Ex vivo modulation of the Foxo1 phosphorylation state does not lead to dysfunction of T regulatory cells.

Kristen Kelley Penberthy,Kodi Ravichandran,Monica Weaver Buckley,Sanja Arandjelovic,Venuprasad K Poojary

doi:10.1371/journal.pone.0173386

Kristen Kelley Penberthy, Kodi Ravichandran + Show 3 more

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https://doi.org/10.1371/journal.pone.0173386

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Journal: PloS one	Publication Date: Mar 7, 2017
Citations: 5	License type: CC BY 4.0

Affiliation: Carter Center, University of Virginia

Abstract

Peripheral regulatory CD4+ T cells (Treg cells) prevent maladaptive inflammatory responses to innocuous foreign antigens. Treg cell dysfunction has been linked to many inflammatory diseases, including allergic airway inflammation. Glucocorticoids that are used to treat allergic airway inflammation and asthma are thought to work in part by promoting Treg cell differentiation; patients who are refractory to these drugs have defective induction of anti-inflammatory Treg cells. Previous observations suggest that Treg cells deficient in the transcription factor FoxO1 are pro-inflammatory, and that FoxO1 activity is regulated by its phosphorylation status and nuclear localization. Here, we asked whether altering the phosphorylation state of FoxO1 through modulation of a regulatory phosphatase might affect Treg cell function. In a mouse model of house dust mite-induced allergic airway inflammation, we observed robust recruitment of Treg cells to the lungs and lymph nodes of diseased mice, without an apparent increase in the Treg cytokine interleukin-10 in the airways. Intriguingly, expression of PP2A, a serine/threonine phosphatase linked to the regulation of FoxO1 phosphorylation, was decreased in the mediastinal lymph nodes of HDM-treated mice, mirroring the decreased PP2A expression seen in peripheral blood monocytes of glucocorticoid-resistant asthmatic patients. When we asked whether modulation of PP2A activity alters Treg cell function via treatment with the PP2A inhibitor okadaic acid, we observed increased phosphorylation of FoxO1 and decreased nuclear localization. However, dysregulation of FoxO1 did not impair Treg cell differentiation ex vivo or cause Treg cells to adopt a pro-inflammatory phenotype. Moreover, inhibition of PP2A activity did not affect the suppressive function of Treg cells ex vivo. Collectively, these data suggest that modulation of the phosphorylation state of FoxO1 via PP2A inhibition does not modify Treg cell function ex vivo. Our data also highlight the caveat in using ex vivo assays of Treg cell differentiation and function, in that while these assays are useful, they may not fully recapitulate Treg cell phenotypes that are observed in vivo.

Highlights

Allergic airway inflammation is the result of maladaptive immune responses to generally innocuous foreign antigens or allergens [1,2,3]
Treg cells are a population of CD4+ T cells that are typically characterized by their expression of the transcription factor FoxP3 [12,13]
Okadaic acid treated Treg cells did not produce IL-17 nor did they demonstrate impaired suppression of CD4+ effector proliferation. These data suggest that ex vivo treatment of Treg cells with okadaic acid and the resultant modulation of PP2A activity and FoxO1 phosphorylation are not sufficient to modulate the functional activity of Treg cells. These findings suggest a caution for others attempting to utilize ex vivo assays to assesses the effects of altering PP2A activity / FoxO1 phosphorylation status in Treg cells

Summary

Introduction

Allergic airway inflammation is the result of maladaptive immune responses to generally innocuous foreign antigens or allergens [1,2,3]. One possible explanation for the development of this maladaptive inflammatory response is the functional insufficiency of the regulatory T cell (Treg) compartment [4,5,6,7,8]. Current evidences in the literature suggest that this functional insufficiency likely results from both decreased Treg cell numbers and Treg cell dysfunction [6,7,9,10,11]. In the context of allergic airway inflammation, Treg cells are thought to suppress airway inflammation to allergens by suppressing dendritic cell activation and by producing the anti-inflammatory cytokine interleukin-10 (IL-10) [14,15]. The hypothesis that asthmatic patients have a dysfunctional Treg cell compartment is supported by the finding that the airways of patients with allergic airway inflammation have decreased IL-10 [16,17]. Glucocorticoids, a well-established treatment for allergy, are thought to work in part by promoting Treg cell differentiation, thereby suppressing the inappropriate inflammatory response to allergens [18]

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