Direct Knockdown of PDZ and LIM Domain 1 Using an Adenoviral Delivery System Accelerates Osteogenesis and Fracture Healing in Mice

Substantial advances have been made in understanding the role of partial PDZ and LIM domain (PDLIM) family’s proteins in skeletal-related diseases. Yet, little is known about the effect of Pdlim1 on osteogenesis and fracture repair. This study aimed to investigate whether direct gene delivery using an adenovirus vector carrying Pdlim1 (Ad-oePdlim1) or encoding shRNA-Pdlim1 (Ad-shPdlim1) could affect the osteogenic activity of pre-osteoblastic MC3T3-E1 cells in vitro, and influence the fracture healing of mice in vivo. We found that Ad-shPdlim1 transfection contributed to the calcified nodule formation in MC3T3-E1 cells. Downregulation of Pdlim1 enhanced the alkaline phosphatase (ALP) activity and increased the expression of osteogenic markers (Runx2, Col1A1, osteocalcin and osteopontin). Further analysis indicated that Pdlim1 knockdown could activate β-catenin signaling, as evidenced by the accumulation of β-catenin in the nucleus and the increase levels of downstream regulators such as Lef1/Tcf7, Axin2, Cyclin D1 and Sox9. By contrast, Pdlim1 overexpression resulted in inhibition of the osteogenic activity of MC3T3-E1 cells. In vivo, at day 3 after fracture, Ad-shPdlim1 adenovirus particles were injected into the fracture site of the femur of mice, and the process of fracture healing was evaluated by X-ray, Micro-CT and histological examination. Local injection of Ad-shPdlim1 promoted the early cartilage callus formation, restored bone mineral density and accelerated cartilaginous ossification, with the upregulation of osteogenic gene (Runx2, Col1A1, osteocalcin and osteopontin) expression and activation of β-catenin signaling. Thus, we concluded that inhibition of Pdlim1 contributed to osteogenesis and fracture healing by activating the β-catenin signaling pathway.