Exocrine pancreas hyperplasia without dysplasia in glucagon receptor knockout mice

Characterization of a naturally occurring mutation V368M in the human glucagon receptor and its association with metabolic disorders

Glucagon is a peptide hormone secreted by islet α cells. It plays crucial roles in glucose homeostasis and metabolism by activating its cognate glucagon receptor (GCGR). A naturally occurring deleterious mutation V368M in the human GCGR leads to reduced ligand binding and down-regulation of glucagon signaling. To examine the association between this mutation and metabolic disorders, a knock-in mouse model bearing homozygous V369M substitution (equivalent to human V368M) in GCGR was made using CRISPR-Cas9 technology. These GcgrV369M+/+ mice displayed lower fasting blood glucose levels with improved glucose tolerance compared with wild-type controls. They also exhibited hyperglucagonemia, pancreas enlargement and α cell hyperplasia with a lean phenotype. Additionally, V369M mutation resulted in a reduction in adiposity with normal body weight and food intake. Our findings suggest a key role of V369M/V368M mutation in GCGR-mediated glucose homeostasis and pancreatic functions, thereby pointing to a possible interplay between GCGR defect and metabolic disorders.

Animal models of spontaneous pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PNETs) are usually low-grade neoplasms derived from the endocrine pancreas. PNETs can be functioning and cause well-described hormonal hypersecretion syndromes or non-functioning and cause only tumor mass effect. PNETs appear to be more common recently likely due to incidental detection by imaging. Although the diagnosis and management of PNETs have been evolving rapidly, much remains to be studied in the areas of molecular pathogenesis, molecular markers of tumor behavior, early detection, and targeted drug therapy. Unique challenges facing PNETs studies are long disease course, the deep location of pancreas and difficult access to pancreatic tissue, and the variety of tumors, which make animal models valuable tools for PNETs studies. Existing animal models of PNETs have provided insights into the pathogenesis and natural history of human PNETs. Future studies on animal models of PNETs should address early tumor detection, molecular markers of tumor behavior, and novel targeted therapies.

Elusive liver factor that causes pancreatic α cell hyperplasia: A review of literature

Tumors and cancers of the gastrointestinal tract and pancreas are commonly derived from precursor lesions so that understanding the physiological, cellular, and molecular mechanisms underlying the pathogenesis of precursor lesions is critical for the prevention and treatment of those neoplasms. Pancreatic neuroendocrine tumors (PNETs) can also be derived from precursor lesions. Pancreatic α cell hyperplasia (ACH), a specific and overwhelming increase in the number of α cells, is a precursor lesion leading to PNET pathogenesis. One of the 3 subtypes of ACH, reactive ACH is caused by glucagon signaling disruption and invariably evolves into PNETs. In this article, the existing work on the mechanisms underlying reactive ACH pathogenesis is reviewed. It is clear that the liver secretes a humoral factor regulating α cell numbers but the identity of the liver factor remains elusive. Potential approaches to identify the liver factor are discussed.

Pancreatic α-cell hyperplasia: facts and myths

CONTEXT

Pancreatic α-cell hyperplasia (ACH) was once an esoteric pathological entity, but it has become an important differential diagnosis of hyperglucagonemia after inactivating glucagon receptor (GCGR) genomic mutations were found in patients with ACH. Recently, the controversy over the pancreatic effects of incretins has stimulated much discussion of ACH that often includes inaccurate statements not supported by the literature.

DATA ACQUISITION

Literature related to ACH was reviewed.

EVIDENCE SYNTHESIS

ACH is defined as a diffuse and specific increase in the number of α-cells. A dozen cases have been reported and fall into three clinical types: reactive, functional, and nonfunctional. Characterized by remarkable hyperglucagonemia without glucagonoma syndrome, reactive ACH is caused by inactivating GCGR mutations, and its main clinical significance is pancreatic neuroendocrine tumors diagnosed at middle age. The Gcgr(-/-) mice, a model of reactive ACH, exhibit a multistage tumorigenesis in their pancreata. Pharmacological agents that inhibit glucagon signaling also cause reactive ACH in animals and possibly in humans as well. The pancreata of incretin-treated humans and those of reactive ACH murine models share similarities. Functional ACH features hyperglucagonemia with glucagonoma syndrome. Nonfunctional ACH is associated with normal glucagon levels. The causes of functional and nonfunctional ACH are unknown as yet.

CONCLUSIONS

ACH is a histological diagnosis and clinically heterogeneous. Caused by GCGR mutations, reactive ACH is a preneoplastic lesion giving rise to slow-developing pancreatic neuroendocrine tumors. The effects of treatments targeting glucagon signaling in this regard remain controversial. The strong negative feedback control of glucagon signaling conserved in all mammals studied, including humans, makes long-term pancreatic tumor surveillance advisable for the glucagon signaling-targeting therapies.