Functions of MDA5 and its domains in response to GCRV or bacterial PAMPs

Area of Science:

• Immunology
• Molecular Biology
• Fish Virology

Background:

• Melanoma differentiation-associated gene 5 (MDA5) is a crucial sensor in the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) family, initiating type I interferon (IFN) responses against RNA viruses.
• Understanding the functional domains of MDA5 is vital for elucidating its role in innate immunity, particularly in fish species like Ctenopharyngodon idella.

Purpose of the Study:

• To investigate the functional roles of different domains of Ctenopharyngodon idella MDA5 (CiMAD5) in innate immune signaling.
• To determine the impact of CiMAD5 and its variants on antiviral responses against grass carp reovirus (GCRV) and bacterial pathogen-associated molecular patterns (PAMPs) in Ctenopharyngodon idella kidney (CIK) cells.

Main Methods:

• Construction and transfection of six CiMAD5 mutants into CIK cells to generate stable cell lines.
• Stimulation of transfected cells with poly(I:C), GCRV, or bacterial PAMPs.
• Analysis of downstream gene expression, including CiIFN-I, CiIL-1β, and CiMx1, and assessment of GCRV replication and viral titers.

Main Results:

• Overexpression of CiMAD5 or its variants repressed GCRV replication in CIK cells.
• The CARD domain of CiMAD5 alone mediated signaling, while the Helicase or RD domain negatively regulated CARD function via intramolecular interaction.
• The RD domain enhanced CiIFN-I, CiIL-1β, and CiMx1 expression through intermolecular interaction, expanding the response spectrum of MDA5.

Conclusions:

• CiMAD5 plays a significant role in the innate immune response of C. idella against viral and bacterial infections.
• Specific domains of CiMAD5 exhibit distinct regulatory functions, with the CARD domain initiating signaling and the Helicase/RD domains modulating it.
• These findings enhance the understanding of MDA5 domain functions and their evolutionary significance in fish innate immunity.