Involvement of complement and coagulation cascade in Retinopathy of Prematurity

Abstract

Purpose: Retinopathy of prematurity (ROP) is a blinding disease caused by the abnormal growth of blood vessels in the retina of premature babies with low birth weight. As the vitreous humor is in contact with the retina, protein components in the vitreous are affected by the physiological and pathological conditions of the retina. We have performed proteomics study of vitreous humor samples to elucidate the mechanism involved in progression of ROP.

Methods: We have separated high- and low-abundant proteins from the individual vitreous samples of ROP patients (n=7) and age-matched controls (n=7) using affinity chromatography. Both fractions were analyzed by on-line liquid chromatography electrospray mass spectrometry (LC-MS/MS), separately. MS/MS data was searched from the International Protein Index database (human IPI v3.80) and PEAKS Studio software was used employing a 1% FDR cut-off to identify proteins and perform label-free quantification (LFQ). Some of the highly up- and down-regulated proteins were validated by western blotting.

Results: We have identified a total of 550 proteins in the vitreous humor of ROP patients and 332 proteins in controls. About 55% proteins were common between ROP patients and controls. Label-free quantification data suggests that ~265 proteins are differentially expressed in ROP patients. Pathway analysis indicates over-expression of the “complement and coagulation cascade” in the vitreous humor of ROP patients. LFQ data shows the down-regulation of superoxide dismutase [Cu-Zn] and all crystallins in ROP patients. Western blot results show that plasminogen, histidine-rich glycoprotein, factor XII, fibrinogen ϒ-chain and complement C3 are significantly up-regulated, whereas αA- and αB-crystallin are significantly down-regulated in ROP patients (p>0.02).

Conclusions: Our study shows that the levels of proteins involved in complement pathway, coagulation cascade and angiogenesis are elevated, whereas the levels of oxidative stress scavenging enzymes and inhibitors of angiogenesis and coagulation are down-regulated in ROP patients. This study suggests that oxidative stress can trigger the complement pathway and coagulation cascade which may lead to promotion of angiogenesis.