Global Remodeling of the Vascular Stem Cell Niche in Bone Marrow of Diabetic Patients: Implication of the miR-155/FOXO3a Signaling Pathway.

Rationale: The impact of diabetes on bone marrow (BM) structure is incompletely understood. Objective: Investigate the effect of type-2 diabetes (T2D) on BM microvascular and hematopoietic cell composition in patients with/out vascular complications. Methods and Results: Bone samples were obtained from T2D patients and non-diabetic controls (C) during hip replacement surgery and from T2D patients undergoing amputation for critical limb ischemia (CLI). BM composition was assessed by histomorphometry, immunostaining and flow cytometry. Expressional studies were performed on CD34(pos) immuno-sorted BM progenitor cells (PCs). Diabetes causes a reduction of hematopoietic tissue, fat deposition, and microvascular rarefaction, especially when associated to CLI. Immunohistochemistry documented increased apoptosis and reduced abundance of CD34(pos)-PCs in diabetic groups. Likewise, flow cytometry showed scarcity of BM PCs in T2D and T2D+CLI compared to C, but similar levels of mature hematopoietic cells. Activation of apoptosis in CD34(pos-)PCs was associated to upregulation and nuclear localization of the pro-apoptotic factor FOXO3a and induction of FOXO3a targets, p21 and p27(kip1). Moreover, miR-155, which regulates cell survival through inhibition of FOXO3a, was downregulated in diabetic CD34(pos)-PCs and inversely correlated with FOXO3a levels. The effect of diabetes on anatomical and molecular endpoints was confirmed when considering background covariates. Furthermore, exposure of healthy CD34(pos)-PCs to high glucose reproduced the transcriptional changes induced by diabetes, with this effect being reversed by forced expression of miR-155. Conclusions: We provide new anatomical and molecular evidence for the damaging effect of diabetes on human BM, comprising microvascular rarefaction and shortage of PCs due to activation of pro-apoptotic pathway.