GPR55 deletion in mice leads to age-related ventricular dysfunction and impaired adrenoceptor-mediated inotropic responses.

G protein coupled receptor 55 (GPR55) is expressed throughout the body and, although its exact physiological function is unknown, studies have suggested that it has a role in the cardiovascular system. In particular, GPR55 has been proposed as mediating the haemodynamic effects of a number of atypical cannabinoid ligands; however this data is conflicting. Thus, given the incongruous nature of our understanding of the GPR55 receptor and the relative paucity of literature regarding its role in cardiovascular physiology, this study was carried out to examine the influence of GPR55 on cardiac function. Cardiac function was assessed via pressure volume loop analysis, and cardiac morphology/composition assessed via histological staining, in both wild-type (WT) and GPR55 knockout (GPR55−/−) mice. Pressure volume loop analysis revealed that basal cardiac function was similar in young WT and GPR55−/− mice. In contrast, mature GPR55−/− mice were characterised by both significant ventricular remodelling (reduced left ventricular wall thickness and increased collagen deposition) and systolic dysfunction when compared to age-matched WT mice. In particular, the load-dependent parameter, ejection fraction, and the load-independent indices, end-systolic pressure-volume relationship (ESPVR) and Emax, were all significantly (P < 0.05) attenuated in mature GPR55−/− mice. Furthermore, GPR55−/− mice at all ages were characterised by a reduced contractile reserve. Our findings demonstrate that mice deficient in GPR55 exhibit maladaptive adrenergic signalling, as evidenced by the reduced contractile reserve. Furthermore, with age these mice are characterised by both significant adverse ventricular remodelling and systolic dysfunction. Taken together, this may suggest a role for GPR55 in the control of adrenergic signalling in the heart and potentially a role for this receptor in the pathogenesis of heart failure

Measurement of ventricular dimensions in WT and GPR55^−/− mice.

<p>Ventricular dimensions did not differ significantly between young WT and GPR55^−/− mice, however mature GPR55^−/− mice were characterised by significant myocardial remodelling; including a reduction in left ventricular (LV) free wall thickness, myocardial nuclei number, and HW∶BW, and increased collagen deposition. Data is expressed as mean±s.e.m. (n = 14–15).</p><p>*P<0.05 vs. WT (Young);</p>#<p>P<0.05 vs. GPR55^−/− (Young);</p>†<p>P<0.05 vs. WT (Mature).</p><p>Measurement of ventricular dimensions in WT and GPR55^−/− mice.</p

Load-independent (ESPVR, EDPVR, and <i>E</i>_max) haemodynamic parameters in both WT and GPR55^−/− mice.

<p>In mature mice with a genetic deletion for GPR55 (GPR55^−/−), baseline systolic function, but not diastolic function, was adversely affected. In particular, significant reductions in both ESPVR (A) and <i>E</i>_max (B) indicate attenuated cardiac contractility, while EDPVR (indicative of relaxation rate) was unaffected (C) in mature GPR55^−/− mice. Data is expressed as mean±s.e.m. (n = 14–15) *P<0.05 vs. WT (Young); #P<0.05 vs. GPR55^−/− (Young); †P<0.05 vs. WT (Mature).</p

Effect of GPR55 gene deletion on contractile reserve in young (10 week old) and mature (8 month old) mice.

<p>Contractile reserve, assessed by the change from baseline cardiac function in response to the α₁/β₁-adrenoceptor agonist dobutamine, was significantly attenuated in both young and mature mice with a gene deletion for GPR55. Data is expressed as mean±s.e.m. (n = 14–15).</p><p>*P<0.05 vs. WT (Young);</p>†<p>P<0.05 vs. WT (Mature).</p><p>Effect of GPR55 gene deletion on contractile reserve in young (10 week old) and mature (8 month old) mice.</p

Representative left ventricular pressure volume loops from all experimental groups are included and illustrate the emerging systolic dysfunction (i.e. downward and rightward shift in the ESPVR curve) associated with mature GPR55^−/− mice.

<p>Representative left ventricular pressure volume loops from all experimental groups are included and illustrate the emerging systolic dysfunction (i.e. downward and rightward shift in the ESPVR curve) associated with mature GPR55^−/− mice.</p

Influence of GPR55 gene deletion on cardiac collagen deposition.

<p>Representative photomicrographs (×400) demonstrating cardiac collagen deposition in young WT (A), young GPR55^−/− (B), mature WT (C), and mature GPR55^−/− (D) mice. Collagen deposition was significantly increased in the left ventricle of mature GPR55^−/− mice (E). Data is expressed as mean±s.e.m. (n = 14–15) #P<0.05 vs. GPR55^−/− (Young); †P<0.05 vs. WT (Mature).</p

Expression of GPR55 in ventricular tissue from WT and GPR55^−/− mice.

<p>Photomicrographs taken at ×200 demonstrate positive staining for GPR55 in ventricular tissue (localised to the cardiomyocytes) from WT mice (A), but not GPR55^−/− mice (B).</p

Load-dependent haemodynamic parameters in control (WT) mice and those with a genetic deletion for GPR55 (GPR55^−/−).

<p>Cardiac function is unaffected by age in WT mice, but undergoes a significant deterioration in GPR55 deficient mice. Data is expressed as mean±s.e.m. (n = 14–15).</p><p>*P<0.05 vs. WT (Young);</p>#<p>P<0.05 vs. GPR55^−/− (Young);</p>†<p>P<0.05 vs. WT (Mature).</p><p>Load-dependent haemodynamic parameters in control (WT) mice and those with a genetic deletion for GPR55 (GPR55^−/−).</p

The APOE∗3-Leiden Heterozygous Glucokinase Knockout Mouse as Novel Translational Disease Model for Type 2 Diabetes, Dyslipidemia, and Diabetic Atherosclerosis

Background. There is a lack of predictive preclinical animal models combining atherosclerosis and type 2 diabetes. APOE∗3-Leiden (E3L) mice are a well-established model for diet-induced hyperlipidemia and atherosclerosis, and glucokinase+/− (GK+/−) mice are a translatable disease model for glucose control in type 2 diabetes. The respective mice respond similarly to lipid-lowering and antidiabetic drugs as humans. The objective of this study was to evaluate/characterize the APOE∗3-Leiden.glucokinase+/− (E3L.GK+/−) mouse as a novel disease model to study the metabolic syndrome and diabetic complications. Methods. Female E3L.GK+/−, E3L, and GK+/− mice were fed fat- and cholesterol-containing diets for 37 weeks, and plasma parameters were measured throughout. Development of diabetic macro- and microvascular complications was evaluated. Results. Cholesterol and triglyceride levels were significantly elevated in E3L and E3L.GK+/− mice compared to GK+/− mice, whereas fasting glucose was significantly increased in E3L.GK+/− and GK+/− mice compared to E3L. Atherosclerotic lesion size was increased 2.2-fold in E3L.GK+/− mice as compared to E3L (p=0.037), which was predicted by glucose exposure (R2=0.636, p=0.001). E3L and E3L.GK+/− mice developed NASH with severe inflammation and fibrosis which, however, was not altered by introduction of the defective GK phenotype, whereas mild kidney pathology with tubular vacuolization was present in all three phenotypes. Conclusions. We conclude that the E3L.GK+/− mouse is a promising novel diet-inducible disease model for investigation of the etiology and evaluation of drug treatment on diabetic atherosclerosis