Retinol-binding protein 4 (RBP4) is the major transport protein for retinol in blood. Recent evidence from genetic mouse models shows that circulating RBP4 derives exclusively from hepatocytes. Because RBP4 is elevated in obesity and associates with the development of glucose intolerance and insulin resistance, we tested whether a liver-specific overexpression of RBP4 in mice impairs glucose homeostasis. We used adeno-associated viruses (AAV) that contain a highly liver-specific promoter to drive expression of murine RBP4 in livers of adult mice. The resulting increase in serum RBP4 levels in these mice was comparable with elevated levels that were reported in obesity. Surprisingly, we found that increasing circulating RBP4 had no effect on glucose homeostasis. Also during a high-fat diet challenge, elevated levels of RBP4 in the circulation failed to aggravate the worsening of systemic parameters of glucose and energy homeostasis. These findings show that liver-secreted RBP4 does not impair glucose homeostasis. We conclude that a modest increase of its circulating levels in mice, as observed in the obese, insulin-resistant state, is unlikely to be a causative factor for impaired glucose homeostasis.
Several studies show an association of maternal diabetes during pregnancy with adverse offspring metabolic health. Other studies, however, suggest that this effect might be biased by obesity, which is independently associated with offspring metabolic disease and often coexistent to maternal diabetes. We performed a prospective study in a rat model to test the hypothesis that the burden of a diabetic pregnancy without obesity deteriorates metabolic health in male offspring. We generated maternal type 2 diabetes before conception that persisted during pregnancy by knockdown of the insulin receptor in small hairpin RNA–expressing transgenic rats. Male WT (wild type) offspring were followed up until adulthood and metabolically challenged by high-fat diet. Blood glucose was measured continuously via a telemetry device. Glucose and insulin tolerance tests were performed, and body composition was analyzed. Weight gain and glucose levels during adolescence and adulthood were similar in male offspring of diabetic and control pregnancies. Body weight and fat mass after high-fat diet, as well as glucose and insulin tolerance tests, were unaltered between male adult offspring of both groups. Glycemic control consisting of up to 49 000 individual glucose measures was comparable between both groups. Intrauterine exposure to maternal hyperglycemia and hyperinsulinemia without obesity had no impact on male offspring metabolic health in our model. We conclude that the intrauterine exposure itself does not represent a mechanism for fetal programming of diabetes and obesity in our model. Other maternal metabolic parameters during pregnancy, such as obesity, might impact long-term offspring metabolic health.
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