CD44 and TLR4 mediate hyaluronic acid regulation of Lgr5⁺ stem cell proliferation, crypt fission, and intestinal growth in postnatal and adult mice

Abstract

Riehl TE, Santhanam S, Foster L, Ciorba M, Stenson WF. CD44 and TLR4 mediate hyaluronic acid regulation of Lgr5 ϩ stem cell proliferation, crypt fission, and intestinal growth in postnatal and adult mice. Am J Physiol Gastrointest Liver Physiol 309: G874 -G887, 2015. First published October 1, 2015; doi:10.1152/ajpgi.00123.2015.-Hyaluronic acid, a glycosaminoglycan in the extracellular matrix, binds to CD44 and Toll-like receptor 4 (TLR4). We previously addressed the role of hyaluronic acid in small intestinal and colonic growth in mice. We addressed the role of exogenous hyaluronic acid by giving hyaluronic acid intraperitoneally and the role of endogenous hyaluronic acid by giving PEP-1, a peptide that blocks hyaluronic acid binding to its receptors. Exogenous hyaluronic acid increased epithelial proliferation but had no effect on intestinal length. PEP-1 resulted in a shortened small intestine and colon and diminished epithelial proliferation. In the current study, we sought to determine whether the effects of hyaluronic acid on growth were mediated by signaling through CD44 or TLR4 by giving exogenous hyaluronic acid or PEP-1 twice a week from 3-8 wk of age to wild-type, CD44Ϫ/Ϫ , and TLR4 Ϫ/Ϫ mice. These studies demonstrated that signaling through both CD44 and TLR4 were important in mediating the effects of hyaluronic acid on growth in the small intestine and colon. Extending our studies to early postnatal life, we assessed the effects of exogenous hyaluronic acid and PEP-1 on Lgr5 ϩ stem cell proliferation and crypt fission. Administration of PEP-1 to Lgr5 ϩ reporter mice from postnatal day 7 to day 14 decreased Lgr5 ϩ cell proliferation and decreased crypt fission. These studies indicate that endogenous hyaluronic acid increases Lgr5 ϩ stem cell proliferation, crypt fission, and intestinal lengthening and that these effects are dependent on signaling through CD44 and TLR4. hyaluronic acid; CD44; Toll-like receptor 4; intestinal growth; crypt fission; Lgr5 stem cell proliferation HYALURONIC ACID (HA), a glycosaminoglycan polymer with repeating units of disaccharides composed of D-glucuronic acid and N-acetyl-D-glucosamine, is an important constituent of the extracellular matrix. HA is secreted by many cell types; it is assembled at the plasma membrane by HA synthases (HASs) and extruded into the extracellular space. The HA chain can extend up to 2 ϫ 10 5 disaccharides and up to 25 m long. HA expression is increased in many injury states, including Crohn's disease in humans, dextran sodium sulfate (DSS)-induced colitis in mice, and intestinal radiation injury (8,16,24). The angiogenic, inflammatory, and immunostimulatory effects of HA are mediated by binding to its receptors. The HA receptor CD44 is expressed on the plasma membrane of most cells, including fibroblasts, smooth muscle cells, epithelial cells, and immune cells (19). In addition to binding to CD44, HA also binds to Toll-like receptors 2 and 4 (TLR2 and TLR4), which are components of the innate immune system (7, 20, 24). TLR2 and TLR4 are widel...

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