Absence of Gem1 (mammalian Miro/Rhot) mitigates alpha-synuclein toxicity in a yeast model of Parkinson's disease.

Alpha-synuclein aggregation is a hallmark of Parkinson's disease (PD). Mutants A30P and A53T alpha-synuclein are known to exacerbate the toxicity of alpha-synuclein, which includes oxidative stress, mitochondrial and endoplasmic reticulum (ER) dysfunction. Saccharomyces cerevisiae (budding yeast) is a cellular model widely used to investigate mechanisms underlying neurodegenerative disorders, such as PD. In yeast, Gem1 (Miro/Rhot mammalian orthologue) coordinates mitochondrial dynamics and ER homeostasis, which is impaired in the presence of mutant alpha-synuclein and can lead to cell death. In this study, A30P or A53T alpha-synuclein were expressed in wild type or ΔGem (deletion of Gem1 gene) yeast strains. ΔGem cells presented decreased viability and increased mitochondrial H2O2 production and ER stress compared to wild type cells. However, in the presence of mutant alpha-synuclein, ΔGem cells showed increased growth compared to cells that do not express mutant alpha-synuclein. ΔGem cells expressing A53T alpha-synuclein also presented reduced ER stress and increased ability to deal with oxidative stress. Together, our results suggest that deletion of Gem1 activates pathways that strengthen cells against other stressful agents such as the presence of mutant alpha-synuclein.

Restoration of Rab1 Levels Prevents Endoplasmic Reticulum Stress in Hippocampal Cells during Protein Aggregation Triggered by Rotenone.

Disrupted neuronal intracellular trafficking is often related with protein aggregates present in the brain during neurodegenerative diseases such as Alzheimer's. Impairment of intracellular transport may be related to Rab proteins, a class of small GTPases responsible for trafficking of organelles and vesicles. Deficit in trafficking between the endoplasmic reticulum (ER) and Golgi apparatus mediated by Rab1 and 6 may lead to increased unfolded protein response (UPR) and ER stress and remodeling. Thus, the objective of this study is to analyze the levels of Rabs 1 and 6 in the hippocampus of aged rats and in vitro during protein aggregation promoted by exposure to rotenone. Levels of Rabs 1 and 6, ATF6 and CHOP were measured by western blotting. PDI immunolabeling and ER-Tracker were employed to study ER morphology. MTT was used to analyze cell metabolism. Rab1 levels and cell viability decreased, whereas Rab6, UPR proteins and ER remodeling increased during protein aggregation, which were restored to normal levels after exogenous expression of Rab1.These results suggest that decrease of Rab1 levels contributes to ER stress and remodeling, while maintaining the elevated expression of Rab1 prevented impairment of cell viability during protein aggregation. In conclusion, Rab1 is a significant player to maintain intracellular homeostasis and its expression may mitigate ER dysfunction in the context of neurodegeneration-related protein inclusions.

Rotenone-dependent changes of anterograde motor protein expression and mitochondrial mobility in brain areas related to neurodegenerative diseases.

The presence of protein aggregates is common in neurodegenerative disorders; however, the real cause and effect of these aggregates during neurodegeneration is still a matter of investigation. We hypothesize that impairment of intracellular traffic may appear in the absence of protein inclusions and might trigger protein aggregation. In the present study, we aimed to evaluate mitochondria mobility as well as protein and messenger RNA expression of KIF1B and KIF5 that are molecular motors for neuronal anterograde traffic, in hippocampus, substantia nigra, and locus coeruleus of 10-month-old Lewis rats and cultured cells, from these same areas, following exposure to low doses of rotenone that do not lead to protein inclusions. The present study showed alteration in KIF1B and KIF5 expression, as well as in mitochondria mobility prior to protein aggregation involved in neurodegenerative disorders. These findings suggest that change in intracellular trafficking might be critical and one of the primary events for impairment of cell physiology during neurodegeneration associated with protein inclusions.

Dynein c1h1, dynactin and syntaphilin expression in brain areas related to neurodegenerative diseases following exposure to rotenone.

Neurodegeneration is often accompanied by protein inclusions which may interfere with cell physiology. On the other hand, alteration in intracellular trafficking may precede impairment of neurotransmission and therefore trigger cell death. In view of this, it is hypothesized that changes in mitochondrial traffic may occur before neurodegeneration triggered by rotenone exposure and could favor this process. The effects of low concentrations of rotenone on the expression of dynein c1h1, dynactin and syntaphilin, which are proteins related to mitochondria transport and anchoring, were evaluated in cell cultures of substantia nigra, locus coeruleus and hippocampus as well as in these same brain areas in Lewis aged rats. The results indicate that low concentrations of rotenone decrease dynein c1h1 protein levels in cell cultures and brain areas of aged rats. Dynactin is decreased after exposure to 0.1 and 0.3 nM of rotenone, and increased after exposure to 0.5 nM of rotenone in cell cultures. Aged rats present increased dynactin expression. Syntaphilin expression decreased in vitro and increased in vivo after rotenone exposure. These findings suggest that changes in protein expression related to mitochondrial retrograde transport and anchoring occur before neurodegeneration induced by rotenone exposure, which may be a primary factor to trigger neurodegenerative mechanisms.

Protein aggregation containing ß-amyloid, α-synuclein and hyperphosphorylated τ in cultured cells of hippocampus, substantia nigra and locus coeruleus after rotenone exposure.

BACKGROUND: Protein aggregates containing alpha-synuclein, beta-amyloid and hyperphosphorylated tau are commonly found during neurodegenerative processes which is often accompanied by the impairment of mitochondrial complex I respiratory chain and dysfunction of cellular systems of protein degradation. In view of this, we aimed to develop an in vitro model to study protein aggregation associated to neurodegenerative diseases using cultured cells from hippocampus, locus coeruleus and substantia nigra of newborn Lewis rats exposed to 0.5, 1, 10 and 25 nM of rotenone, which is an agricultural pesticide, for 48 hours. RESULTS: We demonstrated that the proportion of cells in culture is approximately the same as found in the brain nuclei they were extracted from. Rotenone at 0.5 nM was able to induce alpha-synuclein and beta amyloid aggregation, as well as increased hyperphosphorylation of tau, although high concentrations of this pesticide (over 1 nM) lead cells to death before protein aggregation. We also demonstrated that the 14 kDa isoform of alpha-synuclein is not present in newborn Lewis rats. CONCLUSION: Rotenone exposure may lead to constitutive protein aggregation in vitro, which may be of relevance to study the mechanisms involved in idiopathic neurodegeneration.