Multiple phenotypes in Huntington disease mouse neural stem cells

Neural stem (NS) cells are a limitless resource, and thus superior to primary neurons for drug discovery provided they exhibit appropriate disease phenotypes. Here we established NS cells for cellular studies of Huntington's disease (HD). HD is a heritable neurodegenerative disease caused by a mutation resulting in an increased number of glutamines (Q) within a polyglutamine tract in Huntingtin (Htt). NS cells were isolated from embryonic wild-type (Htt7Q/7Q) and “knock-in” HD (Htt140Q/140Q) mice expressing full-length endogenous normal or mutant Htt. NS cells were also developed from mouse embryonic stem cells that were devoid of Htt (Htt-/-), or knock-in cells containing human exon1 with an N-terminal FLAG epitope tag and with 7Q or 140Q inserted into one of the mouse alleles (HttF7Q/7Q and HttF140Q/7Q). Compared to Htt7Q/7Q NS cells, HD Htt140Q/140Q NS cells showed significantly reduced levels of cholesterol, increased levels of reactive oxygen species (ROS), and impaired motility. The heterozygous HttF140Q/7Q NS cells had increased ROS and decreased motility compared to HttF7Q/7Q. These phenotypes of HD NS cells replicate those seen in HD patients or in primary cell or in vivo models of HD. Huntingtin “knock-out” NS cells (Htt-/-) also had impaired motility, but in contrast to HD cells had increased cholesterol. In addition, Htt140Q/140Q NS cells had higher phospho-AKT/AKT ratios than Htt7Q/7Q NS cells in resting conditions and after BDNF stimulation, suggesting mutant htt affects AKT dependent growth factor signaling. Upon differentiation, the Htt7Q/7Q and Htt140Q/140Q generated numerous BetaIII-Tubulin- and GABA-positive neurons; however, after 15 days the cellular architecture of the differentiated Htt140Q/140Q cultures changed compared to Htt7Q/7Q cultures and included a marked increase of GFAP-positive cells. Our findings suggest that NS cells expressing endogenous mutant Htt will be useful for study of mechanisms of HD and drug discovery.