Ventricular TLR4 Levels Abrogate TLR2-Mediated Adverse Cardiac Remodeling upon Pressure Overload in Mice

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.

Toll-like Receptor 4 Differentially Modulates Cardiac Function in Response to Chronic Exposure to High-Fat Diet and Pressure Overload

“…TLR4 deficiency has previously been shown to cause less cardiac hypertrophy after myocardial infarction (MI) or pressure overload induced by transverse aortic constriction, but the studies did not address physiologic cardiac function in vivo. Furthermore, ablation of downstream metabolites in the TLR pathway in mice, such as NF-κB, was also shown to be protective against post-MI ventricular dilation and fibrosis and preserves LV function [16,17,[29][30][31].…”

“…Interestingly, TLR4-deficient mice alleviated these effects, exerting a protective effect that could be attributed to autophagy and inflammatory response damping [15]. The TLR4 pathway has also been associated with heart failure and implicated in cardiac remodeling and hypertrophy [16][17][18][19]. Additionally, NF-κB activation seems to be necessary for the development of cardiac hypertrophy as a response to aortic constriction (AC), as inhibiting it abates the hypertrophy [20].…”

“…Additionally, NF-κB activation seems to be necessary for the development of cardiac hypertrophy as a response to aortic constriction (AC), as inhibiting it abates the hypertrophy [20]. Moreover, mice subjected to pressure overload exhibited elevated mRNA levels of TLR4 in their hearts and contributed to cardiac remodeling, along with high TLR2 expression [16]. Research has demonstrated that HFD and abdominal aortic constriction (AAC) can have various impacts on different organs, including the heart.…”

“…The development of cardiac hypertrophy as a result of these stresses may be the result of the interaction of multiple pathways, such as TLR4 [15,20,21]. While TLR4 deficiency has been shown to offer cardioprotective benefits when exposed to HFD [15] and AAC [16][17][18]20], other studies showed the exact opposite effect as a response to pressure overload. In such cases, this deficiency led to worsening of the injury [22].…”

A Simplified Herbal Formula Improves Cardiac Function and Reduces Inflammation in Mice Through the TLR-Mediated NF-κB Signaling Pathway

“…TLRs are a conserved family of transmembrane protein signaling receptors that mediate innate immunity. Importantly, ventricular TLR4 contributes to adverse cardiac remodeling during chronic pressure overload ( Kessler et al, 2021 ). TLR4 can stimulate the expression of NF-κB, which is the primary transcription factor that activates and induces inflammation in cardiomyocytes ( Huang et al, 2016 ), thereby stimulating the expression of inflammatory cytokines, such as TNF-α and IL-6 ( Boyd et al, 2006 ).…”