C11995500bt

All the HEK293F-derived cells are maintained in Dulbecco’s Modified Eagle Medium (Gibco C11995500BT) with 10% fetal bovine serum (Biological Industries 04-010-1ACS 500 mL) and 1× penicillin streptomycin solution (Sangon Biotech, China E607011-0100) using a cell culture incubator at 37°C and 5% CO₂. The HEK293F cells stably inserted with a DNA methylation silenced CMV reporter (Figure 1A) and its TET1 KO, TET2 KO, TET3 KO, TET TKO, and RELA KO cells are previously established and described (Li et al., 2018b (link); Zhao et al., 2019 (link)). The MER11B-left KO, MER11B-right KO, MER11B-left+right KO, and ERV KO cells generated in this study are also derived from the HEK293F cells stably inserted with the DNA methylation silenced CMV reporter. The cell lines used in this study are free from mycoplasma contamination and authenticated: The HEK293F cells stably inserted with a DNA methylation silenced CMV reporter is established in Dr. Bing Zhu’s lab and widely used in our previous studies (Dong et al., 2018 (link); Du et al., 2019 (link); Li et al., 2018a (link); Li et al., 2018b (link); Zhao et al., 2019 (link)); the flow cytometry results (Figure 1C) can confirm the insertion of DNA methylation-silenced CMV reporter.

All animal experiments were approved by the Institutional Animal Care and Use Committee of Central South University (Changsha, China).
Cardiac tissue from 1-day-old C57/BL6 neonates were purchased from Hunan SJA Laboratory Animal Co., Ltd. (Hunan, China). To isolate cardiomyocytes, the heart was digested with 2.5 mg mL⁻¹ trypsin(Aladdin Co., Ltd, Shanghai, China)and perfused with digestion buffer containing 2 mg mL⁻¹ DNase I (Sigma, D7291). The cardiomyocytes were collected from the tissue piece suspension upon centrifugation and cultured in DMEM (HyClone, C11995500BT) containing 20% FBS (Biological Industries, 04-001-1ACS), 40 IU mL⁻¹ penicillin (Sigma, P3032), 1.6 μg mL⁻¹ VitB12.
(Sigma, V6629) and 0.1 mmol L⁻¹ 5ˊ-bromo-2ˊ-deoxyuridine (Sigma, B5002) at 37 °C, 5% CO₂, 21% O₂ and 74% N₂.
Male C57/BL6 mice aged 8 to 12 weeks (range 20–30 g) were purchased from Hunan SJA Laboratory Animal Co., Ltd. (Hunan, China), housed and maintained at room-temperature in an air-conditioned environment.