Proprotein convertase subtilisin/kexin type 7 (PCSK7) is a member of the PCSK enzyme family, known for its role in processing and activating various proteins (1, 2). PCSK7 is ubiquitously expressed in tissues and plays a significant role in diverse physiological processes (3), notably lipid metabolism (4). It regulates the formation and release of low-density lipoprotein (LDL) in the liver. Elevated LDL-cholesterol (LDL-c) levels are a well-known risk factor for cardiovascular diseases (5, 6), including myocardial infarction (MI), atherosclerosis, and aneurysms. Although PCSK7’s involvement in lipid metabolism and immune responses suggests its potential role in coronary artery disease (CAD) progression, its specific function within the heart remains largely unexplored.

MI, caused by risk factors such as hypertension and high cholesterol levels, is characterized by severe inflammation, leading to complications like heart failure and adverse remodeling (7) in the heart and other organs (8). Lipoproteins and lipids, key drivers of these inflammatory processes, contribute to cell death and tissue dysfunction. While treatments like statins manage CAD, persistent risks of heart failure (9) and mortality underscore the need for novel therapeutic approaches. Understanding and targeting PCSK7, given its role in lipid metabolism and immune regulation, could provide new avenues to mitigate disease progression and improve patient outcomes.

This study investigates the role of PCSK7 in MI, revealing that its deficiency reduces cholesterol levels, attenuates inflammatory macrophage recruitment and lipid uptake at the infarct site, and enhances cardiac remodeling. These protective effects are linked to the downregulation of tumor necrosis factor-alpha (TNF-α)-related signaling in macrophages. Our findings suggest that PCSK7 exacerbates MI pathology by promoting inflammation and disrupting lipid metabolism.

In conclusion, PCSK7 plays a multifaceted role in cardiovascular disease by influencing lipid metabolism and immune regulation. Targeting PCSK7 could represent a promising therapeutic approach for CAD, potentially enhancing patient outcomes. 

PCSK7 induces cardiac enlargement following myocardial infarction

To investigate the impact of PCSK7 in MI, we conducted left anterior descending coronary artery ligation or sham surgery on PCSK7 knockout (Pcsk7^−/−) mice, with heart tissue collected on days 3 and 7 post-surgery (Fig. 1A). PCSK7 deficiency improved survival rates 7 days after MI (Fig. 1B). Additionally, Pcsk7^−/− mice exhibited a significant reduction in the heart weight to body weight ratio on Day 7 post-MI (Fig. 1C). To further assess the effects of PCSK7 deficiency, we evaluated left ventricular infarct size and cardiac function through trichrome staining and echocardiography. PCSK7 knockout resulted in a smaller infarct size in the LV, along with enhanced cardiac function, including increased ejection fraction, reduced left ventricular end-systolic volume, decreased left ventricular end-diastolic volume, and enhanced cardiac output (Fig. 1D-F and Supplementary Table 1). These findings suggest that PCSK7 contributes to the exacerbation of MI and plays a crucial role in the development of dilated cardiomyopathy.

While the role of PCSK7 in lipid regulation in hepatocytes is well-established (4, 10), knowledge on its role in cardiovascular disease is limited. We investigated whether PCSK7 also influences lipid levels post-MI. In PCSK7 knockout (Pcsk7^−/−) mice, we observed a significant reduction in total cholesterol and LDL-c levels by Day 3 post-MI (Fig. 1G, H and Supplementary Table 2). During the early phase of MI, innate immune cells in the heart become activated (11-13), with macrophages playing a pivotal role in clearing circulating lipids (14). These findings suggest that PCSK7 deficiency may help lower circulating cholesterol levels through immune cell-mediated processes, potentially alleviating the severity of vascular disease after MI.

PCSK7 activates macrophages to promote inflammatory responses and apoptosis

Activation of the immune system is a hallmark of MI, characterized by the recruitment of immune cells to the ischemic site to clear necrotic tissue and facilitate remodeling (11). Among these immune cells, macrophages play a critical role in cardiovascular disease by metabolizing lipids (15-17) and regulating inflammation (18) to maintain cardiac homeostasis. To investigate the role of immune cells in the relationship between PCSK7 and lipid metabolism, we examined immune cell distribution in the ischemic heart. Flow cytometry revealed that PCSK7 deficiency led to a reduction in the cardiac macrophage population, while the distribution of other immune cells, such as CD45^＋ leukocytes, granulocytes, dendritic cells, and monocytes, remained unchanged post-MI (Fig. 2A, B, Supplementary Fig. S1A-E). Furthermore, apoptosis of CD68^＋ macrophages was reduced in the infarcted hearts of Pcsk7^−/− mice compared to control (Pcsk7^＋/＋) mice using a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay (Fig. 2C, D). Notably, the number of proinflammatory macrophages (CD11c^＋CD206⁻; Fig. 2E) decreased, while anti-inflammatory macrophages (CD11c⁻CD206^＋; Fig. 2F) increased in Pcsk7^−/− mice.

Previous studies have shown that the prognosis of MI is heavily dependent on effective cardiac remodeling (19). During the regenerative phase of cardiac healing, myofibroblasts play a critical role in maintaining tissue structure and modulating the immunosuppressive functions of macrophages (20, 21). In Pcsk7^−/− mice, immunofluorescence staining revealed increased densities of myofibroblasts (marked by alpha-smooth muscle actin; α-SMA) and microvascular structures (marked by CD31), suggesting enhanced cardiac repair and improved remodeling (Fig. 2G, H). These findings suggest that PCSK7 deficiency in the injured heart may prevent the activation of inflammatory macrophages while promoting immunosuppressive functions, potentially leading to better cardiac outcomes after MI.

PCSK7 primarily functions intracellularly in cardiac macrophages following ischemia

PCSK7 is a membrane-anchored protease (22) expressed in various tissues and immune cells, and it shuttles between the plasma membrane and trans-Golgi network (1). It functions intracellularly and is not secreted. Plasma levels of PCSK7 in MI model mice were comparable to their respective control groups based on an enzyme-linked immunosorbent (ELISA) assay (Fig. 3A). In contrast, PCSK7 expression was elevated in activated macrophages from infarcted hearts compared to noninfarcted hearts (Fig. 3B). This suggests that the impact of PCSK7 expression in infarcted hearts is driven by its intracellular activity within cardiac macrophages rather than external factors like bone marrow-derived cells.

Macrophages, which play a crucial role in reverse cholesterol transport (15, 16), lipid metabolism (23), and CAD progression, exhibited reduced plasma cholesterol levels in PCSK7-deficient mice compared to controls after MI (Fig. 1G, H). Using the fluorescent probe BODIPY (493/503), we assessed the role of PCSK7 in macrophage lipoprotein uptake. Both F4/80^＋ macrophages from Pcsk7^−/− mice and U937^∆PCSK7 cells exhibited decreased lipid droplet (LD) uptake compared to their respective controls (Pcsk7^＋/＋ and U937^Ctr; Fig. 3C, D). These findings suggest that PCSK7 primarily functions intracellularly and may significantly contribute to pathological development by enhancing the inflammatory response in macrophages.

Tumor necrosis factor-alpha signaling in activated macrophages is repressed by PCSK7 deficiency

To identify factors directly regulating the PCSK7-enhanced inflammatory response in macrophages, we conducted PCSK7 knockdown using Neon Transfection in U937 cells, a human promonocytic cell line. After confirming stable PCSK7 knockdown, the cells were differentiated into macrophages (Fig. 4A). Subsequently, we analyzed the expression of key inflammatory cytokines (TNF-α, IL-1β, and IL-6) in U937 cells activated by IFN-γ, LPS, and CoCl₂. Under ischemic conditions simulated by CoCl₂, TNF-α levels were significantly reduced in U937^∆PCSK7 cells, while other cytokines remained unchanged (Fig. 4B). Furthermore, in PCSK7 knockout mice, F4/80^＋ macrophages post-MI exhibited decreased TNF-α expression (Fig. 4C). These findings suggest that PCSK7 specifically regulates TNF-α expression in macrophages and contributes to the exacerbation of ischemic heart disease.

TNF-α promotes macrophage polarization toward an inflammatory phenotype (24) and enhances apoptosis (25). Elevated levels of TNF-α in macrophages contribute to infarction extension (26) and adverse cardiac remodeling (27). To investigate how PCSK7 exacerbates MI, we investigated TNF-α-related pathways in macrophages. TNF-α binding to its receptors activates MAP kinase pathways, such as Erk, JNK, and p38, which regulate the expression of inflammatory cytokines, including TNF-α itself. Therefore, MAP kinases operate both upstream and downstream of TNF-α receptor signaling (28). In our study, PCSK7 downregulation in hypoxic inflammatory macrophages significantly reduced JNK signaling, while Erk and p38 pathways were unaffected. Furthermore, levels of both membrane-bound (mTNF-α) and soluble TNF-α (sTNF-α) levels were decreased in PCSK7-deficient macrophages (Fig. 4D). These findings demonstrate that PCSK7 exacerbates MI by modulating the TNF-α/JNK signaling pathway in activated inflammatory macrophages. Targeting PCSK7 in macrophages could be a promising therapeutic strategy for CAD. 

This study identified PCSK7 as a significant contributor to MI, worsening cardiac injury by promoting inflammation, lipid accumulation, and adverse cardiac remodeling. Although PCSK7 has been primarily studied in the context of dyslipidemia (4, 10) and atherosclerosis (29), its role in MI has remained largely unexplored. PCSK7 deficiency led to improved survival rates, reduced heart weight, smaller infarct size, and enhanced cardiac function post-MI. These benefits were associated with lower total and LDL-cholesterol levels, a shift in macrophage polarization toward an anti-inflammatory phenotype, and reduced lipid accumulation in macrophages, suggesting enhanced cardiac repair. Mechanistically, PCSK7 modulates lipid metabolism and inflammatory responses by regulating TNF-α signaling and activating the JNK pathway within macrophages, driving inflammatory responses and worsening vascular disease. Collectively, targeting PCSK7 in macrophages may offer a potential therapeutic approach for CAD and MI.

Cardiac macrophages are crucial for inflammation, healing, and tissue remodeling following MI (11, 14). Our findings demonstrate that PCSK7 deficiency in macrophages mitigates cardiac injury by modulating TNF-α signaling, managing cholesterol levels, and reducing lipid uptake, thus limiting foam cell formation—a major contributor to vascular inflammation through cytokine release like TNF-α (30). However, depending on environmental factors, foam cells can also exhibit anti-inflammatory properties (31). Because our study links PCSK7 in macrophages to TNF-α signaling, we focused on the inflammatory roles of lipid-laden macrophages. TNF-α inhibits monocyte differentiation into M2-like macrophages (32), and the M1-M2 macrophage balance is regulated through the MAP kinase signaling pathway (33). PCSK7 deletion reduces proinflammatory M1-like macrophages (CD11c^＋CD206⁻) and increases anti-inflammatory M2-like macrophages (CD11c⁻CD206^＋), whereas it inhibits JNK signaling, indicating that PCSK7 modulates macrophage polarization through TNF-α/JNK-dependent pathways, thereby affecting inflammation and repair mechanisms.

PCSK7 is highly expressed in the liver, particularly in hepatocytes, where it influences triglyceride (TG) metabolism by facilitating apoB100 association with lipids for VLDL secretion. PCSK7 deficiency results in the proteasomal degradation of apoB100, activating the unfolded protein response and autophagy, which reduces hepatic lipid accumulation and circulating lipid levels (4), potentially alleviating cardiac disease. Our findings showed that PCSK7 deficiency reduced LD accumulation in macrophages. Altered lipid metabolism and LD formation are critical for proinflammatory activation, although the precise mechanisms underlying lipid accumulation during inflammation remain incompletely understood (34). LD formation is driven by TG synthesis, essential for inflammatory macrophage activation; inhibiting TG synthesis, and thus LD development, significantly reduces inflammatory mediator production (35). Given that PCSK7 regulates TG levels and influences lipid accumulation, it is reasonable to expect that PCSK7 deficiency limits TG synthesis, reducing LD accumulation in macrophages. Future studies using a macrophage-specific PCSK7 knockout model could explore this further; we anticipate limited effects on plasma lipid levels but reduced intracellular lipid accumulation in macrophages, although this association needs confirmation.

TNF-α, produced by immune cells such as T cells, B cells, and macrophages, exists in membrane-bound and soluble forms (36). It activates TNFR1 and TNFR2, triggering inflammatory pathways that lead to cell death (37), and tissue damage. JNK is essential for differentiating inflammatory macrophages that secrete TNF-α (38). In this study, PCSK7 deficiency reduced TNF-α levels and JNK activity in inflammatory macrophages in MI mice and human macrophages under simulated MI conditions. Data suggest that PCSK7 modulates the TNF-α/JNK pathway, driving macrophage-mediated inflammation and exacerbating vascular disease in the infarcted heart. Although this study focused on the MAP kinase pathway associated with PCSK7, TNF-α can also activate NF-κB pathways in macrophages (39), and NF-κB can inhibit JNK signaling (40). Thus, the interplay between PCSK7, JNK, and NF-κB remains unclear, highlighting the need for further research to clarify PCSK7’s role in inflammatory pathway regulation in CAD. Clarifying whether PCSK7 influences TNF-α expression upstream or downstream of JNK could offer insights into potential therapeutic strategies for CAD.

In conclusion, this study underscores PCSK7 as a critical factor in exacerbating MI by promoting cardiac inflammation and adverse remodeling. PCSK7 deficiency lowered cholesterol levels and shifted macrophages toward an anti-inflammatory phenotype, enhancing cardiac repair. PCSK7 acts within macrophages by inducing TNF-α expression and activating the JNK pathway, leading to inflammatory damage. These findings suggest that targeting PCSK7 in macrophages could be a promising therapeutic strategy for improving cardiac outcomes by reducing inflammation and fostering improved tissue remodeling. 

Materials and methods are available in the Supplementary Material.

The apparatus, including LSM780 and LSM880 NLO (Zeiss), and LSRFortessa (Becton Dickinson) at the Ewha Fluorescence Core Imaging Center, was utilized for major experiments. This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF-2020R1A3B2079811 and RS-2023-00217798). This work was funded thanks to grants to N.G.S. including a Canadian Institutes of Health Research Foundation Scheme grant (# 148363), a CIHR grant (# 191678), and a Canada chair in Precursor Proteolysis (# 950-231335).

G.T.O. is employed by Imvastech Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.