Fig. 1. Experimental approach, and animal groups and treatments.

Mice from both diabetic and age-matched control groups were randomly divided into two groups with and without LDR. Diabetic mice in LDR group (DM/LDR) were further divided into 3 groups (n=24 mice) with multiple exposures to LDR either at 12.5, 25, or 50 mGy every other day. These 3 groups were named as S (small dose: 12.5 mGy), M (medium dose: 25 mGy) and H (high dose: 50 mGy) group, respectively. Unirradiated diabetic mice were given sham exposure, named as DM group. The control mice in LDR group received multiple exposures at dose of 25 mGy every other day, expressed as N/L (normal/LDR) group. Untreated normal mice were given sham LDR in parallel, named as N (normal) group. At the 4^th week of exposure to LDR, 8 mice from each group were euthanized, and the remaining 16 mice in N/L, S, M and H groups were equally divided into 2 groups: one group was continuously given the same regimens of exposures for additional 4 weeks (named as 8N/L, 8S, 8M, and 8H, respectively), and the other group was given multiple sham exposures for 4 weeks (named as 4N/L, 4S, 4M, 4L, respectively). The mice in N and DM groups were continually given sham LDR in parallel, and still named as N and DM groups, respectively. Then all the mice were euthanized at the 8^th week of the study.