Terrestrial Life in Space What Can We Learn From Cells?

1. Terrestrial Life in Space What Can We Learn From Cells? Neal R. Pellis, Ph.D. Director Division of Space Life Sciences Universities Space Research Association Houston, TX 77058 pellis@dsls.usra.edu

2. Clinical Problems in Space • Visual impairment • Exposure to ionizing radiation • Bone density decrease • Muscle Atrophy • Cardiovascular Deconditioning • Psychosocial impacts • Vestibular Dysfunction • Hematological changes • Immune Dysfunction • Delayed wound healing • Gastrointestinal Distress • Orthostatic Intolerance • Fluid Shifting • Renal stones • Nutrition

3. Paradigms Lost • The Earth is the center of the universe • Blood letting ameliorates most disease • Accumulations of old rags in the attic spontaneously generate rats • Read my lips, no new taxes… • I never inhaled… • Humans cannot survive outside the Earth’s environment • Cellular and intracellular components are too insignificant in mass to be affected by the loss of gravity

4. "There is a place in your brain, I think, reserved for 'the melancholy of relationships past.' It grows and prospers as life progresses, forcing you finally, against your grain, to listen to country music." (K.B. Mullis et al., eds., The Polymerase Chain Reaction, Birkhauser: Boston, 1995, p. 427).

5. Terrestrial Life and Microgravity • As life evolved on earth a multiplicity of physical and chemical factors invoked adaptations and participated in the complicated selection process • For many factors there are clear examples of the role of changing physical forces in evolution • A notable exception is gravity. It has been constant for the 4.8 billion years • Therefore, there is little or no genetic memory of life responding to force changes in the low gravity range

6. Why Space Cell Biology? • As is true for terrestrial based biomedicine, analysis of the cellular response to microgravity offers the prospect of elucidating underlying mechanisms that can be the basis for effective treatment. • Observation of the cellular response to variation in ‘G’ reveals novel adaptive mechanisms. • Understanding basic cellular mechanisms necessary for the adaptation of terrestrial life to low gravity environments

7. Interactions in Nature • Gravitational • Electromagnetic • Strong submolecular forces • Weak submolecular forces

8. Interactions in Nature • Gravity is the weakest of the four but has a vast radius of influence • Among the four, gravity is considered the sculptor of the universe • Methods for studying gravitational influences on biological processes (Microgravity Analogs) • Theoretical analysis and computer modeling • Changing the weight loading • Hypergravity • Free fall strategies • Space experiments

9. An Important Question in Space BiologyThe Relationship Between Gravity and Biological Activity Hyper G mG ? Your favorite Biological Response The vast zone of the unknown Known response suites and relationships -6 -5 -4 -3 -2 -1 0 1 Log10 Gravity

10. An Important Question in Space BiologyThe Relationship Between Gravity and Biological Activity Hyper G mG ? Your favorite Biological Response The vast zone of the unknown Known response suites and relationships -6 -5 -4 -3 -2 -1 0 1 Log10 Gravity

11. Hypothesis: Relationship Between Gravity and Biological Activity Fractional-G ? 100 75 Your favorite Biological Response (%of Earth Gravity) 50 Moon Mars Earth 25 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0 Log10 Gravity

12. Areas of Investigationfor Space Exploration • Basic human physiology • Plant life used for O2 and for food • Bioregenerative microbes • Normal flora • Environmental monitoring • Exploration proes Areas of Investigation for Applied Science • Tissue engineering • Vaccine and drug development • Models of human disease • Living reporter sensors

13. Fundamental Questions • What is the basis of the cellular response to microgravity? • Intrinsic response in the cell (gravisensor?) • Cellular response to environmental changes induced by gravity • Shear • Mass transfer • Surface contact • No sedimentation • How is response different in microbial cells (that are bound by a cell wall) vs. eukaryotic/mammalian cells that do not have a cell wall? • How do changes in individual cells relate to tissues, organs, and organisms? • How does microgravity change cell response thresholds to other stimuli (radiation, magnetic fields, shear, toxins, other chemicals)?

14. Scientific Questions to Address • Adaptive responses of cells to microgravity and to the space environment? • Phenotypic and genotypic changes induced by microgravity, space, and planetary environments? • Does the space environment invoke a selective pressure on replicating cells? • How much ‘G’ is required to maintain normal function? • What new cell biology applications can be achieved in low gravity environments?

15. Practical Questions • How do changes in individual cells relate to tissues, organs, and organisms? • How does microgravity change cell response thresholds to other stimuli (radiation, magnetic fields, shear, toxins, other chemicals)? • Can we use cells to conduct missions with unknown consequences?

16. Solid Body Fluid Rotation Analog Systems To investigate the cellular and tissue responses to microgravity it was essential to design systems that approximate the some of the microgravity conditions and provide the opportunity to study these phenomena on Earth in a more controlled and available venue. Isopycnic Solution (Neutral Buoyancy) Parabolic Flight Centrifugation Hyper G 6o Head Down Tilt Bedrest Magnetic Levitation Drop Tower Suborbital Rockets Superconducting Magnet Diamagnetic

17. Unique aspects of mG • No sedimentation • Loss of gravity driven convection • Decreased hydrodynamic shear • No hydrostatic pressure • Mass transfer is limited to the rate of diffusion

18. Animal Cells in Space Return Launch mG Changes: fluid distribution gene expression signal transduction locomotion differentiation Metabolism glycosylation 1 G 1 G

19. Theory of the Effect of mG on Mammalian Cells mG 1 G Potential Change in membrane: Structure Composition Bileaflet organization Lipid rafts Association with the cytoskeleton Perhaps the ‘forced’ shape change induces a cascade of responses otherwise unrelated to mG

20. Bacteria in Space Return Launch mG Changes: Gene expression Shift to secondary metabolism Quorum sensing? Virulence Mechano-responsive mechanisms Replication rates Biofilm formation Bacillus spacecowboyum 1 G 1 G

21. Theory of the Effect of mG on Bacterial CellsResponse of cell with non pliant cell walls Bacteria mG 1 G ?? Pin<<Pout?? In bacteria, the cell wall is a rigid structure that surrounds the cell membrane. Perhaps the decrease in gravity accentuates the attractive forces between fatty acid side chains of triglycerides resulting in outward force on the wall. This in turn activates mechano- and baro- responsive mechanisms leading to the phenotypes seen in space May be applicable to plant cells

22. Cellular Responses to mG • Signal transduction • Shape change • Gene expression • DNA damage • Cell division rates • Orientation of subcellular components • Changes in nucleoli morphology • Synthesis and orientation of macromolecules • Cytoskeleton • Programmed cell death • Cellular movement • Cellular repair • Cytokine synthesis and secretion • Glycosylation • Differentiation and tissue morphogenesis • Biofilm formation and deposition

23. Physical Factors to Consider in Experimental Design • Gravity • Mechanical impacts • Hydrodynamic shear • Convection • Vibration • Radiation • Barometric Pressure • Hydrostatic pressure gradients

24. Significance • There is little doubt that cells as representative of terrestrial life respond decreased gravity environments. • The mechanism of gravity induced responses in cells is unknown. • Nevertheless, microgravity affords a unique tool to probe the underlying mechanisms in life systems at the cellular and organismal level. • We plan use of this tool • novel ways to increase our understanding of the role of gravity in life processes • to achieve goals in applied biological science and technology development • to elucidate the long term effects of microgravity on terrestrial life by using cells as explorers

25. Obstacles in Colonizing Space • Financial • Political and philosophical • Propulsion • Dealing with the reality that it could be a multi-generational mission • Managing health • Managing the logistics • Decreasing the energy requirements for life?

26. We are going to have to learn by exploring the Solar System • Candidates for colonization are: • The Moon • Mars • Candidates for exploration • Europa (Moon of Jupiter) • Titan (Moon of Saturn) • Encelaedus (Moon of Saturn)