Defects in Skin γδ T Cell Function Contribute to Delayed Wound Repair in Rapamycin-Treated Mice

Abstract

Disruptions in the normal program of tissue repair can result in poor wound healing, which perturbs the integrity of barrier tissues such as the skin. Such defects in wound repair occur in transplant recipients treated with the immunosuppressant drug rapamycin (sirolimus). Intraepithelial lymphocytes, such as γδT cells in the skin, mediate tissue repair through the production of cytokines and growth factors. The capacity of skin-resident T cells to function during rapamycin treatment was analyzed in a mouse model of wound repair. Rapamycin treatment renders skin γδ T cells unable to proliferate, migrate and produce normal levels of growth factors. The observed impairment of skin γδ T cell function is directly related to the inhibitory action of rapamycin on mammalian target of rapamycin (mTOR). Skin γδ T cells treated with rapamycin are refractory to IL-2 stimulation and attempt to survive in the absence of cytokine and growth factor signaling by undergoing autophagy. Normal wound closure can be restored in rapamycin-treated mice by addition of the skin γδ T cell-produced factor, insulin-like growth factor-1. These studies not only reveal that mTOR is a master regulator of γδ T cell function but also provide a novel mechanism for the increased susceptibility to nonhealing wounds that occurs during rapamycin administration. This is an author-produced version of a manuscript accepted for publication in The Journal of Immunology (The JI). The American Association of Immunologists, Inc. (AAI), publisher of The JI, holds the copyright to this manuscript. This version of the manuscript has not yet been copyedited or subjected to editorial proofreading by The JI; hence, it may differ from the final version published in The JI (online and in print). AAI (The JI) is not liable for errors or omissions in this author-produced version of the manuscript or in any version derived from it by the U.S. National Institutes of Health or any other third party. The final, citable version of record can be found at www.jimmunol.org.

T cell dependence on mTOR signaling

“…Skin γδ T cells with impaired mTOR signaling instead undergo increased levels of autophagy. 11 From this evidence we conclude that mTOR-mediated signaling is essential for a variety of activation-induced processes in skin γδ T cells, but not necessarily essential for cell survival.…”

“…Prolonged systemic rapamycin treatment of mice over a two-week period did not affect the number of γδ T cells in the murine epidermis, 11 suggesting extending numerous processes that interdigitate between neighboring keratinocytes. This has been proposed as a mechanism to monitor the epidermal barrier and recognize stressed or damaged epithelial cells.…”

“…We have recently demonstrated that the γδ T cell population residing in the murine skin requires mTOR signaling for activation-induced proliferation, cytokine production and migration. 11 Proliferation in response to TCR or mitogen activation was arrested in the transition from G 0 to G 1 upon rapamycin administration. Addition of factors known to induce skin γδ T cell proliferation, such as the cytokine IL-2 or growth factor IGF-1, 23 did not restore proliferation in a cell line or primary cells.…”

“…This phosphorylation is highly sensitive to prolonged treatment with rapamycin. 11 Clearly this T cell subset is highly sensitive to mTORC2 inhibition in the presence of rapamycin, but the extent of this sensitivity may differ between other T cell subsets. Differences in sensitivity to rapamycin have been observed between T cell subsets 12 but the role of mTORC2 signaling has not yet been addressed.…”

“…This may account for the ability of these cells to survive and persist in the murine skin after extended periods of rapamycin treatment. 11 mTOR inhibition in skin γδ T cells does not induce apoptosis, nor enhance activation-induced, starvation-induced or steroidinduced apoptosis (ref. 11 and unpublished data).…”