Abstract
Thymocyte and T cell trafficking relies on signals initiated by G-protein coupled receptors. To address the importance of the G-proteins Gαi2 and Gαi3 in thymocyte and T cell function, we developed several mouse models. Gαi2 deficiency in hematopoietic progenitors led to a small thymus, a double negative (DN)1/DN2 thymocyte transition block, and an accumulation of mature single positive (SP) thymocytes. Loss at the double positive (DP) stage of thymocyte development caused an increase in mature cells within the thymus. In both models an abnormal distribution of memory and naïve CD4 T cells occurred, and peripheral CD4 and CD8 T cells had reduced chemoattractant responses. The loss of Gαi3 had no discernable impact, however the lack of both G-proteins commencing at the DP stage caused a severe T cell phenotype. These mice lacked a thymic medullary region, exhibited thymocyte retention, had a peripheral T cell deficiency, and lacked T cell chemoattractant responses. Yet a noteworthy population of CD4+PD-1+CXCR5+/− cells resided in the spleen of these mice likely due to a loss of regulatory T cell function. Our results delineate a role for Gαi2 in early thymocyte development and for Gαi2/3 in multiple aspects of T cell biology.
Highlights
In thymocytes and peripheral T cells the major functional role ascribed to Gi heterotrimeric G-proteins is to link chemoattractant receptors to downstream effectors that mediate directed cell migration[1]
Generation of mouse models to assess the impact of the loss of Gαi proteins on thymocyte development
To assess early thymocyte development, we examined the expression of CD44 and CD25 on double negative (DN) thymocytes, which allows the separation of DN thymocytes into 4 consecutive developmental stages termed DN1-DN424
Summary
In thymocytes and peripheral T cells the major functional role ascribed to Gi heterotrimeric G-proteins is to link chemoattractant receptors to downstream effectors that mediate directed cell migration[1]. In Gnai2−/− colitis prone mice, regulatory T cells did not normally inhibit effector memory CD4 T cells[23] While intriguing these studies are complicated by variations in mouse genetic backgrounds, and that thymic T cells development occurs in a globally Gαi[2] deficient animal or a Gnai2−/− bone marrow reconstituted wild type animal. To better understand the consequences of loss of Gαi proteins in T cells we have developed several different mouse models to assess the impact of the loss of Gαi[2] and Gαi[3] on T cell development, trafficking, and function These studies confirmed the important of Gαi[2] in T cell development and Gαi[2] and Gαi[3] in both thymocyte and peripheral T cell chemotaxis. They support a role for Gαi[2] in maintaining naïve T cells and reveal an unexpected phenotype in the double deficient peripheral T cells
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