The role of Sirt1: At the crossroad between promotion of longevity and protection against Alzheimer's disease neuropathology

Sirt1, a mammalian member of the sirtuin gene family, holds great potential for promoting longevity, preventing against disease and increasing cell survival. For example, studies suggest that the beneficial impact of caloric restriction in promoting longevity and cellular function may be mediated, in part, by Sirt1 through mechanisms involving PGC-1α, which plays important role in the regulation of cellular metabolism and inflammatory and antioxidant responses. Sirt1 may also interfere with mechanisms implicated in pathological disorders. We will present recent evidence indicating that Sirt1 may protect against Alzheimer's disease by interfering with the generation of β-amyloid peptides. We will discuss Sirt1 as a potential novel target, in addition to the development of Sirt1 activators for the prevention and treatment of Alzheimer's disease.     

Recurrent Tissue-Specific mtDNA Mutations Are Common in Humans

Mitochondrial DNA (mtDNA) variation can affect phenotypic variation; therefore, knowing its distribution within and among individuals is of importance to understanding many human diseases. Intra-individual mtDNA variation (heteroplasmy) has been generally assumed to be random. We used massively parallel sequencing to assess heteroplasmy across ten tissues and demonstrate that in unrelated individuals there are tissue-specific, recurrent mutations. Certain tissues, notably kidney, liver and skeletal muscle, displayed the identical recurrent mutations that were undetectable in other tissues in the same individuals. Using RFLP analyses we validated one of the tissue-specific mutations in the two sequenced individuals and replicated the patterns in two additional individuals. These recurrent mutations all occur within or in very close proximity to sites that regulate mtDNA replication, strongly implying that these variations alter the replication dynamics of the mutated mtDNA genome. These recurrent variants are all independent of each other and do not occur in the mtDNA coding regions. The most parsimonious explanation of the data is that these frequently repeated mutations experience tissue-specific positive selection, probably through replication advantage.     

Identification of genes from the obligate intracellular plant pathogen, Plasmodiophora brassicae

Plasmodiophora brassicae is an intracellular pathogen that infects plants in the Brassicaceae family. Although an important pathogen group, information on the genomic makeup of the plasmodiophorids is almost completely lacking. We performed suppression subtractive hybridization (SSH) between RNA from P. brassicae-infected and uninfected Arabidopsis tissue, then screened 232 clones from the resulting SSH library. In addition, we used an oligo-capping procedure to screen 305 full-length cDNA clones from the infected tissue. A total of 76 new P. brassicae gene sequences were identified, the majority of which were extended to full length at the 5' end by the use of RACE amplification. Many of the unisequences were predicted to contain signal peptides for ER translocation. Although we located few sequences in total, these markedly increase available data from the plasmodiophorids, and provide new opportunities to examine plasmodiophorid biology. Our study also points towards the best methods for future plasmodiophorid gene discovery.     

HIF-VEGF pathways are critical for chronic otitis media in Junbo and Jeff mouse mutants

Otitis media with effusion (OME) is the commonest cause of hearing loss in children, yet the underlying genetic pathways and mechanisms involved are incompletely understood. Ventilation of the middle ear with tympanostomy tubes is the commonest surgical procedure in children and the best treatment for chronic OME, but the mechanism by which they work remains uncertain. As hypoxia is a common feature of inflamed microenvironments, moderation of hypoxia may be a significant contributory mechanism. We have investigated the occurrence of hypoxia and hypoxia-inducible factor (HIF) mediated responses in Junbo and Jeff mouse mutant models, which develop spontaneous chronic otitis media. We found that Jeff and Junbo mice labeled in vivo with pimonidazole showed cellular hypoxia in inflammatory cells in the bulla lumen, and in Junbo the middle ear mucosa was also hypoxic. The bulla fluid inflammatory cell numbers were greater and the upregulation of inflammatory gene networks were more pronounced in Junbo than Jeff. Hif-1α gene expression was elevated in bulla fluid inflammatory cells, and there was upregulation of its target genes including Vegfa in Junbo and Jeff. We therefore investigated the effects in Junbo of small-molecule inhibitors of VEGFR signaling (PTK787, SU-11248, and BAY 43-9006) and destabilizing HIF by inhibiting its chaperone HSP90 with 17-DMAG. We found that both classes of inhibitor significantly reduced hearing loss and the occurrence of bulla fluid and that VEGFR inhibitors moderated angiogenesis and lymphangiogenesis in the inflamed middle ear mucosa. The effectiveness of HSP90 and VEGFR signaling inhibitors in suppressing OM in the Junbo model implicates HIF-mediated VEGF as playing a pivotal role in OM pathogenesis. Our analysis of the Junbo and Jeff mutants highlights the role of hypoxia and HIF-mediated pathways, and we conclude that targeting molecules in HIF-VEGF signaling pathways has therapeutic potential in the treatment of chronic OM.     

Excess of unpaired males in one of the World's most endangered seabirds, the Chatham Island taiko Pterodroma magentae

The Chatham Island taiko Pterodroma magentae (tchaik) is one of the World's most endangered seabirds with a population size of between 120–150 individuals that includes only 8–15 breeding pairs. Molecular techniques were used to identify the sex of taiko, which is difficult to assign morphologically. Blood samples were obtained from almost the entire known living population and from some birds now thought to be dead. We report an approximately even sex ratio in taiko chicks and adults associated with breeding burrows, but a large male-biased ratio in non-breeding adult birds caught on the ground. This finding suggests that unpaired males may be having difficulty in attracting females to burrows and that this situation may be an example of the Allee effect, that reduced density of potential mates acts to decrease population productivity. Identification of the sex of taiko using a molecular technique has important implications for the conservation management of this critically endangered species, including the future transfer of taiko chicks to a predator-excluded breeding site.