Dynein Dysfunction Reproduces Age-Dependent Retromer Deficiency: Concomitant Disruption of Retrograde Trafficking Is Required for Alteration in ß-Amyloid Precursor Protein Metabolism.

It is widely accepted that ß-amyloid (Aß) protein plays a pivotal role in Alzheimer disease pathogenesis, and accumulating evidence suggests that endocytic dysfunction is involved in Aß pathology. Retromer, a conserved multisubunit complex, mediates the retrograde transport of numerous kinds of cargo from endosomes to the trans-Golgi network. Several studies have found that retromer deficiency enhances Aß pathology both in vitro and in vivo. Cytoplasmic dynein, a microtubule-based motor protein, mediates minus-end-directed vesicle transport via interactions with dynactin, another microtubule-associated protein that also interacts with retromer. Aging attenuates the dynein-dynactin interaction, and dynein dysfunction reproduces age-dependent endocytic disturbance, resulting in the intracellular accumulation of beta-amyloid precursor protein (APP) and its ß-cleavage products, including Aß. Here, we report that aging itself affects retromer trafficking in cynomolgus monkey brains. In addition, dynein dysfunction reproduces this type of age-dependent retromer deficiency (ie, the endosomal accumulation of retromer-related proteins and APP. Moreover, we found that knockdown of Rab7, Rab9, or Rab11 did not alter endogenous APP metabolism, such as that observed in aged monkey brains and in dynein-depleted cells. These findings suggest that dynein dysfunction can cause retromer deficiency and that concomitant disruption of retrograde trafficking may be the key factor underlying age-dependent Aß pathology.

Enhanced accumulation of tau in doubly transgenic mice expressing mutant betaAPP and presenilin-1.

Abeta amyloidosis and tauopathy are characteristic changes in the brain of Alzheimer's disease. Although much evidence suggests that Abeta deposit is a critical initiation factor, the pathological pathway between Abeta amyloidosis and tau accumulation remains unclear. Tau accumulation was examined in the doubly transgenic mouse (APP-PS) expressing betaAPP(KM670/671NL) (Tg2576) and presenilin-1 L286V (PS-1 L286Vtg). Accelerated and enhanced Abeta amyloid deposits were detected from 8 weeks. Tau accumulation appeared at 4.5 months and markedly increased in dystrophic neurites around Abeta amyloid. Accumulated tau was phosphorylated, conformationally altered, and argyrophilic. Expression of tau and accumulation of sarkosyl-insoluble phosphorylated tau were increased in APP-PS brains compared with those of Tg2576 mice. Straight or twisted tubules mimicking paired helical filament were revealed at electron microscopic level in 16-month-old APP-PS. These findings suggest that mutant presenilin-1 accelerated Abeta-induced tauopathy and further promoted fibril formation of tau.