FOXC1 up-regulates the expression of toll-like receptors in myocardial ischaemia.

Myocardial ischaemia (MI) remains a major cause of death and disability worldwide. Accumulating evidence suggests a significant role for innate immunity, in which the family of toll-like receptors (TLRs) acts as an essential player. We previously reported and reviewed the changes of Tlr expression in models of MI. However, the underlying mechanisms regulating Tlr expression in MI remain unclear. The present study first screened transcription factors (TFs) that potentially regulate Tlr gene transcription based on in silico analyses followed by experimental verification, using both in vivo and in vitro models. Forkhead box C1 (FOXC1) was identified as a putative TF, which was highly responsive to MI. Next, by focusing on two representative TLR subtypes, an intracellular subtype TLR3 and a cell-surface subtype TLR4, the regulation of FOXC1 on Tlr expression was investigated. The overexpression or knockdown of FoxC1 was observed to up- or down-regulate Tlr3/4 mRNA and protein levels, respectively. A dual-luciferase assay showed that FOXC1 trans-activated Tlr3/4 promoter, and a ChIP assay showed direct binding of FOXC1 to Tlr3/4 promoter. Last, a functional study of FOXC1 was performed, which revealed the pro-inflammatory effects of FOXC1 and its destructive effects on infarct size and heart function in a mouse model of MI. The present study for the first time identified FOXC1 as a novel regulator of Tlr expression and described its function in MI.