Mitochondrial biogenesis and dynamics in neurodegeneration: a causative relationship

Phoenixin 20 promotes neuronal mitochondrial biogenesis via CREB-PGC-1α pathway

Neurodegenerative disorders are dreadful diseases that affect millions of people worldwide. Mitochondrial dysfunction is closely associated with the development of neurodegenerative disorders. Phoenixin 20 is a newly discovered neuropeptide with a pleiotropic effect. This study showed that the presence of Phoenixin 20 promoted neuronal mitochondrial biogenesis in vitro. In cultured neuronal M17 cells, Phoenixin 20 increased the expression of mitochondrial regulators PGC-1α, NRF-1, and TFAM at both mRNA and protein levels. The treatment of Phoenixin 20 increased the ratio of mitochondrial vs nuclear DNA (mtDNA/nDNA) and the multiple mitochondrial gene expression as revealed by increasing mRNA expression of Tomm22, Timm50, Atp5d, Ndufs3, and protein expression of NDUFB8. At a cellular level, Phoenixin 20 promoted mitochondrial respiratory rate and cellular ATP production. Mechanistically, we found that Phoenixin 20 induced the phosphorylation of CREB, which suggests that Phoenixin 20 promoted the activation of the CREB pathway. The blockage of CREB by its selective inhibitor H89 prevented the effect of Phoenixin 20 on mitochondrial regulators and biogenesis. Moreover, the study showed that Phoenixin 20 induced the expression of its tentative receptor GPR173 at the mRNA and protein level, and the silence of GPR173 in neuronal cells ablated all its effect on mitochondrial regulation. Collectively, we showed that Phoenixin 20 promoted neuronal mitochondrial biogenesis via the regulation of CREB-PGC-1α pathway. This study revealed a new role and underlying mechanism of Phoenixin 20 in neuronal cells, suggesting it influences the therapeutic implication of neurodegenerative diseases.

Morphological control of mitochondria as the novel mechanism of Gastrodia elata in attenuating mutant huntingtin-induced protein aggregations

BACKGROUND

According to Compendium of Materia Medica, Gastrodia elata (GE) Blume as a top grade and frequently prescribed herbal medicine has been used in treating dizziness, headaches, and epilepsy, indicating a neuroprotective effect. Because GE is capable of suppressing a hyperactive liver and thus calming endogenous wind, and because Huntington's disease (HD) can be classified as a phenomenon of disturbed liver wind, it is suggested that GE might be beneficial in treating HD. However, although current studies support GE for the prevention of diverse neurodegenerations such as HD, its detailed mechanisms remain elusive.

PURPOSE

To investigate the molecular mechanism of GE in preventing HD by focusing on mitochondrial morphology, which is highly associated with HD etiology and thus proposed as a therapeutic target of neurodegenerations.

STUDY DESIGN/METHODS

The overexpression of the mutant huntingtin (mHTT) gene in rat pheochromocytoma (PC12) cells was used as an in vitro cell model of HD. A filter retardation assay was applied to measure protein aggregations during HTT expression. Cotransfection with mitochondrial fusion and fission genes was used to test their relationships with HTT aggregates by monitoring with a confocal laser scanning microscope and filter retardation assay. Western blot analysis was used to estimate protein expression under different drug treatments or cotransfections with other related genes.

RESULTS

The overexpression of mutant but not normal HTT genes significantly resulted in protein aggregations in PC12 cells. GE dose-dependently attenuated mHTT-induced protein aggregations and free radical formations. GE significantly reversed mHTT-induced mitochondrial fragmentation and dysregulation of mitochondrial fusion and fission molecules. The overexpression of mitochondrial fusion genes attenuated mHTT-induced protein aggregations. Further, Mdivi-1, a DRP1 fission molecule inhibitor, significantly reversed mHTT-induced protein aggregations and mitochondrial fragmentation.

CONCLUSION

GE attenuated mHTT aggregations through the control of mitochondrial fusion and the fission pathway.

HIV in the cART era and the mitochondrial: immune interface in the CNS

HIV-associated neurocognitive disorders (HAND) persist in the era of effective combined antiretroviral therapy (cART). A large body of literature suggests that mitochondrial dysfunction is a prospective etiology of HAND in the cART era. While viral load is often suppressed and the immune system remains intact in HIV+ patients on cART, evidence suggests that the central nervous system (CNS) acts as a reservoir for virus and low-level expression of viral proteins, which interact with mitochondria. In particular, the HIV proteins glycoprotein 120, transactivator of transcription, viral protein R, and negative factor have each been linked to mitochondrial dysfunction in the brain. Moreover, cART drugs have also been shown to have detrimental effects on mitochondrial function. Here, we review the evidence generated from human studies, animal models, and in vitro models that support a role for HIV proteins and/or cART drugs in altered production of adenosine triphosphate, mitochondrial dynamics, mitophagy, calcium signaling and apoptosis, oxidative stress, mitochondrial biogenesis, and immunometabolism in the CNS. When insightful, evidence of HIV or cART-induced mitochondrial dysfunction in the peripheral nervous system or other cell types is discussed. Lastly, therapeutic approaches to targeting mitochondrial dysfunction have been summarized with the aim of guiding new investigations and providing hope that mitochondrial-based drugs may provide relief for those suffering with HAND.

Rosuvastatin Improves Neurite Outgrowth of Cortical Neurons against Oxygen-Glucose Deprivation via Notch1-mediated Mitochondrial Biogenesis and Functional Improvement

Neurogenesis, especially neurite outgrowth is an essential element of neuroplasticity after cerebral ischemic injury. Mitochondria may supply ATP to power fundamental developmental processes including neuroplasticity. Although rosuvastatin (RSV) displays a potential protective effect against cerebral ischemia, it remains unknown whether it modulates mitochondrial biogenesis and function during neurite outgrowth. Here, the oxygen-glucose deprivation (OGD) model was used to induce ischemic injury. We demonstrate that RSV treatment significantly increases neurite outgrowth in cortical neurons after OGD-induced damage. Moreover, we show that RSV reduces the generation of reactive oxygen species (ROS), protects mitochondrial function, and elevates the ATP levels in cortical neurons injured by OGD. In addition, we found that, under these conditions, RSV treatment increases the mitochondrial DNA (mtDNA) content and the mRNA levels of mitochondrial transcription factor A (TFAM) and nuclear respiratory factor 1 (NRF-1). Furthermore, blocking Notch1, which is expressed in primary cortical neurons, reverses the RSV-dependent induction of mitochondrial biogenesis and function under OGD conditions. Collectively, these results suggest that RSV could restore neurite outgrowth in cortical neurons damaged by OGD in vitro, by preserving mitochondrial function and improving mitochondrial biogenesis, possibly through the Notch1 pathway.

C. elegans as a model organism for human mitochondrial associated disorders

Mitochondria are small cytoplasmic organelles whose most important function is to provide the energy required by our cells and organism to live. To maintain an adequate mitochondrial homeostasis cells possess numerous mitochondrial quality controls and protective compensatory pathways, which can be activated to cope with a certain degree of mitochondrial dysfunction. However, when the mitochondrial damage is too severe and these defensive mechanisms are not anymore sufficient to deal with it, pathological signs arise. In the past few decades numerous genetic disorders ascribed to severe mitochondrial defects have been recognized with variable onset and symptomatology ranging from neuromuscular degeneration to cancer syndromes. Unfortunately, to date, only symptomatic and no curative therapies exist for most of these devastating, life-threatening disorders. Model organisms, and especially the nematode Caenorhabditis elegans, with its sequenced and highly conserved genome, and a simple but well-characterized nervous system, have enormously contributed in the past years to gain insight into the pathogenesis and treatment of different diseases. Here, we will summarize some of the advantages offered by the nematode system to model neurodegenerative diseases associated with mitochondrial electron transport chain defects and screen for therapeutic interventions.

Arachidonyl-2-Chloroethylamide Alleviates Cerebral Ischemia Injury Through Glycogen Synthase Kinase-3β-Mediated Mitochondrial Biogenesis and Functional Improvement

Arachidonyl-2-chloroethylamide (ACEA), a highly selective agonist of cannabinoid receptor 1 (CB1R), has been reported to protect neurons in ischemic injury. We sought to investigate whether mitochondrial biogenesis was involved in the therapeutic effect of ACEA in cerebral ischemia. Focal cerebral ischemic injury was induced in adult male Sprague Dawley rats. Intraperitoneal injection of 1 mg/kg ACEA improved neurological behavior, reduced infarct volume, and inhibited apoptosis. The volume and numbers of mitochondria were significantly increased after ACEA administration. Expression of mitochondrial transcription factor A (Tfam), nuclear transcription factor-1 (Nrf-1), and cytochrome C oxidase subunit IV (COX IV) were also significantly up-regulated in animals administered ACEA. One thousand nanomoles of ACEA inhibited mitochondrial dysfunction in primary rat cortical neurons exposed to oxygen-glucose deprivation (OGD). Furthermore, ACEA administration increased phosphorylation of glycogen synthase kinase-3β (GSK-3β) after reperfusion. Phosphorylation of GSK-3β induced mitochondrial biogenesis and preserved mitochondrial function whereas inhibition of phosphatidylinositol 3-kinase (PI3K) dampened phosphorylation of GSK-3β and reversed induction of mitochondrial biogenesis and function following ACEA administration. In conclusion, ACEA could induce mitochondrial biogenesis and improve mitochondrial function at the beginning of cerebral ischemia, thus alleviating cerebral ischemia injury. Phosphorylation of GSK-3β might be involved in the regulation of mitochondrial biogenesis induced by ACEA.

Aging leads to elevation of O-GlcNAcylation and disruption of mitochondrial homeostasis in retina

Retina is particularly susceptible to aging as oxidative damage accumulates within retina, leading to age-related retinal dysfunction or even visual loss. However, the underlying mechanisms still remain obscure and effective therapeutic strategy is urgently in need. Here, we quested for the answer particularly focusing on mitochondrial homeostasis and O-GlcNAcylation in rat retina. By comparing expression of electron transfer chain complexes and key factors in mitochondrial biogenesis and dynamics in retinas of aged and young Sprague-Dawley rats, we found that mitochondrial Complex I, II, IV and V were increased in aged retina with decreased mtTFA and Mfn2. Also, we noticed that p38 and JNK of MAPK signaling were substantially more activated in aged retina, suggesting stress induction. In addition, we found that pan-O-GlcNAcylation was remarkably stronger with lower OGA expression in aged retina. To further elucidate the roles of Mfn2 and O-GlcNAcylation, we employed ARPE-19 cells and found that ATP production, oxygen consumption, and mitochondrial membrane potential were reduced and ROS level was increased by Mfn2 knockdown, while treating with PUGNAc or UDP-GlcNAc heightened oxygen consumption and reduced ROS. Our results suggest disrupted mitochondrial homeostasis may increase oxidative stress; yet enhanced O-GlcNAcylation might defend against oxidative stress and promote mitochondrial respiration in aged retina.