Neurogenesis in Huntington's disease: can studying adult neurogenesis lead to the development of new therapeutic strategies?

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an unstable expansion of CAG repeats in the HD gene. The symptoms include cognitive dysfunction and severe motor impairments. The neuropathology is characterized by neuronal loss mainly in the striatum and cortex, although other regions including the hippocampus are also affected. In this review we discuss the different mouse models of HD, and how the process of neurogenesis in the dentate gyrus (DG) of the hippocampus and the subventricular zone (SVZ) is affected in each. Deficits in adult hippocampal neurogenesis have been repeatedly shown in different genetic models of HD, raising the possibility that an impairment of the neurogenic process might underlie some of the cognitive deficits associated with this neurodegenerative disorder. On the other hand, an increase in SVZ neurogenesis has been observed in human HD brains while no differences in SVZ cell proliferation have been detected in the mouse models. In this review we will discuss the discrepancies between these findings as well as the several mechanisms that might contribute to a dysregulation of adult neurogenesis in HD. Finally, we will provide an overview of the various therapeutic strategies aimed at stimulating the endogenous neurogenic capacity that have been tested in HD genetic models. Ultimately, the insights obtained from these and future studies will greatly improve our understanding of the cognitive impairment characteristic of HD.