405-P: Transcription Factor Tcf21 Regulates Fibrosis in Ischemic or Hyperglycemic State

Cardiac fibrosis after ischemic heart diseases or in diabetic cardiomyopathy is critical for maintaining cardiac functions. Tcf21 is a bHLH transcription factor expressed in epicardium and cardiac fibroblasts. Tcf21 knockout mice die immediately after birth because of cardiac malformation. On the other hand, little is known about its function in the adult heart. Therefore, we aimed to elucidate the role of Tcf21 after cardiac injury. Tcf21 was deleted after birth using inducible Cre-LoxP system to circumvent the lethality (iTcf21 KO). Isoproterenol (ISO) was injected (200 mg/kg) at eight weeks of age. Mice were sacrificed seven days and four weeks after ISO injection, and histological analysis was performed. Besides, cardiac fibroblasts were isolated from Tcf21 knockout embryos and subjected to RNA-seq analysis. Fibroblasts proliferation capacity was also assessed by BrdU uptake. Finally, Tcf21 expression in hyperglycemic state induced by streptozocin (STZ) was evaluated. At day 7, 1.98 ± 0.40% of the total cardiac area showed fibrosis in control, however, the fibrosis area was smaller in iTcf21 KO mice (0.67 ± 0.14%, P < 0.001). Cardiac ultrasound revealed fractional shortening was maintained in iTcf21 KO mice compared to control. Immunostaining demonstrated Ki67-positive cells decreased in iTcf21 KO (57.1% compared to controls, P = 0.032). Isolated cardiac fibroblasts from Tcf21 KO showed lower BrdU uptake (76.0 ± 3.3% for controls and 47.8 ± 7.4% for Tcf21 KO, P = 0.002) and decreased phosphorylation of Erk. RNA-seq analysis revealed potential downstream targets for Tcf21 including Il33 and Col1a1. Gene Ontology analysis demonstrated involvements of Tcf21 in the extracellular matrix and angiogenesis. STZ-induced hyperglycemic state did not evoke significant fibrosis but upregulate Tcf21 expression compared with control. These findings suggest lack of Tcf21 suppresses fibrosis after cardiac injury. Tcf21 and its targets would be a potential novel therapeutic target for cardiac diseases.