Description

Briefing Document: Targeting the Mosquito Prefoldin–Chaperonin Complex to Block Plasmodium Transmission

Citation: Dong, Y., Kang, S., Sandiford, S.L. et al. Targeting the mosquito prefoldin–chaperonin complex blocks Plasmodium transmission. Nat Microbiol (2025). https://doi.org/10.1038/s41564-025-01947-3

Date: Received - 22 November 2024 | Accepted - 27 January 2025 | Published - 06 March 2025

Overview:

This study investigates the role of the conserved Anopheles mosquito prefoldin (PFDN)–chaperonin (CCT/TRiC) system as a potential target for blocking the transmission of multiple Plasmodium species. The researchers demonstrate that disrupting this protein folding complex in mosquitoes, either through gene silencing or antibody inhibition, significantly reduces Plasmodium infection intensity and prevalence. The mechanism of action involves compromising the integrity of the mosquito midgut, leading to immune activation and the disruption of the parasite's immune evasion strategies. The findings suggest that the PFDN–chaperonin complex, particularly the PFDN6 subunit, holds promise as a multispecies transmission-blocking vaccine (TBV) target.

Main Themes and Important Ideas/Facts:

• The Mosquito PFDN–Chaperonin Complex is Essential for Plasmodium Infection:
• The Plasmodium infection cycle in mosquitoes relies on various host factors in the midgut.
• The mosquito prefoldin complex is crucial for the proper folding of proteins and macromolecular complexes, including actin and tubulin, which are essential for cell division, motility, cytoskeletal stability, and signal transduction – all of which influence Plasmodium infection.
• Silencing any of the six PFDN subunits (Pfdn1-6) or the CCT4 subunit via RNA interference significantly reduced Plasmodium falciparum oocyst loads in the Anopheles gambiae midgut.
• "Silencing any prefoldin subunit or its CCT/TRiC partner via RNA interference reduces Plasmodium falciparum oocyst loads in the mosquito midgut..."
• Co-silencing of different PFDN subunits did not have an additive effect, confirming that the complex functions as a unit in supporting parasite development.
• Targeting PFDN6 with Antibodies Blocks Plasmodium Transmission:
• Co-feeding mosquitoes with a PFDN6-specific antibody along with P. falciparum gametocytes resulted in a potent suppression of parasite infection at both the oocyst and sporozoite stages.
• "Ingestion of purified anti-PFDN6 polyclonal antibody (IgG) resulted in a significant decrease in parasite loads (either at the oocyst or sporozoite stage) compared with control cohorts fed on rabbit anti-GFP antibody..."
• The level of inhibition achieved with anti-PFDN6 antibodies was comparable to that of leading TBV candidates like Pfs230 and Pfs25, as well as antibodies targeting mosquito proteins AgAPN1 and FREP1.
• Anti-PFDN6 antibody also effectively blocked P. falciparum transmission in Anopheles stephensi and Plasmodium vivax transmission in Anopheles dirus, indicating a broad-spectrum effect across different mosquito and parasite species.
• Active immunization of mice with recombinant PFDN6 protein resulted in antibodies that, when mosquitoes fed on the immunized, infected mice, significantly reduced Plasmodium berghei oocyst infection intensity and prevalence, supporting its potential as a TBV target.
• PFDN Supports Plasmodium Development After Ookinetes Invade the Midgut Epithelium:
• Antibody blocking assays showed no significant difference in ookinete numbers in the midgut lumen at 24 hours post-infection, but a significant decrease in oocyst loads was observed at 36 hours and 8 days.
• Injection of anti-PFDN6 antibody into the mosquito haemolymph also reduced oocyst numbers, suggesting an effect on the basal side of the midgut epithelium where oocysts develop.
• "These results indicate that PFDN6 host factor function is exerted upon ookinete egress and oocyst formation on the basal side of the epithelium beneath the basal lamina."
• PFDN6 distribution largely overlapped with actin in the midgut epithelium, but it did not co-localize directly with the parasites, suggesting an indirect role in parasite development.
• Disruption of PFDN Compromises Midgut Integrity and Triggers Anti-Plasmodium Immunity:
• Attempting to create a Pfdn6 knockout mosquito line resulted in pre-adult lethality, likely due to cytoskeletal and gut integrity issues.
• Co-immunoprecipitation assays identified interactions between PFDN6 and actin, tubulin, and several extracellular matrix proteins, supporting its role in maintaining cellular and matrix integrity.
• Silencing Pfdn6 or co-feeding with anti-PFDN6 antibodies led to a "leaky gut," characterized by increased permeability and bacterial leakage from the midgut lumen into the haemolymph.
• "Interfering with the PFDN–CCT/TriC chaperonin complex results in a cascade of events, including compromised gut integrity and disrupted extracellular matrix organization. The increased gut permeability leads to bacterial leakage and systemic infection, ultimately augmenting antiplasmodial defences..."
• Bacterial leakage triggered a stronger anti-Plasmodium immune response, with upregulation of key immune factors like Tep1, FBN9, and LRRD7.
• The leaky gut condition also shortened mosquito lifespan in the presence of natural microbiota.
• PFDN Facilitates Parasite Immune Evasion Through Laminin:
• PFDN appears to be involved in maintaining the laminin coating on ookinetes and early oocysts, a basal lamina component previously shown to be important for parasite development and immune evasion.
• Silencing laminin resulted in a significant decrease in oocyst numbers, similar to Pfdn6 silencing.
• In Pfdn6-silenced mosquitoes, the laminin coating on parasites was compromised, leading to increased co-localization with the anti-Plasmodium factor Tep1.
• Co-silencing of Pfdn6 and Tep1 negated the individual effects on parasite infection, suggesting that PFDN's host factor role involves limiting parasite accessibility to Tep1.
• "These processes also compromise the parasite’s laminin-based immune evasion mechanism, enabling the primed immune system to attack it effectively."
• PFDN as a Potential Transmission-Blocking Vaccine Target:
• The high conservation of PFDN6 across mosquito species and its role as a host factor for multiple Plasmodium species make it a promising TBV target.
• In silico analysis identified a potential unique B cell epitope on A. gambiae PFDN6 with low homology to human PFDN6, which could be explored to minimize cross-reactivity concerns.
• The authors suggest that a multivalent vaccine targeting several PFDN–CCT/TriC complex epitopes could be a strategy to mitigate potential selective pressure.
• Conditional genetic inactivation of the PFDN–CCT/TriC complex via gene-drive mechanisms is also proposed as a potential malaria control strategy.

Quotes Highlighting Key Findings:

• "Here we show that the PFDN–CCT/TriC (T-complex protein ring complex) chaperonin complex serves as a host factor system for multiple Plasmodium species in all tested Anopheles species."
• "In summary, we show here that the role of the PFDN–CCT/TriC chaperonin complex Plasmodium host factor is based on maintaining midgut epithelial and extracellular matrix and basal lamina integrity that (1) limits the leakage of midgut microbiota into the haemolymph, where it can prime anti-Plasmodium immunity; (...