iTRAQ-based quantitative proteomic analysis on differentially expressed proteins of rat mandibular condylar cartilage induced by reducing dietary loading.

As muscle activity during growth is considerably important for mandible quality and morphology, reducing dietary loading directly influences the development and metabolic activity of mandibular condylar cartilage (MCC). However, an overall investigation of changes in the protein composition of MCC has not been fully described in literature. To study the protein expression and putative signaling in vivo, we evaluated the structural changes of MCC and differentially expressed proteins induced by reducing functional loading in rat MCC at developmental stages. Isobaric tag for relative and absolute quantitation-based 2D nano-high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) technologies were used. Global protein profiling, KEGG and PANTHER pathways, and functional categories were analyzed. Consequently, histological and tartrate-resistant acid phosphatase staining indicated the altered histological structure of condylar cartilage and increased bone remodeling activity in hard-diet group. A total of 805 differentially expressed proteins were then identified. GO analysis revealed a significant number of proteins involved in the metabolic process, cellular process, biological regulation, localization, developmental process, and response to stimulus. KEGG pathway analysis also suggested that these proteins participated in various signaling pathways, including calcium signaling pathway, gap junction, ErbB signaling pathway, and mitogen-activated protein kinase signaling pathway. Collagen types I and II were further validated by immunohistochemical staining and Western blot analysis. Taken together, the present study provides an insight into the molecular mechanism of regulating condylar growth and remodeling induced by reducing dietary loading at the protein level.