Abstract
Purpose :
Purpose: To determine the role Steap4 plays in retinal endothelial cell angiogenesis in diabetic retinopathy.
Methods :
Methods: Peripheral Blood Mononuclear Cells (PBMC) were collected from the blood of nondiabetics and Type II diabetics with either: no retinopathy, proliferative diabetic retinopathy (PDR), or with both diabetic macular edema and (PDR). Murine and human retinal endothelial cells (mREC, hREC) and patient PBMC RNA was analyzed for Steap4 expression. Next, retinas of non-diabetic and streptozotocin (STZ)- induced diabetic C57BL/6 mice were collected and Steap4 protein levels were determined. Further, angiogenesis signaling was examined in protein lysates of control and Steap4 gene silenced mREC and hREC that were unstimulated or stimulated with recombinant VEGF-A. Finally, untreated and anti-STEAP4 ablated hREC were incubated with plasma of non-diabetics or diabetics with PDR to determine their influence on angiogenesis
Results :
Results: Gradient Steap4 expression of low levels in non-diabetics to successively higher levels in diabetics with more severe retinopathy was detected. Additionally, Steap4 is constitutively expressed in mREC and hREC and upregulated in the diabetic retina. Silencing Steap4 in hREC upregulated Angiopoietin 1 and Angiostatin which both inhibit angiogenesis. Also, Angiopoietin 1 protects against diabetic retinopathy, by its antagonistic signaling against Angiopoietin 2. Notably, VEGF-A and Angiopoietin 2 synergistically promote retinal neovascularization and the onset of PDR. Upregulated VEGF-A enhances Angiopoietin 2 and Tie-2 binding, which initiates sprouting of new blood vessels in the retina. Simultaneously, VEGF-A binds to VEGFR2 and VEGFR3, which induces tube formation and retinal endothelial cell proliferation. Collectively, these two angiogenic signaling pathways impact retinal endothelial cell proliferation, neovascularization, and the onset of PDR. Steap4 silencing downregulated these two angiogenic pathways. Finally, angiogenesis was induced in hREC when incubated with plasma from PDR patients, but halted in hREC when treated with anti-STEAP4.
Conclusions :
Conclusions: These results provide evidence that inhibition of Steap4 halts angiogenic signaling that initiates retinal neovascularization and vascular cell proliferation. Collectively, this suggests that Steap4 could play a pivotal role in the intrinsic pathologies of PDR.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.