Huntingtin loss in hepatocytes is associated with altered metabolism, adhesion, and liver zonation

Huntington's disease arises from a toxic gain of function in the huntingtin (HTT) gene. As a result, many HTT-lowering therapies are being pursued in clinical studies, including those that reduce HTT RNA and protein expression in the liver. To investigate potential impacts, we characterized molecular, cellular, and metabolic impacts of chronic HTT lowering in mouse hepatocytes. Lifelong hepatocyte HTT loss is associated with multiple physiological changes, including increased circulating bile acids, cholesterol and urea, hypoglycemia, and impaired adhesion. HTT loss causes a clear shift in the normal zonal patterns of liver gene expression, such that pericentral gene expression is reduced. These alterations in liver zonation in livers lacking HTT are observed at the transcriptional, histological, and plasma metabolite levels. We have extended these phenotypes physiologically with a metabolic challenge of acetaminophen, for which the HTT loss results in toxicity resistance. Our data reveal an unexpected role for HTT in regulating hepatic zonation, and we find that loss of HTT in hepatocytes mimics the phenotypes caused by impaired hepatic β-catenin function.

Huntingtin loss in hepatocytes is associated with altered metabolism, adhesion, and liver zonation

Huntington's disease arises from a toxic gain of function in the huntingtin ( HTT ) gene. As a result, many HTT-lowering therapies are being pursued in clinical studies, including those that reduce HTT RNA and protein expression in the liver. To investigate potential impacts, we characterized molecular, cellular, and metabolic impacts of chronic HTT lowering in mouse hepatocytes. Lifelong hepatocyte HTT loss is associated with multiple physiological changes, including increased circulating bile acids, cholesterol and urea, hypoglycemia, and impaired adhesion. HTT loss causes a clear shift in the normal zonal patterns of liver gene expression, such that pericentral gene expression is reduced. These alterations in liver zonation in livers lacking HTT are observed at the transcriptional, histological and plasma metabolite level. We have extended these phenotypes physiologically with a metabolic challenge of acetaminophen, for which the HTT loss results in toxicity resistance. Our data reveal an unexpected role for HTT in regulating hepatic zonation, and we find that loss of HTT in hepatocytes mimics the phenotypes caused by impaired hepatic β-catenin function.

Transcriptional regulatory networks underlying gene expression changes in Huntington's disease

Transcriptional changes occur presymptomatically and throughout Huntington's disease (HD), motivating the study of transcriptional regulatory networks (TRNs) in HD We reconstructed a genome-scale model for the target genes of 718 transcription factors (TFs) in the mouse striatum by integrating a model of genomic binding sites with transcriptome profiling of striatal tissue from HD mouse models. We identified 48 differentially expressed TF-target gene modules associated with age- and CAG repeat length-dependent gene expression changes in Htt CAG knock-in mouse striatum and replicated many of these associations in independent transcriptomic and proteomic datasets. Thirteen of 48 of these predicted TF-target gene modules were also differentially expressed in striatal tissue from human disease. We experimentally validated a specific model prediction that SMAD3 regulates HD-related gene expression changes using chromatin immunoprecipitation and deep sequencing (ChIP-seq) of mouse striatum. We found CAG repeat length-dependent changes in the genomic occupancy of SMAD3 and confirmed our model's prediction that many SMAD3 target genes are downregulated early in HD.

Peripheral huntingtin silencing does not ameliorate central signs of disease in the B6.HttQ111/+ mouse model of Huntington's disease

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disease whose predominant neuropathological signature is the selective loss of medium spiny neurons in the striatum. Despite this selective neuropathology, the mutant protein (huntingtin) is found in virtually every cell so far studied, and, consequently, phenotypes are observed in a wide range of organ systems both inside and outside the central nervous system. We, and others, have suggested that peripheral dysfunction could contribute to the rate of progression of striatal phenotypes of HD. To test this hypothesis, we lowered levels of huntingtin by treating mice with antisense oligonucleotides (ASOs) targeting the murine Huntingtin gene. To study the relationship between peripheral huntingtin levels and striatal HD phenotypes, we utilized a knock-in model of the human HD mutation (the B6.Htt^Q111/+ mouse). We treated mice with ASOs from 2–10 months of age, a time period over which significant HD-relevant signs progressively develop in the brains of Htt^Q111/+ mice. Peripheral treatment with ASOs led to persistent reduction of huntingtin protein in peripheral organs, including liver (64% knockdown), brown adipose (66% knockdown), and white adipose tissues (71% knockdown). This reduction was not associated with alterations in the severity of HD-relevant signs in the striatum of Htt^Q111/+ mice at the end of the study, including transcriptional dysregulation, the accumulation of neuronal intranuclear inclusions, and behavioral changes such as subtle hypoactivity and reduced exploratory drive. These results suggest that the amount of peripheral reduction achieved in the current study does not significantly impact the progression of HD-relevant signs in the central nervous system.

Motivational, proteostatic and transcriptional deficits precede synapse loss, gliosis and neurodegeneration in the B6.HttQ111/+ model of Huntington's disease

We investigated the appearance and progression of disease-relevant signs in the B6.Htt^Q111/+ mouse, a genetically precise model of the mutation that causes Huntington’s disease (HD). We find that B6.Htt^Q111/+ mice are healthy, show no overt signs of central or peripheral inflammation, and no gross motor impairment as late as 12 months of age. Behaviorally, we find that 4–9 month old B6.Htt^Q111/+ mice have normal activity levels and show no clear signs of anxiety or depression, but do show clear signs of reduced motivation. The neuronal density, neuronal size, synaptic density and number of glia is normal in B6.Htt^Q111/+ striatum, the most vulnerable brain region in HD, up to 12 months of age. Despite this preservation of the synaptic and cellular composition of the striatum, we observe clear progressive, striatal-specific transcriptional dysregulation and accumulation of neuronal intranuclear inclusions (NIIs). Simulation studies suggest these molecular endpoints are sufficiently robust for future preclinical studies, and that B6.Htt^Q111/+ mice are a useful tool for modeling disease-modifying or neuroprotective strategies for disease processes before the onset of overt phenotypes.

Clinical effects of oleoresin capsicum (pepper spray) on the human cornea and conjunctiva

OBJECTIVE

To evaluate the effects of oleoresin capsicum (OC) on the human cornea and conjunctiva and to test the effectiveness of topical anesthetics for relief of pain.

DESIGN

Prospective, randomized clinical trial.

METHODS

Forty-seven subjects were examined before and at 10 minutes and 1 hour after exposure to pepper spray during a training exercise. Eleven subjects were reexamined at 1 week after exposure. A short, subjective questionnaire was given asking subjects to rate their pain, blurring of vision, and tearing. After exposure, subjects were randomly given a placebo, a topical nonsteroidal antiinflammatory agent, or a topical anesthetic.

MAIN OUTCOME MEASURES

Visual acuity and corneal sensitivity with a Cochet-Bonnet aesthesiometer (scale of 1-6 cm) was measured and the eyes were examined with a portable slit lamp using fluorescein. Symptoms of pain, blurring of vision, and tearing were recorded in a ranking of 0 to 10.

RESULTS

Visual acuity was unaffected by exposure to pepper spray. Corneal sensitivity was reduced from a pretest mean of 5.7 cm to a posttest mean of 0.6 cm 10 minutes after exposure. At 1 hour, the mean corneal sensitivity had recovered to 2.9 cm. Twenty-one percent of eyes had evidence of punctate epithelial erosions, but no corneal abrasions were found. All subjects reported significant pain, blurring of vision, and tearing at 10 minutes that was much improved by 1 hour. Topical flurbiprofen 0.03% improved symptoms in two of 11 subjects, whereas topical proparacaine hydrochloride 0.5% improved symptoms in 16 of 29 eyes. At 1 week after exposure, corneal sensation returned to baseline, and no corneal abnormalities were noted.

CONCLUSIONS

The predominant symptom after exposure to OC was pain. Topical flurbiprofen was not helpful in reducing symptoms of exposure, whereas topical proparacaine was effective in relieving pain in most subjects. Corneal sensitivity was dramatically reduced at 10 minutes after exposure and was improved after 1 hour. At 1 week, corneal sensation had returned to normal, as had slit-lamp appearance on all subjects examined.