The role of [alpha]-Parvin in long bone development

Abstract

α-Parvin is a ubiquitously expressed 42kDa protein responsible for cell-extracellular matrix (ECM) adhesion. α-Parvin binds to Integrin-linked kinase (ILK), Paxillin, and Actin. It is important in relaying the integrin-mediated outside-in signaling. Whole-body knockout of α-Parvin results in embryonic lethality. α-Parvin has been reported essential in skin, endothelial cells, and kidney development. However, the roles of α-Parvin in skeletal development have not been studied. Here, Prx1-Cre were used to induce limb bud mesenchyme-specific deletion of α-Parvin. α-Parvin conditional knockout (cKO) mice exhibited dwarfism. They could not survive to two months of age. Compared with the control, long bones of cKO mice were shorter. In addition, at the neonatal stage, long bones of cKO mice were not only shorter but broader than the control. These data suggest that α-Parvin is crucial for normal long bone development in mice. The growth of long bones relies on endochondral ossification. Growth plate is the key structure in this process where chondrocytes proliferate, differentiate, and leave a cartilaginous mold for mineralization. In α-Parvin cKO mice, the growth plate chondrocytes of the proliferative zone were rounder in shape and showed partial loss of columnar organization. In addition, cKO chondrocytes showed increased binucleation rate and ectopic cell death, suggesting the possible roles of α-Parvin in cytokinesis and cell survival. Moreover, the resting zone of mature cKO growth plates was thicker and dilated, suggesting that α-Parvin may be involved in regulating the differentiation and proliferation of chondroprogenitors. In the proliferative zone of growth plates, daughter chondrocytes undergo rearrangement after cell division, which is termed chondrocyte rotation. The rotation determines the orientation and position of chondrocytes within the lacuna and is crucial for the elongation of long bones. To further illustrate the growth defects of long bones in cKO mice, live imaging was carried out using two-photon microscopy on growth plates of mTmG control or mTmG cKO mice to monitor chondrocyte rotation in vivo. As expected, most chondrocyte rotation events in cKO mice were unsuccessful and incomplete, while the rotation events in control group were mostly normal. These data strongly suggest that α-Parvin regulates chondrocyte rotation. Taken together, α-Parvin regulates multiple cellular processes of chondrocytes during long bone development. This study provides new insights into the regulation of long bone growth and consolidates the importance of cell-ECM adhesion and integrin signaling during endochondral bone formation.