[CD137-CD137L interaction induced the calcification of mouse smooth muscle cells via P38 MAPK signaling]

Objective: To explore whether CD137-CD137L interaction could induce mouse vascular smooth muscle cells(VSMCs) calcification via P38 MAPK signaling. Methods: (1) Mouse VSMCs obtained from 8-week old male C57 mice were cultured by using method of tissue piece inoculation.The cells from 3 to 8 passage were divided into 4 groups: control group, agonist-CD137 group(recombinant CD137L protein), anti-P38 group(agonist-CD137 group+P38 inhibitor), single anti-P38 group(P38 inhibitor). The calcification was induced by adding a mixture of 10 mmol/L β-glycerophosphate+10(-8) mol/L dexamethasone+10(-7) mol/L insulin in the culture medium.Immunofluorescence was used to observe the changes of VSMCs markers(α-SMA and OPN).Real time-PCR was used to observe the mRNA expression of OPN and RUNX-2. Western blot was used to observe the protein expression of p-P38, OPN and RUNX-2. The level of cell calcification was observed by detecting alkaline phosphatase activity and calcium concentration. (2) The degeree of local calcium deposition was also tested on Von Kossa staining and Alizarin red staining methods in following 5 mouse VSMCs groups: control group, agonist-CD137 group(recombinant CD137L protein), anti-P38 group (agonist-CD137 group+P38 inhibitor), anti-CD137 group (agonist-CD137 group+CD137 inhibitor),agonist-P38 group(anti-CD137 group+P38 agonist). Results: (1) Compared with the control group, the fluorescence intensity of α-SMA was lower in the agonist-CD137 group(2.79±0.25 vs. 5.42±0.47,P<0.05), while the fluorescence intensity of OPN was higher(4.91±0.23 vs. 1.63±0.26, P<0.05). The fluorescence intensity of α-SMA was partly recovered after adding P38 inhibitor(4.48±0.27 vs. 2.79±0.25,P<0.05),but it was still lower than the control group (4.48±0.27 vs. 5.42±0.47, P<0.05),the fluorescence intensity of OPN decreased(2.66±0.15 vs. 4.91±0.23,P<0.05),but it was still higher than that in the control group (2.66±0.15 vs. 1.63±0.26,P<0.05).The fluorescence intensity of α-SMA and OPN(5.32±0.67 vs. 5.42±0.47,1.82±0.30 vs.1.63±0.26,both P>0.05) was similar between the control group and single anti-P38 group.(2) Compared with the control group, the protein level of p-P38(4.15±0.24 vs. 3.48±0.26, P<0.05), OPN(2.43±0.21 vs. 1.53±0.08, P<0.05), RUNX-2(3.20±0.23 vs. 1.13±0.10, P<0.05) was significantly increased in agonist-CD137 group,the above effects were blocked by adding specific P38 inhibitor SB203580(1.16±0.12 vs. 4.15±0.24, 0.50±0.02 vs. 2.43±0.21,and 1.74±0.14 vs. 3.20±0.23,all P<0.05);the protein level of p-P38(2.93±0.60 vs. 3.48±0.26,P>0.05),OPN (1.4±0.64 vs. 1.53±0.08,P>0.05),RUNX-2(1.26±0.26 vs.1.13±0.10, P>0.05) was similar between single anti-P38 group and the control group. (3) Compared with the control group, the mRNA level of OPN (1.51±0.34 vs. 1, P<0.05) and RUNX-2(2.67±0.19 vs. 1, P<0.05) was significantly upregulated in agonist-CD137 group, and these effects were blocked by adding specific P38 inhibitor SB203580(0.33±0.14 vs. 1 and 0.45±0.03 vs. 1,P<0.05);the mRNA level of OPN (1.05±0.09 vs. 1, P>0.05) and RUNX-2(1.18±0.10 vs. 1, P>0.05) was similar between the single anti-P38 group and the control group.(4) Compared with the control group,the ALP activity and calcium concentration(2.40±0.25 vs. 1.40±0.21,5.51±0.33 vs. 3.15±0.31,both P<0.05) were significantly increased in agonist-CD137 group,while the effects could be blocked by adding specific P38 inhibitor SB203580((1.99±0.07) king unit/gprot vs. (2.40±0.25) king unit/gprot, (3.74±0.20) mmol/gprot vs. (5.51±0.33) mmol/gprot, both P<0.05).The ALP activity and calcium concentration was similar between single anti-P38 group and the control group((1.60±0.25) king unit/gprot vs. (1.40±0.21)king unit/gprot, (2.66±0.28) mmol/gprot vs. (3.15±0.31) mmol/gprot, both P>0.05). (5) Compared with the control group,the calcification of VSMCs in the agonist-CD137 group was significantly increased,while the calcification in the anti-P38 group was significantly reduced.Compared with the agonist-CD137 group,the level of calcification in the anti-CD137 group was obviously increased,and the calcification in the agonist-P38 group was significantly higher than that in the anti-CD137 group and the control group. Conclusion: These findings suggest that CD137-CD137L signaling may regulate VSMCs calcification via modulating P38 pathway.