Date Published: August 29, 2017
Publisher: Impact Journals LLC
Author(s): Emily C. Moorefield, Sarah F. Andres, R. Eric Blue, Laurianne Van Landeghem, Amanda T. Mah, M. Agostina Santoro, Shengli Ding.
Intestinal epithelial stem cells (IESCs) are critical to maintain intestinal epithelial function and homeostasis. We tested the hypothesis that aging promotes IESC dysfunction using old (18-22 months) and young (2-4 month) Sox9-EGFP IESC reporter mice. Different levels of Sox9-EGFP permit analyses of active IESC (Sox9-EGFPLow), activatable reserve IESC and enteroendocrine cells (Sox9-EGFPHigh), Sox9-EGFPSublow progenitors, and Sox9-EGFPNegative differentiated lineages. Crypt-villus morphology, cellular composition and apoptosis were measured by histology. IESC function was assessed by crypt culture, and proliferation by flow cytometry and histology. Main findings were confirmed in Lgr5-EGFP and Lgr5-LacZ mice. Aging-associated gene expression changes were analyzed by Fluidigm mRNA profiling. Crypts culture from old mice yielded fewer and less complex enteroids. Histology revealed increased villus height and Paneth cells per crypt in old mice. Old mice showed increased numbers and hyperproliferation of Sox9-EGFPLow IESC and Sox9-EGFPHigh cells. Cleaved caspase-3 staining demonstrated increased apoptotic cells in crypts and villi of old mice. Gene expression profiling revealed aging-associated changes in mRNAs associated with cell cycle, oxidative stress and apoptosis specifically in IESC. These findings provide new, direct evidence for aging associated IESC dysfunction, and define potential biomarkers and targets for translational studies to assess and maintain IESC function during aging.
Aging is a complex process resulting in decreased tissue function, and cellular and molecular damage. Adult stem cells that self-renew and maintain progenitors that appropriately differentiate into functional cell types are essential to maintain tissue homeostasis and repair throughout lifespan . Aging-associated exhaustion and dysfunction have been reported in highly prolife-rative hematopoietic stem cells (HSC) , hair follicle stem cells (HFSC) , muscle stem cells  and adipose-derived mesenchymal stem cells . Reduced stem cell function contributes to aging associated degenerative diseases , and is associated with molecular changes including accumulation of reactive oxygen species (ROS) , defects in cell cycle regulation  and cellular senescence .
Until 2007 the study of IESC and the effect of aging on IESC was hampered by a lack of specific biomarkers. Our findings in the Sox9-EGFP reporter mouse, confirmed in Lgr5-EGFP and Lgr5-LacZ reporter mice models, provide new and direct evidence that aging is associated with increases in IESC number, proliferation, and increases in IESC apoptosis in vivo and functional impairment of isolated IESC in vitro. Our findings of increased villus height and expansion of Paneth cells in old mice indicate altered intestinal homeostasis with aging.