Regulation Of AKT On T Follicular Helper Cells

Follicular helper T cells?Tfh?,one subset of effector T cells,are developed from the na?ve T cells after they are primed by APC cells.Tfh cells are different from the other effector T cells,they play important roles in releasing interleukins to interact with B cells,help the formation of germinal center,and promote the maturation of plasma cells and the production of antibodies.The differentiation of Tfh is a multifactorial and multistage process,and regulated by several signaling pathways,including TCR signaling,ICOS signaling,and the others.AKT,also named as Protein kinase B?PKB?,is a serine threonine kinase.It has three isoforms,AKT1,AKT2,and AKT3,which share highly similar protein structure and kinase activity.However,the expression of three isoforms of AKT is tissue and cell specific,and their functions are different.As an important molecular signaling transduction,AKT signaling plays a critical role in regulating cell survival,cell cycle and proliferation,cell migration and the tumor formation.In previous studies,some downstream molecules of AKT pathway had been reported involved in the Tfh development,such as the transcription factor FOXO1,the mTORC signaling and others.These findings suggest that AKT and its signaling pathways might regulate the Tfh development.Here,we hypothesized that AKT is required for the development and function of Tfh cells.Therefore,in this study,we intend to investigate whether Tfh cells would express AKT isoforms,whether these isoforms would affect the development of Tfh cells,and which concrete signaling pathways would mediate AKT regulation on the Tfh cell development and function?In this study,using the sorted Tfh cells in the flu infection mouse model,we found that Tfh cells expressed three isoforms of Akt?Akt1,Akt2,and Akt3?,but the expression of AKT3 was least.The phosphorylation levels of AKT1 and AKT2 were increased with Tfh differentiation,indicating that AKT1 and AKT2 signaling are required for Tfh differentiation.Next,we approached the CD4^creAkt1^f/f/f and Akt2^-/-mice to study the role of AKT in regulating T cell homeostasis.We found that deletion of Akt1 in CD4⁺T cells did not impair T cell development in thymus and peripheral T cell homeostasis.Using the bone marrow chimera model,we confirmed the deletion of Akt2 lead to the decreased expression of CD44.We used the PR8-infected and OT?-OVA immunized mouse models to study whether AKT1 deficiency impaired the Tfh development.We found that the percentage of Tfh cells was significantly decreased in both models,suggesting that AKT1 positively regulated Tfh cells.Meanwhile,we found that deletion of Akt2 reduced Tfh cells in OT?-OVA model,indicating that AKT2 also positively regulate Tfh.Furthermore,when we knockout both Akt1 and Akt2,Tfh cells almost disappeared.Mechanistically,Akt1 or Akt2 deletion did not affect Tfh signature molecules,such as Bcl-6;however,under TCR stimulation,deletion of Akt1 decreased the phosphorylation of p65 in NF-?B signaling pathway,and the phosphorylation of 4EBP.The results suggested that AKT has a role in interfering with Tfh cell metabolism.Interestingly,we found that impaired Tfh cells could be rescued in CD4^creAkt1^f/f/f and Akt2^-/-mice after the second time of OT?-OVA immunization.In summary,we found that AKT1 and AKT2 both positively regulate Tfh development,and AKT1 and AKT2 have synergistic regulation of Tfh cells.Deletion both Akt1 and Akt2,Tfh cells cannot be differentiated and developed normally.This work suggests that AKT subtypes have different regulatory mechanisms for Tfh development.Therefore,further improvement of the signaling network of Tfh development through AKT subtypes analysis will help us to clarify the molecular mechanisms of Tfh development.