Cell Kinetic and Histomorphometric Analysis of Microgravitational Osteopenia

Bone and calcium physiology

Rattus norvegicus (Sprague-Dawley rat)
Flight: 16 Male

Basal: 6, Delayed synchronous: 16, Vivarium: 16

Ambient Temperature Recorder, Animal Enclosure Module

The main hypothesis of this experiment was that space flight blocks osteoblast formation; however, it rapidly recovers upon return to Earth. The study attempted to gain a better understanding of the way that physiological processes adapt both to microgravity and a return to an Earth environment. In order to achieve this, four goals were established: 1) DNA synthesis that lead to preosteoblast cell proliferation was studied through the use of a specific marker—this method would yield new results that could build on previous research; 2) To confirm previous findings that suggested the presence of postflight inhibition of osteoblast formation; 3) To determine if the block to osteoblast formation is confined to specific areas of the skeleton; 4) To determine how long it takes for osteoblast formation to recover after space flight.

The incidence of osteoblast formation sites during a 9-day flight as well as their rates of apposition at 4–6, 24, and 72 hours after space flight were studied. Rat fibroblast-like osteoblast precursor cells from both maxillary molar periodontal ligaments (PDL) and mandibular condyle cells were analyzed using a nuclear morphometric assay. The PDL cells were placed in ~4M Hematoxylin and stained with eosin to obtain the relative number of preosteoblasts. The cell kinetics of osteoblast histogenesis at 4–6, 24, and 72 hours postflight were assessed to record the path of recovery of osteoblast production.

Analysis of fibroblast-like osteoblast precursor cells in rat PDL yielded a statistically significant reduction in osteogenic precursor formation after a return from a microgravity environment. Production quickly returned to normal levels, and after 24 hours most cell populations were at preflight levels. These findings supported the hypothesis that microgravity inhibited osteoblast formation. However, analysis of the rat mandibular condyle cells showed that microgravity had not significantly affected osteoblast production. This was most likely due to the fact that the cells were growing rapidly, and thus the genetic need to produce new cells outweighed the effects of microgravity. Further study of adult mandibular condyle cells is needed and would be most relevant to human space flight, particularly of growing individuals.

Becker, R.F. et al.: The Effect of Hypergravity (2G) on Osteoblast Percursor Cells in Rat Periodontal Ligament. American Society for Gravitational and Space Biology Bulletin, vol. 8(1), 1994, p. 88.†

Garetto, L.P. et al.: Recovery of Osteoblast Histogenesis in Rat Periodontal Ligament following a 9-Day Spaceflight (PARE.03). American Society for Gravitational and Space Biology Bulletin, vol. 8(1), 1994, p. 51.

Jennermann, C. et al.: A Comparison of Bromodeoxyuridine and 3H-Thymidine Labeling of S-Phase Cells in Rat Mandibular Condyle. American Society for Gravitational and Space Biology Bulletin, vol. 7, 1993, p. 80.†

Jennermann, C. et al.: Comparison of Labeling Methods and Embedding Media for Localization of S-Phase Osteogenic Cells. Journal of Histotechnology, vol. 20(1), 1997, pp. 39–44.†