Modulation of microglia polarization dynamics during diabetic retinopathy in db / db mice

Abstract

Retinal diseases linked to inflammation are often accompanied by macrophage/microglial cells activation. However, the dynamics between M1 (pro-inflammatory) and M2 (anti-inflammatory) polarization of microglia during diabetic retinopathy (DR) has not been investigated and it might be therapeutically useful. We assessed microglia polarization in retinas from db/db mice and human diabetic donors and also the microgliamediated anti-inflammatory effects of the bicyclic nojirimycin derivative (1R)-1-dodecylsulfinyl-5N,6O-oxomethylidenenojirimycin (R-DS-ONJ). Visual function in mice was evaluated by electroretinogram (ERG). Expression of pro-and anti-inflammatory markers in the retina was analyzed by immunofluorescence, Western-blot and quantitative real-time PCR. Lipopolysaccharide (LPS)-mediated polarization profile was studied in Bv.2 microglial cells in the absence or presence of anti-inflammatory cytokines (IL4/IL13) or R-DS-ONJ. At 5 weeks of age, reduced ERG amplitude values of rod and mixed waves were detected in db/db compared to db/+ mice that correlated with elevated circulating endotoxemia and pro-inflammatory cytokines. At this early stage of DR, the marker of activated microglia Iba-1 co-localized with the M2 marker arginase-1 in the retina. Conversely, in retinas from 8 weeks old db/db mice Iba-1-colocalized with active caspase-1, a key component of the inflammasome, reflecting an opposite pattern of microglia polarization. Markers of activated microglia were detected in retinas of diabetic donors. Treatment of Bv.2 cells with LPS and IL4/IL13 or R-DS-ONJ switched the M1 response towards M2. In retinal explants from db/db mice, R-DS-ONJ induced a M2 response. In conclusion, the modulation of microglia polarization dynamics towards a M2 status at early stages of DR offers novel therapeutic interventions.

Effects of Diets with Different Proportions of Protein/ Carbohydrate on Retinal Manifestations in db Mice

“…This finding indicates that higher Gfap expression may correspond to the diabetic condition, but that it is not greatly influenced by the different protein and carbohydrate content diets, even in db mice. Although morphological change was not apparent, the higher expression of Gfap (as a retinal astrocyte marker) under diabetic conditions is consistent with previous reports (36)(37)(38). Moreover, db-H showed significantly higher levels of CD11b mRNA, a microglial marker, than db-L, suggesting that a higher dietary protein content may influence the proliferation of microglia.…”

“…Alterations of gene expression in diabetic retinopathy have been reported and corresponded to proliferation of astrocytes and/or microglia (36)(37)(38). In the present study, db-H and -L showed higher mRNA levels of Gfap compared with CT-H and -L, respectively.…”

The sp 2 -iminosugar glycolipid 1-dodecylsulfonyl-5 N ,6 O -oxomethylidenenojirimycin (DSO 2 -ONJ) as selective anti-inflammatory agent by modulation of hemeoxygenase-1 in Bv.2 microglial cells and retinal explants

“…Our previous data in retinal explants from db/db mice at 8 weeks of age have shown that treatment with 1R-DSO-ONJ, another sp 2 -IGL representative, ameliorated reactive gliosis [8]. A step further, the results presented herein revealed that iNOS expression, which was elevated in the retina of diabetic db/db mice, was reduced after treatment of retinal explants with DSO 2 -ONJ that in parallel increased HO-1 levels, reinforcing the link between inflammation and HO-1 in the retina.…”

“…Diabetic retinopathy has an important pro-inflammatory component associated with alterations in the immune responses, including the dynamics of microglia polarization [8]. In fact, targeting neuroinflammation by modulating the polarization state of microglia has been suggested as a therapeutic strategy to delay and/or prevent the deterioration of visual function in diabetic patients [49].…”

“…DR-associated retinal diseases such as proliferative diabetic retinopathy and diabetic macular edema are often accompanied by activation of microglial cells that constitute the immune resident population in the retina [5,6]. In the db/db mouse model that recapitulates the progression of DR [7], we have recently reported that the polarization of microglia is a dynamic process that switches from the anti-inflammatory M2 stage that was increased adaptively in early diabetic retinas attempting to maintain retinal homeostasis to the pro-inflammatory M1 stage in established DR that is characterized by elevations in pro-inflammatory cytokines and the activation of the inflammasome system [8]. In this regard, TNFα, IL1β, IL-8 and MCP-1 have been found elevated in the vitreous of diabetic patients [9,10].…”