ly-379268 and Huntington-Disease

Topics: Amino Acids; Animals; Bridged Bicyclo Compounds, Heterocyclic; Female; Hand Strength; Heterozygote; Huntington Disease; Male; Mice; Mice, Transgenic; Psychomotor Performance; Receptors, Metabotropic Glutamate

We have found that daily subcutaneous injection with a maximum tolerated dose of the mGluR2/3 agonist LY379268 (20 mg/kg) beginning at 4 weeks of age dramatically improves the motor, neuronal and neurochemical phenotype in R6/2 mice, a rapidly progressing transgenic model of Huntington's disease (HD). We also previously showed that the benefit of daily LY379268 in R6/2 mice was associated with increases in corticostriatal brain-derived neurotrophic factor (BDNF), and in particular was associated with a reduction in enkephalinergic striatal projection neuron loss. In the present study, we show that daily LY379268 also rescues expression of BDNF by neurons of the thalamic parafascicular nucleus in R6/2 mice, which projects prominently to the striatum, and this increase too is linked to the rescue of enkephalinergic striatal neurons. Thus, LY379268 may protect enkephalinergic striatal projection neurons from loss by boosting BDNF production and delivery via both the corticostriatal and thalamostriatal projection systems. These results suggest that chronic treatment with mGluR2/3 agonists may represent an approach for slowing enkephalinergic neuron loss in HD, and perhaps progression in general.

Topics: Amino Acids; Animals; Brain-Derived Neurotrophic Factor; Bridged Bicyclo Compounds, Heterocyclic; Corpus Striatum; Disease Models, Animal; Female; Humans; Huntingtin Protein; Huntington Disease; Injections, Subcutaneous; Intralaminar Thalamic Nuclei; Male; Mice; Mice, Transgenic; Neurons; Receptors, Metabotropic Glutamate

Excitotoxic injury to striatum by dysfunctional cortical input or aberrant glutamate uptake may contribute to Huntington's disease (HD) pathogenesis. Since corticostriatal terminals possess mGluR2/3 autoreceptors, whose activation dampens glutamate release, we tested the ability of the mGluR2/3 agonist LY379268 to improve the phenotype in R6/2 HD mice with 120-125 CAG repeats. Daily subcutaneous injection of a maximum tolerated dose (MTD) of LY379268 (20mg/kg) had no evident adverse effects in WT mice, and diverse benefits in R6/2 mice, both in a cohort of mice tested behaviorally until the end of R6/2 lifespan and in a cohort sacrificed at 10weeks of age for blinded histological analysis. MTD LY379268 yielded a significant 11% increase in R6/2 survival, an improvement on rotarod, normalization and/or improvement in locomotor parameters measured in open field (activity, speed, acceleration, endurance, and gait), a rescue of a 15-20% cortical and striatal neuron loss, normalization of SP striatal neuron neurochemistry, and to a lesser extent enkephalinergic striatal neuron neurochemistry. Deficits were greater in male than female R6/2 mice, and drug benefit tended to be greater in males. The improvements in SP striatal neurons, which facilitate movement, are consistent with the improved movement in LY379268-treated R6/2 mice. Our data indicate that mGluR2/3 agonists may be particularly useful for ameliorating the morphological, neurochemical and motor defects observed in HD.

Topics: Amino Acids; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cerebral Cortex; Cohort Studies; Disease Models, Animal; Female; Huntington Disease; Male; Mice; Mice, Transgenic; Motor Activity; Neostriatum; Neurons; Receptors, Metabotropic Glutamate; Sex Factors

We have found that daily subcutaneous injection with a maximum tolerated dose (MTD) of the mGluR2/3 agonist LY379268 (20mg/kg) beginning at 4 weeks dramatically improves the phenotype in R6/2 mice. For example, we observed normalization of motor function in distance traveled, speed, the infrequency of pauses, and the ability to locomote in a straight line, and a rescue of a 15-20% striatal neuron loss at 10 weeks. As acute LY379268 treatment is known to increase cortical BDNF production, and BDNF is known to be beneficial for striatal neurons, we investigated if the benefit of daily LY379268 in R6/2 mice for striatal projection neurons was associated with increases in corticostriatal BDNF, with assessments done at 10 weeks of age after daily MTD treatment since the fourth week of life. We found that LY379268 increased BDNF expression in layer 5 neurons in motor cortex, which project to striatum, partly rescued a preferential loss of enkephalinergic striatal neurons, and enhanced substance P (SP) expression by SP striatal projection neurons. The enhanced survival of enkephalinergic striatal neurons was correlated with the cortical BDNF increase, but the enhanced SP expression by SP striatal neurons was not. Thus, LY379268 may protect the two main striatal projection neuron types by different mechanisms, enkephalinergic neurons by the trophic benefit of BDNF, and SP neurons by a mechanism not involving BDNF. The SP neuron benefit may perhaps instead involve the anti-excitotoxic action of mGluR2/3 receptor agonists.

Topics: Amino Acids; Animals; Brain-Derived Neurotrophic Factor; Bridged Bicyclo Compounds, Heterocyclic; Corpus Striatum; Disease Models, Animal; Female; Huntington Disease; In Situ Hybridization; Male; Mice; Neurons; Neuroprotective Agents; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction

A defective expression or activity of neurotrophic factors, such as brain- and glial-derived neurotrophic factors, contributes to neuronal damage in Huntington's disease (HD). Here, we focused on transforming growth factor-β (TGF-β(1) ), a pleiotropic cytokine with an established role in mechanisms of neuroprotection. Asymptomatic HD patients showed a reduction in TGF-β(1) levels in the peripheral blood, which was related to trinucleotide mutation length and glucose hypometabolism in the caudate nucleus. Immunohistochemical analysis in post-mortem brain tissues showed that TGF-β(1) was reduced in cortical neurons of asymptomatic and symptomatic HD patients. Both YAC128 and R6/2 HD mutant mice showed a reduced expression of TGF-β(1) in the cerebral cortex, localized in neurons, but not in astrocytes. We examined the pharmacological regulation of TGF-β(1) formation in asymptomatic R6/2 mice, where blood TGF-β(1) levels were also reduced. In these R6/2 mice, both the mGlu2/3 metabotropic glutamate receptor agonist, LY379268, and riluzole failed to increase TGF-β(1) formation in the cerebral cortex and corpus striatum, suggesting that a defect in the regulation of TGF-β(1) production is associated with HD. Accordingly, reduced TGF-β(1) mRNA and protein levels were found in cultured astrocytes transfected with mutated exon 1 of the human huntingtin gene, and in striatal knock-in cell lines expressing full-length huntingtin with an expanded glutamine repeat. Taken together, our data suggest that serum TGF-β(1) levels are potential biomarkers of HD development during the asymptomatic phase of the disease, and raise the possibility that strategies aimed at rescuing TGF-β(1) levels in the brain may influence the progression of HD.

Topics: Adult; Aged; Amino Acids; Animals; Astrocytes; Blotting, Western; Brain; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Female; Humans; Huntingtin Protein; Huntington Disease; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Middle Aged; Mutation; Nerve Tissue Proteins; Nuclear Proteins; Positron-Emission Tomography; Postmortem Changes; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction; Time Factors; Transforming Growth Factor beta1; Young Adult

Chronic glutamate mediated excitotoxicity has been suggested to contribute to the pathogenesis of Huntington's disease (HD). Both, inhibition of glutamate release through stimulation of presynaptic metabotropic glutamate receptor (mGluR) 2 and blockade of postsynaptic mGluR5 have been demonstrated to be neuroprotective against excitotoxicity. R6/2 HD transgenic mice which express an expanded CAG triplet repeat serve as a well-characterized mouse model for HD with progressing neurological abnormalities and limited survival. We treated R6/2 HD transgenic mice with either the mGluR2 agonist LY379268 (1.2 mg/kg) or with the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) (100 mg/kg) orally from a presymptomatic stage until death to investigate their potential disease modifying effects. We found that survival time in both the MPEP treated mice and the LY379268 treated mice was significantly increased in comparison to placebo treated transgenic controls (14.87+/-0.14 and 14.22+/-0.11 weeks versus 12.87+/-0.11 weeks, respectively). Additionally, the progressive decline in motor coordination of HD transgenic mice as tested with the rotarod test was significantly attenuated in MPEP- but not in LY379268-treated mice. Early pathological hyperactivity, which can be found in placebo treated HD transgenic mice, was significantly attenuated by both MPEP and LY379268 treatment. Immunohistologial examination of HD characteristic neuronal intranuclear inclusion (NII), however, demonstrated no effect on NII formation by either of the treatments applied. These data suggest that inhibition of glutamate neurotransmission via specific interaction with mGluRs might be interesting for both inhibition of disease progression as well as early symptomatic treatment in HD.

Topics: Amino Acids; Animals; Bridged Bicyclo Compounds, Heterocyclic; Disease Models, Animal; Disease Progression; Female; Huntington Disease; Male; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate