Endothelial-Specific Deletion of Aryl Hydrocarbon Receptor Nuclear Translocator (ARNT) Leads to Microvascular Barrier Dysfunction and Cardiomyopathy

Introduction: Cardiac microvascular hyperpermeability is a key contributor to heart disease in patients with diabetes. Although the link between diabetes and microvascular barrier dysfunction is largely unknown, expression of the transcription factor aryl hydrocarbon receptor nuclear translocator (ARNT) is significantly downregulated in the cardiac microvascular endothelial cells (CMECs) of both diabetic mouse hearts (n=5, p<0.01) and the explanted hearts of patients with diabetes mellitus (n=3, p<0.05). We hypothesize that cardiac microvascular permeability is limited by the expression of ARNT in the endothelium and, consequently that endothelial-cell ARNT (ecARNT) expression is essential for normal cardiac function. Methods and Results: We have recently generated tamoxifen-inducible, endothelial-cell-specific, VE-cadherin-Cre ETR2 ARNT-knockout mice (ecARNT -/- mice). ecARNT deletion is achieved by tamoxifen oral administration for two weeks. Littermates controls are either mice without tamoxifen chow or ARNT flox/flox treated with tamoxifen diet. Induction of the ecARNT -/- mutation led to vascular leakage (as determined via in-vivo endothelial permeability assay) (n=5, p<0.05), which occurred predominantly in the heart, and to increases in matrix metalloproteinase (MMP) expression (microarray analysis), including a 3.8-fold increase in the expression of MMP3 (n=3, p<0.01). Furthermore, MMP3 inhibition attenuated the increase in cell permeability observed in CMECs from ecARNT -/- mouse hearts (as measured via electrical cell-substrate impedance sensing), as well as cardiac vascular leakage in ecARNT -/- mice, while long-term studies indicated that ejection fractions were significantly lower (ecARNT -/- : 22.3±2.6%, Control: 33.2±1.8%;), and Left ventricular end-diastolic diameters were significantly greater (ecARNT -/- : 4.8±0.8 mm, Control: 3.6±0.6 mm; n=8,p<0.01) six months after ecARNT deletion (echocardiography). Conclusion: ARNT-mediated MMP3 downregulation is required for maintaining cardiac microvascular barrier integrity and preserving cardiac function; thus, modulation of the ARNT/MMP3 axis could be a novel approach for the treatment of cardiovascular diseases such as diabetic cardiomyopathy.