Objective. Superoxide dismutase 2 (SOD2) is downregulated in osteoarthritis (OA). This study was undertaken to investigate the functional effects of this downregulation in the context of oxidative damage and mitochondrial dysfunction.Methods. Lipid peroxidation in articular cartilage from OA patients and from lesion-free control subjects with femoral neck fracture was assessed by measuring malondialdehyde levels using the thiobarbituric acid reactive substances assay. Long-range polymerase chain reaction amplification and a mitochondrial DNA (mtDNA) strand break assay were used to investigate the presence of somatic large-scale mtDNA rearrangements in cartilage. Microscale oxygraphy was used to explore possible changes in mitochondrial respiratory activity between OA and control chondrocytes. RNA interference was used to determine the effects of SOD2 depletion on lipid peroxidation, mtDNA damage, and mitochondrial respiration.Results. OA cartilage had higher levels of lipid peroxidation compared to control cartilage, and lipid peroxidation was similarly elevated in SOD2-depleted chondrocytes. SOD2 depletion led to a significant increase in mtDNA strand breaks in chondrocytes, but there was no notable difference in the level of strand breaks between OA and control chondrocytes. Furthermore, only very low levels of somatic, large-scale mtDNA rearrangements were identified in OA cartilage. OA chondrocytes showed less spare respiratory capacity (SRC) and higher proton leak compared to control chondrocytes. SOD2-depleted chondrocytes also showed less SRC and higher proton leak.Conclusion. This is the first study to analyze the effects of SOD2 depletion in human articular chondrocytes in terms of changes to oxidation and mitochondrial function. The findings indicate that SOD2 depletion in chondrocytes leads to oxidative damage and mitochondrial dysfunction, suggesting that SOD2 downregulation is a potential contributor to the pathogenesis of OA.Mitochondria are small organelles that are present in large (but variable) numbers in cells of all eukaryotic organisms. They have their own maternally inherited, ϳ16-kb extrachromosomal DNA, the mitochondrial genome (mtDNA), implying that mitochondrial function is regulated by both nuclear and mitochondrial transcripts (1). Mitochondria are considered the powerhouse of the cell, as they are the main sites of ATP production by oxidative phosphorylation (herein referred to as OXPHOS). Reactive oxygen species (ROS), a major by-product of OXPHOS, can act positively as signaling molecules. However, when the levels of ROS are high, this can cause oxidative damage in the form of mtDNA damage and lipid peroxidation (2). The mitochondria and the cell contain defenses against ROS, such as members of the superoxide dismutase (SOD) family (SOD1, SOD2, and SOD3), catalase, and glutathione peroxidase (3).

Nucleus positioning is key for intracellular organization, cell differentiation, and organ development and is affected in many diseases, including myopathies due to alteration in amphiphysin-2 (BIN1). The actin and microtubule cytoskeletons are essential for nucleus positioning, but their crosstalk in this process is sparsely characterized. Here, we report that impairment of amphiphysin/BIN1 in Caenorhabditis elegans, mammalian cells, or muscles from patients with centronuclear myopathy alters nuclear position and shape. We show that AMPH-1/BIN1 binds to nesprin and actin, as well as to the microtubule-binding protein CLIP170 in both species. Expression of the microtubule-anchoring CAP-GLY domain of CLIP170 fused to the nuclear-envelope-anchoring KASH domain of nesprin rescues nuclear positioning defects of amph-1 mutants. Amphiphysins thus play a central role in linking the nuclear envelope with the actin and microtubule cytoskeletons. We propose that BIN1 has a direct and evolutionarily conserved role in nuclear positioning, altered in myopathies.