LncRNA CASC2 mediates SOCS6 mRNA stabilization via U2AF2 recruitment to modulate macrophage polarisation in diabetic retinopathy.

Background: Diabetic retinopathy (DR) is a prevalent microvascular complication of diabetes and a leading cause of vision loss among diabetic individuals. Retinal pigment epithelium (RPE) cells play a crucial role in the pathophysiology of DR by releasing cytokines and exosomal cargo, such as long non-coding RNAs (lncRNAs), that modulate local immune responses, maintain retinal immune homeostasis and influence macrophage polarisation. Recent studies suggest that lncRNA cancer susceptibility candidate 2 (CASC2) may be involved in the regulation of DR progression. However, the regulatory mechanisms linking CASC2 with RPE cells and its role in macrophage polarisation remain insufficiently understood.

Methods: Various types of cells, including human retinal pigment epithelial cells (ARPE-19), THP-1 monocytes and additional retinal cell lines, were cultured under normal glucose and high glucose conditions. ARPE-19 cells were exposed to oxidative stress, inflammatory stimulation, or hypoxic conditions. Plasma and aqueous humour samples were collected from DR patients and diabetic controls. Exosomes were extracted from AREP-19 cells and characterised. Various gene and protein expression analyses were performed using techniques including quantitative reverse transcription polymerase chain reaction, Western blot, immunofluorescence, flow cytometry, enzyme-linked immunosorbent assay, and histological staining. Cell proliferation and migration were assessed using Cell Counting Kit-8 assays and Transwell migration assays, respectively. The interactions among CASC2, suppressor of cytokine signalling 6 (SOCS6), and U2 small nuclear RNA auxiliary factor 2 (U2AF2) were explored using RNA immunoprecipitation and dual-luciferase reporter assays. An in vivo diabetic rat model was established.

Results: lncRNA CASC2 expression levels were significantly lower in plasma and aqueous humour from DR patients compared to those from diabetic patients without retinopathy. Overexpression of CASC2 significantly attenuated DR and inflammatory damage both in vitro and in vivo. We demonstrated that exosomal CASC2 from ARPE-19 cells mediated macrophage polarisation by inhibiting M1 polarisation and promoting M2 polarisation. Our findings suggest that CASC2 regulates this polarisation through the stabilisation of SOCS6 mRNA via U2AF2.

Conclusion: CASC2 derived from RPE cells was transported to macrophages, inducing M2 polarisation by stabilising SOCS6 mRNA through the recruitment of U2AF2. This research may provide a foundation for developing novel therapeutic strategies for DR.