Inflammatory mechanisms in diabetes: lessons from the beta-cell.

Inflammation plays an important role in the destruction of pancreatic islet beta-cells that leads to type I diabetes. This involves infiltration of T-cells and macrophages into the islets and local production of inflammatory cytokines such as interleukin (IL)-1 beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. Our laboratory has developed several strategies for protecting beta-cells against oxidative stress and cytokine-induced cytotoxicity. These include a cytokine selection strategy that results in cell lines that are resistant to the combined effects of IL-1 beta+IFN-gamma. More recently, we have combined the cytokine selection procedure with overexpression of the antiapoptotic gene bcl-2, resulting in cell lines with greater resistance to oxidative stress and cytokine-induced damage than achieved with either procedure alone. This article summarizes this work and the remarkably divergent mechanisms by which protection is achieved in the different model systems. We also discuss the potential relevance of insights gained from these approaches for enhancing islet cell survival and function in both major forms of diabetes.

Expression of the transcription factor STAT-1 alpha in insulinoma cells protects against cytotoxic effects of multiple cytokines.

Destruction of pancreatic islet beta-cells in type 1 diabetes appears to result from direct contact with infiltrating T-cells and macrophages and exposure to inflammatory cytokines such as interferon (IFN)-gamma, interleukin (IL)-1 beta, and tumor necrosis factor TNF-alpha that such cells produce. We recently reported on a method for selection of insulinoma cells that are resistant to the cytotoxic effects of inflammatory cytokines (INS-1(res)), involving their growth in progressively increasing concentrations of IL-1 beta plus IFN-gamma, and selection of surviving cells. In the current study, we have investigated the molecular mechanism of cytokine resistance in INS-1(res) cells. By focusing on the known components of the IFN-gamma receptor signaling pathway, we have discovered that expression levels of signal transducer and activator of transcription (STAT)-1 alpha are closely correlated with the cytokine-resistant and -sensitive phenotypes. That STAT-1 alpha is directly involved in development of cytokine resistance is demonstrated by an increase of viability from 10 +/- 2% in control cells to 50 +/- 6% in cells with adenovirus-mediated overexpression of STAT-1 alpha (p < 0.001) after culture of both cell groups in the presence of 100 units/ml IFN-gamma plus 10 ng/ml IL-1 beta for 48 h. The resistance to IL-1 beta plus IFN-gamma in STAT-1 alpha-expressing cells is due in part to interference with IL-1 beta-mediated stimulation of inducible nitric-oxide synthase expression and nitric oxide production. Furthermore, overexpression of STAT-1 alpha does not impair robust glucose-stimulated insulin secretion in the INS-1-derived cell line 832/13. We conclude that expression of STAT-1 alpha may be a means of protecting insulin-producing cell lines from cytokine damage, which, in conjunction with appropriate cell-impermeant macroencapsulation devices, may allow such cells to be used for insulin replacement in type 1 diabetes.

Selection of insulinoma cell lines with resistance to interleukin-1beta- and gamma-interferon-induced cytotoxicity.

Engineered insulinoma cell lines may represent an alternative to isolated islets for transplantation therapy of type 1 diabetes. Success of this approach may require development of cell lines that can withstand cytokine-mediated damage. To this end, we have cultured INS-1 insulinoma cells in increasing concentrations of interleukin-1beta (IL-1beta) + gamma-interferon (IFN-gamma), with approximate weekly iterations over an 8-week period. Based on the C,N diphenyl-N'-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium+ ++ bromide (MTT) viability assay, the selected cells, termed INS-1res, were 100% viable after 5 days of treatment with 10 ng/ml of IL-1beta. These cells were also 78 +/- 1.2% viable after 5 days of exposure to the combination of 10 ng/ml IL-1beta and 100 U/ml IFN-gamma, whereas parental INS-1 cells treated in the same manner were only 0.3 +/- 0.03% viable. INS-1res cells were also resistant to treatment with supernatants from activated rat peripheral blood mononuclear cells, whereas only 20% of parental INS-1 cells survived such treatment. The resistance to IL-1beta conferred by this procedure was stable, whereas the partial resistance to IFN-gamma was transient but reinducible by culture in the presence of cytokines. Stable transfection of INS-1res cells with a plasmid containing the human insulin cDNA and expansion of the transfected colonies in the absence of cytokines produced cell lines that were on average more resistant to IL-1beta + IFN-gamma (53 +/- 11%) than similarly transfected clones derived from parental INS-1 cells (15 +/- 7%). Importantly, several INS-1res-derived clones retained the capacity to secrete insulin in response to glucose concentrations over the normal physiological range. With regard to the mechanism by which selection was conferred, we found normal levels of IFN-gamma receptor mRNA, but a 60% reduction in expression of the IL-1 receptor type I (IL-1RI) in INS-1res cells compared with parental INS-1 cells. IL-1beta signaling through p38 MAP kinase was found to be normal in INS-1res cells, suggesting that their expression of IL-1RI is sufficient to maintain cytokine action. However, normal IL-1beta-mediated translocation of NF-kappaB and induction of inducible nitric oxide synthase expression and nitric oxide production was severely impaired in the INS-1res cell lines, suggesting a mechanism for the IL-1beta resistance. In sum, this study defines a strategy for isolation of cytokine-resistant beta-cell lines and provides a new system for studying the mechanisms by which such resistance can be achieved.

Isolation of INS-1-derived cell lines with robust ATP-sensitive K+ channel-dependent and -independent glucose-stimulated insulin secretion.

The biochemical mechanisms involved in regulation of insulin secretion are not completely understood. The rat INS-1 cell line has been used to gain insight in this area because it secretes insulin in response to glucose concentrations in the physiological range. However, the magnitude of the response is far less than that seen in freshly isolated rat islets. In the current study, we have stably transfected INS-1 cells with a plasmid containing the human proinsulin gene. After antibiotic selection and clonal expansion, 67% of the resultant clones were found to be poorly responsive to glucose in terms of insulin secretion (< or =2-fold stimulation by 15 mmol/l compared with 3 mmol/l glucose), 17% of the clones were moderately responsive (2- to 5-fold stimulation), and 16% were strongly responsive (5- to 13-fold stimulation). The differences in responsiveness could not be ascribed to differences in insulin content. Detailed analysis of one of the strongly responsive lines (832/13) revealed that its potent response to glucose (average of 10-fold) was stable over 66 population doublings (approximately 7.5 months of tissue culture) with half-maximal stimulation at 6 mmol/l glucose. Furthermore, in the presence of 15 mmol/l glucose, insulin secretion was potentiated significantly by 100 pmol/l isobutylmethylxanthine (320%), 1 mmol/l oleate/palmitate (77%), and 50 nmol/l glucagon-like peptide 1 (60%), whereas carbachol had no effect. Glucose-stimulated insulin secretion was also potentiated by the sulfonylurea tolbutamide (threefold at 3 mmol/l glucose and 50% at 15 mmol/l glucose) and was abolished by diazoxide, which demonstrates the operation of the ATP-sensitive K+ channel (K(ATP)) in 832/13 cells. Moreover, when the K(ATP) channel was bypassed by incubation of cells in depolarizing K+ (35 mmol/l), insulin secretion was more effectively stimulated by glucose in 832/13 cells than in parental INS-1 cells, which demonstrates the presence of a K(ATP) channel-independent pathway of glucose sensing. We conclude that clonal selection of INS-1 cells allows isolation of cell lines that exhibit markedly enhanced and stable responsiveness to glucose and several of its known potentiators. These lines may be attractive new vehicles for studies of beta-cell function.

Stable expression of manganese superoxide dismutase (MnSOD) in insulinoma cells prevents IL-1beta- induced cytotoxicity and reduces nitric oxide production.

The fact that insulin-producing islet beta-cells are susceptible to the cytotoxic effects of inflammatory cytokines represents a potential hinderance to the use of such cells for transplantation therapy of insulin-dependent diabetes mellitus (IDDM). In the current study, we show that IL-1beta induces destruction of INS-1 insulinoma cells, while having no effect on a second insulinoma cell line RIN1046-38 and its engineered derivatives, and that this difference is correlated with a higher level of expression of manganese superoxide dismutase (MnSOD) in the latter cells. Stable overexpression of MnSOD in INS-1 cells provides complete protection against IL-1beta-mediated cytotoxicity, and also results in markedly reduced killing when such cells are exposed to conditioned media from activated human or rat PBMC. Further, overexpression of MnSOD in either RIN- or INS-1-derived lines results in a sharp reduction in IL-1beta-induced nitric oxide (NO) production, a finding that correlates with reduced levels of the inducible form of nitric oxide synthase (iNOS). Treatment of INS-1 cells with L-NMMA, an inhibitor of iNOS, provides the same degree of protection against IL-1beta or supernatants from LPS-activated rat PBMC as MnSOD overexpression, supporting the idea that MnSOD protects INS-1 cells by interfering with the normal IL-1beta-mediated increase in iNOS. Because NO and its derivatives have been implicated as critical mediators of beta-cell destruction in IDDM, we conclude that well regulated insulinoma cell lines engineered for MnSOD overexpression may be an attractive alternative to isolated islets as vehicles for insulin replacement in autoimmune diabetes.

Engineered cell lines for insulin replacement in diabetes: current status and future prospects.

The recently completed diabetes complications and control trial has highlighted the need for improvement of insulin delivery systems for treatment of insulin-dependent diabetes mellitus. Despite steady improvement in methods for islet and whole pancreas transplantation over the past three decades, the broad-scale applicability of these approaches remains uncertain due in part to the difficulty and expense associated with procurement of functional tissue. To address this concern, we and others have been using the tools of molecular biology to develop cell lines with regulated insulin secretion that might serve as a surrogate for primary islets or pancreas tissue in transplantation therapy. This article seeks to provide a brief summary of the current status of this growing field, with a particular emphasis on progress in producing cell lines with appropriate glucose-stimulated insulin secretion.

Regulation of insulin secretion from novel engineered insulinoma cell lines.

In the accompanying article, we describe the creation of novel cell lines derived from RIN 1046-38 rat insulinoma cells by stable transfection with combinations of genes encoding human insulin, GLUT2, and glucokinase. Herein we describe the regulation of insulin secretion and glucose metabolism in these new cell lines. A cell line (betaG I/17) expressing only the human proinsulin transgene exhibits a clear increase in basal insulin production (measured in the absence of secretagogues) relative to parental RIN 1046-38 cells. betaG I/17 cells engineered for high levels of GLUT2 expression and a twofold increase in glucokinase activity (betaG 49/206) or engineered for a 10-fold increase in glucokinase activity alone (betaG 40/110) exhibit a 66% and 80% suppression in basal insulin secretion relative to betaG I/17 cells, respectively. As a result, betaG 49/206 and betaG 40/110 cells exhibit potent insulin-secretory responses to glucose alone (6.1- and 7.6-fold, respectively) or to glucose plus isobutylmethylxanthine (10.8- and 15.1-fold, respectively) that are clearly larger than the corresponding responses of betaG I/17 or parental RIN 1046-38 cells. betaG 49/206 and betaG 40/110 cells also exhibit a rapid and sustained response to glucose plus isobutyl-methylxanthine in perifusion studies that is clearly larger in magnitude than that of the two control lines. Glucose dose-response studies show that both engineered and non-engineered lines respond maximally to submillimolar concentrations of glucose and that betaG 49/206 cells are the most sensitive to low concentrations of the hexose, consistent with their clearly elevated rate of [5-3H]glucose usage. Finally, 5-thioglucose, a potent inhibitor of low-K(m) hexokinases, most effectively normalizes glucose concentration dependence for insulin secretion in the cell line with highest glucokinase expression (betaG 40/110). We conclude that GLUT2 and/or glucokinase expression imposes tight regulation of basal insulin secretion in cell lines that overexpress human proinsulin, allowing a marked improvement in the range of secretagogue responsiveness in such cells.

[Insulin producing cells as therapy in diabetes mellitus]. / Insulinsezernierende Zellen zur Therapie des Diabetes mellitus.

Even with intensive insulin therapy it is impossible to reach physiological blood glucose levels in insulin-dependent diabetes mellitus. Because of the high costs and technical problems involved in islet cell transplantation broad applicability of this therapy seems uncertain. An alternative approach is the development of molecular-engineered insulin-producing clonal cell lines. The main interest is in rodent insulinoma cell lines and neuroendocrine AtT-20ins cells. This paper reviews the current knowledge about glucose-stimulated insulin secretion and the problems that have to be solved before these cells can be used for therapy in diabetes mellitus.

[Studies on human porin. V. The expression of "porin31HL" in the plasmalemma is not by cell transformation]. / Zur Kenntnis der Porine des Menschen. V. Die Plasmalemmständigkeit von "Porin 31HL" ist keine Folge einer Zell-Transformation.

In recent papers we proved "Porin 31HL" to be located on the surface of human, EBV-transformed B lymphocytes. Here we present proof of "Porin 31HL" in the plasmalemma of normal human blood lymphocytes. For this purpose B and T lymphocytes were isolated from human heparinized blood and examined by indirect immunofluorescence techniques using different monoclonal antibodies against purified "Porin 31HL" and some B and T cell markers, respectively. For comparison a number of established cell lines of different origin were employed. Hence it followed that normal B and T cells as well as transformed and leukemic cells express "Porin 31HL" in their membrane. No significant quantitative differences could be seen. Consequently, the location of "Porin 31HL" in the plasmalemma is not a product of transformation.