Loss of the Parkinson's disease-linked gene DJ-1 perturbs mitochondrial dynamics.

Growing evidence highlights a role for mitochondrial dysfunction and oxidative stress as underlying contributors to Parkinson's disease (PD) pathogenesis. DJ-1 (PARK7) is a recently identified recessive familial PD gene. Its loss leads to increased susceptibility of neurons to oxidative stress and death. However, its mechanism of action is not fully understood. Presently, we report that DJ-1 deficiency in cell lines, cultured neurons, mouse brain and lymphoblast cells derived from DJ-1 patients display aberrant mitochondrial morphology. We also show that these DJ-1-dependent mitochondrial defects contribute to oxidative stress-induced sensitivity to cell death since reversal of this fragmented mitochondrial phenotype abrogates neuronal cell death. Reactive oxygen species (ROS) appear to play a critical role in the observed defects, as ROS scavengers rescue the phenotype and mitochondria isolated from DJ-1 deficient animals produce more ROS compared with control. Importantly, the aberrant mitochondrial phenotype can be rescued by the expression of Pink1 and Parkin, two PD-linked genes involved in regulating mitochondrial dynamics and quality control. Finally, we show that DJ-1 deficiency leads to altered autophagy in murine and human cells. Our findings define a mechanism by which the DJ-1-dependent mitochondrial defects contribute to the increased sensitivity to oxidative stress-induced cell death that has been previously reported.

Hypoxic depression of circadian oscillations in sino-aortic denervated rats.

We hypothesized that hypoxia depresses the circadian oscillations of body temperature (T(b)) and oxygen consumption (V(O(2))) even in the absence of inputs from the peripheral chemoreceptors. Adult rats were sino-aortic denervated bilaterally (SAX, N=17) or sham-operated (Sham, N=17). Ten rats of each group were instrumented for measurements of T(b) and activity by telemetry. Animals were exposed to normoxia (21% O(2)), hypoxia (10.5% O(2)), and again normoxia, each for a 5-day duration, in constant light ('free-running') conditions. Hypoxia almost eliminated the T(b) circadian oscillations, mostly by abolishing the daily rise in T(b). Upon return to normoxia T(b) rapidly increased and the normal oscillation was reestablished at the expected phase of the cycle. The hypoxic effects did not differ between Sham and SAX. During hypoxia the amplitude of the circadian oscillation of activity was reduced by approximately 25%, and that of V(O(2)), measured by an open flow method in the remaining Sham and SAX rats (N=7 each), was reduced by almost 50%. In all cases there was no difference between the two groups. We conclude that activation of the peripheral chemoreceptors is not required for the manifestation of the hypoxic depression of the metabolic and temperature circadian oscillations. The results are compatible with the view that hypoxia depresses thermogenesis acting on the thermoregulatory centers of the hypothalamus.

Light-dark differences in the effects of ambient temperature on gaseous metabolism in newborn rats.

Body temperature (T(b)) of rat pups (7-9 days old) raised under a 12:12-h light-dark (L-D) regimen (L: 0700-1900, D: 1900-0700) was consistently higher in D than in L by approximately 1.1 degrees C. We tested the hypothesis that the L-D differences in T(b) were accompanied by differences in the set point of thermoregulation. Measurements were performed on rat pups at 7-9 days after birth. O(2) consumption (VO(2)) and CO(2) production (VCO(2)) were measured with an open-flow method during air breathing, as ambient temperature (T(a)) was decreased from 40 to 15 degrees C at the constant rate of 0.5 degrees C/min. At T(a) >/=33 degrees C, VO(2) was not significantly different between L and D, whereas VCO(2) was higher in L, suggesting a greater ventilation. Over the 33 to 15 degrees C range the VO(2) values in D exceeded those in L by approximately 30%. Specifically, the difference was contributed by differences in thermogenesis at T(a) = 30 to 20 degrees C. As T(a) was decreased, the critical temperature at which VO(2) began to rise was lower in L. We conclude that the higher T(b) of rat pups in D is accompanied by a higher set point for thermoregulation and a greater thermogenesis. These results are consistent with the idea that, in newborns, endogenous changes in the set point of thermoregulation contribute to the circadian oscillations of T(b).

Continuous circadian measurements of ventilation in behaving adult rats.

Body temperature (Tb) and oxygen consumption (V(O(2))) are important determinants of ventilation (VE). While the circadian rhythms in Tb and V(O(2)) have been well described, the daily pattern of VE has not due to limitations in the available methods for measuring VE. Here we describe an adaptation of the barometric method using a chamber in which a large flow through very small restrictions was generated by the combined action of a positive pressure pump on the entrance and a negative pressure pump at the outlet. In this way the chamber effectively behaved as a closed system, despite having a high enough flow for long-term recording in freely moving, undisturbed small animals. This system was then used to test the hypothesis that VE oscillates with a circadian pattern similar to that of Tb(.) Measurements of tidal volume (VT) and breathing rate (f), in combination with Tb and activity by telemetry, were made in eight adult rats over 4-6 days under 12:12 light:dark conditions. Both VT, f, and thus VE, showed a circadian pattern similar to that of Tb and activity; that is, values were higher during the dark compared to the light phase. The differences in VE levels according to the time of the day suggest that mechanisms involved in the control of breathing may also have circadian patterns.

Hypoxic depression of circadian rhythms in adult rats.

Because the circadian rhythms of oxygen consumption (VO(2)) and body temperature (T(b)) could be contributed to by differences in thermogenesis and because hypoxia depresses thermogenesis in its various forms, we tested the hypothesis that hypoxia blunts the normal daily oscillations in VO(2) and T(b). Adult rats were instrumented for measurements of T(b) and activity by telemetry; VO(2) was measured by an open-flow method. Animals were exposed to normoxia (21% O(2)), hypoxia (10.5% O(2)), and normoxia again, each 1 wk in duration, in either a 12:12-h light-dark cycle ("synchronized") or constant light ("free running"). In this latter case, the period of the cycle was approximately 25 h. In synchronized conditions, hypoxia almost eliminated the T(b) circadian oscillation, because of the blunting of the T(b) rise during the dark phase. On return to normoxia, T(b) rapidly increased toward the maximum normoxic values, and the normal cycle was then reestablished. In hypoxia, the amplitude of the activity and VO(2) oscillations averaged, respectively, 37 and 56% of normoxia. In free-running conditions, on return to normoxia the rhythm was reestablished at the expected phase of the cycle. Hence, the action of hypoxia was not on the clock itself but probably at the hypothalamic centers of thermoregulation. Hyperoxia (40% O(2)) or hypercapnia (3% CO(2)) had no significant effects on circadian oscillations, indicating that the effects of hypoxia did not reflect an undifferentiated response to changes in environmental gases. Modifications of the metabolism and T(b) rhythms during hypoxia could be at the origin of sleep disturbances in cardiorespiratory patients and at high altitude.