SARM1, Not MyD88, Mediates TLR7/TLR9-Induced Apoptosis in Neurons

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Neuronal apoptosis is implicated in various neurological diseases, with unresolved underlying mechanisms.
• Innate immune responses, specifically Toll-like receptors (TLRs) in neurons, are increasingly recognized as a potential driver of neuronal death.
• TLRs can be activated by pathogen- and damage-associated molecular patterns, including microRNAs from damaged neurons.

Purpose of the Study:

• To elucidate the specific mechanism of Toll-like receptor 7 (TLR7) and Toll-like receptor 9 (TLR9)-mediated neuronal apoptosis.
• To identify the signaling pathway involved in TLR-induced neuronal cell death.

Main Methods:

• Investigated the role of endosomal localization and MyD88 signaling in TLR-induced apoptosis.
• Examined the involvement of the TLR adaptor molecule SARM1 in the apoptotic process.
• Assessed mitochondrial localization and accumulation in neurites following TLR activation in the presence and absence of SARM1.

Main Results:

• TLR7/TLR9-mediated apoptosis required endosomal TLR localization but was independent of MyD88 signaling.
• Apoptosis necessitated the TLR adaptor molecule SARM1, which translocated to mitochondria in neurites upon TLR activation.
• SARM1 deficiency prevented mitochondrial accumulation in neurites and TLR-induced neuronal apoptosis.

Conclusions:

• Identified a novel, non-MyD88 signaling pathway for TLR7/TLR9 activation in neurons.
• Demonstrated that SARM1 mediates TLR-induced mitochondrial dysfunction and neuronal apoptosis.
• Established a direct mechanism by which innate immune activation in the central nervous system can lead to neuronal damage.