Over the past ten years my research has focused on the field of epigenetics, which investigates how environmental factors can affect gene activity thereby impacting our health and predisposition to diseases. Unlike genetic factors, epigenetic modifications are flexible and can store cell memories of life exposures such as diet, stress or environmental toxins. As such, they hold great potential in personalized health as biomarkers for exposure-driven chronic diseases such as obesity, diabetes, cardiovascular disease, and cancer.
I am currently leading the epigenetic analysis of the largest study ever undertaken in personalized nutrition on low carb vs. low fat diets – the DIETFITS study by Prof Christopher Gardner. My primary goal is to understand how weight-loss affects gene activity through epigenetic modifications, and whether we can use these modifications to predict diet response for personalized weight-loss strategies.
I also teach Nutritional Genomics at Stanford Continuing Studies, Stanford Sport Medicine and at the Stanford Center for Professional Development. An award-winning science communicator, I use creative forms of communication such as digital drawings to explain complex topics from the world of epigenetics and science. Finally, I serve as an advisor for personal genomics companies, self-tracking technology businesses, and companies interested in investing in precision health research.
Epigenetic Biomarkers for Precision Medicine in Obesity, Stanford University
Sex/Gender Differences in Diet Adherence and Weight Loss, Stanford University
Nutrigenetic Analysis in the iPOP Study, Stanford University
- Brittany Lee, School of Medicine
- Dalia Perelman, Med/Stanford Prevention Rsch, Medicine - Med/Stanford Prevention Research Center, Medicine - Med/Stanford Prevention Research Center
Research Project Leader, Max F. Perutz Laboratories (MFPL) (2011 - 2014)
Visiting Scholar, University of Oxford, UK (2013 - 2014)
Visiting Scholar, University of Southern California (2011 - 2012)
Identification of Nrl1 Domains Responsible for Interactions with RNA-Processing Factors and Regulation of Nrl1 Function by Phosphorylation.
International journal of molecular sciences
2021; 22 (13)
Pre-mRNA splicing is a key process in the regulation of gene expression. In the fission yeast Schizosaccharomyces pombe, Nrl1 regulates splicing and expression of several genes and non-coding RNAs, and also suppresses the accumulation of R-loops. Here, we report analysis of interactions between Nrl1 and selected RNA-processing proteins and regulation of Nrl1 function by phosphorylation. Bacterial two-hybrid system (BACTH) assays revealed that the N-terminal region of Nrl1 is important for the interaction with ATP-dependent RNA helicase Mtl1 while the C-terminal region of Nrl1 is important for interactions with spliceosome components Ctr1, Ntr2, and Syf3. Consistent with this result, tandem affinity purification showed that Mtl1, but not Ctr1, Ntr2, or Syf3, co-purifies with the N-terminal region of Nrl1. Interestingly, mass-spectrometry analysis revealed that in addition to previously identified phosphorylation sites, Nrl1 is also phosphorylated on serines 86 and 112, and that Nrl1-TAP co-purifies with Cka1, the catalytic subunit of casein kinase 2. In vitro assay showed that Cka1 can phosphorylate bacterially expressed Nrl1 fragments. An analysis of non-phosphorylatable nrl1 mutants revealed defects in gene expression and splicing consistent with the notion that phosphorylation is an important regulator of Nrl1 function. Taken together, our results provide insights into two mechanisms that are involved in the regulation of the spliceosome-associated factor Nrl1, namely domain-specific interactions between Nrl1 and RNA-processing proteins and post-translational modification of Nrl1 by phosphorylation.
View details for DOI 10.3390/ijms22137011
View details for PubMedID 34209806
Associations of Changes in Blood Lipid Concentrations with Changes in Dietary Cholesterol Intake in the Context of a Healthy Low-Carbohydrate Weight Loss Diet: A Secondary Analysis of the DIETFITS Trial.
2021; 13 (6)
In 2015, the Dietary Guidelines for Americans (DGA) eliminated the historical upper limit of 300 mg of dietary cholesterol/day and shifted to a more general recommendation that cholesterol intake should be limited. The primary aim of this secondary analysis of the Diet Intervention Examining the Factors Interacting With Treatment Success (DIETFITS) weight loss diet trial was to evaluate the associations between 12-month changes in dietary cholesterol intake (mg/day) and changes in plasma lipids, particularly low-density lipoprotein (LDL) cholesterol for those following a healthy low-carbohydrate (HLC) diet. Secondary aims included examining high-density lipoprotein (HDL) cholesterol and triglycerides and changes in refined grains and added sugars. The DIETFITS trial randomized 609 healthy adults aged 18-50 years with body mass indices of 28-40 kg/m2 to an HLC or healthy low-fat (HLF) diet for 12 months. Linear regressions examined the association between 12-month change in dietary cholesterol intake and plasma lipids in 208 HLC participants with complete diet and lipid data, adjusting for potential confounding variables. Baseline dietary cholesterol intake was 322 ± 173 (mean ± SD). At 12 months, participants consumed an average of 460 ± 227 mg/day of dietary cholesterol; 76% consumed over the previously recommended limit of 300 mg/day. Twelve-month changes in cholesterol intake were not significantly associated with 12-month changes in LDL-C, HDL-C, or triglycerides. Diet recall data suggested participants' increase in dietary cholesterol was partly due to replacing refined grains and sugars with eggs. An increase in daily dietary cholesterol intake to levels substantially above the previous 300 mg upper limit was not associated with a negative impact on lipid profiles in the setting of a healthy, low-carbohydrate weight loss diet.
View details for DOI 10.3390/nu13061935
View details for PubMedID 34200027
Adherence to Ketogenic and Mediterranean Study Diets in a Crossover Trial: The Keto-Med Randomized Trial.
2021; 13 (3)
Adherence is a critical factor to consider when interpreting study results from randomized clinical trials (RCTs) comparing one diet to another, but it is frequently not reported by researchers. The purpose of this secondary analysis of the Keto-Med randomized trial was to provide a detailed examination and comparison of the adherence to the two study diets (Well Formulated Ketogenic Diet (WFKD) and Mediterranean Plus (Med-Plus)) under the two conditions: all food being provided (delivered) and all food being obtained by individual participants (self-provided). Diet was assessed at six time points including baseline (×1), week 4 of each phase when participants were receiving food deliveries (×2), week 12 of each phase when participants were preparing and providing food on their own (×2), and 12 weeks after participants completed both diet phases and were free to choose their own diet pattern (×1). The adherence scores for WFKD and Med-Plus were developed specifically for this study. Average adherence to the two diet patterns was very similar during both on-study time points of the intervention. Throughout the study, a wide range of adherence was observed among participants-for both diet types and during both the delivery phase and self-provided phase. Insight from this assessment of adherence may aid other researchers when answering the important question of how to improve behavioral adherence during dietary trials. This study is registered at clinicaltrials.gov NCT03810378.
View details for DOI 10.3390/nu13030967
View details for PubMedID 33802709
Genetic variants for personalised management of very low carbohydrate ketogenic diets.
BMJ nutrition, prevention & health
2020; 3 (2): 363–73
The ketogenic diet (KD) is a low-carbohydrate, high-fat, adequate-protein diet proven to be effective for the reversal of obesity, metabolic syndrome and type 2 diabetes, and holding therapeutic potential for the prevention and treatment of other chronic diseases. Genetic and dynamic markers of KD response may help to identify individuals most likely to benefit from KD and point to individuals at higher risk for adverse health outcomes. Here, we provide a clinician-friendly review of state-of-the-art research on biomarkers of KD response for a variety of outcomes including weight loss, body composition and cognitive performance drawing data from both intervention trials and case reports of rare inborn errors of metabolism. We also present a selection of the most promising candidate genes to evaluate in future studies and discuss key aspects of study design and variant interpretation that may help accelerate the implementation of these biomarkers in clinical practice.
View details for DOI 10.1136/bmjnph-2020-000167
View details for PubMedID 33521546
Examining differences between overweight women and men in 12-month weight loss study comparing healthy low-carbohydrate vs. low-fat diets.
International journal of obesity (2005)
BACKGROUND/OBJECTIVES: Biological sex factors and sociocultural gender norms affect the physiology and behavior of weight loss. However, most diet intervention studies do not report outcomes by sex, thereby impeding reproducibility. The objectives of this study were to compare 12-month changes in body weight and composition in groups defined by diet and sex, and adherence to a healthy low carbohydrate (HLC) vs. healthy low fat (HLF) diet.PARTICIPANTS/METHODS: This was a secondary analysis of the DIETFITS trial, in which 609 overweight/obese nondiabetic participants (age, 18-50 years) were randomized to a 12-month HLC (n=304) or HLF (n=305) diet. Our first aim concerned comparisons in 12-month changes in weight, fat mass, and lean mass by group with appropriate adjustment for potential confounders. The second aim was to assess whether or not adherence differed by diet-sex group (HLC women n=179, HLC men n=125, HLF women n=167, HLF men n=138).RESULTS: 12-month changes in weight (p<0.001) were different by group. HLC produced significantly greater weight loss, as well as greater loss of both fat mass and lean mass, than HLF among men [-2.98kg (-4.47, -1.50); P<0.001], but not among women. Men were more adherent to HLC than women (p=0.02). Weight loss estimates within group remained similar after adjusting for adherence, suggesting adherence was not a mediator.CONCLUSIONS: By reporting outcomes by sex significant weight loss differences were identified between HLC and HLF, which were not recognized in the original primary analysis. These findings highlight the need to consider sex in the design, analysis, and reporting of diet trials.
View details for DOI 10.1038/s41366-020-00708-y
View details for PubMedID 33188301
- RW-2018-Research Workshop: The Effect of Nutrition on Epigenetic Status, Growth, and Health WILEY. 2019: 627–37
- Changes in blood lipid concentrations associated with changes in intake of dietary saturated fat in the context of a healthy low-carbohydrate weight-loss diet: a secondary analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial AMERICAN JOURNAL OF CLINICAL NUTRITION 2019; 109 (2): 433–41
Changes in blood lipid concentrations associated with changes in intake of dietary saturated fat in the context of a healthy low-carbohydrate weight-loss diet: a secondary analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial.
The American journal of clinical nutrition
Background: For low-carbohydrate diets, a public health approach has focused on the replacement of carbohydrates with unsaturated fats. However, little research exists on the impacts of saturated fat intake on the lipid profile in the context of whole-food-based low-carbohydrate weight-loss diets.Objectives: The primary aim of this secondary analysis of the DIETFITS weight loss trial was to evaluate the associations between changes in percentage of dietary saturated fatty acid intake (%SFA) and changes in low-density lipoproteins, high-density lipoproteins, and triglyceride concentrations for those following a healthy low-carbohydrate (HLC) diet. The secondary aim was to examine these associations specifically for HLC dieters who had the highest 12-month increases in %SFA.Methods: In the DIETFITS trial, 609 generally healthy adults, aged 18-50 years, with body mass indices of 28-40 kg/m2 were randomly assigned to a healthy low-fat (HLF) or HLC diet for 12 months. In this analysis, linear regression, both without and with adjustment for potential confounders, was used to measure the association between 12-month change in %SFA and blood lipids in 208 HLC participants with complete diet and blood lipid data.Results: Participants consumed an average of 12-18% of calories from SFA. An increase of %SFA, without significant changes in absolute saturated fat intake, over 12 months was associated with a statistically significant decrease in triglycerides in the context of a weight-loss study in which participants simultaneously decreased carbohydrate intake. The association between increase in %SFA and decrease in triglycerides was no longer significant when adjusting for 12-month change in carbohydrate intake, suggesting carbohydrate intake may be a mediator of this relationship.Conclusions: Those on a low-carbohydrate weight-loss diet who increase their percentage intake of dietary saturated fat may improve their overall lipid profile provided they focus on a high-quality diet and lower their intakes of both calories and refined carbohydrates. This trial was registered at clinicaltrials.gov as NCT01826591.
View details for PubMedID 30649213
RW-2018-Research Workshop: The Effect of Nutrition on Epigenetic Status, Growth, and Health.
JPEN. Journal of parenteral and enteral nutrition
The goal of the 2018 American Society for Parenteral and Enteral Nutrition (ASPEN) Research Workshop was to explore the influence of nutrition and dietary exposure to xenobiotics on the epigenome during critical periods in development and how these exposures influence both disease incidence and severity transgenerationally. A growing compendium of research indicates that the incidence and severity of common and costly human diseases may be influenced by dietary exposures and deficiencies that modify the epigenome. The greatest periods of vulnerability to these exposures are the periconception period and early childhood. Xenobiotics in the food chain, protein malnutrition, and methyl donor deficiencies could have a profound bearing on the risk of developing heart disease, diabetes, obesity, hypertension, and mental illness over multiple generations. The financial impact and the life burden of these diseases are enormous. These and other aspects of nutrition, epigenetics, and health are explored in this research workshop.
View details for PubMedID 30997688
A systematic review of studies of DNA methylation in the context of a weight loss intervention
2017; 9 (5): 769-787
Obesity results from the interaction of genetic and environmental factors, which may involve epigenetic mechanisms such as DNA methylation (DNAm).We have followed the PRISMA protocol to select studies that analyzed DNAm at baseline and end point of a weight loss intervention using either candidate-locus or genome-wide approaches.Six genes displayed weight loss associated DNAm across four out of nine genome-wide studies. Weight loss is associated with significant but small changes in DNAm across the genome, and weight loss outcome is associated with individual differences in baseline DNAm at several genomic locations.The identified weight loss associated DNAm markers, especially those showing reproducibility across different studies, warrant validation by further studies with robust design and adequate power.
View details for DOI 10.2217/epi-2016-0182
View details for Web of Science ID 000401642200014
View details for PubMedID 28517981
A systematic review of studies of DNA methylation in the context of a weight loss intervention
View details for DOI 10.2217/epi-2016-0182
The spliceosome-associated protein Nrl1 suppresses homologous recombination-dependent R-loop formation in fission yeast.
Nucleic acids research
2016; 44 (4): 1703-1717
The formation of RNA-DNA hybrids, referred to as R-loops, can promote genome instability and cancer development. Yet the mechanisms by which R-loops compromise genome instability are poorly understood. Here, we establish roles for the evolutionarily conserved Nrl1 protein in pre-mRNA splicing regulation, R-loop suppression and in maintaining genome stability. nrl1Δ mutants exhibit endogenous DNA damage, are sensitive to exogenous DNA damage, and have defects in homologous recombination (HR) repair. Concomitantly, nrl1Δ cells display significant changes in gene expression, similar to those induced by DNA damage in wild-type cells. Further, we find that nrl1Δ cells accumulate high levels of R-loops, which co-localize with HR repair factors and require Rad51 and Rad52 for their formation. Together, our findings support a model in which R-loop accumulation and subsequent DNA damage sequesters HR factors, thereby compromising HR repair at endogenously or exogenously induced DNA damage sites, leading to genome instability.
View details for DOI 10.1093/nar/gkv1473
View details for PubMedID 26682798
View details for PubMedCentralID PMC4770224
A Tetrahymena Hsp90 co-chaperone promotes siRNA loading by ATP-dependent and ATP-independent mechanisms
2015; 34 (4): 559-577
The loading of small interfering RNAs (siRNAs) and microRNAs into Argonaute proteins is enhanced by Hsp90 and ATP in diverse eukaryotes. However, whether this loading also occurs independently of Hsp90 and ATP remains unclear. We show that the Tetrahymena Hsp90 co-chaperone Coi12p promotes siRNA loading into the Argonaute protein Twi1p in both ATP-dependent and ATP-independent manners in vitro. The ATP-dependent activity requires Hsp90 and the tetratricopeptide repeat (TPR) domain of Coi12p, whereas these factors are dispensable for the ATP-independent activity. Both activities facilitate siRNA loading by counteracting the Twi1p-binding protein Giw1p, which is important to specifically sort the 26- to 32-nt siRNAs to Twi1p. Although Coi12p lacking its TPR domain does not bind to Hsp90, it can partially restore the siRNA loading and DNA elimination defects of COI12 knockout cells, suggesting that Hsp90- and ATP-independent loading of siRNA occurs in vivo and plays a physiological role in Tetrahymena.
View details for DOI 10.15252/embj.201490062
View details for Web of Science ID 000349695100012
View details for PubMedID 25588944
- How Healthy Eating Could Starve Out Cancer Europe PubMed Central. 2014
The Tetrahymena Argonaute-Binding Protein Giw1p Directs a Mature Argonaute-siRNA Complex to the Nucleus
2010; 140 (5): 692-703
Emerging evidence suggests that RNA interference (RNAi)-related processes act both in the cytoplasm and in the nucleus. However, the process by which the RNAi machinery is transported into the nucleus remains poorly understood. The Tetrahymena Argonaute protein Twi1p localizes to the nucleus and is crucial for small RNA-directed programmed DNA elimination. In this study, we identify Giw1p, which binds to Twi1p and is required for its nuclear localization. Furthermore, the endoribonuclease (Slicer) activity of Twi1p plays a vital role in the removal of one of the two strands of Twi1p-associated small interfering RNAs (siRNAs), leading to a functionally mature Twi1p-siRNA complex. Slicer activity is also shown to be required for nuclear localization of Twi1p and for its association with Giw1p. These results suggest that Giw1p senses the state of Twi1p-associated siRNAs and selectively transports the mature Twi1p-siRNA complex into the nucleus.
View details for DOI 10.1016/j.cell.2010.02.010
View details for Web of Science ID 000275197400018
View details for PubMedID 20211138
Study of an RNA helicase implicates small RNA-noncoding RNA interactions in programmed DNA elimination in Tetrahymena
GENES & DEVELOPMENT
2008; 22 (16): 2228-2241
Tetrahymena eliminates micronuclear-limited sequences from the developing macronucleus during sexual reproduction. Homology between the sequences to be eliminated and approximately 28-nucleotide small RNAs (scnRNAs) associated with an Argonaute family protein Twi1p likely underlies this elimination process. However, the mechanism by which Twi1p-scnRNA complexes identify micronuclear-limited sequences is not well understood. We show that a Twi1p-associated putative RNA helicase Ema1p is required for the interaction between Twi1p and chromatin. This requirement explains the phenotypes of EMA1 KO strains, including loss of selective down-regulation of scnRNAs homologous to macronuclear-destined sequences, loss of H3K9 and K27 methylation in the developing new macronucleus, and failure to eliminate DNA. We further demonstrate that Twi1p interacts with noncoding transcripts derived from parental and developing macronuclei and this interaction is greatly reduced in the absence of Ema1p. We propose that Ema1p functions in DNA elimination by stimulating base-pairing interactions between scnRNAs and noncoding transcripts in both parental and developing new macronuclei.
View details for DOI 10.1101/gad.481908
View details for Web of Science ID 000258486800009
View details for PubMedID 18708581