Abstract
Involvement of the Toll-like receptor 4 (TLR4) in maladaptive cardiac remodeling and heart failure (HF) upon pressure overload has been studied extensively, but less is known about the role of TLR2. Interplay and redundancy of TLR4 with TLR2 have been reported in other organs but were not investigated during cardiac dysfunction. We explored whether TLR2 deficiency leads to less adverse cardiac remodeling upon chronic pressure overload and whether TLR2 and TLR4 additively contribute to this. We subjected 35 male C57BL/6J mice (wildtype (WT) or TLR2 knockout (KO)) to sham or transverse aortic constriction (TAC) surgery. After 12 weeks, echocardiography and electrocardiography were performed, and hearts were extracted for molecular and histological analysis. TLR2 deficiency (n = 14) was confirmed in all KO mice by PCR and resulted in less hypertrophy (heart weight to tibia length ratio (HW/TL), smaller cross-sectional cardiomyocyte area and decreased brain natriuretic peptide (BNP) mRNA expression, p < 0.05), increased contractility (QRS and QTc, p < 0.05), and less inflammation (e.g., interleukins 6 and 1β, p < 0.05) after TAC compared to WT animals (n = 11). Even though TLR2 KO TAC animals presented with lower levels of ventricular TLR4 mRNA than WT TAC animals (13.2 ± 0.8 vs. 16.6 ± 0.7 mg/mm, p < 0.01), TLR4 mRNA expression was increased in animals with the largest ventricular mass, highest hypertrophy, and lowest ejection fraction, leading to two distinct groups of TLR2 KO TAC animals with variations in cardiac remodeling. This variation, however, was not seen in WT TAC animals even though heart weight/tibia length correlated with expression of TLR4 in these animals (r = 0.078, p = 0.005). Our data suggest that TLR2 deficiency ameliorates adverse cardiac remodeling and that ventricular TLR2 and TLR4 additively contribute to adverse cardiac remodeling during chronic pressure overload. Therefore, both TLRs may be therapeutic targets to prevent or interfere in the underlying molecular processes.
Highlights
Hypertension due to chronic pressure overload is a major cardiovascular risk factor affecting a billion individuals worldwide [1,2]
In order to investigate whether ventricular TLR2 deficiency decreases adverse cardiac remodeling during pressure overload, a TLR2 KO mouse model was subjected to either sham or transverse aortic constriction (TAC) surgery
We showed that ventricular Toll-like receptor 4 (TLR4) levels were high in failing murine hearts during cardiac dysfunction and, demonstrated a possible correlation of ventricular TLR2 and TLR4 during pressure overload
Summary
Hypertension due to chronic pressure overload is a major cardiovascular risk factor affecting a billion individuals worldwide [1,2]. Besides TLR4, which is the most abundant and well-studied TLR in the heart, TLR2 is the most abundant cardiac TLR Both are expressed in immune and cardiac nonimmune cells (e.g., cardiomyocytes, fibroblasts, and vascular endothelial cells) [5,7], but knowledge about TLR2 s involvement in adverse cardiac remodeling is scarce. Upon ligand binding and activation of the TLR2 and TLR4 receptor, transcription factors such as the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) are translocated to the nucleus. This induces expression of inflammatory cytokines and chemokines (e.g., interleukin-1beta (IL-1β), IL-6 and tumor necrosis factor-alpha (TNF-α)), leading to an invasion of pro-inflammatory cells [8]
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