Crew members onboard the International Space Station (ISS) exhibit a range of microgravity induced physiological dysfunctions during extended missions (>1 month). Some of the most common effects of long-term microgravity exposure include immune system dysregulation, skeletal muscle atrophy, cardiovascular decline, bone loss, cognitive impairments, and decreased motor control. Unfortunately, the underlying etiology of microgravity induced dysfunction remains unclear. Decades of NASA research on ISS and shuttle missions have demonstrated that mammalian cell cultures exhibit altered morphology, proliferation, motility, differentiation, and often increased oxidative stress when exposed to the microgravity environment. Thus, physiological dysfunction at the tissue and systemic level is likely a result of altered cellular function, subcellular structural alterations, and intracellular communications. It has been well documented that the lack of gravity on-orbit has resulted in a cytoskeletal structural reorganization within a host of adherent mammalian cell cultures. Altered microtubule organization has enormous significance in the context of neurite outgrowth and neuronal intracellular communications. Intracellular effects may include the inability to clear aging and toxic proteins, a loss of trophic factor signaling, and compromised cellular energetics, resulting in axonopathies, synaptic loss, and eventual neuron death. Intracellular trafficking of vesicles is a fundamental subcellular process that can significantly alter cellular, tissue, and systemic processes if impaired in microgravity. Previous studies on Earth have demonstrated that disrupted intracellular communication contributes to abnormal physiological processes and that intracellular processes are sensitive to cytoskeletal organization. Thus, it is likely that microtubule reorganization in microgravity impairs neurite outgrowth, intra- and intercellular communications. However, the extent to which microgravity affects neuron microtubule structure dynamics remains unknown. We hypothesize that neuron microtubule organization is altered in microgravity which leads to inhibited neurite outgrowth and reduced intracellular vesicle trafficking which ultimately contributes to the cognitive impairments, motor control decline, and reduced neuroplasticity observed in microgravity.
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To characterize neuronal function in microgravity, we will quantify microtubule structure dynamics and intracellular vesicle trafficking utilizing the innovative Mobile SpaceLab (MoSL) platform to perform autonomous fluorescence microscopy and microfluidic delivery for the duration of a 4-week mission on-orbit. This investigation will seek to quantify vesicle transport, microtubule organization, neurite outgrowth, cell proliferation, differentiation, and motility with fluorescently labeled SH-SY5Y neuroblastoma cells. Ground control experiments with replicate hardware will be compared to the microgravity MoSL experiment. Preliminary results with the ground based MoSL facility demonstrate that microtubule structure and vesicle transport can be observed in real-time during long-term experimentation.
This work will seek to 1) quantify the effect of microgravity on neuron microtubule organization and neurite outgrowth during differentiation, 2) quantify the effects of microgravity on intracellular vesicle trafficking within terminally differentiated neurons, and 3) delineate the effects of microtubule polymerization on neuronal structure and intracellular communication. This study will be the first of its kind to observe and quantify differentiating neuron function in microgravity on a minute to hour basis during a long-duration mission. This research has far reaching implications towards understanding the effects of microgravity on neuroplasticity, which may lead to future drug targets and therapeutic interventions to attenuate the deleterious effects of long-term microgravity exposure on human physiology.
This experiment is currently in progress. Results will be available at the conclusion of the study.