ABSTRACT
We investigated whether cell proliferation and neurogenesis are altered in R6/2 transgenic Huntington's disease mice. Using bromodeoxyuridine (BrdU), we found a progressive decrease in the number of proliferating cells in the dentate gyrus of R6/2 mice. This reduction was detected in pre-symptomatic mice, and by 11.5 weeks, R6/2 mice had 66% fewer newly born cells in the hippocampus. The results were confirmed by immunohistochemistry for the cell cycle markers Ki-67 and proliferating cell nuclear antigen (PCNA). We did not observe changes in cell proliferation in the R6/2 subventricular zone, indicating that the decrease in cell proliferation is specific for the hippocampus. This decrease corresponded to a reduction in actual hippocampal neurogenesis as assessed by double immunostaining for BrdU and the neuronal marker neuronal nuclei (NeuN) and by immunohistochemistry for the neuroblast marker doublecortin. Reduced hippocampal neurogenesis may be a novel neuropathological feature in R6/2 mice that could be assessed when evaluating potential therapies.
Subject(s)
Cell Proliferation , Hippocampus/growth & development , Hippocampus/metabolism , Huntington Disease/metabolism , Nerve Tissue Proteins/genetics , Neurons/metabolism , Nuclear Proteins/genetics , Animals , Animals, Newborn , Biomarkers/metabolism , Bromodeoxyuridine , Cell Division/genetics , DNA-Binding Proteins , Disease Models, Animal , Doublecortin Domain Proteins , Down-Regulation/genetics , Female , Hippocampus/physiopathology , Humans , Huntingtin Protein , Huntington Disease/genetics , Huntington Disease/physiopathology , Immunohistochemistry , Ki-67 Antigen/metabolism , Male , Mice , Mice, Transgenic , Microtubule-Associated Proteins/metabolism , Nerve Tissue Proteins/metabolism , Neuronal Plasticity/genetics , Neurons/pathology , Neuropeptides/metabolism , Nuclear Proteins/metabolism , Proliferating Cell Nuclear Antigen/metabolism , Stem Cells/metabolismABSTRACT
Overactivation of N-methyl-D-aspartate receptors is known to mediate excitotoxicity due to excessive entry of calcium, leading to the activation of several calcium-dependent enzymes. Calpains are calcium-activated proteases that appear to play a role in excitotoxic neuronal death. Several cellular proteins are substrates for these proteases, particularly the N-methyl-D-aspartate receptor. Recently, cleavage of NR2B subunits has been implicated in excitotoxic neurodegeneration in ischemia. In this work, we investigated the proteolysis by calpains of NR2B subunits of the N-methyl-D-aspartate receptor in the hippocampus of epileptic rats. Our results show that cleaved forms of NR2B subunits are formed after status epilepticus, in the same areas of the hippocampus where calpain activation was detected by immunohistochemical staining of calpain-specific spectrin breakdown products.
Subject(s)
Calpain/metabolism , Epilepsy/metabolism , Hippocampus/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Animals , Enzyme Activation/drug effects , Enzyme Activation/physiology , Hippocampus/drug effects , Kainic Acid/pharmacology , Male , Peptide Hydrolases/metabolism , Rats , Rats, WistarABSTRACT
BACKGROUND: Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an expanded CAG repeat in the HD gene. Both excitotoxicity and oxidative stress have been proposed to play important roles in the pathogenesis of HD. Since no effective treatment is available, this study was designed to explore the therapeutic potential of erythropoietin (EPO), a cytokine that has been found to prevent excitotoxicity, and to promote neurogenesis. To avoid the side effects of a raised hematocrit, we used asialoerythropoietin (asialoEPO), a neuroprotective variant of EPO that lacks erythropoietic effects in mice. R6/2 transgenic HD mice were treated with this cytokine from five to twelve weeks of age. RESULTS: We provide new evidence that cell proliferation in the dentate gyrus of the R6/2 hippocampus is reduced by 50% compared to wild-type littermate controls. However, we found that the asialoEPO treatment did not affect the progression of motor symptoms, weight loss or the neuropathological changes. Furthermore, cell proliferation was not enhanced. CONCLUSIONS: We conclude that the chosen protocol of asialoEPO treatment is ineffective in the R6/2 model of HD. We suggest that reduced hippocampal cell proliferation may be an important and novel neuropathological feature in R6 HD mice that could be assessed when evaluating potential therapies.
