Haploinsufficiency of tau decreases survival of the mouse model of Niemann-Pick disease type C1 but does not alter tau phosphorylation.

Niemann-Pick C1 (NPC1) mouse models show neurofibrillary tangles as do human patients. A previous study in NPC1/tau double-null mutant mice showed that tau knockout nulls and heterozygotes unexpectedly had decreased survival when compared with NPC1 single mutants (Pacheco et al., Hum Molec Genetics 18:956-965, 2009). This was done in a null model of NPC1 (Npc1). We have extended these results to a hypomorphic model (Npc1) and additionally studied tau phosphorylation, which has not been previously done in a tau heterozygote. As before, NPC1/tau double-mutant mice had shortened survival when compared with the NPC1 single mutant. Tau dosage was not affected by the Npc1 mutation. The increased phosphorylation of tau-ser396 previously noted in NPC1 mouse models was also present, but unaffected by the tau knockout, indicating that changes in tau phosphorylation are not the cause of decreased survival in NPC1/tau double mutants. Thus, the reason for shortened survival of NPC1 mouse models with concomitant tau haploinsufficiency is uncertain.