Polyglutamine Expanded Huntingtin Dramatically Alters the Genome-Wide Binding of HSF1

In Huntington's disease (HD), polyglutamine expansions in the huntingtin (Htt) protein cause subtle changes in cellular functions that, over-time, lead to neurodegeneration and death. Studies have indicated that activation of the heat shock response can reduce many of the effects of mutant Htt in disease models, suggesting that the heat shock response is impaired in the disease. To understand the basis for this impairment, we have used genome-wide chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-Seq) to examine the effects of mutant Htt on the master regulator of the heat shock response, HSF1. We find that, under normal conditions, HSF1 function is highly similar in cells carrying either wild-type or mutant Htt. However, polyQ-expanded Htt severely blunts the HSF1-mediated stress response. Surprisingly, we find that the HSF1 targets most affected upon stress are not directly associated with proteostasis, but with cytoskeletal binding, focal adhesion and GTPase activity. Our data raise the intriguing hypothesis that the accumulated damage from life-long impairment in these stress responses may contribute significantly to the etiology of Huntington's disease.National Institutes of Health (U.S.) (Grant R24 DK-090963)National Institutes of Health (U.S.) (Grant R01-GM089903)National Institutes of Health (U.S.) (Grant P30-ES002109)National Science Foundation (U.S.) (Award DB1-0821391

Defective Sphingosine-1-phosphate metabolism is a druggable target in Huntington's disease

Huntington's disease is characterized by a complex and heterogeneous pathogenic profile. Studies have shown that disturbance in lipid homeostasis may represent a critical determinant in the progression of several neurodegenerative disorders. The recognition of perturbed lipid metabolism is only recently becoming evident in HD. In order to provide more insight into the nature of such a perturbation and into the effect its modulation may have in HD pathology, we investigated the metabolism of Sphingosine-1-phosphate (S1P), one of the most important bioactive lipids, in both animal models and patient samples. Here, we demonstrated that S1P metabolism is significantly disrupted in HD even at early stage of the disease and importantly, we revealed that such a dysfunction represents a common denominator among multiple disease models ranging from cells to humans through mouse models. Interestingly, the in vitro anti-apoptotic and the pro-survival actions seen after modulation of S1P-metabolizing enzymes allows this axis to emerge as a new druggable target and unfolds its promising therapeutic potential for the development of more effective and targeted interventions against this incurable condition

Proteomics

Gene expression analyses of embryonic stem cells (ESCs) will help to uncover or further define signaling pathways and molecular mechanisms involved in the maintenance of self-renewal and pluripotency. We employed a 2-DE-based proteomics approach to analyze human ESC line, Royan H5, in undifferentiated cells and different stages of spontaneous differentiation (days 3, 6, 12, and 20) by embryoid body formation. Out of 945 proteins reproducibly detected on gels, the expression of 96 spots changed during differentiation. Using MS, 87 ESC-associated proteins were identified including several proteins involved in cell proliferation, cell apoptosis, transcription, translation, mRNA processing, and protein folding. Transcriptional changes accompanying differentiation of Royan H5 were also analyzed using microarrays. We developed a comprehensive data set that shows the use of human ESC lines in vitro to mimic gastrulation and organogenesis. Our results showed that proteomics and transcriptomics data are complementary rather than duplicative. Although regulation of many genes during differentiation were observed only at transcript level, modulation of several proteins was revealed only by proteome analysis

APOE4 is Associated with Differential Regional Vulnerability to Bioenergetic Deficits in Aged APOE Mice

The ε4 allele of apolipoprotein E (APOE) is the dominant genetic risk factor for late-onset Alzheimer's disease (AD). However, the reason for the association between APOE4 and AD remains unclear. While much of the research has focused on the ability of the apoE4 protein to increase the aggregation and decrease the clearance of Aβ, there is also an abundance of data showing that APOE4 negatively impacts many additional processes in the brain, including bioenergetics. In order to gain a more comprehensive understanding of APOE4's role in AD pathogenesis, we performed a transcriptomics analysis of APOE4 vs. APOE3 expression in the entorhinal cortex (EC) and primary visual cortex (PVC) of aged APOE mice. This study revealed EC-specific upregulation of genes related to oxidative phosphorylation (OxPhos). Follow-up analysis utilizing the Seahorse platform showed decreased mitochondrial respiration with age in the hippocampus and cortex of APOE4 vs. APOE3 mice, but not in the EC of these mice. Additional studies, as well as the original transcriptomics data, suggest that multiple bioenergetic pathways are differentially regulated by APOE4 expression in the EC of aged APOE mice in order to increase the mitochondrial coupling efficiency in this region. Given the importance of the EC as one of the first regions to be affected by AD pathology in humans, the observation that the EC is susceptible to differential bioenergetic regulation in response to a metabolic stressor such as APOE4 may point to a causative factor in the pathogenesis of AD