Comparison of Kindlin-2 deficiency-stimulated osteoarthritis-like lesions induced by Prg4 CreERT2 versus Aggrecan CreERT2 transgene in mice.

BACKGROUND: Genetically modified mice are the most useful tools for investigating the gene functions in articular cartilage biology and the pathogenesis of osteoarthritis. The Aggrecan CreERT2 mice are one of the most reported mouse lines used for this purpose. The Prg4 (proteoglycan 4) gene encodes the lubricin protein and is expressed selectively in chondrocytes located at the superficial layer of the articular cartilage. While the Prg4 GFPCreERT2 knock-in inducible-Cre transgenic mice were generated a while ago, so far, few studies have used this mouse line to perform gene functional studies in cartilage biology.

METHODS: We have recently reported that deleting the Fermt2 gene, which encodes the key focal adhesion protein Kindlin-2, in articular chondrocytes by using the Aggrecan CreERT2 transgenic mice, results in spontaneous osteoarthritis (OA) lesions, which highly mimics the human OA pathologies. In this study, we have compared the Kindlin-2 deficiency-caused OA phenotypes induced by Prg4 GFPCreERT2 with those caused by Aggrecan CreERT2 using imaging and histological analyses.

RESULTS: We find that Kindlin-2 protein is deleted in about 75% of the superficial articular chondrocytes in the tamoxifen (TAM)-treated Prg4 GFPCreERt2/+ ; Fermt2 fl/fl mice compared to controls. At 6 months after TAM injections, the OARSI scores of Aggrecan CreERT2/+ ; Fermt2 fl/fl and Prg4 GFPCreERt2/+ ; Fermt2 fl/fl mice were 5 and 3, respectively. The knee joints histological osteophyte and synovitis scores were also significantly decreased in Prg4 GFPCreERT2/+ ; Fermt2 fl/fl mice compared to those in Aggrecan CreERT2/+ ; Fermt2 fl/fl mice. Furthermore, magnitudes of upregulation of the extracellular matrix-degrading enzymes Mmp13 and hypertrophic chondrocyte markers Col10a1 and Runx2 were decreased in Prg4 GFPCreERT2/+ ; Fermt2 fl/fl versus Aggrecan CreERT2/+ ; Fermt2 fl/fl mice. We finally examined the susceptibility of Prg4 GFPCreERT2/+ ; Fermt2 fl/fl mouse model to surgically induce OA lesions. The pathological features of OA in the TAM-DMM model exhibited significant enhancement in cartilage erosion, proteoglycan loss, osteophyte, and synovitis and an increase in OARSI score in articular cartilage compared with those in corn-oil DMM mice.

CONCLUSION: Kindlin-2 loss causes milder OA-like lesions in Prg4 GFPCreERT2/+; Fermt2 fl/fl than in Aggrecan CreERT2/+ ; Fermt2 fl/fl mice. In contrast, Kindlin-2 loss similarly accelerates the destabilization of the medial meniscus-induced OA lesions in both mice. Translational Potential of this Article : Our study demonstrates that Prg4 GFPCreERT2 is a useful tool for gene functional study in OA research. This study provides useful information for investigators to choose appropriate Cre mouse lines for their research in cartilage biology.