Background: A growing body of evidence recognizes the balance between graft-reactive effector T cells and graft-protective regulatory T cells (Tregs) as the ultimate determinant of long-term allograft survival. We have shown that PI3K/mTOR signaling regulates the metabolic switch that controls the balance between effector and regulatory T cell activities. Recent data has emerged in support of the fundamental role of Wnt/β-catenin pathway in the functional fitness of Treg cells.

Objective: We investigated the effect of the Wnt/β-catenin signaling inhibitor FH535 in Treg cells and the potential interplay with the PI3K/mTOR pathway.

Methods: Sorted CD25⁺ Treg cells were placed in culture with different doses of FH535, Rapamycin, or a combination of both drugs. Multi-parametric FACS analyses were used to monitor the expansion rates, viability, phenotype, mitochondrial function and integrity, and suppressor function of the cells. Cellular bioenergetic parameters, including mitochondrial oxidative phosphorylation (OXPHOS) and glycolytic rates, were assessed on an extracellular flux analyzer.

Results: Addition of FH535 to the Treg cell culture induced a rapid enlargement of Treg cell size associated with a temporary fast expansion rate and reduced suppressor function. Following an early short period of over-activation, the presence of FH535 promoted a subsequent increase in cell death. These changes were linked to a dysregulation in mitochondrial function, with increased mitochondrial membrane potential and reduced oxygen consumption rates. Addition to the mTOR inhibitor Rapamycin protects against the deleterious effects of FH535. In fact, the combination of FH535 and Rapamycin yielded enhancing effects in Treg cell expansion and suppressor activity when compared to Rapamycin alone.

Conclusions: These results are consistent with a model by which the mTOR pathway plays a necessary role in the damaging effects induced by the Wnt/β-catenin inhibitor FH535, while the FH535-promoted mTOR-independent effects contribute to enhance the expansion rates and suppressor activity of Treg cells.

CITATION INFORMATION: Marti F., Turcios L., Mohamed A., Mitov M., Butterfield D., Gedaly R. Contribution of mTOR Signaling to the β-Catenin Pathway in Regulatory T Cells Am J Transplant. 2017;17 (suppl 3).

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