Reduced cardiac hypertrophy in toll-like receptor 4-deficient mice following pressure overload.

Abstract

OBJECTIVE:

We have previously demonstrated that nuclear factor kappa B (NFkappaB) activation is needed for the development of cardiac hypertrophy in vivo. NFkappaB is a downstream transcription factor in the Toll-like receptor (TLR)-mediated signaling pathway; therefore, we investigated a role of TLR4 in cardiac hypertrophy in vivo.

METHODS:

TLR4-deficient mice (C.C3H-Tlr4(lps-d), n = 6), wild-type (WT) genetic background mice (BALB/c, n = 6), TLR4-deleted strain (C57BL/10ScCr, n = 8), and WT controls (C57BL/10ScSn, n = 8) were subjected to aortic banding for 2 weeks. Age-matched surgically operated mice served as controls. In a separate experiment, rapamycin (2 mg/kg, daily) was administered to TLR4-deficient mice and WT mice immediately following aortic banding. The ratio of heart weight/body weight (HW/BW) was calculated, and cardiac myocyte size was examined by FITC-labeled wheat germ agglutinin staining of membranes. NFkappaB binding activity and the levels of phospho-p70S6K in the myocardium were also examined.

RESULTS:

Aortic banding significantly increased the ratio of HW/BW by 33.9% (0.601 +/- 0.026 vs. 0.449 +/- 0.004) and cell size by 68.4% in WT mice and by 10.00% (0.543 +/- 0.011 vs. 0.495 +/- 0.005) and by 11.8% in TLR4-deficient mice, respectively, compared with respective sham controls. NFkappaB binding activity and phospho-p70S6K levels were increased by 182.6% and 115.2% in aortic-banded WT mice and by 78.0% and 162.0% in aortic-banded TLR4-deficient mice compared with respective sham controls. In rapamycin-treated aortic-banded mice, the ratio of HW/BW was increased by 18.0% in WT mice and by 3.5% in TLR4-deficient mice compared with respective sham controls.

CONCLUSION:

Our results demonstrate that TLR4 is a novel receptor contributing to the development of cardiac hypertrophy in vivo and that both the TLR4-mediated pathway and PI3K/Akt/mTOR signaling are involved in the development of cardiac hypertrophy in vivo.

• Authors: Tuanzhu Ha, Yuehua Li, Fang Hua, Jinag Ma, Xiang Gao, Jim Kelley, Aiqiu Zhao, Georges E Haddad, David L Williams, I William Browder, Race L Kao, Chuanfu Li
• Journal: Cardiovascular research (Cardiovasc Res) Vol. 68 Issue 2 Pg. 224-34 (Nov 01 2005) ISSN: 0008-6363 [Print] England
• PMID: 15967420 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• NF-kappa B
• Tlr4 protein, mouse
• Toll-Like Receptor 4
• Ribosomal Protein S6 Kinases, 70-kDa
• Sirolimus

Topics

• Animals
• Cardiomegaly (drug therapy, metabolism)
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Models, Animal
• Myocardial Infarction
• Myocardium (chemistry, metabolism)
• NF-kappa B (metabolism)
• Ribosomal Protein S6 Kinases, 70-kDa (analysis)
• Signal Transduction (physiology)
• Sirolimus (therapeutic use)
• Toll-Like Receptor 4 (deficiency)