Retinal blood flow dysregulation precedes neural retinal dysfunction in type 2 diabetic mice

Abstract

We investigated and compared the susceptibility of retinal blood flow regulation and neural function in mice developing type 2 diabetes. The longitudinal changes in retinal neuronal function and blood flow responses to a 10-min systemic hyperoxia and a 3-min flicker stimulation were evaluated every 2 weeks in diabetic db/db mice and nondiabetic controls (db/m) from age 8 to 20 weeks. The retinal blood flow and neural activity were assessed using laser speckle flowgraphy and electroretinography (ERG), respectively. The db/db mice had significantly higher blood glucose levels and body weight. The resting retinal blood flow was steady and comparable between two groups throughout the study. Hyperoxia elicited a consistent decrease, and flicker light an increase, in retinal blood flow in db/m mice independent of age. However, these flow responses were significantly diminished in db/db mice at 8 weeks old and then the mice became unresponsive to stimulations at 12 weeks. Subsequently, the ERG implicit time for oscillatory potential was significantly increased at 14 weeks of age while the a-wave and b-wave amplitudes and implicit times remained unchanged. The deficiencies of flow regulation and neurovascular coupling in the retina appear to precede neural dysfunction in the mouse with type 2 diabetes.

The Effect of Sodium-Dependent Glucose Cotransporter 2 Inhibitor Tofogliflozin on Neurovascular Coupling in the Retina in Type 2 Diabetic Mice

“…We previously confirmed that the RBF response to systemic hyperoxia and flicker stimulation remains stable from 8 to 20 weeks of age in db/m non-diabetic control mice [9]. Due to the animal welfare criteria in our institution, we performed only one RBF and ERG experiment at 14 weeks of age in db/m mice.…”

“…Persistent hyperglycemia drives complex biochemical and molecular changes that lead to oxidative stress/inflammation, vascular endothelial cell damage, capillary ischemia, and tissue hypoxia [10]. Indeed, we recently confirmed that RBF dysregulation in response to flicker stimulation, which indicates impaired neurovascular coupling in the retina [11], occurred from 8 to 20 weeks of age in db/db mice before the apparent neuronal abnormalities, which can be detected by ERG [9]. As pericyte loss was observed at 24 weeks of age but not 12 weeks of age in db/db mice [12], the impaired neurovascular coupling in the retina may be the earliest event in the diabetic retina.…”

“…At 14 weeks of age, the same protocol for systemic hyperoxia and flicker stimulation was performed in two diabetic mice and db/m control mice groups (Figure 6). We previously confirmed that the RBF response to both stimulations remained stable in db/m non-diabetic control mice from 8 to 20 weeks of age [9]. RBF measurements were performed only once at only 14 weeks of age in line with animal welfare criteria for our institution.…”

“…Our recent study revealed that retinal blood flow (RBF) does not respond to systemic hyperoxia and flicker stimulations in db/db mice with early type 2 diabetes, and no apparent changes in resting retinal perfusion were observed [9]. These results suggest that long-term glucotoxicity is a central mechanism for impaired retinal neurovascular coupling in type 2 diabetic mice.…”

“…RBF was measured using the LSFG Micro system (Softcare Co., Ltd., Fukutsu, Japan), as previously described [9]. In brief, the LSFG-Micro system includes a standard chargecoupling device camera (700 × 480 pixels) and a diode laser (830 nm wavelength) mounted on a stereomicroscope (SZ61TR, Olympus Corporation, Tokyo, Japan).…”