Aging and Telomere Dysfunction in the Intestinal Stem Cell Niche

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Intestinal stem cell (ISC) activity declines with age, contributing to malabsorption and loss of intestinal barrier function. ISC aging is accompanied by telomere uncapping, and the ISC defects in humans and mice with prematurely uncapped telomeres (e.g. dyskeratosis congenita patients and mTerc KO mice) demonstrate that telomere uncapping is a cause of ISC dysfunction. Remarkably, both aging and telomere uncapping inhibit the canonical Wnt/β-catenin pathway, which is normally required for ISCs to support the tissue's rapid cell turnover. Moreover, experimental restoration of Wnt pathway activity rescues ISC defects in both settings. Although we and others have found Wnt defects in both aged and telomereopathic intestinal epithelium and underlying stroma of mice and humans, the identities of key cellular players re poorly understood. Recently, populations of mesenchymal cells in the lamina propria directly underlying the epithelium have been identified as a critical source of Wnt ligands required for ISC proliferative self- renewal. In the context of telomere dysfunction (or normal aging), ISCs exhibit a loss of self-renewal activity and a broad downregulation of Wnt target gene expression, corresponding to the downregulation of Wnt ligands now known to be secreted from this subepithelial mesenchyme. The goal of this proposal is to understand the consequences of telomere dysfunction and aging on ISC niche function. We hypothesize that both natural aging and acute telomere failure suppress stromal niche support for ISCs, contributing to the intestinal phenotypes associated with aging and telomeropathies such as dyskeratosis congenita. To address this hypothesis, we developed a novel mouse line that allows for direct in situ visualization and prospective isolation of stromal niche cells (telocytes) which supply Wnt ligands to the stem cell compartment. We will examine telocytes, along with additional niche components, in the context of temporal aging and acute telomere failure in mTerc-/- mice lacking the telomerase RNA component (mTerc), which leads to progressive telomere dysfunction. We will determine how aging and telomere defects alter niche function using a combination of in situ assays, single-cell transcriptomics, and organotypic co-culture assays in which primary stroma and intestinal organoids from either aged (vs. young) or telomereopathic (vs. control) epithelium are isolated and co-cultured in heterochronic or genotype admixed contexts, respectively. We will also pursue provocative preliminary observations that wildtype bone marrow transplantation restores ISC activity in mTerc-/- mice to address the hypothesis that marrow-derived cells can engraft into the subepithelial stroma and rescue failing epithelium. Ultimately, this proposal will elucidate how aging and telomere dysfunction alter the ISC niche, and will begin to evaluate novel strategies to ameliorate niche dysfunction.