Abstract 462: Diabetes Alters the Bone Marrow Vascular Niche and Impairs the Transendothelial Trafficking of Bone Marrow-derived Progenitor Cells
Background: Dysfunction of vascular endothelial cells (EC) and endothelial progenitor cells (EPC) contributes to cardiovascular complications in diabetes (D). We propose the novel hypothesis that D impairs EPC function both directly and by altering the bone marrow (BM) vascular niche, which normally supports stem cell maturation and mobilization.
Aim of the study: To determine the impact of D on BM vascular and stem cell niches.
Methods: 8-week-old mice were made diabetic by streptozotocin and sacrificed 8 or 26 weeks thereafter, together with age-matched non-diabetic controls (C), for IHC of BM microvasculature and flow cytometry of BM progenitor cells. Transendothelial migration of human or murine EPC (labeled with PKH67) was performed on HUVEC or murine BM EC, seeded on transwell filters after 48h preconditioning in EGM-2 containing 5 or 25mM D-glucose. Migration was then performed in normal glucose using SDF-1 as a stimulus.
Results: In D mice, capillary rarefaction developed from week 8 (19.9±4.6 vs 23.4±2.3 cap/mm2 in C, P=N.S.) to week 26 (11.7±2.1 vs 22.5±2.8 cap/mm2 in C, P<0.02), which was paralleled by doubling of TUNEL-positive capillaries (P<0.05). Flow cytometry revealed an age-related increase in lymphocytes and decrease in granulocytes in BM of D mice. Mononuclear cells (MNC) and Lin−cKit+Sca1+, Lin−Sca+CD31+ and Lin−Flk1+CD31+ progenitor cells were similarly abundant in BM of D and C mice. However, D BM MNC and progenitor cells expressed Annexin V high with higher frequency (MNC, 5.4±1.2 vs 2.3±0.1% in C; Lin−cKit+ Sca1+, 11.1±3.8 vs. 2.3±1.0% in C, P<0.01). Limb ischemia resulted in reduction of BM capillary density and triggered cell necrosis in ipsilateral BM of D mice, as revealed by 7-aminoactinomycin D staining (P<0.05 vs. C). In vitro, SDF-1 stimulated transendothelial migration of human EPC, which was completely abolished in the presence of glucose-conditioned EC. Likewise, murine BM EPC became insensitive to SDF-1 when interacting with glucose-conditioned BM EC.
Conclusions: Results newly demonstrate the presence of BM microangiopathy in D mice. Rarefaction and dysfunction of vascular niche may have detrimental effects on the mobilization of stem cells and thereby negatively influence vasculogenesis.