Page:Human wild-type full-length tau accumulation disrupts mitochondrial dynamics and the functions via increasing mitofusins.pdf/5



'''Figure 3. Expression of htau induces mitochondrial dysfunction with reduced cell viability and retraction of processes. (a–d)''' HEK293 cells were transiently transfected with htau (T293tau) or the vector (T293vec) for 24 and 72 h, and then the levels of ATP (a) (24 h, p = 0.789; 72 h, p = 0.00051), the activity of complex I (b) (24 h, p = 0.814; 72 h, p = 0.00011), the ratio of ATP/ADP (c) (24 h, p = 0.484; 72 h, p = 0.000041), and the cell viability (d) (24 h, p = 0.988; 72 h, p = 0.0228) were analyzed. The experiments were repeated at least three times with triplicates. Data were presented as mean ± SD. *,p < 0.05, ***,p < 0.001 vs vec. (e–h) Representative images show retraction/loss of cell processes and accumulation of mitochondria in rat primary hippocampal neurons co-transfected with htau and mito-DsRed2 for 48 h (e) and in S293tau cells co-transfected with htau and mito-AcGFP for 48 h (f), and quantification of the average length of the cell processes in primary neurons (g) or 293 cells (h). ((h) vec vs tau, p24 h = 0.45, p48 h < 0.0001; 24 h vs 48 h, pvec = 0.540, ptau = 0.0197. (i) S293vec vs S293tau, p$24 h$ = 0.398, p$48 h$ < 0.0001; 24 h vs 48 h, p$S293vec$ = 0.7967, p$S293tau$ < 0.0001). At least 100 HEK293 cells or 40 primary hippocampal neurons were counted each group. Data were expressed as mean ± SD, unpaired student t test. ***,p < 0.001, ,p < 0.05, ,p < 0.001.

Intracellular accumulation of wild-type tau is the major cause of neurodegeneration in sporadic AD; however, the mechanism is not fully elucidated. As mitochondria homeostasis is vital for neuronal survival and death, we investigated the effects of htau on mitochondrial homeostasis and the molecular mechanisms. We found that intracellular htau accumulation, as seen in sporadic AD brains, resulted in an enhanced mitochondrial fusion and their perinuclear congestion with mitochondrial dysfunctions and neurodegeneration. The molecular mechanisms involve an impaired ubiquitination-associated increase of mitofusins, because simultaneous downregulation of the mitofusins rescued the htau-induced mitochondrial impairments and cell viability. Our findings provide new insights in the htau-induced neurodegeneration.

Upon overexpression of htau, apparent perinuclear accumulation of mitochondria was seen in both cultured cells and the htau transgenic mice. Simultaneously, we observed an enhanced retrograde axonal transport of mitochondria in the htau-expressing cells, though unexpected, these data can perfectly explain the perinuclear accumulation of the mitochondria as observed in our current study. The mitochondria fusion is dependent on increased motility and fluctuations in microtubule post translational modifications. We find that overexpression of htau increases Mfn1 and Mfn2, which not only promote mitochondria fusion but also interacts with Miro/Milton complex during mitochondrial transport ; Knockdown of Miro2 in cultured neurons induces transport Scientific Reports