Chronic injury of hematopoietic stem and progenitor cells induced by different doses of radiation / 环境与职业医学

Background The chronic injury of the hematopoietic system caused by ionizing radiation (IR) is often ignored. The essential cause of this injury is the damage of hematopoietic stem and progenitor cells (HSPCs). Objective To explore the long-term effects of IR at different radiation doses and at different radiation fractions of the same radiation dose on HSPCs in the bone marrow of mice, and to provide a scientific basis for reducing the chronic damage to the hematopoietic system caused by IR. Methods A total of 16 male C57BL/6 mice aged 8-10 weeks were randomly divided into four groups that received different doses or fractions of total body X-ray irradiation, including 1.5 Gy×4 irradiation group (n=5), 3 Gy irradiation group (n=4), 6 Gy irradiation group (n=4), and non-irradiation group (n=3). Two months after irradiation, bone marrow cells from each mouse were collected and counted. The clone forming ability of bone marrow cells was analyzed by cobblestone area-forming cell (CAFC) assay. The proportion of HSPCs was measured by flow cytometry. The cell cycle of HSPCs was assessed by antigen identified by monoclonal antibody Ki 67 (Ki-67) and 7-amino-actinomycin D (7-AAD) double staining. The reactive oxygen species (ROS) levels of HSPCs were estimated with a 2,7-dichlorodihydrofluorescein diacetate (DCFDA) probe. The cellular senescence of HSPCs was evaluated with a 5-dodecanoylaminofluorescein di-β-D-galactopyranoside (C12FDG) probe. The expression of senescence related genes such as P16, P19, P21, and P27 was measured by real-time fluorescence quantitative PCR. Results There was no significant change in the numbers of bone marrow cells 2 months after different doses and fractions of radiation (P>0.05). The clone forming ability of bone marrow cells was significantly decreased after 3 Gy and 6 Gy irradiation when compared to non-irradiated mice (P<0.01). HSPCs responded inconsistently to different doses and fractions of irradiation. Overall, there was no significant change in long-term hematopoietic stem cells (LT-HSCs) proportion after irradiation (P>0.05), the proportions of hematopoietic progenitor cells (HPCs), hematopoietic stem cells (HSCs), short-term hematopoietic stem cells (ST-HSCs), and multipotent progenitors 2 (MPP2) increased after irradiation (P<0.05), and the proportions of LSK, MPP1, MPP3, and MPP4 cells decreased after irradiation (P<0.05); except for HPCs and MPP2, the proportion of HSPCs in G0 phase was decreased (P<0.05). The ROS production in HSPCs was increased significantly after 6 Gy irradiation (P<0.05), while the ROS levels after 3 Gy and 1.5 Gy×4 irradiation were similar to that of the non-radiation group (P>0.05). The cellular senescent proportion of HPCs, LSK, and HSCs increased after irradiation (P<0.05). The expression levels of senescence related genes P16, P19, and P21 in HSCs were significantly increased (P<0.05). Conclusion The responses of HSPCs in bone marrow to IR vary depending on doses and fractions of irradiation. Increased ROS production and cellular senescence may be involved in the damage process of HSPCs under radiation settings.

Effects of salt concentration, pH, and their interaction on plant growth, nutrient uptake, and photochemistry of alfalfa (Medicago sativa) leaves.

In order to explore the main limiting factors affecting the growth and physiological function of alfalfa under salt and alkali stress, the effect of the salt and alkali stress on the growth and physiological function of alfalfa was studied. The results showed that effects of the excessive salt concentration (100 and 200 mM) on the growth and physiological characteristics were significantly greater than that of pH (7.0 and 9.0). Under 100 mM salt stress, there was no significant difference in the growth and photosynthetic function between pH 9.0 and pH 7.0. Under the 200 mM salt concentration the absorption of Na+ by alfalfa treated at the pH 9.0 did not increase significantly compared with absorption at the pH 7.0. However, the higher pH directly reduced the root activity, leaf's water content, and N-P-K content also decreased significantly. The PSII and PSI activities decreased with increasing the salt concentration, especially the damage degree of PSI. Although the photoinhibition of PSII was not significant, PSII donor and electron transfer from the QA to QB of the PSII receptor sides was inhibited. In a word, alfalfa showed relatively strong salt tolerance capacity, at the 100 mM salt concentration, even when the pH reached 9.0. Thus, the effect on the growth and photosynthetic function was not significant. However, at 200 mM salt concentration, pH 9.0 treatment caused damage to root system and the photosynthetic function in leaves of alfalfa was seriously injured.

Toxic effects of heavy metals Pb and Cd on mulberry (Morus alba L.) seedling leaves: Photosynthetic function and reactive oxygen species (ROS) metabolism responses.

To explore the mechanism of how lead (Pb) and cadmium (Cd) stress affects photosynthesis of mulberry (Morus alba L.), we looked at the effects of different concentrations of Pb and Cd stress (at 100 and 200 µmol L-1), which are two heavy metal elements, on leaf chlorophyll (Chl), photosynthesis gas exchange, Chl fluorescence, and reactive oxygen species (ROS) metabolism in mulberry leaves. The results showed that higher concentrations of Pb and Cd reduced leaf Chl content, especially in Chl a where content was more sensitive than in Chl b. Under Pb and Cd stress, the photosynthetic carbon assimilation capacity of mulberry leaves was reduced, which was a consequence of combined limitations of stomatal and non-stomatal factors. The main non-stomatal factors were decreased photosystem II (PSII) and photosystem I (PSI) activity and carboxylation efficiency (CE). Damage to the donor side of the PSII reaction center was greater than the acceptor side. After being treated with 100 µmol L-1 of Pb and Cd, mulberry leaves continued to be able to dissipate excess excitation energy by starting non-photochemical quenching (NPQ), but when Pb and Cd concentrations were increased to 200 µmol L-1, the protection mechanism that depends on NPQ was impaired. Excessive excitation energy from chloroplasts promoted a great increase of ROS, such as superoxide anion (O2•-) and H2O2. Moreover, under high Pb and Cd stress, superoxide dismutase (SOD) and ascorbate peroxidase (APX) were also inhibited to some extent, and excessive ROS also resulted in a significantly higher degree of oxidative damage. Compared with Cd, the effect of Pb stress at the same concentration level displayed a significantly lower impact on Chl content, photosynthetic carbon assimilation, and stomatal conductance. Meanwhile, Pb stress mainly damaged activity of the oxygen-evolving complex (OEC) located on PSII donor side, but it reduced the electronic pressure on the PSII acceptor side and PSI. Furthermore, under Pb stress, the NPQ, SOD, and APX activity were all significantly higher than those under Cd stress. Thus under Pb stress, the degree of photoinhibition and oxidative damage of PSII and PSI in mulberry leaves were significantly lower than under Cd stress.