NASA Human Research Program Investigators' Workshop (2012)
4144.pdf
INDUCTION OF EARLY STAGES OF OSTEOARTHRITIS AFTER EXPOSURE TO
MICROGRAVITY
1
L. Mellor1, W. Knudson2 and J.T. Oxford1
Boise State University, Biomolecular Research Center, Boise, ID 83725, lilianamellor@boisestate.edu, 2 East
Carolina University, Brody School of Medicine, Greenville, NC 27834
Articular cartilage of the synovial joints such as hip and knee joints, are constantly exposed to mechanical forces
produced by daily activities. Similar to bone, cartilage is a type of connective tissue that requires a balance between
synthesis and degradation of extracellular matrix components to maintain tissue homeostasis; changes in this
balance leads to cartilage degradation. However, unlike bone tissue, cartilage lacks innervation, blood supply and
cell-cell contact, and has a very limited regeneration capacity. Proper communication between individual
chondrocytes and the extracellular matrix is crucial to maintain cartilage homeostasis, and disruption in cell-matrix
interactions can trigger cartilage degradation.
It has been shown that astronauts experience bone density loss after space flight resembling osteoporotic conditions
due to prolonged exposure to microgravity. Although bone density loss in space is a growing field of interest in
space related biomedical research, there are no current publications on the possible effects of microgravity on the
adjacent articular cartilage of synovial joints. We therefore hypothesize that cartilage homeostasis is also
compromised during space missions, resulting in early stages of arthritis. Arthritis is a progressive degenerative
disease that can take years or even decades before becoming symptomatic, and early detection of the disease can be
a key component for successful treatment. Our proposed research addresses the molecular mechanisms involved in
articular cartilage loss after exposure to microgravity, which can result in impaired mobility and painful joints. Our
goal is to use two chondrocyte cell lines widely used in arthritis cell research, RCS (rat chondrosarcoma cells) and
C-28/I2 (immortal human chondrocyte cell line), and expose them to a modeled microgravity environment using a
rotating wall vessel (RWV) bioreactor. Molecular markers closely associated with arthritis, such as matrix metalloproteinases and genes involved in matrix catabolism, will be investigated. It is also expected that matrix protein
receptors will transduce the effects of gravity into the cell by first altering the underlying intracellular cytoskeleton.
Cell culturing of chondrocytes using the RWV bioreactor forms the foundation of our research. We have tried to
optimize cell culture conditions in a 3-D environment by testing different available microcarriers and assessing cell
viability after several days in the bioreactor. In addition, we have developed several protocols to successfully stain
cells after exposure to modeled microgravity, avoiding centrifugation steps. Preliminary data of chondrocytes
exposed to modeled microgravity for 7 days show changes in the actin cytoskeleton morphology when compared to
control cells cultured under normal gravitational forces.
A better understanding of the molecular signaling pathways involved in cartilage degradation, will not only help
prevent astronauts developing osteoarthritis from exposure to microgravity, but will also help us prevent further
degradation in patients experiencing early stages of arthritis on Earth.