Role and mechanism of REG2 depletion in insulin secretion augmented by glutathione peroxidase-1 overproduction

We previously reported a depletion of murine regenerating islet-derived protein 2 (REG2) in pancreatic islets of glutathione peroxidase-1 (Gpx1) overexpressing (OE) mice. The present study was to explore if and how the REG2 depletion contributed to an augmented glucose stimulated insulin secretion (GSIS) in OE islets. After we verified a consistent depletion (90%, p < 0.05) of REG2 mRNA, transcript, and protein in OE islets compared with wild-type (WT) controls, we treated cultured and perifused OE islets (70 islets/sample) with REG2 (1 μg/ml or ml · min) and observed 30-40% (p < 0.05) inhibitions of GSIS by REG2. Subsequently, we obtained evidences of co-immunoprecipitation, cell surface ligand binding, and co-immunofluorescence for a ligand-receptor binding between REG2 and transmembrane, L-type voltage-dependent Ca2+ channel (CaV1.2) in beta TC3 cells. Mutating the C-type lectin binding domain of REG2 or deglycosylating CaV1.2 removed the inhibition of REG2 on GSIS and(or) the putative binding between the two proteins. Treating cultured OE and perifused WT islets with REG2 (1 μg/ml or ml · min) decreased (p < 0.05) Ca2+ influx triggered by glucose or KCl. An intraperitoneal (ip) injection of REG2 (2 μg/g) to OE mice (6-month old, n = 10) decreased their plasma insulin concentration (46%, p < 0.05) and elevated their plasma glucose concentration (25%, p < 0.05) over a 60 min period after glucose challenge (ip, 1 g/kg). In conclusion, our study identifies REG2 as a novel regulator of Ca2+ influx and insulin secretion, and reveals a new cascade of GPX1/REG2/CaV1.2 to explain how REG2 depletion in OE islets could decrease its binding to CaV1.2, resulting in uninhibited Ca2+ influx and augmented GSIS. These findings create new links to bridge redox biology, tissue regeneration, and insulin secretion.

Regenerating islet-derived protein (Reg)3β plays a crucial role in attenuation of ileitis and colitis in mice

Regenerating islet-derived protein (Reg)3β belongs to a member of the Reg family of proteins and has pleiotropic functions, including antimicrobial activity and tissue repair. However, whether Reg3β plays a protective role in the development of colitis and ileitis has not been fully investigated. We generated transgenic mice expressing a short form of cellular FLICE-inhibitory protein (cFLIPs) that promotes necroptosis, a regulated form of cell death. cFLIPs transgenic (CFLARs Tg) mice develop severe ileitis in utero. Although Reg3β is undetectable in the small intestine of wild-type embryos, its expression is aberrantly elevated in the small intestine of CFLARs Tg embryos. To test whether elevated Reg3β attenuates or exacerbates ileitis in CFLARs Tg mice, we generated a Reg3b^−/− strain. Reg3b^−/− mice grew to adulthood without apparent abnormalities. Deletion of Reg3b in CFLARs Tg mice exacerbated the embryonic lethality of CFLARs Tg mice. Dextran sulfate sodium-induced colitis, characterized by body weight loss and infiltration of neutrophils, was exacerbated in Reg3b^−/− compared to wild-type mice. Moreover, the expression of Interleukin 6, an inflammatory cytokine and Chitinase-like 3, a marker for tissue repair macrophages was elevated in the colon of Reg3b^−/− mice compared to wild-type mice after DSS treatment. Together, these results suggest that attenuation of colitis and ileitis is a result of Reg3β′s real function.

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The expression of Reg3β is elevated in the embryonic small intestine of CFLARs Tg mice.

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Reg3b^−/− mice grow to adulthood without apparent abnormalities.

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Dextran sulfate sodium-induced colitis is exacerbated in Reg3b^−/− mice.

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Deletion of Reg3b exacerbates ileitis in CFLARs Tg mice.

Comparative Analysis of Expression Profiles of Reg Signaling Pathways-Related Genes Between AHF and HCC

Regenerating islet-derived protein (Reg) could participate in the occurrence of diabetes mellitus, inflammation, tumors, and other diseased or damaged tissues. However, the correlation of Reg with acute hepatic failure (AHF) and hepatocellular carcinoma (HCC) is poorly defined. To reveal the expression profiles of Reg family and their possible regulatory roles in AHF and HCC, rat models of HCC and AHF were separately established, and Rat Genome 230 2.0 was used to detect expression profiles of Reg-mediated signaling pathways-associated genes from liver tissues in AHF and HCC. The results showed that a total of 79 genes were significantly changed. Among these genes, 67 genes were the AHF-specific genes, 45 genes were the HCC-specific genes, and 33 genes were the common genes. Then, K-means clustering classified these genes into 4 clusters based on the gene expression similarity, and DAVID analysis showed that the above altered genes were mainly associated with stress response, inflammatory response, and cell cycle regulation. Thereafter, IPA software was used to analyze potential effects of these genes, and the predicted results suggested that the Reg-mediated JAK/STAT, NF-κB, MAPK (ERK1/2, P38 and JNK), PLC, and PI3K/AKT signaling pathways may account for the activated inflammation and cell proliferation, and the attenuated apoptosis and cell death during the occurrence of AHF and HCC.