Osteoblastic N-cadherin is not required for microenvironmental support and regulation of hematopoietic stem and progenitor cells

Abstract

Hematopoietic stem cell (HSC) regulation is highly dependent on interactions with the marrow microenvironment. Controversy exists on N-cadherin's role in support of HSCs. Specifically, it is unknown whether microenvironmental N-cadherin is required for normal marrow microarchitecture and for hematopoiesis. To determine whether osteoblastic N-cadherin is required for HSC regulation, we used a genetic murine model in which deletion of IntroductionThe molecular signals that mediate regulatory microenvironmental osteoblastic-hematopoietic interactions provide potential therapeutic targets for hematopoietic stem cell (HSC) manipulation 1 but are still largely unknown. Based on the essential role of cadherins in fate specification of germline stem cells 2 and the close proximity of N-cadherin-expressing osteoblastic cells to HSCs, [3][4][5][6] it was initially proposed that N-cadherin may provide HSCs with instructive interactions with their niche. However, much debate was subsequently raised by reports questioning N-cadherin expression by HSCs, 7 whereas others suggested that different N-cadherin levels characterize functionally distinct HSC populations, 5,8,9 which may respond to niche manipulation. 10 Moreover, inducible global genetic N-cadherin deletion lacks hematopoietic defects, 11 but knockdown of N-cadherin in HSCs suppresses their long-term engraftment. 12 Whereas in HSCs N-cadherin, when present, is expressed at very low levels, 13 osteoblastic cells express N-cadherin at several differentiation stages, both in immature and mature cells. 3,14 Indeed, whereas germline deletion of the gene encoding N-cadherin (Cdh2) is embryonically lethal, 15 hemizygous mice already display osteoblastic defects, having accentuated bone loss with ovariectomy. 16 Moreover, recent data have suggested differential roles of N-cadherin at various stages of osteoblastic differentiation, with actions of N-cadherin both on osteogenic commitment as well as at terminal differentiation. 14 In this work, our goal was to determine whether targeted deletion of Cdh2 in maturing osteoblasts alters the BM microarchitecture, HSC number, and function in homeostasis and disrupts the action of parathyroid hormone (PTH) on the skeleton and/or on hematopoietic stem and progenitor cells (HSPCs). Methods MiceCol2.3-Cre mice expressing the Cre-recombinase under the control of the 2.3-kb fragment of the ␣1(I) collagen gene promoter were kindly provided by Dr Gerard Karsenty. 17 Mating of Col2.3-Cre with Cdh2 fl mice (generated in Dr Glenn L. Radice's laboratory, Thomas Jefferson University, Philadelphia, PA) 18 resulted in mice carrying the Col2.3-Cre ϩ Cadh2 fl/fl genotype, which had specific inactivation of N-cadherin in cells of the osteoblastic lineage, designated as OB-NCadh for the rest of the manuscript. 14 This line was maintained in the C57bl/6 background, and expression of the CD45.2 congenic marker was confirmed. Wild-type (WT) mice expressing the CD45.1 congenic marker (B6.SJL-Ptprc a Pep3 b /BoyJ CD45.1) were purchased from The Jackson L...

Tissue-Engineered Model of Human Osteolytic Bone Tumor

“…A number of studies have demonstrated a direct relationship between osteoclast activity and bone remodeling and an increase in connectivity density. 33,34 Importantly, and as expected, the connectivity density (Conn D) was slightly higher in the group with osteoclasts (Fig. 3B).…”

The hematopoietic stem cell niche in homeostasis and disease

“…9,78,79 Notably, activation of the PTH receptor solely in osteocytes is not sufficient to expand HSPCs, suggesting differential effects of PTH on osteolineage cells depending on maturation stages. 9,80 The ability of PTH (1-34) to promote HSPC support and maintenance is likely the result of its stimulatory effect on various cell types in the marrow, including osteolineage cells and, indirectly, osteoclasts and even macrophages.…”

Adhesion in the stem cell niche: biological roles and regulation

“…In the HSC niche, HSCs and osteoblasts express N-cadherin (Zhang et al, 2003), and multiple studies have suggested that N-cadherin is required for maintaining HSCs in the niche for long-term self-renewal (Haug et al, 2008;Hosokawa et al, 2010a;Hosokawa et al, 2010b). However, other independent studies have disputed the role of Ncadherin in controlling HSC self-renewal (Bromberg et al, 2012;Greenbaum et al, 2012;Kiel et al, 2009). The contradictory conclusions concerning the role of N-cadherin in the regulation of HSC self-renewal could arise from different experimental methods.…”