Huntington's disease (HD) is an inherited, neurodegenerative disorder caused by the expansion of a glutamine repeat in the N-terminus of the huntingtin protein. To gain insight into the pathogenesis of HD, we generated transgenic mice that express a cDNA encoding an N-terminal fragment (171 amino acids) of huntingtin with 82, 44 or 18 glutamines. Mice expressing relatively low steady-state levels of N171 huntingtin with 82 glutamine repeats (N171-82Q) develop behavioral abnormalities, including loss of coordination, tremors, hypokinesis and abnormal gait, before dying prematurely. In mice exhibiting these abnormalities, diffuse nuclear labeling, intranuclear inclusions and neuritic aggregates, all immunoreactive with an antibody to the N-terminus (amino acids 1-17) of huntingtin (AP194), were found in multiple populations of neurons. None of these behavioral or pathological phenotypes were seen in mice expressing N171-18Q. These findings are consistent with the idea that N-terminal fragments of huntingtin with a repeat expansion are toxic to neurons, and that N-terminal fragments are prone to form both intranuclear inclusions and neuritic aggregates.

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Dentatorubral and pallidoluysian atrophy (DRPLA) is a member of a family of progressive neurodegenerative diseases caused by polyglutamine repeat expansion. Transgenic mice expressing full-length human atrophin-1 with 65 consecutive glutamines exhibit ataxia, tremors, abnormal movements, seizures, and premature death. These mice accumulate atrophin-1 immunoreactivity and inclusion bodies in the nuclei of multiple populations of neurons. Subcellular fractionation revealed 120 kDa nuclear fragments of mutant atrophin-1, whose abundance increased with age and phenotypic severity. Brains of DRPLA patients contained apparently identical 120 kDa nuclear fragments. By contrast, mice overexpressing atrophin-1 with 26 glutamines were phenotypically normal and did not accumulate the 120 kDa fragments. We conclude that the evolution of neuropathology in DRPLA involves proteolytic processing of mutant atrophin-1 and nuclear accumulation of truncated fragments.

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Although CYP2C8, CYP2C9, and CYP2C19 play an important role in drug biotransformation, factors influencing the expression and activity of these CYP2C P450s in human liver remain largely undefined. We used primary cultures of human hepatocytes from 15 subjects to assess the inducibility of CYP2C enzyme expression by prototypical inducer agents, including rifampicin, dexamethasone, and phenobarbital. After culture for 72 h in serum-free medium on collagen, Western blotting revealed that CYP2C9 was the only CYP2C enzyme expressed at appreciable levels in untreated hepatocytes. Subsequent treatment with 25 M rifampicin for 48 h elicited marked increases in CYP2C8 (700 Ϯ 761%), CYP2C19 (854%), and CYP2C9 (209 Ϯ 176%) protein content versus a 550 Ϯ 170% enhancement of CYP3A4 enzyme levels. Parallel increases in CYP2C mRNAs, measured by Northern blotting and/or RNase protection, were found in rifampicintreated hepatocytes, with CYP2C8, CYP2C9, and CYP2C19 transcripts exhibiting increases of 688 Ϯ 635, 207 Ϯ 49, and 230 Ϯ 60%, respectively, versus an 8.8-fold enhancement of CYP3A4 mRNA levels. Dexamethasone (10 M) treatment enhanced CYP2C8 mRNA (360 Ϯ 100%) and protein (274%) content, although this steroid had less effect on CYP2C9 and CYP2C19 transcripts (23 Ϯ 21% and 21 Ϯ 36%, respectively) and enzyme levels (55 and 143%, respectively). Phenobarbital (100 M) was a powerful inducer of CYP2C9 (850%) and CYP2C19 (735%) mRNA content, and also increased CYP2C8 (610%) and CYP3A4 (205%) transcripts. Our results show that CYP2C enzyme expression in human hepatocytes is highly inducible by rifampicin, dexamethasone, and phenobarbital. Because these xenobiotics are ligands and/or activators of the pregnane X receptor and/or constitutive androstane receptor, such orphan nuclear receptors and their response elements may partake in regulating CYP2C gene expression in humans.

Dentato-rubral and pallido-luysian atrophy (DRPLA) is one of the family of neurodegenerative diseases caused by expansion of a polyglutamine tract. The drpla gene product, atrophin-1, is widely expressed, has no known function or activity, and is found in both the nuclear and cytoplasmic compartments of neurons. Truncated fragments of atrophin-1 accumulate in neuronal nuclei in a transgenic mouse model of DRPLA, and may underlie the disease phenotype.Using the yeast two-hybrid system, we identified ETO/MTG8, a component of nuclear receptor corepressor complexes, as an atrophin-1–interacting protein. When cotransfected into Neuro-2a cells, atrophin-1 and ETO/MTG8 colocalize in discrete nuclear structures that contain endogenous mSin3A and histone deacetylases. These structures are sodium dodecyl sulfate–soluble and associated with the nuclear matrix. Cotransfection of ETO/MTG8 with atrophin-1 recruits atrophin-1 to the nuclear matrix, while atrophin-1 and ETO/MTG8 cofractionate in nuclear matrix preparations from brains of DRPLA transgenic mice. Furthermore, in a cell transfection–based assay, atrophin-1 represses transcription. Together, these results suggest that atrophin-1 associates with nuclear receptor corepressor complexes and is involved in transcriptional regulation.Emerging links between disease-associated polyglutamine proteins, nuclear receptors, translocation-leukemia proteins, and the nuclear matrix may have important repercussions for the pathobiology of this family of neurodegenerative disorders.

Peroxisome proliferator-activated receptor γ is a master regulator of adipocyte differentiation and function. Expression of PPARγ in mammals is regulated by DNA methylation; however, it is currently unknown whether chicken PPARγ expression is regulated by DNA methylation. To enhance our understanding of molecular mechanisms underlying chicken adipose tissue development and adipogenesis, we investigated the promoter methylation status and gene expression of PPARγ gene in Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF). Deoxyribonucleic acid methylation was analyzed by bisulfite sequencing method, and mRNA expression was detected by real-time quantitative real time reverse-transcription polymerase chain reaction (RT-PCR). The analyzed region located from -1,175 to -301 bp upstream of the translation start codon ATG contains 6 CpG dinucleotides, which are located at positions -1,014, -796, -625, -548, -435, and -383 bp, respectively. The results revealed that the 3 CpGs at positions -548, -435, and -383 bp showed differential methylation between the lean and fat chicken lines, but the other 3 CpG sites at positions -1,014, -796, and -625 bp did not. PPARγ gene promoter methylation in both chicken lines decreased with age, and PPARγ promoter methylation levels were significantly higher in lean than fat broilers at 2 wk of age (79.9 to 64.5%; P < 0.0001), at 3 wk of age (66.7 to 58.3%; P < 0.0001), and at 7 wk of age (50.0 to 42.7%; P = 0.0004). Real-time quantitative RT-PCR analysis showed that, negatively correlated with DNA methylation (Pearson's r = -0.653, P = 0.0057), PPARγ expression was increased with age and significantly lower in lean than fat chicken lines at 2, 3, and 7 wk of age (P < 0.0001). In conclusion, our findings suggest that chicken PPARγ is regulated by DNA methylation during adipose tissue development.

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