Huntington's Disease (HD) is caused by an expansion of a polyglutamine tract within the huntingtin (htt) protein. Pathogenesis in HD appears to include the cytoplasmic cleavage of htt and release of an amino-terminal fragment capable of nuclear localization. We have investigated potential consequences to nuclear function of a pathogenic amino-terminal region of htt (httex1p) including aggregation, protein–protein interactions, and transcription. httex1p was found to coaggregate with p53 in inclusions generated in cell culture and to interact with p53 in vitro and in cell culture. Expanded httex1p represses transcription of the p53-regulated promoters, p21 ^WAF1/CIP1 and MDR-1 . httex1p was also found to interact in vitro with CREB-binding protein (CBP) and mSin3a, and CBP to localize to neuronal intranuclear inclusions in a transgenic mouse model of HD. These results raise the possibility that expanded repeat htt causes aberrant transcriptional regulation through its interaction with cellular transcription factors which may result in neuronal dysfunction and cell death in HD.

A truncated form of the Huntington's disease (HD) protein that contains the polyglutamine repeat, Httex1p, causes HD-like phenotypes in multiple model organisms. Molecular signatures of pathogenesis appear to involve distinct domains within this polypeptide. We studied the contribution of each domain, singly or in combination, to sub-cellular localization, aggregation and intracellular Ca ²⁺ ([Ca ²⁺ ] _i ) dynamics in cells. We demonstrate that sub-cellular localization is most strongly influenced by the first 17 amino acids, with this sequence critically controlling Httex1p mitochondrial localization and also promoting association with the endoplasmic reticulum (ER) and Golgi. This domain also enhances the formation of visible aggregates and together with the expanded polyQ repeat acutely disrupts [Ca ²⁺ ] _i levels in glutamate-challenged PC12 cells. Isolated cortical mitochondria incubated with Httex1p resulted in uncoupling and depolarization of these organelles, further supporting the idea that Httex1p-dependent mitochondrial dysfunction could be instrumental in promoting acute Ca ²⁺ dyshomeostasis. Interestingly, neither mitochondrial nor ER associations seem to be required to promote long-term [Ca ²⁺ ] _i dyshomeostasis.

Brain microvascular endothelial cells (BMECs) are an essential component of the blood-brain barrier (BBB) that shields the brain against toxins and immune cells. While BBB dysfunction exists in neurological disorders, including Huntington's disease (HD), it is not known if BMECs themselves are functionally compromised to promote BBB dysfunction. Further, the underlying mechanisms of BBB dysfunction remain elusive given limitations with mouse models and post-mortem tissue to identify primary deficits. We undertook a transcriptome and functional analysis of human induced pluripotent stem cell (iPSC)-derived BMECs (iBMEC) from HD patients or unaffected controls. We demonstrate that HD iBMECs have intrinsic abnormalities in angiogenesis and barrier properties, as well as in signaling pathways governing these processes. Thus, our findings provide an iPSC-derived BBB model for a neurodegenerative disease and demonstrate autonomous neurovascular deficits that may underlie HD pathology with implications for therapeutics and drug delivery.

The Huntington's disease (HD) induced pluripotent stem cell (iPSC) consortium describe the combined use of differentiated patient-derived iPSCs and systems biology to discover underlying mechanisms in HD. They identify neurodevelopmental deficits in HD cells that can be corrected in cells and in vivo with a small molecule. Neural cultures derived from Huntington's disease (HD) patient-derived induced pluripotent stem cells were used for 'omics' analyses to identify mechanisms underlying neurodegeneration. RNA-seq analysis identified genes in glutamate and GABA signaling, axonal guidance and calcium influx whose expression was decreased in HD cultures. One-third of gene changes were in pathways regulating neuronal development and maturation. When mapped to stages of mouse striatal development, the profiles aligned with earlier embryonic stages of neuronal differentiation. We observed a strong correlation between HD-related histone marks, gene expression and unique peak profiles associated with dysregulated genes, suggesting a coordinated epigenetic program. Treatment with isoxazole-9, which targets key dysregulated pathways, led to amelioration of expanded polyglutamine repeat-associated phenotypes in neural cells and of cognitive impairment and synaptic pathology in HD model R6/2 mice. These data suggest that mutant huntingtin impairs neurodevelopmental pathways that could disrupt synaptic homeostasis and increase vulnerability to the pathologic consequence of expanded polyglutamine repeats over time.

Several dominant, late-onset neurodegenerative diseases (e.g. Huntington’s disease) are caused by expansion of polyglutamine (polyQ) repeats within specific proteins. The diverse, yet overlapping, pathology of these diseases could be due to novel deleterious functions unique to each protein or to a common pathophysiology mediated by the long polyQ chains themselves. By engineering Drosophila to express different polyQ peptides, we find that expanded polyQ chains alone are intrinsically cytotoxic and cause neuronal degeneration and early adult death. We further find that this intrinsic toxicity is dependent on cell type and polyQ length and that the inclusion of other amino acids modifies and reduces toxicity. This is the first in vivo evidence that polyQs, when removed from their disease gene context, cause neurotoxicity. These studies provide a basis for understanding the diverse clinical presentations in terms of the intrinsic cytotoxic effect of polyQ peptides being modulated by protein context. Parallel experiments in which cytotoxic polyQ expansions were engineered into Dishevelled, a Drosophila protein containing a naturally occurring polyQ tract, strongly suggest that the effect of a toxic polyQ peptide can be neutralized by protein context. This animal model provides a simple and effective means of screening for therapeutics that relieves the polyQ-induced lethality, independent of any particular disease gene. By quantifying the degree of lethality in several transgenic lines, we have identified a number of genetically modified strains that are suitable for eventual testing of compounds or genes that ameliorate the pathology of polyQ peptides.

Answer ALS is a biological and clinical resource of patient-derived, induced pluripotent stem (iPS) cell lines, multi-omic data derived from iPS neurons and longitudinal clinical and smartphone data from over 1,000 patients with ALS. This resource provides population-level biological and clinical data that may be employed to identify clinical–molecular–biochemical subtypes of amyotrophic lateral sclerosis (ALS). A unique smartphone-based system was employed to collect deep clinical data, including fine motor activity, speech, breathing and linguistics/cognition. The iPS spinal neurons were blood derived from each patient and these cells underwent multi-omic analytics including whole-genome sequencing, RNA transcriptomics, ATAC-sequencing and proteomics. The intent of these data is for the generation of integrated clinical and biological signatures using bioinformatics, statistics and computational biology to establish patterns that may lead to a better understanding of the underlying mechanisms of disease, including subgroup identification. A web portal for open-source sharing of all data was developed for widespread community-based data analytics.