Cardiac Fibroblast-Specific Activating Transcription Factor 3 Promotes Myocardial Repair after Myocardial Infarction.

Background: Myocardial ischemia injury is one of the leading causes of death and disability worldwide. Cardiac fibroblasts (CFs) have central roles in modulating cardiac function under pathophysiological conditions. Activating transcription factor 3 (ATF3) plays a self-protective role in counteracting CF dysfunction. However, the precise function of CF-specific ATF3 during myocardial infarction (MI) injury/repair remains incompletely understood. The aim of this study was to determine whether CF-specific ATF3 affected cardiac repair after MI.

Methods: Fifteen male C57BL/6 wild-type mice were performed with MI operation to observe the expression of ATF3 at 0, 0.5, 1.0, 3.0, and 7.0 days postoperation. Model for MI was constructed in ATF3TGfl/flCol1a2-Cre+ (CF-specific ATF3 overexpression group, n = 5) and ATF3TGfl/flCol1a2-Cre- male mice (without CF-specific ATF3 overexpression group, n = 5). In addition, five mice of ATF3TGfl/flCol1a2-Cre+ and ATF3TGfl/flCol1a2-Cre- were subjected to sham MI operation. Heart function was detected by ultrasound and left ventricular remodeling was observed by Masson staining (myocardial fibrosis area was detected by blue collagen deposition area) at the 28th day after MI surgery in ATF3TGfl/flCol1a2-Cre+ and ATF3TGfl/flCol1a2-Cre- mice received sham or MI operation. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect cell proliferation/cell cycle-related gene expression in cardiac tissue. BrdU staining was used to detect fibroblast proliferation.

Results: After establishment of an MI model, we found that ATF3 proteins were increased in the heart of mice after MI surgery and dominantly expressed in CFs. Genetic overexpression of ATF3 in CFs (ATF3TGfl/flCol1a2-Cre+ group) resulted in an improvement in the heart function as indicated by increased cardiac ejection fraction (41.0% vs. 30.5%, t = 8.610, P = 0.001) and increased fractional shortening (26.8% vs. 18.1%, t = 7.173, P = 0.002), which was accompanied by a decrease in cardiac scar area (23.1% vs. 11.0%, t = 8.610, P = 0.001). qRT-PCR analysis of CFs isolated from ATF3TGfl/flCol1a2-Cre+ and ATF3TGfl/flCol1a2-Cre- ischemic hearts revealed a distinct transcriptional profile in ATF3-overexpressing CFs, displaying pro-proliferation properties. BrdU-positive cells significantly increased in ATF3-overexpressing CFs than control CFs under angiotensin II stimuli (11.5% vs. 6.8%, t = 31.599, P = 0.001) or serum stimuli (31.6% vs. 20.1%, t = 31.599, P = 0.001). The 5(6)-carboxyfluorescein N-hydroxysuccinimidyl ester assay showed that the cell numbers of the P2 and P3 generations were higher in the ATF3-overexpressing CFs at 24 h (P2: 91.6% vs. 71.8%, t = 8.465, P = 0.015) and 48 h (P3: 81.6% vs. 51.1%, t = 9.029, P = 0.012) after serum stimulation. Notably, ATF3 overexpression-induced CF proliferation was clearly increased in the heart after MI injury.

Conclusions: We identify that CF-specific ATF3 might contribute to be MI repair through upregulating the expression of cell cycle/proliferation-related genes and enhancing cell proliferation.