Effects of inflammaging on intestinal epithelial cells and aspirin chemoprevention.

PROJECT ABSTRACT
Previous randomized controlled trials (RCT)s demonstrate that low-dose aspirin (LDA, 81-100mg/day) reduces
the risk of colorectal cancer (CRC). The U.S. Preventive Services Task Force (USPSTF) recommends LDA to
prevent CRC in adults aged 50-59. However, a recent RCT among 19,114 older (65+) individuals reported that
initiating LDA late in life had no benefit on CRC incidence and was potentially detrimental for mortality. Because
CRC incidence rises with age, understanding the relationship and functional impact of aging on the
chemopreventive effects of LDA is a high priority. Our working model is that the effect of LDA on the colon
differs in older individuals due to age-related changes in intestinal stem cell (ISC) number and function secondary
to a process of higher basal inflammatory tone, a.k.a. “inflammaging”. Normally, CRC appears to be primarily
driven by oncogenic mutations in Lgr5+ ISCs and aspirin-like NSAIDs appear to preferentially eliminate
premalignant Lgr5+ ISCs. However, our preliminary data demonstrates that old mice (20-22 months [mos]), as
compared to young mice (2-3 mos), have fewer, less regenerative small intestinal Lgr5+ ISCs, which are also
less tumorigenic in an Apc tumor suppressor model. Nonetheless, like humans, aged mice spontaneously
develop a greater number of tumors, indicating that non-Lgr5+ cells are also the origin of intestinal cancers in
aged mice and that these cells are less sensitive to LDA. LDA modulates prostaglandin (PG) levels, including
PGE2. We also find that PGE2 impacts ISC function through its receptor Ptger4 and this signaling can drive ISCs
into a fetal-like state (Hopx+) that is mediated by Hippo/Yap signaling. Thus, in the setting of inflammaging,
elevated PGE2 may irreversibly compromise the colon (cISC) pool leading to compensatory functions within
select cISCs that promote tumorigenesis. Through our double-blind, placebo-controlled RCT, we demonstrated
that modulation of PG tone and inhibition of PG synthesis is central to aspirin’s mode of action. Our central
hypothesis is that aging and age-related processes promote a decrease in the cISC pool (Lgr5+ cISCs) that is
normally sensitive to aspirin chemoprevention. We propose that initiation of LDA earlier in life protects against
this age-related, inflammation-associated, and/or PGE2-mediated damage to the cISC pool. In contrast, with
advancing age there may be a “point-of-no-return” in which initiation of LDA is no longer protective against age-
related changes in the cISC pool. In this proposal, we will expand our existing RCT to examine the impact of
LDA on colonic epithelium at single cell resolution, patient-derived organoids, and urinary PGs in older adults.
We will use novel in vivo preclinical models to dissect the role of inflammaging on PG signaling and LDA on
cISCs. We will then examine the causality of these pathways on colon tumor incidence and progression. These
studies may offer a biological explanation for the unexpected finding of a differential effect of LDA in older adults,
which may influence clinical guidelines or the development of biomarkers to optimize LDA’s risk-benefit profile.

Grant Number: 5R01CA257523-05
NIH Institute/Center: NIH
Principal Investigator: Andrew Chan