Astrocytes and Microglia Are Resistant to NAD⁺-Mediated Cell Death Along the ARTC2/P2X7 Axis

Area of Science:

• Neuroimmunology
• Cellular Signaling
• Immunology

Background:

• Extracellular nicotinamide adenine dinucleotide (NAD+) acts as a danger signal, triggering cell death (NICD) in T cells via ADP-ribosylation of the P2X7k splice variant by ARTC2.2.
• The impact of NICD on non-T cell populations, particularly brain-resident glia like astrocytes and microglia, remains largely uninvestigated.
• Understanding glia susceptibility to NICD is crucial given their role in neuroinflammation and response to tissue damage.

Purpose of the Study:

• To investigate the susceptibility of astrocytes and microglia to NAD+-induced cell death (NICD).
• To determine the expression patterns of P2X7 receptor variants and ARTC2 isoforms in these glia.
• To elucidate the mechanisms underlying glia resistance or sensitivity to NICD.

Main Methods:

• Primary astrocyte and microglia cultures were treated with lipopolysaccharide (LPS) and U0126 (MEK inhibitor) to assess ARTC2 expression and ADP-ribosylation.
• Cells were exposed to extracellular NAD+ to evaluate P2X7 activation and cell death induction.
• Quantitative PCR or Western blotting was used to analyze P2X7 splice variant (P2X7a vs. P2X7k) and ARTC2 isoform expression.

Main Results:

• Astrocytes and microglia upregulated cell surface ARTC2.1 and ADP-ribosylation upon LPS and U0126 treatment.
• These glia populations did not exhibit P2X7 activation or cell death in response to extracellular NAD+.
• Astrocytes and microglia preferentially express the ADP-ribosylation-insensitive P2X7a splice variant, conferring resistance to NICD.

Conclusions:

• Brain-resident astrocytes and microglia are resistant to NAD+-induced cell death (NICD).
• This resistance is attributed to the expression of the P2X7a splice variant, which is insensitive to ADP-ribosylation.
• While glia can upregulate ARTC2, their P2X7 receptor repertoire dictates their non-responsiveness to NICD, highlighting cell-type-specific vulnerability to danger signals.