Mitochondrial function in Parkinson's disease cybrids containing an nt2 neuron-like nuclear background.

Mitochondria likely play a role in Parkinson's disease (PD) neurodegeneration. We modelled PD by creating cytoplasmic hybrid (cybrid) cell lines in which endogenous mitochondrial DNA (mtDNA) from PD or control subject platelets was expressed within human teratocarcinoma (NT2) cells previously depleted of endogenous mtDNA. Complex I activity was reduced in both PD cybrid lines and in the platelet mitochondria used to generate them. Under basal conditions PD cybrids had less ATP, more LDH release, depolarized mitochondria, less mitochondrial cytochrome c, and higher caspase 3 activity. Equivalent MPP+ exposures are more likely to trigger programmed cell death in PD cybrid cells than in control cybrid cells. Our data support a relatively upstream role for mitochondrial dysfunction in idiopathic PD.

Calpain-mediated MPP+ toxicity in mitochondrial DNA depleted cells.

MPP+ (1-methyl-4-phenylpyridium ion), a complex I - inhibiting metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), causes anatomic-specific neurodegeneration. To evaluate the broader role of mitochondria in MPP+-induced cell death, we exposed neuron-like NT2 human teratocarcinoma cells with mtDNA rho+ and without mtDNA (rho0) to MPP+. MPP+ minimized the ability of both rho+ and rho0 cells to reduce MTT. Only rho+ cells, though, initiated intrinsic pathway-mediated apoptosis. MPP+ also activated calpains in both rho+ and rho0 cell lines. The calpain inhibitor MDL 28710 was able to prevent the MPP+-related MTT reduction change in rho0 but not rho+ cells. We conclude that 1) MPP+-induced apoptosis requires functional mitochondria, 2) MPP+ activates calpains independent of respiratory chain inhibition, and 3) calpain activation mediates some aspects of MPP+ toxicity.