Distinct differences in the responses of the human pancreatic β-cell line EndoC-βH1 and human islets to proinflammatory cytokines

While insulinoma cells have been developed and proven to be extremely useful in studies focused on mechanisms controlling β-cell function and viability, translating findings to human β-cells has proven difficult because of the limited access to human islets and the absence of suitable insulinoma cell lines of human origin. Recently, a human β-cell line, EndoC-βH1, has been derived from human fetal pancreatic buds. The purpose of this study was to determine whether human EndoC-βH1 cells respond to cytokines in a fashion comparable to human islets. Unlike most rodent-derived insulinoma cell lines that respond to cytokines in a manner consistent with rodent islets, EndoC-βH1 cells fail to respond to a combination of cytokines (IL-1, IFN-γ, and TNF) in a manner consistent with human islets. Nitric oxide, produced following inducible nitric oxide synthase (iNOS) expression, is a major mediator of cytokine-induced human islet cell damage. We show that EndoC-βH1 cells fail to express iNOS or produce nitric oxide in response to this combination of cytokines. Inhibitors of iNOS prevent cytokine-induced loss of human islet cell viability; however, they do not prevent cytokine-induced EndoC-βH1 cell death. Stressed human islets or human islets expressing heat shock protein 70 (HSP70) are resistant to cytokines, and, much like stressed human islets, EndoC-βH1 cells express HSP70 under basal conditions. Elevated basal expression of HSP70 in EndoC-βH1 cells is consistent with the lack of iNOS expression in response to cytokine treatment. While expressing HSP70, EndoC-βH1 cells fail to respond to endoplasmic reticulum stress activators, such as thapsigargin. These findings indicate that EndoC-βH1 cells do not faithfully recapitulate the response of human islets to cytokines. Therefore, caution should be exercised when making conclusions regarding the actions of cytokines on human islets when using this human-derived insulinoma cell line.

The VGF-derived peptide TLQP-62 modulates insulin secretion and glucose homeostasis

Insulin secretion control is critical for glucose homeostasis. Paracrine and autocrine molecules secreted by cells of the islet of Langerhans, as well as by intramural and autonomic neurons, control the release of different hormones that modulate insulin secretion. In pancreatic islets, the abundant presence of the granin protein VGF (nonacronymic; unrelated to VEGF) suggests that some of its proteolytically derived peptides could modulate hormone release. Thus, in the present study, we screened several VGF-derived peptides for their ability to induce insulin secretion, and we identified the VGF C-terminal peptide TLQP-62 as the most effective fragment. TLQP-62 induced a potent increase in basal insulin secretion as well as in glucose-stimulated insulin secretion in several insulinoma cell lines. We found that this peptide stimulated insulin release via increased intracellular calcium mobilization and fast expression of the insulin 1 gene. Moreover, the peripheral injection of TLQP-62 in mice improved glucose tolerance. Together, the present findings suggest that TLQP-62, acting as an endocrine, paracrine, or autocrine factor, can be considered a new, strong insulinotropic peptide that can be targeted for innovative antidiabetic drug discovery programs.

Reduction of insulin secretion in the insulinoma cell line INS-1 by overexpression of a Ca(v)2.3 (alpha1E) calcium channel antisense cassette

OBJECTIVE: Multiple types of voltage-activated Ca(2+) channels (T, L, N, P, Q and R type) coordinate a variety of Ca(2+)-dependent processes in neurons and neuroendocrine cells. In insulinoma cell lines as well as in endocrine tissues, the non-L-type alpha1E (Ca(v)2.3) subunit is expressed as the tissue-specific splice variant alpha1Ee. DESIGN AND METHODS: To understand the functional role of alpha1E-containing Ca(2+) channels, antisense alpha1E mRNA was overexpressed in INS-1 cells by stable transfection of an antisense alpha1E cassette cDNA. As controls, either a sense alpha1E cassette or a control vector containing enhanced green fluorescent protein as an unrelated gene was stably transfected. The overexpression of each transfected cassette cDNA was recorded by RT-PCR. RESULTS: In three independent antisense alpha1E INS-1 clones, the glucose-induced insulin release was significantly reduced as compared with wild-type INS-1 cells and with a sense alpha1E INS-1 clone. However, in the antisense INS-1 clones, the KCl-induced insulin release was less impaired by overexpressing the antisense alpha1E cassette than the glucose-induced insulin release, leading to the assumption that glucose (15 mmol/l) and KCl (25 mmol/l) finally depolarize the membrane potential to a different extent. CONCLUSION: alpha1E is involved in glucose-induced insulin secretion probably by influencing the excitability of INS-1 cells.