Characterization of Insulin-Immunoreactive Cells and Endocrine Cells Within the Duct System of the Adult Human Pancreas

GPR30 is a potential player between islet cells and ductal HCO3- secretion

The primary role of pancreatic ductal HCO3- secretion is to prevent premature activation of digestive enzymes and to provide a vehicle for the delivery of enzymes to the duodenum. In addition, HCO3-is responsible for the neutralization of gastric juice and protect against the formation of protein plugs and viscous mucus. Due to this multifaceted role of HCO3- in the pancreas, its altered functioning can greatly contribute to the development of various exocrine diseases. It is well known that the exocrine and endocrine pancreas interact lively with each other, but not all details of this relationship are known. An interesting finding of a recent study by Jo-Watanabe et al. is that the G protein-coupled oestrogen receptor, GPR30, which is expressed in the endocrine pancreas, can be also activated by HCO3-. This raises the possibility that ductal cells play a key role not only in the exocrine pancreas, but presumably also in endocrine function through HCO3- secretion.

Enteroendocrine Cell Formation Is an Early Event in Pancreatic Tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a 5-year survival rate of only 11%, due, in part, to late diagnosis, making the need to understand early events in tumorigenesis critical. Acinar-to-ductal metaplasia (ADM), when not resolved, is a PDAC precursor. Recently, we showed that ADM is constituted by a heterogenous population of cells, including hormone-producing enteroendocrine cells (EECs: gamma, delta, epsilon, and enterochromaffin cells). In this study, we employed histopathological techniques to identify and quantify the abundance of EEC subtypes throughout pancreatic tumorigenesis in mouse models and human disease. We found that EECs are most abundant in ADM and significantly decrease with lesion progression. Co-immunofluorescence identifies distinct lineages and bihormonal populations. Evaluation of EEC abundance in mice lacking Pou2f3 demonstrates that the tuft cell master regulator transcription factor is not required for EEC formation. We compared these data to human neoplasia and PDAC and observed similar trends. Lastly, we confirm that EECs are a normal cellular compartment within the murine and human pancreatic ductal trees. Altogether, these data identify EECs as a cellular compartment of the normal pancreas, which expands early in tumorigenesis and is largely lost with disease progression.

Coxsackievirus-B4 Infection of Human Primary Pancreatic Ductal Cell Cultures Results in Impairment of Differentiation into Insulin-Producing Cells

Coxsackievirus-B4 (CV-B4) E2 can persist in the pancreatic ductal-like cells (Panc-1 cell line), which results in an impaired differentiation of these cells into islet-like cell aggregates (ICA). In this study, primary pancreatic ductal cells obtained as a by-product of islet isolation from the pancreas of seven brain-dead adults were inoculated with CV-B4 E2, followed-up for 29 days, and the impact was investigated. Viral titers in culture supernatants were analyzed throughout the culture. Intracellular viral RNA was detected by RT-PCR. Levels of ductal cell marker CK19 mRNA and of insulin mRNA were evaluated by qRT-PCR. The concentration of c-peptide in supernatants was determined by ELISA. Ductal cells exposed to trypsin and serum-free medium formed ICA and resulted in an increased insulin secretion. Ductal cells from five brain-dead donors were severely damaged by CV-B4 E2, whereas the virus persisted in cultures of cells obtained from the other two. The ICAs whose formation was induced on day 14 post-inoculation were scarce and appeared tiny in infected cultures. Also, insulin mRNA expression and c-peptide levels were strongly reduced compared to the controls. In conclusion, CV-B4 E2 lysed human primary pancreatic ductal cells or persisted in these cells, which resulted in the impairment of differentiation into insulin-producing cells.

Adverse impact of carbon tetrachloride on metabolic function in mice

Carbon tetrachloride (CCl₄ ), a potent hepatotoxin, is linked to the histopathological outcomes of inflammatory or oxidative stress, and cell death. However, further study of additional dysmetabolism induced by CCl ₄ toxicant has not yet been investigated. In current study, chronical and acute exposures of CCl ₄ in mice were used to unmask the biological molecular mechanism responsible for insulin-dependent metabolic disorder. In experimental methods, a number of biochemical assays were used in assessment of biological impacts on insulin-produced pancreas and insulin-responsive hepatocyte after long- and short-term exposures of CCl ₄ toxicant, respectively. As a result, data from oral glucose tolerance test showed that CCl ₄ exposures induced glucose tolerance and disrupted blood insulin and glucagon levels time-dependently. Meanwhile, biochemical and histocytological analyses further indicated that CCl ₄ exposures significantly resulted in liver cell damage, induced abnormal changes of hepatic and skeletal glycogen synthesis. In addition, acute CCl ₄ -exposed mice showed reduced functional proteins of glucose transporter 2 (GLUT2), insulin receptor β, insulin receptor substrate 1, glycogen synthase kinase 3β (GSK3β), p-AKT ^Ser473 associated with AKT signaling pathway in liver cells, whereas acute CCl ₄ exposure downregulated the endogenous expressions of the insulin and glucagon hormonal proteins in the pancreas. Taken together, the current findings highlight that CCl ₄ impaired insulin-dependent glucose homeostasis through modulating hepatocellular AKT signaling pathway in acute CCl ₄ exposure and GLUT2/GSK3β pathway in chronic CCl ₄ -exposed liver cells.

FGF21 functions as a sensitive biomarker of APAP-treated patients and mice

Acetaminophen (APAP) is a common medication that induces hepatocellular damage in a time- or dose-dependent manner. Fibroblast growth factor 21 (FGF21) exerts a series of biological effects, including cellular repair. Compared to clinical diagnosis parameters, we aimed to evaluate whether FGF21 can serve as a sensitive biomarker for APAP-induced liver impairment. In the present study, we discussed comparable data from APAP-treated patients and parallelly established APAP-exposed mice for investigation. The resulting human serological data showed that APAP-treated patients have a visible reduction of FGF21 expression in undetected liver impairment of clinical diagnosis. In the animal study, APAP-exposed livers exhibited normal metabolic functions and liver functions, as revealed by biochemical test and histopathological examination. Endogenous FGF21 concentrations in APAP-treated mice were decreased in sera and liver cells. Moreover, comparable immunoassay data showed that hepatocellular FGF21 expression was reduced in a time-dependent manner. Taken together, these findings elucidate the involvement of abnormal FGF21 expression in early APAP-induced liver impairment. Interestingly, FGF21 may be a promising biomarker of APAP-exposed livers.

Perfluorooctanoic acid impaired glucose homeostasis through affecting adipose AKT pathway

Perfluorooctanoic acid (PFOA) is commonly applied in manufactured products, and its potential health risk is concerned greatly. Increasing evidences have indicated PFOA-induced liver dysfunction. However, detailed molecular mechanism has not been completely identified. In this study, we aimed to investigate the mechanical association between PFOA exposure and AKT pathway in white adipose tissue. As results, PFOA-treated mice showed increased blood glucose and insulin levels, and induced insulin resistance. In addition, serum levels of leptin and adiponectin in PFOA-treated mice were elevated. As shown in histological examination, increased cell death counts in PFOA-treated adipose were observed, as well as ultrastructural impairment in adipose cells was found. Further, immunohistochemical stains exhibited GLUT4, p-AKT positive cells were down-regulated in PFOA-treated adipose, while PTEN immune-labeled cells were reduced. In validated data, RT-PCR assay suggested adipose AKT mRNA was down-regulated in PFOA-treated mice, and PTEN mRNA was increased. Western blot data showed that intracellular PTEN protein level in PFOA-treated adipose was up-regulated, while phosphorylation of AKT, GSK3β levels were lowered dose-dependently. Taken together, the present findings indicate that PFOA impaired glucose homeostasis via negatively regulating AKT pathway in white adipose tissue.

Dapagliflozin modulates glucagon secretion in an SGLT2-independent manner in murine alpha cells

AIM

SGLT2 inhibitors reduce renal glucose uptake through an insulin-independent mechanism. They also increase glucagon concentration, although the extent to which this is due to a direct effect on pancreatic alpha cells remains unclear.

METHODS

In the present work, αTC1 cells treated with the SGLT2 inhibitor dapagliflozin (Dapa) were analyzed for glucose transporters, molecular mediators of hormone secretion, glucagon and GLP-1 release, and the effects of somatostatin. Data were validated in murine and human pancreatic islets.

RESULTS

SLC5A2 (the SGLT2-encoding gene) was nearly undetectable in αTC1 cells, not even by a digital PCR technique using different probes. In contrast, SLC5A1 (the SGLT1-encoding gene) was constitutively abundant in αTC1 cells and in islets, and increased with Dapa. This was associated with greater glucagon release, preceded by increased expression of preproglucagon and HNF4α. Looking at the candidate intracellular signalling pathway, reduced PASK and increased AMPK-α2 expression were also detected. GLUT1 and GLUT2, as well as regulators of glucagon release and alpha-cell phenotype (chromogranin A, paired box 6, proprotein convertase 1/2, synaptophysin), were unaffected by Dapa, as were GLP-1 receptor expression and GLP-1 release. Low glucose did not influence the stimulatory effect of Dapa on glucagon release, but was instead almost fully reverted by SLC5A1 silencing. When the effect of Dapa on AMPK and PASK, emerging regulators of lipid and glucose metabolism, was tested, upregulated AMPK-α2 appeared to be involved in molecular signalling.

CONCLUSION

Our study has shown that, in αTC1 cells, Dapa acutely upregulates SGLT1 expression and increases glucagon release through an SGLT1-dependent mechanism, with SGLT2 expression virtually undetectable. These results suggest the involvement of SGLT1 in modulating glucagon increases following SGLT2 inhibition.

The Vascular Microarchitecture of the Human Fetal Pancreas: A Corrosion Casting and Scanning Electron Microscopy Study

OBJECTIVES

Detailed knowledge on the development of the pancreas is required to understand the variability in its blood supply. The aim of our study was to use the corrosion casting method combined with scanning electron microscopy to study the organization of the pancreatic microcirculation in human fetuses.

METHODS

The study was conducted on 28 human fetuses aged 18 to 25 gestational weeks. The fetal vasculature was appropriately prepared and then perfused with a low-viscosity Mercox CL-2R resin. The prepared vascular casts of the surface of the fetal pancreas were then examined in scanning electron microscopy and digitally analyzed.

RESULTS

The lobular structure of the pancreas has a strong impact on the organization of the microvasculature. The lobular networks were supplied by the interlobular arteries and drained by the interlobular veins. The vascular system of fetal human pancreas has many portal connections, including islet-lobule and islet-duct portal circulations, which likely play a key role in the coordination of both endocrine and exocrine pancreatic functions.

CONCLUSIONS

The organization of the microvascular network of the human pancreas in fetuses aged 18 to 25 gestational weeks is very similar to that of an adult but with more prominent features suggesting active processes of angiogenesis and vascular remodeling.