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. 2019 May;33(5):1135-1147.
doi: 10.1038/s41375-018-0269-8. Epub 2018 Oct 1.

Mlh1 Deficiency Increases the Risk of Hematopoietic Malignancy After Simulated Space Radiation Exposure

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Free PMC article

Mlh1 Deficiency Increases the Risk of Hematopoietic Malignancy After Simulated Space Radiation Exposure

Rutulkumar Patel et al. Leukemia. .
Free PMC article

Abstract

Cancer-causing genome instability is a major concern during space travel due to exposure of astronauts to potent sources of high-linear energy transfer (LET) ionizing radiation. Hematopoietic stem cells (HSCs) are particularly susceptible to genotoxic stress, and accumulation of damage can lead to HSC dysfunction and oncogenesis. Our group recently demonstrated that aging human HSCs accumulate microsatellite instability coincident with loss of MLH1, a DNA Mismatch Repair (MMR) protein, which could reasonably predispose to radiation-induced HSC malignancies. Therefore, in an effort to reduce risk uncertainty for cancer development during deep space travel, we employed an Mlh1+/- mouse model to study the effects high-LET 56Fe ion space-like radiation. Irradiated Mlh1+/- mice showed a significantly higher incidence of lymphomagenesis with 56Fe ions compared to γ-rays and unirradiated mice, and malignancy correlated with increased MSI in the tumors. In addition, whole-exome sequencing analysis revealed high SNVs and INDELs in lymphomas being driven by loss of Mlh1 and frequently mutated genes had a strong correlation with human leukemias. Therefore, the data suggest that age-related MMR deficiencies could lead to HSC malignancies after space radiation, and that countermeasure strategies will be required to adequately protect the astronaut population on the journey to Mars.

Conflict of interest statement

This research was funded by NASA grant NNX14AC95G. Authors also declare no conflicts of interest.

Figures

Figure 1:
Figure 1:. Long-term tumorigenesis assay.
(A) Schematic representation of long-term tumorigenesis assay design. Tumor free survival of Mlh1+/+ and Mlh1+/− mice post (B) 100 or 250 cGy γ-rays, or (C) 10 or 100 cGy 56Fe ions (n=36–44, number of Mlh1+/+ or Mlh1−/− mice used for each radiation exposure). (D) Tumor free survival of Mlh1+/+ mice post 0, 100 or 250 cGy γ-rays, or 10 or 100 cGy 56Fe ions. (E) Tumor free survival of Mlh1+/− mice post 0, 100 or 250 cGy γ-rays, or 10 or 100 cGy 56Fe ions. (F) Days post-irradiation to reach 70% survival. Variance between groups is not significantly different.
Figure 2:
Figure 2:. Histopathology of tumors from Mlh1+/+ and Mlh1+/− mice.
(A) Lymphoma in sections of liver, characterized by sheets of neoplastic lymphocytes infiltrating and effacing normal hepatic parenchyma (arrowheads) (40X, bar = 20um). (B) Histiocytic sarcoma composed of round to spindyloid neoplastic cells with occasional multinucleate giant cells (arrowhead) (20X, bar = 50um). (C) Hepatocellular carcinoma composed of lobules, cords, and trabeculae of atypical hepatocytes replacing normal parenchyma (bar = 50um). (D) Hemangiosarcoma composed of sheets and bundles of spindle-shaped cells forming haphazard vascular channels (arrowhead) lined by neoplastic endothelial cells (40X, bar = 20um). (E) Harderian gland adenoma characterized by an expansile proliferation (arrowhead) of tubules and acini of fairly well differentiated glandular epithelial cells (bar = 100um). (F) Ovarian granulosa cell tumor composed of solid lobules and nests of neoplastic cells often forming rudimentary follicular structures (arrowhead) (40X, bar = 20um). (G) Percentage tumor distribution based on histology of tumors collected from Mlh1+/+ mice treated with sham-, γ-, or 56Fe ion irradiation. (H) Percentage tumor distribution based on histology of tumors collected from Mlh1+/− mice treated with sham-, γ-, or 56Fe ion irradiation. (I) Aggressive cancer measured by percentage of mice with multiple tumor types or same tumor type in multiple organs. Histopathology was performed on 13–27 tumors of Mlh1+/+ origin and 18–44 tumors of Mlh1+/− origin. Tumor distribution was analyzed by Chi-square and multiple tumor incidence was analyzed by two-way ANOVA; ns = non-significant.
Figure 3:
Figure 3:. Immunohistochemistry of lymphomas from Mlh1+/+ and Mlh1+/− mice.
(A) B-cell lymphoma in a mesenteric lymph node shows diffuse and strong positive membrane immunoreactivity for B220 antibody. (B) T-cell lymphoma in mesenteric lymph node shows diffuse membrane and cytoplasmic immunoreactivity to CD3 antibody. (C) Histiocytic sarcoma in the liver shows strong and diffuse membrane immunoreactivity to F4/80 antibody. (D-F) The majority of neoplasms had an immunophenotype of T-cell rich, B-cell lymphomas, characterized by a dominant population of neoplastic B cells immunoreactive to B220 antibody (D), with a minority population of well-differentiated T-cells immunoreactive to CD3 antibody (E), and only a few resident macrophages illustrated by F4/80 immunoreactivity (F). (A-F) 40X, bar = 20um. (G) Distribution, based on immunohistochemistry, of lymphomas collected from Mlh1+/+ mice treated with sham-, γ-, or 56Fe ion irradiation. (H) Distribution, based on immunohistochemistry, of lymphomas collected from Mlh1+/− mice treated with sham-, γ-rays, or 56Fe ion irradiation. IHC was performed on 8–12 lymphomas of Mlh1+/+ origin and 15–31 lymphomas of Mlh1+/− origin.
Figure 4:
Figure 4:. Microsatellite instability found in Mlh1+/+ and Mlh1+/− tumors.
Stable MSI (MSI-S) was found in control tissue (Mlh1+/+) via the markers mBat-26 (A), mBat-37 (B), mBat-59 (C), and mBat-64 (D). Similarly, high MSI (MSI-H) was observed in Mlh1+/− tumor sample also via mBat-26 (E), mBat-37 (F), mBat-59 (G), and mBat-64 (H). MSI distribution in Mlh1+/+ vs Mlh1+/− tumors (I). MSI-H distribution found in tumors of irradiated Mlh1+/− mice (J). Number of Mlh1+/+ and Mlh1+/− tumors used for the analysis were 15 and 43, respectively. Distributions were tested using Chi-square tests.
Figure 5:
Figure 5:. WES analysis of Mlh1+/+ and Mlh1+/− TRB lymphomas.
(A) Number of SNVs and INDELs found in each TRB lymphoma arising from sham- (n = 3 and 7 for Mlh1+/+ and Mlh1+/−, respectively), γ-rays (n = 4 and 12 for Mlh1+/+ and Mlh1+/−, respectively), or 56Fe ion irradiation (n = 7 and 12 for Mlh1+/+ and Mlh1+/−, respectively). (B) Average number of SNVs per Mlh1+/+ and Mlh1+/− cohorts. (C) Average number of INDELs per Mlh1+/+ and Mlh1+/− cohorts. (D) Size of INDELs ≥ 5 bp in each cohort of Mlh1+/+ and Mlh1+/− TRB lymphomas. (E) Size of INDELs ≥ 10 bp in each cohort of Mlh1+/+ and Mlh1+/− TRB lymphomas. Venn Diagram shows number of frequently mutated genes found in (F) Mlh1+/+, and (G) Mlh1+/− cohorts. P values were determined by a two-way ANOVA model. Data plotted are means ± SEM.
Figure 6:
Figure 6:. Correlation between frequently mutated mouse TRB lymphoma genes vs human leukemia genes.
Heatmap represents human leukemia genes also found to be frequently mutated in (A) Mlh1+/+, and (B) Mlh1+/− mouse TRB lymphoma cohorts. Solid aqua lines in each Heatmap represent actual mutational frequency of a gene in that particular cohort. (C) Different types of mutations (mis-sense, non-sense, frameshift, intron, and silent) found in each gene of Mlh1+/− TRB lymphomas.

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References

    1. Cucinotta FA, Schimmerling W, Wilson JW, Peterson LE, Badhwar GD, Saganti PB, et al. Space radiation cancer risks and uncertainties for Mars missions. Radiation research 2001. November; 156(5 Pt 2): 682–688. - PubMed
    1. Edwards AA. RBE of radiations in space and the implications for space travel. Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics 2001; 17 Suppl 1: 147–152. - PubMed
    1. Schimmerling W, Cucinotta FA, Wilson JW. Radiation risk and human space exploration. Advances in space research : the official journal of the Committee on Space Research 2003; 31(1): 27–34. - PubMed
    1. Heinrich W, Roesler S, Schraube H. Physics of cosmic radiation fields. Radiation protection dosimetry 1999; 86(4): 253–258. - PubMed
    1. Chancellor JC, Scott GB, Sutton JP. Space Radiation: The Number One Risk to Astronaut Health beyond Low Earth Orbit. Life 2014. September 11; 4(3): 491–510. - PMC - PubMed

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