Tlr4 Deficiency Protects against Cardiac Pressure Overload Induced Hyperinflammation

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

BACKGROUND/AIM

The impact of myocardial stressors such as high-fat diet (HFD) and pressure overload has been extensively studied. Toll-like receptor 4 (TLR4) deficiency has been suggested to have a protective role in response to these stressors, although some conflicting data exist. Furthermore, there is limited information about the role of TLR4 on cardiac remodeling in response to long-term exposure to stressors. This study aims to investigate the effects of TLR4 deficiency on cardiac histology and physiology in response to chronic stressors.

METHODS

TLR4-deficient (TLR4-/-) and wild-type (WT) mice were subjected to either HFD or a normal diet (ND) for 28 weeks. Another group underwent abdominal aortic constriction (AAC) or a sham procedure and was monitored for 12 weeks. Inflammatory markers, histology, and echocardiography were used to assess the effects of these interventions.

RESULTS

TLR4-/- mice exhibited reduced cardiac hypertrophy and fibrosis after long-term HFD exposure compared to ND without affecting cardiac function. On the other hand, TLR4 deficiency worsened cardiac function in response to AAC, leading to decreased ejection fraction (EF%) and increased end-systolic volume (ESV).

CONCLUSIONS

TLR4 deficiency provided protection against HFD-induced myocardial inflammation but impaired hemodynamic cardiac function under pressure overload conditions. These findings highlight the crucial role of TLR4 and its downstream signaling pathway in maintaining cardiac output during physiologic cardiac hypertrophy in response to pressure overload.

The direct effect of lipopolysaccharide on an isolated heart is different from the effect on cardiac myocytes in vitro

INTRODUCTION

Lipopolysaccharide (LPS) is widely used to induce experimental animals. However, its effects on cardiac contraction is controversial. Although LPS probably induces its influence in vivo both directly and indirectly, we focused on the direct effects of LPS in this report.

MATERIAL AND METHODS

Isolated ventricular myocytes mounted on a Langendorff apparatus were perfused with LPS. The changes in cultured H9c2 cells incubated with LPS over a 3-h exposure were compared with the changes after a 24-h incubation. Apoptosis was identified using flow cytometry and Western blotting. The mRNA levels were also determined.

RESULTS

LPS directly stimulated cardiac contractility at low doses, although it produced inhibition at higher doses. The TLR4-coupled JAK2/STAT3 pathway was identified in H9c2 cells after LPS treatment, with an increase in intracellular calcium levels. LPS dose-dependently activated hypertrophic signals in H9c2 cells and induced apoptosis at the high dose. However, apoptosis was observed in H9c2 cells after a 24-h exposure to LPS, even at low doses. This observation appears to be associated with the level of paracrine cytokines. Changes in H9c2 cells by LPS were diminished by NPS2390, an inhibitor of the calcium-sensing receptor (CaSR). LPS also promoted CaSR mRNA expression in H9c2 cells, which may be unrelated to the changes in cytokine expression influenced by an inflammasome inhibitor.

CONCLUSIONS

In contrast to the isolated hearts, LPS activated hypertrophic signals prior to apoptotic signals in cardiac cells. Thus, LPS injury appears to be associated with CaSR, which was not markedly influenced by an inflammasome inhibitor.

Characterization of Transverse Aortic Constriction in Mice Based on the Specific Recruitment of Leukocytes to the Hypertrophic Myocardium and the Aorta Ascendens

Transverse aortic constriction (TAC) is a model that mimics pressure overload-induced left ventricular (LV) hypertrophy in mice. Alterations in immune cell functionality can promote cardiac and vascular remodeling. In the present study, we characterized the time course in innate immune cell dynamics in response to TAC in the different tissues of mice. It was determined whether TAC induces a characteristic leukocyte-driven immune response in the myocardium, aorta ascendens and descendens, spleen, blood, and draining lymph nodes supported by cytokine-driven chemotaxis in mice at 3, 6, and 21 days following surgery. We used complex flow cytometry staining combinations to characterize the various innate immune cell subsets and a multiplex array to determine cytokine concentrations in the serum. The results of the current study indicated that leukocytes accumulate in the myocardium and aorta ascendens in response to TAC. The leukocyte dynamics in the myocardium were dominated by the Ly6C^low macrophages with an early accumulation, whereas the response in the aorta ascendens was characterized by a long-lasting proinflammatory phenotype driven by Ly6C^high macrophages, neutrophils, and activated DCs. In contrast to the high-pressure environment of the aorta ascendens, the tissue of the aorta descendens did not react to TAC with any leukocyte increase. The levels of proinflammatory cytokines in the blood were elevated in response to TAC, indicating a systemic reaction. Moreover, our findings strongly suggest that cardiac macrophages could origin from splenic pools and reach the site of the inflammation via the blood. Based on the current findings, it can be concluded that the high-pressure conditions in the aorta ascendens cause a characteristic immune response, dominated by the accumulation of leukocytes and the activation of DCs that varies in comparison to the immune cell dynamics in the myocardium and the aorta descendens.

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

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.

Key Player in Cardiac Hypertrophy, Emphasizing the Role of Toll-Like Receptor 4

Toll-like receptor 4 (TLR4), a key pattern recognition receptor, initiates the innate immune response and leads to chronic and acute inflammation. In the past decades, accumulating evidence has implicated TLR4-mediated inflammatory response in regulation of myocardium hypertrophic remodeling, indicating that regulation of the TLR4 signaling pathway may be an effective strategy for managing cardiac hypertrophy's pathophysiology. Given TLR4's significance, it is imperative to review the molecular mechanisms and roles underlying TLR4 signaling in cardiac hypertrophy. Here, we comprehensively review the current knowledge of TLR4-mediated inflammatory response and its interaction ligands and co-receptors, as well as activation of various intracellular signaling. We also describe the associated roles in promoting immune cell infiltration and inflammatory mediator secretion, that ultimately cause cardiac hypertrophy. Finally, we provide examples of some of the most promising drugs and new technologies that have the potential to attenuate TLR4-mediated inflammatory response and prevent or reverse the ominous cardiac hypertrophy outcomes.

TLR4 contributes to the damage of cartilage and subchondral bone in discectomy-induced TMJOA mice

The abundance of inflammatory mediators in injured joint indicates innate immune reactions activated during temporomandibular joint osteoarthritis (TMJOA) progression. Toll‐like receptor 4 (TLR4) can mediate innate immune reaction. Herein, we aimed to investigate the expression profile and effect of TLR4 in the cartilage and subchondral bone of the discectomy‐induced TMJOA mice. The expression of TLR4 and NFκB p65 in the synovium of TMJOA patients was measured by immunohistochemistry, Western blotting and RT‐PCR. H&E and Masson staining were utilized to assess the damage of cartilage and subchondral bone of the discectomy‐induced TMJOA mice. A TLR4 inhibitor, TAK‐242, was used to assess the effect of TLR4 in the cartilage and subchondral bone of the discectomy‐induced TMJOA mice by Safranin O, micro‐CT, immunofluorescence and immunohistochemistry. Western blotting was used to quantify the expression and effect of TLR4 in IL‐1β–induced chondrocytes. The expression of TLR4 and NFκB p65 was elevated in the synovium of TMJOA patients, compared with the normal synovium. TLR4 elevated in the damaged cartilage and subchondral bone of discectomy‐induced TMJOA mice, and the rate of TLR4 expressing chondrocytes positively correlated with OA score. Intraperitoneal injections of TAK‐242 ameliorate the extent of TMJOA. Furthermore, TLR4 promotes the expression of MyD88/NFκB, pro‐inflammatory and catabolic mediators in cartilage of discectomy‐induced TMJOA. Besides, TLR4 participates in the production of MyD88/NFκB, pro‐inflammatory and catabolic mediators in IL‐1β–induced chondrocytes. TLR4 contributes to the damage of cartilage and subchondral bone in discectomy‐induced TMJOA mice through activation of MyD88/NFκB and release of pro‐inflammatory and catabolic mediators.

Left ventricular hypertrophy is associated with overexpression of HSP60, TLR2, and TLR4 in the myocardium

Left ventricular hypertrophy is a common adaptive response to increased cardiac workload. Cardiomyocytes growth and increase in contractile force are conditioned by sufficient energy production, which implies appropriate mitochondrial function. The 60 kDa heat shock protein (HSP60) is a chaperone essential for mitochondrial proteostasis, but when translocates from mitochondria, it can also act as a potent inflammatory mediator binding to toll-like receptors (TLRs). In this study, we aimed to compare the expression pattern of HSP60, TLR2, and TLR4 in hypertrophic vs non-hypertrophic, normal human myocardium. We further examined whether HSP60 in situ binds to TLRs in hypertrophic myocardial tissue. In addition, expression of activated downstream targets of TLR 2/4 pathways was also evaluated.For this purpose, immunohistochemical expression analyses were performed on myocardial tissue samples obtained during the autopsy of human subjects in which left ventricular hypertrophy was the only cardiopathological finding and had died from sudden cardiac death, as well as from the subjects without any cardiac pathology, that died by unnatural death (accident or suicide). Double immunofluorescence was used to examine HSP60 translocation, while proximity ligation assay (PLA) was performed to assess HSP60 and TLRs interactions.Hypertrophic myocardium showed significantly higher expression of HSP60, TLR2, and TLR4 compared to normal myocardium. Furthermore, in hypertrophic cardiomyocytes, we found membrane translocation of HSP60 and signs of HSP60/TLR interactions.Conclusion: The obtained data point to an important supportive role of HSP60 in adaptive cardiomyocytes growth, while concomitant induction of TLR2 and TLR4 candidates HSP60-TLRs interactions as an early events during pathogenesis of secondary complications consequently to the left ventricular hypertrophy.

UBE3A alleviates isoproterenol-induced cardiac hypertrophy through the inhibition of the TLR4/MMP-9 signaling pathway

Cardiac hypertrophy is considered to be a leading factor in heart function-related deaths. In this study, we explored the potential mechanism underlying cardiac hypertrophy induced by isoproterenol. Our results showed that isoproterenol induced cardiac hypertrophy in AC16 cells, as reflected by the increased cell surface area and increased hypertrophic markers, which was accompanied by increased ubiquitin-protein ligase E3a (UBE3A) expression. Moreover, UBE3A knockdown by siRNAs accelerated cardiac hypertrophy, suggesting that increased UBE3A expression induced by isoproterenol might be a protective response and UBE3A might be a protective factor against cardiac hypertrophy. Our study also revealed that UBE3A knockdown increased the protein expression of the TLR4/MMP-9 pathway that has been shown to be associated with cardiac hypertrophy, which suggested that UBE3A-mediated protection is likely to be associated with the blockade of the TLR4/MMP-9 signaling pathway. UBE3A might be thus a potential target gene for the treatment of cardiac hypertrophy.

New Approaches to Target Inflammation in Heart Failure: Harnessing Insights from Studies of Immune Cell Diversity

Despite mounting evidence implicating inflammation in cardiovascular diseases, attempts at clinical translation have shown mixed results. Recent preclinical studies have reenergized this field and provided new insights into how to favorably modulate cardiac macrophage function in the context of acute myocardial injury and chronic disease. In this review, we discuss the origins and roles of cardiac macrophage populations in the steady-state and diseased heart, focusing on the human heart and mouse models of ischemia, hypertensive heart disease, and aortic stenosis. Specific attention is given to delineating the roles of tissue-resident and recruited monocyte-derived macrophage subsets. We also highlight emerging concepts of monocyte plasticity and heterogeneity among monocyte-derived macrophages, describe possible mechanisms by which infiltrating monocytes acquire unique macrophage fates, and discuss the putative impact of these populations on cardiac remodeling. Finally, we discuss strategies to target inflammatory macrophage populations.

Inflammation and NLRP3 Inflammasome Activation Initiated in Response to Pressure Overload by Ca2+/Calmodulin-Dependent Protein Kinase II δ Signaling in Cardiomyocytes Are Essential for Adverse Cardiac Remodeling

BACKGROUND

Inflammation is associated with cardiac remodeling and heart failure, but how it is initiated in response to nonischemic interventions in the absence of cell death is not known. We tested the hypothesis that activation of Ca²⁺/calmodulin-dependent protein kinase II δ (CaMKIIδ) in cardiomyocytes (CMs) in response to pressure overload elicits inflammatory responses leading to adverse remodeling.

METHODS

Mice in which CaMKIIδ was selectively deleted from CMs (cardiac-specific knockout [CKO]) and floxed control mice were subjected to transverse aortic constriction (TAC). The effects of CM-specific CaMKIIδ deletion on inflammatory gene expression, inflammasome activation, macrophage accumulation, and fibrosis were assessed by quantitative polymerase chain reaction, histochemistry, and ventricular remodeling by echocardiography.

RESULTS

TAC induced increases in cardiac mRNA levels for proinflammatory chemokines and cytokines in ≤3 days, and these responses were significantly blunted when CM CaMKIIδ was deleted. Apoptotic and necrotic cell death were absent at this time. CMs isolated from TAC hearts mirrored these robust increases in gene expression, which were markedly attenuated in CKO. Priming and activation of the NOD-like receptor pyrin domain-containing protein 3 inflammasome, assessed by measuring interleukin-1β and NOD-like receptor pyrin domain-containing protein 3 mRNA levels, caspase-1 activity, and interleukin-18 cleavage, were increased at day 3 after TAC in control hearts and in CMs isolated from these hearts. These responses were dependent on CaMKIIδ and associated with activation of Nuclear Factor-kappa B and reactive oxygen species. Accumulation of macrophages observed at days 7 to 14 after TAC was diminished in CKO and, by blocking Monocyte Chemotactic Protein-1 signaling, deletion of CM Monocyte Chemotactic Protein-1 or inhibition of inflammasome activation. Fibrosis was also attenuated by these interventions and in the CKO heart. Ventricular dilation and contractile dysfunction observed at day 42 after TAC were diminished in the CKO. Inhibition of CaMKII, Nuclear Factor-kappa B, inflammasome, or Monocyte Chemotactic Protein-1 signaling in the first 1 or 2 weeks after TAC decreased remodeling, but inhibition of CaMKII after 2 weeks did not.

CONCLUSIONS

Activation of CaMKIIδ in response to pressure overload triggers inflammatory gene expression and activation of the NOD-like receptor pyrin domain-containing protein 3 inflammasome in CMs. These responses provide signals for macrophage recruitment, fibrosis, and myocardial dysfunction in the heart. Our work suggests the importance of targeting early inflammatory responses induced by CM CaMKIIδ signaling to prevent progression to heart failure.

TLR (Toll-Like Receptor) 4 Antagonism Prevents Left Ventricular Hypertrophy and Dysfunction Caused by Neonatal Hyperoxia Exposure in Rats

Preterm birth is associated with proinflammatory conditions and alterations in adult cardiac shape and function. Neonatal exposure to high oxygen, a rat model of prematurity-related conditions, leads to cardiac remodeling, fibrosis, and dysfunction. TLR (Toll-like receptor) 4 signaling is a critical link between oxidative stress, inflammation, and the pathogenesis of cardiovascular diseases. The current study sought to investigate the role of TLR4 signaling in neonatal oxygen-induced cardiomyopathy. Male Sprague-Dawley pups were kept in 80% oxygen or room air from day 3 to 10 of life and treated with TLR4 antagonist lipopolysaccharide from the photosynthetic bacterium Rhodobacter sphaeroides(LPS-RS) or saline. Echocardiography was performed at 4, 7, and 12 weeks. At 12 weeks, intraarterial blood pressure was measured before euthanization for histological and biochemical analyses. At day 10, cardiac TLR4, Il (interleukin) 18, and Il1β expression were increased in oxygen-exposed compared with room air controls. At 4 weeks, compared with room air-saline, saline-, but not LPS-RS treated-, oxygen-exposed animals, exhibited increased left ventricle mass index, reduced ejection fraction, and cardiac output index. Findings were similar at 7 and 12 weeks. LPS-RS did not influence echocardiography in 12 weeks room air animals. Systolic blood pressure was higher in saline- but not LPS-RS treated-oxygen-exposed animals compared with room air-saline and -LPS-RS controls. LPS-RS prevented cardiac fibrosis and cardiomyocytes hypertrophy, the increased TLR4, Myd88, and Il18 gene expression, TRIF expression, and CD68+ macrophages infiltration associated with neonatal oxygen exposure, without impact in room air rats. This study indicates that neonatal exposure to high oxygen programs TLR4 activation, which contributes to cardiac remodeling and dysfunction.

Unveiling the Interplay between the TLR4/MD2 Complex and HSP70 in the Human Cardiovascular System: A Computational Approach

While precise mechanisms underlying cardiovascular diseases (CVDs) are still not fully understood, previous studies suggest that the innate immune system, through Toll-like receptor 4 (TLR4), plays a crucial part in the pathways leading to these diseases, mainly because of its interplay with endogenous molecules. The Heat-shock protein 70 family (HSP70-70kDa) is of particular interest in cardiovascular tissues as it may have dual effects when interacting with TLR4 pathways. Although the hypothesis of the HSP70 family members acting as TLR4 ligands is becoming widely accepted, to date no co-crystal structure of this complex is available and it is still unknown whether this process requires the co-adaptor MD2. In this study, we aimed at investigating the interplay between the TLR4/MD2 complex and HSP70 family members in the human cardiovascular system through transcriptomic data analysis and at proposing a putative interaction model between these proteins. We report compelling evidence of correlated expression levels between TLR4 and MD2 with HSP70 cognate family members, especially in heart tissue. In our molecular docking simulations, we found that HSP70 in the ATP-bound state presents a better docking score towards the TLR4/MD2 complex compared to the ADP-bound state (-22.60 vs. -10.29 kcal/mol, respectively). Additionally, we show via a proximity ligation assay for HSP70 and TLR4, that cells stimulated with ATP have higher formation of fluorescent spots and that MD2 might be required for the complexation of these proteins. The insights provided by our computational approach are potential scaffolds for future in vivo studies investigating the interplay between the TLR4/MD2 complex and HSP70 family members in the cardiovascular system.

NF-κB inhibitor on Toll-like receptor 4 signal-induced expression of angiotensinogen and AT1a receptor in neonatal rat left ventricular myocytes

Effects of toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway on expression of angiotensinogen and AT_1a receptor were investigated, to explore the role of TLR4/NF-κB signaling pathway in cardiovascular disease. Neonatal rat left ventricular myocytes (NRVMs) were cultured and cardiomyocytes were identified by immunocytochemical staining of sarcomeric α-actin. NRVMs were treated with lipopolysaccharide (LPS) at a dose of 10, 100 and 1,000 ng/ml, and RT-PCR was performed 24 h later to detect the expression of TLR4, angiotensinogen (ATG) and AT_1a at mRNA level. NRVMs were cultured and pretreated with caffeic acid phenethylester (CAPE) for 30 min. Then NRVMs were stimulated with LPS (1,000 ng/ml) for 24 h. Nuclear translocation of NF-κB p65 was detected by immunocytochemistry. Expression of TLR4, angiotensinogen and AT_1a receptor after CAPE stimulation was detected by RT-PCR. TLR4 mRNA was highly expressed in in vitro cultured NRVMs, and the expression level was significantly increased by LPS (10-1,000 ng/ml) stimulation in a dose-dependent manner (P<0.05). LPS stimulation also significantly increased the expression levels of angiotensinogen and AT_1a receptor in a dose-dependent manner (P<0.05). NF-κB was activated and nuclear translocation of NF-κB p65 occurred after stimulation with LPS (1,000 ng/ml) for 24 h, while CAPE (20 µg/ml) inhibited the nuclear translocation of NF-κB p65 and inhibited LPS-induced expression of angiotensinogen and AT_1a receptor. With LPS stimulation, TLR4 signaling positively regulates the expression of TLR4 and upregulates the expression of angiotensinogen and AT_1a receptor in NRVMs. CAPE, an inhibitor of NF-κB, inhibited NF-κB p65 activation and inhibited the upregulation of TLR4, angiotensinogen and AT_1a receptors induced by LPS. These results suggest that NF-κB plays a key regulatory role in the above-mentioned effects induced by LPS. Intervention with TLR4/NF-κB signaling may become a new target for prevention and treatment of cardiovascular diseases.

Ferulic acid may target MyD88-mediated pro-inflammatory signaling - Implications for the health protection afforded by whole grains, anthocyanins, and coffee

Higher dietary intakes of anthocyanins have been linked epidemiologically to decreased risk for metabolic syndrome, type 2 diabetes and cardiovascular events; clinical trials and rodent studies evaluating ingestion of anthocyanin-rich extracts confirm favorable effects of these agents on endothelial function and metabolic syndrome. However, these benefits of anthocyanins are lost in rats whose gut microbiome has been eliminated with antibiotic treatment - pointing to bacterial metabolites of anthocyanins as the likely protective agents. A human pharmacokinetic assessment of orally administered cyanidin-3-O-glucoside, a prominent anthocyanin, has revealed that, whereas this compound is minimally absorbed, ferulic acid (FA) is one of its primary metabolites that appears in plasma. FA is a strong antioxidant and phase 2 inducer that has exerted marked anti-inflammatory effects in a number of rodent and cell culture studies; in particular, FA is highly protective in rodent models of diet-induced weight gain and metabolic syndrome. FA, a precursor for lignan synthesis, is widely distributed in plant-based whole foods, mostly in conjugated form; whole grains are a notable source. Coffee ingestion boosts plasma FA owing to gastrointestinal metabolism of chlorogenic acid. Hence, it is reasonable to suspect that FA mediates some of the broad health benefits that have been associated epidemiologically with frequent consumption of whole grains, anthocyanins, coffee, and unrefined plant-based foods. The molecular basis of the anti-inflammatory effects of FA may have been clarified by a recent study demonstrating that FA can target the adaptor protein MyD88; this plays an essential role in pro-inflammatory signaling by most toll-like receptors and interleukin-1β. If feasible oral intakes of FA can indeed down-regulate MyD88-dependent signaling, favorable effects of FA on neurodegeneration, hypothalamic inflammation, weight gain, adipocyte and beta cell function, adiponectin secretion, vascular health, and cartilage and bone integrity can be predicted. Since FA is well tolerated, safe, and natural, it may have great potential as a protective nutraceutical, and clinical trials evaluating its effects are needed.

Toll-Like Receptor 4 Inhibition Improves Oxidative Stress and Mitochondrial Health in Isoproterenol-Induced Cardiac Hypertrophy in Rats

BACKGROUND

Inflammation remains a crucial factor for progression of cardiac diseases and cardiac hypertrophy remains an important cause of cardiac failure over all age groups. As a key regulator of inflammation, toll-like receptor 4 (TLR4) plays an important role in pathogenesis of cardiac diseases. Being an important regulator of innate immunity, the precise pathway of TLR4-mediated cardiac complications is yet to be established. Therefore, the primary objective of the present study was to find the role of TLR4 in cardiac hypertrophy and the molecular mechanism thereof.

METHODS

Cardiac hypertrophy was induced with administration of isoproterenol (5 mg/kg/day, sc). TLR4 receptor inhibitor RS-LPS (lipopolysaccharide from the photosynthetic bacterium Rhodobacter sphaeroides; 5 μg/day) and agonist lipopolysaccharide (LPS) (from Escherichia coli; 3.12 μg/day) were administered through osmotic pump along with isoproterenol. Cardiac hypertrophy as well as oxidative stress and mitochondrial parameters were evaluated.

RESULTS

Cardiac hypertrophy was confirmed with increased heart weight/body weight ratio as well as assessment of hypertrophic markers in heart. There was a marked increase in the TLR4 expression and oxidative stress along with mitochondrial dysfunction in ISO group. TLR4 inhibition significantly decreased heart weight/body weight ratio and ANP, collagen, and β-MHC expression and restored the disturbed cellular antioxidant flux. The mitochondrial perturbations that were observed in hypertrophy heart was normalized after administration of TLR4 inhibitor but not with the agonist. TLR4 agonism further exaggerated the oxidative stress in heart and hence accelerated the disease development and progression.

CONCLUSION

Our data show that increased TLR4 ligand pool in cardiac hypertrophy may exaggerate the disease progression. However, inhibition of TLR4 attenuated cardiac hypertrophy through reduced cardiac redox imbalance and mitochondrial dysfunction.