Evidence for Involvement of Uncoupling Proteins in Cerebral Mitochondrial Oxidative Phosphorylation Deficiency of Rats Exposed to 5,000 m High Altitude

Ucp4 Knockdown of Cerebellar Purkinje Cells Induces Bradykinesia

Although uncoupling protein 4 (UCP4) is the most abundant protein reported in the brain, the biological function of UCP4 in cerebellum and pathological outcome of UCP4 deficiency in cerebellum remain obscure. To evaluate the role of Ucp4 in the cerebellar Purkinje cells (PCs), we generated the conditional knockdown of Ucp4 in PCs (Pcp2cre;Ucp4fl/fl mice) by breeding Ucp4fl/fl mice with Pcp2cre mice. Series results by Western blot, immunofluorescent staining, and triple RNAscope in situ hybridization confirmed the specific ablation of Ucp4 in PCs in Pcp2cre;Ucp4fl/fl mice, but did not affect the expression of Ucp2, the analog of Ucp4. Combined behavioral tests showed that Pcp2cre;Ucp4fl/fl mice displayed a characteristic bradykinesia in the spontaneous movements. The electromyogram recordings detection excluded the possibility of hypotonia in Pcp2cre;Ucp4fl/fl mice. And the electrical patch clamp recordings showed the altered properties of PCs in Pcp2cre;Ucp4fl/fl mice. Moreover, transmission electron microscope (TEM) results showed the increased mitochondrial circularity in PCs; ROS probe imaging showed the increased ROS generation in molecular layer; and finally, microplate reader assay showed the significant changes of mitochondrial functions, including ROS, ATP, and MMP in the isolated cerebellum tissue. The results suggested that the specific knockdown of mitochondrial protein Ucp4 could damage PCs possibly by attacking their mitochondrial function. The present study is the first to report a close relationship between UCP4 deletion with PCs impairment, and suggests the importance of UCP4 in the substantial support of mitochondrial function homeostasis in bradykinesia. UCP4 might be a therapeutic target for the cerebellar-related movement disorder.

Benefit of a single simulated hypobaric hypoxia in healthy mice performance and analysis of mitochondria-related gene changes

Simulated hypobaric hypoxia (SHH) training has been used to enhance running performance. However, no studies have evaluated the effects of a single SHH exposure on healthy mice performance and analyzed the changes of mitochondria-related genes in the central nervous system. The current study used a mouse decompression chamber to simulate mild hypobaric hypoxia at the high altitude of 5000 m or severe hypobaric hypoxia at 8000 m for 16 h (SHH5000 & SHH8000, respectively). Then, the mouse behavioral tests were recorded by a modified Noldus video tracking. Third, the effects of SHH on 8 mitochondria-related genes of Drp1, Mfn1, Mfn2, Opa1, TFAM, SGK1, UCP2 and UCP4, were assessed in cerebellum, hippocampus and gastrocnemius muscles. The results have shown that a single mild or severe HH improves healthy mice performance. In cerebellum, 6 of all 8 detected genes (except Mfn2 and UCP4) did not change after SHH. In hippocampus, all detected genes did not change after SHH. In muscles, 7 of all 8 detected genes (except Opa1) did not change after SHH. The present study has indicated the benefit of a single SHH in healthy mice performance, which would due to the stabilized mitochondria against a mild stress state.

Rhodiola crenulata attenuates apoptosis and mitochondrial energy metabolism disorder in rats with hypobaric hypoxia-induced brain injury by regulating the HIF-1α/microRNA 210/ISCU1/2(COX10) signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Rhodiola crenulata, a traditional Tibetan medicine, has shown promise in the treatment of hypobaric hypoxia (HH)-induced brain injury. However, the underlying mechanisms remain unclear. This study investigated the protective effects of R. crenulata aqueous extract (RCAE) on HH-induced brain injury in rats.

MATERIALS AND METHODS

An animal model of high-altitude hypoxic brain injury was established in SD rats using an animal decompression chamber for 24 h. Serum and hippocampus levels of superoxide dismutase (SOD), malondialdehyde (MDA), glutathione (GSH), oxidized glutathione (GSSG), and lactate dehydrogenase (LDH) were then determined using commercial biochemical kits. Neuron morphology and vitality were also evaluated using H&E and Nissl staining, and TUNEL staining was used to examine apoptosis. Gene and protein expression of HIF-1α, microRNA 210, ISCU1/2, COX10, Apaf-1, cleaved Caspase-3, Caspase-3, Bax, Bcl-2, and Cyto-c were determined by western blot, immunohistochemical and qRT-PCR analysis.

RESULTS

RCAE administration attenuated HH-induced brain injury as evidenced by decreased levels of MDA, LDH, and GSSG, increased GSH and SOD, improvements in hippocampus histopathological changes, increased cell vitality and ATP level, and reduced apoptotic cell numbers. RCAE treatment also enhanced HIF-1α, ISCU1/2, COX10, and Bcl-2 protein expression, while dramatically inhibiting expression of Apaf-1, Bax, Cyto-c, and cleaved Caspase-3. Treatment also increased gene levels of HIF-1α, microRNA 210, ISCU1/2, and COX10, and decreased Caspase-3 gene production.

CONCLUSIONS

RCAE attenuated HH-induced brain injury by regulating apoptosis and mitochondrial energy metabolism via the HIF-1α/microRNA 210/ISCU1/2 (COX10) signaling pathway.

Alcohol hangover effects on brain cortex non-synaptic mitochondria and synaptosomes bioenergetics

Alcohol hangover (AH) has been associated with oxidative stress and mitochondrial dysfunction. We herein postulate that AH-induced mitochondrial alterations can be due to a different pattern of response in synaptosomes and non-synaptic (NS) mitochondria. Mice received intraperitoneal (i.p.) injections of ethanol (3.8 g/kg) or saline and were sacrificed 6 h afterward. Brain cortex NS mitochondria and synaptosomes were isolated by Ficoll gradient. Oxygen consumption rates were measured in NS mitochondria and synaptosomes by high-resolution respirometry. Results showed that NS-synaptic mitochondria from AH animals presented a 26% decrease in malate-glutamate state 3 respiration, a 64% reduction in ATP content, 28-37% decrements in ATP production rates (malate-glutamate or succinate-dependent, respectively), and 44% inhibition in complex IV activity. No changes were observed in mitochondrial transmembrane potential (ΔΨ) or in UCP-2 expression in NS-mitochondria. Synaptosome respiration driving proton leak (in the presence of oligomycin), and spare respiratory capacity (percentage ratio between maximum and basal respiration) were 30% and 15% increased in hangover condition, respectively. Synaptosomal ATP content was 26% decreased, and ATP production rates were 40-55% decreased (malate-glutamate or succinate-dependent, respectively) in AH mice. In addition, a 24% decrease in ΔΨ and a 21% increase in UCP-2 protein expression were observed in synaptosomes from AH mice. Moreover, mitochondrial respiratory complexes I-III, II-III, and IV activities measured in synaptosomes from AH mice were decreased by 18%, 34%, and 50%, respectively. Results of this study reveal that alterations in bioenergetics status during AH could be mainly due to changes in mitochondrial function at the level of synapses.

Mitochondrial function in rat cerebral cortex and hippocampus after short- and long-term hypobaric hypoxia

Taking into account the importance of aerobic metabolism in brain, the aim of the present work was to evaluate mitochondrial function in cerebral cortex and hippocampus in a model of sustained hypobaric hypoxia (5000 m simulated altitude) during a short (1 mo) and a long (7 mo) term period, in order to precise the mechanisms involved in hypoxia acclimatization. Hippocampal mitochondria from rats exposed to short-term hypobaric hypoxia showed lower respiratory rates than controls in both states 4 (45%) and 3 (41%), and increased NO production (1.3 fold) as well as eNOS and nNOS expression associated to mitochondrial membranes, whereas mitochondrial membrane potential decreased (7%). No significant changes were observed in cortical mitochondria after 1 mo hypobaric hypoxia in any of the mitochondrial functionality parameters evaluated. After 7 mo hypobaric hypoxia, oxygen consumption was unchanged as compared with control animals both in hippocampal and cortical mitochondria, but mitochondrial membrane potential decreased by 16% and 8% in hippocampus and cortex respectively. Also, long-term hypobaric hypoxia induced an increase in hippocampal NO production (0.7 fold) and in eNOS expression. A clear tendency to decrease in H2O2 production was observed in both tissues. Results suggest that after exposure to hypobaric hypoxia, hippocampal mitochondria display different responses than cortical mitochondria. Also, the mechanisms responsible for acclimatization to hypoxia would be time-dependent, according to the physiological functions of the brain studied areas. Nitric oxide metabolism and membrane potential changes would be involved as self-protective mechanisms in high altitude environment.

Developmental programming by high fructose decreases phosphorylation efficiency in aging offspring brain mitochondria, correlating with enhanced UCP5 expression

Fructose has recently been observed to affect brain metabolism and cognitive function in adults. Yet, possible late-onset effects by gestational fructose exposure have not been examined. We evaluated mitochondrial function in the brain of aging (15 months) male offspring of Fischer F344 rat dams fed a high-fructose diet (50% energy from fructose) during gestation and lactation. Maternal fructose exposure caused a significantly lower body weight of the offspring throughout life after weaning, while birth weight, litter size, and body fat percentage were unaffected. Isolated brain mitochondria displayed a significantly increased state 3 respiration of 8%, with the substrate combinations malate/pyruvate, malate/pyruvate/succinate, and malate/pyruvate/succinate/rotenone, as well as a significant decrease in the P/O₂ ratio, compared with the control. Uncoupling protein 5 (UCP5) protein levels increased in the fructose group compared with the control (P=0.03) and both UCP5 mRNA and protein levels were inversely correlated with the P/O₂ ratio (P=0.008 and 0.03, respectively), suggesting that UCP5 may have a role in the observed decreased phosphorylation efficiency. In conclusion, maternal high-fructose diet during gestation and lactation has long-term effects (fetal programming) on brain mitochondrial function in aging rats, which appears to be linked to an increase in UCP5 protein levels.