Perilipin 2-positive mononuclear phagocytes accumulate in diabetic retina and promote PPARγ-dependent vasodegeneration

Type 2 diabetes mellitus (T2DM), characterized by hyperglycemia and dyslipidemia leads to non-proliferative diabetic retinopathy (NPDR). NPDR is associated with blood-retinal barrier disruption, plasma exudates, microvascular degeneration, elevated inflammatory cytokine levels and monocyte (Mo) infiltration. Whether and how the diabetes-associated changes in plasma lipid and carbohydrate levels modify Mo differentiation. Here, we show that mononuclear phagocytes (MPs) in areas of vascular leakage in DR donor retinas express PLIN2, a marker of intracellular lipid load. Strong upregulation of PLIN2 was also observed when healthy donor Mos were treated with plasma from T2DM patients or with palmitate concentrations typical of T2DM plasma, but not under high glucose conditions. PLIN2 expression correlated with the expression of other key genes involved in lipid metabolism (ACADVL, PDK4) and the DR biomarkers ANGPTL4 and CXCL8. Mechanistically, we show that lipid-exposed MPs induce capillary degeneration in ex vivo explants, which was inhibited by pharmaceutical inhibition of PPARγ signaling. Our study provides a novel mechanism linking dyslipidemia-induced MP polarization to the increased inflammatory cytokine levels and microvascular degeneration that characterize NPDR. This study provides comprehensive insights into the glycemia-independent activation of Mos in T2DM and identifies MP PPARγ as a target to inhibit lipid-activated MPs in DR To study monocyte differentiation in a lipid-rich environment, replicates of monocytes isolated from a healthy donor were cultured for 18h and treated with 500 µM Palmitate /0.88% BSA, BSA alone (0.88%) and compared to DMEM culture condition (3 replicate per condition). After 18h of culture, cells were collected and RNA extracted to build expression libraries