Overexpression of endothelial β₃ -adrenergic receptor induces diastolic dysfunction in rats

Diastolic dysfunction is common in cardiovascular diseases, particularly in the case of heart failure with preserved ejection fraction. The challenge is to develop adequate animal models to envision human therapies in the future. It has been hypothesized that this diastolic dysfunction is linked to alterations in the nitric oxide (^• NO) pathway. To investigate this issue further, we investigated the cardiac functions of a transgenic rat model (Tgβ₃ ) that overexpresses the human β₃ -adrenoceptor (hβ₃ -AR) in the endothelium with the underlying rationale that the ^• NO pathway should be stimulated in the endothelium.

Transgenic rats (Tgβ₃ ) that express hβ₃ -AR under the control of intercellular adhesion molecule 2 promoter were developed for a specific expression in endothelial cells. Transcriptomic analyses were performed on left ventricular tissue from 45-week-old rats. Among all altered genes, we focus on ^• NO synthase expression and endothelial function with arterial reactivity and evaluation of ^• NO and O₂ ^•- production. Cardiac function was characterized by echocardiography, invasive haemodynamic studies, and working heart studies. Transcriptome analyses illustrate that several key genes are regulated by the hβ₃ -AR overexpression. Overexpression of hβ₃ -AR leads to a reduction of Nos3 mRNA expression (-72%; P < 0.05) associated with a decrease in protein expression (-19%; P < 0.05). Concentration-dependent vasodilation to isoproterenol was significantly reduced in Tgβ₃ aorta (-10%; P < 0.05), while ^• NO and O₂ ^•- production was increased. In the same time, Tgβ₃ rats display progressively increasing diastolic dysfunction with age, as shown by an increase in the E/A filing ratio [1.15 ± 0.01 (wild type, WT) vs. 1.33 ± 0.04 (Tgβ₃ ); P < 0.05] and in left ventricular end-diastolic pressure [5.57 ± 1.23 mmHg (WT) vs. 11.68 ± 1.11 mmHg (Tgβ₃ ); P < 0.05]. In isolated working hearts, diastolic stress using increasing preload levels led to a 20% decrease in aortic flow [55.4 ± 1.9 mL/min (WT) vs. 45.8 ± 2.5 mL/min (Tgβ₃ ); P < 0.05].

The Tgβ₃ rat model displays the expected increase in ^• NO production upon ageing and develops diastolic dysfunction. These findings provide a further link between endothelial and cardiac dysfunction. This rat model should be valuable for future preclinical evaluation of candidate drugs aimed at correcting diastolic dysfunction.