Urocortin 3 (Ucn3) is a neuropeptide that was discovered by our group (Lewis et al., 2001). Ucn3 is specifically expressed in mouse beta cells, but is in human islets also expressed by alpha cells (Li et al., 2003; van der Meulen et al., 2012). Ucn3 is a member of the same neuropeptide family as corticotropin-releasing factor (CRF) and both peptides activate related receptors; CRF predominantly activates the type 1 CRF receptor, while Ucn3 exclusively activates the type 2 CRF receptor. We have in recent years discovered that CRF and Ucn 3 both contribute to the regulation of insulin secretion and the maintenance of functional beta cell mass by virtue of locally expressed CRF receptors in mouse and human islets (Huising et al., 2010, 2011). Interestingly, Ucn3 is not detectable in the developing mouse pancreas until embryonic day 17.5 and is not expressed by all beta cells until postnatal day 14 (van der Meulen et al., 2012). This is considerably later than the onset of expression of transcription factors that mark mature beta cells, such as Pdx1, Nkx6.1 and MafA as well as markers of functional beta cell maturity, including Pcks1, Znt8 (Scl30a8) or Glut2 (Scl2a2; in mouse).

In line with findings in mouse pancreas, Ucn3 expression in human embryonic pancreas is not detectable until the end of the first trimester and trails the onset of expression of insulin and glucagon by several weeks (van der Meulen et al., 2013). However, in marked contrast to murine pancreas, where Ucn3 demonstrates exquisite selectivity for the beta cells, Ucn3 in both human and macaque (Macaca nemestrina) pancreas and in freshly isolated human donor islets is expressed in both beta and alpha cells (van der Meulen et al., 2012). Moreover, and perhaps to emphasize the species differences that exist regarding the local network of CRF-family neuropeptides, CRF expression is selective for human alpha cells and is not detected in mouse islets. In agreement to the above observations, Ucn3 in human embryonic stem cell-derived pancreatic endocrine cells is expressed relatively late and only after an extensive period of in vivo maturation in recipient mice and is then detectable in both mature beta and alpha cells (van der Meulen et al., 2012). These findings have established Ucn3 as a marker of beta cell maturity. We therefore hypothesize that Ucn3 is a biomarker of functional, mature beta cells, and is down regulated during diabetic conditions that are associated with beta cell dysfunction and dedifferentiation. Supported by nPOD, we will establish if Ucn3 expression is reduced in alpha or beta cells of T1D and T2D donors compared to non-diabetic controls.