Thrombopoietin the primary regulator of platelet production

c-MPL Is a Candidate Surface Marker and Confers Self-Renewal, Quiescence, Chemotherapy Resistance, and Leukemia Initiation Potential in Leukemia Stem Cells

Acute myeloid leukemia (AML) is initiated and maintained by a unique, small subset of leukemia cells known as leukemia stem cells (LSCs). Self-renewal, quiescence, and chemotherapy resistance are key stemness properties of LSCs that are essential for poor clinical responses to conventional therapies. Identifying LSC surface markers and targeting LSCs are important for the development of potential therapies. In this study, application of chemotherapy treatment in AML-ETO9a (AE9a) leukemia mice led to the enrichment of a chemotherapy-resistant cell population identified as Lin^- c-Kit⁺ c-MPL⁺ . In addition, this c-MPL-positive cell population within Lin^- c-Kit⁺ leukemia cells included a high percentage of cells in a quiescent state, enhanced colony formation ability, and increased homing efficiency. Serial transplantation demonstrated that Lin^- c-Kit⁺ c-MPL⁺ cells displayed a significantly high potential for leukemia initiation. Furthermore, it was demonstrated that in AML patients, c-MPL was expressed on the majority of CD34⁺ leukemia cells and that the proportion of c-MPL⁺ cells in CD34⁺ leukemia cells is associated with poor prognosis. Finally, AMM2, an inhibitor of c-MPL, was shown to significantly enhance the survival of AE9a leukemia mice when combined with chemotherapeutic agent. These results indicate that c-MPL is a candidate LSC surface marker that may serve as a therapeutic target for the elimination of LSCs. Stem Cells 2018;36:1685-1696.

Correlation between bone metastasis and thrombocytosis in pulmonary adenocarcinoma patients

Thrombocytosis is commonly observed in patients exhibiting a variety of malignancies, including pulmonary, gastrointestinal and hepatic cancer. In the present study, the correlation between distant metastasis and thrombocytosis was retrospectively reviewed in 308 cases of histopathologically confirmed pulmonary adenocarcinoma. The patients were classified as having thrombocytosis or not, based on their platelet counts upon diagnosis; thrombocytosis was documented in 82/308 patients (26.6%). A log-rank test indicated a statistically significant difference in survival between patients exhibiting thrombocytosis compared with patients not exhibiting thrombocytosis (P<0.001). In addition, the occurrence of distant metastasis and the survival period were correlated with the presence of thrombocytosis upon diagnosis. In descending order of frequency, metastases were documented at the following sites: Lymph nodes (218/308 patients; 70.8%), bone (138/308 patients; 44.8%), lung (93/308 patients; 30.2%), brain (67/308 patients; 21.8%), liver (46/308 patients; 4.9%), adrenal glands (11/308 patients; 3.6%) and kidneys (5/308 patients; 1.6%). Bone metastasis occurred significantly more frequently in patients exhibiting thrombocytosis (50/82 patients: 61.0%; P<0.05) compared with patients not exhibiting thrombocytosis (88/226 patients; 38.9%). Furthermore, according to univariate analysis, thrombocytosis, weight loss, an Eastern Cooperative Oncology Group performance status score of ≥2 points, anemia, increased erythrocyte sedimentation rate, and increased alkaline phosphatase (AKP) and carcinoembryonic protein (CEA) levels were risk factors for bone metastasis. According to multivariate analysis, thrombocytosis, weight loss, and increased AKP and CEA levels were correlated with bone metastasis. Therefore, patients exhibiting pulmonary adenocarcinoma and thrombocytosis have a higher risk of bone metastasis compared with patients not exhibiting thrombocytosis.

Identification of a new Mpl-interacting protein, Atp5d

Thrombopoietin (TPO) can regulate hematopoiesis and megakaryopoiesis via activation of its receptor, c-Mpl, and multiple downstream signal transduction pathways. Using the cytoplasmic domain of Mpl as bait, we performed yeast two-hybrid screening, and found that the protein Atp5d might associate with Mpl. Atp5d is known as the δ subunit of mitochondrial ATP synthase, but little is known about the function of dissociative Atp5d. The interaction between Mpl and Atp5d was confirmed by the yeast two-hybrid system, mammalian two-hybrid assay, pull-down experiment, and co-immunoprecipitation study in vivo and in vitro. An additional immunofluorescence assay showed that the two proteins can colocalize along the plasma membrane in the cytoplasm. Using the yeast two-hybrid system, we tested a series of cytoplasmic truncated mutations for their ability to bind Atp5d and found an association between Atp5d and the Aa98-113 domain of Mpl. The dissociation of Atp5d from Mpl after TPO stimulation suggests that Atp5d may be a new component of TPO signaling.

Quantitative trait loci for porcine white blood cells and platelet-related traits in a White Duroc x Erhualian F resource population

White blood cell count and platelets are implicated as risk factors for common complex diseases. Genetic factors substantially affect these traits in humans and mice. However, little is known about the genetic architecture of these traits in pigs. To identify quantitative trait loci (QTL) for leucocyte- and platelet-related traits in pigs, the total leucocyte number and differential leucocyte counts including the fraction of basophils, eosinophils, lymphocytes, monocytes, neutrophils, and a series of platelet parameters including platelet count, mean platelet volume, platelet distribution width and plateletcrit were measured in 1033 F(2) animals on 240 days from a White Duroc x Erhualian intercross resource population. A total of 183 informative microsatellites distributed across 19 pig chromosomes (SSC) were genotyped across the entire resource population. Thirty-three QTL were identified for the examined traits, including eight genome-wide significant QTL for white blood cells and differential leucocyte counts on SSC2, 7, 8, 12 and 15 and six significant QTL for platelet-related traits on SSC2, 8, 13 and X. Erhualian or White Duroc alleles were not systematically associated with increased phenotypic values. These results not only confirmed many QTL identified previously in the mouse and swine, but also revealed a number of novel QTL for the traits recorded. Moreover, it is the first time that QTL for platelet-related traits in pigs have been reported.