Inhibition of Collagen Production by Diabetic Rat Serum: Response to Insulin and Insulin-Like Growth Factor-I Addedin Vitro*

Abstract

Diabetes mellitus is associated with a generalized defect in connective tissue metabolism. Since collagen is the major protein of connective tissues, we used collagen as a probe to examine the role of factors in diabetic rat serum (DRS) in the etiology of these defects. Serum and skin fibroblasts were isolated from nondiabetic rats, and serum was taken from rats 48 h after injection of 200 mg/kg streptozotocin. Within 24 h of confluency, the fibroblast medium was changed to experimental serum for 24 h, with 5 microCi [3H]proline added for the final 6 h. Collagen and noncollagen proteins were quantitated using purified collagenase. Compared to cells incubated in medium without serum, collagen fell to 58% with 0.5% DRS (P less than 0.05) and continued to decrease with increasing concentrations of DRS. Noncollagen protein decreased below levels in cells incubated in medium without serum only when concentrations of diabetic serum were 1% or greater and did not decrease further with higher concentrations of diabetic serum. Collagen was decreased to a greater degree than noncollagen protein at each concentration of DRS, such that collagen relative to total protein production was significantly reduced at 0.5% or more DRS. Addition of 10(-7)-10(-9) M insulin or insulin-like growth factor-I (0.1-1000 ng/ml) to DRS did not return collagen production to the level seen in cells incubated in medium with no added serum (basal production). After separation of serum components based on size, incubation of cells with the low mol wt fraction (less than 5000 daltons) of normal and diabetic rat serum resulted in equivalent collagen production, while incubation with the high mol wt fraction of DRS resulted in 200-fold less collagen compared to the similar fraction of normal serum. This decrease in collagen production appeared due to the presence of a high mol wt factor(s) in diabetic serum which had a direct inhibitory effect on collagen and was not due to deficiency of growth peptides. The degree and specificity of these changes in collagen production probably contribute to long term complications in diabetes through altered connective tissue metabolism.