ABSTRACT
Huntington's disease (HD) is a late onset neurodegenerative disorder caused by a CAG/polyglutamine (polyQ) repeat expansion. PolyQ aggregates can be detected in the nuclei and processes of neurons in HD patients and mouse models prior to the onset of symptoms. The misfolding and aggregation pathway is an important therapeutic target. To better test the efficacy of aggregation inhibitors, we have developed an organotypic slice culture system. We show here that the formation of polyQ aggregates in hippocampal slices established from the R6/2 mouse follows the same prescribed sequence as occurs in vivo. Using this assay, we show that Congo red and chrysamine G can modulate aggregate formation, but show complex dose-response curves. Oral administration of creatine has been shown to delay the onset of all aspects of the phenotype and neuropathology in R6/2 mice. We show here that creatine can similarly inhibit aggregate formation in the slice culture assay.
Subject(s)
Hippocampus/drug effects , Huntington Disease/drug therapy , Neurons/drug effects , Neuroprotective Agents/pharmacology , Peptides/drug effects , Protein Folding , Trinucleotide Repeat Expansion/drug effects , Animals , Benzoates/pharmacology , Biphenyl Compounds/pharmacology , Cells, Cultured , Coloring Agents/pharmacology , Congo Red/pharmacology , Creatine/pharmacology , Cysteine Endopeptidases/drug effects , Cysteine Endopeptidases/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Drug Evaluation, Preclinical , Energy Metabolism/drug effects , Energy Metabolism/physiology , Female , Hippocampus/metabolism , Hippocampus/pathology , Huntingtin Protein , Huntington Disease/genetics , Huntington Disease/metabolism , Immunohistochemistry , Male , Mice , Mice, Transgenic , Multienzyme Complexes/drug effects , Multienzyme Complexes/metabolism , Nerve Tissue Proteins/drug effects , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Neurons/metabolism , Neurons/pathology , Nuclear Proteins/drug effects , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Organ Culture Techniques , Peptides/genetics , Peptides/metabolism , Proteasome Endopeptidase Complex , Trinucleotide Repeat Expansion/genetics , Ubiquitin/drug effects , Ubiquitin/genetics , Ubiquitin/metabolismABSTRACT
A transgenic mouse containing the first exon of the human Huntington's disease (HD) gene has revealed a variety of behavioral and pathophysiological anomalies reminiscent of certain aspects of human Huntington's disease (HD). The present study has found that expression of the extracellular matrix glycoprotein tenascin-C appears to be unaffected in astroglial cells in wild-type and R6/2 transgenic mice that express the mutant huntingtin protein but that it is conspicuously absent in two neuronal populations within the cerebral cortex and thalamus of the R6/2 mice. Loss of tenascin-C expression begins between the fourth and eighth postnatal weeks, coincidental with the onset of abnormal behavioral phenotype and the appearance of intranuclear inclusion bodies and neuropil aggregates. By 12 weeks, R6/2 mice exhibit a complete absence of tenascin-C neuronal immunolabeling, a disappearance of cRNA probe-positive neurons across discrete cytoarchitectonic regions of the dorsal thalamus (e.g., the ventromedial, parafascicular, lateral posterior, and posterior thalamic groups) and frontal cortex, and an accompanying thalamic astrogliosis. The loss of neuronal tenascin-C expression includes structures that are known to send converging excitatory axonal projections to the caudate-putamen, the structure that is most at risk for neurodegeneration in HD. Altered neuronal expression of tenascin-C in R6/2 mice implicates altered transcriptional activities of the mutant huntingtin protein. The abnormal biochemistry and possibly abnormal activity of thalamostriate and corticostriate projection neurons may also affect abnormal neuronal activities in their primary connectional target, the neostriatum, which is severely compromised in HD.
Subject(s)
Cerebral Cortex/physiology , Huntington Disease/physiopathology , Mice, Knockout/physiology , Tenascin/genetics , Thalamus/physiology , Animals , Brain Chemistry/genetics , Cerebral Cortex/cytology , Disease Models, Animal , Exons , Female , Gene Expression/physiology , Humans , Immunohistochemistry , In Situ Hybridization , Lac Operon , Male , Mice , Mice, Inbred C57BL , Neuroglia/physiology , Neurons/physiology , RNA, Messenger/analysis , Tenascin/analysis , Thalamus/cytologyABSTRACT
Transgenic mice expressing exon 1 of the human Huntington's disease (HD) gene carrying a 141-157 CAG repeat (line R6/2) develop a progressive neurological phenotype with motor symptoms resembling those seen in HD. We have characterized the motor deficits in R6/2 mice using a battery of behavioral tests selected to measure motor aspects of swimming, fore- and hindlimb coordination, balance, and sensorimotor gating [swimming tank, rotarod, raised beam, fore- and hindpaw footprinting, and acoustic startle/prepulse inhibition (PPI)]. Behavioral testing was performed on female hemizygotic R6/2 transgenic mice (n = 9) and female wild-type littermates (n = 22) between 5 and 14 weeks of age. Transgenic mice did not show an overt behavioral phenotype until around 8 weeks of age. However, as early as 5-6 weeks of age they had significant difficulty swimming, traversing the narrowest square (5 mm) raised beam, and maintaining balance on the rotarod at rotation speeds of 33-44 rpm. Furthermore, they showed significant impairment in prepulse inhibition (an impairment also seen in patients with HD). Between 8 and 15 weeks, R6/2 transgenic mice showed a progressive deterioration in performance on all of the motor tests. Thus R6/2 mice show measurable deficits in motor behavior that begin subtly and increase progressively until death. Our data support the use of R6/2 mice as a model of HD and indicate that they may be useful for evaluating therapeutic strategies for HD, particularly those aimed at reducing the severity of motor symptoms or slowing the course of the disease.