The Role of Calreticulin in Normal Hematopoiesis and Neoplastic Hematopoiesis of Myeloproliferative Neoplasms

• Published in: Blood 2019-11, Vol.134 (Supplement_1), p.309-309
• Main Authors: Shide, Kotaro, Kameda, Takuro, Kamiunten, Ayako, Ozono, Yoshinori, Tahira, Yuki, Sekine, Masaaki, Ono, Masaya, Yokomizo, Takako, Kubota, Sho, Akizuki, Keiichi, Kubuki, Yoko, Hidaka, Tomonori, Sashida, Goro, Shimoda, Kazuya
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2019-130034

Mutations in the Calreticulin (CALR) gene were identified in cases of myeloproriferative neoplasms (MPNs), and various functions of the CALR mutant protein are being elucidated. On the other hand, few data are available on the role of CALR in the hematopoietic system. The knockout (KO) mice of Calr are impaired in expression of transcription factors necessary for cardiac development and are embryonic lethal. To clarify the role of CALR in normal hematopoiesis and MPN pathogenesis, we generated hematopoietic cell-specific Calr KO mice. Mice carrying floxed allele targeted exons 4-7 of Calr (Calrf/+ mice) and Calr heterozygous KO mice (Calr+/− mice) (Tokuhiro et al., Sci Rep 2015) were crossed with Mx1-Cre transgenic mice and obtained mice with three genotypes; Mx1-cre;Calr+/+, Mx1-cre;Calr+/−, and Mx1-cre;Calrf/−. Floxed alleles were then deleted by intraperitoneal injection with polyinosinic: polycytidilic acid. No differences were found in the peripheral blood (PB) leukocyte count, hemoglobin levels, or platelet count among the three genotypes of mice. The proportions of Mac1+ or Gr1+ myeloid lineage cells, B220+ B cells, and CD3+ T cells among the three groups were comparable. In the bone marrow (BM), cell pellet from Mx1-cre;Calrf/− mice appeared anemic and the proportion of CD71+/Ter119+ erythroid cells and the number of CFU-E were significantly lower in Mx1-cre;Calrf/− BM cells compared to the other two genotypes of BM cells. On the other hand, no difference was found in other mature cells such as myeloid, T, B, or CD41+ megakaryocytes (Mks) in BM. As for HSCs and progenitors, Mx1-cre;Calrf/− mice exhibited a higher proportion of MPP and GMP compared to the other two genotypes of mice. We found no difference in other progenitor compartments including long- and short-term HSCs among the three groups. In contrast to the minor effect on BM and PB cells, The spleen weight in Mx1-cre;Calrf/− mice was about 2-fold heavier than that in Mx1-cre;Calr+/+ mice. In spleens from Mx1-cre;Calrf/− mice, the border between the white and red pulp was obscured. Mks and maturing myeloid cells had markedly infiltrated into the red pulp. In FACS analysis, mature myeloid cells, erythroid cells, and Mks were significantly increased in spleens from Mx1-cre;Calrf/− mice compared to those from the other two genotypes of mice. HSCs and most types of myeloid progenitors were also increased in the spleen. Hematopoiesis in the spleen may compensate for the reduced erythropoiesis in