UCN2: a new candidate influencing pancreatic β-cell adaptations in pregnancy.

The corticotropin-releasing hormone (CRH) family of peptides, including urocortin (UCN) 1, 2 and 3, are established hypothalamic neuroendocrine peptides, regulating the physiological and behaviour responses to stress indirectly, via the hypothalamic-pituitary-adrenal (HPA) axis. More recently, these peptides have been implicated in diverse roles in peripheral organs through direct signalling, including in placental and pancreatic islet physiology. CRH has been shown to stimulate insulin release through activation of its cognate receptors, CRH receptor 1 (CRHR1) and 2. However, the physiological significance of this is unknown. We have previously reported that during mouse pregnancy, expression of CRH peptides increase in mouse placenta suggesting that these peptides may play a role in various biological functions associated with pregnancy, particularly the pancreatic islet adaptations that occur in the pregnant state to compensate for the physiological increase in maternal insulin resistance. In the current study, we show that mouse pregnancy is associated with increased circulating levels of UCN2 and that when we pharmacologically block endogenous CRHR signalling in pregnant mice, impairment of glucose tolerance is observed. This effect on glucose tolerance was comparable to that displayed with specific CRHR2 blockade and not with specific CRHR1 blockade. No effects on insulin sensitivity or the proliferative capacity of β-cells were detected. Thus, CRHR2 signalling appears to be involved in β-cell adaptive responses to pregnancy in the mouse, with endogenous placental UCN2 being the likely signal mediating this.