Abstract 030: Angiotensin II-induced Hypertension and Cardiac Hypertrophy are Mediated Differentially by TLR3- and TLR4-dependent Pathways

Abstract

The innate immune system plays a key role in onset and maintenance of hypertension. We showed that the toll-like receptor (TLR) adaptor protein TRIF (toll interleukin receptor domain-containing adaptor-inducing interferon-b), but not MyD88 (myeloid differentiation 88), is required for angiotensin II (Ang II) induced hypertension in mice. TRIF transduces signals from TLR3 and TLR4, to induce inflammatory gene expression. In this study, we sought to determine which TLR is responsible for TRIF-mediated hypertensive effects of Ang II. We used a TLR4 deficient mice (TLR4-del) that have TLR4 gene deleted and the wild type (WT) control strain (C57BL/10). We also used a TLR3-knockout mice (TLR3ko) that have the exon 1 of the Tlr3 gene deleted. Saline or Ang II (1000 ng/kg/min) was infused subcutaneously for 3 weeks using mini-osmotic pumps and systolic blood pressure (SBP) was measured by tail cuff. Ang II increased peak SBP in WT (from 108 ± 1.3 mmHg to 136.0 ± 12.7 mmHg, n= 3) and TLR4-del (from 115.6 ± 2.7 mmHg to 154.4 ± 3.3 mmHg, n=3) mice. In contrast, peak SBP was not increased significantly with Ang II infusion in TLR3ko mice (from 111.3 ± 4.5 to 122.2 ± 18.6 mmHg, n=6) nor was it increased in WT mice after selective inhibition of TLR3 signaling with CU CPT 4a. Thus, the TLR3/TRIF, but not TLR4, pathway is essential for Ang II hypertension. In parallel with the pressure responses to Ang II, renal expression of Nox4 was significantly decreased in TLR3ko mice but was unchanged in TLR4-del and WT mice. In contrast to Ang II-induced hypertension, AngII-induced cardiac hypertrophy, measured as heart weight to body weight ratio, after 3 weeks of Ang II infusion was reduced in both TLR4-del (5.38 ± 0.19 mg/g) and TLR3ko (4.99 ± 0.15 mg/g) compared to WT (7.14 ± 0.49 mg/g). Thus, cardiac hypertrophy is abrogated in TLR4-del despite a robust pressor response to Ang II. The cardiac pro-inflammatory gene expression of tumor necrosis factor alpha ( Tnfa ), NADPH oxidase 4 ( Nox4 ), and matrix metalloproteinase 9 ( Mmp9 ) was increased in WT heart but attenuated in both TLR4-del and TLR3ko hearts. The results indicate a selective dependence of Ang II hypertension on TLR3/TRIF pathway whereas Ang II-induced cardiac hypertrophy depends on both TLR3 and TLR4, likely through the common TRIF adaptor protein.