Reduced Levels of mTOR and TGF- β Signaling Pathway-Associated Proteins in Patients with High Risk MDSsamia AL-Shouli. , Pilar Perezabellan, Frederic Toulza. Shahram Kordasti, Ghulam Mufti

Background:

T cell mediated immune dysregulation is an important feature of MDS. The expansion of regulatory T cells (Tregs) is one of the important factors in the progression of intermediate/high risk myelodysplastic syndrome (MDS) to acute myeloid leukemia. However, the exact mechanism for the expansion of Tregs in MDS is not known. Intracellular complements (particularly C3a and C5a) play a crucial role in the polarization of CD4+ T cells toward regulatory or effector phenotypes through Transforming growth factor-beta (TGF-β) pathway (C5aR2 mediated) or Mammalian Target of Rapamycin (mTOR)(C5aR mediated) respectively. The aim of this study was to investigate the potential role of mTOR and Akt as important proteins in complement related polarization of CD4+ T cells toward pro-inflammatory T helper cells in MDS. We have also studied the TGF-β signaling pathway related proteins, which are crucial for the expansion of Tregs. We investigated the level of TGF- β related proteins (phosphorylated (p) SMADs), as well as mTORc and Akt (Ser473) in high risk MDS and healthy donors (HD) before and after stimulation with CD3 and CD46 as a complement related co-stimulatory molecule.

Methods:

Peripheral blood mononuclear cell (PBMCs) from healthy controls and high-risk MDS patients were used for this study. Anti-CD3 (2.0 µg/mL), anti-CD28 (3.0 µg/mL) and/or anti-CD46 (2.0 µg/mL) antibodies were used to stimulate cells. The total protein was extracted by Bicinchoninic Acid (BCA) assay and quantified by nano-drop. The MILLIPLEX MAP Human TGF-β Signaling Magnetic Bead Panel 6-plex was used to detect the signaling changes in cell lysates using the Luminex® system following the manufacturer's instructions. Data were analysed using Microsoft Excel and expressed in means and standards deviation. The students T-test were used to assess the difference in means between groups.

Results:

TGF-β signaling pathway proteins pSMAD2, pSMAD3 and pSMAD4 as well as mTORc were evaluated. Unstimulated PBMCs from high-risk MDS patients showed a significantly lower level of m-TOR (p=0.01), pSMAD2 (p=0.01), pSMAD3 (p=0.02) and pSMAD4 (p=0.044) as compared to healthy donors. Following stimulation with anti-CD3±CD46 for 24 hours, there was no significant increase in protein levels of mTORc or Akt. However, in high-risk MDS patients the level of pSMAD2 (p=0.02) and pSMAD4 (p=0.006) remain significantly lower than healthy donors after 24 hours of stimulation with anti-CD3 and CD46.

An aliquot of cells were used for flowcytometry following stimulation. Interestingly Tregs phenotype CD4+CD25^highCD127^lowexpressed higher level of intracellular C5aR2 in MDS (n=5) compared to HD (n=5).

Conclusion:

mTORc protein level in MDS is reduced and does not change in response to complement receptor stimulation neither does the level of Akt. This may prevent T cells to polarize toward pro-inflammatory T cells (Th1 or Th17) therefore avert an effective immune-surveillance against malignant clone. Lack of response to complement related co-stimulation and increase in C5aR2 expression suggest a potential mechanism for Treg expansion in MDS. These findings may lead to identification of new therapeutic targets in MDS, although need further studies on larger cohort of patients.