Abstract
Vascular endothelium is a secretory organ which not only regulates vascular function but also secretes bioactive compounds to modulate tissue homeostasis. We aimed to characterize the physiological effects of up regulating endothelial heme oxygenase-1 (HO-1) on adipogenesis in mesenchymal stem cells (hMSCs). Human microvessel endothelial cells (hMEC-1) were cultured along with a lentiviral construct expressing human HO-1 under the control of endothelium specific promoter VE-cadherin (VECAD-HO1) with VECAD-GFP used as a negative control. In complementary experiments hMEC-1 cells were cultured in the presence or absence of siRNA-HO-1 with scrambled siRNA as a negative control. Three days post-transfection, the conditioned media (CM) from hMEC-1 cells was used, along with adipogenic growth factors, to promote adipogenesis in hMSCs. Supporting in vivo experiments were conducted in SD rats injected with either VECAD-HO-1 or VECAD-GFP construct via the tail vein. Transduction efficiency was confirmed in hMEC-1 cells by demonstrating over expression (p<0.05) of HO-1 or GFP in respectively treated cells. hMSCs exposed to CM from VECAD-HO-1 transfected cells demonstrated reduced (p<0.05) adipogenesis (0.16± 0.008 vs 0.12±0.006 ) as compared to hMSCs exposed to CM from VECAD-GFP cells. On the contrary, CM from hMEC-1 cells treated with siRNA for HO-1 promoted higher adipogenesis (p<0.05) with increased adipocyte hypertrophy as opposed to hMSCs treated with CM from hMEC-1 cells transfected with the control siRNA (p<0.05) (0.17±0.008 vs 0.14±0.04). These effects on hMSCs were corroborated by immunoblot analysis demonstrating reduced expression (p<0.05) of positive regulators of adipogenesis, PPARγ, and increased levels (p<0.05) of negative regulators, β-catenin, Wnt 5b and hedgehog in cells treated with CM from hMEC-1 transfected with VECAD-HO1. In SD rats transfected with VECAD-HO-1, plasma adiponectin levels were enhanced (p<0.05) along with increased (p<0.05) adipose tissue levels of pAKT and pAMPK. In conclusion, we show here that a crosstalk between the vascular endothelium and its microenvironment has the potential to regulate adipogenesis and improve adipocyte function via HO-1-depndent pathways.
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