[Effect and mechanism of 1, 25(OH)2D3 on myocardial inflammation induced by Coxsackie virus B3 in mice].

Objective: To explore the effect and mechanism of 1, 25(OH)2D3 on myocardial inflammation induced by Coxsackie virus B3 (CVB3) in mice. Methods: Wild type (WT) and 1α-hydroxylase knockout [1(OH)ase-/-] male mice were divided into four groups: WT group, WT+CVB3 group, 1(OH)ase-/-+CVB3 group and 1(OH)ase-/-+CVB3+VD3 group, with 8 mice in each group. The indicators for evaluating myocardial cell injury were examined by different methods. The mRNA levels of pro-inflammatory cytokines [interlenkin (IL)-1ß, IL-6, interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α)] were determined by quantitative real-time PCR. Hematoxylin-eosin (HE) staining was used to observe the myocardial histopathological changes. The apoptosis of myocardial cells was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining and flow cytometry. Fluo-4/AM fluorescence probe was used to detect intracellular calcium ion content. Meanwhile, the expression levels of Ca2+/Calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) protein as well as endoplasmic reticulum stress-related proteins like glucose-related protein 78 (GRP78) and C/EBP homologous protein (CHOP) in the myocardial tissues were detected by Western blot. Results: Compared with WT group, the mRNA levels of pro-inflammatory factors increased in the cardiomyocytes of mice in WT+CVB3 group, including IL-1ß (14.88±3.32 vs 1.03±0.02, P=0.009), IL-6 (7.00±1.09 vs 1.81±0.18, P=0.005), IFN-γ (4.70±1.11 vs 1.34±0.34, P=0.006) and TNF-α (17.20±3.22 vs 1.02±0.12, P<0.001). Similarly, the infiltration of inflammatory cells, and the apoptosis rate of cardiomyocytes elevated (16.66%±1.09% vs 7.85%±1.12%, P=0.012). The level of calcium ions in myocardial cytoplasm was significantly higher in WT+CVB3 group than that in the WT group (2.98±1.05 vs 0.96±0.10, P=0.006). Likewise, the expression levels of pCaMKⅡ(1.97±0.34 vs 1.00±0, P<0.001), GRP78 (1.78±0.19 vs 1.00±0, P=0.005) and CHOP (1.62±0.09 vs 1.00±0, P=0.002) in WT+CVB3 group up-regulated. The above myocardial cell injury markers were more significant in the 1(OH)ase-/-+CVB3 group. In the 1(OH)ase-/-+CVB3+VD3 group, 1, 25(OH)2D3 supplementation significantly improved myocardial cell injury indicators. Meanwhile, the specific inhibitors of CaMKⅡ can also reduce the myocardial injury and apoptosis rate of CVB3-infected mice. Conclusion: 1, 25(OH)2D3 deficiency can aggravate myocardial inflammation through over activation of CaMKⅡ.