Fragmentation of the Golgi Apparatus Induced by the Overexpression of Wild-Type and Mutant Human Tau Forms in Neurons

Abstract

Tau is a microtubule-associated protein enriched in the axonal compartment. In several neurodegenerative diseases including Alzheimer's disease, hyperphosphorylated tau accumulates in the somatodendritic compartment, self-aggregates, and forms neurofibrillary tangles. A fragmentation of the neuronal Golgi apparatus (GA) was also observed in Alzheimer's disease. In the present study, we examined the effect of overexpressing human tau on the organization of the neuronal GA in rat hippocampal cultures and in JNPL3 mice expressing tau mutant P301L. GA fragmentation was noted in a significantly higher percentage of hippocampal neurons overexpressing wild-type human tau than in control neurons over-expressing green fluorescent protein (GFP) alone. Most importantly, in neurons overexpressing mutant forms of human tau (P301L, V337M, or R406W), the percentage of neurons with a fragmented GA was 10% higher than that of neurons overexpressing wild-type human tau. In JNPL3 mice, a significantly higher percentage of motor neurons presented a fragmented GA compared to control mice. Interestingly, fragmentation of the GA was more frequent in neurons containing an accumulation and aggregation of hyperphosphorylated tau in the cell body than in neurons without these features. In both primary hippocampal neurons and JNPL3 mice, the tau-induced GA fragmentation was not caused by apoptosis. The pre-sent results implicate tau in GA fragmentation and show that this event occurs before the formation of neurofibrillary tangles.

NMDA receptor mediates tau-induced neurotoxicity by calpain and ERK/MAPK activation

“…Moreover, overexpression of Ad-Bcl2, a key antiapoptotic regulator of neuronal cell death in a variety of in vivo and in vitro paradigms, failed to rescue tau-(1-441)-infected neurons from death (Table 1). These data suggest that the mode of taumediated cell death, in both cerebellar granule and cortical neurons, is not classic apoptosis as also reported by other authors (9,13,14). Moreover, we obtained data suggesting that this observation could also be extended to hippocampal neurons overexpressing tau (data not shown).…”

“…Morphological changes consistent with apoptosis, with or without activation of caspases, have been detected ''in vitro '' in neurons overexpressing pseudohyperphosphorylated tau (4) or tau cleaved at residue D421 (8) as well as ''in vivo '' in some neuronal and glial cells of transgenic mice expressing human tau (htau) isoforms (9) and in oligodendrocytes of mutant htau-transgenic mice (10). However, a nonapoptotic neurodegeneration process has been described in transgenic mice overexpressing the mutated forms of htau P301S (11), V337M (12), and P301L (13) and in astrocytes expressing the longest htau isoform (14). Furthermore, other studies have provided evidence that overexpression of htau in transgenic mice caused extensive organelle swelling and cytoplasmic vacuolization more suggestive of necrosis and likely of glutamatemediated excitotoxicity (9).…”

Untangling the role of tau in Alzheimer’s disease: A unifying hypothesis

“…Disease-associated tau interactions with the membrane have also been showed in vivo [168], and may involve the tau N-terminus interacting with and being phosphorylated by srk family kinases such as fyn [75][76][77]175]. This pathway is consistent with demonstrations by LeClerc and coworkers showing that in both tau overexpression and in AD, tau becomes localized to the Golgi despite its lack of an ERtargeting signal sequence [176,177]. Finally, there is increasing evidence that vulnerable cellular protein turnover pathways (e.g.…”

Studies of Optineurin, a Glaucoma Gene

“…The Golgi fragmentation was defined as the presence of disconnected, small and round Golgi fragments dispersed in the cell. 28 The percentage of TM cells with Golgi alteration (Table 1) was greater (P ϭ 0.0036) in cells expressing OPTN E50K -GFP (87.6 Ϯ 1.0%) than in those expressing OPTN WT -GFP (59.1 Ϯ 2.3%). Both were significantly (P Ͻ 0.004) higher than the GFP-expressing controls (11.3 Ϯ 2.4%).…”

“…The judgment of a broken Golgi complex was based on the presence of disconnected, small and round GM130-immunolabeled Golgi membranes dispersed in the cell. 28 Percentage of transfected cells that displayed broken or fragmented Golgi and the degree of Golgi fragmentation were analyzed manually and through the Metamorph software. Significance of the data was determined by Student's t-tests.…”