Simultaneous Exposure of Cultured Human Lymphoblastic Cells to Simulated Microgravity and Radiation Increases Chromosome Aberrations

Abstract

During space travel, humans are continuously exposed to two major environmental stresses, microgravity (μG) and space radiation. One of the fundamental questions is whether the two stressors are interactive. For over half a century, many studies were carried out in space, as well as using devices that simulated μG on the ground to investigate gravity effects on cells and organisms, and we have gained insights into how living organisms respond to μG. However, our knowledge on how to assess and manage human health risks in long-term mission to the Moon or Mars is drastically limited. For example, little information is available on how cells respond to simultaneous exposure to space radiation and μG. In this study, we analyzed the frequencies of chromosome aberrations (CA) in cultured human lymphoblastic TK6 cells exposed to X-ray or carbon ion under the simulated μG conditions. A higher frequency of both simple and complex types of CA were observed in cells exposed to radiation and μG simultaneously compared to CA frequency in cells exposed to radiation only. Our study shows that the dose response data on space radiation obtained at the 1G condition could lead to the underestimation of astronauts' potential risk for health deterioration, including cancer. This study also emphasizes the importance of obtaining data on the molecular and cellular responses to irradiation under μG conditions.

Keywords: chromosome aberration; lymphoblast; microgravity; space radiation.

Figure 1

Scheme of experimental flow for cell survival and chromosome aberrations (CA) studies. Cells grown in disposable, sealed irradiation cell culture chambers (DCC) cassettes were mounted on the clinostat and exposed to X-ray or C-ion, with or without rotating clinostat.

Figure 2

Cell growth and survival. (a) The growth of TK6 cells cultured in RPMI medium (white) or in CO₂-independent medium (COI) (black) is shown. The error bar indicated the standard error of the mean. n = 3 for each time point. (b) Survival fraction of TK6 cells irradiated by 0.2 s pulses of X-ray (blue circle) or 290 MeV/n C-ion (red triangle) under the μG (unfilled) or 1G (filled) condition. Experimental data represent the mean of two to three plates for each dose experiment.

Figure 3

Examples of 3-color whole-chromosome FISH staining images of TK6 cells: chromosome 1 (red), chromosome 2 (green) and chromosome 4 (yellow). CA are identified by arrows as simple (reciprocal exchanges between two chromosomes) or complex-type exchanges (three or more breaks in two or more chromosomes). (a): normal chromosome spread; (b): simple type of exchange between chromosome 4 and another chromosome (dicentrics); (c): simple type of exchange between chromosome 1 and another chromosome (incomplete exchanges) and chromosome 2 and another chromosome; (d): fragmentation of chromosome 1; (e): complex type of exchange between chromosome 2 and other chromosomes; (f): complex type of exchange involving chromosomes 1, 2 and another chromosome.

Figure 4

Frequencies of total chromosome exchanges induced by X-ray (blue circle) or C-ion beam (red triangle), while cells were under either 1G (filled) or simulated μG conditions (unfilled). Error bars indicated the standard error of the mean. “n” for each data point is shown in Table 1.

Figure 5

Frequencies of simple and complex types of chromosome exchange induced by X-ray or C-ion beam while cells were under either 1G or simulated μG conditions. The blue column shows a simple type of CA and the red column shows a complex type of CA. Error bars indicated the standard error of the mean value. “n” is shown in Table 1.