Bone morphogenetic protein 2: A potential new player in the pathogenesis of diabetic retinopathy

Abstract

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus. Vision loss in DR principally occurs due to breakdown of the blood-retinal barrier (BRB), leading to macular edema, retinal detachment and inner retinal and vitreous hemorrhage. Several growth factors have been shown to play crucial role in the development of these vascular changes; however, the cellular and molecular mechanisms of DR are not yet fully revealed. In the current study we investigated the role of bone morphogenetic protein-2 (BMP2) in DR. We examined the changes in the protein levels of BMP2 in human vitreous and retina in addition to the mouse retina of streptozotocin-induced diabetes. To detect the source of BMP2 during diabetes, human retinal endothelial cells (hRECs) were subjected to high glucose (HG) for 5 days and levels of BMP2 protein were analyzed in conditioned media of these cells relative to control. We also evaluated the effect of BMP2 on the levels of VEGF in cultured rat Müller cells (rMC1). In addition, we tested the pro-inflammatory effects of BMP2 by examining its effect on leukocyte adhesion to cultured hRECs, and levels of adhesion molecules and cytokines production. Finally, the effect of different concentrations of BMP2 on permeability of confluent monolayer of hRECs was evaluated using FITC-Dextran flux permeability assay and by measuring Transcellular Electrical Resistance (TER) using Electric Cell-substrate Impedance Sensing (ECIS). Our results show, for the first time, the up-regulation of BMP2 in diabetic human and mouse retinas in addition to its detection in vitreous of patients with proliferative DR (72±7 pg/ml). In vitro, hRECs showed upregulation of BMP2 in HG conditions suggesting that these cells are a potential source of BMP2 in diabetic conditions. Furthermore, BMP2 induced VEGF secretion by Müller cells in-vitro; and showed a dose response in increasing permeability of cultured hRECs. Meanwhile, BMP2 pro-inflammatory effects were recognized by its ability to induce leukocyte adhesion to the hRECs, intercellular adhesion molecule-1 (ICAM-1) and upregulation of interleukin-6 and 8 (IL-6 and IL-8). These results show that BMP2 could be a contributing growth factor to the development of microvascular dysfunction during DR via enhancing both pro-angiogenic and inflammatory pathways. Our findings suggest BMP2 as a potential therapeutic target to prevent/treat DR.

Inhibition of beta cell growth and function by bone morphogenetic proteins

“…Recently published studies demonstrate a positive correlation between local tissue-specific upregulation of BMP2 and/ or -4 expression and diabetes-mediated diseases including retinopathy [41] and nephropathy [42], and vascular defects including atherosclerosis, calcification and hypertension [16,19,43]. Moreover, inhibition of BMP was demonstrated to have beneficial effects on these variables [16,17,42,43].…”

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

“…BMP2/4 expression has been reported to be upregulated in arteries, kidneys, retina, and islets in the diabetic environment [76,90,[113][114][115]. Systemic inhibition of BMP2/4 by noggin improves glucose homeostasis in type 2 diabetic mice.…”

A lipidomic screen of hyperglycemia-treated HRECs links 12/15-Lipoxygenase to microvascular dysfunction during diabetic retinopathy via NADPH oxidase

“…The experiment was terminated after 24 h of 15-HETE treatment for analysis of leukocyte adhesion and tube formation. Conditioned media were used for multiplex assay of various cytokines as previously described ( 30 ). Meanwhile, the HG experiment was terminated 5 days after initiation of treatment and cell lysates were collected and analyzed for 15-LOX and 5-LOX protein expression using Western blot analysis.…”

“…Cytotoxicity of tested inhibitors was assessed by MTT assay as previously described ( 29 ). Transcellular electrical resistance (TER) and cell migration were done using electric cell-substrate impedance sensing (ECIS) (Model 1600R, Applied BioPhysics) as previously described ( 30,31 ). The experiment was terminated after 24 h of 15-HETE treatment for analysis of leukocyte adhesion and tube formation.…”