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ABSTRACT
Purpose: To determine concentrations of endoplasmic reticulum (ER) stress-related factors activating transcription factor 4 (ATF4) and glucose-regulated 78 kDa protein (GRP78) in vitreous and aqueous humor (AqH) of patients with proliferative diabetic retinopathy (PDR) and the correlation of ATF4, GRP78 and inflammatory cytokines interleukin-6(IL-6) and monocyte chemoattractant protein-1 (MCP-1).
Materials and Methods: AqH and vitreous samples were collected from eyes of patients with PDR and idiopathic macular hole (IMH) which needed vitrectomy. Protein Levels of ATF4, GRP78, and IL-6, MCP-1 in samples were evaluated using enzyme-linked immunosorbent assay (ELISA).
Results: ELISA analysis revealed significantly increased levels in both AqH and vitreous of ATF4 and GRP78 in eyes affected with PDR compared to the controls (all p < 0.001). The mean concentrations of IL-6, MCP-1 were also higher in both AqH and vitreous samples from patients with PDR compared to those of IMH (all p < 0.001). (Independent Student t-test, normality test followed with Skewness–Kurtosis Test).
In addition, correlations of ATF4 and GRP78 with inflammatory factors IL-6 and MCP-1 in subjects of patients were analyzed. No significant correlation between the AqH concentrations of ATF4/IL-6 and ATF4/MCP-1 was detected in eyes of PDR patients (r = 0.346, p = 0.072 and r = 0.275, p = 0.157). Significant correlations were observed between AqH concentrations of GRP78/IL-6 (r = 0.724, p < 0.001), GRP78/MCP-1 (r = 0.654, p < 0.001) in PDR patients. Significant correlations were observed between vitreous concentrations of ATF4/IL-6 (r = 0.918, p < 0.001), ATF4/MCP-1 (r = 0.921, p < 0.001), GRP78/IL-6 (r = 0.978, p < 0.001), GRP78/MCP-1 (r = 0.979, p < 0.001) in PDR patients.
No significant correlations was observed between AqH concentrations of ATF4/IL-6 (r = 0.187, p = 474), ATF4/MCP-1 (r = 0.240, p = 0.353), GRP78/IL-6 (r = 0.321, p = 0.209) and GRP78/MCP-1 (r = 0.169, p = 0.516) in eyes of IMH patients. And also no significant correlation was observed between vitreous concentrations of ATF4/IL-6 (r = 0.130, p = 0.563), ATF4/MCP-1(r = 0.029, p = 0.897), GRP78/IL-6 (r = 0.078, p = 0.717), GRP78/MCP-1 (r = 0.005, p = 0.982) in IMH patients. (Pearson correlation coefficient (two-tailed)).
Conclusions: Our results demonstrated that ATF4 and GRP78 may play an important role in the pathogenesis of PDR and work in concert with inflammatory cytokines IL-6 and MCP-1 in pathological process. ATF4 and GRP78 may be good diagnostic biomarkers and new therapeutic targets for PDR.
Abbreviations: ER stress, endoplasmic reticulum stress; ATF4, activating transcription factor 4; GRP78, glucose-regulated 78 kDa protein; AqH, aqueous humor; PDR, proliferative diabetic retinopathy; IL-6, interleukin-6; MCP-1, monocyte chemoattractant protein-1; IMH, idiopathic macular hole.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
Funding
This work was supported by the National Nature Science Foundation of China [grant number 81470639], [grant number 81670861] and the Shanghai Nature Science Foundation [grant number 14411968400]. The study was approved by the Ethical Committee of Ruijin Hospital, Shanghai, China and adhered to the tenets of the Declaration of Helsinki.