Gene-metabolite profile integration to understand the cause of spaceflight induced immunodeficiency

Abstract

Spaceflight presents a spectrum of stresses very different from those associated with terrestrial conditions. Our previous study (BMC Genom. 15: 659, 2014) integrated the expressions of mRNAs, microRNAs, and proteins and results indicated that microgravity induces an immunosuppressive state that can facilitate opportunistic pathogenic attack. However, the existing data are not sufficient for elucidating the molecular drivers of the given immunosuppressed state. To meet this knowledge gap, we focused on the metabolite profile of spaceflown human cells. Independent studies have attributed cellular energy deficiency as a major cause of compromised immunity of the host, and metabolites that are closely associated with energy production could be a robust signature of atypical energy fluctuation. Our protocol involved inoculation of human endothelial cells in cell culture modules in spaceflight and on the ground concurrently. Ten days later, the cells in space and on the ground were exposed to lipopolysaccharide (LPS), a ubiquitous membrane endotoxin of Gram-negative bacteria. Nucleic acids, proteins, and metabolites were collected 4 and 8 h post-LPS exposure. Untargeted profiling of metabolites was followed by targeted identification of amino acids and knowledge integration with gene expression profiles. Consistent with the past reports associating microgravity with increased energy expenditure, we identified several markers linked to energy deficiency, including various amino acids such as tryptophan, creatinine, dopamine, and glycine, and cofactors such as lactate and pyruvate. The present study revealed a molecular architecture linking energy metabolism and immunodeficiency in microgravity. The energy-deficient condition potentially cascaded into dysregulation of protein metabolism and impairment of host immunity. This project is limited by a small sample size. Although a strict statistical screening was carefully implemented, the present results further emphasize the need for additional studies with larger sample sizes. Validating this hypothesis using an in vivo model is essential to extend the knowledge towards identifying markers of diagnostic and therapeutic value.

Microgravity-Induced Alterations of Inflammation-Related Mechanotransduction in Endothelial Cells on Board SJ-10 Satellite

“…To assess if exposure of ECs to space microgravity has a significant impact on cell energy metabolism, we quantified the glucose ( Figure 3A ) and L -lactate ( Figure 3B ) concentrations from the cell culture supernatants. Compared with ground control, the glucose concentration increased additional 129% ( Figure 3A ) and the L -lactate concentration was reduced to 16% ( Figure 3B ) for EA.hy926 cells cultured for 3 days in space, implying a suppressed metabolism with lower glucose consumption and lactate production in agreement with previous study ( Chakraborty et al, 2018 ). The significant difference disappeared between the cells cultured for 10 days in space and on ground ( Figure 3 ), probably due to the slowed growth associated with contact inhibition in long-term space culture.…”

“…ECs are highly sensitive to mechanical forces such as fluid shear stress, cyclic tensile strain and substrate stiffness, and contribute to cardiovascular deconditioning and immune dysfunction faced by astronauts upon the removal of gravitational forces during spaceflight ( Byfield et al, 2009 ; Chancellor et al, 2010 ; Maier et al, 2015 ). Exposure to microgravity in space can induce the morphological and gene expression changes in ECs, displaying the heterogeneity of cell size and shape ( Kapitonova et al, 2012 ), three-dimensional growth ( Pietsch et al, 2017 ), energy and protein metabolism deficiency ( Chakraborty et al, 2018 ), significant suppression of genes associated with host defense ( Chakraborty et al, 2014 ), and alterations in genes involved in cell adhesion, oxidative phosphorylation, and stress responses ( Versari et al, 2013 ). To date, only a few relevant studies in space have been reported and the impact of real microgravity on EC functions is still unclear mainly due to the rareness and high costs of spaceflight missions.…”

Gene-Metabolite Network Linked to Inhibited Bioenergetics in Association With Spaceflight-Induced Loss of Male Mouse Quadriceps Muscle

“…Recent studies further linked spaceflight to immune deficiencies, metabolic syndrome, bioenergetics dysfunction, and vascular remodeling. (14)(15)(16)(17)(18) Each of these factors individually has shown detrimental effects on musculoskeletal health; in this perspective, this Rodent Research 4 (RR4) project presented us a unique opportunity to investigate the cumulative effects of all of these stress factors on muscle fitness. Our previous studies (11,19) showed that femoral and tibial trabecular bone volume was significantly reduced during spaceflight.…”

“…In either case, it is also notable that our data on the immune functions in spaceflight correlated well with previous works that have associated these immunodeficiencies to energy deprivation in space. (12,16,46) It is known that oxidative stress and inflammation have a negative impact on muscle health and contribute to sarcopenia, (45,46) and it has been speculated that to mitigate this damage, cells downregulate metabolism and immune functions that typically produce reactive oxygen species. (49) At the background of the rampant negative consequences of spaceflight on healthy rodent quadriceps, there are potentially certain mitigation strategies in effect, again vital information, namely the initiation time of these biofunctions, remained obscure.…”

microRNA and Metabolite Signatures Linked to Early Consequences of Lethal Radiation

“…Global metabolite mass spectroscopy assay. The metabolite profiling of serum samples was conducted as per the report published previously 32 . Here each sample (5 μL) was injected onto a reverse-phase 50 × 2.1 mm Acquity 1.7-μm C18 column (Waters Corp, Milford, MA) using an Acquity UPLC system (Waters) with a gradient mobile phase consisting of 2% acetonitrile in water containing 0.1% formic acid (Solvent A) and 2% water in acetonitrile containing 0.1% formic acid (Solvent B) and resolved for 10 min at a flow rate of 0.5 mL/min.…”