Molecular characterisation of pancreatic zymogen granule ion channel and regulator proteins involved in exocytosis

Total Pancreatectomy with Islet Auto Transplantation Outcomes in Pancreatitis Patients of Genetic Etiology: A Single Center Experience with a Large Cohort of Patients

PURPOSE

Total pancreatectomy with islet autotransplantation (TPIAT) is an effective treatment for patients with chronic pancreatitis (CP) when other interventions are unsuccessful. CP has many etiologies including heredity. Metabolic and pain relief outcomes following TPIAT are presented among patients with a genetic CP etiology when compared to those with a nongenetic etiology in a large cohort of patients who underwent this procedure at our center.

METHODS

A retrospective analysis was performed of 237 TPIAT patients from 2006 to 2023. We analyzed the differences in patients with genetic (n = 56) versus nongenetic (n = 181) CP etiologies in terms of pre-TPIAT factors including patient characteristics and disease state, results from the isolation process, and outcomes such as long-term glycemic and pain control.

RESULTS

Patients with genetic CP underwent TPIAT at a significantly younger age (32.3 years vs 41.3 years nongenetic, p < 0.0001) and endured symptoms for a significantly longer period (10 vs 6 years, p < 0.01). A significantly lower mass of islets was isolated from patients with genetic CP (p < 0.01), which increased with body mass index in both groups. Despite lower yields, genetic CP patients maintained metabolic function like nongenetic CP patients, as indicated by insulin independence and C-peptide, blood glucose, and hemoglobin A1c levels after TPIAT. Posttransplant narcotic usage and pain scores significantly decreased compared to pre-TPIAT, and more genetic CP patients were pain free and narcotic free post-TPIAT.

CONCLUSIONS

Our data validate TPIAT as a beneficial procedure for patients enduring CP of genetic etiology. Pain that is inevitably recurrent after minor interventions due to the nature of the disease and favorable TPIAT outcomes should be considered in the decision to perform early TPIAT in cases of genetic CP.

Chromogranin B (CHGB) is dimorphic and responsible for dominant anion channels delivered to cell surface via regulated secretion

Regulated secretion is conserved in all eukaryotes. In vertebrates granin family proteins function in all key steps of regulated secretion. Phase separation and amyloid-based storage of proteins and small molecules in secretory granules require ion homeostasis to maintain their steady states, and thus need ion conductances in granule membranes. But granular ion channels are still elusive. Here we show that granule exocytosis in neuroendocrine cells delivers to cell surface dominant anion channels, to which chromogranin B (CHGB) is critical. Biochemical fractionation shows that native CHGB distributes nearly equally in soluble and membrane-bound forms, and both reconstitute highly selective anion channels in membrane. Confocal imaging resolves granular membrane components including proton pumps and CHGB in puncta on the cell surface after stimulated exocytosis. High pressure freezing immuno-EM reveals a major fraction of CHGB at granule membranes in rat pancreatic β-cells. A cryo-EM structure of bCHGB dimer of a nominal 3.5 Å resolution delineates a central pore with end openings, physically sufficient for membrane-spanning and large single channel conductance. Together our data support that CHGB-containing (CHGB+) channels are characteristic of regulated secretion, and function in granule ion homeostasis near the plasma membrane or possibly in other intracellular processes.

Renal insufficiency is associated with an increased risk of papillary renal cell carcinoma histology

PURPOSE

End-stage renal disease (ESRD) and acquired renal cystic disease associated with dialysis are known risk factors of papillary renal cell carcinoma (pRCC); however, it is not known whether renal insufficiency alone is a risk factor for pRCC. Our aim was to test whether renal insufficiency is associated with an increased preponderance of pRCC.

METHODS

Retrospective review of institutional database to identify all patients who underwent extirpative renal surgery for renal cell carcinoma (RCC) with complete records from 1992 to 2012. We excluded those patients with preoperative ESRD as defined by GFR < 15 mL/min/1.73 m(2). The dependent variable was histologic RCC subtype. Independent variables included demographic data, comorbidities, and renal functional data. Multivariate analysis by binary logistic regression was used to determine factors that independently were associated with pRCC development.

RESULTS

A total of 1,226 patients met inclusion criteria, of which 15 % were pRCC. There was a positive association between likelihood of pRCC histology of RCC and increasing preoperative chronic kidney disease (CKD) stage (p = 0.021). Multivariate regression analysis indicated that male gender, race, and declining renal function categorized both by GFR and CKD stage were independently associated with a higher likelihood of pRCC histology as compared to other RCC histology.

CONCLUSIONS

Within a large cohort of patients with a diagnosis of RCC, declining renal function was independently associated with an increased likelihood of pRCC histology. This finding and the available molecular evidence indicating protein expression similarity between pRCC and resident stem cells, which appear to be upregulated with kidney damage, suggest a possible causal relationship between renal injury and pRCC.

Patch clamped single pancreatic zymogen granules: direct measurements of ion channel activities at the granule membrane

BACKGROUND/AIM

Pancreatic acinar cells are involved in the secretion of digestive enzymes. Digestive enzymes in pancreatic acinar cells are stored in membrane-bound secretory vesicles called zymogen granules (ZGs). The swelling of ZGs is implicated in the regulation of the expulsion of intravesicular contents during secretion. The molecular mechanism of ZG swelling has been previously elucidated. It has been further demonstrated that the water channel aquaporin-1, the potassium channel IRK-8, and the chloride channel CLC-2, are present in the ZG membrane and involved in ZG swelling. However, a direct measurement of these ion channels at the ZG membrane in intact ZGs had not been performed. The aim of this study was to investigate the electrical activity of single ZGs and verify the types of channels found within their membrane.

METHODS

ZGs from pancreatic acinar cells were isolated from the pancreas of Sprague-Dawley rats. Direct measurements of whole vesicle currents, in the presence and absence of ion channel blockers (quinine, glyburide and DIDS), were recorded following successful patching of single ZGs.

CONCLUSION

In this study, we were able, for the first time, to patch single ZGs and study ion channels in their membrane. We were able to record currents across the ZG membrane and, utilizing ion channel blockers, confirm the presence of the chloride channels CLC-2 and the potassium channel IRK-8 (Kir6.1), and additionally demonstrate the presence of a second chloride channel CLC-3.

Ion channels in secretory granules of the pancreas and their role in exocytosis and release of secretory proteins

Regulated secretion in exocrine and neuroendocrine cells occurs through exocytosis of secretory granules and the subsequent release of stored small molecules and proteins. The introduction of biophysical techniques with high temporal and spatial resolution, and the identification of Ca(2+)-dependent and -independent "docking" and "fusion" proteins, has greatly enhanced our understanding of exocytosis. The cloning of families of ion channel proteins, including intracellular ion channels, has also revived interest in the role of secretory granule ion channels in exocytotic secretion. Thus secretory granules of pancreatic acinar cell express a ClC-2 Cl(-) channel, a HCO-permeable member of the CLCA Ca(2+)-dependent anion channel family, and a KCNQ1 K(+) channel. Evidence suggests that these channels may facilitate the release of digestive enzymes and/or prevent exocytosed granules from collapsing during "kiss and run" recycling. In pancreatic beta-cells, a granular ClC-3 Cl(-) channel provides a shunt pathway for a vacuolar-type H(+)-ATPase. Acidification "primes" the granules for Ca(2+)-dependent exocytosis and release of insulin. In summary, secretory granules are equipped with specific sets of ion channels, which modulate regulated exocytosis and the release of macromolecules. These channels could represent excellent targets for therapeutic interventions to control exocytotic secretion in relevant diseases, such as pancreatitis, cystic fibrosis, or diabetes mellitus.