Mitochondrial Sirt3 contributes to the bone loss caused by aging or estrogen deficiency.

Altered mitochondria activity in osteoblasts and osteoclasts has been implicated in the loss of bone mass associated with aging and estrogen deficiency - the 2 most common causes of osteoporosis. However, the mechanisms that control mitochondrial metabolism in bone cells during health or disease remain unknown. The mitochondrial deacetylase sirtuin-3 (Sirt3) has been earlier implicated in age-related diseases. Here, we show that deletion of Sirt3 had no effect on the skeleton of young mice but attenuated the age-related loss of bone mass in both sexes. This effect was associated with impaired bone resorption. Osteoclast progenitors from aged Sirt3-null mice were able to differentiate into osteoclasts, though the differentiated cells exhibited impaired polykaryon formation and resorptive activity, as well as decreased oxidative phosphorylation and mitophagy. The Sirt3 inhibitor LC-0296 recapitulated the effects of Sirt3 deletion in osteoclast formation and mitochondrial function, and its administration to aging mice increased bone mass. Deletion of Sirt3 also attenuated the increase in bone resorption and loss of bone mass caused by estrogen deficiency. These findings suggest that Sirt3 inhibition and the resulting impairment of osteoclast mitochondrial function could be a novel therapeutic intervention for the 2 most important causes of osteoporosis.

Characterization of an alternative oxidase activity of Histoplasma capsulatum.

Histoplasma capsulatum possesses a branched mitochondrial electron transport chain, with both cyanide-sensitive and -insensitive oxygen-consuming activities. The latter, carried out by a single subunit enzyme termed 'alternative oxidase', is the focus of this report. AOX1 cDNA clones were isolated and direct evidence that the cDNA ORF encodes functional alternative oxidase is reported. Also reported are the generation of an antiserum to the AOX1 protein product, and specific detection in vivo of the mRNA and protein products of the AOX1 gene. Finally, initial studies of regulation of H. capsulatum AOX1 gene expression demonstrated that RNA abundance was increased after hydrogen peroxide-mediated oxidative stress and after inhibition of mitochondrial electron transport enzymes with antimycin A or sodium cyanide. This pattern of regulation is consistent with the hypothesis that alternative oxidase contributes to survival of H. capsulatum after oxidative or metabolic stress and may be important for virulence of this pathogenic organism. The GenBank Accession Nos for the cDNA sequences reported in this paper are AF133236, AF133237 (AOX1).