Osteoblastic Wntless deletion differentially regulates the fate and functions of bone marrow-derived stem cells in relation to age.

Although functional association between Wnt signaling and bone homeostasis has been well described through genetic ablation of Wntless (Wls), the mechanisms of how osteoblastic Wls regulates the fate of bone marrow stromal cells (BMSCs) and hematopoietic stem cells (HSCs) in relation to age are not yet understood. Here, we generated Col2.3-Cre;Wls mice that were free from premature lethality and investigated age-related impacts of osteoblastic Wls deficiency on hematopoiesis, BM microenvironment, and maintenance of BMSCs (also known as BM-derived mesenchymal stem/stromal cells) and HSCs. Ablation of osteoblastic Wls deteriorated BM microenvironment and bone mass accrual along with age-independent effects on functions of BMSCs. Osteoblastic Wls deletion impaired HSC repopulation and progeny with skewing toward myeloid lineage cells only at old stage. As proven by hallmarks of stem cell senescence, osteoblastic Wls ablation differentially induced senescence of BMSCs and HSCs in relation to age without alteration in their BM frequency. Our findings support that deletion of Wls in Col2.3-expressing cells induces senescence of BMSCs and impairs BM microenvironment in age-independent manner. Overall, long-term deterioration in BM microenvironment contributes to age-related HSC senescence with impaired progeny and hematopoiesis, which also suggests possible roles of osteoblastic Wls on the maintenance of BM HSCs.