Telomere length analysis in the CALERIE trial

PROJECT SUMMARY Long-term caloric restriction (CR) is one of the most effective and well-studied intervention to extend both average and maximum life spans in a variety of species, from yeast to primates. Recent evidence from the Comprehensive Assessment of Long term Effects of Reducing Intake of Energy (CALERIE) suggests CR slows biological aging in humans, as measured by an algorithm applied to blood chemistry data. The mechanisms through which CR affects healthy lifespan involve a complex array of molecular pathways, from reduced inflammation and oxidative stress, improved mitochondrial function, enhanced autophagy and increased stress resistance. Notably, the aforementioned mechanisms are implicated in telomere length regulation. Yet, whether CR slows biological aging as indicated by telomere length, has not been addressed, as well as the role of inflammation and oxidative stress in the hypothesized mechanism. Understanding the molecular pathways by which CR increases healthspan could pinpoint new targets for anti-aging therapies. Here we will assay leukocyte telomere length (LTL) in CALERIE to test whether CR is associated with decreased LTL erosion as compared to the ad libitum control. LTL assays will be conducted using both the T/S ratio and the absolute qPCR assay, and communicated based on new qPCR reporting guidelines set by the Telomere Research Network. Further, making full use of the repeated measures of LTL obtained across the trial, we will examine when, during the two-year span, the differences in LTL emerge (e.g., earlier or later). Utilizing CALERIE biorepository, we will further test whether the hypothesized reduced LTL erosion in the CR arm is mediated by reduced level of inflammation and oxidative stress. In Aim 1a, intent-to-treat analysis will test whether CR is associated with reduced LTL erosion over 24 months, compared to the ad libitum control. Aim 1b will conduct dose-response analyses and investigate whether intervention effects are mediated by weight loss, and examine when, earlier or later in the 24-month trial, the CR effects on LTL change emerge. Aim 2 will test whether CR is associated with LTL changes over 24 months through reduced levels of inflammation at 12 and 24 months (factor analysis of CRP, ICAM1, IL1β, IL6, IL8, Leptin, MCP1, and TNF-α), and reduced levels of oxidative stress at 12 and 24 month (factor analysis of F2‐isoprostanes—iPF(2α)‐III, 2,3‐dinor‐iPF(2 α)‐III, iPF(2 α)‐VI, and 8,12‐iso‐iPF(2α)‐VI). This innovative work will determine from a first-ever randomized trial design if human caloric restriction slows cellular aging as measured by telomere length. Findings will help generate new knowledge about CR mechanisms in humans at the cellular level. The data generated will be shared with the CALERIE Biorepository upon completion of assays for investigators use.