Down modulation of β≥-cystathionase in transplant tolerance controls dendritic cell activation and Th-1 type immune responses

Romain Vuillefroy de Silly^2,3, Flora Coulon^2,3, Nicolas Poirier^2,3, Véronique Ferchaud-Roucher¹, Gilles Blancho^2,3, Bernard Vanhove^2,3

¹INSERM UMR915; ²INSERM UMR643, ITUN; ³University of Nantes, Nantes University Hospital Center; Nantes, France

γ-cystathionase (CSE) is a rate-limiting enzyme of the trans-sulfuration
pathway which converts methionine and cystathionine into cysteine and H₂S.
T cells are deficient in CSE and cysteine import and therefore are
metabolically dependent on accessory cells for cysteine supply.   In the current
study, we demonstrated that immune tolerance induced by costimulation blockade
or immunosuppression after heart and kidney allotransplantation in the LEW.1W
to LEW.1A rat model is associated with a two to five fold repression of intragraft
CSE, as well as of several other enzymes of the trans-sulfuration pathway. Pharmacological
blockade of CSE with the irreversible inhibitor propargylglycine (PPG) delayed
heart allograft rejection (median survival of 26.5 days intead of 9 in
controls) and abrogated type IV hypersensitivity to keyhole limpet haemocyanin
(Th-1 response), but did not modify antibody responses (Th-2 response). The
dominant biological effect of CSE blockade was a repression of IL-12 p40
transcripts into the graft and in recipient dendritic cells (DCs).  In
vitro, human monocytes and DCs treated by PPG or by the reversible CSE
inhibitor, b-cyano alanine, as well as by siRNA specific for CSE, dose-dependently
and differentially regulated production of IL-12 cytokine. The effect was
independent of NFkB or H₂S production, but could be assigned to a
modulation of intracellular cysteine content. Our results identify CSE as a
novel factor that plays a critical role in IL-12 production by monocytes and
DCs by modulating intracellular cysteine levels. CSE is down-modulated in
transplant tolerance, presumably participating in the maintenance of the
tolerant state by controlling DCs activation, and by lowering cysteine supply
to alloreactive T cells.