The role of Twist1 in mutant huntingtin-induced transcriptional alterations and neurotoxicity.

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by an abnormal expansion of polyglutamine repeats in the huntingtin protein (Htt). Transcriptional dysregulation is an early event in the course of HD progression and is thought to contribute to disease pathogenesis, but how mutant Htt causes transcriptional alterations and subsequent cell death in neurons is not well understood. RNA-Seq analysis revealed that expression of a mutant Htt fragment in primary cortical neurons leads to robust gene expression changes before neuronal death. Basic helix-loop-helix transcription factor Twist1, which is essential for embryogenesis and is normally expressed at low levels in mature neurons, was substantially up-regulated in mutant Htt-expressing neurons in culture and in the brains of HD mouse models. Knockdown of Twist1 by RNAi in mutant Htt-expressing primary cortical neurons reversed the altered expression of a subset of genes involved in neuronal function and, importantly, abrogated neurotoxicity. Using brain-derived neurotrophic factor (Bdnf), which is known to be involved in HD pathogenesis, as a model gene, we found that Twist1 knockdown could reverse mutant Htt-induced DNA hypermethylation at the Bdnf regulatory region and reactivate Bdnf expression. Together, these results suggest that Twist1 is an important upstream mediator of mutant Htt-induced neuronal death and may in part operate through epigenetic mechanisms.

Pricing behavior of monopoly market with the implementation of green technology decision under emission reduction subsidy policy.

Carbon emissions are one of the major constraints considered under a Cap-and-Trade (C-and-T) system, regarding the implementation of green technologies in the operations of emissions-generating companies. Green technology implementation, based on optimal pricing decisions, has become an inevitability due to rising carbon emissions. We studied the profit-maximizing behavior of a firm considering whether to implement of green technology due to subsidies offered on emission-reduction rates. In order to achieve the desired results, we used a simulation-based model and developed a conceptual model for the verification of functions. When the product price was high, the firm achieved a high profit, which was the main focus of the firm. The firm thus had sufficient resources to implement green technology. However, when the product price was low, the firm could achieve its goal of profit maximization, but did so without implementing green technology. To solve this problem, we studied government involvement in the market to incentivize emissions reduction and to benefit the firm. We decided to model emissions-reduction policy to encourage the implementation of green technology and support firm profits. We found that subsidies enabled a firm to maximize its profits while ensuring green technology implementation, while the firm would not have adopted green technology without subsidies or mandates. This study should help decision makers understand pricing strategies in the maximization of the profit. Additionally, this study helps demonstrate that the government plays an important role in monopolized markets by reducing negative externalities.

Inhibition of DNA Methyltransferases Blocks Mutant Huntingtin-Induced Neurotoxicity.

Although epigenetic abnormalities have been described in Huntington's disease (HD), the causal epigenetic mechanisms driving neurodegeneration in HD cortex and striatum remain undefined. Using an epigenetic pathway-targeted drug screen, we report that inhibitors of DNA methyltransferases (DNMTs), decitabine and FdCyd, block mutant huntingtin (Htt)-induced toxicity in primary cortical and striatal neurons. In addition, knockdown of DNMT3A or DNMT1 protected neurons against mutant Htt-induced toxicity, together demonstrating a requirement for DNMTs in mutant Htt-triggered neuronal death and suggesting a neurodegenerative mechanism based on DNA methylation-mediated transcriptional repression. Inhibition of DNMTs in HD model primary cortical or striatal neurons restored the expression of several key genes, including Bdnf, an important neurotrophic factor implicated in HD. Accordingly, the Bdnf promoter exhibited aberrant cytosine methylation in mutant Htt-expressing cortical neurons. In vivo, pharmacological inhibition of DNMTs in HD mouse brains restored the mRNA levels of key striatal genes known to be downregulated in HD. Thus, disturbances in DNA methylation play a critical role in mutant Htt-induced neuronal dysfunction and death, raising the possibility that epigenetic strategies targeting abnormal DNA methylation may have therapeutic utility in HD.

A CDC20-APC/SOX2 Signaling Axis Regulates Human Glioblastoma Stem-like Cells.

Glioblastoma harbors a dynamic subpopulation of glioblastoma stem-like cells (GSCs) that can propagate tumors in vivo and is resistant to standard chemoradiation. Identification of the cell-intrinsic mechanisms governing this clinically important cell state may lead to the discovery of therapeutic strategies for this challenging malignancy. Here, we demonstrate that the mitotic E3 ubiquitin ligase CDC20-anaphase-promoting complex (CDC20-APC) drives invasiveness and self-renewal in patient tumor-derived GSCs. Moreover, CDC20 knockdown inhibited and CDC20 overexpression increased the ability of human GSCs to generate brain tumors in an orthotopic xenograft model in vivo. CDC20-APC control of GSC invasion and self-renewal operates through pluripotency-related transcription factor SOX2. Our results identify a CDC20-APC/SOX2 signaling axis that controls key biological properties of GSCs, with implications for CDC20-APC-targeted strategies in the treatment of glioblastoma.

Inhibition of mitochondrial protein import by mutant huntingtin.

Mitochondrial dysfunction is associated with neuronal loss in Huntington's disease (HD), a neurodegenerative disease caused by an abnormal polyglutamine expansion in huntingtin (Htt). However, the mechanisms linking mutant Htt and mitochondrial dysfunction in HD remain unknown. We identify an interaction between mutant Htt and the TIM23 mitochondrial protein import complex. Remarkably, recombinant mutant Htt directly inhibited mitochondrial protein import in vitro. Furthermore, mitochondria from brain synaptosomes of presymptomatic HD model mice and from mutant Htt-expressing primary neurons exhibited a protein import defect, suggesting that deficient protein import is an early event in HD. The mutant Htt-induced mitochondrial import defect and subsequent neuronal death were attenuated by overexpression of TIM23 complex subunits, demonstrating that deficient mitochondrial protein import causes mutant Htt-induced neuronal death. Collectively, these findings provide evidence for a direct link between mutant Htt, mitochondrial dysfunction and neuronal pathology, with implications for mitochondrial protein import-based therapies in HD.

Muscle-derived but not centrally derived transgene GDNF is neuroprotective in G93A-SOD1 mouse model of ALS.

Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for motoneurons (MNs), and is considered a potential agent for the treatment of amyotrophic lateral sclerosis (ALS) and other MN diseases. The effectiveness of GDNF may depend significantly upon its route of delivery to MNs. In this study we tested the neuroprotective effects of target-derived and centrally derived GDNF in the G93A-SOD1 mouse model of ALS using a transgenic approach. We found that overexpression of GDNF in the skeletal muscle (Myo-GDNF mice) significantly delayed the onset of disease and increased the life span of G93A-SOD1 mice by 17 days. The duration of disease also increased by 8.5 days, indicating that GDNF slowed down the progression of disease. Locomotor performance in Myo-GDNF/G93A-SOD1 mice was also significantly improved. The behavioral improvement correlated well with anatomical and histological data. We demonstrated that muscle-derived GDNF resulted in increased survival of spinal MNs, and twice as many MNs survived in end-stage double transgenic mice compared to end-stage G93A-SOD1 mice. Muscle-derived GDNF also had profound effects on muscle innervation and axonal degeneration. Significantly higher numbers of completely or partially innervated NMJs and large caliber myelinated axons were found in double transgenic mice. In contrast, we demonstrated that overexpression of GDNF in astrocytes in the CNS (GFAP-GDNF mice) failed to demonstrate any neuroprotective effects in G93A-SOD1 mice both on behavioral and histological levels. These data indicate that retrograde transport and signaling of GDNF is more physiological and effective for ALS treatment than anterogradely transported GDNF.

Astrocyte-derived transgene GDNF promotes complete and long-term survival of adult facial motoneurons following avulsion and differentially regulates the expression of transcription factors of AP-1 and ATF/CREB families.

Glial-cell-line-derived neurotrophic factor (GDNF) is a potent survival factor for motoneurons (MNs). We have previously demonstrated that overexpression of GDNF in astrocytes of GFAP-GDNF mice promotes long-term survival of neonatal MNs after facial nerve axotomy. In the present study, we investigated whether astrocyte-derived GDNF could also have a neuroprotective effect on adult MNs following facial nerve avulsion. We also examined avulsion- and GDNF-induced changes in the expression pattern of several members of the AP-1 and ATF/CREB families of transcription factors, which are involved in the fate determination of neurons following injury. We demonstrated that GDNF promotes complete rescue of avulsed MNs for at least 4 months post-injury. Transgene GDNF significantly upregulates c-Jun expression in naive MNs, further upregulates injury-induced c-Jun expression in facial MNs, and results in its activation in most surviving MNs. No significant changes were found in c-Fos expression. We found that GDNF has an opposing effect on ATF2 and ATF3 expression. It dramatically downregulates increased levels of ATF3 in response to injury, whereas the expression of ATF2, which is normally reduced after injury, is completely preserved in GFAP-GDNF mice. Our data suggest that maintenance of high levels of ATF2 in injured MNs could be crucial in modulating c-Jun function, and c-Jun/ATF2 signaling could be involved in GDNF-mediated survival of mature MNs.