Pharmacological rescue of mitochondrial deficits in iPSC-derived neural cells from patients with familial Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder caused by genetic and environmental factors that results in degeneration of the nigrostriatal dopaminergic pathway in the brain. We analyzed neural cells generated from induced pluripotent stem cells (iPSCs) derived from PD patients and presymptomatic individuals carrying mutations in the PINK1 (PTEN-induced putative kinase 1) and LRRK2 (leucine-rich repeat kinase 2) genes, and compared them to those of healthy control subjects. We measured several aspects of mitochondrial responses in the iPSC-derived neural cells including production of reactive oxygen species, mitochondrial respiration, proton leakage, and intraneuronal movement of mitochondria. Cellular vulnerability associated with mitochondrial dysfunction in iPSC-derived neural cells from familial PD patients and at-risk individuals could be rescued with coenzyme Q(10), rapamycin, or the LRRK2 kinase inhibitor GW5074. Analysis of mitochondrial responses in iPSC-derived neural cells from PD patients carrying different mutations provides insight into convergence of cellular disease mechanisms between different familial forms of PD and highlights the importance of oxidative stress and mitochondrial dysfunction in this neurodegenerative disease.

Histamine N-methyltransferase Thr105Ile polymorphism is associated with Parkinson's disease

Histamine is a central neurotransmitter degraded by histamine-N-methyltransferase (HNMT). Several abnormalities in the histaminergic system were found in patients with Parkinson's disease (PD), thus we tested the possible association of a Thr105Ile functional polymorphism in HNMT with PD. A total of 913 patients with PD and 958 controls were genotyped using a TaqMan RT-PCR Genotyping Assay (Foster City, California, USA). Lower frequency of HNMT Ile105 allele that is associated with decreased enzymatic activity was found in patients compared with controls (χ(2) = 11.65; p = 0.0006). We performed meta-analysis to confirm the association of Thr105Ile functional polymorphism with PD. Our results indicate that lower HNMT activity plays a role in the pathogenesis of PD.

Dopamine-modified alpha-synuclein blocks chaperone-mediated autophagy

Altered degradation of alpha-synuclein (alpha-syn) has been implicated in the pathogenesis of Parkinson disease (PD). We have shown that alpha-syn can be degraded via chaperone-mediated autophagy (CMA), a selective lysosomal mechanism for degradation of cytosolic proteins. Pathogenic mutants of alpha-syn block lysosomal translocation, impairing their own degradation along with that of other CMA substrates. While pathogenic alpha-syn mutations are rare, alpha-syn undergoes posttranslational modifications, which may underlie its accumulation in cytosolic aggregates in most forms of PD. Using mouse ventral medial neuron cultures, SH-SY5Y cells in culture, and isolated mouse lysosomes, we have found that most of these posttranslational modifications of alpha-syn impair degradation of this protein by CMA but do not affect degradation of other substrates. Dopamine-modified alpha-syn, however, is not only poorly degraded by CMA but also blocks degradation of other substrates by this pathway. As blockage of CMA increases cellular vulnerability to stressors, we propose that dopamine-induced autophagic inhibition could explain the selective degeneration of PD dopaminergic neurons.