Improving the understanding of Shwachman-Diamond Syndrome

Shwachman-Diamond syndrome (SDS) is a rare autosomal recessive disorder with an incidence of 1 in 50.000 births. In 2001, the genetic defect of SDS was mapped to the centromeric region of chromosome 7 and in 2003 the defect was narrowed down to a single gene, which was named the Shwachman-Bodian-Diamond Syndrome (SBDS) gene. The mutations in the SBDS gene were identified in 90% of patients. Pancreatic exocrine insufficiency, bone marrow dysfunction with peripheral blood cytopenias, skeletal abnormalities, short stature and immune dysfunction characterize the disorder. Neutropenia plays a crucial role in the occurrence of recurrent and severe infectious complications representing one of the major causes of death in SDS patients. The aim of our study is to better comprehend the marrow dysfunction occurring in SDS patients, by analysing the functional properties of bone marrow (BM)-derived mesenchymal stem cells (MSCs). BM cells obtained from patients and healthy donors (HDs) were plated in sterile tissue culture flasks. At the third passage of the culture, cells were tested for the expression of specific surface markers, their ability to differentiate into mesengenic lineages, their capability to abrogate T cell proliferation and their ability to prevent neutrophil apoptosis. MSCs derived from SDS patients (SDS-MSCs) displayed typical fibroblastoid morphology; they were consistently devoid of contaminating hematopoietic cells, being negative for CD34, CD45, HLA-DR, CD11b, CD19, and CD14, but expressed common MSC markers including CD90, CD73, CD105 and HLA-ABC. Similarly to MSCs obtained from healthy donors (HD-MSCs), these cells were able to differentiate into adipocytes, osteoblasts and chondrocytes. In addition, SDS-MSCs drastically decreased the mitogen-induced lymphocyte proliferation, in a dose dependent manner. We also cultured neutrophils obtained from HD in presence or absence of MSCs at different time points. We demonstrated that SDS-MSCs were comparable to HD-MSCs in supporting the viability of neutrophils. More importantly, SDS-MSC were able to produce high amount of IL-6, a crucial cytokine involved in the protection of neutrophils from apoptosis. In addition, a genome wide gene expression analysis was carried out using HG-U133 Plus 2.0 Arrays. Results showed a SDS-MSCs specific profile, significantly different from HD-MSCs. All the genes, differentially expressed in mesenchymal cells obtained from Shwachman patients, are involved in the embryogenesis and in the development of different organs. In conclusion, we successfully isolated and characterized MSCs from 27 SDS patients. Further studies are needed to better comprehend the functional and molecular features of SDS-MSCs, which are potentially involved in the hematological abnormalities typical of SDS patients.