A-007 Cardiomyocyte-monocyte Cross-talk Exploits Cellular Stress Pathways Leading to Myocyte Apoptosis in Dilated Cardiomyopathy of Idiopathic Origin
Authors: Sikder K , Talukdar D , Haldar A , Dastidar R , Kumar S 
Published: September 2023

Abstract

Background
Dilated cardiomyopathy (DCM) is the most prevalent form of cardiovascular diseases (CVDs) results in dilation and disruption of pumping mechanism of heart. Most strikingly, about 50% DCM cases do not have any identified aetiology, hence known as idiopathic DCM (IDCM). The aim of this study is to investigate major inflammatory markers and cellular stress pathways in the circulating leukocytes and cardiomyocytes to find out the cross-talk between these cell types in vitro condition by mimicking the in vivo inflammatory milieu.

Methods
The study is divided into two parts, first part comprising patient study and the second part is the in vitro cell culture based mechanistic study. 50 IDCM patients and 30 age and sex matched control subjects were recruited from our in-house Ramakrishna Mission Seva Pratishthan (RKMSP) hospital based on their NYHA discomfort criteria followed by intra thoracic echocardiography. Exclusively the IDCM subjects were selected for this study. Blood was collected from the patients for biochemical and inflammatory parameters and to isolate PBMCs. mRNA and protein expressions were studied by real time PCR and immunoblotting respectively. H9C2 cardiomyocyte cells alone or with LPS-activated THP-1 monocyte/macrophage line were co-cultured in presence of the major inflammatory cytokines in the same in vivo concentration as found in the IDCM patients in presence or absence of ER stress agonist or antagonists. Immunofluorescence, RT-PCR and immunoblotting were done for markers specific to myocyte stress, inflammation and apoptosis.

Results
Inflammatory and cardiac blood biomarkers NLR, hs-CRP, IL-6, pro-BNP and troponin-I were found to be significantly high (P &lt; 0.05) in IDCM. Subsequently, the mRNA expressions of pro-inflammatory genes TNF-α (2.6 fold), IFN-γ (10.2 fold), IL-1β (8.5 fold) and NF-κβ (2.427 fold) were all significantly increased (P &lt; 0.05). Looking into the cellular stress pathways, we further found upregulations of antioxidant genes SOD (2.59 fold) and catalase (2.17 fold) and ER stress markers Grp78 (2.794 fold), CHOP (3.407 fold), IRE1-α (2.104 fold) and ATF-6 (40.618 fold) mRNA expression in the PBMCs. When we stimulated the H9C2 cardiomyocytes with IL-1B and TNF-α at comparable conc. as found in the IDCM patients, the ER stress and inflammation were observed. Further, when we co-cultured these H9C2 with LPS stimulated THP-1 macrophages an exaggerated inflammation and myocyte stress was observed that led to apoptosis of the cells. Interestingly using ER stress inhibitor TUDCA, remarkably blocked the apoptosis and promotes cell survival.

Conclusion
Our results showed that a systemic inflammation caused by stressed PBMCs leads to cardiac deterioration and dilation in the unknown DCM cases. So far we have established that an exaggerated inflammation induce the circulating PBMCs to migrate and infiltrate the cardiac musculature where they induce oxidative stress and ER stress to the cardiomyocytes leading to apoptosis of the later. In long run these unknown forms of dilated cardiomyopathy patients suffer from a dilated heart due to a decline in the myocyte population. Our findings may warrant for a treatment strategy that alleviate the intracellular stress of the circulating leukocytes and cardiomyocytes to minimize the inflammatory changes of the heart.