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. 2022 Feb 14;13(2):152. doi: 10.1038/s41419-021-04455-4

Fig. 5. Inhibition of GPR4 promoted ECM production and suppressed cartilage catabolism in human articular cartilage explants.

Fig. 5

A–C Representative images of Safranin-O staining and Alcian blue (A.B.) staining in human articular cartilage explants. Relatively intact articular cartilage explants were cut from knee OA patients, and then the explants were treated with vehicle control or GPR4 antagonist NE52-QQ57 (NE, 10 μM) for 1 week. The explants were collected and subject to Safranin-O staining (A). Proteoglycan staining area (%) was analyzed (B). The sulfated GAG (sGAG) released from explants was measured by 1, 9, dimethyl methylene blue (DMMB) binding assay (C). The released amount of sGAG was normalized to the wet weight of the cartilage explant. n = 4, Data are presented as mean ± s.d. **p < 0.01, ***p < 0.001, using unpaired two-tailed Student’s t test. Scale bar, 100 μm. D The mRNA levels of MMP3 and COL2A1 in human articular cartilage explants treated with or without NE52-QQ57 (10 μM) for 1 week were determined by qRT-PCR. n = 3, data are presented as mean ± s.d. *p < 0.05, ***p < 0.001 using unpaired two-tailed Student’s t test. E Representative images of IHC and immunofluorescence staining of MMP13, MMP3, and COL2 of human articular cartilage explants treated with or without NE52-QQ57 (NE, 10 μM) for 1 week. Scale bar, 50 μm.