Abstract
AimsRetinoic acid receptor-related orphan nuclear receptor γt (RORγt) is a transcriptional factor responsible for IL-17-producing T-cell differentiation. Although it was demonstrated that RORγt plays essential roles in the onset of autoimmune myocarditis, pathophysiological significance of RORγt in cardiac remodeling after myocardial infarction (MI) remains to be fully elucidated.Methods and resultsMI was generated by ligating coronary artery. The expression of RORγt and IL-17A transcripts increased in murine hearts after MI. Additionally, immunohistochemical staining revealed that RORγt-expressing cells infiltrated in the border zone after MI. Flow cytometric analysis showed that RORγt-expressing cells were released from the spleen at day 1 after MI. Though RORγt-expressing cells in spleen expressed γδTCR or CD4, γδTCR+ cells were major population of RORγt-expressing cells that infiltrated into post-infarct myocardium. To address the biological functions of RORγt-expressing cells in infarcted hearts, we used mice with enhanced GFP gene heterozygously knocked-in at RORγt locus (RORγt+/- mice), which physiologically showed reduced expression of RORγt mRNA in thymus. Kaplan-Meier analysis showed that MI-induced mortality was higher in RORγt+/- mice than wild-type (WT) mice. Masson’s trichrome staining demonstrated that cardiac injury was exacerbated in RORγt+/- mice 7 days after MI (Injured area: RORγt+/-; 42.1±6.5%, WT; 34.0±3.7%, circumference of injured myocardium: RORγt+/-; 61.8±4.8%, WT; 49.6±5.1%), accompanied by exacerbation of cardiac function (fractional shortening: RORγt+/-; 32.9±2.9%, WT; 38.3±3.6%). Moreover, immunohistochemical analyses revealed that capillary density in border zone was significantly reduced in RORγt+/- mice after MI, compared with WT mice, associated with the reduced expression of angiopoietin 2. Finally, the mRNA expression of RORγt, IL-17A, IL-17F and IL-23 receptor (IL-23R) mRNA and protein expression of IL-10 were decreased in RORγt+/- hearts.ConclusionsHeterozygous deletion of RORγt gene resulted in aggravated cardiac remodeling, accompanied by reduced capillary density, after MI, suggesting that RORγt-expressing cells contribute to tissue repair in infarcted myocardium.
Highlights
Myocardial infarction (MI) is one of the major causes of heart failure
Heterozygous deletion of receptor γt (RORγt) gene resulted in aggravated cardiac remodeling, accompanied by reduced capillary density, after MI, suggesting that RORγt-expressing cells contribute to tissue repair in infarcted myocardium
We examined the expression of RORγt and IL-17A mRNA in post-infarct myocardium by quantitative RT-PCR (Fig 1A)
Summary
Myocardial infarction (MI) is one of the major causes of heart failure. MI induces cardiomyocyte death, followed by infiltration of immune cells into post-infarct myocardium. The immune cells positively or negatively regulate myocardial inflammation and modulate adverse cardiac remodeling [1,2,3]. Neutrophils infiltrate into infarcted myocardium immediately after coronary occlusion and aggravate tissue damage by producing reactive oxygen species (ROS) [4,5]. Macrophages contribute to the clearance of dead cells after MI and promote angiogenesis, leading to wound healing [6,7,8]. In order to understand the importance of immune cells in cardiac remodeling, it would be required to make clear the biological functions of immune cells based on cell-lineage in more detail
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