Hardy-Weinberg Equilibrium in different mitochondrial haplogroups of four genes associated with neuroprotection and neurodegeneration

ABSTRACT Background: Malfunctioning or damaged mitochondria result in altered energy metabolism, redox equilibrium, and cellular dynamics and is a central point in the pathogenesis of neurological disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and Amyotrophic Lateral Sclerosis. Therefore, it is of utmost importance to identify mitochondrial genetic susceptibility markers for neurodegenerative diseases. Potential markers include the respiratory chain enzymes Riboflavin kinase (RFK), Flavin adenine dinucleotide synthetase (FAD), Succinate dehydrogenase B subunit (SDHB), and Cytochrome C1 (CYC1). These enzymes are associated with neuroprotection and neurodegeneration. Objective: To test if variants in genes RFK, FAD, SDHB and CYC1 deviate from Hardy-Weinberg Equilibrium (HWE) in different human mitochondrial haplogroups. Methods: Sequence variants in genes RFK, FAD, SDHB and CYC1 of 2,504 non-affected individuals of the 1,000 genomes project were used for mitochondrial haplogroup assessment and HWE calculations in different mitochondrial haplogroups. Results: We show that RFK variants deviate from HWE in haplogroups G, H, L, V and W, variants of FAD in haplogroups B, J, L, U, and C, variants of SDHB in relation to the C, W, and A and CYC1 variants in B, L, U, D, and T. HWE deviation indicates action of selective pressures and genetic drift. Conclusions: HWE deviation of particular variants in relation to global populational HWE, could be, at least in part, associated with the differential susceptibility of specific populations and ethnicities to neurodegenerative diseases. Our data might contribute to the epidemiology and diagnostic/prognostic methods for neurodegenerative diseases.

Brownian dynamics simulation of cytochrome c diffusion and binding with cytochrome c1 in mitochondrial crista

Cytochrome c (Cc) protein shuttles electrons from respiratory chain complex III — from cytochrome c1 (Cc1) subunit — to complex IV during oxidative phosphorylation, in intermembrane space of mitochondria and cristae lumen. With Leigh syndrome (LS), the crista lumen width (CLW) increases, and ATP production declines. One of the questions raised by this situation is to find out how ATP production impairs at LS. Using the simulation of Brownian dynamics, we tested whether the increase in CLW declines respiration at the stage of electron transport of Cc to Cc1. We designed a Brownian dynamics model of horse Cc diffusion and binding with bovine Cc1 in solution by the ProKSim software. The values of the model parameters were estimated to obtain the same dependence of the second-order association rate constant on the ionic strength as in the experiment [1]. Estimated values of the model parameters were used in the model of the reaction in the cristae lumen. The model scene was a parallelepiped. The distance between the two surfaces simulated crystal membranes varied. We received increasing of half-life time of Cc diffusion and binding with Cc1 at increasing CLW. For membrane surface 90Åx100Å (close to the membrane size of complex III), the half-life time of the process changed from 0.098 to 0.22 µs with increasing cristae lumen width from 120 to 160 Å. But due to the half-life time of electron transfer between proteins in the complex, estimated in [1], is higher (100.5µs), the overall time shouldn’t change. To simulate impair of ATP production in the model with an increase in the crista lumen width, we probably need to add to the model IV complex and take into account the dimerization defect of ATP synthase.

MicroRNA-661 Enhances TRAIL or STS Induced Osteosarcoma Cell Apoptosis by Modulating the Expression of Cytochrome c1

Aim: Osteosarcoma (OS) is an aggressive bone malignancy that affects rapidly growing bones and is associated with a poor prognosis. Our previous study showed that cytochrome c1 (CYC1), a subunit of the cytochrome bc1 complex (complex III) of the mitochondrial electron chain, is overexpressed in human OS tissues and cell lines and its silencing induces apoptosis in vitro and inhibits tumor growth in vivo. Here, we investigated the mechanism underlying the modulation of CYC1 expression in OS and its role in the resistance of OS to apoptosis. Methods: qRT-PCR, luciferase reporter assay, western blotting, fow cytometry, and animal experiments were performed in this study. Results: MicroRNA (miR)-661 was identified as a downregulated miRNA in OS tissues and cells and shown to directly target CYC1. Ectopically expressed miR-661 inhibited OS cell growth, promoted apoptosis, and reduced the activity of mitochondrial complex III. miR-661 overexpression enhanced TRAIL or STS induced apoptosis and promoted the release of cytochrome c into the cytosol, which induced caspase-9 activation, and these effects were abolished by a caspase-3 inhibitor. Overexpression of CYC1 rescued the effects of miR-661 on sensitizing OS cells to TRAIL or STS induced apoptosis, indicating that the antitumor effect of miR-661 is mediated by the downregulation of CYC1. In vivo, miR-661 overexpression sensitized tumors to TRAIL or STS induced apoptosis in a xenograft mouse model, and these effects were attenuated by co-expression of CYC1. Conclusion: Taken together, our results indicate that miR-661 plays a tumor suppressor role in OS mediated by the downregulation of CYC1, suggesting a potential mechanism underlying cell death resistance in OS.