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Summary Emerging evidence suggests that Parkinson's disease (PD), besides being an age-associated disorder, might also have a neurodevelopment component. Disruption of mitochondrial homeostasis has been highlighted as a crucial cofactor in its etiology. Here, we show that PD patient-specific human neuroepithelial stem cells (NESCs), carrying the LRRK2-G2019S mutation, recapitulate key mitochondrial defects previously described only in differentiated dopaminergic neurons. By combining high-content imaging approaches, 3D image analysis, and functional mitochondrial readouts we show that LRRK2-G2019S mutation causes aberrations in mitochondrial morphology and functionality compared with isogenic controls. LRRK2-G2019S NESCs display an increased number of mitochondria compared with isogenic control lines. However, these mitochondria are more fragmented and exhibit decreased membrane potential. Functional alterations in LRRK2-G2019S cultures are also accompanied by a reduced mitophagic clearance via lysosomes. These findings support the hypothesis that preceding mitochondrial developmental defects contribute to the manifestation of the PD pathology later in life.

a b s t r a c tParkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of a-synuclein (a-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to a-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves a-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.

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Alpha-synuclein (α-syn) is a major component of Lewy bodies found in sporadic and inherited forms of Parkinson's disease (PD). Mutations in the gene encoding α-syn and duplications and triplications of wild-type (WT) α-syn have been associated with PD. Several mechanisms have been implicated in the degeneration of dopaminergic neurons in PD, including oxidative stress and mitochondrial dysfunction. Here we defined the occurrence of oxidative stress in SH-SY5Y cells overexpressing WT α-syn in a doxycycline (Dox) regulated manner, before and after exposure to iron (500 µM), and determined the changes in proteins involved in the intracellular antioxidant defense system. Data evidenced an increase in caspase-3 activation and diminished reducing capacity of -Dox cells, associated with decreased activity of mitochondria complex I and reduced mitochondrial transcription factor A (TFAM) levels in these cells. Furthermore, total and mitochondrial reactive oxygen species levels were higher under basal conditions in cells overexpressing α-syn (-Dox) and this increase was apparently correlated with diminished levels and activities of SOD1 and SOD2 in -Dox cells. Moreover, both reduced and oxidized glutathione levels were diminished in -Dox cells under basal conditions, concomitantly with decreased activity of GCL and reduced protein levels of GCLc. The effects caused by iron (500 µM) were mostly independent of α-syn expression and triggered different antioxidant responses to possibly counterbalance higher levels of free radicals. Overall, data suggest that overexpression of α-syn modifies the antioxidant capacity of SH-SY5Y cells due to altered activity and protein levels of SOD1 and SOD2, and decreased glutathione pool.

Highlights d LRRK2-G2019S accelerates cell-cycle exit and dopaminergic differentiation d LRRK2-G2019S reduces the viability of differentiating dopaminergic neurons d LRRK2-G2019S downregulates the core regulatory circuit transcription factor NR2F1 d Dopaminergic differentiation is accelerated in NR2F1 mutant mouse embryos

Polyglutamine (polyQ) diseases are a family of neurodegenerative disorders with very heterogeneous clinical presentations, although with common features such as progressive neuronal death. Thus, at the time of diagnosis patients might present an extensive and irreversible neuronal death demanding cell replacement or support provided by cell-based therapies. For this purpose stem cells, which include diverse populations ranging from embryonic stem cells (ESCs), to fetal stem cells, mesenchymal stromal cells (MSCs) or induced pluripotent stem cells (iPSCs) have remarkable potential to promote extensive brain regeneration and recovery in neurodegenerative disorders. This regenerative potential has been demonstrated in exciting pre and clinical assays. However, despite these promising results, several drawbacks are hampering their successful clinical implementation. Problems related to ethical issues, quality control of the cells used and the lack of reliable models for the efficacy assessment of human stem cells. In this chapter the main advantages and disadvantages of the available sources of stem cells as well as their efficacy and potential to improve disease outcomes are discussed.