Abstract 2470: Adhesion-mediated dysfunctions in myelodysplastic syndromes microenvironment

Objectives: The recent evidences demonstrate that in myelodysplastic syndromes (MDS) a particular role is played by stromal microenvironment dysfunctions, which mediate the direct contact with hematopoietic precursor cells (HPC). The aims of our study were to assess the putative growth deficiencies of mesenchymal stromal cells (MSC) selected from MDS individuals, with regard to their ability to generate a microenvironment suitable to HPC development. Then, we intended to decode the focal adhesion (FA) signalling pathways and to understand whether adhesion-mediated processes contribute to transduction of intrinsic proliferative signals, as well as their impact on HPC-to-MSC interactions. Methods: To this end, we imagined a selection procedure using MSC specific markers expression (STRO-1 and CD73), we performed their phenotypic evaluation, and we conducted the functional assays on MSC and HPC selected from MDS patients vs. healthy volunteers. Finally, we have used the immunofluorescence microscopy to characterize the FA proteins (paxillin and focal adhesion kinase [FAK]), and of their regulators, p130CAS and HSP90. Results: The MSC production in STRO-1+ and CD73+ cell cultures from refractory cytopenia (RC) marrows was deficient, and, in addition, the clonogenic ability of these fractions was strongly diminished. The relative proliferation in MSC cultures from RC is the result of a continuous division process occurring at a low rate and lacking the ability to generate the normal functional progenitors required to form colonies. By contrast, in refractory anemia with excess of blasts (RAEB) settings, the proliferation rate is moderately improved due to the reduced doubling time of STRO-1 cells. However, this was not accompanied, at the end point, by complete functional maturity as reflected in the CFU-F number. Likewise, we have to point out the diminution of CFU-F capacity of CD73+ fractions in MDS that directly correlates with the CD44 mitigate on their surface. In addition, the doubling time of MSC from MDS inversely correlate with their expression for CD49e (Δ5-integrin). The proliferation differences occur in MDS cultures compared to normal settings can be attributed equally to the qualitative defects of FA proteins (FAK, and paxillin). The MSC from RAEB cultures highlight a strong complexation of FA proteins to HSP90 in nuclear area, which support a proliferative behaviour of these cells. Moreover, this high colocalisation to HSP90 indicates the cessation of proteasome-mediated recycling of these proteins. Furthermore, the preliminary results indicate the fact that the clonogenic potential of HPC is controlled by adhesion mechanisms dependent on stroma, and FAK is one of the molecules involved in this process. Conclusions: These data prove that MSC selected from MDS patients are intrinsically pathological and they could influence HSC behaviour by their direct interactions via FA proteins signalling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2470. doi:1538-7445.AM2012-2470