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.