Dyslipidemia and Diabetic Retinopathy

Recent advances using pharmacotherapy greatly expand treatment options for diabetic retinopathy. Intravitreal anti-VEGF immunotherapy has proven to be effective in resolving both neovascular diabetic retinopathy (DR) and diabetic macular edema (DME)(1-5). Large clinical studies, however, reveal that about 40% of patients do not respond to anti-VEGF therapy(1-3) and the withdrawal of anti-VEGF after the long-term use can lead to rebound effects with worsening of the symptoms. Importantly, anti-VEGF treatments are directed at the very late stage in the disease, when full reversal of retinal damage is difficult. Thus, a conceptual and technical breakthrough to identify novel targets and a strategy to cure this complication is paramount. Unique metabolic demands and highly specialized structure and function of the retina dictate complex regulatory pathways to support retinal metabolism while preserving autonomy behind the blood-retinal barrier (BRB)(6). This intricate balance is lost in a diabetic environment(7-9). An important example of such dysregulation is the shift in the dial of sphingolipid rheostat from protective, pro-barrier very long chain (VLC) ceramides (C≥26) to pro-inflammatory and pro-apoptotic Short Chain (SC) ceramides (C≤24). SC ceramides in the retina are mainly produced from sphingomyelins by acid sphingomyelinase (ASM) (10-14). Production of VLC ceramides involves Elongation of very long chain fatty acids protein 4 (ELOVL4)-mediated synthesis of VLC saturated fatty acids that are then incorporated into ceramides by the action of ceramide synthases (CerS)(15). We have previously demonstrated that ASM is highly upregulated(10) and ELOVL4 is downregulated(19) in the diabetic retina. Downregulation of ASM or upregulation of ELOVL4 were protective against diabetes-induced retinal vascular degeneration in cell culture and animal models(10, 20). We hypothesize that the shift in the ceramide rheostat dial from SC to VLC ceramides will improve the outcome of diabetic retinopathy by: 1) preventing SC ceramide-mediated pro-inflammatory and pro-apoptotic changes while 2) maintaining VLC-ceramide barrier function.