HOCM is a kind of HCM, characterized by LVOTO caused by the cardiac hypertrophy of IVS. Emerging evidence has revealed the central role of immune-related pathways in cardiac hypertrophy. Our research found that the infiltration of monocyte, macrophages M2, naïve B cells, NK cells resting, and Tregs in cardiac tissues were closely associated with HOCM. Through further analysis, our study also suggested that CCL2, MAP2K1, NFKBIA, STAT3, TNFRSF1A may be the core regulatory genes of immune-related pathways and were closely correlated with the degree of infiltration of monocytes, indicating that these genes may be critical regulatory markers in HOCM.
A greater understanding of the immune system itself has accelerated the progress in defining the cell populations of the immune system that plays a role in HOCM. Monocytes are key innate immune system mediators of inflammatory responses. In our analysis, the monocytes in HOCM samples had the most significant difference compared with healthy samples. Meanwhile, we found that the monocyte had the moderate correlation with 5 hub genes. In addition, CCL2 and TNFRSF1A were validated by PCR. Monocytes can differentiate into macrophages and have a proved significant relationship with HF and myocardial infarction in both animal and human research [17, 18]. Additionally, monocytes infiltration can cause cardiac hypertrophy and remodeling [19]. Considering the vital participation of monocytes, immune regulation is a promising treatment direction for HOCM and more work is needed to reveal the detailed mechanism. Our results revealed that monocytes may play an important role in HOCM and may serve as a predictive tool in HOCM progression.
Activation of natural killer T cells can attenuate myocardial infarction-induced cardiac remodeling [20], and inhibition of T cell immune activity can ameliorate maladaptive cardiac remodeling in mouse model [21]. Meanwhile, macrophages have a much more substantial role in regulating cardiac hypertrophy and remodeling during heart injury [10]. According to the function of macrophages, it is classified into two types, type M1 (classically activated) and type M2 (alternatively activated). Type M1 macrophage can secrete TNF, IL-1, IL-12, and other chemokines to play a proinflammatory function, and the type M2 macrophage mainly secretes anti-inflammatory factors, like epidermal cell growth factor (EGF) and transforming growth factor β (TGF-β) in the late stage of inflammation [22, 23]. M1 macrophages mainly facilitate tissue destruction; M2 macrophages promote tissue remodeling and repair, and previous studies showed an increase in M2 macrophage infiltration in myocardium promotes fibrosis [23–25], so altering macrophage phenotype in the heart may be a potential direction to modify cardiac fibrosis. In consequence, our results suggested the higher relative infiltration value of M2 and NK cells may influence the pathogenesis of HOCM.
Resting naïve B cell is defined as B cell before activation and further differentiation into specific subtypes. At present, we have not found any report about the direct correlation of resting naïve B cells and cardiac hypertrophy or fibrosis. Zouggari Y et al. found that B-cell depletion can decline left ventricular fibrosis and cardiac function in the model of myocardial infarction [26]. Furthermore, adoptive transfer of activated Treg cells to cardiac hypertrophic mouse model alleviated CD4+, CD8 + T cells, and macrophages infiltration into the heart and alleviated cardiac hypertrophy and fibrosis [27]. In our research, the higher relative infiltration values of Tregs and naïve B cells may be associated with the pathogenesis of HOCM, consistent with the previous studies.
There are a few studies investigating cardiac immune-related genes in HOCM patients. Among the candidate biomarkers, Zhu et al. have reported that FOS was related to immune inflammatory responses, cardiomyocyte apoptosis, cardiac remodeling and myocardial dysfunction [28, 29]. Schunkert et al. also found FOS gene was associated with hypertrophic rat hearts. And, in vivo, the expression of MAP2K1 in the hearts of transgenic mice promoted concentric cardiac hypertrophy [30], Bueno OF et al. reviewed many literature and got the intermediate signaling pathway consisting of MAP2K1 (MEK1) and extracellular signal-regulated kinases (ERK1/2) as important regulators of cardiac hypertrophy and myocytes survival [31]. STAT3 has a key role in inflammation that underlies cardiovascular disease and impacts on cardiac structure and function and is important for maintaining endothelial cell function and capillary integrity with aging and hypertension [32]. Besides, STAT3 also involves the cardiac hypertrophy and fibrosis in TAC mouse models [33, 34]. Duerr GD et al. suggested that in the cardiac hypertrophy group CCL2 and CXCL8 had increased expression and anti-inflammatory IL-10 had a suppression which indicated the persistent inflammatory reaction [35]. About TNFRSF1A, it is a member of TNF receptor protein and has have effects on remodeling, hypertrophy, inflammation, and apoptosis in HF [36].
Finally, the TFs analysis results show that GATA5, BCL3, and ATF1 were significantly predicted in hub genes’ regulatory network. Herein, GATA5, a zinc-finger transcription factor essential for cardiovascular development and structural remodeling[37], was the sole and potent transactivator for the β-myosin heavy chain promoter, can bind to nuclear factors induced by leukemia inhibitory factor stimulation during myocardial cell hypertrophy [38]. ATF1, a member of activating transcription factor (ATF) subfamily and basic-region leucine zipper family, is a key driver of human plaque monocytes to acquire the atheroprotective macrophage state [39]. That is to say, ATF1 can promote monocytes to differentiate into a macrophage, in accordance with our analysis.