Low-Intensity Exercise in Mice Is Sufficient to Protect Retinal Function During Light-Induced Retinal Degeneration

PURPOSE. We previously reported that a specific treadmill running exercise regimen protects against light-induced retinal degeneration (LIRD) in mice. We hypothesized that this protective effect varies with running intensity. To test this, mice undergoing LIRD were run at different treadmill speeds and retinal function was assessed. METHODS. BALB/c mice were assigned to LIRD groups at varying treadmill speeds-0, 5, 10, or 20 m/min labeled inactive, low, medium, and high, respectively-and compared with naive mice exposed to standard lighting (50 lux; naive). Following 2 weeks of exercise, a subset of mice were exposed to toxic light (10,000 lux; LIRD) for 4 hours. After 5 additional days of exercise, retinal function was assessed by ERG. Corticosterone levels in serum and cathepsin B (CTSB) protein levels in muscle, brain, serum, and retina were measured. The retinal gene expression of complement factor 1qa (C1qa) and CTSB were measured. RESULTS. The low+LIRD and medium+LIRD exercise groups had greater a- and b-wave ERG amplitudes when compared with the inactive+LIRD group (P < 0.02). The high+LIRD mice only differed from the inactive+LIRD mice in their dark-adapted b-waves. Serum corticosterone increased in the high+LIRD mice (P < 0.006). Retinal CTSB protein levels were higher in the low+LIRD versus high+LIRD mice (P < 0.004) but were otherwise unchanged. Exercise of any intensity decreased C1qa gene expression. CONCLUSIONS. Faster running did not additionally protect against LIRD, but it did increase serum corticosterone, suggesting stress-induced limits to exercise benefits. Unexpectedly, exercise did not increase CTSB proteins levels in muscle or serum, suggesting that it may not mediate exercise effects. Our results have implications for the use of low-intensity exercise as a vision loss treatment.