Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity

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Abstract

While the canonical function of IRE1α is to detect misfolded proteins and activate the unfolded protein response (UPR) to maintain cellular homeostasis, microbial pathogens can also activate IRE1α, which modulates innate immunity and infection outcomes. However, how infection activates IRE1α and its associated inflammatory functions have not been fully elucidated. Recognition of microbe-associated molecular patterns can activate IRE1α, but it is unclear whether this depends on protein misfolding. Here, we report that a common and deadly fungal pathogen, Candida albicans , activates macrophage IRE1α through C-type lectin receptor signaling, reinforcing a role for IRE1α as a central regulator of host responses to infection by a broad range of pathogens. This activation did not depend on protein misfolding in response to C. albicans infection. Moreover, lipopolysaccharide treatment was also able to activate IRE1α prior to protein misfolding, suggesting that pathogen-mediated activation of IRE1α occurs through non-canonical mechanisms. During C. albicans infection, we observed that IRE1α activity promotes phagolysosomal fusion that supports the fungicidal activity of macrophages. Consequently, macrophages lacking IRE1α activity displayed inefficient phagosome maturation, enabling C. albicans to lyse the phagosome, evade fungal killing, and drive aberrant inflammatory cytokine production. Mechanistically, we show that IRE1α activity supports phagosomal calcium flux after phagocytosis of C. albicans , which is crucial for phagosome maturation. Importantly, deletion of IRE1α activity decreased the fungicidal activity of phagocytes in vivo during systemic C. albicans infection. Together, these data provide mechanistic insight for the non-canonical activation of IRE1α during infection, and reveal central roles for IRE1α in macrophage antifungal responses.

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  1. Note: This response was posted by the corresponding author to Review Commons. The content has not been altered except for formatting.

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    Reply to the reviewers

    Manuscript number:

    RC-2024-02569

    Corresponding author(s): Mary O'Riordan, Teresa O'Meara

    1. General Statements

    We thank the reviewers for their positive feedback, highlighting the significance and novelty of our work, especially regarding the novel functions of IRE1a in regulating phagosome biology during infection. We also appreciate some overarching themes that were focused on by multiple reviewers, including the role of XBP1S protein and RIDD activity, which we have addressed here. We have also added additional data, made adjustments to data presentation, and added clarifying language to address concerns from Reviewer 3. We appreciate these …

  2. Note: This preprint has been reviewed by subject experts for Review Commons. Content has not been altered except for formatting.

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    Referee #3

    Evidence, reproducibility and clarity

    Reviewer comments for "Non-canonical activation of IRE1a by Candida albicans infection promotes macrophage phagosomal calcium flux to enhance fungal killing"

    This paper describes a role for IRE1 in controlling Candida albicans (Ca) infection in macrophages. The authors show that Ca infection slightly induces IRE1 activity as monitored by XBP1 splicing, however this does not result in XBP1 protein expression, nor in IRE1-dependent target gene expression. The authors propose that IRE1 controls phagosomal maturation, as measured by defects in LAMP1 recruitment to Ca containing phagosomes. This would be due to a defect in calcium flux …

  3. Note: This preprint has been reviewed by subject experts for Review Commons. Content has not been altered except for formatting.

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    Referee #2

    Evidence, reproducibility and clarity

    This an interesting report in a widely explored area. This makes it necessary to pigeonhole the new data provided by the study. The paper addresses two issues encompassing a scope distinct from studies focusing on the cytokine-signature and the role of sXbp1. This research singles out fungal killing and Ire1α versus sXbp1 function. More precisely, the reduction of cytokine expression in Ire1fl/fl LysMCre as compared to WT discloses an opposing function of Ire1α and its target sXbp1 in cytokine expression that requires mechanistic explanation.

    1. A point that should be addressed with more detail is the correlation of fungal killing with …
  4. Note: This preprint has been reviewed by subject experts for Review Commons. Content has not been altered except for formatting.

    Learn more at Review Commons


    Referee #1

    Evidence, reproducibility and clarity

    The authors show that in macrophages, IRE1 activation (independent of improperly folded proteins) is essential to promote fungicidal activity towards candida albicans (CA) in vitro and in vivo by ensuring phagosome maturation through the preservation of calcium fluxes

    Major comments

    1. The demonstration of protein misfolding independent IRE1 activation should also be demonstrated using molecules such as TUDCA or 4PBA that should be innocuous regarding the splicing of XBP1s. It would also be interesting to evaluate the activation of the other arms of the UPR in particular through the phosphorylation of eIF2a, expression of ATF4 and …