Although living and medical standards have undergone remarkable progress, heart failure remains a worldwide challenge, which costs countries a tremendous amount of money and affects the quality of life for patients at different degrees. Ischemic cardiomyopathy is one of the most common causes of heart failure; moreover, a portion of these patients also suffer from other diseases, such as type 2 diabetes mellitus, which complicates the treatment interventions for heart failure. Angiotensin converting enzyme inhibitors, beta-blockers, diuretics, positive inotropic drugs, and cardiac resynchronization therapy (CRT) have been widely used in post-ischemic heart failure therapy, but quite a few patients inevitably go into end-stage heart failure for a variety of reasons [8]. Thus, they experience repeated hospitalizations, a severe decline in quality of life, complications in other organs, and even death. Serum BNP, encoded by NPPB, is secreted primarily by atria muscle cells and increases when the heart is overloaded. It has been applied in clinics as a diagnostic and prognostic biomarker of HF for a long time, which is a great achievement [28]. Besides, BNP is also reported associated with the development of T2DM, and in turn, diabetes affected its expression in patients with HF. Some early researches reveal that the serum BNP level in HF patients without diabetes is higher than in the one with diabetes, while the opposite reports. Up to now, the mechanism is still completely clear. In this study, NPPB co-expression genes and their GO and KEGG pathways were identified in post-ischemic HF with T2DM and without T2DM, respectively, in order to further understand the potential mechanism of NPPB in post-ischemic HF patients with and without T2DM.
Heart failure is the result of the contradiction between the supply and demand of oxygen, blood, and energy, and the tricarboxylic acid cycle (TCA cycle) and mitochondrial respiratory transport chain are important links in glycolysis. As screened by the Venn diagram, a total of 64 positively co-expression genes were identified. Carnitine palmitoyl transferase 1 (CPT1) encodes an important enzyme in the body, involved in fatty acid metabolism. As a subtype of CPT1, CPT1C can promote cell survival under metabolic stress conditions [29]. Further, HtrA serine peptidase 1 (HTRA1) encodes a protein that is suggested to be a cell growth regulator, and its loss impairs smooth muscle cell maturation [30]. In previous research, hypermethylation of SOCS3 gene could be an underlying mechanism of intimal hyperplasia and restenosis. SOCS3 can also regulate cavin-1 function by enhancing its stability and consequently maintaining expression levels of caveolin-1 and cell surface caveolae. Moreover, proteins encoded by cavin-1 are also believed to modify lipid metabolism and insulin-regulated gene expression [31, 32]. In terms of vascular function, CCN1 not only functions as an inhibitory regulator of SMC muscle contractility through inhibiting actomyosin interactions but also regulates TNF-α induced vascular endothelial cell apoptosis [33]. The PDLIM7 gene product is involved in actin filament-associated complex assembly, which is essential for the transmission of ret/ptc2 mitogenic signaling. In addition, its expression is positively correlated to typical smooth muscle cell markers in atherosclerosis plaques, and PDLIM7 silencing in vitro led to downregulation of smooth muscle cell (SMC) markers, disruption of actin cytoskeleton, decreased cell spreading, and increased proliferation [34]. The data from Stine B Thomsen et al. suggested that, in patients with ischemic heart disease, increased plasma MGP levels are indicative of a progressing calcification process [35]. Moreover, protease-activated receptor 2 (PAR2) in microvascular endothelial cells is indispensable for vascular stability, and its deficiency attenuates atherosclerosis [36, 37]. The above-mentioned genes mainly play a role in energy supply and metabolism, cell proliferation and apoptosis, and vessel function and development, and have been reportedly associated with blood and oxygen supply and cardiac remodeling in patients with HF.
On the other hand, a Venn diagram allowed identifying 106 genes negatively co-expressed with NPPB. Coq8p and human COQ8A are related to CoQ biosynthesis and acute inhibition of Coq8p is sufficient to cause CoQ deficiency and respiratory dysfunction [38]. NDUFS2 and NDUFA9 encode compound I subunits in the mitochondrial membrane respiratory chain, while SDHC encodes compound II subunits. Also, DECR1 encodes an enzyme, referred to as NADPH, which provides H+ ions for NAD+ and then converts to NADH to participate in the respiratory chain. In addition to the respiratory chain, the TCA cycle also features several genes that are mainly active in its processes [39]. PDHB encodes a pyruvate dehydrogenase compound, which catalyzes the conversion of pyruvate into acetyl-coa and carbon dioxide for the TCA cycle. Citrate synthase, which is encoded by CS, catalyzes citric acid synthesis from oxaloacetic acid and acetyl coa; further, citric acid synthesis by oxaloacetic acid and acetylcoa are catalyzed by cisaconitum, which is encoded by ACO2. ALAS1 encodes mitochondrial enzymes that catalyze rate-limiting steps in the heme (iron protoporphyrin) biosynthesis pathway. In the context of cell proliferation and vascular function, Chen Yan reported that, in senescent vascular SMCs, PDE1A and PDE1C mRNA levels are significantly upregulated, and cellular senescent makers were reduced when PDE1 was inhibited [40]. Data from Wilson LS et al. suggest that therapies specifically aimed at inhibiting the PDE3A isoform may lead to amelioration of excessive vascular SMC growth and decrease the atherosclerosis process [41]. Thus, the above-mentioned genes are mainly involved in the regulation of the tricarboxylic acid cycle and respiratory transport chain in terms of energy supply and maintain the normal function of vascular SMC. Finally, CACNB2, KCNAB2, and TIMM22 encode subunits that participate in dysfunctional voltage-gated channels that may be associated with arrhythmia events rather than aggravated heart failure [42, 43]. Thus, these are factors that are associated with the development of heart failure.
In addition, Table 1 shows us the shared pathway that occurs in both post-ischemic HF with or without T2DM. Most of the pathways are related to metabolism, such as the following: the citrate cycle (TCA cycle); butanoate, carbon, pyruvate, and 2-oxocarboxylic acid metabolism; and valine, leucine, isoleucine, and fatty acid degradation. Figure 4 shows that it is similar to the pathways of the intersection of co-expression genes and the genes of the module that it is enriched in within the PPI network. Further, the HIF-1 signaling pathway is a hot topic that researchers focus on. In M1 macrophages, HIF-1α activates the expression of the iNOS gene, increasing nitric oxide synthesis, which expands the blood vessels. As such, in hypoxia macrophages, the HIF-1α - pyruvate dehydrogenase kinase (PDK1) axis can induce active glycolysis [44]. In addition, an investigation from Ya-Fang Chen et al. [45] suggests that HIF-1α and FoxO3a show synergistic effects of cardiomyocyte apoptosis under hypoxia, as well as elevated glucose levels. Another pathway, the TGF-β signaling pathway, is also a popular hot topic. TGF-β is a multifunctional cytokine, which can regulate the macrophage phenotype, promote Treg cell activation, and reduce adhesion molecule synthesis by endothelial cells that lend a powerful anti-inflammatory effect [46]. Data from the study by Jooyeon Kim shows us that the TGF-β signaling pathway plays an important role in the regulation of cardiac fibrosis [47]. Lastly, as a classical pathway, the calcium signaling pathway was also found in both the DHF and nDHF patient groups. Ca2+ participates in excitation-contraction coupling, regulating myocardial contraction and diastole. In addition, it also takes part in the regulation of the cardiomyocyte action potential, which plays an essential role in managing heart rhythm [48, 49]. Thus, regulation disorders of the calcium signaling pathway will lead to heart rate disorders, myocardial contraction, and adrenal dysfunction. The above-mentioned pathways affect patients with post-ischemic heart failure in terms of energy supply, metabolism, inflammation, and myocardial fibrosis.
Compared to the HF patients without T2DM, the NPPB co-expression genes enriched in several other pathways, such as arrhythmogenic right ventricular cardiomyopathy (ARVC), dilated cardiomyopathy, hypertrophic cardiomyopathy (HCM), cardiac muscle contraction, alcoholism, PI3K-Akt signaling pathway and so on. The former three are different types of cardiomyopathy, mainly affect the morphology and function of ventricular muscle cells, result in deterioration of cardiac function [50]. Alcohol abuse may increase 2 times risk of chronic HF than the one who do not has alcohol abuse [51], and the BNP level would increase markedly [34]. In context to PI3K-Akt signaling pathway, it has been revealed involved in the expression level of BNP and the cardio-protection afforded by BNP infusion [52, 53]. Thus, these pathways and the genes enriched in would affect the level of BNP and the development of HF.
Although we use the micro-array dataset to help us identify the NPPB co-expression genes and pathways they enriched in in post-ischemic HF patients, either with T2DM or without T2DM, the occurrence and development of HF is complex, and variety aspects should be taken in consideration of the management of HF. We hope our finding could give a hand to a deeper understanding of the role and function of NPPB gene in HF patients and provide aspects for the research and management of HF in the future.