Pediatric MDS is a very rare disease and

Pediatric MDS is a very rare disease and publications on the role of stroma in the ontogeny and maintenance of pediatric MDS are limited to a case report on aberrant hematopoietic support by MSC derived from an MDS patient with trisomy 8 (Narendran et al., 2004), a study using stroma testes of of 7 MDS patients (Borojevic et al., 2004), and a gene-expression analysis of the stromal compartment by the same research group (Roela et al., 2007). Nevertheless these scarce reports suggest an aberrant support of hematopoiesis associated with an altered gene expression profile of MSCs. In the present study we compared MSCs derived from children with RCC and RAEB(t)/MDS-AML to MSCs expanded from age-matched healthy controls. Biological characteristics, e.g., differentiation capacity and phenotype were analyzed. MSC function in vitro was evaluated by immunomodulatory and hematopoietic assays. In addition, genome wide gene-expression profiles were studied using Deep-SAGE sequencing.
Materials and methods
Results
Discussion The spectrum of pediatric MDS ranges from aplasia to myeloproliferative disease. The pathophysiology of the disease has been attributed to different cytogenetic abnormalities (Gohring et al., 2010). Previous studies in mice and in human adults have linked the interaction of hematopoietic progenitors and the micro-environment to the progression of disease in several hematopoietic disorders (Zhang et al., 2012; Schepers et al., 2013). In adult MDS specific alterations in the MSCs have been reported as summarized in Table S1. Data on pediatric MDS are limited (Table S2). In this study, we compared the MSC characteristics and function in children with different types of MDS with healthy controls. Differences were neither observed with respect to the differentiation capacity of MSCs, their immunomodulatory capacity using T-cell proliferation and monocyte differentiation to dendritic cells as read-out, nor regarding their impact on maintenance and differentiation of hematopoietic progenitor cells. In addition, cell viability in co-cultures was equally increased by both groups of MSCs, as assessed by trypan-blue staining (data not shown). However, evaluation of total mRNA expression profiles demonstrated gene expression differences between MSCs derived from pediatric MDS patients and controls. Cytogenetic abnormalities present in the hematopoietic cells could not be detected in the stromal compartment, and, therefore, this cannot explain the differential gene expression. The partial normalization of IL6 and DAPK1 expressions in MSCs after HSCT in these patients demonstrates that the expression differences can be reversed. Of note, using chimerism analysis, the presence of donor MSCs in the expanded cells has been excluded. Differential gene expression between pediatric MDS in general and healthy controls was most prominent for IL6. This gene has previously been reported to be over-expressed in adult MDS and in one child with MDS and a constitutional trisomy 8 (Zhao et al., 2012a; Narendran et al., 2004). In contrast, other studies in adults did not show differential IL6 expression between MDS patients and healthy controls (Flores-Figueroa et al., 2002, 2008; Zhao et al., 2012a; Klaus et al., 2010). IL6 has been described to increase myeloid differentiation via STAT3 activation and support multiple myeloma cell growth and survival (Minami et al., 1996; Zhang et al., 2010; Csaszar et al., 2013; Gunn et al., 2006). STAT3 up-regulation was not observed in this pediatric MDS cohort. In addition, IL-6 is one of the cytokines responsible for bone-remodeling in inflammatory and malignant diseases (Ara and Declerck, 2010; Dayer and Choy, 2010). Suppression of monocyte to dendritic cell differentiation is dependent on IL-6 (Melief et al., 2013). However, we did not observe a correlation between the degree of the suppressive effect of MSCs and the level of IL-6 expression, suggesting that IL-6 is not the sole factor hampering this differentiation.