Vasculogenic potential of Adipose stromal cells in hyperglycemic environment

Abstract

Purpose: Adipose Stromal Cells (ASC) have been shown to play a regenerative therapeutic role in early stage diabetic retinopathy (DR), a leading cause of blindness in working-age adults. We have shown that ASC in co-cultures with human retinal endothelial cells (HREC) enhance endothelial survival and collaborate to form vascular networks. In this study we evaluated the effects of hyperglycemia on bioactivity of ASC and its ability to maintain sustained vascular networks.

Methods: Human ASC expressing both pericyte and mesenchymal cell surface markers were exposed to varying doses of glucose (5.5mM to 100mM) for 7 days. For vascular network formation (VNF) assay, ASC were co-cultured with HREC at a 6:1 ratio. At day 6 of co-cultivation vascular networks were visualized by staining the cultures with Agglutinin I and anti-α-smooth muscle actin IgG. Total tube length (TTL) of the networks was assessed by Angiogenesis Tube formation assay module of MetaMorph software. Human cord blood derived endothelial cells (HCBDEC) served as a non-retinal control endothelial cell type. Accumulation of bioactive molecules secreted into the media by ASC exposed to physiological and hyperglycemic conditions was evaluated by ELISA and confirmed by Western blotting.

Results: ASC cultured under chronic hyperglycemic state secreted both VEGF and HGF at the same rates as those cells incubated with physiological glucose level. While the densities of the vascular networks at high glucose levels were the same as observed in normal glucose cultures, co-cultures exposed only to 100mM glucose demonstrated a significant decrease in TTL. Interestingly, a similar observation were made when ASC were co-cultivated with HCBDEC. Short term (6 days) pre-treatment of ASC monolayers with 25mM glucose did not affect their vasculogenic potency when evaluated in subsequent in vitro tests: 1) media collected from ASC after exposure to hyperglycemia was able to promote HREC survival to the same degree as media conditioned by ASC in control environment; 2) ASC potency to promote HREC to organize into vascular cords was independent from glucose level.

Conclusions: Our findings demonstrate that ASC have a high tolerance to hyperglycemia, suggesting that ASC could be a potential candidate for cell therapy in DR. In our future studies we will explore the significance of specific biomolecules in this vascular stabilization.

Keywords: 499 diabetic retinopathy • 721 stem cells • 715 signal transduction: pharmacology/physiology