Effect of thiram on avian growth plate chondrocytes in culture

Thiram is a dithiocarbamate pesticide that causes tibial dyschondroplasia (TD), a growth plate defect, in poultry. Deaths of transitional zone chondrocytes appear to interrupt endochondral bone development leading to the broadening of growth plate. The mechanism of action of thiram on chondrocytes is not well understood. Since proteins play major roles in different aspects of cell's metabolism, growth, and survival, the objective of this study was to find whether thiram produces proteomic changes that could impair the development of chondrocytes. The chondrocytes, isolated from proximal tibial growth plates, were cultured with or without a sub-lethal concentration of thiram for 48 hr, and the cell proteins were extracted, and subjected to 2-D gel electrophoresis. The gel images were compared and statistically evaluated using Melanie software to identify differentially expressed protein spots. Of a total of 72 identifiable spots 3 were down-regulated and 2 up-regulated in thiram treated chondrocytes. In-gel trypsin digestion of the protein spots followed by their characterization by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry identified 25 spots comprising of 23 proteins. Two of 3 down-regulated proteins were identified as a heat shock protein 70 (HSP 70) and a GALE (UDP-galactose-4 epimerase) protein isoform I. The up-regulated proteins were Serpin H1, a protein involved in collagen metabolism and a redox sensor NmrA-like (NMRAL) family domain protein-1. Both GALE and NMRAL proteins are implicated in energy metabolism and redox regulation whereas the HSP 70 protects cells against stress, and implicated in chondrocyte hypertrophy, an important event in endochondral bone formation. The failure of chondrocyte protective mechanisms such as associated with protection against cellular stress and energy metabolism appear to be the likely cause for chondrocyte death induced by thiram.