Age-related decrease in brain-derived neurotrophic factor gene expression in the brain of the zitter rat with genetic spongiform encephalopathy

Molecular process in acute liver injury and regeneration induced by carbon tetrachloride

Injection of carbon tetrachloride (CCl4) intraperitoneally into model animals induces acute liver injury mediated by reactive oxygen species (ROS) as normal metabolites in hepatocytes. In this study, the molecular process in this type of liver injury was analyzed from the aspect of liver function and regulatory factors. Down-regulation of liver-specific genes was accomplished through suppression of liver-enriched transcription factors and box A factors found in the catalase gene, and induction of NF-kappaB, AP-1 and a novel factor denoted as 'cx' in the catalase gene. Expression profiles of these genes were restored to normal levels in the late stage of injury (48 h). On the other hand, hepatocyte growth factor (HGF) and proliferating cell nuclear antigen (PCNA) were induced in the early stage (6 h) and 36 h, respectively. Interestingly, ERK2 was transiently activated at 3 h CCl4-treatment. These observations suggested that hepatotoxin by CCl4-injection concomitantly induces both processes in acute injury and liver regeneration.

Loss of D 3 receptors in the zitter mutant rat is not reversed by l -dopa treatment

In Parkinson's disease (PD) and animal models of parkinsonism the destruction of nigrostriatal (NSB) system results in a marked loss of the dopamine D(3) receptor and mRNA in the islands of Calleja (ICj) and the nucleus accumbens shell (NAS). In animal models, it has been reported that both measures are elevated by repeated intermittent administration of L-dopa. However, a large proportion of PD cases are resistant to L-dopa-induced elevation of D(3) receptor number. The zitter mutant (Zi/Zi) rat replicates the slow progressive degeneration of the NSB observed in PD and also exhibits a loss of D(3) receptor number in the NAS or ICj. To test if this could be reversed with subchronic L-dopa treatment, injections of carbidopa (10 mg/kg i.p.) were followed an hour later with injection of L-dopa (100 mg/kg i.p.) twice a day for 10 days. In control Sprague-Dawley (SD) and zitter heterozygote (Zi/-) rats that do not show a loss of D(3) receptors with vehicle treatment, L-dopa produced no change in D(3) receptor number or in DA terminal density as measured by dopamine transporter (DAT) binding and tyrosine hydroxylase immunoautoradiography (TH-IR). There was a marked loss of DAT and TH-IR in caudate-putamen (CPu) and NA, as well as D(3) receptors in NAS and ICj in Zi/Zi rats but no further change with L-dopa treatment. To determine if the resistance to L-dopa-induced increase in D(3) receptor was due to a deficiency in expression of cortical BDNF or its receptor, TrkB, in CPu and NAS, we examined BDNF mRNA by ISHH in frontal cortex and TrkB mRNA in frontal cortex, CPu, and NA. The loss of the NSB in the Zi/Zi did not alter levels of BDNF or TrkB mRNA, nor did L-dopa administration alter levels BDNF or TrkB mRNA. Thus, unlike in 6-hydroxydopamine-treated rats, in Zi/Zi rats administered L-dopa does not reverse the loss of BDNF mRNA or lead to an elevation of D(3) receptor number.

Perturbed signal transduction in neurodegenerative disorders involving aberrant protein aggregation

Aggregation of abnormal proteins, both inside and outside of cells, is a prominent feature of major neurodegenerative disorders, including Alzheimer's, Parkinson's, polyglutamine expansion, and prion diseases. Other articles in this special issue of NeuroMolecular Medicine describe the genetic and molecular factors that promote aberrant protein aggregation. In the present article, we consider how it is that pathogenic aggregation-prone proteins compromise signal transduction pathways that regulate neuronal plasticity and survival. In some cases the protein in question may have widespread and relatively nonspecific effects on signaling. For example, amyloid beta-peptide induces membrane-associated oxidative stress, which impairs the function of various receptors, ion channels and transporters, as well as downstream kinases and transcription factors. Other proteins, such as polyglutamine repeat proteins, may affect specific protein -protein interactions, including those involved in signaling pathways activated by neurotransmitters, neurotrophins, and steroid hormones. Synapses are particularly sensitive to abnormal protein aggregation and impaired synaptic signaling may trigger apoptosis and related cell death cascades. Impairment of signal transduction in protein aggregation disorders may be amenable to therapy as demonstrated by a recent study showing that dietary restriction can preserve synaptic function and protect neurons in a mouse model of Huntington's disease. Finally, emerging findings are revealing how activation of certain signaling pathways can suppress protein aggregation and/or the cytotoxicity resulting from the abnormal protein aggregation. A better understanding of how abnormal protein aggregation occurs and how it affects and is affected by specific signal transduction pathways, is leading to novel approaches for preventing and treating neurodegenerative disorders.

Methamphetamine-induced loss of striatal dopamine innervation in BDNF heterozygote mice does not further reduce D3 receptor concentrations

Depletion of dopamine (DA) reduces D(3) receptor number, but D(3) receptor expression is also regulated by brain-derived neurotrophic factor (BDNF). We took advantage of transgenic heterozygous BDNF mutant mice (+/-) to determine if reduced BDNF and loss of DA fibers produced by methamphetamine were additive in their impact on D(3) receptor number. We assessed selective markers of the dopaminergic system including caudate-putamen DA concentrations and quantitative autoradiographic measurement of tyrosine hydroxylase (TH) levels, DA transporter (DAT), and DA D(3) receptor binding between vehicle and methamphetamine-treated BDNF +/- and their wildtype (WT) littermate control mice. Caudate-putamen DA concentrations, TH and DAT levels were significantly reduced following methamphetamine treatment in both WT and BDNF +/- mice. The extent of methamphetamine-induced reduction in TH and DAT was greater for the WT than BDNF +/- mice and DAT levels were also decreased to a greater extent in nucleus accumbens of WT as compared to BDNF +/- mice. Lower D(3) receptor existed in caudate-putamen and nucleus accumbens in BDNF +/- mice and these differences were not affected by methamphetamine treatment. Taken together, these results not only substantiate the importance of BDNF in controlling D(3) receptor expression, but also indicate that a methamphetamine-induced depletion of DA fibers fails to produce an additive effect with lowered BDNF for control of D(3) receptor expression. In addition, the reduction of D(3) receptor expression is associated with a decreased neurotoxic response to methamphetamine in BDNF +/- mice.

Pivotal role of attractin in cell survival under oxidative stress in the zitter rat brain with genetic spongiform encephalopathy

Accumulation of reactive oxygen species (ROS), which is generated during energy metabolism, is a cause of physiological aging, neuropathogenesis and numerous diseases, such as Parkinson's and Alzheimer's diseases. Zitter rat is an autosomal recessive mutant, characterized by spongiform degeneration and hypomyelination in the brain, and the phenotype has been suggested to be involved in oxidative stress by the accumulation of ROS. To determine the relation between neurodegeneration of the zitter rat and Attractin (Atrn) gene expression, which was identified as a gene responsible for the zitter, we established fibroblast cells from the zitter rat (Fz) and the Wistar tremor control (WTC) rat (Fw), and transduced Fz cells with the Atrn gene (Fz/Atrn). In the Fz/Atrn cells, accumulation of ROS was repressed, and cell survival against oxidative stress was enhanced to the same level as in Fw cells. Interestingly, phosphorylation of ERK was significantly increased in Fz/Atrn cells by H(2)O(2) stimulus, similarly to Fw cells. Furthermore, activation of ERK was confirmed in the brains of WTC and zitter rats by Western blot analysis and immunohistochemistry. These observations suggested that lack of Atrn gene expression induced neurodegeneration by a decrease in active ERK through an intracellular signaling via oxidative stress.

Neurotrophin receptor TrkB activation is not required for the postnatal survival of retinal ganglion cells in vivo

During early postnatal development, apoptosis of retinal ganglion cells (RGCs) is regulated by target contact with the optic tectum. The neurotrophins BDNF and NT-4, but not NGF, prevent the apoptosis of retinal ganglion cells that is otherwise observed after target ablation or axotomy. Thus receptors activated by BDNF and NT-4 are candidates to mediate the early postnatal survival of RGCs. BDNF and NT-4, but not NGF, bind to all isoforms of the receptor TrkB, whether or not they contain a tyrosine kinase domain. To examine the roles of TrkB receptor isoforms in early postnatal survival, we compared RGC numbers in wild-type mice to those in a mutant lacking all isoforms of TrkB. Surprisingly, no reduction in RGCs was observed in the mutant at postnatal day 16, the latest age at which these animals are consistently viable, so TrkB signaling is not essential for target-dependent survival of these cells. In wild-type mice, RGCs also are lost gradually during adulthood, possibly due to oxidative stress. To determine whether TrkB signaling regulates this phase of RGC degeneration, RGC numbers were examined in a viable mutant of TrkB that expresses only about 25% the normal level of TrkB receptor kinase. Compared to controls, approximately 20% of the RGC were lost in mutant 3-month-old-animals. Thus, TrkB signaling is not required for survival of RGCs during the period of target-dependent survival, but does appear to reduce degeneration of RGCs in adult animals.