Ho Nguyen Quynh Chi, Hoang Nghia Son, Doan Chinh Chung, Le Dinh Huan, Tran Hong Diem, Le Thanh Long.
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The cytoskeleton plays a key role in cellular proliferation, cellshape ...maintenance and internal cellular organization. Cells are highly sensitive to changes in microgravity, which can induce alterations in the distribution of the cytoskeletal and cell proliferation. This study aimed to assess the effects of simulated microgravity (SMG) on the proliferation and expression of major cell cycle-related regulators and cytoskeletal proteins in human umbilical cord mesenchymal stem cells (hucMSCs). A WST-1 assay showed that the proliferation of SMG-exposed hucMSCs was lower than a control group. Furthermore, flow cytometry analysis demonstrated that the percentage of SMG-exposed hucMSCs in the G0/G1 phase was higher than the control group. A western blot analysis revealed there was a downregulation of cyclin A1 and A2 expression in SMG-exposed hucMSCs as well. The expression of cyclin-dependent kinase 4 (cdk4) and 6 (cdk6) were also observed to be reduced in the SMG-exposed hucMSCs. The total nuclear intensity of SMG-exposed hucMSCs was also lower than the control group. However, there were no differences in the nuclear area or nuclear-shape value of hucMSCs from the SMG and control groups. A western blot and quantitative RT-PCR analysis showed that SMG-exposed hucMSCs experienced a downregulation of β-actin and α-tubulin compared to the control group. SMG generated the reorganization of microtubules and microfilaments in hucMSCs. Our study supports the idea that the downregulation of major cell cycle-related proteins and cytoskeletal proteins results in the remodeling of the cytoskeleton and the proliferation of hucMSCs.
Exposure to actual or simulated weightlessness is known to induce orthostatic intolerance in humans. Many different methods have been suggested to counteract orthostatic hypotension. The repetitive ...or prolonged application of lower body negative pressure (LBNP) has shown beneficial effects to counter orthostatic intolerance, but devoting so much time to countermeasures is not compatible with space mission objectives or costs. The purpose of the present study was to assess the effects of brief LBNP sessions against orthostatic intolerance during a 21-d head-down tilt (HDT) bed rest.
There were 12 healthy male volunteers who were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mm Hg LBNP sessions for 1 h x d(-1) from day 15 to day 21 of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test.
Before HDT, all the subjects in the two groups completed the tilt tests. After 21 d of HDT, five subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean upright time in the control group 13.0 +/- 4.0 min) was significantly shorter (p < 0.05) than that in the LBNP group (19.0 +/- 2.2 min). Body weight decreased significantly in the control group during HDT, while increasing significantly on day 21 of HDT in the LBNP group. Urine volume increased on days 15-21 of HDT in the control group, but remained unchanged throughout HDT in the LBNP group. A significant decrease in cardiac output and cardiac index, and a significant increase in total peripheral resistance, pre-ejection period, plasma renin activity, aldosterone, and prostaglandin 12 were observed during HDT in both groups. There were no significant differences in these parameters between the two groups.
Brief daily LBNP sessions were effective in preventing orthostatic intolerance induced by 21 d HDT bed rest. However, it did not improve cardiac pump and systolic functions and did not preserve volume regulating hormones.
Alterations in autonomic function are commonly seen during and after spaceflight, and its ground-based analog, 6 degrees head-down bed rest (HDBR). They may include peripheral vascular regulation, ...but vasomotor sympathetic efferent nerve discharges to peripheral vasculatures have not been examined. The aim of our study was to examine changes in vasomotor sympathetic nerve activity during HDBR and under orthostasis after HDBR.
We performed 6 d of HDBR on six male subjects, and measured muscle sympathetic nerve activity (MSNA) together with plasma norepinephrine concentrations in the supine position before HDBR and in 6 degrees head-down position on the sixth day (HDBR6) of HDBR. We also measured MSNA in head-up tilt (HUT) test before and after HDBR.
On HDBR6, MSNA burst rate was the same (17+/-4 bursts x min(-1)) as that in supine position before HDBR (15+/-2 bursts min(-1)), but plasma norepinephrine concentrations were decreased to 1.14+/-0.10 pmol x ml(-1) compared with the supine value before HDBR (1.56+/-0.20 pmol x ml(-1), p<0.05). After HDBR, supine MSNA burst rate significantly increased by 58% to 24+/-4 bursts x min(-1). MSNA increment in response to HUT was similar between before (34+/-3 bursts min(-1) x sin HUT(-1)) and after (40+/-6 bursts x min(-1) x sin HUT(-1)) HDBR.
Our findings suggest that: a) the relationship between MSNA and plasma norepinephrine concentrations was altered on the sixth day during HDBR; b) the vasomotor sympathetic nerve activity was enhanced after HDBR; and c) the augmentation of vasomotor sympathetic outflow to muscles under orthostasis was preserved after HDBR.
