. Gene expression profiling in Werner syndrome closely resembles that of normal aging. Proc Natl Acad Sci U S A. 2003 Oct 14;100(21):12259-64. PubMed.

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  1. This compelling report provides cDNA microarray and RT-PCR evidence that a premature aging disorder, Werner syndrome (WS), closely resembles the expression profile of normal aging in a cultured cell line. WS is an autosomal recessive disorder of premature aging, displaying features including gray hair, vascular disease, diabetes, and cataracts (1). A single mutation in the WRN gene causes a truncation in the Werner syndrome protein (WRN) (2). WRN belongs to the RecQ family of helicases, and may play a role in transcription. Defects in DNA replication, recombination, repair, and transcription have also been reported in WS (1).

    The authors used P33 labeled nylon membrane-based cDNA arrays from the DNA Array Unit, National Institute on Aging, containing 6,912 genes and ESTs to evaluate fibroblast cell lines (n=15) obtained from young (mean 22.5 years), old (90 years), and WS (29 years) subjects. Extracted RNA from each condition was pooled prior to hybridizing to the array platform. This "preprofile" mixing of input RNA is a different strategy than the conventional method of using one input RNA per array platform. However, the authors provide statistical evidence that sources of potential variation from individual observations is attenuated, lessening some of the concern surrounding this experimental design. Approximately six percent (or 435) of ESTs displayed a significant, i.e., greater than 1.5-fold, difference between the young cell lines and the WS cell lines. Seventy percent of alterations indicated a downregulation of transcripts. Of the 435 differences in gene expression, 249 were linked to genes with a known function. Some of the downregulated genes relevant to neuroscience included RNA polymerase II polypeptide A (POLR2A), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor receptor 2 (IGF2R).

    Interestingly, regulated genes in WS overlapped approximately 90 percent with genes regulated in old fibroblast cell lines as compared to the young reference group. Thus, the old and WS cell lines were remarkably similar, suggesting that a genetic program of normal aging accelerates in WS. The authors provide many well-designed statistical and graphical analyses to demonstrate these results, including clustering genes into relevant classes of transcripts such as DNA/RNA metabolism, cell growth, and stress-related markers. Moreover, cDNA array observations were validated by several RT-PCR experiments, showing similar relative changes, although quantitative real-time PCR was not performed.

    In summary, the authors provide evidence in cultured skin fibroblasts that normal aging and WS display similar deficits in gene expression. The authors present the concept that the WRN protein and its helicase activity are upstream regulators of "aging pathways." Clearly, this hypothesis needs further research, but it is intriguing, and it may shed light on both accelerated aging as well as gene expression underlying normal aging processes. The paradigm outlined by Kyng et al. is a useful strategy to identify disease-related genes in relation to human aging. Finally, although cultured fibroblasts were used as a source of input RNA in the present study, it is tempting to speculate what age-related changes would (or would not) be observed when using brain tissues with the inherent heterogeneous cell types as a source.

    References:

    . Werner syndrome and the function of the Werner protein; what they can teach us about the molecular aging process. Carcinogenesis. 2003 May;24(5):791-802. PubMed.

    . Impaired nuclear localization of defective DNA helicases in Werner's syndrome. Nat Genet. 1997 Aug;16(4):335-6. PubMed.