LAUSR

OBJECTIVE To explore the role of tropomyosin 3 (TPM3) in hypoxia/reoxygenation (H/R)-induced cardiomyocyte pyroptosis and fibroblast activation. METHODS Rat cardiomyocytes (H9c2 cells) were treated with H/R method to simulate myocardial ischemia/reperfusion (I/R) injury, and cell proliferation activity was evaluated with cell counting kit-8 (CCK8). The expression of TPM3 mRNA and protein was detected by quantitative real-time polymerase chain reaction (RT-qPCR) and Western blotting. H9c2 cells with stable TPM3-short hairpin RNA (shRNA) expression were constructed and treated with H/R (hypoxia for 3 hours, and reoxygenation for 4 hours). The expression of TPM3 was measured by RT-qPCR. The expressions of TPM3, pyroptosis-related proteins including caspase-1, NOD-like receptor protein 3 (NLRP3) and Gasdermin family proteins-N (GSDMD-N) were measured by Western blotting. The expression of caspase-1 was also observed by immunofluorescence assay. The levels of human interleukins (IL-1β, IL-18) in the supernatant were determined by enzyme-linked immunosorbent assay (ELISA) to elucidate the effect of sh-TPM3 on pyroptosis of cardiomyocytes. Rat myocardial fibroblasts were incubated with the above cell supernatant, and the expressions of human collagen I, collagen III, matrix metalloproteinase-2 (MMP-2), and matrix metalloproteinase inhibitor 2 (TIMP2) were detected by Western blotting to determine the effect of TPM3-interfered cardiomyocytes on the activation of fibroblasts under H/R conditions. RESULTS Compared with the control group, H/R treatment for 4 hours significantly decreased the survival rate of H9c2 cells [(25.81±1.90)% vs. (99.40±5.54)%, P < 0.01], promoted the expression of TPM3 mRNA and protein [TPM3/GAPDH (2-ΔΔCt): 3.87±0.50 vs. 1, TPM3/β-Tubulin: 0.45±0.05 vs. 0.14±0.01, both P < 0.01], and promoted the expressions of caspase-1, NLRP3, GSDMD-N, and the enhanced release of cytokines IL-1β and IL-18 [cleaved caspase-1/caspase-1: 0.89±0.04 vs. 0.42±0.03, NLRP3/β-Tubulin: 0.39±0.03 vs. 0.13±0.02, GSDMD-N/β-Tubulin: 0.69±0.05 vs. 0.21±0.02, IL-1β (μg/L): 13.84±1.89 vs. 4.31±0.33, IL-18 (μg/L): 17.56±1.94 vs. 5.36±0.63, all P < 0.01]. However, compared with the H/R group, sh-TPM3 significantly weakened the promoting effects of H/R on these proteins and cytokines [cleaved caspase-1/caspase-1: 0.57±0.05 vs. 0.89±0.04, NLRP3/β-Tubulin: 0.25±0.04 vs. 0.39±0.03, GSDMD-N/β-Tubulin: 0.27±0.03 vs. 0.69±0.05, IL-1β (μg/L): 8.56±1.22 vs. 13.84±1.89, IL-18 (μg/L): 9.34±1.04 vs. 17.56±1.94, all P < 0.01]. In addition, the expressions of collagen I, collagen III, TIMP2, and MMP-2 in myocardial fibroblasts were significantly increased by the cultured supernatants from the H/R group (collagen I/β-Tubulin: 0.62±0.05 vs. 0.09±0.01, collagen III/β-tubulin: 0.44±0.03 vs. 0.08±0.00, TIMP2/β-tubulin: 0.73±0.04 vs. 0.20±0.03, TIMP2/β-Tubulin: 0.74±0.04 vs. 0.17±0.01, all P < 0.01). However, these boosting effects were weakened by sh-TPM3 (collagen I/β-Tubulin: 0.18±0.01 vs. 0.62±0.05, collagen III/β-Tubulin: 0.21±0.03 vs. 0.44±0.03, TIMP2/β-Tubulin: 0.37±0.03 vs. 0.73±0.04, TIMP2/β-Tubulin: 0.45±0.03 vs. 0.74±0.04, all P < 0.01). CONCLUSIONS Interference with TPM3 can alleviate H/R-induced cardiomyocyte pyroptosis and fibroblast activation, suggesting that TPM3 may be a potential target of myocardial I/R injury.