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Growing evidence highlights a tight connection between circadian rhythms, molecular clockworks, and mitochondrial function. In particular, mitochondrial quality control and bioenergetics have been proven to undergo circadian oscillations driven by core clock genes. Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by a selective loss of dopaminergic neurons. Almost half of the autosomal recessive forms of juvenile parkinsonism have been associated with mutations in the PARK2 gene coding for parkin, shown to be involved in mitophagy-mediated mitochondrial quality control. The aim of this study was to investigate, in fibroblasts from genetic PD patients carrying parkin mutations, the interplay between mitochondrial bioenergetics and the cell autonomous circadian clock. Using two different in vitro synchronization protocols, we demonstrated that normal fibroblasts displayed rhythmic oscillations of both mitochondrial respiration and glycolytic activity. Conversely, in fibroblasts obtained from PD patients, a severe damping of the bioenergetic oscillatory patterns was observed. Analysis of the core clock genes showed deregulation of their expression patterns in PD fibroblasts, which was confirmed in induced pluripotent stem cells (iPSCs) and induced neural stem cells (iNSCs) derived thereof. The results from this study support a reciprocal interplay between the clockwork machinery and mitochondrial energy metabolism, point to a parkin-dependent mechanism of regulation, and unveil a hitherto unappreciated level of complexity in the pathophysiology of PD and eventually other neurodegenerative diseases.

Unlabelled: Hepatitis C virus (HCV) infection induces a state of oxidative stress that is more pronounced than that in many other inflammatory diseases. In this study we used well-characterized cell lines inducibly expressing the entire HCV open-reading frame to investigate the impact of viral protein expression on cell bioenergetics. It was shown that HCV protein expression has a profound effect on cell oxidative metabolism, with specific inhibition of complex I activity, depression of mitochondrial membrane potential and oxidative phosphorylation coupling efficiency, increased production of reactive oxygen and nitrogen species, as well as loss of the Pasteur effect. Importantly, all these effects were causally related to mitochondrial calcium overload, as inhibition of mitochondrial calcium uptake completely reversed the observed bioenergetic alterations., Conclusion: Expression of HCV proteins causes deregulation of mitochondrial calcium homeostasis. This event occurs upstream of further mitochondrial dysfunction, leading to alterations in the bioenergetic balance and nitro-oxidative stress. These observations provide new insights into the pathogenesis of hepatitis C and may offer new opportunities for therapeutic intervention.

Recent measurements of the flux control exerted by cytochrome c oxidase on the respiratory activity in intact cells have led to a re-appraisal of its regulatory function. We have further extended this in vivo study in the framework of the Metabolic Control Analysis and evaluated the impact of the mitochondrial transmembrane electrochemical potential (Deltamu(H+)) on the control strength of the oxidase. The results indicate that, under conditions mimicking the mitochondrial State 4 of respiration, both the flux control coefficient and the threshold value of cytochrome oxidase are modified with respect to the uncoupled condition. The results obtained are consistent with a model based on changes in the assembly state of the oxidative phosphorylation enzyme complexes and possible implications in the understanding of exercise-intolerance of human neuromuscular degenerative diseases are discussed.