Simulated microgravity induces an inflammatory response in the common carotid artery of rats

Cardiovascular adaptations in microgravity conditions

Gravity has had a significant impact on the evolution of life on Earth with organisms developing necessary biological adaptations over billions of years to counter this ever-existing force. There has been an exponential increase in experiments using real and simulated gravity environments in the recent years. Although an understanding followed by discovery of counter measures to negate diminished gravity in space had been the driving force of research initially, there has since been a phenomenal leap wherein a force unearthly as microgravity is beginning to show promising potential. The current review summarizes pathophysiological changes that occur in multiple aspects of the cardiovascular system when exposed to an altered gravity environment leading to cardiovascular deconditioning and orthostatic intolerance. Gravity influences not just the complex multicellular systems but even the survival of organisms at the molecular level by intervening fundamental cellular processes, directly affecting those linked to actin and microtubule organization via mechano-transduction pathways. The reach of gravity ranges from cytoskeletal rearrangement that regulates cell adhesion and migration to intracellular dynamics that dictate cell fate commitment and differentiation. An understanding that microgravity itself is not present on Earth propels the scope of simulated gravity conditions to be a unique and useful environment that could be explored for enhancing the potential of stem cells for a wide range of applications as has been highlighted here.

The OPG/RANKL/RANK system modulates calcification of common carotid artery in simulated microgravity rats by regulating NF-κB pathway

Functional and structural adaptation of common carotid artery could be one of the important causes of postflight orthostatic intolerance after microgravity exposure, the mechanisms of which remain unclear. Recent evidence indicates that long-term spaceflight increases carotid artery stiffness, which might present a high risk to astronaut health and postflight working ability. Studies have suggested that vascular calcification is a common pathological change in cardiovascular diseases that is mainly manifested as an increase in vascular stiffness. Therefore, this study aimed to investigate whether simulated microgravity induces calcification of common carotid artery and to elucidate the underlying mechanisms. Four-week hindlimb-unweighted (HU) rats were used to simulate the deconditioning effects of microgravity on cardiovascular system. We found that simulated microgravity induced vascular smooth muscle cell (VSMC) osteogenic differentiation and medial calcification, increased receptor activator of nuclear factor κB ligand (RANKL) and RANK expression, and enhanced NF-κB activation in rat common carotid artery. In vitro activation of the RANK pathway with exogenous RANKL, a RANK ligand, increased RANK and osteoprotegerin (OPG) expression in HU rats. Moreover, the expression of osteogenic markers and activation of NF-κB in HU rats were further enhanced by exogenous RANKL but suppressed by the RANK inhibitor OPG-Fc. These results indicated that the OPG/RANKL/RANK system modulates VSMC osteogenic differentiation and medial calcification of common carotid artery in simulated microgravity rats by regulating NF-kB pathway.

Arterial structure and function during and after long-duration spaceflight

Spaceflight missions expose astronauts to increased risk of oxidative stress and inflammatory damage that might accelerate the development of asymptomatic cardiovascular disease. The purpose of this investigation was to determine whether long-duration spaceflight (>4 mo) results in structural and functional changes in the carotid and brachial arteries. Common carotid artery (CCA) intima-media thickness (cIMT), CCA distensibility and stiffness, and brachial artery endothelium-dependent and -independent vasodilation were measured in 13 astronauts (10 men, 3 women) ~180 and 60 days before launch, during the mission on ~15, 60, and 160 days of spaceflight, and within 1 wk after landing. Biomarkers of oxidative stress and inflammation were measured at corresponding times in fasting blood samples and urine samples from 24- or 48-h pools. Biomarkers of oxidative stress and inflammation increased during spaceflight, but most returned to preflight levels within 1 wk of landing. Mean cIMT, CCA stiffness, and distensibility were not significantly different from preflight at any time. As a group, neither mean endothelium-dependent nor -independent vasodilation changed from preflight to postflight, but changes within individuals in endothelial function related to some biomarkers of oxidative stress. Whereas biomarkers of oxidative stress and inflammation are elevated during spaceflight, CCA and brachial artery structure and function were not changed by spaceflight. It is unclear whether future exploration missions, with an extended duration in altered gravity fields and higher radiation exposure, may be problematic.NEW & NOTEWORTHY Carotid artery structure and stiffness did not change on average in astronauts during long-duration spaceflight (<12 mo), despite increased oxidative stress and inflammation. Most oxidative stress and inflammation biomarkers returned to preflight levels soon after landing. Brachial artery structure and function also were unchanged by spaceflight. In this group of healthy middle-aged male and female astronauts, spaceflight in low Earth orbit does not appear to increase long-term cardiovascular health risk.

The Impact of Spaceflight and Simulated Microgravity on Cell Adhesion

Microgravity induces a number of significant physiological changes in the cardiovascular, nervous, immune systems, as well as the bone tissue of astronauts. Changes in cell adhesion properties are one aspect affected during long-term spaceflights in mammalian cells. Cellular adhesion behaviors can be divided into cell-cell and cell-matrix adhesion. These behaviors trigger cell-cell recognition, conjugation, migration, cytoskeletal rearrangement, and signal transduction. Cellular adhesion molecule (CAM) is a general term for macromolecules that mediate the contact and binding between cells or between cells and the extracellular matrix (ECM). In this review, we summarize the four major classes of adhesion molecules that regulate cell adhesion, including integrins, immunoglobulin superfamily (Ig-SF), cadherins, and selectin. Moreover, we discuss the effects of spaceflight and simulated microgravity on the adhesion of endothelial cells, immune cells, tumor cells, stem cells, osteoblasts, muscle cells, and other types of cells. Further studies on the effects of microgravity on cell adhesion and the corresponding physiological behaviors may help increase the safety and improve the health of astronauts in space.

Acid sphingomyelinase/ceramide mediates structural remodeling of cerebral artery and small mesenteric artery in simulated weightless rats

AIMS

Weightlessness exposure conduces to substantial vascular remodeling, mechanisms behind which remain unclear. Acid sphingomyelinase (ASM) catalyzed ceramide (Cer) generation accounts for multiple vascular disorders, so the role of it in adjustment of cerebral artery (CA) and small mesenteric artery (MA) was investigated in simulated weightless rats.

MAIN METHODS

Rats were hindlimb unloaded tail suspended (HU) to simulate the effect of weightlessness. Arterial morphology was examined by hematoxylin-eosin staining. Cer abundance was measured by immunohistochemistry. Western blotting was used to detect protein content. Apoptosis was detected by transferase-mediated dUTP nick end labeling.

KEY FINDINGS

During 4 weeks of tail suspension, intima-media thickness (IMT) and media cross section area (CSA) were increased gradually in CA but decreased gradually in MA (P < 0.05). Correspondingly, the apoptosis and proliferation of vascular smooth muscle cells were reduced and enhanced respectively in CA (P < 0.05), while promoted and restrained in MA (P < 0.05). As compared to control, both ASM protein expression and Cer content were lowered in CA and elevated in MA of HU rats (P < 0.05). Permeable Cer incubation reversed the change of apoptosis and proliferation in CA of HU rats, while ASM inhibition recapitulated it in control rats. On the contrary, ASM inhibitors restored the alteration of apoptosis and proliferation in MA of HU.

SIGNIFICANCE

The results suggest that by controlling the balance between apoptosis and proliferation, ASM/Cer exerts an important role in structural adaptation of CA and MA to simulated weightlessness.

Reduction of Movement in Neurological Diseases: Effects on Neural Stem Cells Characteristics

Both astronauts and patients affected by chronic movement-limiting pathologies face impairment in muscle and/or brain performance. Increased patient survival expectations and the expected longer stays in space by astronauts may result in prolonged motor deprivation and consequent pathological effects. Severe movement limitation can influence not only the motor and metabolic systems but also the nervous system, altering neurogenesis and the interaction between motoneurons and muscle cells. Little information is yet available about the effect of prolonged muscle disuse on neural stem cells characteristics. Our in vitro study aims to fill this gap by focusing on the biological and molecular properties of neural stem cells (NSCs). Our analysis shows that NSCs derived from the SVZ of HU mice had shown a reduced proliferation capability and an altered cell cycle. Furthermore, NSCs obtained from HU animals present an incomplete differentiation/maturation. The overall results support the existence of a link between reduction of exercise and muscle disuse and metabolism in the brain and thus represent valuable new information that could clarify how circumstances such as the absence of load and the lack of movement that occurs in people with some neurological diseases, may affect the properties of NSCs and contribute to the negative manifestations of these conditions.

Focal adhesions are involved in simulated-microgravity-induced basilar and femoral arterial remodelling in rats

Recent studies have suggested that microgravity-induced arterial remodelling contributes to post-flight orthostatic intolerance and that multiple mechanisms are involved in arterial remodelling. However, the initial mechanism by which haemodynamic changes induce arterial remodelling is unknown. Focal adhesions (FAs) are dynamic protein complexes that have mechanotransduction properties. This study aimed to investigate the role of FAs in simulated-microgravity-induced basilar and femoral arterial remodelling. A 4-week hindlimb-unweighted (HU) rat model was used to simulate the effects of microgravity, and daily 1-hour intermittent artificial gravity (IAG) was used to prevent arterial remodelling. After 4-week HU, wall thickness, volume of smooth muscle cells (SMCs) and collagen content were increased in basilar artery but decreased in femoral artery (P < 0.05). Additionally, the expression of p-FAK Y397 and p-Src Y418 was increased and reduced in SMCs of basilar and femoral arteries, respectively, by HU (P < 0.05). The number of FAs was increased in basilar artery and reduced in femoral artery by HU (P < 0.05). Furthermore, daily 1-hour IAG prevented HU-induced differential structural adaptations and changes in FAs of basilar and femoral arteries. These results suggest that FAs may act as mechanosensors in arterial remodelling by initiating intracellular signal transduction in response to altered mechanical stress induced by microgravity.

miRNA-132-3p inhibits osteoblast differentiation by targeting Ep300 in simulated microgravity

Recent studies have demonstrated that miRNAs can play important roles in osteoblast differentiation and bone formation. However, the function of miRNAs in bone loss induced by microgravity remains unclear. In this study, we investigated the differentially expressed miRNAs in both the femur tissues of hindlimb unloading rats and primary rat osteoblasts (prOB) exposed to simulated microgravity. Specifically, miR-132-3p was found up-regulated and negatively correlated with osteoblast differentiation. Overexpression of miR-132-3p significantly inhibited prOB differentiation, whereas inhibition of miR-132-3p function yielded an opposite effect. Furthermore, silencing of miR-132-3p expression effectively attenuated the negative effects of simulated microgravity on prOB differentiation. Further experiments confirmed that E1A binding protein p300 (Ep300), a type of histone acetyltransferase important for Runx2 activity and stability, was a direct target of miR-132-3p. Up-regulation of miR-132-3p by simulated microgravity could inhibit osteoblast differentiation in part by decreasing Ep300 protein expression, which, in turn, resulted in suppression of the activity and acetylation of Runx2, a key regulatory factor of osteoblast differentiation. Taken together, our findings are the first to demonstrate that miR-132-3p can inhibit osteoblast differentiation and participate in the regulation of bone loss induced by simulated microgravity, suggesting a potential target for counteracting decreases in bone formation.