Modulation of P75^NTR receptor protects against ischemic retinopathy: possible contribution of mesenchymal stem cells (MSCs)

Abstract

Purpose : Proliferative diabetic retinopathy (PDR) is characterized by accelerated cell death, impaired vascular repair and pathological retinal neovascularization (RNV). Mesenchymal stem cells (MSCs) are promising therapy to improve vascular repair, yet their role in PDR is not fully understood. We have shown that genetic deletion of neurotrophin receptor; p75^NTR enhanced vascular repair and ameliorated RNV in ischemic retinopathy model. Furthermore, its deletion preserved the expression of angiogenic markers; SDF-1, CXCR-4 and CXCR-7 responsible for MSCs homing to vasculature in diabetic ischemic limbs. The aim of this study is to investigate the contribution of MSCs to vascular protection associated with p75^NTR deletion in ischemic retina.

Methods : WT and p75KO mice were subjected to ischemia reperfusion (IR) injury by increasing intra-ocular pressure to 120 mmHg for 45 minutes followed by perfusion. Murine GFP-labeled MSCs (100,000 cells/eye) were injected intravitreally 2 days post-surgery and vascular homing was assessed 1-week later. Acellular capillaries were counted using trypsin digest 10-days post IR. In vitro, MSCs were treated with a specific pharmacological inhibitor against p75^NTR receptor (LM11A-31, 200 nM, Stanford University) and conditioned media was co-cultured with human retinal endothelial (HREs) to examine the angiogenic response.

Results : IR increased number of acellular capillaries (~ 2.3 fold) in WT mice, but not in p75KO compared to sham-controls. GFP-MSCs showed better incorporation into retinal vasculature in p75KO mice compared to WT. Administration of MSCs decreased number of acellular capillaries in all groups (~ 2.3 fold decrease in WT-sham, 2.7 fold decrease in WT-IR, 3 fold decrease in KO-Sham and 2.5 fold decrease in KO-IR). In vitro, inhibition p75^NTR in MSCs enhanced the angiogenic response of their conditional media in HREs, where HREs showed enhanced migration (~ 1.3 fold) and tube formation (~ 2.7 fold) compared to controls.

Conclusions : Our results showed that deletion of p75^NTR protects against retinal ischemia by mechanisms that partially involve improved MSCs homing to ischemic vasculature to prevent vascular degeneration and support newly grown blood vessels. Thus, combination of MSCs injection and p75^NTR inhibitor can serve as potential therapeutic strategy to harness vascular repair in ischemic retinopathy diseases.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.