Nitric oxide mediates antimicrobial peptide gene expression by activating eicosanoid signaling

Area of Science:

• Insect immunology
• Molecular biology
• Biochemistry

Background:

• Nitric oxide (NO) is known to mediate insect cellular immunity via eicosanoids.
• The crosstalk between NO and eicosanoids in insect humoral immunity, specifically in antimicrobial peptide (AMP) induction, remains largely uncharacterized.

Purpose of the Study:

• To investigate the crosstalk between nitric oxide (NO) and eicosanoids in the induction of antimicrobial peptide (AMP) gene expression in the lepidopteran insect, Spodoptera exigua.
• To elucidate the signaling pathway involved in NO-mediated AMP gene expression.

Main Methods:

• Gene expression analysis of eight AMPs in S. exigua.
• Pharmacological inhibition of NO synthase (using L-NAME) and eicosanoid biosynthesis (using dexamethasone).
• RNA interference (RNAi) targeting NO synthase (SeNOS) and components of the Toll/IMD pathway (Toll receptors, Relish).
• Treatment with NO analog (SNAP) and arachidonic acid.

Main Results:

• Bacterial challenge induced the expression of eight AMPs in S. exigua.
• Inhibition of NO synthase (L-NAME) or NO production (SeNOS RNAi) suppressed AMP induction.
• Direct administration of NO (SNAP) mimicked bacterial challenge by inducing AMP expression.
• Eicosanoid biosynthesis inhibition (dexamethasone) blocked NO-induced AMP expression, an effect reversed by arachidonic acid.
• The Toll/IMD pathway regulates AMP expression by modulating NO levels and PLA2 activity.

Conclusions:

• Nitric oxide (NO) acts upstream of eicosanoids in the signaling pathway that induces antimicrobial peptide (AMP) gene expression in Spodoptera exigua.
• Eicosanoids function as downstream signaling molecules for NO in mediating humoral immune responses against bacterial challenges.
• The Toll/IMD pathway integrates NO signaling and eicosanoid production for effective insect immunity.