Elevated soluble CD163 in gestational diabetes mellitus: secretion from human placenta and adipose tissue

Abstract

Recently soluble CD163 (sCD163), a cleaved form of the macrophage receptor CD163, was identified as a macrophage-specific risk-predictor for developing Type 2 Diabetes. Here, we investigate circulating levels of sCD163 in gestational diabetes mellitus (GDM). Furthermore, given the role of the placenta in the pathogenesis of GDM, we assessed placental contribution to sCD163 secretion. Paired maternal (venous) and umbilical vein blood samples from GDM (n = 18) and Body Mass Index (BMI) matched control women (n = 20) delivered by caesarean section at 39-40 week gestation were assessed for circulating levels of sCD163, Tumour necrosis factor alpha (TNF-α) and Interleukin 6 (IL-6). Media from explant culture of maternal subcutaneous fat and corresponding placental tissues were assayed for these same molecules. CD163 positive cell numbers were determined in placental and adipose tissues of GDM and control women. We found significantly elevated circulating sCD163 levels in GDM mothers (688.4±46.9 ng/ml vs. 505.6±38.6 ng/ml) and their offspring (418.2±26.6 ng/ml vs. 336.3±24.4 ng/ml [p<0.05 for both]) as compared to controls, together with elevated circulating TNF-α and IL-6 levels. Moreover, both GDM placentae (268.1±10.8 ng/ml/mg vs. 187.6±20.6 ng/ml/mg) and adipose explants (41.1±2.7 ng/ml/mg vs. 26.6±2.4 ng/ml/mg) released significantly more sCD163 than controls. Lastly, significantly more CD163 positive cells were observed in GDM placentae (25.7±1.1 vs. 22.1±1.2) and adipose tissue (19.1±1.1 vs 12.7±0.9) compared to controls. We describe elevated sCD163 levels in GDM and identify human placenta as a novel source of sCD163 suggesting that placental tissues might contribute to the increased levels of circulating sCD163 in GDM pregnancies.

Figure 1. Circulating levels of maternal and fetal IL-6, TNF-alpha and sCD163.

ELISA measurements of maternal (A, B and C) and fetal (D, E and F) circulating levels of IL6 (A and D), TNF-alpha (B and E) and sCD163 (C and F). GDM = gestational diabetes; sCD163 = Soluble CD163; IL-6 = Interleukin 6; TNF-alpha = Tumor necrosis factor alpha [*p<0.05 =  statistically significant]) Details in Materials & Methods.

Figure 2. Secretion of IL-6, TNF-alpha and sCD163 from placental and adipose tissue explants.

Measurements of adipose (A, B and C) and placental (D, E and F) explants secretion of IL6 (A and D) TNF-alpha (B and E) and sCD163 (C and F). Explants were cultured in CMRL-1066 medium (Invitrogen, Paisley, UK) supplemented with 5% Fetal Calf Serum (Invitrogen, Paisley, UK), 100 µg/ml streptomycin sulphate and 100 IU/ml penicillin. (GDM = gestational diabetes; sCD163 = Soluble CD163; IL-6 = Interleukin 6; TNF-alpha = Tumor necrosis factor alpha [*p<0.05]).

Figure 3. Immunohistochemistry and cell count of CD163 positive cells in GDM (A and B) and controls (C and D) of placental (A and C) and adipose tissues (B and D).

CD163 positive cells, in ten random areas at 40× magnification for placenta and adipose tissues respectively were counted and analysed using image J. Mean with SEM of CD163 positive cell in placenta (E) and adipose tissues (F) [*p<0.05, **p<0.001].