Single-nuclei transcriptome analysis of Huntington disease iPSC and mouse astrocytes implicates maturation and functional deficits.

Huntington disease (HD) is a neurodegenerative disorder caused by expanded CAG repeats in the huntingtin gene that alters cellular homeostasis, particularly in the striatum and cortex. Astrocyte signaling that establishes and maintains neuronal functions are often altered under pathological conditions. We performed single-nuclei RNA-sequencing on human HD patient-induced pluripotent stem cell (iPSC)-derived astrocytes and on striatal and cortical tissue from R6/2 HD mice to investigate high-resolution HD astrocyte cell state transitions. We observed altered maturation and glutamate signaling in HD human and mouse astrocytes. Human HD astrocytes also showed upregulated actin-mediated signaling, suggesting that some states may be cell-autonomous and human specific. In both species, astrogliogenesis transcription factors may drive HD astrocyte maturation deficits, which are supported by rescued climbing deficits in HD drosophila with NFIA knockdown. Thus, dysregulated HD astrocyte states may induce dysfunctional astrocytic properties, in part due to maturation deficits influenced by astrogliogenesis transcription factor dysregulation.

An altered extracellular matrix-integrin interface contributes to Huntington's disease-associated CNS dysfunction in glial and vascular cells.

Astrocytes and brain endothelial cells are components of the neurovascular unit that comprises the blood-brain barrier (BBB) and their dysfunction contributes to pathogenesis in Huntington's disease (HD). Defining the contribution of these cells to disease can inform cell-type-specific effects and uncover new disease-modifying therapeutic targets. These cells express integrin (ITG) adhesion receptors that anchor the cells to the extracellular matrix (ECM) to maintain the integrity of the BBB. We used HD patient-derived induced pluripotent stem cell (iPSC) modeling to study the ECM-ITG interface in astrocytes and brain microvascular endothelial cells and found ECM-ITG dysregulation in human iPSC-derived cells that may contribute to the dysfunction of the BBB in HD. This disruption has functional consequences since reducing ITG expression in glia in an HD Drosophila model suppressed disease-associated CNS dysfunction. Since ITGs can be targeted therapeutically and manipulating ITG signaling prevents neurodegeneration in other diseases, defining the role of ITGs in HD may provide a novel strategy of intervention to slow CNS pathophysiology to treat HD.

Cooperation of cell adhesion and autophagy in the brain: Functional roles in development and neurodegenerative disease.

Cellular adhesive connections directed by the extracellular matrix (ECM) and maintenance of cellular homeostasis by autophagy are seemingly disparate functions that are molecularly intertwined, each regulating the other. This is an emerging field in the brain where the interplay between adhesion and autophagy functions at the intersection of neuroprotection and neurodegeneration. The ECM and adhesion proteins regulate autophagic responses to direct protein clearance and guide regenerative programs that go awry in brain disorders. Concomitantly, autophagic flux acts to regulate adhesion dynamics to mediate neurite outgrowth and synaptic plasticity with functional disruption contributed by neurodegenerative disease. This review highlights the cooperative exchange between cellular adhesion and autophagy in the brain during health and disease. As the mechanistic alliance between adhesion and autophagy has been leveraged therapeutically for metastatic disease, understanding overlapping molecular functions that direct the interplay between adhesion and autophagy might uncover therapeutic strategies to correct or compensate for neurodegeneration.

Childbearing vs. clinical trial participation: is it one or the other?

Recent advances have shed light on the importance of early therapeutic intervention for neurodegenerative diseases. Primary prevention trials present a potential disease-modifying strategy for pre-symptomatic patients of autosomal dominant neurodegenerative diseases (ADND), such as early onset familial Alzheimer's disease (AD) and Huntington's disease (HD). As trials target earlier disease stages, however, prospective participants face new ethical and logistical challenges, namely childbearing and reproductive health decisions. Since pregnancy is an exclusion criteria for such trials, participants of reproductive age must choose between participating in research and having a family. Such decisions carry significant burdens for ADND patients that if left unaddressed could impact patient well-being and the field as whole. We use our perspective as scientists, advocates, and ADND family members to highlight current shortcomings in the field regarding trial participation and family planning issues for ADND patients and call for the establishment of a normative standard to address these concerns.

Aberrant Development Corrected in Adult-Onset Huntington's Disease iPSC-Derived Neuronal Cultures via WNT Signaling Modulation.

Aberrant neuronal development and the persistence of mitotic cellular populations have been implicated in a multitude of neurological disorders, including Huntington's disease (HD). However, the mechanism underlying this potential pathology remains unclear. We used a modified protocol to differentiate induced pluripotent stem cells (iPSCs) from HD patients and unaffected controls into neuronal cultures enriched for medium spiny neurons, the cell type most affected in HD. We performed single-cell and bulk transcriptomic and epigenomic analyses and demonstrated that a persistent cyclin D1+ neural stem cell (NSC) population is observed selectively in adult-onset HD iPSCs during differentiation. Treatment with a WNT inhibitor abrogates this NSC population while preserving neurons. Taken together, our findings identify a mechanism that may promote aberrant neurodevelopment and adult neurogenesis in adult-onset HD striatal neurons with the potential for therapeutic compensation.

Longitudinal Biochemical Assay Analysis of Mutant Huntingtin Exon 1 Protein in R6/2 Mice.

BACKGROUND: Biochemical analysis of mutant huntingtin (mHTT) aggregation species in HD mice is a common measure to track disease. A longitudinal and systematic study of how tissue processing affects detection of conformers has not yet been reported. Understanding the homeostatic flux of mHTT over time and under different processing conditions would aid in interpretation of pre-clinical assessments of disease interventions. OBJECTIVE: Provide a systematic evaluation of tissue lysis methods and molecular and biochemical assays in parallel with behavioral readouts in R6/2 mice to establish a baseline for HTT exon1 protein accumulation. METHODS: Established biochemical methods were used to process tissue from R6/2 mice of specific ages following behavior tasks. Aggregation states and accumulation of mHTT exon 1 protein were evaluated using multiple break and assay methods to determine potential conformational flux assay specificity in detection of mHTT species, and tissue specificity of conformers. RESULTS: Detection of mHTT exon 1 protein species varied based on biochemical processing and analysis providing a baseline for subsequent studies in R6/2 mice. Insoluble, high molecular weight species of mHTT exon 1 protein increased and tracked with onset of behavioral impairments in R6/2 mice using multiple assay methods. CONCLUSIONS: Conformational flux from soluble monomer to high molecular weight, insoluble species of mHTT exon 1 protein was generally consistent for multiple assay methods throughout R6/2 disease progression; however, the results support the use of multiple biochemical techniques to detect mHTT exon 1 protein species for preclinical assessments in HD mouse models expressing mHTT exon 1 protein.

PRMT8 demonstrates variant-specific expression in cancer cells and correlates with patient survival in breast, ovarian and gastric cancer.

Recent emphasis has been placed on the role of epigenetic regulators and epigenetic marks as biomarkers for cancer diagnosis and prognosis, and as therapeutic targets for treatment. One such class of regulators is the protein arginine methyltransferase (PRMT) family. The present study examined available curated data regarding the expression and alteration of one of the least studied PRMT family members, PRMT8, in various types of cancer and cancer cell lines. Publicly available cancer data on PRMT8 expression were examined using the Human Protein Atlas and the Kaplan-Meier Plotter, and reverse transcription-polymerase chain reaction was used to screen a selection of human cell lines for variant-specific PRMT8 expression. High levels of PRMT8 expression in breast, ovarian and cervical cancer was observed. Additionally, in patients with breast and ovarian cancer, high PRMT8 expression was correlated with increased patient survival, whereas in gastric cancer, high PRMT8 expression was correlated with decreased patient survival. The present study also investigated the expression of PRMT8 variant 2, a novel transcript variant recently identified in our laboratory, in various cancer cell lines. Variant-specific expression of PRMT8 in numerous distinct cancer cell lines derived from different tissues, including the expression of the novel PRMT8 variant 2 in U87MG glioblastoma cells was demonstrated. The present study proposes the possibility of PRMT8 as a cancer biomarker, based on the high level of PRMT8 expression in various types of cancer, particularly in tissues that would not normally be expected to express PRMT8, and on the correlation of PRMT8 and patient lifespan in several cancer types. Variant-specific expression of PRMT8 in diverse cancer cell lines suggests the possibility of alternate PRMT8 isoforms to have diverse effects on cancer cell phenotypes.