Lin et al. (1) report that complement factor C3 is required in mice for induction of diabetes by multiple low-dose streptozotocin injections. However, we have ourselves induced diabetes in both wild-type (WT) and C3−/− female mice on C57BL/6J background with the use of similarly sized doses of streptozotocin (Sigma-Aldrich). More than five injections were required in both groups (WT: 12 injections; C3−/−: 11 injections, P = 0.19). Mean blood glucose reached the same level (mean ± SEM 437 ± 20 mg/dl) in these groups (P = 0.21 of area under the curve [glucose × days]) (Fig. 1). After 82 days of diabetes, diabetic WT and diabetic C3−/− mice had developed well-described diabetic kidney alternations when compared with control WT and control C3−/− mice, respectively. In WT and C3−/− animals, diabetes led to increased urinary albumin-to-creatinine ratio (P < 0.001), increased glomerulus volume (P = 0.03), and increased renal mRNA expression of transforming growth factor-β (P = 0.02), and fibronectin (P < 0.001). Collagen IVα1 expression was increased in diabetes only in WT animals (P = 0.002) but not in C3−/− animals. VEGF-A expression was decreased in diabetes (P = 0.001) in both WT and C3−/− animals.
We observed an effect of C3, because the diabetic increase in kidney-to-body weight ratio and glomerular basement membrane thickness were different between the groups when interaction between diabetes (control vs. diabetes) and C3 (WT vs. C3 knockout) was analyzed by two-way ANOVA (P = 0.002 and P < 0.001, respectively). Prominent differences between the two groups in kidney-to-body weight ratio and glomerulus basement membrane thickness were observed as both parameters were increased in C3−/− compared with WT animals (P < 0.001 in both cases).
The C3−/− animals we used were purchased from The Jackson Laboratory (Bar Harbor, ME), which gives a status of six generations of backcrossing on C57BL/6J background. These animals have then been further backcrossed in our local animal facility for more than six generations on. WT animals were purchased from Taconic (Ry, Denmark). Study design and methods are described previously except for the use of C3 knockout mice in the data reported above (2).
We performed our experiments to explore the importance of complement in diabetic kidney disease because we have observed that in patients with type 1 diabetes, higher levels of mannose-binding lectin (MBL) are associated with negative kidney outcomes (3). In mice, causality between MBL and later diabetic kidney changes is described (2).
We find the results of Lin et al. very interesting and would like to investigate why we see a difference. We suggest that future studies should also investigate the role of other components of the MBL pathway of the complement system on the development of diabetes.
No potential conflicts of interest relevant to this article were reported.