The identification and sequence analysis of a new Reg3gamma and Reg2 in the Syrian golden hamster

Regenerating proteins and their expression, regulation and signaling

The regenerating (Reg) protein family comprises C-type lectin-like proteins discovered independently during pancreatitis and pancreatic islet regeneration. However, an increasing number of studies provide evidence of participation of Reg proteins in the proliferation and differentiation of diverse cell types. Moreover, Reg family members are associated with various pathologies, including diabetes and forms of gastrointestinal cancer. These findings have led to the emergence of key roles for Reg proteins as anti-inflammatory, antiapoptotic and mitogenic agents in multiple physiologic and disease contexts. Yet, there are significant gaps in our knowledge regarding the regulation of expression of different Reg genes. In addition, the pathways relaying Reg-triggered signals, their targets and potential cross-talk with other cascades are still largely unknown. In this review, the expression patterns of different Reg members in the pancreas and extrapancreatic tissues are described. Moreover, factors known to modulate Reg levels in different cell types are discussed. Several signaling pathways, which have been implicated in conferring the effects of Reg ligands to date, are also delineated. Further efforts are necessary for elucidating the biological processes underlying the action of Reg proteins and their involvement in various maladies. Better understanding of the function of Reg genes and proteins will be beneficial in the design and development of therapies utilizing or targeting this protein group.

Coordinated age-dependent and pancreatic-specific expression of mouse Reg2Reg3α, and Reg3β genes

Reg family proteins such as Reg1 and islet neogenesis-associated protein (INGAP) have long been implicated in the growth and/or neogenesis of pancreatic islet cells. Recent reports further suggest similar roles to be played by new members such as Reg2, Reg3α, and Reg3β. We have studied their age-, isoform-, and tissue-specific expressions. RNA and protein were isolated from C57BL/6 mice aged 7, 30, and 90 days. Using real-time polymerase chain reaction, the levels of Reg gene expression in the pancreas were 20-600-fold higher than that in other tissues (≫duodenum>stomach>liver); gene expression of Reg2, Reg3α, and Reg3β was age dependent as it was hardly detectable at day 7, increased drastically at day 30, and significantly decreased at day 90; the levels of pancreatic proteins displayed similar age-dependent variations. Using dual-labeled immunofluorescence, Reg2, Reg3α, and Reg3β were abundantly expressed in most acinar cells of the pancreas, in contrast to INGAP which exhibited stepwise increases from day 7 to day 90 and colocalized with the α-cells. These new Reg genes were mainly expressed in the pancreas, with clear age-dependent and isoform-specific patterns.

Adjuvant immunotherapy increases beta cell regenerative factor Reg2 in the pancreas of diabetic mice

Insulin-producing β cells can partially regenerate in adult pancreatic tissues, both in human and animal models of type 1 diabetes (T1D). Previous studies have shown that treatment with mycobacterial adjuvants such as CFA and bacillus Calmette-Guérin prevents induction and recurrence of T1D in NOD mice with partial recovery of β cell mass. In this study, we investigated factors involved in the regeneration of β cells in the pancreas of NOD mice during diabetes development and after treatment with adjuvants. The Regeneration (Reg) gene family is known to be involved in regeneration of various tissues including β cells. Reg2 expression was found to be upregulated in pancreatic islets both during diabetes development and as a result of adjuvant treatment in diabetic NOD mice and in C57BL/6 mice made diabetic by streptozotocin treatment. The upregulation of Reg2 by adjuvant treatment was independent of signaling through MyD88 and IL-6 because it was not altered in MyD88 or IL-6 knockout mice. We also observed upregulation of Reg2 in the pancreas of diabetic mice undergoing β cell regenerative therapy with exendin-4 or with islet neogenesis-associated protein. Reg2 expression following adjuvant treatment correlated with a reduction in insulitis, an increase in insulin secretion, and an increase in the number of small islets in the pancreas of diabetic NOD mice and with improved glucose tolerance tests in streptozotocin-treated diabetic C57BL/6 mice. In conclusion, adjuvant immunotherapy regulates T1D in diabetic mice and induces Reg2-mediated regeneration of β cells.

Pancreatic acinar-specific overexpression of Reg2 gene offered no protection against either experimental diabetes or pancreatitis in mice

Reg proteins are normally expressed in pancreatic acinar cells, and the level of several of these proteins was significantly induced upon damage to the endocrine or exocrine pancreas. It has been established that Reg1 and pancreatic islet neogenesis-associated protein [INGAP, Reg3delta] promote the growth or regeneration of the endocrine islet cells. Recent reports suggest that Reg2 is an autoantigen normally expressed in islet beta-cells. Reg2 overexpression in vitro offered protection to insulinoma cells. Overexpressed Reg3alpha increased cyclin D1 and CDK4 levels and the rate of proliferation in insulinoma cells. Acinar-specific overexpression of INGAP increased beta-cell mass and protected the animals from streptozotocin-induced diabetes. Moreover, Reg2 gene expression was induced during pancreatitis. We hypothesized that Reg2 is a secreted protein that promotes the growth, survival, and/or regeneration of pancreatic endocrine and exocrine cells. To test its effectiveness, we used elastase-1 promoter (Ela-Reg2) to develop an acinar cell-specific overexpression of the Reg2 gene. Western blot analysis, real-time PCR, and immunohistochemistry revealed barely detectable levels of endogenous Reg2 in the pancreas of normal wild-type mice and increased Reg2 levels in the pancreas of Ela-Reg2 mice that were similar to or higher than Reg2 levels induced in experimental diabetes or pancreatitis. Compared with wild-type littermates, growth, blood glucose and insulin levels, and glucose tolerance were normal in Ela-Reg2 mice; pancreatic histology revealed no change in endocrine or exocrine tissues. Acinar-specific overexpression of the Reg2 gene offered no protection against streptozotocin-induced beta-cell damage and diabetes, in hyperglycemia and weight loss, and no advantage in restoring glucose homeostasis and islet function within 3 mo. Furthermore, serum amylase level and pancreatic histochemistry showed that Reg2 overexpression did not protect acinar cells against caerulein-induced acute pancreatitis. In contrast to INGAP or Reg3beta, exocrine overexpression of Reg2 offered no protection to the endocrine or exocrine pancreas, indicating clear subtype specificities of the Reg family of proteins.

Distinctions between islet neogenesis and β-cell replication: implications for reversal of Type 1 and 2 diabetes

The terms "islet" and "β-cell" are often used interchangeably, yet islets are highly complex multicellular organelles that contain the insulin-producing β-cells and four other cells types, all of which play a role in maintaining glucose homeostasis within a very narrow range. Although the formation of new islets in adults is rare, occurring primarily in response to pancreatic injury and major stress to the pancreas, β-cell replication from existing cells occurs throughout adulthood. An understanding of the regulatory factors controlling pancreatic development has more clearly defined the differences between new islet formation from progenitor cells located throughout the adult pancreas and β-cell replication occurring within existing islets. The present review sets forth to more clearly distinguish the differences between the postnatal pathways of islet neogenesis and β-cell replication with a discussion of the potential implications for reversal of Type 1 and 2 diabetic patients using islet neogenesis agents that are now in development. For Type 1 diabetic patients, an immune tolerance agent in conjunction with an islet neogenesis agent may allow achievement of adequate islet mass, perhaps with subsequent potential to withdraw medications. For Type 2 diabetic patients, lifestyle changes and/or medications may sustain the production of new islets and limit the accelerated β-cell apoptosis characteristic of the condition.

Production and characterization of the recombinant Islet Neogenesis Associated Protein (rINGAP)

Islet Neogenesis Associated Protein (INGAP) is implicated in pancreatic islet neogenesis. INGAP peptide, a pentadecapeptide comprising amino acids 104-118, reverses diabetes in rodents and improves glucose homeostasis in patients with diabetes. The mechanism of INGAP action is unknown, but such studies would benefit from the availability of the full-length recombinant protein (rINGAP). Here we report the production of rINGAP from 293-SF cells following lentiviral transduction, and its characterization by MALDI-TOF and Q-TOF Mass Spectrometry, and HPLC. Importantly, we show that rINGAP exhibits 100x the bioactivity of INGAP peptide on a molar basis in an in vitro assay of human islet regeneration.