinson's disease (PD). A simple assumption about the effects of PD-linked mutations in parkin is that they impair or ablate the enzyme activity. However, a number of recent studies, including ours, have indicated that many disease-linked point mutants of parkin retain substantial catalytic activity. To understand how the plethora of mutations on parkin contribute to its dysfunction, we have conducted a systematic analysis of a significant number of parkin point mutants (22 in total), which represent the majority of parkin missense/nonsense mutations reported to date. We found that more than half of these mutations, including many located outside of the parkin RING fingers, produce alteration in the solubility of parkin which influences its detergent extraction property. This mutation-mediated alteration in parkin solubility is also associated with its propensity to form intracellular, aggresome-like, protein aggregates. However, they do not represent sites where parkin substrates become sequestered. As protein aggregation sequesters the functional forms away from their normal sites of action, our results suggest that alterations in parkin solubility and intracellular localization may underlie the molecular basis of the loss of function caused by several of its mutations.

Compensatory caspase activation in MPP+-induced cell death in dopaminergic neurons

Many have hypothesized that cell death in Parkinson's disease is via apoptosis and, specifically, by the mitochondrial-mediated apoptotic pathway. We tested this hypothesis using a mouse dopaminergic cell line of mesencephalic origin, MN9D, challenged with the Parkinsonism-causing neurotoxin MPP+ (1-methyl-4-phenylpyridinium ion). Apoptosis was the main mode of cell death when the cells were subjected to MPP+ treatment under serum-free conditions for 24 h. Caspase-3 and caspase-9, however, were not activated, thus indicating the existence of alternate or compensatory cell death pathway(s) in dopaminergic neuronal cells. Using caspase inhibitors, we demonstrated that these pathways involve caspase-2, -8, -6 and -7. A time-course study indicated that activation of caspase-2 and -8 occurred upstream of caspase-6 and caspase-7. Upon MPP+ challenge, the apoptosis-inducing factor was translocated from the mitochondria into the MN9D cytosol and nucleus. These results suggest the existence of alternative apoptotic pathways in dopaminergic neurons.

Neurogranin expression in stably transfected N2A cell line affects cytosolic calcium level by nitric oxide stimulation

To test a cellular effect of rodent neurogranin (Ng) oxidation as compared to Ng phosphorylation, we develop a cell model capable of stable expression of Ng using the Tet-On system, and determine whether Ng oxidation regulates intracellular calcium level. Our results show that Ng oxidation by nitric oxide donor induces an increase of [Ca(2+)](i) in Ng-expressed cells as compared to the control cells without expressing Ng. These results suggest that Ng oxidation plays a significant role in intracellular Ca(2+) homeostasis, essential for the activated signaling networks in learning and memory.

Photocatalytic degradation of toluene by platinized titanium dioxide photocatalysts

A photoreactor has been set up to study the photodegradation of volatile organic compound (VOC) in situ. In the reactor, TiO2 and Pt/TiO2 photocatalysts were immobilized on to UV-transparent quartz support. Scanning electron microscope (SEM) studies and Brunauer-Emmett-Teller (BET) surface area measurements revealed that the quartz fiber support was mostly coated with catalyst with a total surface area of 4.0 +/- 0.3 m2/g. The photocatalytic activity of the photocatalysts was evaluated for the photodegradation of 160 ppm toluene-laden air. It was found that 50-70% of toluene was degraded within the first 5 min of UV illumination. Both TiO2 and Pt/TiO2 photocatalysts suffered from deactivation after 18 hours of continuous operation, and the photocatalysts' activity was significantly reduced. However, platinization doubled the photocatalyst life and delayed the onset of de-activation. The presence of moisture was found to shift the onset of catalyst de-activation to an earlier time. It is concluded that the de-activation of the photocatalyst was due to the accumulation of intermediates on the photocatalysts surface preventing the toluene being adsorbed on the photocatalyst surface for degradation.

Cloning and tissue expression of 6-pyruvoyl tetrahydropterin synthase and xanthine dehydrogenase from Poecilia reticulata

Guppy is a popular ornamental fish owing to its diverse body and fin coloration. More than 40 established color varieties have been selectively bred. The complementary DNAs for 2 enzymes that are involved in the de novo synthesis of pteridines and purines, which are important for the production of color pigments, were cloned from the caudal fin. Two cDNA isoforms for 6-pyruvoyl tetrahydropterin synthase (PTPS), with an open reading frame of 130 and 147 amino acids, respectively, were cloned from the Red Tail variety. The deduced amino acid sequence of the longer isoform shows an overall identity of about 65% to the mammalian PTPS sequences. The cDNA for xanthine dehydrogenase (XDH) was cloned from the Yellow Tail variety, and consists of an open reading frame of 1331 amino acids. Although it shows a higher overall identity to bovine aldehyde oxidase (AO; 54%) than to chicken XDH (51%), it has a NAD-binding domain that is specific to XDHs. Northern blot analysis indicated that both PTPS and XDH messenger RNAs were highly expressed in the liver, but absent in the muscle. In the caudal fins, guppy varieties with a higher proportion of xanthophores and erythrophores showed higher expression of PTPS, while XDH mRNA levels were too low to indicate obvious differential expression among the color guppy varieties. The results implied that high expression of PTPS is correlated with the biosynthesis of pteridines in the erythrophores and xanthophores, while the association between the putative guppy XDH with specific chromatophores is less clear.

An audit of upper gastrointestinal bleeding at Seremban Hospital

We retrospectively analyzed all patients presenting with upper gastrointestinal bleeding to Seremban Hospital over a one-year period. A quarter of the oesophagogastro-duodenoscopies (OGD) performed were performed as emergency for upper gastrointestinal tract bleeding. Gastric ulcers and duodenal ulcers were the two most common findings. Our results suggest that there is a male preponderance of 2:1, the Chinese were more likely to be affected and the elderly (> 60 years) were at highest risk.

Molecular mechanisms of neurodegeneration in Parkinson's disease: clues from Mendelian syndromes

The recent identification and characterization of gene products responsible for familial forms of Parkinson disease (PD) have provided significant insights into the pathogenesis of PD. Collectively, these studies point towards ubiquitin-proteasome system (UPS) dysfunction as an underlying mechanism responsible for dopaminergic cell death in PD. Emerging evidence further indicates a complex interplay between UPS derangements and other PD pathogenetic factors, all interwoven in an integrated network leading to dopaminergic cell death in PD. Taken together, these findings suggest that neuronal degeneration in PD is a result of a cascade of events, rather than a primary pathogenic event. Here, we review the clues uncovered from various Mendelian-inherited forms of PD that have helped shaped our understanding of the molecular mechanisms underlying PD pathogenesis.

Genetic linkage maps of the guppy ( Poecilia reticulata): assignment of RAPD markers to multipoint linkage groups

Genetic linkage maps of the guppy ( Poecilia reticulata) were constructed from independent crosses between the Tuxedo strain and a feral line (Wildtype). Segregation patterns of random amplified polymorphic DNA (RAPD) markers and phenotypic markers were investigated in F(2) offspring of Tuxedo male symbol male symbol x Wildtype female symbol female symbol and Wildtype male symbol male symbol x Tuxedo female symbol female symbol crosses. Among the 300 and 276 RAPD markers scored for the respective crosses, linkages were identified for 230 and 212, respectively. The Tuxedo male symbol male symbol x Wildtype female symbol female symbol and Wildtype male symbol male symbol x Tuxedo female symbol female symbol maps spanned 2100 Kosambi centiMorgans (cM(K)) and 1900 cM(K), respectively, in 28 linkage groups. Average marker resolution was 10 cM(K). Genome length was estimated at 4410 cM(K) and 4060 cM(K) for the respective crosses, with an average physical distance of 166 kbp/cM(K). Several RAPD markers were closely linked to or mapped onto the loci for the sex-determining region (SdR), and the sex-linked black caudal-peduncle ( Bcp) and red tail ( Rdt) genes. These primary linkage maps are the initial step toward the construction of a composite high-density map to facilitate map-based cloning and marker-assisted selection of quantitative trait loci that are essential for the development of comprehensive breeding programs for the guppy.

Functional genomics approach to the identification of virulence genes involved in Edwardsiella tarda pathogenesis

Edwardsiella tarda is an important cause of hemorrhagic septicemia in fish and also of gastro- and extraintestinal infections in humans. Here, we report the identification of 14 virulence genes of pathogenic E. tarda that are essential for disseminated infection, via a genome-wide analysis. We screened 490 alkaline phosphatase fusion mutants from a library of 450,000 TnphoA transconjugants derived from strain PPD130/91, using fish as an infection model. Compared to the wild type, 15 mutants showed significant decreases in virulence. Six mutants had insertions in the known virulence-related genes, namely, fimA, gadB, katB, pstS, pstC, and ssrB. Some mutants corresponded to known genes (astA, isor, and ompS2) that had not been previously shown to be involved in pathogenesis, and three had insertions in two novel genes. In vivo infection kinetics experiments confirmed the inability of these attenuated mutants to proliferate and cause fatal infection in fish. Screening for the presence of the above-described virulence genes in six virulent and seven avirulent strains of E. tarda indicated that seven of the genes were specific to pathogenic E. tarda. The genes identified here may be used to develop vaccines and diagnostic kits as well as for further studying the pathogenesis of E. tarda and other pathogenic bacteria.

Genetic diversity within and among feral populations and domesticated strains of the guppy (Poecilia reticulata) in Singapore

Genetic variability within and among feral populations and cultured strains of the guppy (Poecilia reticulata) was investigated by random amplification of polymorphic DNA (RAPD) fingerprinting. Feral guppies were collected from 6 isolated populations (BT, Bukit Timah; NS, Nee Soon; TS, Tuas; MF, Mount Faber; KR, Kranji; LI, laboratory-inbred feral line), while the Tuxedo and Green Variegated strains were sampled from 2 guppy farms in Singapore. Pairwise genetic distances analyzed by unweighted pair-group method with arithmetic means revealed distinct clustering of guppy individuals into their respective populations and strains. Percentage polymorphic loci ranged from 54.96% (TS) to 68.70% (KR), while average heterozygosity ranged from 0.220 (GV) to 0.271 (KR). In contrast, TS guppies had the highest (0.850) intrapopulation genetic similarity (S), whereas KR had the lowest (0.781). Among populations and strains, S ranged from 0.703 (between GV and LI) to 0.809 (between NS and MB). The GV strain S was closer to TX (0.784) than to the feral guppies. Bootstrapped genetic distance trees depicted 3 major nodes comprising BT-TS, NS-MF, and TX-GV. Principal coordinate analysis also differentiated the 6 feral populations from the 2 cultured strains.

Opsonized virulent Edwardsiella tarda strains are able to adhere to and survive and replicate within fish phagocytes but fail to stimulate reactive oxygen intermediates

Edwardsiella tarda is responsible for hemorrhagic septicemia (edwardsiellosis) in fish and also causes diseases in higher vertebrates such as birds, reptiles, and mammals, including humans. Interactions of E. tarda with blue gourami phagocytes were studied by light microscopy as well as by adherence, intracellular replication, and superoxide anion assays. Both nonopsonized virulent (PPD130/91 and AL9379) and avirulent (PPD125/87 and PPD76/87) bacteria could adhere to and survive and replicate within phagocytes, while only opsonized virulent strains replicated within the phagocytes. Furthermore, only avirulent E. tarda elicited a higher rate of production of reactive oxygen intermediates (ROIs) by phagocytes, indicating that they were unable to avoid and/or resist reactive oxygen radical-based killing by the fish phagocytes. TnphoA transposon mutagenesis was used to construct a library of 200 alkaline phosphatase (PhoA+) fusion mutants from a total of 182,000 transconjugants derived from E. tarda PPD130/91. Five of these mutants induced more ROI production in phagocytes than the wild-type strain. Two mutants had lower replication ability inside phagocytes and moderately higher 50% lethal dose values than the wild-type strain. Sequence analysis revealed that three of these mutants had insertions at sequences having homology to PhoS, dipeptidase, and a surface polymer ligase of lipid A core proteins of other pathogens. These three independent mutations might have changed the cell surface characteristics of the bacteria, which in turn induced phagocytes to produce increased ROIs. Sequences from two other mutants had no homology to known genes, indicating that they may be novel genes for antiphagocytic killing. The present study showed that there are differences in the interactions of virulent and avirulent E. tarda organisms with fish phagocytes and PhoA+ fusion mutants that could be used successfully to identify virulence genes. The information elucidated here would help in the development of suitable strategies to combat the disease caused by E. tarda.

Mortality in the Department of Surgery, Alor Setar Hospital

This is a retrospective study of the annual mortality that occurred in the Department of Surgery, Alor Setar Hospital, for the years 1995 to 1997. This study looks at the number of admissions to the surgical wards and categorizes the causes of death. The annual mortality rates were 2.60, 2.89 and 3.25 per hundred admissions for the year 1995, 1996 and 1997 respectively. Head injury was the leading cause of death whilst sepsis and advanced malignancies second and third commonest causes. We hope that with the publication of these figures, we can initiate more studies to analyse similar local data.

Edwardsiella tarda mutants defective in siderophore production, motility, serum resistance and catalase activity

Edwardsiella tarda is a Gram-negative bacterium that causes a systemic infection, edwardsiellosis, in fish. The virulence factors of this pathogen and its genetic determinants have not been systematically examined. In this study, TnphoA transposon mutagenesis was used to construct a library of 440 alkaline phosphatase (PhoA(+)) fusion mutants from a total of 400000 transconjugants derived from Ed. tarda PPD130/91. This library included genes for secreted and membrane-associated proteins normally involved in virulence. The library was screened for four virulence factors: siderophore production, motility, serum resistance and catalase production. Eight mutants deficient in one or more of these phenotypes were grouped into four classes. They were further characterized for their stimulation of reactive oxygen intermediate production by fish phagocytes, for their adhesion to and internalization into EPC (epithelioma papillosum of carp) cells, and for attenuation of virulence in blue gourami. Mutants 2A and 34 were highly attenuated in fish, with LD(50) values about 10 times higher than for the wild-type. These strains had mutations in the genes encoding arylsulfate sulfotransferase (mutant 2A) and a catalase precursor protein (mutant 34). One hyperinvasive/adhesive mutant and four pst mutants that were pleiotropic and slightly attenuated in fish were also isolated.

Green fluorescent protein-tagged Edwardsiella tarda reveals portal of entry in fish

The application of green fluorescent protein (GFP) to identify the portal(s) of entry of bacterial pathogens in animal hosts was studied using the fish pathogen Edwardsiella tarda and blue gourami, Trichogaster trichopterus. An immersion challenge model was utilized to mimic natural infection conditions in fish. Gastrointestinal tract, gills and the body surface of fish were found to be the sites of entry of virulent E. tarda (PPD130/91) by histological and infection kinetics studies. On the other hand, avirulent E. tarda (PPD125/87) was mainly found in the gastrointestinal tract, and the bacterial population in tissue declined over a period of 7 days.

Asynchronous activation of 10 muscle-specific protein (MSP) genes during zebrafish somitogenesis

In the present study, 10 zebrafish cDNA clones coding for muscle-specific proteins (MSPs) were characterized and most of them encode fast skeletal muscle isoforms. They are skeletal muscle alpha-actin (acta1), fast skeletal muscle a-tropomyosin (tpma), fast skeletal muscle troponin C (tnnc), fast skeletal muscle troponin T (tnnt), fast skeletal muscle myosin heavy chain (myhz1), fast skeletal muscle myosin light chain 2 (mylz2), fast skeletal muscle myosin light chain 3 (mylz3), muscle creatine kinase (ckm), parvalbumin (pvalb), and desmin (desm). Using these cDNA probes, their expression patterns in developing embryos and adults were compared by Northern blot hybridization and whole-mount in situ hybridization. All of the 10 genes are expressed in both embryos and adult fish, and the expression is highly abundant in skeletal muscle. Among them, acta1, tpma, tnnc, tnnt, myhz1, mylz2, mylz3 and pvalb, are expressed specifically in fast skeletal muscle while ckm and desm are expressed in both fast and slow skeletal muscles. In addition, tpma, ckm, and desm are also expressed in the heart. Ontogenetically, the onset of expression of these MSP genes in zebrafish skeletal muscle varies and the expression occurs rostral-caudally in developing somites. Shortly after the expression of myoD, desm is the first to be activated at approximately 9 hpf, followed by tpma (approximately 10 hpf), tnnc (approximately 12 hpf), acta1 (approximately 12 hpf), ckm (approximately 14 hpf), myhz1 (approximately 14 hpf), mylz2 (approximately 16 hpf), mylz3 (approximately 16.5 hpf), tnnt (approximately 16.5 hpf), and pvalb (approximately 16.5 hpf). At later stages (after 48 hpf), these MSP genes are also expressed in fin buds and head muscles including eye, jaw, and gill muscles. Thus, our experiment demonstrated the order of expression of the 10 MSP genes, which may reflect the sequence of muscle filament assembly. In spite of the asynchrony in activation of these MSP genes, the timing of expression for each individual MSP gene appears to be synchronous to somite development as each somite has an identical timetable to express the set of MSP genes.

Type I and type II cytokeratin cDNAs from the zebrafish (Danio rerio) and expression patterns during early development

Full-length cDNAs of a type I (zfCKI), and a type II (zfCKII) cytokeratin from the adult zebrafish, Danio rerio, were characterized and their expressions studied during early development and in the adult. The 1,426 bp long zfCKI cDNA encodes a 46.7 kD protein, whereas the 2,398 bp zfCKII cDNA encodes a protein of 58.6 kD. zfCKI and zfCKII each have a central rod domain that is characteristic of intermediate filaments and which share 73%-91% and 87%-93% similarity, respectively, with those of type I and type II cytokeratins from zebrafish, goldfish, and the rainbow trout. The central rod domains of zfCKI and zfCKII also contain the IF signature motif, IA[T/E]YR[K/R]LL[D/E]. zfCKI has, in addition, a leucine-zipper motif at a.a. residues 184-205 and 191-212. Both zfCKI and zfCKII mRNAs are expressed in the epidermis of the zebrafish. zfCKII mRNA was both maternally inherited and zygotically transcribed and was detected from the one-cell embryo to adult stages. zfCKII was also strongly expressed specifically during the 20-somites, protruding-mouth, and adult stages. In the adult, it was uniformly expressed in the skin, fins and scale epidermis. In contrast, zfCKI mRNA was undetectable in the oocyte but was zygotically transcribed from the epiboly stage onwards. Its expression in the skin was strong only up to the swimming larva stage and was weak and patchy in the adult. Both zfCKI and zfCKII were expressed in the neurons and glial cells of the brain and spinal cord. In the adult eye, zfCKI and zfCKII were expressed in the ganglion cell layer and the retina, but zfCKII was also strongly expressed in the cornea as well as in chondrocytes in the skull.

Neuronal localization of sterol regulatory element binding protein-1 in the rodent and primate brain: a light and electron microscopic immunocytochemical study

Sterol regulatory element binding proteins are membrane-bound transcription factors that activate expression of several genes controlling cellular cholesterol and fatty acid homeostasis. The present study aimed to investigate the in vivo expression of sterol regulatory element binding protein-1 in the normal rodent and primate brain, and in the brain in Niemann-Pick type C disease mice. These mutant animals have lysosomal cholesterol accumulation and progressive neurodegeneration caused by an inactivating mutation of the NPC1 gene whose protein product functions in vesicular lipid trafficking. Western blot analysis of rat hippocampal homogenates with an affinity purified rabbit polyclonal antibody directed against an internal epitope of sterol regulatory element binding protein-1 identified a major 68,000 mol. wt protein consistent with the amino-terminal, transcriptionally active fragment of sterol regulatory element binding proteins-1. Immunocytochemically, this antibody revealed dense sterol regulatory element binding protein-1 staining of nuclei and light staining of the cytoplasm of cells in the neocortex and hippocampus in the rat, mouse and monkey brain. By electron microscopy of immunogold-labeled brain sections, these densely labeled cells were found to be neurons. In contrast, normal glial cells had little or no sterol regulatory element binding protein-1 immunoreactivity even at a developmental stage (postnatal day 9) which coincides with active myelination in the rat brain. Also, in contrast to the normal mouse brain, Niemann-Pick type C mice showed reduced staining of cortical and hippocampal neuronal nuclei. Since sterol regulatory element binding protein-1 has been shown to be a transcriptional regulator of fatty acid synthesis in vivo, the current findings of a predominantly neuronal nuclear expression of the 68,000 mol. wt transcriptionally active fragment of sterol regulatory element binding protein-1 highlights the established role of phospholipid metabolites and other fatty-acid containing lipids in neuronal signal transduction and other neuronal functions. Reduced sterol regulatory element binding protein-1 expression in neurons in Niemann-Pick type C may reflect a deficiency in fatty acid synthesis that could contribute to the neuronal dysfunction in this disorder.

Characterization of a zebrafish (Danio rerio) desmin cDNA: an early molecular marker of myogenesis

Desmin is a muscle-specific protein and a constitutive subunit of the intermediate filaments (IF) in skeletal, cardiac and smooth muscles. It is an early marker of skeletal muscle myogenesis. We have characterized a clone of desmin cDNA from an embryonic zebrafish (Danio rerio) cDNA library. The full-length cDNA comprised 1798 nucleotides, encoding a protein of 473 amino acids. The predicted amino acid sequence of the zebrafish desmin shares a high degree of similarity to other vertebrate desmins, but also contains a sequence at the carboxyl terminal of the tail domain that is unique to the zebrafish. It carries many features which are distinctive of IF subunit proteins. These include the T/SSYRRXF/Y motif in the head domain, and the intermediate filament signature consensus, [I/V]-X-[T/A/C/I]-Y-[R/K/H]-X-[L/M]-L-[D/E], located in the carboxyl terminus of the central helical rod. Unlike other 3' UTR sequences, the 3' UTR of the zebrafish cDNA sequence has two CAYUG elements flanking a single polyadenylation site. The temporal and spatial expression patterns of desmin mRNA during early zebrafish development were studied. The onset of desmin expression occurred at the 1-3 somite stage (11 hpf). It increased throughout somitogenesis, with maximum expression at the Prim-6 stage (25 hpf), and decreasing expression towards the protruding-mouth stage (72 hpf). Desmin mRNA was initially localised exclusively to the somites, but was subsequently also detected in other musculature in the developing heart and fins. The onset of expression and the spatial localization of desmin mRNA in the zebrafish coincides with that reported for MyoD and myogenin.

Kainate-induced neuronal injury leads to persistent phosphorylation of cAMP response element-binding protein in glial and endothelial cells in the hippocampus

Intracerebroventricular kainate treatment in rats induces neuronal cell death, followed by proliferation and hypertrophy of glial cells in the lesioned area. To further understand the activated signal transduction pathways and to get insights into potential target gene activation, the present study aims to elucidate long-term effects on the phosphorylation state of cAMP response element-binding protein (CREB) in the hippocampal formation. One to four weeks after kainate injection, we found high levels of phosphorylated and hence activated CREB (pCREB) in glial cells of the degenerating CA fields. As shown by electron microscopy, pCREB immunoreactivity was present in reactive astrocytes, oligodendrocyte precursor cells and endothelial cells of blood vessels. It is postulated that pCREB could drive the expression of downstream genes in these cells to promote cell proliferation and survival.

Use of green fluorescent protein (GFP) to study the invasion pathways of Edwardsiella tarda in in vivo and in vitro fish models

Edwardsiella tarda is a fish pathogen that causes systemic infections in many food and ornamental fish. E. tarda PPD130/91 and PPD125/87 were selected as representatives of the virulent and avirulent groups, respectively, from eight fish isolates, and transformed with plasmids encoding either green fluorescent protein (pGFPuv) or blue fluorescent protein (pBFP2). Two host models were used to study the invasion pathway of E. tarda in vitro and in vivo. Epithelioma papillosum of carp (EPC) was used as the first model. Virulent and avirulent E. tarda strains were found to adhere to and invade EPC cells. Interactions between E. tarda and host cells examined under confocal microscopy and intracellular growth were followed at different time points. Bacterial internalization of PPD130/91 and PPD125/87 involved microfilaments and protein tyrosine kinase since cytochalasin D (an inhibitor of microfilament polymerization) and genistein (an inhibitor of protein tyrosine kinase) prevented internalization. Confocal studies revealed co-localization of polymerized actin with bacteria. Staurosporine, a protein kinase C inhibitor, accelerated internalization of PPD125/87, whereas PD098059, a mitogen-activated protein kinase (MAPK) kinase inhibitor prevented internalization of PPD130/91. In the second model, blue gourami were infected with E. tarda intramuscularly. Mortalities were observed in PPD130/91(pGFPuv)-infected fish with high bacterial numbers detectable in all organs. PPD125/87(pBFP2)-infected fish did not die and the bacterial population decreased over time. Mixed infections comprised of both PPD130/91(pGFPuv) and PPD125/87(pBFP2), where inoculum size was similar to the single infections, caused mortalities in fish. High bacterial populations were noted only in the fish body muscle. The PPD125/87(pBFP2) population in the fish decreased after 5 d. The number of PPD130/91(pGFPuv) also decreased in the fish organs, except for continued high growth in the body muscle. Histology revealed necrosis of the tissue (body muscle and liver) and fluorescent bacteria in fish that were infected with PPD130/91(pGFPuv) but not with PPD125/87(pBFP2). This study showed that fluorescent proteins are a useful tool for investigating bacterial host cell infection, and information elucidated here sheds new light on the interactions between E. tarda and its hosts.