Objective:
We previously demonstrated that angiotensin II (AngII) infusion into myeloid differentiation factor 88 deficient mice (MyD88−/−) resulted in a profound reduction of atherosclerosis and abdominal aortic aneurysms (AAAs) in apoE−/− mice. Furthermore, AngII directly regulated toll-like receptor (TLR) mRNA in cell types associated with these diseases. The objective of this study was to determine the specific TLR responsible for the MyD88 mediated reduction in vascular pathology.
Methods and Results:
MyD88 mice were bred onto an LDLr−/− background. Deficiency in this hyperlipidemic strain caused similar decreases in AngII-induced atherosclerosis and aneurysm to those we previously noted in apoE−/− mice. Male TLR4+/+ (n = 14) or −/− (n = 19), on an LDLr−/− background, were fed a fat-enriched diet (21% milk fat, 0.15% cholesterol) and infused with AngII (1,000ng/kg/min) for 28 days. TLR4−/− mice had significantly attenuated systolic blood pressure from TLR4+/+ mice both prior to and during AngII infusion (P < .01). However, AngII did increase systolic blood pressure similarly in both groups (+/+: pre-infusion 142 ± 2, post-infusion 169 ± 3 mmHg; −/−: pre-infusion 130 ± 1, post-infusion 158 ± 3 mmHg; P < .001). Neither TLR4 genotype nor AngII infusions had significantly different effects on total plasma cholesterol concentrations or lipoprotein-cholesterol distributions. TLR4 deficiency dramatically decreased AngII-induced atherosclerotic lesion areas in both the aortic arch (50% decrease, P < .004), and thoracic aorta (66% decrease, P < .001). TLR4 deficiency decreased the diameter of the suprarenal abdominal aortic region from 2.31 ± 0.3 to 1.2 ± 0.06 mm (P < 0.001) and the incidence of AAAs from 93% to 26% (P < 0.001), versus control animals. Conversely, TLR2 deficiency reduced AngII-induced atherosclerosis in LDLr−/− mice, but had no significant effect on AAA formation.
Conclusion:
TLR4 deficiency attenuated both AngII-induced atherosclerosis and AAAs, in LDLr−/− mice, in a manner similar to the effects of MyD88 deficiency. TLR2 deficiency decreased AngII-induced atherosclerosis, but had no effect on AAAs. These data are consistent with TLR4 being the major receptor for MyD88-induced effects on AngII-induced AAAs.
This research has received full or partial funding support from the American Heart Association, AHA Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).
Differential Effects of Doxycycline, a Broad-Spectrum Matrix Metalloproteinase Inhibitor, on Angiotensin II–Induced Atherosclerosis and Abdominal Aortic Aneurysms
