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Rel 3.2 - 8th March 1998



Sex differences in brain aging: a quantitative magnetic resonance imaging study.

Coffey CE, Lucke JF, Saxton JA, Ratcliff G, Unitas LJ, Billig B, Bryan RN

Department of Psychiatry, Henry Ford Health System, Detroit, Mich 48202, USA.

Arch Neurol 1998 Feb;55(2):169-179

BACKGROUND: Little is known about the effect of sex on age-related changes in brain structure. METHODS: Quantitative magnetic resonance imaging of the brain was performed in 330 elderly (age range, 66-96 years) volunteers living independently in the community, all of whom were participants in the Cardiovascular Health Study. Blinded measurements of global and regional brain size were made from T1-weighted axial images by means of computer-assisted edge detection and trace methods. High measurement reliabilities were obtained. RESULTS: Age-specific changes in brain size were significantly greater in men than women for the peripheral (sulcal) cerebrospinal fluid volume, the lateral (sylvian) fissure cerebrospinal fluid volume, and the parieto-occipital region area. Main effects of age were observed for all the remaining brain regions examined (cerebral hemisphere volume, frontal region area, temporoparietal region area, lateral ventricular volume, and third ventricle volume), but these effects were similar in men and women. Asymmetries in brain structures were not affected by aging in either sex. CONCLUSIONS: Our results are generally consistent with the few published studies on sex differences in brain aging and suggest that, for at least some structures, aging effects may be more apparent in men than women. The neurobiological bases and functional correlates of these sex differences require further investigation.

Role of mitochondrial DNA mutations in human aging: implications for the central nervous system and muscle.

Brierley EJ, Johnson MA, Lightowlers RN, James OF, Turnbull DM

Department of Neurology, The Medical School, University of Newcastle upon Tyne, UK.

Ann Neurol 1998 Feb;43(2):217-223

It has been proposed that one mechanism for nerve and muscle dysfunction with age involves the mitochondria. Mitochondria contain the only DNA outside the nucleus in mammalian cells. Mitochondrial DNA (mtDNA) has a high mutation rate, and low levels of pathogenic mutations have been found in tissues from elderly subjects. However, the role of these mutations in the aging process is uncertain unless a mechanism can be identified that would lead to a biochemical defect. In muscle tissue from normal elderly subjects we show that there are muscle fibers with very low activity of cytochrome c oxidase, suggestive of a mtDNA defect. In these cytochrome c oxidase-deficient fibers we have found very high levels of mutant mtDNA. In addition, different mtDNA mutations are present in different fibers, which explains why there is a low overall incidence of an individual mutation in tissues from elderly subjects. These studies show a direct age-related correlation between a biochemical and genetic defect in normal human tissues and that mtDNA abnormalities are involved in the aging process in human muscle.

TRF2 protects human telomeres from end-to-end fusions.

van Steensel B, Smogorzewska A, de Lange T

The Rockefeller University, New York, New York 10021, USA.

Cell 1998 Feb 6;92(3):401-413

The mechanism by which telomeres prevent end-to-end fusion has remained elusive. Here, we show that the human telomeric protein TRF2 plays a key role in the protective activity of telomeres. A dominant negative allele of TRF2 induced end-to-end chromosome fusions detectable in metaphase and anaphase cells. Telomeric DNA persisted at the fusions, demonstrating that TTAGGG repeats per se are not sufficient for telomere integrity. Molecular analysis suggested that the fusions represented ligation of telomeres that have lost their single-stranded G-tails. Therefore, TRF2 may protect chromosome ends by maintaining the correct structure at telomere termini. In addition, expression of mutant forms of TRF2 induced a growth arrest with characteristics of senescence. The results raise the possibility that chromosome end fusions and senescence in primary human cells may be caused by loss by TRF2 from shortened telomeres.



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