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Increased glycolysis and HIF-1α activity are characteristics of cells under hypoxic or inflammatory conditions. Besides, in normal O 2 environments, elevated rates of glycolysis support critical cellular mechanisms such as cell survival. The purpose of this study was to analyze the contribution of HIF-1α to the energy metabolism and survival of human synovial fibroblasts (SF) under normoxic conditions. HIF-1α was silenced using lentiviral vectors or small-interfering RNA (siRNA) duplexes. Expression analysis by qRT-PCR and western blot of known HIF-1α target genes in hypoxia demonstrated the presence of functional HIF-1α in normoxic SF and confirmed the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a HIF-1α target even in normoxia. HIF-1α silencing induced apoptotic cell death in cultured SF and, similarly, treatment with glycolytic, but not with OXPHOS inhibitors, induced SF death. Finally, in vivo HIF-1α targeting by siRNA showed a significant reduction in the viability of human SF engrafted into a murine air pouch. Our results demonstrate that SF are highly dependent on glycolytic metabolism and that HIF-1α plays a regulatory role in glycolysis even under aerobic conditions. Local targeting of HIF-1α provides a feasible strategy to reduce SF hyperplasia in chronic arthritic diseases.

Mutations on the mitochondrial-expressed Branched Chain α-Keto acid Dehydrogenase Kinase (BCKDK) gene have been recently associated with a novel dietary-treatable form of autism. But, being a mitochondrial metabolism disease, little is known about the impact on mitochondrial performance. Here, we analyze the mitochondrial response to the BCKDK-deficiency in patient's primary fibroblasts by measuring bioenergetics, ultra-structural and dynamic parameters. A two-fold increase in superoxide anion production, together with a reduction in ATP-linked respiration and intracellular ATP levels (down to 60%) detected in mutants fibroblasts point to a general bioenergetics depletion that could affect the mitochondrial dynamics and cell fate. Ultrastructure analysis of BCKDK-deficient fibroblasts shows an increased number of elongated mitochondria, apparently associated with changes in the mediator of inner mitochondria membrane fusion, GTPase OPA1 forms, and in the outer mitochondrial membrane, mitofusin 2/MFN2. Our data support a possible hyperfusion response of BCKDK-deficient mitochondria to stress. Cellular fate also seems to be affected as these fibroblasts show an altered proportion of the cells on G0/G1 and G2/M phases. Knockdown of BCKDK gene in control fibroblasts recapitulates most of these features. Same BCKDK-knockdown in a MSUD patient fibroblasts unmasks the direct involvement of the accelerated BCAAs catabolism in the mitochondrial dysfunction. All these data give us a clue to understand the positive dietary response to an overload of branched-chain amino acids. We hypothesize that a combination of the current therapeutic option with a protocol that considers the oxidative damage and energy expenditure, addressing the patients' individuality, might be useful for the physicians., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background: Complex I (CI) deficiency is the most frequent cause of OXPHOS disorders. Recent studies have shown increases in reactive oxygen species (ROS) production and mitochondrial network disturbances in patients' fibroblasts harbouring mutations in CI subunits., Objectives: The present work evaluates the impact of mutations in the NDUFA1 and NDUFV1 genes of CI on mitochondrial bioenergetics and dynamics, in fibroblasts from patients suffering isolated CI deficiency., Results: Decreased oxygen consumption rate and slow growth rate were found in patients with severe CI deficiency. Mitochondrial diameter was slightly increased in patients' cells cultured in galactose or treated with 2'-deoxyglucose without evidence of mitochondrial fragmentation. Expression levels of the main proteins involved in mitochondrial dynamics, OPA1, MFN2, and DRP1, were slightly augmented in all patients' cells lines. The study of mitochondrial dynamics showed delayed recovery of the mitochondrial network after treatment with the uncoupler carbonyl cyanide m-chlorophenyl hydrazone (cccp) in patients with severe CI deficiency. Intracellular ROS levels were not increased neither in glucose nor galactose medium in patients' fibroblasts., Conclusion: Our main finding was that severe CI deficiency in patients harbouring mutations in the NDUFA1 and NDUFV1 genes is linked to a delayed mitochondrial network recovery after cccp treatment. However, the CI deficiency is neither associated with massive mitochondrial fragmentation nor with increased ROS levels. The different genetic backgrounds of patients with OXPHOS disorders would explain, at least partially, differences in the pathophysiological manifestations of CI deficiency., (Copyright 2010 Elsevier B.V. All rights reserved.)