Fig. 5

Activation of MAPK7 in chondrocytes is essential for hypoxic adaptation and enhancement of HIF1α signaling under hypoxia. a, b Immunofluorescence staining of (a) MAPK7 (b) P-MAPK7 on representative sections of distal femoral growth plates at P1. Scale bar, 200 μm. RZ, resting zone; PZ, proliferative zone; HZ, hypertrophic zone. c Western blot analysis of MAPK7 and p- MAPK7 in primary chondrocytes cultured under hypoxic conditions for 0, 1, 4, 12, or 24 h. d Immunofluorescence staining of SOX9 on representative sections of distal femoral growth plates at P1. Scale bar, 200 μm. e Western blot analysis of SOX9, COL2A1, MAPK7, HIF1α, and VEGFA in CON and Mapk7 CKO chondrocytes cultured under normoxic or hypoxic conditions for 48 h. f Western blot analysis of SOX9, COL2A1, MAPK7, p-MAPK7, HIF1α, and VEGFA protein levels in XMD8-92- or DMSO-treated primary chondrocytes cultured under normoxic or hypoxic conditions. Primary chondrocytes harvested from wild-type mouse knees were cultured in the presence of 5 μM XMD8-92 or an equal amount of DMSO under normoxia for 3 h, followed by normoxia or hypoxia for 48 h. XMD, XMD8-92. g, h mRNA levels of (g) Sox9 and (h) Col2a1 in CON and Mapk7 CKO chondrocytes cultured under normoxia or hypoxia were measured by real-time quantitative PCR (n = 3). *P < 0.05 (one-way ANOVA followed by Dunnett’s post hoc test). Data are presented as mean ± SD. i Immunofluorescence staining of HIF1α on representative proximal tibial growth plate sections from P1 mice. Scale bar, 200 μm. j mRNA levels of Hif1a and its known target genes were measured in growth plate cartilage from P1 Mapk7 CKO mice by real-time quantitative PCR. k HIF1α activity in CON and Mapk7 CKO chondrocytes cultured under normoxia or hypoxia, as evaluated by HIF1α-responsive element luciferase reporter (HRE-luc) assay (n = 5). *P < 0.05 (one-way ANOVA followed by Dunnett’s post hoc test). Data are presented as mean ± SD. l mRNA level of hif1a in CON and Mapk7 CKO chondrocytes cultured under normoxia or hypoxia were measured by real-time quantitative PCR (n = 3). *P < 0.05 (one-way ANOVA followed by Dunnett’s post hoc test). Data are presented as mean ± SD. m Free ATP levels in CON and Mapk7 CKO chondrocytes cultured under normoxic or hypoxic conditions (n = 4). *P < 0.05 (one-way ANOVA followed by Dunnett’s post hoc test). Data are presented as mean ± SD. n Primary chondrocytes were transfected with WT-MAPK7 or DN-MAPK7 expression vector in the presence of CA-MEK5 expression vector. Cells were harvested 48 h after transfection and protein levels of HIF1α, MAPK7 and p-MAPK7 were assayed by western blot