Space and Height

In our analysis of what affects the differentiation and dedifferentiation of mesenchymal stem cells Runx2 was unveiled as a key compound that encourages osteogenic differentiation.  It was hypothesized that the down regulation of Runx2 by the lack of loading due to space flight followed by the upregulation after return on land could play a role in the astronaut height gain.  However, no official studies could be found that explored the height gain of the astronauts in space(the effects of microgravity on other organisms were explored however).  Just because a large component of the height gain is due to spinal decompression does not mean that a smaller component could be permanent.  According to one study "Simulated microgravity inhibits the proliferation and osteogenesis of rat bone marrow mesenchymal stem cells"<-title is the same.  Microgravity could also potentially induce dedifferentiation of osteoblastic cells allowing them to undergo into a chondrogenic lineage giving a more youthful taller growing bone.

The effect of a 5-day space flight on the immature rat spine.

"In September 1991, 8 neonatal rats were flown aboard the Space Shuttle Columbia flight STS-48 during a 5-day mission. Upon return to earth, the spines were dissected, frozen and shipped to our laboratory. Matched ground-based rats were used as controls. The spines were radiographed and then slowly thawed. Individual vertebrae were subjected to compressive biomechanical testing using an Instron tester and then processed for determination of calcium and phosphorus content. The intervertebral discs were placed in physiological saline and the stress-relaxation characteristics measured. The discs were then lyophilized and assayed for collagen and proteoglycan content. Disc height on radiographs was measured by image analysis.
After space flight, the heights of the discs were found to be 150 to 200 microns greater, although the values were not statistically significant[height of discs were greater explaining for some of the height gain]. There was no difference in the resiliency of the thoracic discs as determined by stress-relaxation. However, in the lumbar discs, space flight increased the resiliency. There was no difference in water content. In both the thoracic and lumbar discs there was a 3.3-fold increase in hydroxyproline-proteoglycan ratio after space flight. In the vertebrae, there was no difference in calcium-phosphate ratio or compressive strength.
Even after a short 5-day flight, the spine begins to undergo biomechanical and biochemical changes."

Nothing though about Runx2.  However, the problem is that non-microgravity seems to be essential to normal growth plate development.  The next study also studies the hypothesis that maybe a period of unloading followed by loading could help growth.

The Spacelab 3 simulation: basis for a model of growth plate response in microgravity in the rat.

"Data from Spacelab 3 (SL3) suggested that spaceflight significantly reduces the activity of the rat tibial growth plate. Animal processing after SL3 began twelve hours post-landing, so data reflect post-flight re-adaptation in addition to spaceflight effects. To determine if a twelve-hour period of weight bearing after seven days of unloading could affect the physes of spaceflown rats, the present study assessed the growth plate response to unloading with or without a reloading period. Rats were subjected to hind-limb suspension for seven days and then euthanized, with or without twelve hours of reloading. Activity of the growth plate was assessed. Rats suspended without reloading had reserve zone (RZ) height greater than controls[so there was less differentiation of cells], and shorter hypertrophy/calcification zone (HCZ) with fewer cells. The greater RZ was associated with a larger cell area, indicating a possible mitotic delay or secretion defect[likely due to a compound upregulated by loading such as Runx2 not being present]. Twelve hours of reloading decreased RZ height and cell number, and restored the number of cells in HCZ to control values, but the number of cells in the proliferative zone and height in HCZ were reduced. The rebound response to preserve/restore skeletal function after a period of unloading involves an acceleration of growth associated with a decreased cell cycle time in PZ. Changes during the reloading period in this simulation support our hypothesis that the effects of spaceflight on SL3 growth plates were altered by changes that occurred post-landing."

If cells were dedifferentiating due to absence of Runx2 you would expect that the number of cells in the twelve hours of reloading group to have a larger reserve cell number(due to osteoblasts dedifferentiating).

Gravitational changes affect tibial growth plates according to Hert's curve.

"Microgravity significantly affects chondrocyte differentiation within the tibial epiphyseal growth plate of space flown rats[it likely always affects chondrogenic differentiation including exogenously induced chondrogenic differentiation like with LSJL]. The changes produced in height and number of cells in different zones of the plate are associated with ultrastructural changes in the extracellular matrix. Given the importance of the growth plate in endochondral ossification, we began to assess the response of the plate to hypergravity, and the countermeasure value of excess G.
Rats of the strain used in Cosmos biosatellite missions were housed under conditions similar to Cosmos flights and subjected to continuous hypergravity (2 G) for 14 d, in a 12-ft radius centrifuge.Histomorphometrical analyses of tibial growth plates from these rats found the hypertrophic/calcification zone to be significantly reduced in both height and cell number, and the proliferation zone in cell number.
[The] rat growth plate responds to gravitational changes according to Hert's curve: i.e., a) an increased baseline (minimal) loading reduces cartilage differentiation; and b) a reduced baseline loading may lead to increased cartilage differentiation but only within a range, beyond which lack of differentiation results{So lowering the baseline to a specific point less than 9.8m/s^2 but greater than 0m/s^2 may help increase chondrogenic differentiation?}. The plasticity of the plate, i.e., its ability to increase or decrease its activity in response to changes in gravity suggests the possibility of a range of G that will produce the load necessary to maintain normal growth of the plate, i.e., possible countermeasures to the effects of either hypo- or hyper-gravity."

Baseline loading refers to the smallest loading you incur during a day.  So maybe experiencing microgravity during one short burst during the day may help encourage chondrogenic differentiation.  Like inversion maybe?

Height increase, neuromuscular function, and back pain during 6 degrees head-down tilt with traction.

"Spinal lengthening and back pain are commonly experienced by astronauts exposed to microgravity.
To develop a ground-based simulation for spinal adaptation to microgravity, we investigated height increase, neuromuscular function and back pain in 6 subjects all of whom underwent two forms of bed rest for 3 d. One form consisted of 6 degrees of head-down tilt (HDT) with balanced traction, while the other was horizontal bed rest (HBR). Subjects had a 2-week recovery period in between the studies.
Total body and spinal length increased significantly more and the subjects had significantly more back pain during HDT with balanced traction compared to HBR[The height increase lasted for two weeks following inversion for three days?]. The distance between the lower endplate of L4 and upper endplate of S1, as measured by ultrasonography, increased significantly in both treatments to the same degree[The inversion group grew taller than the bed rest group despite both groups having equal decompression of the spinal discs]. Intramuscular pressures in the erector spinae muscles and ankle torque measurements during plantarflexion and dorsiflexion did not change significantly during either treatment.
Compared to HBR, HDT with balanced traction may be a better method to simulate changes of total body and spinal lengths, as well as back pain seen in microgravity."

So inversion seems to have effects other than just spinal decompression.  This inversion may allow for a lower threshold microgravity and may allow for bone to expand more than just bed rest.  Same with chondrocytes a lower threshold microgravity allows for chondrocytes to expand wider during the lowest microgravity point of the day(the inversion point).

Here's a study on weightlessness and height:

Structural and Mineral Content in Weight-bearing bones following hindlimb suspension in young rats

After 1 week suspension of growing rats bone length was lower by about 10% less change than control.  This study mentions studies where hindlimb suspension did not inhibit bone length.


So sustained microgravity followed by normal gravity(space flight) doesn't seem to have permanent height increasing effects.  However, intermittent periods of microgravity like those achieved by inversion may help increase height(Body Champ IT8070 Inversion Therapy Table) in addition to the temporary height achieved by changes in intravertebral disc shape.  To know for sure the effect of exposure to microgravity will have to be studied.