Imatinib prevents dexamethasone-induced pancreatic β-cell apoptosis via decreased TRAIL and DR5

Prolonged administration of dexamethasone, a potent anti-inflammatory drug, can lead to steroid-induced diabetes. Imatinib, a medication commonly prescribed for chronic myeloid leukemia (CML), has been shown to improve diabetes in CML patients. Our recent study demonstrated that dexamethasone induces pancreatic β-cell apoptosis by upregulating the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptor, death receptor 5 (DR5). We hypothesized that imatinib may protect against dexamethasone-induced pancreatic β-cell apoptosis by reducing the expression of TRAIL and DR5, thereby favorably modulating downstream effectors in apoptotic pathways. We test this hypothesis by assessing the effects of imatinib on dexamethasone-induced apoptosis in rat insulinoma cell line cells. As anticipated, dexamethasone treatment led to increased TRAIL and DR5 expression, as well as an elevation in superoxide production. Conversely, expression of the TRAIL decoy receptor (DcR1) was decreased. Moreover, key effectors in the extrinsic and intrinsic apoptosis pathways, such as B-cell lymphoma 2 (BCL-2) associated X (BAX), nuclear factor kappa B (NF-κb), P73, caspase 8, and caspase 9, were upregulated, while the antiapoptotic protein BCL-2 was downregulated. Interestingly and importantly, imatinib at a concentration of 10 µM reversed the effect of dexamethasone on TRAIL, DR5, DcR1, superoxide production, BAX, BCL-2, NF-κB, P73, caspase 3, caspase 8, and caspase 9. Similar effects of imatinib on dexamethasone-induced TRAIL and DR5 expression were also observed in isolated mouse islets. Taken together, our findings suggest that imatinib protects against dexamethasone-induced pancreatic β-cell apoptosis by reducing TRAIL and DR5 expression and modulating downstream effectors in the extrinsic and intrinsic apoptosis pathways.

Cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis

Steroid-induced diabetes is a well-known metabolic side effect of long-term use of glucocorticoid (GC). Our group recently demonstrated dexamethasone-induced pancreatic β-cell apoptosis via upregulation of TRAIL and TRAIL death receptor (DR5). Genistein protects against pancreatic β-cell apoptosis induced by toxic agents. This study aimed to investigate the cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis in cultured rat insulinoma (INS-1) cell line and in isolated mouse islets. In the absence of genistein, dexamethasone-induced pancreatic β-cell apoptosis was associated with upregulation of TRAIL, DR5, and superoxide production, but downregulation of TRAIL decoy receptor (DcR1). Dexamethasone also activated the expression of extrinsic and intrinsic apoptotic proteins, including Bax, NF-κB, caspase-8, and caspase-3, but suppressed the expression of the anti-apoptotic Bcl-2 protein. Combination treatment with dexamethasone and genistein protected against pancreatic β-cell apoptosis, and reduced the effects of dexamethasone on the expressions of TRAIL, DR5, DcR1, superoxide production, Bax, Bcl-2, NF-κB, caspase-8, and caspase-3. Moreover, combination treatment with dexamethasone and genistein reduced the expressions of TRAIL and DR5 in isolated mouse islets. The results of this study demonstrate the cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis in both cell line and islets via reduced TRAIL and DR5 protein expression.

Dexamethasone induces pancreatic β-cell apoptosis through upregulation of TRAIL death receptor

Long-term medication with dexamethasone - a synthetic glucocorticoid (GC) drug - results in hyperglycemia, or steroid-induced diabetes. Although recent studies revealed that dexamethasone directly induces pancreatic β-cell apoptosis, its molecular mechanisms remain unclear. In our initial analysis of mRNA transcripts, we discovered the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway may be involved in dexamethasone-induced pancreatic β-cell apoptosis. In the present study, a mechanism of dexamethasone-induced pancreatic β-cell apoptosis through the TRAIL pathway was investigated in cultured cells and isolated mouse islets. INS-1 cells were cultured with and without dexamethasone in the presence or absence of a glucocorticoid receptor (GR) inhibitor, RU486. We found that dexamethasone induced pancreatic β-cell apoptosis in association with the upregulation of TNSF10 (TRAIL) mRNA and protein expression. Moreover, dexamethasone upregulated the TRAIL death receptor (DR5) protein but suppressed the decoy receptor (DcR1) protein. Similar findings were observed in mouse isolated islets: dexamethasone increased TRAIL and DR5 compared to that of control mice. Furthermore, dexamethasone stimulated pro-apoptotic signaling including superoxide production, caspase-8, -9, and -3 activities, NF-κB, and Bax but repressed the anti-apoptotic protein, Bcl-2. All these effects were inhibited by the GR-inhibitor, RU486. Furthermore, knock-down DR5 decreased dexamethasone-induced caspase 3 activity. Caspase-8 and caspase-9 inhibitors protected pancreatic β-cells from dexamethasone-induced apoptosis. Taken together, dexamethasone induced pancreatic β-cell apoptosis by binding to the GR and inducing DR5 and TRAIL pathway.

Prunetin Protects Against Dexamethasone-Induced Pancreatic Β-Cell Apoptosis via Modulation of p53 Signaling Pathway

Long-term administration of dexamethasone results in insulin resistance and pancreatic β-cell apoptosis. Prunetin (an O-methylated isoflavone, a type of flavonoid) is demonstrated to protect diabetes, but the molecular mechanism of this protection is still unclear. This study thus aims to investigate how prunetin protects against dexamethasone-induced pancreatic β-cell apoptosis. Rat insulinoma (INS-1) cells were cultured in medium with or without dexamethasone in the presence or absence of prunetin or pifithrin-α, a p53 inhibitor. Cell apoptosis was measured by Annexin V/propidium iodide staining. Dexamethasone significantly induced INS-1 apoptosis but dexamethasone plus prunetin significantly reduced INS-1 apoptosis. Dexamethasone-treated INS-1 upregulated p53 protein expression; the induction of p53 was also reduced in the presence of RU486, a glucocorticoid receptor (GR) inhibitor. This suggested that dexamethasone induced P53 via GR. Dexamethasone-treated INS-1 significantly increased p53, Bax, and Rb protein expressions, whereas treatments of dexamethasone plus prunetin or pifithrin-α significantly decreased these protein expressions. In addition, dexamethasone significantly decreased B-cell lymphoma 2 (Bcl2), while dexamethasone plus prunetin or pifithrin-α significantly increased Bcl2. Dexamethasone significantly increased caspase-3 activity while co-treatment of dexamethasone plus prunetin or pifithrin-α significantly decreased caspase-3 activity to the control level. Taken together, our results revealed that prunetin protected against dexamethasone-induced pancreatic β-cells apoptosis via modulation of the p53 signaling pathway.

Estradiol Prevents High Glucose-Induced β-cell Apoptosis by Decreased BTG2 Expression

Hyperglycemia stimulates several pathways to induce pancreatic β-cell apoptosis. In our previous study by mRNA analysis, we demonstrated that B-cell translocation gene 2 (BTG₂) expression was up-regulated in INS-1 cells cultured under high glucose conditions, but this effect was reversed by estrogen. In the present study, we demonstrated that BTG₂ mRNA and protein expressions in both INS-1 cells and mouse pancreatic islets increased under high glucose conditions compared to those cultured under basal glucose conditions, while in the presence of estrogen, the BTG₂ mRNA and protein expressions decreased. SiRNA-BTG₂ significantly reduced cell apoptosis, cleaved-caspase 3, and Bax, compared to the siRNA-control in INS-1 cultured under high glucose conditions. We further demonstrated that BTG₂ promoter activity was activated under high glucose conditions whereas estrogen significantly reduced it. The effects of estrogen on BTG₂ expression were inhibited by estrogen receptor inhibitors. Also, under high glucose conditions, p53 and Bax mRNA and protein expressions increased, but they decreased in the presence of estrogen. Again, the effect of estrogen on p53 and Bax expression was inhibited by estrogen receptor inhibitors. Taken together, this study demonstrates that estrogen reduces pancreatic β-cell apoptosis under high glucose conditions via suppression of BTG2, p53, and Bax expressions.