Supplementary Material for: Effects of Initiation Time of Glycemic Control on Skin Collagen Recovery in Streptozotocin-Induced Diabetic Rats

<b><i>Background:</i></b> Diabetes damages the collagen in the skin. No study has investigated the relationship between the treatment initiation time and the degree of collagen recovery. This study aimed to evaluate the effects of the initiation time of glycemic control on collagen recovery and to determine the basic molecules mediating the process. <b><i>Methods:</i></b> Streptozotocin-induced diabetic rats were divided into five groups: normal controls (C), those with untreated diabetes (DM), and those with diabetes treated with daily insulin injections from 7 weeks (7W), 10 weeks (10W), and 13 weeks (13W) after diabetes induction. The levels of collagen and several molecules were compared among skin tissues collected at 14 weeks. <b><i>Results:</i></b> The amounts of total collagen, collagen 1, and collagen 3 were significantly lower in DM than in C. Among the treated groups, recovery reaching normal levels was only observed in 7W and 10W. The earlier the treatment began, the greater was the collagen recovery. Similar to that of collagen, the expression of transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), and insulin-like growth factor 1 receptor (IGF-1R) significantly decreased in DM compared with that in C. Higher recovery of TGF-β1 and VEGF was detected in groups with earlier treatment, whereas the IGF-1R level was identically elevated in all treated groups. The results suggest that these molecules affect collagen recovery at different time points during glycemic control. <b><i>Conclusion:</i></b> The initiation time of glycemic control is expected to have a considerable effect on collagen recovery in the diabetic skin through modulation of TGF-β1, VEGF, and IGF-1R.