Parkinson's disease-associated DJ-1 mutations impair mitochondrial dynamics and cause mitochondrial dysfunction

Mitochondrial dysfunction represents a critical event during the pathogenesis of Parkinson's disease (PD) and expanding evidences demonstrate that an altered balance in mitochondrial fission/fusion is likely an important mechanism leading to mitochondrial and neuronal dysfunction/degeneration. In this study, we investigated whether DJ-1 is involved in the regulation of mitochondrial dynamics and function in neuronal cells. Confocal and electron microscopic analysis demonstrated that M17 human neuroblastoma cells over-expressing wild-type DJ-1 (WT DJ-1 cells) displayed elongated mitochondria while M17 cells over-expressing PD-associated DJ-1 mutants (R98Q, D149A and L166P) (mutant DJ-1 cells) showed significant increase of fragmented mitochondria. Similar mitochondrial fragmentation was also noted in primary hippocampal neurons over-expressing PD-associated mutant forms of DJ-1. Functional analysis revealed that over-expression of PD-associated DJ-1 mutants resulted in mitochondria dysfunction and increased neuronal vulnerability to oxidative stress (H(2) O(2)) or neurotoxin. Further immunoblot studies demonstrated that levels of dynamin-like protein (DLP1), also known as Drp1, a regulator of mitochondrial fission, was significantly decreased in WT DJ-1 cells but increased in mutant DJ-1 cells. Importantly, DLP1 knockdown in these mutant DJ-1 cells rescued the abnormal mitochondria morphology and all associated mitochondria/neuronal dysfunction. Taken together, these studies suggest that DJ-1 is involved in the regulation of mitochondrial dynamics through modulation of DLP1 expression and PD-associated DJ-1 mutations may cause PD by impairing mitochondrial dynamics and function.

Cyclosporin A delays mitochondrial depolarization induced by N-methyl-D-aspartate in cortical neurons: evidence of the mitochondrial permeability transition

N-Methyl-D-aspartate causes a rapid increase in intracellular Ca2+ leading to collapse of the mitochondrial membrane potential and eventually cell death in cortical neurons. The aim of this study was to investigate the mechanism responsible for mitochondrial depolarization using laser scanning confocal microscopy of single cultured rate cortical neurons. To monitor mitochondrial membrane potential, neuronal mitochondria were labeled with tetramethylrhodamine methyl ester, a cationic fluorophore that accumulates in polarized mitochondria. In neurons cultured on poly-D-lysine-coated coverslips, N-methyl-D-aspartate caused mitochondrial depolarization in 88% of cells in 30 min. Cyclosporin A, an inhibitor of the mitochondrial permeability transition, delayed depolarization in a dose-dependent manner (0.2-1 microM). In neurons cultured on an astrocyte feeder layer, N-methyl-D-aspartate also caused mitochondrial depolarization. Cyclosporin A again delayed mitochondrial depolarization, although higher concentrations were needed. These data show for the first time that mitochondrial depolarization induced by N-methyl-D-aspartate may be due to the induction of the mitochondrial permeability transition.

Changes in resistance and ventilatory timing that accompany apnea in premature infants

To characterize the changes in respiratory mechanics and ventilatory timing that accompany apnea in premature infants, we evaluated 36 apneas in 13 premature infants (birth weight, 1,200 +/- 350 g, postconceptional age at study 34 +/- 3 wk). Apnea was defined as a ventilatory pause > or = 10s accompanied by a decrease in heart rate of 20 beats/min. Nasal airflow was recorded with a pneumotachometer, and esophageal, pharyngeal, and nasal mask pressures were continuously measured. Inspiratory time (TI), expiratory time (TE), tidal volume (VT), and VT/TI were determined over five breaths before and after apnea. In addition, total pulmonary resistance (RT) and supraglottic resistance (Rs) were measured over the same epochs in inspiration and expiration. Before apnea, TE and RT increased (P < 0.05 and < 0.01, respectively); however, Rs did not change. Immediately after apnea, prolongation of TI occurred and both RT and Rs were increased (P < 0.01), consistent with continued upper airway instability. However, within two breaths after resolution of the apnea, RT and Rs returned to normal, reflecting rapid recovery of upper airway and total pulmonary resistance. The ventilatory changes that precede and follow apnea closely resemble those occurring during periodic breathing.