Location: Jean Mayer Human Nutrition Research Center On Aging
2024 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
Gut microbiome composition profoundly impacts host physiology and is modulated by several environmental factors, most prominently diet. The composition of gut microbiota change over the lifespan, particularly during the earliest and latest stages. However, we know less about diet-aging interactions on the gut microbiome, which are critical for our interpretation of data generated for Objectives 1 and 2. We previously showed that diets with different glycemic indices, based on the ratio of rapidly-digested amylopectin to slowly-digested amylose, led to altered composition of gut microbiota in C57BL/6J mice. We have now examined the role of aging in influencing dietary effects on microbiota composition. We studied three age groups of mice: young (4 months), middle-aged (13.5 months), and old (22 months), all fed either high glycemic (HG) or low glycemic (LG) diets matched for caloric content and macronutrient composition. Young mice displayed lower alpha diversity scores than middle-aged counterparts, but exhibited more pronounced differences in beta diversity between diets. In contrast, old mice had slightly lower alpha diversity scores than middle-aged mice, with significantly higher beta diversity distances. Within-group variance was lowest in young, LG-fed mice and highest in old, HG-fed mice. Differential abundance analysis revealed taxa associated with both aging and diet. Most differential taxa demonstrated significant interactions between diet and aging. Notably, several members of the Lachnospiraceae family increased with aging and HG diet, while taxa from the Bacteroides H genus increased with the LG diet. Akkermansia muciniphila decreased with aging. These findings illustrate the complex interplay between diet and aging in shaping the gut microbiota, potentially contributing to age-related disease, such as age-related macular degeneration (AMD) and cataracts.
A High Glycemic Index (HGI) diet induces hyperglycemia, an etiologic risk factor in major diseases affecting multiple organ systems. As part of Objective 1, we evaluated tissue-specific adaptation to HGI diet after one- or 12-months in the liver and retina of C57BL/6J wild-type mice. In the liver, genes associated with inflammation and fatty acid metabolism were altered within one-month of HGI diet, whereas 12-month HGI diet-fed group showed dysregulated expression of cytochrome P450 genes and overexpression of key lipogenic factors including Srebf1 and Elovl5. In contrast, retinal transcriptomes exhibited fewer HGI-related changes after one-month, and notable alterations in energy metabolism genes were apparent after 12-months. Fatty acid profiles of liver samples revealed elevated levels of monounsaturated fatty acids and reduced saturated and polyunsaturated fatty acids in the HGI group. Additionally, HGI resulted in an increase in blood low-density lipoprotein, and diet-aging interactions were found to affect liver expression of mitochondrial oxidative phosphorylation genes, and disease-associated genes in the retina. Our findings provide new insights into retinal and hepatic adaptive mechanisms to dietary hyperglycemia.
Ubiquitination is a key regulator of protein stability and function. The multifunctional protein p27 is known to be degraded by the proteasome following K48-linked ubiquitination. As part of Objective 3, we recently reported that when the ubiquitin conjugating enzyme UbcH7 (UBE2L3) is overexpressed, p27 is stabilized and cell cycle is arrested in multiple diverse cell types including eye lens, retina, HEK-293 and HELA cells. But the ubiquitin ligase associated with this stabilization of p27 remained a mystery. Starting with an in vitro ubiquitination screen, we identified RSP5 as the yeast E3 ligase partner of UbcH7 in the ubiquitination of p27. Screening of the homologous human NEDD4 family of E3 ligases revealed that SMURF1, but not its close homolog SMURF2, stabilizes p27 in cells. We found that SMURF1 ubiquitinates p27 with K29O but not K29R or K63O ubiquitin in vitro, demonstrating a strong preference for K29 chain formation. Consistent with SMURF1/UbcH7 stabilization of p27, we also found that SMURF1, UbcH7, and p27 promote cell migration, whereas knockdown of SMURF1 or UbcH7 reduces cell migration. We further demonstrated colocalization of SMURF1/p27 and UbcH7/p27 at the leading edge of migrating cells. In sum, these results indicate that SMURF1 and UbcH7 work together to produce K29-linked ubiquitin chains on p27, resulting in stabilization of p27 and promoting its cell-cycle independent function of regulating cell migration.
The function of the lens is to focus light on the retina and lens clarity is necessary for proper vision. To achieve clarity, the lens undergoes a programmed removal of its organelles, including the cell nuclei in the central lens fiber cells. As part of Objective 3, we hypothesized that a similar process may be responsible for the removal of nuclei in lens fiber cells. We used a chick lens culture model to demonstrate that compounds which inhibit nuclear envelope breakdown during cell division also inhibit nuclear removal in the lens. Furthermore, using three mouse models, we showed that an inhibitor of cell division also decreased nuclear removal in lens fiber cells. Thus, the lens utilizes proteins involved in cell division to achieve lens clarity by removing rather than replicating nuclei in the central lens fibers.
Accomplishments
Review Publications
Mondal, A.K., Brock, D.C., Rowan, S., Yang, Z., Rojulpote, K.V., Smith, K.M., Francisco, S.G., Bejarano-Fernandez, E., English, M., Deik, A., Jeanfavre, S., Clish, C.B., Remaley, A.T., Taylor, A., Swaroop, A. 2024. Selective transcriptomic dysregulation of metabolic pathways in liver and retina by short and long-term dietary hyperglycemia. iScience. https://doi.org/10.1016/j.isci.2024.108979.
Bejarano, E., Whitcomb, E., Pfeiffer, R.L., Rose, K.L., Asensio, M.J., Rodriguez-Navarro, J.A., Ponce-Mora, A., Canto, A., Almansa, I., Schey, K.L., Jones, B.W., Taylor, A., Rowan, S. 2023. Unbalanced redox status network as an early pathological event in congenital cataracts. Redox Biology. https://doi.org/10.1016/j.redox.2023.102869.
Bejarano-Fernandez, E., Weinberg, J., Clark, M., Taylor, A., Rowan, S., Whitcomb, E. 2023. Redox regulation in age-related cataracts: roles for glutathione, vitamin C, and the NRF2 signaling pathway. Nutrients. https://doi.org/ 10.3390/nu15153375.