Neuropeptide Y modifies the disease course in the R6/2 transgenic model of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by progressive neuronal dysfunction and cell loss, especially striatal GABAergic neurons, generating motor, cognitive and affective problems. Although the disease-causing gene is known, the exact mechanism by which it induces its pathological effect remains unknown, and no cure is currently available for this disease. Interestingly, striatal neurons that express neuropeptide Y (NPY) are preferentially spared in HD and the number of such cells is increased in the striatum of HD patients. Furthermore, neurogenesis in the subventricular zone (SVZ) also appears to be up-regulated in HD patients, and previously we also demonstrated in wild-type mice that intracerebroventricular (ICV) NPY promotes SVZ neurogenesis with migration of the newborn cells towards the striatum where they differentiate into GABAergic neurons. Therefore, we sought to determine whether NPY could be of therapeutic benefit in a transgenic mouse model of HD (R6/2) through an action on SVZ neurogenesis. We found that a single ICV injection of NPY in R6/2 mice increased survival time through reduced weight loss as well as having a beneficial effect on motor function as evidenced by improving rotarod performance and reducing paw-clasping. We also demonstrated that the degree of cerebral and striatal atrophy was reduced following such a single NPY injection and that whilst the peptide also increased the number of BrdU-positive cells in the SVZ (but not in the dentate gyrus) of R6/2 mice, this was not sufficient to account for the changes in anatomy and function that we found.. These results suggest that NPY may be of some therapeutic interest in patients with HD, although further work is needed to ascertain exactly how it mediates its beneficial effects.