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Mitochondria play essential roles in cardiac pathophysiology and the murine model has been extensively used to investigate cardiovascular diseases. In the present study, we characterized murine cardiac mitochondria using an LC/MS/MS approach. We extracted and purified cardiac mitochondria; validated their functionality to ensure the final preparation contains necessary components to sustain their normal function; and subjected these validated organelles to LC/MS/MS-based protein identification. A total of 940 distinct proteins were identified from murine cardiac mitochondria, among which, 480 proteins were not previously identified by major proteomic profiling studies. The 940 proteins consist of functional clusters known to support oxidative phosphorylation, metabolism, and biogenesis. In addition, there are several other clusters, including proteolysis, protein folding, and reduction/oxidation signaling, which ostensibly represent previously under-appreciated tasks of cardiac mitochondria. Moreover, many identified proteins were found to occupy other subcellular locations, including cytoplasm, ER, and golgi, in addition to their presence in the mitochondria. These results provide a comprehensive picture of the murine cardiac mitochondrial proteome and underscore tissue- and species-specification. Moreover, the use of functionally intact mitochondria insures that the proteomic observations in this organelle are relevant to its normal biology and facilitates decoding the interplay between mitochondria and other organelles.

ObjectiveTo compare effectiveness on correcting cranial and ear asymmetry between helmet therapy and counter positioning for deformational plagiocephaly (DP).MethodsRetrospective data of children diagnosed with DP who visited our clinic from November 2010 to October 2012 were reviewed. Subjects ≤10 months of age who showed ≥10 mm of diagonal difference were included for analysis. For DP treatment, information on both helmet therapy and counter positioning was given and either of the two was chosen by each family. Head circumference, cranial asymmetry measurements including diagonal difference, cranial vault asymmetry index, radial symmetry index, and ear shift were obtained by 3-dimensional head-surface laser scan at the time of initiation and termination of therapy.ResultsTwenty-seven subjects were included: 21 had helmet therapy and 6 underwent counter positioning. There was no significant difference of baseline characteristics, head circumferences and cranial asymmetry measurements at the initiation of therapy. The mean duration of therapy was 4.30±1.27 months in the helmet therapy group and 4.08±0.95 months in the counter positioning group (p=0.770). While cranial asymmetry measurements improved in both groups, significantly more improvement was observed with helmet therapy. There was no significant difference of the head circumference growth between the two groups at the end of therapy.ConclusionHelmet therapy resulted in more favorable outcomes in correcting cranial and ear asymmetry than counter positioning on moderate to severe DP without compromising head growth.

Mitochondrial calcium uptake proteins 1 and 2 (MICU1 and MICU2) mediate mitochondrial Ca2+ influx via the mitochondrial calcium uniporter (MCU). Its molecular action for Ca2+ uptake is tightly controlled by the MICU1–MICU2 heterodimer, which comprises Ca2+ sensing proteins which act as gatekeepers at low [Ca2+] or facilitators at high [Ca2+]. However, the mechanism underlying the regulation of the Ca2+ gatekeeping threshold for mitochondrial Ca2+ uptake through the MCU by the MICU1–MICU2 heterodimer remains unclear. In this study, we determined the crystal structure of the apo form of the human MICU1–MICU2 heterodimer that functions as the MCU gatekeeper. MICU1 and MICU2 assemble in the face-to-face heterodimer with salt bridges and methionine knobs stabilizing the heterodimer in an apo state. Structural analysis suggests how the heterodimer sets a higher Ca2+ threshold than the MICU1 homodimer. The structure of the heterodimer in the apo state provides a framework for understanding the gatekeeping role of the MICU1–MICU2 heterodimer.

ObjectiveOsteoarthritis (OA) appears to be associated with various metabolic disorders, but the potential contribution of amino acid metabolism to OA pathogenesis has not been clearly elucidated. Here, we explored whether alterations in the amino acid metabolism of chondrocytes could regulate OA pathogenesis.MethodsExpression profiles of amino acid metabolism-regulating genes in primary-culture passage 0 mouse chondrocytes were examined by microarray analysis, and selected genes were further characterised in mouse OA chondrocytes and OA cartilage of human and mouse models. Experimental OA in mice was induced by destabilisation of the medial meniscus (DMM) or intra-articular (IA) injection of adenoviruses expressing catabolic regulators. The functional consequences of arginase II (Arg-II) were examined in Arg2−/− mice and those subjected to IA injection of an adenovirus encoding Arg-II (Ad-Arg-II).ResultsThe gene encoding Arg-II, an arginine-metabolising enzyme, was specifically upregulated in chondrocytes under various pathological conditions and in OA cartilage from human patients with OA and various mouse models. Adenovirus-mediated overexpression of Arg-II in mouse joint tissues caused OA pathogenesis, whereas genetic ablation of Arg2 in mice (Arg2−/−) abolished all manifestations of DMM-induced OA. Mechanistically, Arg-II appears to cause OA cartilage destruction at least partly by upregulating the expression of matrix-degrading enzymes (matrix metalloproteinase 3 [MMP3] and MMP13) in chondrocytes via the nuclear factor (NF)-κB pathway.ConclusionsOur results indicate that Arg-II is a crucial regulator of OA pathogenesis in mice. Although chondrocytes of human and mouse do not identically, but similarly, respond to Arg-II, our results suggest that Arg-II could be a therapeutic target of OA pathogenesis.

Ca2+ regulates several cellular functions, including signaling events, energy production, and cell survival. These cellular processes are mediated by Ca2+-binding proteins, such as EF-hand superfamily proteins. Among the EF-hand superfamily proteins, allograft inflammatory factor-1 (AIF-1) and swiprosin-1/EF-hand domain-containing protein 2 (EFhd2) are cytosolic actin-binding proteins. AIF-1 modulates the cytoskeleton and increases the migration of immune cells. EFhd2 is also a cytoskeletal protein implicated in immune cell activation and brain cell functions. EFhd1, a mitochondrial fraternal twin of EFhd2, mediates neuronal and pro-/pre-B cell differentiation and mitoflash activation. Although EFhd1 is important for maintaining mitochondrial morphology and energy synthesis, its mechanism of action remains unclear. Here, we report the crystal structure of the EFhd1 core domain comprising a C-terminus of a proline-rich region, two EF-hand domains, and a ligand mimic helix. Structural comparisons of EFhd1, EFhd2, and AIF-1 revealed similarities in their overall structures. In the structure of the EFhd1 core domain, two Zn2+ ions were observed at the interface of the crystal contact, suggesting the possibility of Zn2+-mediated multimerization. In addition, we found that EFhd1 has Ca2+-independent β-actin-binding and Ca2+-dependent β-actin-bundling activities. These findings suggest that EFhd1, an actin-binding and -bundling protein in the mitochondria, may contribute to the Ca2+-dependent regulation of mitochondrial morphology and energy synthesis.

Objective. Osteoarthritis (OA) is initiated by pathogenic factors produced by multiple stimuli, including mechanical stress, metabolic stress, and/or inflammaging. This study was undertaken to identify novel low-grade inflammationassociated pathogenic mediators of OA.Methods. Candidate pathogenic molecules were screened using microarray data obtained from chondrocytes exposed to OA-associated catabolic factors. In mice with OA generated by destabilization of the medial meniscus (DMM), low-grade inflammation was induced by a high-fat diet or endotoxemia. Functions of candidate molecules in OA pathogenesis were examined using primary-culture chondrocytes from mice with DMM-induced OA, following intraarticular injection of adenovirus expressing the candidate gene. Specific functions of candidate genes were evaluated using whole-body gene-knockout mice.Results. Bioinformatics analysis identified multiple candidate pathogenic factors that were associated with lowgrade inflammation, including components of the Toll-like receptor (TLR) signaling pathways (e.g., TLR-2, TLR-4, lipopolysaccharide binding protein [LBP], and CD14). Overexpression of the individual TLR signaling components in mouse joint tissue did not alter cartilage homeostasis. However, the low-grade inflammation induced by a high-fat diet or endotoxemia markedly enhanced posttraumatic OA cartilage destruction in mice, and this exacerbation of cartilage destruction was significantly abrogated in LBP −/− and CD14 −/− mice. Additionally, LBP and CD14 were found to be necessary for the expression of matrix-degrading enzymes in mouse chondrocytes treated with proinflammatory cytokines.Conclusion. LBP and CD14, which are accessory molecules of TLRs, are necessary for the exacerbation of posttraumatic OA cartilage destruction resulting from low-grade inflammation, such as that triggered by a high-fat diet or endotoxemia.

During glycerol metabolism, the initial step of glycerol oxidation is catalysed by glycerol dehydrogenase (GDH), which converts glycerol to dihydroxyacetone in a NAD+‐dependent manner via an ordered Bi‐Bi kinetic mechanism. Structural studies conducted with GDH from various species have mainly elucidated structural details of the active site and ligand binding. However, the structure of the full GDH complex with both cofactor and substrate bound is not determined, and thus, the structural basis of the kinetic mechanism of GDH remains unclear. Here, we report the crystal structures of Escherichia coli GDH with a substrate analogue bound in the absence or presence of NAD+. Structural analyses including molecular dynamics simulations revealed that GDH possesses a flexible β‐hairpin, and that during the ordered progression of the kinetic mechanism, the flexibility of the β‐hairpin is reduced after NAD+ binding. It was also observed that this alterable flexibility of the β‐hairpin contributes to the cofactor binding and possibly to the catalytic efficiency of GDH. These findings suggest the importance of the flexible β‐hairpin to GDH enzymatic activity and shed new light on the kinetic mechanism of GDH.