Location: Jean Mayer Human Nutrition Research Center On Aging
2023 Annual Report
Objectives
Objective 1: Determine how diet, the interactions of diet and specific foods/food components with individual/population genetics and/or the microbiome, as well as how etiologic factors including nutrients, metabolites, and enzymes, are related to eye health and the onset, prevalence, and progress of age-related macular degeneration (AMD) and cataract during aging.
Sub-objective 1A: Accumulation of AMDf and advanced glycation end products (AGEs) in high-glycemic (HG) fed mice can be arrested or reversed using GLO1 overexpression(GLO1-OE) or low-glycemic (LG) diet, but deletion of Nrf2 will compromise the eyes in the animals.
Objective 2: Identify mechanisms by which retina and lens function are maintained throughout life.
Sub-objective 2A: To test the hypothesis that specific gut microbiota are related to risk for AMDf and cataract, using microbe transfer and gnotobiotic mice.
Subobjective 2B: To test the hypothesis that enhancing autophagic lysosomal proteolytic system (ALPS) will improve protein quality control.
Subobjective 2C: To test the novel hypothesis that in order to accomplish the unidirectional process of lens fiber cell denucleation (LFCD), the lens has adopted many of the regulators, including the activation of cyclin dependent kinase (Cdk1) and the Cdk1 autoregulatory loop.
Objective 3: Find new biomarkers of eye tissue function using readily available samples, i.e., blood, urine, tears, cornea, skin, for in vivo assessment.
Sub-objective 3A: In order to gain more insight into the mechanisms behind the relationships between dietary glycemia, retina and lens phenotypes, AGEs, inflammatory markers, etc. we will identify and quantify the products produced and the changes to metabolism due to the diet in each genotype of animals from Objective 1. We use three platforms to accomplish these analyses. Together, they identify and quantify the broadest array of metabolites. These analyses will also identify many new potential biomarkers in urine and plasma from HG-, LG- mice.
Sub-objective 3B: Identification of novel biomarkers of human AMD.
Approach
Vision is our most cherished sense. Eyesight, however, deteriorates with age, leading to lowered quality of life among aged populations and increased public health expenditures. While no known cures exist for cataract and dry age-related macular degeneration (AMD), the most prevalent age-related eye diseases, our lab is discovering nutritional interventions that appear to delay onset or progression of these diseases. Micronutrients, including vitamin E, vitamin C, vitamin A, lutein and zinc, have been established as vital to eye health. We have new evidence that limiting intake of certain types of macronutrients, specifically, highly refined grains and highly processed carbohydrates – now a big part of the Western diet – can prolong visual function. We are building on this discovery. Our research will further define relations between diet, genotypes, the microbiome and metabolic products produced in response to dietary carbohydrate. This research will use human data, laboratory models and cell free approaches to find ways to stave off age-related eye disease and prolong vision. This includes elucidating pathways via which development is regulated and damaged proteins are removed. As people continue to live longer in the United States, it becomes imperative to identify ways to prevent the onset of these debilitating diseases, especially as we know almost all older adults will be affected by cataracts and close to 30 percent of people over 75 years will be diagnosed with age-related macular degeneration.
Progress Report
a) We have aged wild-type mice, Nrf2-knockout mice, p62-knockout mice, and Glyoxalase 1 overexpressing mice (Glo1-Tg) on high glycemic (HG) and low glycemic (LG) diets and have evaluated ocular health, microbiomes, and metabolomes from these mice. Wild-type mice fed HG diets develop age-related macular degeneration-like phenotypes, while those fed LG diets do not. The microbiomes and metabolomes are substantially affected by these diets.
b) Nrf2-knockout mice show the same dietary relationship as wild-type mice, with HG diet causing age-related macular degeneration-like phenotypes. Aged HG-fed Nrf2-knockout mice develop more severe ocular phenotypes than wild-type mice. Nrf2-knockout microbiomes and metabolomes are significantly different than wild-type mice, indicating important roles for Nrf2 in the intestine.
c) p62-knockout mice have been aged and fed HG and LG diets until 18-months. In vivo imaging of eyes has not revealed a gross phenotype, but careful histologic and ultrastructural evaluation may reveal phenotypes.
d) Glo1-Tg mice have been aged and fed HG and LG diets until 24-months. In vivo imaging of eyes revealed that the eyes of Glo1-Tg mice fed HG diets look significantly healthier and have fewer indications of retinal lesions than control mice fed HG diets. Paradoxically Glo1-Tg mice fed LG diets had increased retinal lesions relative to control mice fed LG diets. This may indicate a potential gene-diet interaction, something that we have observed previously in complement factor H knockout mice fed LG diets. The Glo1-Tg microbiome was not different than the wild-type microbiome. Metabolomics is underway that will reveal specific alterations that relate to the role of Glo1 in glycation.
e) Fecal microbiota transplants (FMT) were used to introduce HG microbiota into LG-fed mice and LG microbiota into HG-fed mice. Metabolic health appeared similar between LG-fed mice with or without HG microbiota; however, metabolic health was improved in HG-fed mice with LG microbiota. Ocular phenotypes depended on the source of microbiota and not the diet. HG-fed mice with LG microbiota were protected from eye disease, whereas LG-fed mice with HG microbiota developed retinopathy resembling that seen in HG-fed mice. We have completed evaluation of the gut microbiome and the plasma metabolome and have identified metabolites whose levels depend on gut microbiota and that correlate with ocular changes. These studies have identified two bacteria associated with eye health, Akkermansia muciniphila and Bacteroides thetaiotaomicron. Both bacteria are associated with metabolic health in preclinical research studies.
f) We have performed a series of in vitro and in vivo experiments to demonstrate that p62 is involved in cellular removal of advanced glycation end-products (AGEs) via autophagic degradation. First, we showed that inhibition of autophagy, either using chloroquine to prevent lysosomal acidification, or in aged animals led to increased accumulation of AGEs. Similar findings were observed in tissues and cells lacking p62, including within the retinal pigmented epithelium. This increased glycative burden was associated with increased cellular stress sensitivity. Finally, we showed that enhancing autophagy, either by overexpressing p62, or by addition of rapamycin reduced the accumulation of AGEs in tissues and in nematodes. We are now measuring the levels of AGEs in aged p62 knockout mice fed HG and LG diets.
g) We have performed extensive metabolomics analysis on plasma samples from wild-type mice, microbiome manipulated mice, and genetic knockout/transgenic mice that are fed HG or LG diets and that have divergent retinal outcomes. Through integrative analysis of metabolomics findings with retinal outcomes, metabolic outcomes, and inflammatory outcomes, we have identified metabolites that serve as dietary, retinal, or microbiome biomarkers. One class of these metabolites are bile acids, whose levels increase with LG diet, depend on the gut microbiome, and who may signal neuroprotectively to the eye. Another class of these metabolites are organic acids and dicarboxylic acids that increase with LG diet. Surprisingly, these metabolites appear to depend on gut microbiota and appear to connect with each other via citric acid cycle intermediates, particularly malate, fumarate, maleate, and succinate. Decreases in oxidative phosphorylation in the retinal pigmented epithelium are linked to age-related macular degeneration in humans and may indicate important roles for signals from the gut in communicating cellular energetics.
Accomplishments
Review Publications
Weinberg, J., Gaur, M., Swaroop, A., Taylor, A. 2022. Proteostasis in aging-associated ocular disease. Molecular Aspects of Medicine. https://doi.org/10.1016/j.mam.2022.101157.
Taylor, A., Gu, Y., Chang, M., Yang, W., Francisco, S., Rowan, S., Bejarano, E., Pruitt, S., Zhu, L., Weiss, G., Brennan, L., Kantorow, M., Whitcomb, E. 2023. Repurposing a cyclin dependent kinase 1 (CDK1) mitotic regulatory network to complete terminal differentiation in lens fiber cells. Investigative Ophthalmology and Visual Science. 64(2). https://doi.org/10.1167/iovs.64.2.6.
Taylor, A., Bejarano-Fernandezel, E. 2021. Boosting proteolytic pathways as a treatment against glycation-derived damage in the brain? Neural Regeneration Research. 17(2):320-322. https://doi.org/10.4103/1673-5374.317971.
Grant, M.B., Bernstein, P.S., Boesze-Battaglia, K., Chew, E.0., Curcio, C.A., Kenney, M.C., Klaver, C., Philp, N., Rowan, S., Sparrow, J., Spaide, R.F., Taylor, A. 2022. Inside out: relations between the microbiome, nutrition, and eye health. Experimental Eye Research. https://doi.org/10.1016/j.exer.2022.109216.
Rowan, S., Jiang, S., Francisco, S., Pomatto, L., Ma, Z., Jiao, X., Campos, M., Aryal, S., Patel, S., Mahaling, B., Riazuddin, S.A., Duh, E., Lachke, S., Hejtmancik, J.F., De Cabo, R., Fitzgerald, P., Taylor, A. 2021. Aged Nrf2-null mice develop all major types of age-related cataracts. Investigative Ophthalmology and Visual Science. 62(15):10. https://doi.org/10.1167/iovs.62.15.10.
