CD34 ⁺ mesenchymal cells are a major component of the intestinal stem cells niche at homeostasis and after injury

Abstract

The intestinal epithelium is continuously renewed by intestinal epithelial stem cells (IESCs) positioned at the base of each crypt. Mesenchymal-derived factors are essential to maintain IESCs; however, the cellular composition and development of such mesenchymal niche remains unclear. Here, we identify pericryptal CD34 + Gp38 + αSMA -mesenchymal cells closely associated with Lgr5+ IESCs. We demonstrate that CD34 + Gp38 + cells are the major intestinal producers of the niche factors Wnt2b, Gremlin1, and R-spondin1, and are sufficient to promote maintenance of Lgr5 + IESCs in intestinal organoids, an effect mainly mediated by Gremlin1. CD34+ Gp38 + cells develop after birth in the intestinal submucosa and expand around the crypts during the third week of life in mice, independently of the microbiota. We further show that pericryptal CD34+ cells are rapidly activated by intestinal injury, up-regulating niche factors Gremlin1 and R-spondin1 as well as chemokines, proinflammatory cytokines, and growth factors with key roles in gut immunity and tissue repair, including IL-7, Ccl2, Ptgs2, and Amphiregulin. Our results indicate that CD34 + Gp38 + mesenchymal cells are programmed to develop in the intestine after birth to constitute a specialized microenvironment that maintains IESCs at homeostasis and contribute to intestinal inflammation and repair after injury.T he adult intestinal epithelium is one of the most rapidly selfrenewing tissues in mammals. Intestinal epithelial cells renewal is ensured by intestinal epithelial stem cells (IESCs) located in the crypts and identified by expression of Lgr5 (1). IESCs are responsible for the continuous production of rapidly dividing transit-amplifying (TA) cells and of Paneth cells while maintaining the size of their own population. Upon leaving the crypts, TA cells proliferate and migrate upwards, differentiating into enterocytes, goblet cells, Tuft cells, and enteroendocrine cells, before undergoing apoptosis at the villus tip and being shed into the intestinal lumen (2).A complex gradient of factors maintains IESC stemness and proliferation, and supports enterocyte differentiation along the crypt-villus axis. Notably, Wnt signals are required to maintain the IESC niche (3, 4). In the crypts, Paneth cells express factors that promote stem cells growth, including the Wnt ligand Wnt3a, Notch ligands (Dll4, Dll1), and epidermal growth factor (EGF) (3,5, 6). In addition, a number of factors produced by mesenchymal cells have an essential role in the maintenance of IESCs such as Wnt2b, a canonical Wnt ligand that activates the Wnt/ β-catenin pathway (7); the Lgr4/5 ligand R-spondin1 (Rspo1), a strong mitogen for Wnt-responsive intestinal crypts (8-10); and Gremlin1 (Grem1), a bone morphogenetic protein (BMP) antagonist (11, 12). As epithelial cells ascend the crypt, BMPs produced by alpha-smooth muscle actin positive (αSMA + ) myofibroblasts restrain Wnt-induced epithelial proliferation while promoting their differentiation into secretory or absorptive epithelial cells (13,14). W...

Epithelial WNT Ligands Are Essential Drivers of Intestinal Stem Cell Activation

“…These findings have led to the hypothesis that mesenchymal WNT secretion is the primary mechanism for regulating the proliferative response in the stem cell niche. This idea is supported by several recent studies that have identified key mesenchymal cell types, marked by transcription factor Foxl1 and surface antigen CD34, which can potentiate WNT signaling (Aoki et al, 2016; Stzepourginski et al, 2017). By contrast, our results show that epithelial-secreted WNT ligands are essential for the expansion of LGR5 + cells and that proliferation and migration occur following virus-induced villus damage (Figures 3 and 4).…”

“…Studies in mice have indicated that cells in the intestinal epithelium and mesenchyme are two independent sources of WNT secretion (Farin et al, 2012; Gregorieff et al, 2005; Valenta et al, 2016). Paneth cells in the intestinal epithelium secrete WNT3, WNT6, and WNT9B; and myofibroblasts in the mesenchyme express WNT2, WNT4, and WNT5A (Gregorieff et al, 2005; Farin et al, 2012; Aoki et al, 2016; Stzepourginski et al, 2017; Valenta et al, 2016). Importantly, the epithelium and the mesenchyme are thought to be redundant sources of WNT secretion, with epithelial secreted WNT ligands being nonessential (Farin et al, 2012; Kabiri et al, 2014; San Roman et al, 2014; Valenta et al, 2016).…”

Development of organoids from mouse and human endometrium showing endometrial epithelium physiology and long-term expandability

“…Co-culture systems within the organoid field have just started to be developed (e.g. intestinal epithelial organoids combined with mesenchymal cells; Stzepourginski et al, 2017). Endometrial stroma may be needed to induce hormone responses to their full extent.…”

The hair follicle enigma

“…• Are some CD34+ connective tissue sheath cells [87] involved in ORS stem cell niches and homoeostasis? [88] • What is the functional significance of the restricted presence of Langerhans cells in the upper ORS? • What role do the few Merkel cells residing in the upper ORS play?…”