No change in progenitor cell proliferation in the hippocampus in Huntington's disease

Increases in cell proliferation in the hippocampus have been robustly demonstrated in animal models of neurodegenerative diseases like Huntington's disease (HD). However, in the subventricular zone, animal models of HD have demonstrated no change in cell proliferation compared to wild types, while in humans there is a distinct increase in cell proliferation in HD cases. Interestingly, there have been no reports on cell proliferation in the human subgranular zone (SGZ) of the hippocampus in HD, despite numerous transgenic mouse models of HD showing decreased proliferation in the SGZ. Furthermore, HD can be divided into those with mainly mood and mainly motor symptomatology. We hypothesized that HD cases with mainly mood symptomatology would show a greater change in hippocampal proliferation, which has previously been implicated in mood disorders such as depression. Therefore, in the current study we examined and compared proliferation in the SGZ in normal vs. HD, HD mood, and HD motor affected cases. However, our results revealed no significant differences in SGZ proliferation between normal and HD cases, and no differences when divided into groups based on mood and motor symptomatology. Our results were confirmed using a range of cell-cycle protein markers and, overall, were comparable with previous studies of the human hippocampus, where very little proliferation was detected in the adult SGZ. These results demonstrate that in humans the SGZ is far less proliferative than the SVZ, and suggests that hippocampal plasticity in humans does not primarily involve cell proliferation.