Nucleolin Improves Heart Function During Recovery From Myocardial Infarction by Modulating Macrophage Polarization

Abstract

Background: Nucleolin has multiple functions within cell survival and proliferation pathways. Our previous studies have revealed that nucleolin can significantly reduce myocardial ischemia-reperfusion injury by promoting myocardial angiogenesis and reducing myocardial apoptosis. In this study, we attempted to determine the role of nucleolin in myocardial infarction (MI) injury recovery and the underlying mechanism. Methods: Male BALB/c mice aged 6–8 weeks were used to set up MI models by ligating the left anterior descending coronary artery. Nucleolin expression in the heart was downregulated by intramyocardial injection of a lentiviral vector expressing nucleolin-specific small interfering RNA. Macrophage infiltration and polarization were measured by real-time polymerase chain reaction, flow cytometry, and immunofluorescence. Cytokines were detected by enzyme-linked immunosorbent assay. Results: Nucleolin expression in myocardium after MI induction decreased a lot at early phase and elevated at late phase. Nucleolin knockdown impaired heart systolic and diastolic functions and decreased the survival rate after MI. Macrophage infiltration increased in the myocardium after MI. Most macrophages belonged to the M1 phenotype at early phase (2 days) and the M2 phenotype increased greatly at late phase after MI. Nucleolin knockdown in the myocardium led to a decrease in M2 macrophage polarization with no effect on macrophage infiltration after MI. Furthermore, Notch3 and STAT6, key regulators of M2 macrophage polarization, were upregulated by nucleolin in RAW 264.7 macrophages. Conclusions: Lack of nucleolin impaired heart function during recovery after MI by reducing M2 macrophage polarization. This finding probably points to a new therapeutic option for ischemic heart disease.

Ribosome biogenesis in disease: new players and therapeutic targets

“…Mechanistically, Ncl improves cardiac function during MI by enhancing M2 macrophage polarization. 169 In mouse models of MI, autophagy-related gene deletion or drug inhibition aggravates cardiac dysfunction and myocardial remodeling. 170 Deng et al 166 found that the Ncl/autophagy signaling pathway is upregulated in the infarcted myocardium.…”

“…Macrophage phenotype-switching between the pro-inflammatory M1 and the anti-inflammatory M2 phenotype exhibit plasticity during the post-MI inflammatory response and tissue repair. 201 Using a mouse MI model, Tang et al 169 found that the expression of Ncl mRNA and protein decreased gradually from day 3 after MI, then increased gradually, reaching a peak on day 7. The macrophages in the myocardium switch from the M1 phenotype 2 days after MI to the M2 phenotype 5 days after MI, suggesting a potential correlation between Ncl expression and macrophage phenotype-switching.…”

Nucleolar stress: Friend or foe in cardiac function?

“…NCL was subjected to protein cleavage in the very early phases of cardiac ischaemia-reperfusion injury ( 77 ). Further investigations indicated that NCL expression was dramatically reduced in the early stage of experimental myocardial infarction, and then recovered at late stages ( 78 ). Overexpression of NCL protects cultured cardiomyocytes from hypoxia- and H 2 O 2 -induced death ( 77 ).…”

“…These studies demonstrated that NCL may facilitate the recovery of cardiomyocytes following exposure to stress stimuli. Moreover, NCL has been reportedly implicated in inflammatory induction in experimental myocardial infarction, as well as in cultured cardiomyocytes following hypoxia-reoxygenation injury ( 78 , 79 ). NCL plays a key role in the induction of a variety of cytokines important for inflammatory responses and cardiac repair, such as IL-6 and IL-1β ( 79 ).…”

“…NCL plays a key role in the induction of a variety of cytokines important for inflammatory responses and cardiac repair, such as IL-6 and IL-1β ( 79 ). In vivo data revealed that NCL expression is critical for alternative (M2) polarization of macrophages, and depletion of NCL reduced M2 polarization but had no effect on general macrophage infiltration ( 78 ). Given the fact that macrophage M2 polarization is of vital importance to cardiac tissue repair following injury, it is anticipated that NCL expression may critically contribute to cardiac recovery via the initiation of alternative inflammatory responses ( 80 ).…”