Obligatory Role of Early Ca(2+) Responses in H2O2-Induced β-Cell Apoptosis

Area of Science:

• Cell Biology
• Biochemistry
• Endocrinology

Background:

• Hydrogen peroxide (H2O2) can induce apoptosis in pancreatic beta-cells.
• Previous studies suggested a role for calcium (Ca2+) signaling in H2O2-induced beta-cell apoptosis.
• Inositol 1,4,5-trisphosphate (IP3) receptors and store-operated channels (SOCs) are implicated in Ca2+ release and influx.

Purpose of the Study:

• To investigate the role of early Ca2+ responses in H2O2-induced beta-cell apoptosis.
• To elucidate the mechanisms by which H2O2 affects intracellular and mitochondrial Ca2+ concentrations.
• To determine the involvement of IP3 receptors, SOCs, and mitochondrial Ca2+ uptake in the apoptotic pathway.

Main Methods:

• Treatment of beta-cells with H2O2 and measurement of cytosolic Ca2+ concentration ([Ca2+]c) over time.
• Pharmacological inhibition of IP3 receptors and SOCs using 2-aminoethoxydiphenylborate (2-APB).
• Assessment of mitochondrial Ca2+ concentration ([Ca2+]m) and cytochrome c release.
• Inhibition of mitochondrial calcium uniporter (MCU) using Ru360.

Main Results:

• H2O2 induced a biphasic increase in [Ca2+]c, with an initial transient elevation within 30 minutes.
• 2-APB significantly inhibited the early phase of [Ca2+]c elevation and subsequent mitochondrial Ca2+ ([Ca2+]m) increase and cytochrome c release.
• Inhibition of mitochondrial Ca2+ uptake via MCU did not prevent H2O2-induced [Ca2+]m elevation or cell death.

Conclusions:

• The initial Ca2+ response within 30 minutes, mediated by IP3 receptors and SOCs, is crucial for H2O2-induced beta-cell apoptosis.
• This early Ca2+ signaling leads to mitochondrial Ca2+ overload and cytochrome c release, likely through an MCU-independent pathway.
• Targeting early Ca2+ signaling events may offer therapeutic strategies for conditions involving beta-cell apoptosis.