Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk.

Authors: WITKOP, ERIN - University Of Rhode Island; WIKFORS, GARY - National Oceanic & Atmospheric Administration (NOAA); Proestou, Dina; Markey Lundgren, Kathryn; Sullivan, Mary; GOMEZ-CHIARRI - University Of Rhode Island

Submitted to: Developmental and Comparative Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2022
Publication Date: 1/5/2022
Citation: Witkop, E., Wikfors, G.H., Proestou, D.A., Markey Lundgren, K.R., Sullivan, M.E., Gomez-Chiarri 2022. Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk. Developmental and Comparative Immunology. https://doi.org/10.1016/j.dci.2022.104339.
DOI: https://doi.org/10.1016/j.dci.2022.104339

Interpretive Summary: Through a combination of phenotypic assays, treatment with chemical inhibitors of apoptosis pathway proteins, and dual transcriptomic analysis of C. virginica and P. marinus, we conclude that hemocyte apoptosis in C. virginica is IAP-dependent, P. marinus apoptosis suppression involves caspase-independent apoptosis pathways downstream of mitochondrial permeabilization. These are novel findings that highlight the need for future work to determine the functions of members of the expanded and diverse IAP gene family. This research also indicates that the mechanism of P. marinus apoptosis suppression in hemocytes involves oxidation-reduction processes and modulation of TNFR and NF-kB pathways. Synthesis of the phenotype and gene expression evidence presented here, combined with knowledge from previous research, suggests a new, hypothetical model for mechanisms of apoptosis suppression in eastern oyster hemocytes following P. marinus intracellular infection. Overall, this study informs future research of P. marinus apoptosis suppression mechanisms in the eastern oyster, advancing our general understanding of apoptosis in invertebrate host-parasite interactions.

Technical Abstract: The intracellular parasite Perkinsus marinus causes Dermo disease in eastern oysters, Crassostrea virginica, and can suppress apoptosis of infected hemocytes using poorly understood mechanisms. This study challenged hemocytes with P. marinus for 1hr in the presence or absence of caspase inhibitor Z-VAD-FMK or Inhibitor of Apoptosis protein (IAP) inhibitor GDC-0152. Hemocyte exposure to P. marinus significantly reduced granulocyte apoptosis and pre-incubation with Z-VAD-FMK did not affect P. marinus-induced apoptosis suppression. Hemocyte pre-incubation with GDC-0152 prior to P. marinus challenge further reduced apoptosis of granulocytes with engulfed parasite, but not mitochondrial permeabilization. This suggests P. marinus-induced apoptosis suppression is caspase-independent, affects an IAP-involved pathway, and occurs downstream of mitochondrial permeabilization. P. marinus challenge stimulated hemocyte differential expression of oxidation-reduction, TNFR and NF-kB pathways. WGCNA analysis of P. marinus expression in response to hemocyte exposure revealed correlated protease, kinase and hydrolase expression that could contribute to P. marinus-induced apoptosis suppression.