Erythropoietin modulates bone marrow stromal cell differentiation

Abstract

Erythropoietin is essential for bone marrow erythropoiesis and erythropoietin receptor on non-erythroid cells including bone marrow stromal cells suggests systemic effects of erythropoietin. Tg6 mice with chronic erythropoietin overexpression have a high hematocrit, reduced trabecular and cortical bone and bone marrow adipocytes, and decreased bone morphogenic protein 2 driven ectopic bone and adipocyte formation. Erythropoietin treatment (1 200 IU·kg–1) for 10 days similarly exhibit increased hematocrit, reduced bone and bone marrow adipocytes without increased osteoclasts, and reduced bone morphogenic protein signaling in the bone marrow. Interestingly, endogenous erythropoietin is required for normal differentiation of bone marrow stromal cells to osteoblasts and bone marrow adipocytes. ΔEpoRE mice with erythroid restricted erythropoietin receptor exhibit reduced trabecular bone, increased bone marrow adipocytes, and decreased bone morphogenic protein 2 ectopic bone formation. Erythropoietin treated ΔEpoRE mice achieved hematocrit similar to wild-type mice without reduced bone, suggesting that bone reduction with erythropoietin treatment is associated with non-erythropoietic erythropoietin response. Bone marrow stromal cells from wild-type, Tg6, and ΔEpoRE-mice were transplanted into immunodeficient mice to assess development into a bone/marrow organ. Like endogenous bone formation, Tg6 bone marrow cells exhibited reduced differentiation to bone and adipocytes indicating that high erythropoietin inhibits osteogenesis and adipogenesis, while ΔEpoRE bone marrow cells formed ectopic bones with reduced trabecular regions and increased adipocytes, indicating that loss of erythropoietin signaling favors adipogenesis at the expense of osteogenesis. In summary, endogenous erythropoietin signaling regulates bone marrow stromal cell fate and aberrant erythropoietin levels result in their impaired differentiation.

The Many Facets of Erythropoietin Physiologic and Metabolic Response

“…Osteoclast differentiation assays using marrow mononuclear cells (Shiozawa et al, 2010), non-adherent bone marrow cells (Hiram-Bab et al, 2015) and RAW264.7 mouse monocyte/macrophage cell line show EPO increasing osteoclast numbers (Li et al, 2015), but not osteoclast activity (Shiozawa et al, 2010;Li et al, 2015). However, increase in osteoclast numbers was not reported in other studies using mouse bone marrow cultures (Suresh et al, 2019) and in osteoblastosteoclast cocultures treated with EPO (Singbrant et al, 2011). In cultures of preosteoclasts, EPO activates JAK2/PI3K pathways without affecting proliferation and in osteoclasts, EPOR expression decreases with differentiation (Hiram-Bab et al, 2015).…”

“…For osteoblast differentiation assays, studies have utilized mouse primary calvarial osteogenic cells as well as adherent BMSCs. EPO treatment of primary mouse calvarial osteogenic cells did not affect differentiation (Hiram-Bab et al, 2015;Suresh et al, 2019). However, in transgenic mice expressing high human EPO, calvarial osteoblasts produced human EPO and showed increased ALP expression and mineralization (Suresh et al, 2019).…”

“…EPO treatment of primary mouse calvarial osteogenic cells did not affect differentiation (Hiram-Bab et al, 2015;Suresh et al, 2019). However, in transgenic mice expressing high human EPO, calvarial osteoblasts produced human EPO and showed increased ALP expression and mineralization (Suresh et al, 2019). Conversely, primary calvarial osteoblasts lacking endogenous EPO signaling had reduced ALP expression and mineralization (Suresh et al, 2019).…”

“…In bone, functional EPO receptors are expressed by osteoblasts and osteoclasts that remodel the bone and by BMSCs that differentiate into osteoblasts, bone marrow adipocytes and chondrocytes. Studies on the effects of EPO on these specific cell types and overall bone homeostasis have utilized in vitro cultures (Kim et al, 2012;Rolfing et al, 2014a;Li et al, 2015), in vivo BMSC osteogenic assays using ectopic ossification models (Suresh et al, 2019), bone fracture healing models (Holstein et al, 2007;Mihmanli et al, 2009;Rolfing et al, 2014b;Omlor et al, 2016), transgenic mouse model with high human EPO (model for chronic EPO exposure) (Hiram-Bab et al, 2015;Suresh et al, 2019), administration of exogenous EPO in healthy mice (Shiozawa et al, 2010;Singbrant et al, 2011;Hiram-Bab et al, 2015;Suresh et al, 2019) (model for acute EPO exposure) and, recently, EpoR E mice that do not express EPOR in non-erythroid cells (Suresh et al, 2019) (model for endogenous EPO signaling).…”

“…Transgenic mice with chronic exposure to high levels of human EPO had more osteoclasts lining the bone surface (Hiram-Bab et al, 2015). Osteoclasts from these mice produced EPO and corresponding BMSC derived cultures from these mice exhibited a greater number of giant multinucleated osteoclasts (Suresh et al, 2019).…”