Aim: To confirm the role of angiopoietin-like protein 8 (Angptl 8) in proliferative diabetic retinopathy (PDR).
Methods: The sera and aqueous humor of 10 PDR patients and 10 non-diabetic retinopathy (NDR) patients (idiopathic macular hole patients) were collected and the expression of Angptl 8 was detected by enzyme linked immune-sorbent assay (ELISA). Experimental diabetes mice model was induced with streptozotocin. The expression of glycosylated hemoglobin and Angptl 8 in sera was detected. Recombinant Angptl 8 was re-infused into wild type (WT) diabetic mice and spatial frequency threshold and contrast sensitivity were measured. In vitro retinal pigment epithelium (RPE) were stimulated by recombinant Angptl 8 for 24h. MMT assay were used to detect cell proliferation. At the same time, qRT-PCR and Western blot was used to measure the expression of proliferation-related factors in PRE cells.
Results: The expression of Angptl 8 was markedly increased in the sera and aqueous humor of PDR patients (F=99.02, P<0.0001 in sera; t=10.42, P<0.0001 in aqueous). After successfully establishing the diabetic mice model, we found that glycosylated hemoglobin and Angptl 8 expression levels were increased. Re-infusion of recombinant Angptl 8 into WT diabetic mice could further decrease spatial frequency threshold and contrast sensitivity (P<0.01). In vitro, RPE cells stimulated by recombinant Angptl 8 could increase the relative absorbance of MMT assay (1.486±0.042 vs 1.000±0.104, P<0.05) and proliferating cell nuclear antigen (PCNA) expression (0.55±0.01 vs 0.29±0.03, P<0.05). The proliferative effect of Angptl 8 is mainly mediated by increasing the expression of proliferation-activating factors cyclin A1 (4.973±0.205 vs 2.720±0.197, P<0.05), cyclin F (5.690±0.219 vs 4.297±0.292, P<0.05) and E2F2 (2.297±0.102 vs 1.750±0.146, P<0.05), and reducing the expression of proliferation-inhibiting factors cdkn1 (2.370±0.074 vs 3.317±0.135, P<0.05) and cdkn2 (4.793±0.065 vs 5.387±0.149, P<0.05).
Conclusion: The expression of Angptl 8 is increased in PDR, and the increased Angptl 8 can promote proliferation and increase proliferation-related factors.
Keywords: angiopoietin-like protein 8; proliferation; proliferative diabetic retinopathy; retinal pigment epithelium.