Adipose-derived stromal cells contribute to microvascular stabilization in diabetic proliferative retinopathy: To be or notch to be?

Introduction: Pericyte loss in the retina is an early microvascular complication diabetes patients. To date, ADSC (adipose-derived stromal cells) have been shown to resemble pericyte activity and phenotype. However, little is known about molecular mechanisms controlling ADSC-endothelial cells communication. In this study, we hypothesized that Notch signaling in ADSC contributes to the homeostasis and stabilization of retinal microvascular endothelial cells in diabetic retinopathy.

Methods: Molecules of the Notch pathway and the role of hyperglycemia on Notch activity were identified on primary cultured ADSC and HUVEC (human umbilical cord endothelial cells) by qRT-CR. The effects of ligand-dependent Notch signaling were analyzed in a mono and coculture system of a pre-formed network of sprouted HUVEC and ADSC by Notch pathway inhibitors.

Results: Primary cultured ADSC have shown a solid expression of ligand jagged1 and receptor Notch2 while their expression was refractory to hyperglycemia. HUVEC expressed delta-like ligand4 and receptor Notch1, both of which are indispensable to coordinate angiogenesis. Moreover, the perivascular positioning of ADSC co-cultured with sprouting networks of HUVEC was inhibited by DAPT (Notch inhibitor). In contrast, Jagged1 inhibitor increased ADSC connection and wrapping on HUVEC sprouting network. We identified that Jagged1 inhibition downregulates HEY1, a transcriptional factor of Notch signaling, in monocultured ADSC. The latter linked to downregulation of pro-angiogenic genes such as VEGF-A and Ang-2, known growth factors upregulated during DR.

Conclusion: Our findings have identified key Notch components on ADSC and suggest their therapeutic function upon cell-to-cell communication regulating microvascular endothelial cells homeostasis and survival.