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Nitric oxide-induced apoptosis in pancreatic beta cells is mediated by the endoplasmic reticulum stress pathway
S Oyadomari1, K Takeda, M Takiguchi
1Department of Molecular Genetics, Kumamoto University School of Medicine, Honjo 2-2-1, Kumamoto 860-0811, Japan.
Abstract:
Excessive nitric oxide (NO) production in cytokine-activated beta cells has been implicated in beta cell disruption in type 1 diabetes. beta cells are very vulnerable to NO-induced apoptosis. However, the mechanism underlying this phenomenon is unclear. Low concentrations of NO that lead to apoptosis apparently do not cause severe DNA damage in mouse MIN6 beta cells. CHOP, a C/EBP homologous protein that is induced by endoplasmic reticulum (ER) stress and plays a role in growth arrest and cell death, was induced by a NO donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP). SNAP increased cytosolic Ca(2+), and only agents depleting ER Ca(2+) induced CHOP expression and led to apoptosis, suggesting that NO depletes ER Ca(2+). Overexpression of calreticulin increased the Ca(2+) content of ER and afforded protection to cells against NO-mediated apoptosis. Furthermore, pancreatic islets from CHOP knockout mice showed resistance to NO. We conclude that NO depletes ER Ca(2+), causes ER stress, and leads to apoptosis. Thus, ER Ca(2+) stores are a new target of NO, and the ER stress pathway is a major mechanism of NO-mediated beta cell apoptosis.
Insights
Excessive nitric oxide (NO) causes beta cell apoptosis in type 1 diabetes by depleting endoplasmic reticulum (ER) calcium stores, inducing ER stress and cell death. This reveals ER calcium as a novel NO target and ER stress as a key pathway in beta cell failure.
Area of Science:
- Endocrinology
- Cell Biology
- Immunology
Background:
- Cytokine-activated beta cells produce excessive nitric oxide (NO), implicated in type 1 diabetes.
- Beta cells are highly susceptible to NO-induced apoptosis, but the underlying mechanisms remain unclear.
Purpose of the Study:
- To elucidate the mechanism by which nitric oxide induces apoptosis in beta cells.
- To investigate the role of endoplasmic reticulum (ER) calcium and ER stress in NO-mediated beta cell death.
Main Methods:
- Utilized mouse MIN6 beta cells and pancreatic islets from CHOP knockout mice.
- Administered NO donor (SNAP) and agents affecting ER calcium levels.
- Measured cytosolic Ca(2+), CHOP expression, and apoptosis rates.
- Assessed the protective effect of calreticulin overexpression.
Main Results:
- Nitric oxide (NO) donor (SNAP) induced apoptosis without significant DNA damage.
- SNAP increased cytosolic Ca(2+) and induced CHOP expression, a marker of ER stress.
- Agents depleting ER Ca(2+) mimicked NO's effect, inducing CHOP and apoptosis.
- Overexpression of calreticulin protected cells against NO-induced apoptosis.
- Pancreatic islets from CHOP knockout mice were resistant to NO-induced apoptosis.
Conclusions:
- Nitric oxide (NO) depletes endoplasmic reticulum (ER) Ca(2+) stores, leading to ER stress and subsequent beta cell apoptosis.
- ER Ca(2+) stores represent a novel target of NO action.
- The ER stress pathway is a critical mechanism mediating NO-induced beta cell apoptosis, relevant to type 1 diabetes pathogenesis.