| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Institut des Neurosciences, Centre National de la Recherche Scientifique UMR 7624, Université Pierre et Marie Curie-Paris VI, Paris, France 75252; 2 Ames Research Center, National Aeronautics and Space Administration, Moffett Field, California 95034; 3 Centre National d'Etudes Spatiales (French Space Agency), Direction des Programmes, Paris, France 75001; and 4 Cardiovascular Research Institute, University of California, San Francisco, California 94143
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Aquaporin-1 (AQP1) is a water channel expressed abundantly at the apical pole of choroidal epithelial cells. The protein expression was quantified by immunocytochemistry and confocal microscopy in adult rats adapted to altered gravity. AQP1 expression was decreased by 64% at the apical pole of choroidal cells in rats dissected 5.5-8 h after a 14-day spaceflight. AQP1 was significantly overexpressed in rats readapted for 2 days to Earth's gravity after an 11-day flight (48% overshoot, when compared with the value measured in control rats). In a ground-based model that simulates some effects of weightlessness and alters choroidal structures and functions, apical AQP1 expression was reduced by 44% in choroid plexus from rats suspended head down for 14 days and by 69% in rats suspended for 28 days. Apical AQP1 was rapidly enhanced in choroid plexus of rats dissected 6 h after a 14-day suspension (57% overshoot, in comparison with control rats) and restored to the control level when rats were dissected 2 days after the end of a 14-day suspension. Decreases in the apical expression of choroidal AQP1 were also noted in rats adapted to hypergravity in the NASA 24-ft centrifuge: AQP1 expression was reduced by 47% and 85% in rats adapted for 14 days to 2 G and 3 G, respectively. AQP1 is downregulated in the apical membrane of choroidal cells in response to altered gravity and is rapidly restored after readaptation to normal gravity. This suggests that water transport, which is partly involved in the choroidal production of cerebrospinal fluid, might be decreased during spaceflight and after chronic hypergravity.
water transport; cerebrospinal fluid; spaceflight; hindlimb suspension; hypergravity; immunocytochemistry
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
THE CEREBROSPINAL FLUID (CSF) is mainly secreted by the choroid plexus, the circumventricular organ found in lateral, third, and fourth ventricles that produces up to 90% of the ventricular CSF (23). We recently showed alterations in the organization of microvilli and the distribution of ezrin in choroidal epithelial cells from 1) rats after 14 days in the space shuttle, during the Space Life Sciences-2 (SLS-2) experiments; 2) rats flown in space for 11 days and dissected after 2 days of readaptation to earth gravity during the National Institutes of Health-Rodent 1 (NIH-R1) experiments; and 3) hindlimb-suspended rats, maintained for 14 days under antiorthostatic restraint, an experimental condition known to simulate several effects of weightlessness (18). Thus spaceflight (SLS-2 experiments) or hindlimb suspension [head-down tilt (HDT) experiments] induced major alterations in the choroidal cell polarity, suggesting that a reduced production of CSF could be an adaptative response to simulated or actual weightlessness (5, 8).
Physiological processes mediating CSF production and reabsorption and water metabolism are regulated (23). Water channel aquaporin-1 (AQP1), isolated from erythrocyte membranes (2, 5a, 26), has been proposed to be the major water-transporting protein in the choroid plexus, involved in the CSF production (4, 11, 14, 19, 22, 31), together with proteins generating the necessary ionic gradients (7, 16, 23). Indeed, its specific distribution at the apical pole of the choroidal cells, but not elsewhere in the brain, and its colocalization with Na-K-ATPase (16) suggest involvement in CSF secretion.
To further investigate the choroidal effects of the altered gravity, we studied the expression of AQP1 protein in rats adapted to spaceflight, head-down suspension, and centrifugation. Fluorescence immunocytochemistry, confocal microscopy, and image analysis were used to quantify AQP1 in the choroid plexus of adult rats flown for 11-14 days aboard a space shuttle and dissected either 5.5-8 h (14 days in space, SLS-2 experiments) or 2 days after landing, with longer readaptation to Earth's gravity (11 days in space, NIH-R1 experiments). We compared these observations with data obtained from head-down suspended rats, dissected immediately after 14 or 28 days of antiorthostatic restraint. To test the effects of delayed postflight dissections, which generally begin 3-8 h after landing, we also studied choroid plexus of rats dissected 6 h after return to the orthostatic position. Lastly, AQP1 was studied in choroid plexus from rats maintained for 14 days in a hypergravity environment (2 G or 3 G), in the National Aeronautics and Space Administration (NASA) 24-ft centrifuge located at Ames Research Center (Moffett Field, CA).
| |
MATERIALS AND METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Animals
Sprague-Dawley-derived rats (Rattus norvegicus, Taconic Farms, NY, Simonsen, CA, or Centre d'Elevage Dépré, France) were used for spaceflight (SLS-2 or NIH-R1 experiments), centrifugation (hypergravity; HG), or HDT experiments. All SLS-2, NIH-R1, and HG experimental protocols were reviewed and approved by the Ames Research Center Animal Care and Use Committee. HDT protocols were approved by the ad hoc Committee of the French Space Agency. Animal care and use were in accordance with the guidelines of the National Institutes of Health (Bethesda, MD). The present study used 20 SLS-2 males and 24 NIH-R1 pregnant females, previously studied for the expression of carbonic anhydrase II and ezrin after spaceflight (5), 18 HG males, and 40 ground-based HDT males (Table 1). The rats were ~2 mo old, weighing 200-250 g at the beginning of the experimental protocols and 300-350 g at dissection, except for 2 G and 3 G animals, which were still in the 225-280 g range.
|
Orbital flight protocols and controls. Flight rats (F animals) were housed in the shuttle according to flight-specific protocols. SLS-2 rats were housed singly in cages in the Research Animal Holding Facility of the SpaceLab designed for flight from 2 days before launch until the end of the experiment (for details, see Ref. 8). The NIH-R1 rats were housed five each in two Animal Enclosure Modules, placed in lockers in the middeck of the shuttle (5). All flight and control rats were maintained with a 12:12-h light-dark cycle, 25-70% of relative humidity and at 24-26°C. They received water and flight food-bar diet ad libitum.
The SLS-2 flight nominal group (F1) was derived from a pool of rats that were launched into orbit from Kennedy Space Center (KSC) on October 18, 1993, aboard the Space Transportation System (STS) 58 mission, flew for a 14-day spaceflight, and were dissected during the Biospecimen Sharing Program (5) 5.5-8 h after the shuttle landing at Edwards Air Force Base, California. Pregnant females from the NIH-R1 flight nominal group (F2), launched into orbit from KSC on November 3, 1994, aboard the STS 66 mission, flew for an 11-day spaceflight (day 9 to day 20 of gestation). Brains were dissected at Edwards Air Force Base on day 22 of gestation, 2 days after landing, just after natural delivery of living pups, which were studied in accordance with the protocol selected by NIH and NASA (17). Several groups of ground control rats were compared with experimental animals (Table 1). SLS-2 and NIH-R1 synchronous ground controls were housed in cages similar to those designed for the flights. For these controls, temperature and humidity profiles were replicated, taking into account the values registered aboard the shuttle. Noise, acceleration, and vibration profiles were not reproduced. In addition, other control rats (vivarium controls) were maintained in polycarbonate vivarium cages and dissected at KSC on the day of the launch, during the SLS-2 operations, or at the same time as the synchronous control animals, during the NIH-R1 operations (Table 1).Ground-based models for simulation of weightlessness. The Morey-Holton tail-suspension model (18) was used with an antiorthostatic angle of 30-45°. These HDT experiments were performed as previously described (8). Briefly, male rodents were maintained in three successive adaptive periods: first, a 7-day habituation period in polycarbonate cages; second, a 7-day period in suspension cages, with the suspension device attached on the tail but with the rats maintained in a typical orthostatic position, for habituation to the suspension device; and third, in suspension cages, for an antiorthostatic tilt induced by lifting up the hindlimb of the rats, for 14 or 28 additional days.
Thirty-one HDT rats were assigned to four experimental groups (Table 1): 1) rats dissected directly after a 14-day suspension (S1); 2) rats dissected directly after a 28-day suspension (S2); 3) rats suspended for 14 days and dissected after a 6-h return to an orthostatic position (S3) to reproduce the conditions of the SLS-2 Biospecimen Sharing Program; and 4) rats suspended for 14 days and dissected after a 2-day return to an orthostatic position (S4) to reproduce the conditions of the NIH-R1 Biospecimen Sharing Program. A fifth group was composed of control rats dissected after 28 or 42 days in polycarbonate cages, without head-down tilt, to be compared with the 14-day or 28-day head-down suspended rats.Ground-based model for simulation of HG. HG was simulated by using the animal model previously described for administration of 2-G and 3-G forces (32). Briefly, increased gravitational forces were obtained by centrifugation (rotation speed of 25 rotations/min) with the 24-ft centrifuge located at the NASA Gravitational Facility at Ames Research Center. For the present study, 18 HG male rodents were maintained for 14 days in three different positions (Table 1): 1) six rats receiving 2-G forces (2-G rats) were housed in swinging cages located on centrifuge arms, at 7.5 ft from the center; 2) six rats receiving 3-G forces (3-G rats) were similarly housed on the centrifuge arms, but at 12.5 ft from the center; 3) six control rats were housed in polycarbonate vivarium cages located in the centrifuge room, in the same conditions of temperature, humidity, noise, and light cycle. In this experiment, the gravity vector was applied perpendicularly (Gz) to the bottom of the cages. Animals were dissected immediately after the 14-day centrifugation.
Dissection and Fixation Procedures
Brains from the different groups of rodents (F, HDT, HG, or ground control animals) were excised after decapitation of anesthetized (SLS-2, NIH-R1, HDT experiments; for details, see Ref. 5) or nonanesthetized rats (HG experiments). Brains of SLS-2, NIH-R1, HG, and HDT rats (Table 1) were fixed in whole by immersion in Bouin's fixative solution (Sigma, St. Louis, MO) overnight as previously described (5, 8). To evaluate the effects of this protocol on choroidal structures, nine rats (two S1, two S2, two S3, one S4, and two HDT control rats) were perfused intracardially with Bouin's, after anesthesia, to compare these brains with immersion-fixed brains and to observe the effects of fixative protocols on the AQP1 distribution. A comparison was also performed with 4% formaldehyde-perfused brains from control rats, in the conditions described by Hasegawa and co-workers (10).In addition, isolated choroid plexuses from SLS-2, NIH-R1, HG, and HDT animals (Table 1) were fixed in 3% formaldehyde freshly prepared from paraformaldehyde powder in PBS (PBS tablets, Sigma). Small fragments of choroidal tissue were infused in buffered 1.2 M sucrose and frozen.
Immunocytochemical Distribution of AQP1
After being washed in tap water, Bouin's-fixed brains were dehydrated with a progressive ethanol series, incubated in butanol for 16 h, and embedded within Paraplast Plus (Sigma). Sections (5-10 µm) containing choroid plexuses from the lateral, third, and fourth ventricles were selected by using a stereotaxic atlas. After removal of Paraplast in xylene baths, sections were incubated with anti-AQP1 antibodies (11), using immunofluorescence (for details, see Ref. 8).Thin-frozen sections (200-300 nm) of choroidal tissues were
prepared at 
75°C by use of a Reichert Ultracut with FC4
cryoequipment, put on polylysine-coated glass slides, and immunostained
according to Tokuyasu's method, as previously described for choroidal
tissues (25). Briefly, frozen sections attached to glass slides were postfixed in 3% formaldehyde in PBS, thoroughly washed in PBS containing 50 mM NH4Cl, and incubated overnight at 4 or
20°C with specific antibodies diluted 1:1,000 in PBS containing
0.2% gelatin and 1% normal goat serum. After thorough washing and
incubation with secondary fluorescein- or rhodamine-labeled antibodies,
sections were washed and mounted in Moviol 4.88 (Calbiochem, La Jolla, CA). Immunoreactions were observed with a Zeiss epifluorescence microscope, using ×25 and ×40 Plan-apochromat objectives
and interference filters. Seven-micrometer-thick sections were
analyzed with Bio-Rad or Leica argon-krypton laser scan
confocal microscopes.
Quantitative Image Analysis
Digital images (pixel size x, y = 0.50 µm; pixel size z = 0.95 µm) were obtained by confocal microscopy in controlled conditions with the Leica TCS 4D microscope. Images used for the quantification corresponded to the maximal projection (~7 µm) of a series of eight focal plans. Data were analyzed using the Adobe Photoshop 4.0 program: fluorescent areas were quantified by comparing, for each digital image, the choroidal total surface (ChT) and the anti-AQP1-labeled area (AQP1'), and calculating the ratio AQP1'/ChT. ChT was obtained by subtracting the areas occupied by the nonchoroidal tissues from the whole image surface. AQP1' was measured after threshold at the pixel value that corresponded to the negative immunoreactive choroidal cytoplasm.Calculated values of the ratio AQP1'/ChT are expressed as means ± SE and were statistically analyzed. Values from experimental groups were compared with control groups, by using the SigmaStat program and Mann-Whitney's nonparametric U tests. Significance was taken as P < 0.05. Values obtained for control rats were taken as equivalent to 100 measuring units (MU) of anti-AQP1 labeling and percentages of increase or decrease were expressed for each experimental group by comparison with control rats.
| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
AQP1 in Choroid Plexus of Control Rats
As expected, AQP1 was abundantly identified at the apical pole of choroidal cells, as a large and regular margin, in all groups of control rats (Fig. 1). Vivarium and synchronous control rats from the SLS-2 and NIH-R1 experiments as well as control rats from HDT and HG experiments showed similar labeling. Choroid plexuses fixed in either Bouin's or formaldehyde solutions, under perfusion or immersion protocols, provided similar positive reactions. In all conditions, the protein was asymmetrically distributed in the apical membrane domain, and the fluorescent labeling was intense, homogenous, and coincident with the microvilli profiles (Fig. 1a). No differences were noted between the AQP1 distribution in choroidal cells from the lateral, third, or fourth ventricles of control rats (Figs. 1, b-d). Variation between the different control groups was not significant, and it was decided to establish a single control value for the ratio AQP1'/ChT, which was 25.5 ± 1.7 (see Fig. 5). This value was taken as the 100-MU level of labeling for all experiments.
|
AQP1 in Choroid Plexus of SLS-2 Rats
A strongly reduced labeling with anti-AQP1 antibodies (Fig. 2, a-c; see also Fig. 5) was observed in choroidal cells from F1 rats space flown for 14 days aboard the space shuttle within the framework of the SLS-2 experiments and dissected 5.5-8 h after landing. It was clear that the distribution of the water channel in the apical membrane domain was altered after adaptation to spaceflight. In this group, AQP1'/ChT was dramatically lowered to 9.2 ± 0.9, reflecting a significant decrease by 64% when compared with the control rats (P = 0.002).
|
AQP1 in Choroid Plexus of NIH-R1 Pregnant Rats
An intense immunoreaction (Fig. 2, d-f; see also Fig. 5) was observed at the apical pole of every choroidal cell from F2 pregnant dams (space flown for 11 days aboard the space shuttle), which were dissected 2 days after landing, just after natural delivery (NIH-R1 experiments). AQP1'/ChT was elevated to 37.8 ± 4.5, reflecting a significant overshoot of 148 MU when compared with the level measured in control rats (P = 0.04). This increased labeling was not observed in choroid plexus of similarly delivered control dams, which displayed immunoreactions similar to those described for male control rats. This indicated that readaptation to Earth's gravity was accompanied by the restoration of an important insertion of the water channel AQP1 in the apical membrane domain.AQP1 in Choroid Plexus of HDT Rats
The comparison of the AQP1 distribution in choroidal cells from F1 rats with that of rats maintained under antiorthostatic restraint simulating weightlessness for 14 days allowed us to note a strong reduction in the apical distribution of the protein, in particular in the choroidal cells from the lateral (Fig. 3a) and third ventricles (not shown). The reduction was less apparent in choroid plexus from the fourth ventricle (Fig. 3b). This was more obvious in choroidal cells of rats exposed for 28 days to the same conditions (Fig. 3, c and d; see also Fig. 5). Very little immunoreactivity was observed under this condition, which showed a long-term downregulation of water channels in choroid plexus of rats adapted to head-down suspension. In these groups, AQP1'/ChT was significantly lowered to 14.2 ± 2.2 in S1 rats, choroid plexus from all ventricles being considered for the calculation, and to 7.9 ± 1.5 in S2 rats, respectively. The percentages of labeled surfaces were significantly decreased by 44% (P = 0.004) and 69% (P = 0.001) when compared with the control rats.
|
Because biological samples were always dissected with delays after landing of the spacecraft during space experiments, we decided to compare AQP1 distribution in brains of rats dissected either just after 14 days of hindlimb-suspension (S1), or 6 h (S3, to be compared with SLS-2 rats) or 2 days (S4, to be compared with NIH-R1 rats) after the 14 days in antiorthostatic suspension. We noted a strong restoration of the apical distribution of the protein in choroid plexuses of S3 rats, which was clearly more intense than that observed in SLS-2 rats dissected 5.5-8 h after spaceflight or in S2 rats (compare Figs. 2, a-c and 3, e and f; see also Fig. 5). The intensity of the reaction was quite similar to that found in NIH-R1 dams dissected 2 days after landing (compare Figs. 2, d-f and 3, e and f; see also Fig. 5). AQP1'/ChT was also clearly elevated to 39.9 ± 1.7, representing a significant increase (i.e., a 57% overshoot, when compared with the control rats, P = 0.002). In contrast, when the AQP1 expression was tested in choroid plexus of S4 rats (see Fig. 5), the intensity of the immunoreaction returned to a value that was quite similar to that observed in control rats (AQP1'/ChT in S4 = 21.7 ± 0.8, nonsignificantly different from the control value, P > 0.5).
This finding suggested that AQP1 protein expression might be more quickly restored after hindlimb suspension than after spaceflight. However, it is noteworthy that, in both spaceflight and head-down suspension, the strong decrease in AQP1 was followed by a clear reappearance of the molecule in the apical membrane, when animals returned to normal gravity or position.
AQP1 in Choroid Plexus of HG Rats
Choroidal AQP1 was similarly reduced at the apical pole in epithelial cells from rats loaded for 14 days aboard cages fastened to the arms of the Ames Research Center 24-ft centrifuge, and it was clear that the highest Gz level induced the highest decrease in the AQP1 distribution in choroidal cells (Figs. 4 and 5). AQP1'/ChT was clearly lowered to 13.5 ± 1.8 in 2-G rats and to 3.7 ± 0.9 in 3-G rats. The percentages of labeled areas were also significantly decreased by 47% (P = 0.002) and 85% (P = 0.01) when compared with the control rats. These observations suggest that adaptation to hypergravity impacted the choroidal AQP1 distribution as drastically as adaptations to actual or simulated weightlessness.
|
|
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The apical distribution of AQP1 found in controls is in accordance with the results of Nielsen et al. (19) and Hasegawa et al. (10, 11). This distribution pattern suggests that water fluxes from the choroidal cells to the ventricular CSF compartment involve AQP1 in the apical membrane of choroid plexus. It was found in the present study that altered gravity decreased choroidal AQP1 expression. Spaceflight and head-down suspension, as well as hypergravity, reduced the apical expression of AQP1, whereas readaptation to Earth's gravity (2 days) or to the orthostatic position (as soon as 6 h) strongly restored AQP1 at the apical pole of the choroidal cells.
During a spaceflight, one of the earliest effects of microgravity is the cephalad body fluid shift and redistribution toward the thoracocephalic region. In addition, symptoms such as headache, nasal stuffiness, or sense of fullness in the head are frequently encountered by astronauts during motion sickness in space. Some of these symptoms are thought to be related to volume changes in the CSF compartment (7) and could be consequences of microgravitational adaptations of cerebral fluids (9, 28). Thus we reasoned that it was important to consider the effects of altered gravity on the CSF compartment and the responses of choroidal structures involved in the CSF secretion.
The choroidal effects of actual or simulated microgravity are not well understood. As mentioned above, alterations have been reported in the fine structure of choroid plexus dissected from rats undergoing spaceflight or head-down suspension (5, 8). Partial losses of microvilli, accompanied by decreases in apical ezrin and partial loss of cell polarity, have shown that the apical membrane and cytoskeleton were strongly impaired by a life at near-zero gravity. Accumulations of apical vesicles and a decrease in cytoplasmic carbonic anhydrase II contents also suggested that the choroidal CSF production might be lowered.
Ionic and water transport implicated in CSF production are regulated by mechanisms involving several hormones and enzyme effectors. Natriuretic peptides (NP) and arginine vasopressin (AVP) are involved in the regulation of choroidal CSF production (for a review, see Ref. 23). However, AQP1-dependent water transport does not appear to be hormonally regulated (20), in contrast with aquaporin-2, a kidney member of the same family of proteins, regulated by AVP through a cAMP-dependent mechanism (14, 21, 31). Because AQP1 is expressed in a wide variety of tissues, it was expected that mutations leading to a lack of or a nonfunctional AQP1 may have severe or lethal consequences (27). However, transgenic mice lacking the AQP1 water channel appeared grossly normal when not fluid deprived, but they became severely dehydrated and hyperosmolar in response to water deprivation (15). Surprisingly, a few individuals presenting a total absence of AQP1 in erythrocytes, in the very rare Colton-null phenotype (14), have no overt clinical abnormality, but formal testing of these subjects was not done.
Considering the responses to actual or simulated weightlessness or hypergravity, it appears that the expression of AQP1 can be downregulated. In addition, return to the 1-G environment or orthostatic position was followed by an overshoot in the AQP1 protein expression, which might result from an important and rapid requirement in water transport during readaptation to normal conditions. The mechanisms that are involved in these responses were not defined in this study. In recent studies, it was reported that forskolin and 8-bromo-cAMP might increase the water transport in Xenopus oocytes microinjected with AQP1 cRNA (33). However, several groups could not reproduce these findings (1). Patil and co-workers (24) demonstrated that AQP1-dependent water transport could be increased by AVP through a cAMP-regulated pathway, whereas the atrial natriuretic peptide (ANP) inhibited the AQP1-mediated water transport through a cGMP-independent mechanism. These latter observations remain controversial and await confirmation.
However, it was shown that AVP and ANP, respectively, have stimulatory and inhibitory effects on the choroidal CSF secretion (23, 29). In rats, adaptation to spaceflight induces decreases in hypothalamic (6) and neurohypophyseal AVP content (13) and increases in choroidal NP receptor number (12) and cGMP content (C. Carcenac, S. Herbuté, C. Masseguin, L. Mani-Ponset, D. Maurel, R. Briggs, A. Güell, and J. Gabrion, unpublished observations). It is important to note that cGMP is produced in choroidal cells after activation of the guanylate cyclase domain of the biologically active NP receptors (30), particularly when the CSF production is reduced (29). Such data, in parallel with our previous structural and immunocytochemical observations, might suggest that spaceflight, hindlimb suspension, and hypergravity could reduce the secretory activity in choroid plexus. As CSF is also produced by choroidal cells through physicochemical gradients generated by ionic pumps and enzymes, preliminary results obtained from an Na-K-ATPase immunodetection showed that this protein, like AQP1, is reduced at the apical pole of choroidal cells after HDT (C. Masseguin, C. Carcenac, J. M. Verbavatz, and J. Gabrion, unpublished observations), which suggests that water transport and ionic gradients are similarly affected by hindlimb suspension. This point should be further investigated in a future experiment in space.
Readaptation to Earth's gravity or to an orthostatic position induced an increase in the apical AQP1 expression. Interestingly, the restoration was more rapid after head-down suspension than after spaceflight. The levels of AQP1 expressed were quite similar after 6 h of readaptation to orthostatic position and after 2 days of recovery from a spaceflight, whereas the values returned to a control level in rats readapted for 2 days in orthostatic position (S4 rats) and were still very low 6 h after landing and return to Earth's gravity (SLS-2 rats). Until now, no choroidal samples have been dissected and fixed for immunocytochemical investigations in flight. However, longer delays of restoration in flight rats might suggest a stronger decrease in the choroidal AQP1 expression in flight than in HDT.
Surprisingly, hypergravity also strongly decreased choroidal AQP1 expression in rats adapted for 14 days to 2 G and 3 G. The few investigations devoted to the cerebrovascular and/or CSF effects of acute hypergravity suggested that arterial blood pressure in brain as well as CSF volume are concomitantly reduced in acute hypergravity conditions (3). Both spaceflight and simulated weightlessness were suspected to induce a central hypovolemia after more than 1-2 days of adaptation, and both resulted in a reduced AQP1 protein expression. The cardiovascular parameters of rats chronically adapted to hypergravity are not known. Low levels of AQP1 in the choroidal apical domain suggest that hypergravity and microgravity could have similar consequences on choroidal water transport capability. The mechanisms of this adaptation remain to be elucidated. To better understand consequences of altered gravity on CSF production, which is difficult to measure in such experimental rats, it will be interesting to also consider protein expression of molecules generating ionic gradients (e.g., Na-K-ATPase). In addition, because of the impact of altered gravity on AQP1 protein expression in choroid plexus, it might be very interesting to study the expression of other brain aquaporins, in particular those that are distributed in tissues involved in CSF reabsorption.
| |
ACKNOWLEDGEMENTS |
|---|
We are grateful to NASA and to Lockheed-Martin Engineering and
Sciences SLS-2 and NIH-R1 Biospecimen Sharing teams. We would like to
thank in particular D. Reiss-Bubenheim, P. Dumars, V. Vizir, C. Elland,
L. Eward, and K. O'Mara for help in SLS-2 and NIH-R1 Sharing Programs.
Special thanks are also addressed to Drs. W. Berry, L. Garetto, and T. Fast for efficient support during SLS-2 brain dissections, Drs. C. Wade
and I. Poliakov for help during hypergravity experiments, and Dr. S. Herbuté (UMR CNRS 5539, Université Montpellier II, France)
for helpful discussions. We are particularly grateful to Drs. C. André-Deshays and M. Viso from CNES, Paris and Toulouse, France,
for support and encouragement. Lastly, we thank Dr. J. Oliver, Dr. J. Davet, B. N'Guyen, A. Sahuquet (UMR CNRS 5539, Université
Montpellier II, France), G. Géraud (UMR CNRS 9922, Université Paris VI
Paris VII, France), and P. N'Guyen (UMR
CNRS 7624, Université Paris VI, France) for technical assistance.
| |
FOOTNOTES |
|---|
This study was supported by Centre National d'Etudes Spatiales (Grants 93/348, 94/224, 95/223, and 96/264, to J. Gabrion).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: J. Gabrion, Institut des Neurosciences, UMR 7624 CNRS, Université Pierre et Marie Curie Paris VI, Boîte 2, 7, Quai Saint Bernard, F-75252 Paris cédex 05, France (E-mail: jacqueline.gabrion{at}snv.jussieu.fr).
Received 16 November 1998; accepted in final form 5 November 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Agre, P.,
M. D. Lee,
S. Devidas,
W. B. Guggino,
P. M. Deen,
S. M. Mulders,
S. M. Kansen,
C. H. van Os,
J. Fischbarg,
K. Kuang,
J. Li,
P. Iserovich,
Q. Wen,
R. V. Patil,
Z. Han,
M. B. Wax,
S. Sasaki,
S. Uchida,
M. Kuwahara,
K. Fushimi,
F. Marumo,
A. S. Verkman,
and
B. Yang.
Aquaporins and ion conductance.
Science
275:
1490-1492,
1997
2.
Agre, P.,
A. M. Saboori,
A. Asimos,
and
B. L. Smith.
Purification and partial characterization of the Mr 30,000 integral membrane protein associated with the erythrocyte Rh (D) antigen.
J. Biol. Chem.
262:
17497-17503,
1987
3.
Bagshaw, R. J.,
and
J. E. Whinnery.
Mammalian cardiovascular morphology and the maintenance of cerebral function at high Gz.
Aviat. Space Environ. Med.
65:
666-669,
1994[Medline].
4.
Bondy, C.,
E. Chin,
B. L. Smith,
G. M. Preston,
and
P. Agre.
Developmental gene expression and tissue distribution of the CHIP28 water-channel protein.
Proc. Natl. Acad. Sci. USA
90:
4500-4504,
1993
5.
Davet, J.,
B. Clavel,
L. Datas,
L. Mani-Ponset,
D. Maurel,
S. Herbuté,
M. Viso,
W. Hinds,
J. Jarvi,
and
J. Gabrion.
Choroidal readaptation to gravity in rats after spaceflight and head-down tilt.
J. Appl. Physiol.
84:
19-29,
1998
5a.
Denker, B. M.,
B. L. Smith,
F. P. Kuhajda,
and
P. Agre.
Identification, purification, and partial characterization of a novel Mr 28,000 integral membrane protein from erythrocytes and renal tubules.
J. Biol. Chem.
263:
15634-15642,
1988
6.
Fareh, J.,
J. M. Cottet-Emard,
J. M. Pequignot,
G. Jahns,
J. Meylor,
M. Viso,
D. Vassaux,
G. Gauquelin,
and
C. Gharib.
Norepinephrine content in discrete brain areas and neurohypophysial vasopressin in rats after a 9-d spaceflight (SLS-1).
Aviat. Space Environ. Med.
64:
507-511,
1993[Medline].
7.
Fishman, R. A.
Cerebrospinal Fluid in Diseases of the Nervous System. Philadelphia, PA: Saunders, 1992.
8.
Gabrion, J.,
D. Maurel,
B. Clavel,
J. Davet,
J. Fareh,
S. Herbuté,
K. O'Mara,
C. Gharib,
W. Hinds,
I. Krasnov,
and
A. Güell.
Changes in apical organization of choroidal cells in rats adapted to spaceflight or head-down tilt.
Brain Res.
734:
301-315,
1996[Web of Science][Medline].
9.
Gharib, C.,
A. Güell,
L. Pourcelot,
and
R. Bost.
Circulatory and hormonal changes induced by microgravity.
J. Physiol. (Paris)
80:
182-188,
1985[Medline].
10.
Hasegawa, H.,
R. Zhang,
A. Dohrman,
and
A. S. Verkman.
Tissue-specific expression of mRNA encoding rat kidney water channel CHIP28k by in situ hybridization.
Am. J. Physiol. Cell Physiol.
264:
C237-C245,
1993
11.
Hasegawa, H.,
S. C. Lian,
W. E. Finkbeiner,
and
A. S. Verkman.
Extrarenal tissue distribution of CHIP28 water channels by in situ hybridization and antibody staining.
Am. J. Physiol. Cell Physiol.
266:
C893-C903,
1994
12.
Herbuté, S.,
J. Oliver,
J. Davet,
M. Viso,
R. W. Ballard,
C. Gharib,
and
J. Gabrion.
ANP binding sites are increased in choroid plexus of SLS-1 rats after 9 days of spaceflight.
Aviat. Space Environ. Med.
65:
134-138,
1994[Medline].
13.
Keil, L.,
J. Evans,
R. Grindeland,
and
I. Krasnov.
Pituitary oxytocin and vasopressin content of rats flown on COSMOS 2044.
J. Appl. Physiol.
73:
166S-168S,
1992.
14.
Lee, M. D.,
L. S. King,
and
P. Agre.
The aquaporin family of water channel proteins in clinical medicine.
Medicine
76:
141-156,
1997[Medline].
15.
Ma, T.,
B. Yang,
A. Gillespie,
E. J. Carlson,
C. J. Epstein,
and
A. S. Verkman.
Severely impaired urinary concentrating ability in transgenic mice lacking aquaporin-1 water channels.
J. Biol. Chem.
273:
4296-4299,
1998
16.
Marrs, J. A.,
E. W. Napolitano,
C. Murphy-Erdosh,
R. W. Mays,
L. F. Reichardt,
and
W. J. Nelson.
Distinguishing roles of the membrane-cytoskeleton and cadherin mediated cell-cell adhesion in generating different Na+-K+-ATPase distributions in polarized epithelia.
J. Cell. Biol.
123:
149-164,
1993
17.
Mani-Ponset, L.,
C. Masseguin,
J. Davet,
S. Herbuté,
D. Maurel,
M. S. Ghandour,
D. Reiss-Bubenheim,
A. Güell,
and
J. Gabrion.
Effects of an 11-day spaceflight on the choroid plexus of developing rats.
Dev. Brain Res.
99:
187-200,
1997[Medline].
18.
Morey, E. R.
A new rat model simulating some aspect of space flight.
Physiologist
22:
S23-S24,
1979[Medline].
19.
Nielsen, S.,
B. L. Smith,
E. I. Christensen,
and
P. Agre.
Distribution of the aquaporin-CHIP in secretory and resorptive epithelia and capillary endothelia.
Proc. Natl. Acad. Sci. USA
90:
7275-7279,
1993
20.
Nielsen, S.,
B. L. Smith,
E. I. Christensen,
M. A. Knepper,
and
P. Agre.
CHIP28 water channels are localized in constitutively water-permeable segments of the nephron.
J. Cell Biol.
120:
371-383,
1993
21.
Nielsen, S.,
D. Marples,
H. Birn,
M. Mohtashami,
N. O. Dalby,
M. Trimble,
and
M. Knepper.
Expression of VAMP-2-like protein in kidney collecting duct intracellular vesicles. Colocalization with aquaporin-2 water channels.
J. Clin. Invest.
96:
1834-1844,
1995.
22.
Nielsen, S.,
L. S. King,
B. M. Christensen,
and
P. Agre.
Aquaporins in complex tissues. II. Subcellular distribution in respiratory and glandular tissues of rat.
Am. J. Physiol. Cell Physiol.
273:
C1549-C1561,
1997
23.
Nilsson, C.,
M. Lindvall-Axelsson,
and
C. Owman.
Neuroendocrine regulatory mechanisms in choroid plexus cerebrospinal fluid system.
Brain Res. Rev.
17:
109-138,
1992[Medline].
24.
Patil, R. V.,
Z. Han,
and
M. B. Wax.
Regulation of water channel activity of aquaporin 1 by arginine vasopressin and atrial natriuretic peptide.
Biochem. Biophys. Res. Commun.
238:
392-396,
1997[Web of Science][Medline].
25.
Péraldi, S.,
B. Nguyen,
P. Brabet,
V. Homburger,
B. Rouot,
M. Toutant,
C. Bouillé,
I. Assenmacher,
J. Bockaert,
and
J. Gabrion.
Apical localization of alpha-subunit of the GTP-binding protein Go in choroidal and ciliated epithelial cells.
J. Neurosci.
9:
156-169,
1989.
26.
Preston, G. M.,
and
P. Agre.
Isolation of the cDNA for erythrocyte integral membrane protein of 28 kilodaltons: member of an ancient channel family.
Proc. Natl. Acad. Sci. USA
88:
11110-11114,
1991
27.
Preston, G. M.,
B. L. Smith,
M. L. Zeidel,
J. J. Moulds,
and
P. Agre.
Mutations in aquaporin-1 in phenotypically normal humans without functional CHIP water channels.
Science
265:
1585-1587,
1994
28.
Severs, W. B.,
B. A. Morrow,
and
L. C. Keil.
Cerebrospinal fluid pressure in conscious head-down tilted rats.
Aviat. Space Environ. Med.
62:
944-946,
1991[Medline].
29.
Steardo, L.,
and
J. A. Nathanson.
Brain barrier tissues: end organs for atriopeptins.
Science
235:
470-473,
1987
30.
Tsutsumi, K.,
M. Niwa,
T. Kawano,
M. Ibaragi,
M. Ozaki,
and
K. Mori.
Atrial natriuretic polypeptides elevate the level of cyclic GMP in the rat choroid plexus.
Neurosci. Lett.
79:
174-178,
1987[Web of Science][Medline].
31.
Verkman, A. S.,
A. N. Van Hoek,
T. Ma,
A. Frigeri,
W. R. Skach,
A. Mitra,
B. K. Tamarappoo,
and
J. Farinas.
Water transport across mammalian cell membranes.
Am. J. Physiol. Cell Physiol.
270:
C12-C30,
1996
32.
Wade, C. E.,
J. Harper,
N. Daunton,
M. Corcoran,
and
E. Morey-Holton.
Body weight gain during altered gravity: spaceflight, centrifugation and return to 1G.
J. Gravit. Physiol.
4:
47-52,
1997.
33.
Yool, A. J.,
W. D. Stamer,
and
J. W. Regan.
Forskolin stimulation of water and cation permeability in aquaporin 1 water channels.
Science
273:
1216-1218,
1996[Abstract].
This article has been cited by other articles:
|
|
 |
|
  J. G. Kim, Y. J. Son, C. H. Yun, Y. I. Kim, I. S. Nam-goong, J. H. Park, S. K. Park, S. R. Ojeda, A. V. D'Elia, G. Damante, et al. Thyroid Transcription Factor-1 Facilitates Cerebrospinal Fluid Formation by Regulating Aquaporin-1 Synthesis in the Brain J. Biol. Chem., May 18, 2007; 282(20): 14923 - 14931. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L.-F. Zhang Vascular adaptation to microgravity: what have we learned? J Appl Physiol, December 1, 2001; 91(6): 2415 - 2430. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
