Abstract
Gene expression profiles (GEPs) were obtained from marrow hematopoietic precursor cells (HPC)(CD34+ cells) from 30 myelodysplastic syndrome (MDS) patients: RARS 2, RA 15, RAEB 9, RAEBT 4; IPSS Low 11, Int-1 10, Int-2 5, High 4, and 6 Normal individuals. Fluorescently labeled cDNA was prepared from CD34+ cells (>90% purity), isolated by immunomagnetic column separation, after reverse transcription of high fidelity PCR-amplified poly(A) RNA (aRNA). The Cy-conjugated nucleotides for aRNA were hybridized to 40,000 gene chip microarrays obtained from the Stanford Functional Genomics Microarray Facility. aRNA from pooled normal CD34+ marrow cells was used as a Reference standard. High resolution scans were obtained to compile a dataset for each microarray, through files submitted to the Stanford Microarray Database. Dendrograms generated by unsupervised hierarchical gene clustering indicated major differences of GEP between Normal and MDS patients. Significance Analysis for Microarray (SAM) yielded 2327 genes significantly differentially expressed by MDS vs Normal: 2269 genes overexpressed, 58 underexpressed, with a false positive rate of ~10%. Prediction Analysis of Microarray (PAM) distinctly separated the MDS and Normal patients, requiring a minimum of 31 genes (which were also SAM significant). Class analysis by PAM correctly predicted 29 of the 30 to be MDS and 5 of the 6 to be Normal. Four disparate differential GEP regions in the dendrograms, comprising predominantly genes of differing functional categories provided signatures associated with differing MDS clinical subgroups. Nine of 10 patients with poor clinical outcomes were associated with a differing GEP signature than that which occurred in 14 of 20 patients with relatively good outcomes. Compared to the remainder of MDS patients, those with 5q- syndrome (n=5) had a differing GEP signature, with under-expression of 1018 genes, 11 of which were within the 5q31–32 CDS. Two of these genes (antioxidant protein1 and interferon regulatory factor1) have previously been proffered as candidate genes for this syndrome. Analysis of FACS-sorted highly purified marrow HPC subsets: CD34+38+ (late) and CD34+38- (early HPCs), indicated these ratios to be 4.3±2.1 (n=2) for MDS and 3.2±1.2 (n=12) for Normals. These findings suggest that the differing GEPs between the MDS and Normal CD34+ cells were not due to major differences in their proportions of CD38 cell subsets. SAM and PAM significant differential GEPs were noted between these cell subsets (also differing between MDS and Normal), indicating alteration of gene expression during differentiation. Wnt1 and β-catenin1 (genes involved in cell self-renewal) were over-expressed in both MDS CD38- and CD38+ cells compared to Normal. These data demonstrate: (1) molecular differences between MDS and Normal HPCs and within HPC subsets; (2) GEP signatures characterizing MDS patients with differing cytogenetic abnormalities (eg, 5q-) and clinical outcomes; (3) molecular criteria refining the prognostic categorization of MDS; and (4) gene expression data aiding characterization of the heterogeneous nature of this spectrum of diseases.
On triangular inequalities of correlation-based distances for gene expression profiles