TRIM40 ameliorates diabetic retinopathy through suppressing inflammation via Reelin/DAB1 signaling disruption: A mechanism by proteasomal degradation of DAB1.

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus. Reelin, an extracellular matrix protein, and its effector protein Disabled1 (DAB1) have been linked to cellular events and retinal development. However, whether and how Reelin/DAB1 signaling causes DR remains to be investigated. In our study, significantly increased expression of Reelin, very low density lipoprotein receptor (VLDLR), ApoE receptor 2 (ApoER2) and phosphorylated DAB1 in retinas of streptozotocin (STZ)-induced DR mouse model was observed, along with enhanced expression of proinflammatory factors. Similar results are confirmed in high glucose (HG)-treated human retinal pigment epithelium cell line ARPE-19. Surprisingly, dysregulated tripartite motif-containing 40 (TRIM40), an E3 ubiquitin ligase, is found to be involved in DR progression by bioinformatic analysis. We observe a negative correlation between TRIM40 and p-DAB1 protein expression levels under HG conditions. Importantly, we find that TRIM40 over-expression markedly ameliorates HG-induced p-DAB1, PI3K, p-protein B kinase (AKT) and inflammatory response in HG-treated cells, but dose not affect Reelin expression. Of note, Co-IP and double immunofluorescence identify an interaction between TRIM40 and DAB1. Furthermore, we show that TRIM40 enhances K48-linked polyubiquitination of DAB1, thereby promoting DAB1 degradation. Finally, promoting TRIM40 expression by intravenous injection of the constructed adeno-associated virus (AAV-TRIM40) markedly ameliorates DR phenotypes in STZ-treated mice, as indicated by the decreased blood glucose and glycosylated hemoglobin (HbAlc) levels, and increased hemoglobin contents. Additionally, diabetes-related elevation of acellular capillaries was also meliorated in mice over-expressing TRIM40. The electroretinogram (ERG) deficits were strongly rescued in mice receiving AAV-TRIM40 injection. Moreover, AAV-TRIM40 attenuates the inflammation and p-DAB1 expression in retinal tissues of STZ-treated mice. Collectively, our findings disclose a mechanism through which TRIM40 limits DAB1 stability under physiological conditions and reveals TRIM40 as a potential therapeutic target for the intervention of Reelin/DAB1 signaling, contributing to DR treatment.