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[Background]: Diabetes type 1 is characterized by the failure of beta cells to produce insulin. Suppressor of cytokine signaling (SOCS) proteins are important regulators of the Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway. Previous studies have shown that GH can prevent the development of type I diabetes in mice and that SOCS2 deficiency mimics a state of increased GH sensitivity. [Methodology]: The elevated sensitivity of SOCS2 mice to GH and possibly to PRL was the rationale to analyze the effects of multiple low dose streptozotocin (MLDSTZ)-induced diabetes in SOCS2 mice. [Results]: We show that 6-month-old SOCS2 mice, but not 2-month-old mice, were less sensitive to MLDSTZ-induced diabetes, compared to controls. MLDSTZ treatment induced glucose intolerance in both SOCS2 and SOCS2 mice, as shown by glucose tolerance tests, with SOCS2 mice showing a more marked intolerance, compared to SOCS2 mice. Furthermore, insulin tolerance tests showed that the SOCS2 mice have an improved hypoglycemic response to exogenous insulin, compared to SOCS2 mice. Moreover, in isolated islets, lipotoxic effects on insulin release could partly be overcome by ligands, which bind to GH or PRL receptors. [Conclusion]: Knockdown of SOCS2 makes mice less sensitive to MLDSTZ. These results are consistent with the proposal that elimination of SOCS2 in pancreatic islets creates a state of β-cell hypersensitivity to GH/PRL that mimics events in pregnancy, and which is protective against MLDSTZ-induced type I diabetes in mice. SOCS2-dependent control of β-cell survival may be of relevance to islet regeneration and survival in transplantation., The Spanish Ministry of Science and Innovation, with the European Regional Development Fund, supported this research by grants-in-aid to L.F.-P. (SAF2012– 37344). L.F.-P. was also supported by grants-in-aid from ACIISI (PI2010/0110) and Alfredo Martin-Reyes Foundation (Arehucas)-FICIC. The Danish Council for Independent Research and the Novo Nordisk Foundation supports A.F-M. G.N. is supported by a grant from Swedish Heart and Lung Foundation. A.A is supported by a fellowship from Sultan Qaboos University, Muscat, Oman. M.M-G. is a recipient of predoctoral fellowship from ULPGCMEC (AP2001–3499) and Fundación Universitaria de Las Palmas (INNOVA).

Liver X receptor (LXR) agonists have been shown to influence the development of hyperlipidemia and atherosclerosis in mouse models. It has also been demonstrated that some LXR agonists can cause hepatic steatosis in experimental animals. Growth hormone (GH) is known to regulate hepatic metabolism and the absence of hepatic GH receptors (GHR) leads to hepatic steatosis. In this study, we analyzed whether the actions of LXR agonists could involve interference with GH signaling. We showed that LXR agonists impair GH signaling in hepatocytes. LXR agonist treatment attenuated GH induction of suppressor of cytokine signaling 2 (SOCS2), SOCS3, and CIS mRNA levels in BRL-4 cells. Likewise, the activity of a luciferase reporter vector driven by the GH response element (GHRE) of the SOCS2 gene was inhibited by simultaneous treatment with an LXR agonist. The inhibitory effect of LXR agonists on GH signals can be mimicked by overexpression of the LXR regulated factors, sterol regulatory element binding protein 1 (SREBP1) and SREBP2, in hepatic cells. In both cases total and phosphorylated signal transducers and activators of transcription 5b (STAT5b) protein levels were significantly reduced. DNA binding assays demonstrated that SREBP1 binds to an E-box within a previously defined GHRE in the SOCS2 gene promoter, but does not compete with STAT5b binding to a nearby site in the same promoter construct. Taken together, our findings indicate that the inhibitory effects of LXR agonists on GH signaling are mediated by SREBP1, through the downregulation of STAT5b gene transcription and stimulation of STAT5b protein degradation. The findings provide a new insight into the understanding of the molecular actions of LXR agonists, which may be of relevance to their pharmacological actions.