Leukemia Decreased TREM-1 Expression In Hematopoiesis Stem/ Progenitor Cells

Triggering receptor expressed on myeloid cells (TREM) -1 is a receptor expressed on the cell-surface of neutrophils, monocytes and macrophages. This receptor is a molecule crucial for the triggering and amplification of inflammatory responses. TREM-1 is shed from the membrane of activated macrophages and can be found as soluble TREM (sTREM)-1. Soluble TREM-1 is thought to negatively regulate TREM receptor signaling. In current study, we confirmed that TREM-1 were down-expressed in leukemic cells. The aims of this study was to investigate if there is a functional link between myelogenous leukemia cells and TREM-1 in hematopoiesis stem/progenitor cells.

10 cord blood were collected from full-term normal cesarean-section infants. The study was approved by the ethic committee. Hematopoiesis stem/progenitor cells isolation started within 4h from partum. Plasma was used to evaluate sTREM-1. Set up a control group and leukemia cells induced group. Leukemia cells induced group processed as following: culture hematopoiesis stem/progenitor cells with 1:1 microvesicles-free leukemia cell line condition supernatant and DMEM medium with high glucose. Collect cells and condition supernatant from control group and leukemia cells induced group at 0h, 6h, 12h, and 24h. The expressions of TREM-1 on hematopoiesis stem/progenitor cells were measured by flow cytometry. sTREM-1 levels of condition supernatant were detected by the ELISA.

In this study, our results provide the first evidence that TREM-1 was expressed in hematopoiesis stem/progenitor cells (CD34+/CD38-, CD34+/CD38+). The TREM-1 mean ratio of median fluorescence intensity (mean ratio of MFI) was 3.79 ± 0.96 and 9.51 ± 1.56 in hematopoiesis stem cells (CD34+/CD38- cells) and hematopoiesis progenitor cells (CD34+/CD38+ cells), respectively. The expression of TREM-1 in hematopoiesis stem cell was weaker than that in hematopoiesis progenitor cell. In addition, our results showed that sTREM-1 level was 6.04 ± 3.92 pg/mL in cord blood plasma.

In order to assess a functional link between myelogenous leukemia cells and TREM-1 in hematopoiesis stem/progenitor cells, we separately cultured CD34+/CD38-, CD34+/CD38+ cells with 1:1 microvesicles-free condition medium from K562 cells and DMEM medium with high glucose for 48 hs. As a result, the TREM-1 mean ratio of MFI went from 3.79 ± 0.96 to 2.45 ± 1.29 in CD34+/CD38- cells and from 9.51 ± 1.56 to 4.22± 1.73 in CD34+/CD38+ cells in a period from 0 to 24 hours; The same results were obtained from cultured with 48h microvesicles-free condition medium from THP-1 cells. These suggested that the leukemia could induce the decreased expression of TREM-1 in hematopoiesis stem/progenitor cells in time-dependent manner. There was no obvious difference between 48h and 24h cultured with condition medium, TREM-1 expression of hematopoiesis stem/progenitor cells began to stabilize within 24 hours.

Similarly, we cultured CD34+/CD38-, CD34+/CD38+ cells with conditional medium from differential number 48h microvesicles-free condition medium from K562 cells (K562 cells numberset six levels: 2*10⁶, 1*10⁶, 5*10⁵, 2.5*10⁵, 1*10⁵, 5*10⁴). As a result, the TREM-1 mean ratio of MFI went from 1.81±1.46 to 3.45±0.93 rising in turn in CD34+/CD38- cells and went from 3.49 ± 1.95 to 11.62 ± 3.60 rising in turn in CD34+/CD38+ cells. The same results were also obtained from THP-1 cells. These suggested that the leukemia cells could induce the decreased expression of TREM-1 in hematopoiesis stem/progenitor cells in number-dependent manner. The higher the number of leukemia cells, the more significant is in inhibition to TREM-1 expression in hematopoiesis stem/ progenitor cell.

Furthermore, our results showed that sTREM-1 levels was increased in supernatants of normal cord blood cells cultured with conditional medium from K562 cells (6.04 ± 3.92 pg/mL for 0 hour; 17.51 ± 3.8 pg/mL for 48 hours, P < 0.05). Compared with quiescent cord blood cells, in vitro leukemia induced normal blood cells secreted high levels of sTREM-1.

In this study, our results provide the first evidence that TREM-1 was expressed in hematopoiesis stem/progenitor cells. The leukemia cells could induce the decreased expression of TREM-1 in hematopoiesis stem/progenitor cells and facilitates the generation of sTREM-1.

No relevant conflicts of interest to declare.