Wingless-related integration site (WNT) signaling is activated during the inflammatory response upon cardiac surgery: A translational study

Abstract

Objective: Cardiac surgery and the use of cardiopulmonary bypass initiate a systemic inflammatory response. Wingless-related integration site (WNT) signaling is part of the innate immunity and has been attributed a major role in the regulation of inflammation. In preclinical research, WNT-5a may sustain an inflammatory response and cause endothelial dysfunction. Our aim was to investigate WNT signaling after cardiac surgery and its association with postoperative inflammation (Clinicaltrials.gov, NCT04058496).

Methods: In this prospective, single-center, observational study, 64 consecutive patients for coronary artery bypass grafting (CABG) ± valve surgery were assigned into three groups: off-pump CABG (n = 28), on-pump CABG (n = 16) and combined valve-CABG surgery (n = 20). Blood samples were acquired before surgery, at intensive care unit (ICU) admission and 4, 8, and 48 h thereafter. Plasma concentrations of WNT-5a and its antagonists Secreted frizzled-related protein 1 (sFRP-1), Secreted frizzled-related protein 5 (sFRP-5), and WNT inhibitory factor 1 (WIF-1) were determined by enzyme-linked immunosorbent assay. In addition, plasma concentrations of six inflammatory cytokines were measured by multiplex immunoassay. Parameters were analyzed for evolution of plasma concentration over time, interactions, intergroup differences, and association with clinical outcome parameters.

Results: At baseline, WNT-5a, sFRP-1, and WIF-1 were present in a minimal concentration, while sFRP-5 was elevated. A higher baseline value of WNT-5a, sFRP-5, and WIF-1 resulted in higher subsequent values of the respective parameter. At ICU admission, WNT-5a and sFRP-5 reached their maximum and minimum value, respectively. WIF-1 decreased over time and was lowest 8 h after surgery. sFRP-1 changed minimally over time. While WNT-5a returned to the baseline within 48 h, sFRP-5 and WIF-1 did not reach their baseline value at 48 h. Of the investigated WNT system components, only WIF-1 partially reflected the severity of surgery. WNT-5a and WIF-1 had an impact on postoperative fluid balance and noradrenaline requirement.

Conclusion: WNT-5a, sFRP-5, and WIF-1 are part of the systemic inflammatory response after cardiac surgery. WNT-5a peaks immediately after cardiac surgery and returns to baseline within 48 h, presumably modulated by its antagonist sFRP-5. Based on this translational study, WNT-5a antagonism may be further investigated to assess potentially beneficial effects in patients with a dysregulated inflammation after cardiac surgery.

Keywords: SIRS; WNT signaling; WNT-5a; cardiac surgery; cardiopulmonary bypass; inflammation; inflammatory biomarkers; systemic inflammatory response syndrome.

FIGURE 1

Preclinical studies investigating Wingless-related integration site (WNT) signaling components (–11, 30) are graphically summarized to elucidate the background of this translational study. Damage and pathogen associated molecular patterns (DAMPs and PAMPs) activate macrophages via Toll-like receptors (TLR) which in turn promote transcription factor NF-κB to upregulate the expression of WNT-5a and a wide array of inflammatory cytokines. After secretion, WNT-5a binds to the membrane bound Frizzled-5 (FZD-5) receptor on the activated macrophages leading to an augmentation of the inflammatory cytokine production. This autocrine action enables WNT-5a to sustain the inflammatory response unrelated to the original stimulus. The positive feedback loop of WNT-5a is antagonized by Secreted frizzled-related protein 1 (sFRP-1) and Secreted frizzled-related protein 5 (sFRP-5) at the FZD-5 receptor. In vascular endothelial cells (VEC), WNT-5a promotes the loosening of intercellular tight junctions leading to increased paracellular permeability. This paracrine effect of WNT-5a is antagonized by WNT inhibitory factor 1 (WIF-1) at the membrane bound Ryk-receptor on VEC.

FIGURE 2

Blood sampling timeline. T1–T5, blood sampling time points used for statistical analysis. BL, Baseline; CS, cardiac surgery; CS + 4 h, 4 h after skin incision; ICU, intensive care unit. *, main study; #, pilot study.

FIGURE 3

Evolution of (A) Wingless-related integration site 5a (WNT-5a), (B) Secreted frizzled-related protein 5 (sFRP-5), and (C) WNT inhibitory factor 1 (WIF-1) over time (T1–T5) in the overall population (All) and the three groups (OPCAB, CABG on-pump, and valve-CABG). Values are presented as median and interquartile range (IQR) (box), within 1.5× IQR (line) and outliers (dots). T1, baseline; T2, time of intensive care unit (ICU) admission; T3, 4 h after surgery; T4, 8 h after surgery; T5, 48 h after surgery; CABG, coronary artery bypass grafting; OPCAB, off-pump coronary artery bypass grafting.

FIGURE 4

Evolution of ratios between (A) Wingless-related integration site 5a (WNT-5a) and Secreted frizzled-related protein 5 (sFRP-5), and (B) WNT-5a and WNT inhibitory factor 1 (WIF-1) over time (T1–T5) in the overall population (All) and the three groups (OPCAB, CABG on-pump and valve-CABG). Values are presented as median and interquartile range (IQR) (box), within 1.5× IQR (line) and outliers (dots). ln, natural logarithm; T1, baseline; T2, time of intensive care unit (ICU) admission; T3, 4 h after surgery; T4, 8 h after surgery; T5, 48 h after surgery; CABG, coronary artery bypass grafting; OPCAB, off-pump coronary artery bypass grafting.

FIGURE 5

Evolution of (A) interleukin-6 (IL-6) and (B) monocyte chemoattractant protein 1α (MCP-1α) over time (T1–T5) in the overall population (All) and the three groups (OPCAB, CABG on-pump and valve-CABG). Values are presented as median and interquartile range (IQR) (box), within 1.5× IQR (line) and outliers (dots). T1, baseline; T2, time of intensive care unit (ICU) admission; T3, 4 h after surgery; T4, 8 h after surgery; T5, 48 h after surgery; CABG, coronary artery bypass grafting; OPCAB, off-pump coronary artery bypass grafting.

FIGURE 6

This figure summarizes how Wingless-related integration site 5a (WNT-5a) may come into play in a systemic inflammation caused by cardiac surgery and how its plasma concentration may be modulated by Secreted frizzled-related protein 5 (sFRP-5). Cardiac surgery and the use of cardiopulmonary bypass lead to the formation of damage associated molecular patterns which activate cells of the mononuclear phagocyte system. These cells produce and secrete WNT-5a which enters the circulatory system. In the blood stream, WNT-5a is bound by its antagonist sFRP-5 forming a soluble complex. Between the baseline (T1), the time of intensive care unit (ICU) admission (T2) and 48 h after surgery (T5), the blood plasma concentrations of WNT-5a and sFRP-5 move in the opposite direction compared to each other. This may demonstrate the modulatory effect of sFRP-5 on the WNT-5a plasma concentration leading to an attenuation of the WNT-5a peak value during the promotion of a systemic inflammation upon cardiac surgery and a timely return of WNT-5a to its baseline value during the resolution of the inflammatory response.