Autophagy-related proteases accompany the transition of pre-chondrogenic cells into chondroblasts

Abstract Background Autophagy is classified as a form of programmed cell death. Nevertheless, besides the death-inducing function, autophagy enables removal of damaged organelles, energy savings, and thus cell survival. This applies in particular to cells with poor renewal capabilities, such as chondroblasts. Autophagy is regulated by a complex molecular network, including proteases and their substrates. In autopodium, autophagy-related proteases have been examined particularly within the context of the elimination of the interdigital tissue. However, the death-inducing effects of their expression/activation have not been specified yet. This work focuses on autophagy-associated proteases (cathepsins, matrix metalloproteinases, and caspases) involved in phalangeal cartilage of the mouse autopodium. Methods PCR Array, Real Time PCR, and immunohistochemistry were used to follow the expression of autophagy-associated genesin vivo at two developmental stages prenatal/embryonic (E)12 vs. E14. Real Time PCR was then applied to investigate the influence of rapamycin (an inductor of autophagy) on the expression of autophagy-associated proteases in chondroblasts in vitro using micromass culture. Results Several proteases showed increased expression levels during the transition of pre-chondrogenic cells into chondroblastsin vivo. The most significant increases were observed for Ctsb (fold regulation 2.22), Ctsd (fold regulation 2.37), Ctss (fold regulation 2.92), Mmp9 (up to 445%), and Casp8 (up to 250%). The transition was associated also with high expression of crucial autophagic inducers, such as Atgs. The in vitro treatment of chondroblasts by autophagy inductor rapamycin showed significantly decreased expression of cathepsins, a mild increase in expression of metalloproteinases, and no effect in caspase expression. Conclusions The present data provide a screening of autophagy-associated proteases accompanying the formation of cartilage in vivo and specify their expression under rapamycin treatment in vitro. Notably, the selected proteases are assigned to osteoarthritis, therefore their regulation might be used in clinically oriented studies.