Caspase inhibitors protect neurons by enabling selective necroptosis of inflamed microglia

Area of Science:

• Neuroimmunology
• Cellular signaling
• Neuroinflammation

Background:

• Microglia, resident brain macrophages, contribute to neuronal damage in various brain diseases when activated.
• Caspase-8 plays dual roles in apoptosis and preventing RIPK1-dependent necroptosis, varying by cell type and stimulus.
• Understanding caspase-8's function in microglia is crucial for neuroprotective strategies.

Purpose of the Study:

• To investigate the role of caspase-8 in activated primary rat microglia.
• To determine the mechanism of microglial death upon caspase-8 inhibition.
• To evaluate the potential of targeting caspase-8 for neuroprotection in inflamed conditions.

Main Methods:

• Primary rat microglia were treated with inflammatory stimuli (LPS, lipoteichoic acid, TNF-α).
• Caspase-8 activity was measured; apoptosis and necrosis were assessed.
• Inhibitors of caspase-8 (Z-VAD-fmk, IETD-fmk) and RIPK1 (Necrostatin-1) were used.
• Mixed cerebellar cultures (neurons, astrocytes, microglia) were used to model neuroinflammation.

Main Results:

• Inflammatory stimuli increased caspase-8 activity in microglia without inducing apoptosis.
• Inhibiting caspase-8 led to microglial necrosis, identified as RIPK1-dependent necroptosis.
• This microglial necroptosis protected neurons from LPS-induced death in mixed cultures.

Conclusions:

• Caspase-8 activation in inflamed microglia prevents their death by necroptosis.
• Inhibiting caspase-8 selectively induces necroptosis in activated microglia.
• Targeting caspase-8 may offer a neuroprotective strategy by eliminating detrimental activated microglia.