Protein nitration increased by simulated weightlessness and decreased by melatonin and quercetin in PC12 cells

Formaldehyde initiates memory and motor impairments under weightlessness condition

During space flight, prolonged weightlessness stress exerts a range of detrimental impacts on the physiology and psychology of astronauts. These manifestations encompass depressive symptoms, anxiety, and impairments in both short-term memory and motor functions, albeit the precise underlying mechanisms remain elusive. Recent studies have revealed that hindlimb unloading (HU) animal models, which simulate space weightlessness, exhibited a disorder in memory and motor function associated with endogenous formaldehyde (FA) accumulation in the hippocampus and cerebellum, disruption of brain extracellular space (ECS), and blockage of interstitial fluid (ISF) drainage. Notably, the impairment of the blood-brain barrier (BBB) caused by space weightlessness elicits the infiltration of albumin and hemoglobin from the blood vessels into the brain ECS. However, excessive FA has the potential to form cross-links between these two proteins and amyloid-beta (Aβ), thereby obstructing ECS and inducing neuron death. Moreover, FA can inhibit N-methyl-D-aspartate (NMDA) currents by crosslinking NR1 and NR2B subunits, thus impairing memory. Additionally, FA has the ability to modulate the levels of certain microRNAs (miRNAs) such as miRNA-29b, which can affect the expression of aquaporin-4 (AQP4) so as to regulate ECS structure and ISF drainage. Especially, the accumulation of FA may inactivate the ataxia telangiectasia-mutated (ATM) protein kinase by forming cross-linking, a process that is associated with ataxia. Hence, this review presents that weightlessness stress-derived FA may potentially serve as a crucial catalyst in the deterioration of memory and motor abilities in the context of microgravity.

Melatonin Suppresses Autophagy Induced by Clinostat in Preosteoblast MC3T3-E1 Cells

Microgravity exposure can cause cardiovascular and immune disorders, muscle atrophy, osteoporosis, and loss of blood and plasma volume. A clinostat device is an effective ground-based tool for simulating microgravity. This study investigated how melatonin suppresses autophagy caused by simulated microgravity in preosteoblast MC3T3-E1 cells. In preosteoblast MC3T3-E1 cells, clinostat rotation induced a significant time-dependent increase in the levels of the autophagosomal marker microtubule-associated protein light chain (LC3), suggesting that autophagy is induced by clinostat rotation in these cells. Melatonin treatment (100, 200 nM) significantly attenuated the clinostat-induced increases in LC3 II protein, and immunofluorescence staining revealed decreased levels of both LC3 and lysosomal-associated membrane protein 2 (Lamp2), indicating a decrease in autophagosomes. The levels of phosphorylation of mammalian target of rapamycin (p-mTOR) (Ser2448), phosphorylation of extracellular signal-regulated kinase (p-ERK), and phosphorylation of serine-threonine protein kinase (p-Akt) (Ser473) were significantly reduced by clinostat rotation. However, their expression levels were significantly recovered by melatonin treatment. Also, expression of the Bcl-2, truncated Bid, Cu/Zn- superoxide dismutase (SOD), and Mn-SOD proteins were significantly increased by melatonin treatment, whereas levels of Bax and catalase were decreased. The endoplasmic reticulum (ER) stress marker GRP78/BiP, IRE1α, and p-PERK proteins were significantly reduced by melatonin treatment. Treatment with the competitive melatonin receptor antagonist luzindole blocked melatonin-induced decreases in LC3 II levels. These results demonstrate that melatonin suppresses clinostat-induced autophagy through increasing the phosphorylation of the ERK/Akt/mTOR proteins. Consequently, melatonin appears to be a potential therapeutic agent for regulating microgravity-related bone loss or osteoporosis.

Comparative proteomic analysis of human SH-SY5Y neuroblastoma cells under simulated microgravity

Microgravity is one of the most important features in spaceflight. Previous evidence has shown that neurophysiological impairment signs occurred under microgravity. The present study was undertaken to explore the change in protein abundance in human SH-SY5Y neuroblastoma cells that were grown in a microgravity environment. The comparative proteomic method based on the (18)O labeling technique was applied to investigate the up-regulated proteins and down-regulated proteins in SH-SY5Y under simulated microgravity. Twenty-two differentially abundant proteins were quantified in human SH-SY5Y neuroblastoma cells. The cell microfilament network was disrupted under simulated microgravity, which was determined by the immunocytochemistry. The concentration of reactive oxygen species, malondialdehyde, and free Ca2+ ion significantly increased, and the level of ATP significantly decreased under simulated microgravity. However, there was no obvious cell apoptosis observed under simulated microgravity. These results provide new molecular evidence for the change in protein abundance in SH-SY5Y cells under simulated microgravity, which might unfold biological mechanisms and the development of effective countermeasures to deal with microgravity-related neurological problems. We believe that the state-of-the-art proteomic assay may be a means by which aerospace scientists will begin to understand the underlying mechanisms of space life activities at the protein level.

Protein pattern of Xenopus laevis embryos grown in simulated microgravity

Numerous studies indicate that microgravity affects cell growth and differentiation in many living organisms, and various processes are modified when cells are placed under conditions of weightlessness. However, until now, there is no coherent explanation for these observations, and little information is available concerning the biomolecules involved. Our aim has been to investigate the protein pattern of Xenopus laevis embryos exposed to simulated microgravity during the first 6 days of development. A proteomic approach was applied to compare the protein profiles of Xenopus embryos developed in simulated microgravity and in normal conditions. Attention was focused on embryos that do not present visible malformations in order to investigate if weightlessness has effects at protein level in the absence of macroscopic alterations. The data presented strongly suggest that some of the major components of the cytoskeleton vary in such conditions. Three major findings are described for the first time: (i) the expression of important factors involved in the organization and stabilization of the cytoskeleton, such as Arp (actin-related protein) 3 and stathmin, is heavily affected by microgravity; (ii) the amount of the two major cytoskeletal proteins, actin and tubulin, do not change in such conditions; however, (iii) an increase in the tyrosine nitration of these two proteins can be detected. The data suggest that, in the absence of morphological alterations, simulated microgravity affects the intracellular movement system of cells by altering cytoskeletal proteins heavily involved in the regulation of cytoskeleton remodelling.

Protective effects of flavonoids against oxidative stress induced by simulated microgravity in SH-SY5Y cells

Many lines of evidence suggest that microgravity results in increased oxidative stress in the nervous system. In order to protect neuronal cells from oxidative damage induced by microgravity, we selected some flavonoids that might prevent oxidative stress because of their antioxidant activities. Among the 20 flavonoids we examined, we found that isorhamnetin and luteolin had the best protective effects against H(2)O(2) or SIN-1-induced cytotoxicity in SH-SY5Y cells. Using a clinostat to simulate microgravity, we found that isorhamnetin and luteolin treatment protected SH-SY5Y cells by preventing microgravity-induced increases in reactive oxygen species (ROS), nitric oxide (NO) and 3-nitrotyrosine (3-NT) levels, and a decrease in antioxidant power (AP). Moreover, isorhamnetin and luteolin treatment downregulated the expression of inducible nitric oxide synthase (iNOS), and oxidative stress was significantly inhibited by an iNOS inhibitor in SH-SY5Y cells exposed to simulated microgravity (SMG). These results indicate that isorhamnetin and luteolin could protect against microgravity-induced oxidative stress in neuroblastoma SH-SY5Y cells by inhibiting the ROS-NO pathway. These two flavonoids may have potential for preventing oxidative stress induced by space flight or microgravity.

Simulated microgravity promotes cellular senescence via oxidant stress in rat PC12 cells

Microgravity has a unique effect on biological organisms. Organs exposed to microgravity display cellular senescence, a change that resembles the aging process. To directly investigate the influence of simulated microgravity on neuronal original rat PC12 cells, we used a rotary cell culture system that simulates the microgravity environment on the earth. We found that simulated microgravity induced partial G1 phase arrest, upregulated senescence-associated beta-galactosidase (SA-beta-gal) activity, and activated both p53 and p16 protein pathways linked to cell senescence. The amount of reactive oxygen species (ROS) was also increased. The activity of intracellular antioxidant enzymes, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), was all significantly increased at 12h after the microgravity onset, yet decreased at 96h. Furthermore, concomitant block of ROS by the antioxidant N-acetylcysteine significantly inhibited the microgravity-induced upregulation of SA-beta-gal activity. These results suggest that exposure to simulated microgravity induces cellular senescence in PC12 cells via an increased oxidant stress.

Polyphenols prevent clinorotation-induced expression of atrogenes in mouse C2C12 skeletal myotubes

Oxidative stress is a key factor in stimulating the expression of atrogenes, which are muscle atrophy-related ubiquitin ligases, in skeletal muscle, and it induces muscle atrophy during unloading. However, the effects of antioxidative nutrients on atrogene expression have not been demonstrated. We report on the inhibitory effects of polyphenols, such as epicatechin (EC), epicatechin gallate (ECg) and epigallocatechin gallate (EGCg) and quercetin, on atrogene expression up-regulated by three dimensional (3D)-clinorotation or glucocorticoid. These treatments markedly elevated the expression of atrogenes, including atrogin-1 and MuRF-1, in mouse C2C12 myoblasts and myotubes. Interestingly, EC, ECg, EGCg and quercetin significantly decreased the expression of atrogin-1 and MuRF-1 up-regulated by 3D-clinorotation, whereas they hardly affected atrogene expression induced by dexamethasone. ERK signaling is a well known MAPK pathway to mediate oxidative stress. Therefore, we also investigated the effect of these polyphenols on phosphorylation of ERK in C2C12 myotubes. As expected, EC, ECg, EGCg, and quercetin significantly suppressed phosphorylation of ERK, corresponding to the up-regulation of atrogenes induced by 3D-clinorotation. These results suggest that antioxidative nutrients, such as catechins and quercetin, suppress atrogene expression in skeletal muscle cells, possibly through the inhibition of ERK signaling. Thus, catechins and quercetin may prevent unloading-mediated muscle atrophy.

Brain development, environment and sex: what can we learn from studying graviperception, gravitransduction and the gravireaction of the developing CNS to altered gravity?

As man embarks on space exploration and contemplates space habitation, there is a critical need for basic understanding of the impact of the environmental factors of space, and in particular gravity, on human survival, health, reproduction and development. This review summarizes our present knowledge on the effect of altered gravity on the developing CNS with respect to the response of the developing CNS to altered gravity (gravireaction), the physiological changes associated with altered gravity that could contribute to this effect (gravitransduction), and the possible mechanisms involved in the detection of altered gravity (graviperception). Some of these findings transcend gravitational research and are relevant to our understanding of the impact of environmental factors on CNS development on Earth.

Potential Role of Oxidative Stress in Mediating the Effect of Altered Gravity on the Developing Rat Cerebellum

We have previously reported that perinatal exposure to hypergravity affects cerebellar structure and motor coordination in rat neonates. In the present study, we explored the hypothesis that exposure to hypergravity results in oxidative stress that may contribute to the decrease in Purkinje cell number and the impairment of motor coordination in hypergravity-exposed rat neonates. To test this hypothesis we compared cerebellar oxidative stress marker 3-nitrotyrosine (3-NT; an index of oxidative protein modification) and 8-hydroxy-2'-deoxyguanosine (8-OH-dG; an index of oxidative DNA damage) between stationary control (SC) and rat neonates exposed to 1.65 G (HG) on a 24-ft centrifuge from gestational day (G) 8 to P21. The levels of 3-NT and 8-OH-dG were determined by specific ELISAs. We also compared the Purkinje cell number (stereorologically) and rotarod performance between the two groups. The levels of 3-NT were increased only in HG females on P6 and on P12 in the cerebellum, and only in HG females on P12 in the extracellabellar tissue. Limited cerebellar data suggests an increase in the levels of 8-OH-dG on P12 only in HG females. In extracerebellar tissue the increase in 8-OH-dG levels was observed in both HG males and HG females except on P6 when it was only observed in HG males. While preliminary, these data suggest that the effect of hypergravity on the developing brain is sex-dependent and may involve oxidative stress. Oxidative stress may, in turn, contribute to the decrease Purkinje cell number and impaired motor behavior observed in hypergravity-exposed rats.