[Ineffective erythropoiesis in myelodysplastic syndrome]

Ineffective hematopoiesis is one of the hallmarks of myelodysplastic syndrome (MDS). Recently, several signaling pathways responsible for inefficient erythropoiesis in MDS have been uncovered. The p53-S100a8/S100a9-TLR4 pathway is involved in ineffective erythropoiesis in 5q minus (5q-) syndrome. Somatic mutations target multiple components of the messenger RNA (mRNA) splicing machinery including Splicing Factor 3 Subunit b1 (SF3b1) and Serine Arginine Rich Splicing Factor 2 (SRSF2) in patients with MDS. SF3b1 is the most frequently mutated spliceosome component in MDS and is mutated approximately 85% of the time in MDS with ring sideroblasts (MDS-RS). SF3b1 mutations are not simple loss-of-function or inactivating mutations but result in a change of function and cause aberrant splicing of genes that may be involved in the pathogenesis of MDS-RS. Recurrent mutations are also found in epigenetic regulator genes in MDS, including polycomb repressive complex 2 (PRC2) genes. The loss of enhancer of zeste homolog 2 (EZH2), an enzymatic component of PRC2 in mice, markedly accelerates the development of MDS in combination with representative driver mutations. The loss of EZH2 causes impaired erythropoiesis and increases ineffective hematopoiesis. Of interest, EZH2 is one of the targets of SRSF2 mutants in MDS, and mis-spliced EZH2 mRNA undergoes nonsense-mediated decay (NMD) -dependent degradation. All these data suggest that EZH2 insufficiency causes ineffective erythropoiesis.