Knockdown of Hspa9, a del(5q31.2) gene, results in a decrease in hematopoietic progenitors in mice

Abstract

IntroductionThe myelodysplastic syndromes (MDS) are a group of clonal hematopoietic disorders exhibiting ineffective hematopoiesis characterized by peripheral blood cytopenias. Whole chromosome 5 loss or interstitial deletions spanning 1 copy of 5q31.2 are among the most common abnormalities detected by conventional cytogenetic analysis in de novo (6%-20% of patients) and therapyrelated MDS (up to 40% of patients). [1][2][3] The commonly deleted segment in 5q31.2 has been mapped, 4,5 and mutational analysis of the residual nondeleted allele has not identified a classic tumorsuppressor gene. [4][5][6] Therefore, we and others hypothesize that haploinsufficiency of a gene(s) in 5q31.2, not the loss of both alleles, may be a critical initiating event in MDS pathogenesis and may contribute to acute myeloid leukemia (AML) transformation when combined with additional cooperating mutations.The minimally deleted region on chromosome 5q31.2 is distinct from the minimally deleted region on 5q33.1, 7 which is associated with the 5q minus syndrome and carries a lower risk of progressing to AML compared with 5q31.2 deletions. Haploinsufficiency of the RPS14 gene, located in the 5q33.1 region, causes abnormal erythroid differentiation and accelerated apoptosis both in vitro and in a murine knockout model, supporting its role in the pathogenesis of the 5q minus syndrome. 8,9 Deletions on the long arm of chromosome 5 typically encompass both 5q31.2 and 5q33.1 minimally deleted regions, suggesting that haploinsufficiency of multiple genes may be necessary to recapitulate the full spectrum of abnormalities observed in patients with MDS. Haploinsufficiency of Egr1 (located on 5q31.2), Apc (located proximal to the 5q31.2 minimally deleted region), or Npm (located distal to the 5q31.2 minimally deleted region) are associated with abnormal hematopoiesis in mice, further supporting the possibility that the deletion of multiple 5q genes may cooperate in MDS initiation or progression. [10][11][12][13][14] We hypothesized that haploinsufficiency of HSPA9, a gene located on the 5q31.2 interval, may also influence hematopoiesis in MDS patients based on several observations. HSPA9 mRNA levels are reduced by 50% in CD34 ϩ -purified hematopoietic progenitors isolated from patients with del(5q) MDS compared with MDS patients without del(5q) and normal control CD34 ϩ cells, consistent with haploinsufficient expression levels in del(5q) patients. 6 An N-ethyl-N-nitrosourea mutagenesis screen in zebrafish identified that a bi-allelic mutation in Hspa9 resulted in anemia, dysplastic immature erythroblasts, accelerated apoptosis, and leukopenia. 15 Heterozygous Hspa9 mutant fish also displayed accelerated apoptosis in erythroid cells consistent with ineffective hematopoiesis. 15 In mice, Hspa9 is a gene in the 5q31.2 interval that is a common retroviral insertional mutagenesis site associated with development of AML (see the Mouse Retrovirus Tagged Cancer Gene Database at: http://rtcgd.ncifcrf.gov/). 16 Finally, HSPA9 was identified as a mediator o...

Mortalin and DJ-1 coordinately regulate hematopoietic stem cell function through the control of oxidative stress

“…11,12 It has been shown that mortalin KD impairs erythroid differentiation and reduces the number of colony-forming progenitor cells in the murine BM. 38 However, the precise role of mortalin in HSC maintenance has yet to be clarified. Here, we examined mortalin KD and mortalin-OE HSCs, and showed that mortalin is critical for the preservation of HSC faculties under both ex vivo culture and in vivo transplantation conditions.…”

Recent developments in myelodysplastic syndromes

“…55 Subsequently, several more 5q-CDR-encoded genes including microRNAs miR145 and miR146a have been implicated in the pathogenesis and clinical presentation of MDS. [56][57][58][59] Unfortunately, investigation of genes in the MDS-associated CDRs of chromosomes 20q and 7q have been less conclusive, and the pathogenic mechanisms associated with these and other recurring chromosomal abnormalities remain unknown.…”

Genetics of Myelodysplastic Syndromes: New Insights

“…16 Reduced expression of HSPA9 in primary human CD34 ϩ cells results in delayed erythroid maturation and increased apoptosis in vitro and decreased hematopoietic progenitors in mice. 17 Npm ϩ/Ϫ mice develop erythroid macrocytosis, megakaryocytic dysplasia, and are predisposed to myeloid malignancies (AML and MPNs) at 10-24 months of age. 18 Finally, Apc ϩ/Ϫ mice have alterations in their stem cell compartment with concomitant changes in cell cycle and apoptosis which may be relevant for MDS.…”