Infiltrating immune cells and pathophysiology in Diabetic Retinopathy (DR)

Abstract

Purpose : Inflammation is now thought to be a key player in DR, a common complication of diabetes; however, the exact underlying molecular and cellular mechanisms remain elusive. This study was undertaken to determine if abnormalities in the retinal glial population contribute to DR pathology by triggering infiltration of immune cells that release high levels of soluble factors associated with pathologic retinal remodeling.

Methods : Diabetes was induced in 10-week old Nuc1 (a spontaneous mutation in Cryba1 gene with retinal abnormalities) rats via intra-peritoneal injections of streptozotocin (STZ). Retinal flatmounts and immunostaining were used to investigate STZ-induced diabetic retinopathy. Infiltrating immune cells in STZ-injected rats were identified from posterior eye cups by FACS analysis using CD45, GR-1 and CD68 antibodies. In addition, infiltrating immune cells were also examined in vitreous humor from human DR patients (n=15) and controls (n=16) by staining leukocytes, macrophages and neutrophils with antibodies to CD45, CD163 and CD66b, respectively. Cytometric Bead Array was used to determine levels of soluble factors in human vitreous humor from DR and control subjects.

Results : We found severe astrogliosis, microglial activation and vascular abnormalities in STZ-induced diabetic Nuc1 rats compared to those not injected with STZ or wild type rats. In human DR patients, as well as in STZ-treated Nuc1 rats, there was a significant increase in the levels of leukocytes, macrophages and neutrophils. In addition, we also identified increased soluble factors (such as VEGF, PDFG-AA, MCP1, FasL, IL-13, IL-6, IL-8 & IL-1a) in human DR patients compared to controls.

Conclusions : We postulate that high glucose levels in diabetes trigger glial (particularly astrocytes) abnormalities that affect the homeostasis of retinal neurons. This causes microglial activation and immune dysregulation in the retina, leading to breakdown of the blood-retinal barrier (BRB) with consequent infiltration of immune cells into the retina. The infiltrating immune cells release multiple soluble factors that likely are significant contributors to retinal degeneration in DR. Therefore, targeting activated astrocytes may be a beneficial strategy for therapy of the disease.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.