Thrombospondin-1 (TSP1), Transforming Growth Factor-Beta (TGFb) and Connective Tissue Growth Factor (CTGF) are Involved in the Pathophysiology of Diabetic Retinopathy,

Diabetic retinopathy (DR) is a progressive disease that affects over 4 million people in the United States and is one of the leading causes of blindness. The pathophysiology of the early events (no evidence of DR) leading to diabetic retinopathy is still not fully understood. Recent studies have proposed that levels of TSP1 (Arch Ophthalmol 127:507, 2009) and CTGF (Diabetes Care 27:758, 2004) may play a role in shifting the angiogenic balance and pathogenesis of DR. We postulate that during acute and chronic inflammation, as seen in type-2 diabetes a pro-inflammatory axis comprised by TSP1, transforming growth factor-beta (TGF-b) and CTGF may play a significant role in the progression of NPDR to PDR. Methods: This is a prospective control study comprised to date of: a) six (6) human subjects with NPDR, b) eleven (11) subjects with PDR, c) five (5) subjects without type-2 diabetes but in need of pars plana vitrectomy, and d) seventeen (17) normal human volunteers. Plasma samples were obtained from all groups (a-d) after signing an informed consent approved by our institution's IRB committee. Vitreous fluid (VF) was collected from subjects in b and c. Cytokine profile was determined by Multiplex Assay. TSP1, TGF-b and CTGF were assessed by commercially available ELISA assays and visualized by Western-blotting technique. Results: TNFa in conjunction with other pro-inflammatory cytokines was found elevated in NPDR subjects when compared to subjects in control groups (c-d, P<0.05). The evidence of acute inflammation in the NPDR group was not only evident by higher levels of TNFa but also TSP1 and TGF-b when compared to control groups (P<0.002 and P<0.001 respectively). Interestingly, the TSP1 profile seen in the NPDR subjects changed significantly (lower levels) when compared to PDR subjects (P<0.002) and was even significantly different from that one seen in control subjects. This early foot print observed for TSP1 was similar to the IL-4 profile (P<0.003 NPDR vs PDR, P<0.0002 NPDR vs controls) a molecule considered to be anti-angiogenic like TSP1. CTGF plasma levels were increased in PDR subjects in plasma (mean 1.67 + 0.27 SEM pg/ml) when compared to NPDR subjects (0.77 + 0.22 pg/ml, P<0.05) and the levels were also higher in VH of PDR subjects when compared with VH controls subjects. On Western-blotting analysis, CTGF and TSP1 in plasma and in VH showed evidence of proteolytic fragmentation, a phenomenon that has been associated with potential promotion of angiogenesis and fibrosis. Summary: Our findings are in agreement with the proposed hypothesis that TSP1 in systemic circulation or in the micro environment (vitreous fluid) in conjunction with TGF-b represent a pro-inflammatory axis in the disease progression from NPDR to PDR with CTGF as the effector molecule placing this axis as a potential therapeutic intervention to prevent progression of disease and to improve quality of life in patients afflicted by NPDR.

No relevant conflicts of interest to declare.