Guilu Erxian Glue(龟鹿二仙胶)Inhibits Chemotherapy-Induced Bone Marrow Hematopoietic Stem Cell Senescence in Mice May via p16INK4a-Rb Signaling Pathway

Objective To evaluate the effect of Guilu Erxian Glue(龟鹿二仙胶,GEG)on cyclophosphamide(CTX)-induced bone marrow hematopoietic stem cells(HSCs)senescence in mice and explore the underlying mechanism.Methods The H22 liver cancer ascites lump model was established in male Kunming mice by injecting intraperitoneally(i.p.)with 5×10^6/mL H22 cells per mouse.Fifty tumor-bearing mice were divided into the control,model,pifithrin-α,GEG,and GEG+pifithrin-αgroups using a random number table,10 mice in each group.CTX(100 mg/kg i.p.)was administrated to mice from day 1 to day 3(d1–d3)continuously except for the control group.The mice in the pifithrin-α,GEG and GEG+pifithrin-αgroups were treated with pifithrin-α(2.2 mg/(kg·d)i.p.)for 6 consecutive days(d4–d9),GEG(9.5 g/(kg·d)i.p.)for 9 consecutive days(d1–d9),and GEG plus pifithrin-α,respectively.HSCs were collected after 9-d drug treatment.The anti-aging effect of GEG was studied by cell viability,cell cycle,andβ-galactosidase(β-gal)assays.The mRNA and protein expressions of cyclin-dependent kinase 2(CDK2),CDK4,inhibitor of cyclin-dependent kinase 4a encoding the tumor suppressor protein p16^(p16^INK4a),p21^Cip1/Waf1,p53,and phosphorylated retinoblastoma(pRb)were evaluated by quantitative real-time reverse transcription-polymerase chain reaction and semi-quantitative Western blot,respectively.Results Compared with the model group,GEG increased cell viability as well as proliferation(P<0.05 or P<0.01)and reducedβ-gal expression.Furthermore,GEG significantly decreased the expressions of p16^INK4a,p53 and p21^Cip1/Waf1 proteins,and increased the expressions of CDK2,CDK4 and pRb proteins compared with the model group(P<0.05 or P<0.01).Conclusion GEG can alleviate CTX-induced HSCs senescence in mice,and the p16^INK4a-Rb signaling pathway might be the underlying mechanism.

Lower Phosphorylation of p38 MAPK Blocks the Oxidative Stress-induced Senescence in Myeloid Leukemic CD34^+CD38^- Cells

Leukemia seems to depend on a small population of ＂leukemia stem cells （LSCs）＂ for its growth and metastasis. However, the precise surviving mechanisms of LSCs remain obscure. Cellular senescence is an important obstacle for production and surviving of tumor cells. In this study we investigated the activated state of a pathway, in which reactive oxygen species （ROS） induces cellular senescence through DNA damage and phophorylation of p38 MAPK （p38）, in myeloid leukemic CD34＋CD38- cells. Bone marrow samples were obtained from patients with acute myeloid leukemia （AML, n=11） and chronic myeloid leukemia （CML, n=9）. CD34＋CD38- cells were isolated from mononuclear cells from these bone marrow samples, and K562 and KG1a cells （two kinds of myeloid leukemia cell lines） by mini-magnetic activated cell sorting. Hematopoietic stem cells （HSCs） from human cord blood served as controls. Intracellular ROS level was detected by flow cytometry. DNA damage defined as the γH2AX level was measured by immunofluorescence staining. Real-time RT-PCR was used to detect the expression of p21, a senescence-associated gene. Western blotting and immunofluo-rescence staining were employed to determine the p38 expression and activation. The proliferation and apoptosis of CD34＋CD38- cells were detected by MTT assay and flow cytometry. Our results showed that ROS and DNA damage were substantially accumulated and p38 was less phosphorated in myeloid leukemic CD34＋CD38- cells as compared with HSCs and H2O2-induced senescent HSCs. Furthermore, over-phosphorylation of p38 by anisomycin, a selective activator of p38, induced both the senescence-like growth arrest and apoptosis of CD34＋CD38- cells from K562 and KG1a cell lines. These findings suggested that, although excessive accumulation of oxidative DNA damage was present in LSCs, the relatively decreased phosphorylation of p38 might help leukemic cells escape senescence and apoptosis.