Global Gene Expression Profile of Human Bone Marrow before and after Hydroxyurea Administration in Sickle Cell Anemia.

The levels of HbF in sickle cell disease (SCD) can be increased by pharmacological agents such as hydroxyurea (HU), which has been shown to reduce the frequency of pain crises, hospitalizations and acute chest events requiring blood transfusions in adults with SCD. However, there is some evidence to suggest that some SCD patients show benefits from HU treatment without increase in their HbF levels. Thus, the molecular mechanism by which HU increases HbF levels and improves the clinical evolution in SCD remains unclear. This study aims to provide the global gene profile of human bone marrow of a homozygous patient three months before beginning treatment and after the initial administration of HU and to investigate groups of differentially expressed genes that could be involved in the pathways by which HU improves the clinical evolution in SCD. Using the Serial Analysis of Gene Expression (SAGE) technique, two libraries, before HU administration (HbS profile) and after HU administration (HbSHU) were performed. A total of 47.192 and 46.697 tags were analyzed for the HbS and HbSHU profiles and represented 15.735 and 15.901 distinct tags, respectively. Among these, 4.151 and 3.817 tags were no match tags that could represent new genes that remain to be identified. When both profiles were compared, 518 transcripts were determined to have statistically significant differential levels of expression (P value < 0.05). The functional annotation of transcripts, according to the Gene Ontology Consortium, showed that the categories of binding and structural molecule activity were up-regulated following HU treatment. For example, genes associated with nucleic acid binding such as Signal Transducer and Activator of Transcription 5 A, v-fos FBJ murine osteosarcoma viral oncogene homolog, Early Growth Response 1 and several ribosomal and zinc finger proteins were induced by HU treatment. Conversely, the transporter activity category was down regulated by HU treatment. Genes associated with oxygen transporter activity and other genes associated with ion binding, like S100 calcium binding protein A8 (calgranulin A) and transferrin were found to be down regulated by HU treatment. Taken together, these results strongly suggest that HU produces a significant change in the expression of bone marrow cells. Future studies of these described genes that are differentially expressed during HU treatment may contribute to further the understanding of the mechanism by which HbF acts in SCD and improves the clinical evolution of the disease. The description of new genes involved in these pathways may also represent a potential tool to identify new targets for the therapy of SCD.