Autophagy prior to chondrocyte cell death during the degeneration of Meckel's cartilage.

The central portion of Meckel's cartilage degenerates almost immediately after birth. Whether autophagy is involved in this process remains unclear. Thus, to explore the role of autophagy during this process, we have detected the expression of autophagy and apoptosis-related markers in embryonic mice. In E15, Beclin1 and LC3 expressions were weak and negative in Meckel's cartilage, respectively. In E16, chondrocytes of the central portion became hypertrophic. Moderate immunoreactivities of Beclin1 and LC3 were observed in prehypertrophic and hypertrophic chondrocytes of the central portion. In E17, the degradation occurred in the central portion and expanded anteriorly and posteriorly. Beclin1 expression was observed in Meckel's cartilage with an increase in the hypertrophic chondrocytes of the central portion. The expression of LC3 was detected specifically in terminally differentiated hypertrophic chondrocytes. The mRNA expressions of LC3 and Beclin1 from E15 to E17 significantly increased. This result is in accord with the histologic findings. Terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling assay and Caspase 3 expression demonstrated that apoptosis was detected in the lateral part of terminal hypertrophic chondrocytes along the degeneration area of Meckel's cartilage. In addition, Bcl2 expression increased significantly from E15 to E17. These results indicate that autophagy is involved in hypertrophic chondrocytes during the degradation of Meckel's cartilage and occurs prior to chondrocyte cell death during this process.