FOXO transcription factor regulation: a 'molecular code' for longevity?

A goal of the laboratory is to determine the molecular mechanisms by which FOXO factors translate environmental stimuli into changes in gene expression programs that prolong lifespan (1, 2). We use a combination of molecular, genomic, and proteomic approaches to analyze the regulation of FOXO expression and post-translational modifications in response to environmental conditions known to affect longevity, including caloric restriction and oxidative stress stimuli. Our underlying hypothesis is that FOXO3 post-translational modifications may serve as a 'molecular code' to recruit protein partners to specific subsets of target genes in response to oxidative stress. We are currently testing this hypothesis in mammalian cell culture systems using genomic tools.

Stem cells and aging: role of FOXO and SIRT1

During aging, the pool of functional adult neural stem cells (NSC) decreases. The depletion of functional adult neural stem cells (NSC) may contribute to cognitive changes associated with normal or pathological aging. Preserving the pool of stem cells may help in the repair of the nervous system in response to oxidative stress and may prevent the decline in age-dependent behaviors (3). To gain insight into the mechanisms responsible for the maintenance of adult NSC, we are currently examining how the families of FOXO factors and SIRT deacetylases regulate the adult NSC pool during aging in NSC cultures and in vivo. Understanding the mechanisms underlying the maintenance of adult NSC should provide critical insights into the regenerative potential of these stem cells.

Aging in the nervous system

FOXO transcription factors and SIRT deacetylase play a central role in longevity in invertebrates. However, several important questions remain regarding the importance of these 'pro-longevity' genes at the organismal level in mammals. Our laboratory studies the importance of FOXO factors and SIRT deacetylases in the nervous system by creating and studying mouse mutants for the genes encoding these factors. We are particularly interested in identifying the role of FOXO and SIRT in the aging nervous system. Understanding the specific role of FOXO in age-dependent behaviors will help identify ways to prevent the decline in these functions during aging. 

Mechanisms of dietary restriction-induced longevity

Dietary restriction (DR) -- restriction in food intake without malnutrition-- extends lifespan in a wide range of species. DR has the remarkable ability to slow the onset of age-dependent traits and diseases. To understand the molecular mechanisms underlying the beneficial effects of DR on longevity, we developed a DR assay (sDR) in the nematode worm Caenorhabditis elegans (4). We found that AMPK (aak-2 in worms), a protein kinase involved in energy-sensing, is crucial for this method of DR to extend lifespan. AMPK acts in part by enhancing the activity of DAF-16, the worm FOXO transcription factor (4). Using tandem mass spectrometry in collaboration with Steve Gygi at Harvard Medical School, we showed that AMPK directly phosphorylates FOXO/DAF-16 at previously unidentified regulatory sites. AMPK also regulates FOXO factors in mammals (5). Using genome wide microarray analysis, we found that AMPK phosphorylation of human FOXO3 induces changes in the expression of specific target genes, including energy metabolism and stress resistance genes. We are currently studying the mechanisms underlying the extension of lifespan by DR in worms and in mammals.

 

Development of the killifish Nothobranchius furzeri as a model to study longevity

The search for genes that control longevity has greatly benefited from invertebrate model organisms. However, identifying and studying novel longevity genes in higher animals has been hampered by the absence of short-lived vertebrate models. To circumvent this limitation, we are studying a new aging model system, the exceptionally short-lived killifish Nothobranchius furzeri (6, 7). This vertebrate species has a maximal lifespan of only 2.5 months and it comprises several natural populations that strikingly differ in life expectancy. We are developing genetics and genomics tools to study longevity and aging in N. furzeri. Our goal is to use this rapidly aging model system to discover novel genes and mechanisms underlying longevity in vertebrates.