IL-6 Promotes Islet β-Cell Dysfunction in Rat Collagen-Induced Arthritis

Abstract

The aim of this study was to explore the possible mechanism of rheumatoid arthritis- (RA-) related abnormal glucose metabolism. The model of collagen-induced arthritis (CIA) was established by intradermal injection of type II collagen into Wistar rats; complete Freund's adjuvant injections were used as the control group. Fasting plasma glucose (FBG) was measured by the glucose oxidase method. Fasting insulin (FIns) and the expressions of IL-6 were detected by ELISA. Islet caspase-3 was examined by immunohistochemistry. On day 17 after immunization, FBG of the CIA group showed an elevated FBG value compared with the control group. Meanwhile, the FIns of group CIA was lower when compared with the control group. Interestingly, the inflammatory cytokine IL-6 expression was significantly increased when compared with the control group. As expected, the abnormal glucose metabolism was accompanied by the increased IL-6 expression. Furthermore, in line with the upregulated IL-6 expression, the apoptosis related enzyme caspase-3 was also markedly increased. These data showed that the elevated FBG in CIA may be associated with the reduced FIns level secondary to the overapoptosis of pancreas islet cells induced by IL-6.

Figure 1

Establishment of rat collagen-induced arthritis. After day 17 of immunization, the macroscopic change of hind limbs and the histology of joint tissue sections from CIA rats and control rats were analyzed. All data are representative of one out of three independent experiments.

Figure 2

Glucose metabolism dysfunction in CIA rats. Blood samples were collected from the intraocular adjoined veins of the rats on day 17 after initial immunization from CIA rats and control rats. FBG and FIns in sera of both groups were determined as described in the Materials and Methods. The data are presented as mean ± SD (n = 6–8/group) and are representative of three independent experiments. ^∗ p < 0.05.

Figure 3

Increased IL-6 expression in rat collagen-induced arthritis. Blood samples were collected from the intraocular adjoined veins of the rats on day 17 after initial immunization from CIA rats and control rats. IL-6 in sera was determined by ELISA kit. The data are presented as mean ± SD (n = 6–8/group) and are representative of three independent experiments. ^∗ p < 0.05.

Figure 4

Correlation between IL-6 and FBG and FIns. The sera were harvested after day 17 of immunization. Levels of IL-6, FBG, and FIns were determined. The correlations between IL-6 and these factors in all the rats were analyzed by Spearman correlation test. p value < 0.05 was considered as statistically significant. Data are representative of three independent experiments.

Figure 5

Potential of IL-6 in the apoptosis of β-cells. The pancreas islets were harvested after day 17 of immunization. (a) The apoptosis related gene caspase-3 was analyzed by immunohistochemistry. (b) The expression of caspase-3 was analyzed by OD value. Image-Pro Plus 6.0 was used to delineate the scope of each field in the islets and measure the mean absorbance of the islets. (c) The proteins of pancreas islets were extracted for analyzing cleaved caspase-3 expression by immunoblots assays. Data are representative of three independent experiments (d) Paired Student's t-test was used for analyzing the paired data of IL-6 and caspase-3. Data are shown as the mean ± SD (n = 6–8/group) and are representative of three independent experiments. ^∗ p < 0.05.