18th IAA Humans in Space Symposium (2011)
2215.pdf
Ionizing Radiation Inhibits IGF-1 Signaling and Proteoglycan Synthesis In Pig Cartilage
J.S. Willey1, D.L. Long2, and R.F. Loeser2
1
Wake Forest University School of Medicine Department of Radiation Oncology, 2 Wake Forest University School
of Medicine Section of Molecular Medicine
While exposure to ionizing radiation is known to cause bone deterioration, effects on articular cartilage are poorly
studied. Damage observed in joints that absorb therapeutic radiation during childhood suggests radiation can
negatively impact cartilage. IGF-1 is an important growth factor for articular cartilage. IGF-1 stimulates
proteoglycan (PG) and collagen synthesis, producing new matrix, through activation of the PI3-kinase-Akt pathway.
We examined the effects of a 10 Gy single dose (137) Cs gamma-rays on IGF-1 signaling and PG synthesis in
porcine articular chondrocytes and explants using tissue harvested from distal femoral condyles of 6-month old pigs.
Chondrocytes were isolated from digested cartilage. Confluent cultures were irradiated and then one hour postirradiation were stimulated with IGF-1. One hour after stimulation Akt phosphorylation was measured by
immunoblotting. Cells were also IGF-1 stimulated for 24 hours post-exposure to quantify PG synthesis via S35
incorporation. Whole cartilage explants were removed and cultured. Proteoglycan content of explants and
surrounding media was quantified four days post-exposure using a DMB assay and immunoblotting of conditioned
media was used to measure the matrix degrading enzymes MMP-3 and ADAMTS5. We found that IGF-1
stimulation increased Akt phosphorylation at Thr 308 and Ser 473 and increased PG synthesis by control
chondrocytes, whereas radiation inhibited both IGF-induced Akt activation and PG synthesis. Irradiation also
reduced PG content in explants by 4 days. However, radiation did not increase the presence of MMP-3, ADAMTS5,
or PG within the conditioned media. Radiation appears to impair normal IGF-1 signaling in porcine chondrocytes:
exposure prevented IGF-1-mediated increase in both Akt phosphorylation and PG synthesis. Though active
degradation did not occur post-irradiation, lower matrix production could decrease compressive strength over time.
These findings suggest further animal studies are warranted to determine if spaceflight-relevant radiation scenarios
will negatively impact articular cartilage.