Doctor of Philosophy, University of California Berkeley (2012)
Bachelor of Science, McGill University (2007)
Roeland Nusse, Postdoctoral Faculty Sponsor
Assessing the role of Wnt ligands in stem cell biology
Deterioration of adult stem cells accounts for much of aging-associated compromised tissue maintenance. How stem cells maintain metabolic homeostasis remains elusive. Here, we identified a regulatory branch of the mitochondrial unfolded protein response (UPR(mt)), which is mediated by the interplay of SIRT7 and NRF1 and is coupled to cellular energy metabolism and proliferation. SIRT7 inactivation caused reduced quiescence, increased mitochondrial protein folding stress (PFS(mt)), and compromised regenerative capacity of hematopoietic stem cells (HSCs). SIRT7 expression was reduced in aged HSCs, and SIRT7 up-regulation improved the regenerative capacity of aged HSCs. These findings define the deregulation of a UPR(mt)-mediated metabolic checkpoint as a reversible contributing factor for HSC aging.
View details for DOI 10.1126/science.aaa2361
View details for PubMedID 25792330
Despite recent controversy about their function in some organisms, sirtuins are thought to play evolutionarily conserved roles in lifespan extension. Whether sirtuins can reverse aging-associated degeneration is unknown. Tissue-specific stem cells persist throughout the entire lifespan to repair and maintain tissues, but their self-renewal and differentiation potential become dysregulated with aging. We show that SIRT3, a mammalian sirtuin that regulates the global acetylation landscape of mitochondrial proteins and reduces oxidative stress, is highly enriched in hematopoietic stem cells (HSCs) where it regulates a stress response. SIRT3 is dispensable for HSC maintenance and tissue homeostasis at a young age under homeostatic conditions but is essential under stress or at an old age. Importantly, SIRT3 is suppressed with aging, and SIRT3 upregulation in aged HSCs improves their regenerative capacity. Our study illuminates the plasticity of mitochondrial homeostasis controlling stem cell and tissue maintenance during the aging process and shows that aging-associated degeneration can be reversed by a sirtuin.
View details for DOI 10.1016/j.celrep.2013.01.005
View details for Web of Science ID 000321895200007
View details for PubMedID 23375372
A major cause of aging and numerous diseases is thought to be cumulative oxidative stress, resulting from the production of reactive oxygen species (ROS) during respiration. Calorie restriction (CR), the most robust intervention to extend life span and ameliorate various diseases in mammals, reduces oxidative stress and damage. However, the underlying mechanism is unknown. Here, we show that the protective effects of CR on oxidative stress and damage are diminished in mice lacking SIRT3, a mitochondrial deacetylase. SIRT3 reduces cellular ROS levels dependent on superoxide dismutase 2 (SOD2), a major mitochondrial antioxidant enzyme. SIRT3 deacetylates two critical lysine residues on SOD2 and promotes its antioxidative activity. Importantly, the ability of SOD2 to reduce cellular ROS and promote oxidative stress resistance is greatly enhanced by SIRT3. Our studies identify a defense program that CR provokes to reduce oxidative stress and suggest approaches to combat aging and oxidative stress-related diseases.
View details for DOI 10.1016/j.cmet.2010.11.015
View details for Web of Science ID 000285569100014
View details for PubMedID 21109198
Post-translational modifications play a critical role in regulating protein function. Increasingly, determination of protein identity, estimation of abundance, and characterization of post-translational modifications are required for analysis of protein-mediated cell signaling networks. As such, we report an integrated and rapid multispectral immunoprobed isoelectric focusing technique for identifying specific proteins bearing post-translational modifications. Immunoprobed isoelectric focusing is composed of isoelectric focusing in a large pore-size polyacrylamide gel to determine protein pI followed by immobilization of pI-resolved proteins. Proteins are immobilized via covalent attachment to a channel-filling benzophenone-functionalized polyacrylamide gel via brief UV exposure (photoblot), followed by multispectral antibody-based detection. The assay correlates observed post-translational modifications to pI shifts relative to the unmodified protein of interest. During the electrokinetically driven antibody probing stage, we observed nonuniform electrophoretic probe mobility along the channel axis. The spatially varying mobility is attributed to nonuniform charge arising from covalent attachment of ampholytes to the benzophenone-functionalized gel matrix during the photoblotting step. Using the multistep microfluidic assay, phosphorylated and acetylated forms of heat shock protein 27 and superoxide dismutase 2 were detected, respectively. The assay reported protein isoforms in immune-purified sample and raw cell lysate in 2 hours with sample volume requirements of 2 μL. This new assay is well-matched to systems biology frameworks for study of protein post-translational modifications.
View details for DOI 10.1021/ac3035053
View details for Web of Science ID 000317031600048
View details for PubMedID 23363036
Folic acid fortification and supplementation has increased folate intake and blood folate concentrations and successfully reduced the incidence of neural tube defects. However, the developmental consequences of high folate intake are unknown. This study investigated the impact of high folate intake, alone or with methylenetetrahydrofolate reductase (MTHFR) deficiency, on embryonic and placental development in mice.Mthfr +/+ or +/- pregnant mice on a control diet (CD; recommended intake of folic acid for rodents) or folic acid-supplemented diet (FASD; 20-fold higher than the recommended intake) were examined for embryonic loss, delay, and defects at 10.5 and 14.5 days post coitum (dpc); 10.5-dpc placenta, and 14.5-dpc embryo hearts were studied histologically.Total plasma folate was 10-fold higher in FASD compared to CD mice; plasma homocysteine levels were not affected by diet. At 10.5 dpc, the FASD was associated with embryonic delay and growth retardation, and may confer susceptibility to embryonic defects. The FASD did not adversely affect 10.5-dpc placental development. At 14.5 dpc, embryos from the FASD Mthfr +/+ group were delayed and the FASD was associated with thinner ventricular walls in embryonic hearts. There was a significant interaction between maternal MTHFR deficiency and a high folate diet for several developmental outcomes.Our study suggests that high folate intake may have adverse effects on fetal mouse development and that maternal MTHFR deficiency may improve or rescue some of the adverse outcomes. These findings underscore the need for additional studies on the potential negative impact of high folate intake during pregnancy.
View details for DOI 10.1002/bdra.20754
View details for Web of Science ID 000286401700002
View details for PubMedID 21254354
The beneficial effects of calorie restriction diet in extending lifespan and preventing diseases have long been recognized. Recent genetic and molecular studies in model organisms began to uncover the molecular regulation of calorie restriction response, with the gene SIR2 playing an essential role. This article summarizes the latest development on how mammalian SIR2 homologs coordinately regulate the calorie restriction response.
View details for DOI 10.1016/j.bbapap.2009.09.015
View details for Web of Science ID 000279571200003
View details for PubMedID 19782772
Despite extensive research on mild methylenetetrahydrofolate reductase (MTHFR) deficiency and low dietary folate in different disorders, the association of these metabolic disturbances with a variety of congenital defects and pregnancy complications remains controversial. In this study we investigated the effects of MTHFR and dietary folate deficiency at 10.5 days post coitum (dpc) in our mouse model of mild MTHFR deficiency.Mthfr +/+ and +/- female mice were fed a control or folic acid-deficient diet for 6 weeks, then mated with Mthfr +/- males. At 10.5 dpc, embryos were examined and placentae were collected for histologic evaluation.Maternal MTHFR and folate deficiencies resulted in increased developmental delays and smaller embryos. We also observed a low frequency of a variety of embryonic defects in the experimental groups, such as neural tube, heart looping, and turning defects; these results mimic the low incidence and multifactorial nature of these anomalies in humans. Folate-deficient mice also had increased embryonic losses and severe placental defects, including placental abruption and disturbed patterning of placental layers. Folate-deficient placentae had decreased ApoA-I expression, and there was a trend toward a negative correlation between ApoA-I expression with maternal homocysteine concentrations.Our study provides biological evidence linking maternal MTHFR and dietary folate deficiencies to adverse pregnancy outcomes in mice. It underscores the importance of folate not only in reducing the incidence of early embryonic defects, but also in the prevention of developmental delays and placental abnormalities that may increase susceptibility to other defects and to reproductive complications.
View details for DOI 10.1002/bdra.20575
View details for Web of Science ID 000267471400003
View details for PubMedID 19215022