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Aims/hypothesis The pathophysiology of diabetic retinopathy is linked to hyperglycaemia and its effect on retinal microvascular tissues. The resulting endothelial injury changes the endothelial cell phenotype to acquire mesenchymal properties (i.e. endothelial-mesenchymal transition [EndMT]). Such changes can be regulated by epigenetic mechanisms, including long non-coding RNAs (lncRNAs). lncRNA H19 may influence EndMT through TGF-β. We investigated the role of H19 in regulating EndMT during diabetic retinopathy. Methods H19 was overexpressed or silenced in human retinal endothelial cells exposed to various glucose levels. The cells were examined for H19, endothelial and mesenchymal markers. We then expanded the study to retinal tissues in a mouse model of diabetic retinopathy and also examined vitreous humour samples from individuals with proliferative diabetic retinopathy. Results Expression of H19 was downregulated in high glucose conditions (25 mmol/l). H19 overexpression prevented glucoseinduced EndMT. Such changes appear to involve TGF-β through a Smad-independent mechanism. Diabetes caused downregulation of retinal H19. Using H19 knockout mice, we demonstrated similar EndMT in the retina. Examination of vitreous humour from individuals with proliferative diabetic retinopathy also reinforced the downregulation of H19 in diabetes. Conclusions/interpretationWe therefore concluded that H19 regulates EndMT in diabetic retinopathy through specific mechanisms. Data availability The results from our previous microarray can be found online using the GEO accession number GSE122189.

Despite possessing limited protein-coding potential, long non-coding RNAs (lncRNAs) have been implicated in a myriad of pathologic conditions. Most well documented in cancer, one prominent intergenic lncRNA known as MALAT1 is notorious for its role in impacting epigenetic mechanisms. In this study, we established a novel epigenetic paradigm for MALAT in diabetic retinopathy (DR) by employing siRNA-mediated MALAT1 knockdown in human retinal endothelial cells (HRECs), a Malat1 knockout animal model, vitreous humor from diabetic patients, pharmacological inhibitors for histone and DNA methylation, RNA immunoprecipitation, western blotting, and a unique DNA methylation array to determine glucose-related alterations in MALAT1. Our findings indicated that MALAT1 is capable of impacting the expressions of inflammatory transcripts through its association with components of the PRC2 complex in diabetes. Furthermore, the vitreous humors from diabetic patients revealed increased expressions of MALAT1, TNF-α, and IL-6. Intriguingly, our DNA methylation array demonstrated that transient high glucose exposure in HRECs does not contribute to significant methylation alterations at CpG sites across the MALAT1 gene. However, global inhibition of DNA methyltransferases induced significant increases in MALAT1 and associated inflammatory transcripts in HRECs. Our findings collectively demonstrate the importance of MALAT1 in inflammation and epigenetic regulation in DR.

Use of a well-established animal model of chronic diabetic complications and cultured endothelial cells showed that diabetes-induced upregulation of oncofetal fibronectin is, in part, dependent on hyperglycemia-induced transforming growth factor-beta1 and endothelin-1. Furthermore, the data suggest that oncofetal fibronectin is involved in endothelial cell proliferation.

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