Activation of toll like receptor 4 (TLR4) promotes cardiomyocyte apoptosis through SIRT2 dependent p53 deacetylation

Parmeshwar Bajirao Katare,Amit K Dinda,Sanjay K Banerjee,Hina Lateef Nizami,Bugga Paramesha

doi:10.1038/s41598-020-75301-4

Abstract

Cardiomyocyte inflammation followed by apoptosis and fibrosis is an important mediator for development and progression of heart failure. Activation of toll-like receptor 4 (TLR4), an important regulator of inflammation, causes the progression of cardiac hypertrophy and injury. However, the precise mechanism of TLR4-mediated adverse cardiac outcomes is still elusive. The present study was designed to find the role of TLR4 in cardiac fibrosis and apoptosis, and molecular mechanism thereof. Rats were treated with TLR4 agonist (LPS 12.5 μg/kg/day) through osmotic pump for 14 days. To simulate the condition in vitro, H9c2 cells were treated with LPS (1 μg/ml). Similarly, H9c2 cells were transfected with TLR4 and SIRT2 c-DNA clone for overexpression. Myocardial oxidative stress, inflammation, fibrosis and mitochondrial parameters were evaluated both in vitro and in vivo. Cardiac inflammation after LPS treatment was confirmed by increased TNF-α and IL-6 expression in rat heart. There was a marked increase in oxidative stress as observed by increased TBARS and decreased endogenous antioxidants (GSH and catalase), along with mitochondrial dysfunction as measured by mitochondrial complex activity in LPS-treated rat hearts. Histopathological examination showed the presence of cardiac fibrosis after LPS treatment. Protein expression of nuclear p53 and cleaved caspase-7/caspase-9 was significantly increased in LPS treated heart. Similar to in vivo study, nuclear translocation of p53, mitochondrial dysfunction and cellular apoptosis were observed in H9c2 cells treated with LPS. Our data also indicate that decreased expression of SIRT2 was associated with increased acetylation of p53 after LPS treatment. In conclusion, TLR4 activation in rats promotes cardiac inflammation, mitochondrial dysfunction, apoptosis and fibrosis. p53 and caspase 7/caspase 9 were found to play an important role in TLR4-mediated apoptosis. Our data suggest that, reducing TLR4 mediated fibrosis and apoptosis could be a novel approach in the treatment of heart failure, keeping in the view the major role played by TLR4 in cardiac inflammation.

Highlights

The heart is an organ that works continuously with limited capacity for repair and r egeneration[1]
We found that heart weight-to-tail length ratio (Fig. 1A) was decreased significantly (p < 0.05) in LPS group as compared to CON group indicating the cardiac atrophy induced after LPS treatment
We have demonstrated that toll-like receptor 4 (TLR4) is an important mediator for the development of cardiac fibrosis

Summary

Introduction

The heart is an organ that works continuously with limited capacity for repair and r egeneration[1]. Mani et al had hypothesized that 0.1% apoptosis rate can lead to approximately 37% cardiomyocyte loss over a span of a year[3] This hypothesis was tested with cardiac myocyte-specific expression inducible caspase 8 transgenic mice. There are several mechanisms by which apoptosis is activated in diseased heart One of these mechanisms is toll-like receptor (TLR) 4 induced inflammation. TLR4 mediated inflammatory immune response characterised by leucocyte activation and infiltration in myocardium, initiates cytokine secretion and protease release, thereby aggravates apoptosis and necrosis of cardiomyocytes. Damaged myocardium could further release several DAMPs, including HMGB1, HSPs and mitochondrial components recognized by T LR410,11 These DAMPs promote DCM formation via a positive feedback loop that aggravate cardiac inflammation and injury. This study was undertaken to elucidate the role of TLR4 activation in cardiac apoptosis and fibrosis, and the underlying molecular mechanism

Methods

Results

Discussion

Conclusion