An expanded polyglutamine domain in huntingtin underlies the pathogenic events in Huntington disease (HD), characterized by chorea, dementia and severe weight loss, culminating in death. Transglutaminase (TGase) may be critical in the pathogenesis, via cross-linking huntingtin. Administration of the TGase competitive inhibitor, cystamine, to transgenic mice expressing exon 1 of huntingtin containing an expanded polyglutamine repeat, altered the course of their HD-like disease. Cystamine given intraperitoneally entered brain where it inhibited TGase activity. When treatment began after the appearance of abnormal movements, cystamine extended survival, reduced associated tremor and abnormal movements and ameliorated weight loss. Treatment did not influence the appearance or frequency of neuronal nuclear inclusions. Unexpectedly, cystamine treatment increased transcription of one of the two genes shown to be neuroprotective for polyglutamine toxicity in Drosophila, dnaj (also known as HDJ1 and Hsp40 in humans and mice, respectively). Inhibition of TGase provides a new treatment strategy for HD and other polyglutamine diseases.

Autism spectrum disorders (ASD) are a group of neurodevelopmental conditions characterized by dysfunction in social interaction, communication and stereotypic behavior. Genetic and environmental factors have been implicated in the development of ASD, but the molecular mechanisms underlying their interaction are not clear. Epigenetic modifications have been suggested as molecular mechanism that can mediate the interaction between the environment and the genome to produce adaptive or maladaptive behaviors. Here, using the Illumina 450 K methylation array we have determined the existence of many dysregulated CpGs in two cortical regions, Brodmann area 10 (BA10) and Brodmann area 24 (BA24), of individuals who had ASD. In BA10 we found a very significant enrichment for genomic areas responsible for immune functions among the hypomethylated CpGs, whereas genes related to synaptic membrane were enriched among hypermethylated CpGs. By comparing our methylome data with previously published transcriptome data, and by performing real-time PCR on selected genes that were dysregulated in our study, we show that hypomethylated genes are often overexpressed, and that there is an inverse correlation between gene expression and DNA methylation within the individuals. Among these genes there were C1Q, C3, ITGB2 (C3R), TNF-α, IRF8 and SPI1, which have recently been implicated in synaptic pruning and microglial cell specification. Finally, we determined the epigenetic dysregulation of the gene HDAC4, and we confirm that the locus encompassing C11orf21/TSPAN32 has multiple hypomethylated CpGs in the autistic brain, as previously demonstrated. Our data suggest a possible role for epigenetic processes in the etiology of ASD.

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The protein huntingtin (htt), aggregated in neuronal nuclear inclusions, is pathognomonic of Huntington's disease (HD). Constructs, translated in vitro from the N terminus of htt, containing either polyQ23 from a normal individual, or polyQ41 or polyQ67 from an HD patient, were all soluble. Transglutaminase (TGase) crosslinked these proteins, and the aggregations did not have the staining properties of amyloid. More TGase-catalyzed aggregates formed when the polyglutamine domain of htt exceeded the pathologic threshold of polyQ36. Furthermore, shorter htt constructs, containing 135 aa or fewer, formed more aggregates than did larger htt constructs. TGase activity in the HD brain was increased compared with the control, with notable increases in cell nuclei. The increased TGase activity was brain specific. In lymphoblastoid cells from HD patients, TGase activity was decreased. TGase-mediated crosslinking of htt may be involved in the formation of the nonamyloidogenic nuclear inclusions found in the HD brain. The staining properties of nuclear inclusions in the HD brain revealed that they were not amyloid.The protein huntingtin (htt) contains a stretch of glutamines near its N terminus. When the length of the polyQ domain exceeds 36Q in htt, the lethal neurological disease called Huntington's disease (HD) occurs. Aggregated htt in the nuclei of neurons and in dystrophic neurites in the brain are the pathologic hallmarks of HD (1-3), although it remains unknown whether the aggregates are deleterious for neurons, or whether they represent an adaptive response to a desperate situation. Two hypotheses dominate our perception of how htt is aggregated: Perutz et al. (4) proposed that polyglutamine domains on neighboring proteins organize themselves into polar zippers. Such aggregations have the classic properties of amyloid (5, 6). Green proposed (7,8), in the second hypothesis, that TGase polymerizes htt.In Vitro Studies on Polar Zipper Formation with htt and PolyQ Peptides. Synthetic polyglutamine polymers, containing polyQ domains far shorter than the pathologic threshold of 36Q in HD, form polar zippers and aggregate in an aqueous medium (9). Polymerized htt is not seen in the brains of normal individuals with htt Ͻ Q36. The polar zipper hypothesis cannot easily explain this. Scherzinger et al. (1) reported that there is a threshold for polar zipper formation, and that aggregates form in vitro only when the polyQ domain is above 36Q. They showed that glutathione S-transferase (GST) fusion proteins from exon 1 of htt, with Q Ͼ 36, aggregate, but only after proteolytic cleavage of the GST domain (1).In Vitro Studies with htt and TGase. Kahlem et al. (8) studied guinea pig TGase and TGase isolated from rat brain; they showed that htt isolated from the brains of juvenile HD patients could be crosslinked in vitro into aggregates. To date, no one has reported on the activity of TGase in the HD brain, on the biophysical properties of the aggregates catalyzed by TGase, or on the optical properties of inclusions in...