Fig. 1: Mono-methylation of DDX1 lysine 234 in NP cells during IVDD.

A LC-MS/MS experimental workflow schematic. Cell lysates from degenerated and non-degenerated NP tissues were digested and applied to LC-MS/MS. B LC-MS/MS of the Lys234 residue of the peptide segment NQALFPACVLK, with a molecular weight of +14.016 Da. C, D Detection of endogenous DDX1 lysine methylation in NP and HEK-293T cells by CO-IP (n = 3). E IF analysis of collagen II and MMP3 expression (green: collagen II; red: MMP3; scale bar: 50μm). F Expression of endogenous DDX1 lysine methylation was detected by CO-IP in normal and TBHP-treated NP cells (n = 3). G CO-IP of the DDX1 K234 methylation (R2 was the R1 clone system, n = 3). H, J Schematic illustration showing the experiment design. Compared with the control group (n = 5), the rat IVDD model was established by needle puncture (model group, n = 20), LV-scrambled or LV-shDDX1 were used to knock down DDX1 in model group rats (scrambled group, n = 5 and shDDX1 group, n = 5). Subsequently, shRNA-resistant LV-DDX1 WT (DDX1 WT group, n = 5) and LV-DDX1 K234R (DDX1 K234R group, n = 5) were re-overexpressed in the shDDX1 group rat and injected weekly into the NP. I H&E and SO&FG of discs from rats. Scale bar: 1 mm. K–M X-ray K, CT L, MRI M of rat vertebrae (n = 5). N, O DHI N, Pfirrmann grades (O) of discs (n = 10). Data information: *P < 0.05, **P < 0.01, ***P < 0.001. Data are represented as mean ± SEM. P value was quantified by two-way ANOVA (N, O). Panels (C–G) show the results of a representative similar result from one of three independent experiments. Panels (I, K–M) the results of a representative similar result from one of five independent experiments.