Hyperglycaemia-induced pro-inflammatory responses by retinal Müller glia are regulated by the receptor for advanced glycation end-products (RAGE)

Abstract

Aims/hypothesis Up-regulation of the receptor for AGEs (RAGE) and its ligands in diabetes has been observed in various tissues. Here, we sought to determine levels of RAGE and one of its most important ligands, S100B, in diabetic retina, and to investigate the regulatory role of S100B and RAGE in Müller glia. Methods Streptozotocin-diabetes was induced in SpragueDawley rats. RAGE, S100B and glial fibrillary acidic protein (GFAP) were detected in retinal cryosections. In parallel, the human retinal Müller cell line, MIO-M1, was maintained in normal glucose (5.5 mmol/l) or high glucose (25 mmol/l). RAGE knockdown was achieved using small interfering RNA (siRNA), while soluble RAGE was used as a competitive inhibitor of RAGE ligand binding. RAGE, S100B and cytokines were detected using quantitative RT-PCR, western blotting, cytokine protein arrays or ELISA. Activation of mitogen-activated protein kinase (MAPK) by RAGE was determined by western blotting. Results Compared with non-diabetic controls, RAGE and S100B were significantly elevated in the diabetic retina with apparent localisation in the Müller glia, occurring concomitantly with upregulation of GFAP. Exposure of MIO-M1 cells to high glucose induced increased production of RAGE and S100B. RAGE signalling via MAPK pathway was linked to cytokine production. Blockade of RAGE prevented cytokine responses induced by high glucose and S100B in Müller glia. Conclusions/interpretation Hyperglycaemia in vivo and in vitro exposure to high glucose induce upregulation of RAGE and its ligands, leading to RAGE signalling, which links to pro-inflammatory responses by retinal Müller glia. These data shed light on the potential clinical application of RAGE blockade to inhibit the progression of diabetic retinopathy.

Protection against methylglyoxal-derived AGEs by regulation of glyoxalase 1 prevents retinal neuroglial and vasodegenerative pathology

“…AGE localisation has been previously demonstrated in the retina and it is established that many of these adducts show a considerable degree of accumulation in Müller glia during diabetes [28][29][30]. MG-derived CEL has not been previously reported in the retina and this adduct demonstrated increased immunoreactivity in the diabetic retina, even after 3 months of hyperglycaemia, and localisation was in a pattern consistent with Müller glia (Fig.…”

“…RAGE is known to be highly expressed by Müller glia in the diabetic retina [30] and, although ligands such as S100B are important in this context, it is possible that receptor activation by MGderived AGEs could be playing an important role in diabetic retinopathy. Ongoing research is seeking to examine the pathophysiological implications of RAGE and MG-derived AGEs in Müller glia and their contribution to retinal lesions during diabetes.…”

Biomarkers in Diabetic Retinopathy

“…Isoforms of the RAGE protein, which lack the transmembrane and signaling domain, exist in man and are thought to be protective against AGE-and RAGE-related damage, perhaps by acting as a decoy, binding and inactivating AGEs [176]. RAGE is expressed by many cells in the retina, with the highest expression achieved in Müller glia [177]. Blockade of RAGE may be a useful therapeutic strategy.…”

“…Blockade of RAGE may be a useful therapeutic strategy. sRAGE has been shown to prevent diabetes-related Müller glia dysfunction during diabetes [177], and to inhibit retinal vessel leukostasis in AGE-infused (non-diabetic) mice [178]. Importantly, RAGE antagonists can prevent acellular capillary formation in diabetic mice [179], and mice, in which RAGE has been genetically deleted, show significant protection against diabetic retinopathy [180].…”

Diabetes-related adduct formation and retinopathy

“…For example, S100B is found in several retinal cell types including photoreceptors and Müller glia [20]. S100B has neurotrophic role at low levels although upregulation occurs in the Müller glia of diabetic animal models where it can induce inflammatory cytokine expression [89].…”