Radiation-induced, cell cycle-related gene expression in aging hematopoietic stem cells: enigma of their recovery

Osteoblastic Wls Ablation Protects Mice from Total Body Irradiation-Induced Impairments in Hematopoiesis and Bone Marrow Microenvironment

Ionizing irradiation (IR) causes bone marrow (BM) injury, with senescence and impaired self-renewal of hematopoietic stem cells (HSCs), and inhibiting Wnt signaling could enhance hematopoietic regeneration and survival against IR stress. However, the underlying mechanisms by which a Wnt signaling blockade modulates IR-mediated damage of BM HSCs and mesenchymal stem cells (MSCs) are not yet completely understood. We investigated the effects of osteoblastic Wntless (Wls) depletion on total body irradiation (TBI, 5 Gy)-induced impairments in hematopoietic development, MSC function, and the BM microenvironment using conditional Wls knockout mutant mice (Col-Cre;Wls^fl/fl) and their littermate controls (Wls^fl/fl). Osteoblastic Wls ablation itself did not dysregulate BM frequency or hematopoietic development at a young age. Exposure to TBI at 4 weeks of age induced severe oxidative stress and senescence in the BM HSCs of Wls^fl/fl mice but not in those of the Col-Cre;Wls^fl/fl mice. TBI-exposed Wls^fl/fl mice exhibited greater impairments in hematopoietic development, colony formation, and long-term repopulation than TBI-exposed Col-Cre;Wls^fl/fl mice. Transplantation with BM HSCs or whole BM cells derived from the mutant, but not Wls^fl/fl mice, protected against HSC senescence and hematopoietic skewing toward myeloid cells and enhanced survival in recipients of lethal TBI (10 Gy). Unlike the Wls^fl/fl mice, the Col-Cre;Wls^fl/fl mice also showed radioprotection against TBI-mediated MSC senescence, bone mass loss, and delayed body growth. Our results indicate that osteoblastic Wls ablation renders BM-conserved stem cells resistant to TBI-mediated oxidative injuries. Overall, our findings show that inhibiting osteoblastic Wnt signaling promotes hematopoietic radioprotection and regeneration.

SVP-B5 peptide from Buthus martensii Karsch scorpion venom exerts hyperproliferative effects on irradiated hematopoietic cells

Previous studies have demonstrated the radioprotective efficacy of scorpion venom peptide, fraction II (SVPII) from the venom of Buthus martensii Karsch. In the present study, the SVP-B5 polypeptide, which is one of the active components of SVPII, was purified using a two-step chromatographic process. SVP-B5 significantly promoted the proliferation of irradiated M-NFS-60 mouse-derived myelocytic leukemia cells. In addition, SVP-B5 effectively and persistently promoted hematopoietic recovery and expansion of hematopoietic cells after irradiation as demonstrated by cobblestone area forming cell and long-term bone marrow culture assays. Treatment of M-NFS-60 cells with SVP-B5 upregulated the expression of interleukin 3 receptor and activated the Janus kinase-2/signal transducer and activator of transcription 5 signaling pathway. In conclusion, the present study demonstrated that SVP-B5 has growth factor-like properties and may be used as a therapeutic modality in the recovery of severe myelosuppression, which is a common side effect of radiotherapy.

A systematic review on the role of environmental toxicants in stem cells aging

Stem cells are an important target for environmental toxicants. As they are the main source for replenishing of organs in the body, any changes in their normal function could affect the regenerative potential of organs, leading to the appearance of age-related disease and acceleration of the aging process. Environmental toxicants could exert their adverse effect on stem cell function via multiple cellular and molecular mechanisms, resulting in changes in the stem cell differentiation fate and cell transformation, and reduced self-renewal capacity, as well as induction of stress-induced cellular senescence. The present review focuses on the effect of environmental toxicants on stem cell function associated with the aging process. We categorized environmental toxicants according to their preferred molecular mechanism of action on stem cells, including changes in genomic, epigenomic, and proteomic levels and enhancing oxidative stress. Pesticides, tobacco smoke, radiation and heavy metals are well-studied toxicants that cause stem cell dysfunction via induction of oxidative stress. Transgenerational epigenetic changes are the most important effects of a variety of toxicants on germ cells and embryos that are heritable and could affect health in the next several generations. A better understanding of the underlying mechanisms of toxicant-induced stem cell aging will help us to develop therapeutic intervention strategies against environmental aging. Meanwhile, more efforts are required to find the direct in vivo relationship between adverse effect of environmental toxicants and stem cell aging, leading to organismal aging.

Long-term loss of osteoclasts and unopposed cortical mineral apposition following limited field irradiation

Late-onset fragility fractures are a common complication following radiotherapy for metastatic disease and soft tissue sarcomas. Using a murine hindlimb focal irradiation model (RTx), we quantified time-dependent changes in osteoclasts and mineral apposition rate (MAR). Mice received either a single, unilateral 5 Gy exposure or four fractionated doses (4 × 5 Gy). Osteoclast numbers and MAR were evaluated histologically at 1, 2, 4, 8, 12, and 26 weeks post-RTx. Radiation induced an early, transient increase in osteoclasts followed by long-term depletion. Increased osteoclast numbers correlated temporally with trabecular resorption; the resorbed trabeculae were not later restored. Radiotherapy did not attenuate MAR at any time point. A transient, early increase in MAR was noted in both RTx groups, however, the 4 × 5 Gy group exhibited an unexpected spike in MAR eight weeks. Persistent depletion of osteoclasts permitted anabolic activity to continue unopposed, resulting in cortical thickening. These biological responses likely contribute to post-radiotherapy bone fragility via microdamage accumulation and matrix embrittlement in the absence of osteoclastic remodeling, and trabecular resorption-induced decrease in bone strength. The temporal distribution of osteoclast numbers suggests that anti-resorptive therapies may be of clinical benefit only if started prior to radiotherapy and continued through the following period of increased osteoclastic remodeling.

Bone Marrow Protein Oxidation in Response to Ionizing Radiation in C57BL/6J Mice

The bone marrow is one of the most radio-sensitive tissues. Accidental ionizing radiation exposure can damage mature blood cells and hematopoietic progenitor/stem cells, and mortality can result from hematopoietic insufficiency and infection. Ionizing radiation induces alterations in gene and protein expression in hematopoietic tissue. Here we investigated radiation effects on protein carbonylation, a primary marker for protein oxidative damage. C57BL/6 mice were either sham irradiated or exposed to 7.5 Gy ⁶⁰Co (0.6 Gy/min) total body irradiation. Bone marrow was obtained 24 h post-irradiation. Two dimensional (2-D) gel electrophoresis and Oxyblot immunodetection were used to discover carbonylated proteins, and peptide mass fingerprinting was performed for identification. 2D gels allowed the detection of 13 carbonylated proteins in the bone marrow; seven of these were identified, with two pairs of the same protein. Baseline levels of carbonylation were found in 78 kDa glucose-related protein, heat shock protein cognate 71 KDa, actin, chitinase-like protein 3 (CHI3L1), and carbonic anhydrase 2 (CAII). Radiation increased carbonylation in four proteins, including CHI3L1 and CAII, and induced carbonylation of one additional protein (not identified). Our findings indicate that the profile of specific protein carbonylation in bone marrow is substantially altered by ionizing radiation. Accordingly, protein oxidation may be a mechanism for reduced cell viability.