Plasma proteoglycan 4: a novel biomarker for acute lung injury after pediatric cardiac surgery

Background

Identification of biological molecules related to post cardiopulmonary bypass (CPB) lung injury could help diagnose, predict and potentially impact patient's clinical course after cardiac surgery. Proteoglycan 4 (PRG4) initially identified as potential biomarker for patients with prolonged mechanical ventilation following CPB in a prior study. To further validate these findings, we sought to understand the association of lower plasma PRG4 with prolonged mechanical ventilation and worse lung compliance in a larger cohort of pediatric patients post CPB.

Methods

Retrospective chart review study. Pediatric Cardiac Intensive Care Unit, Tertiary Hospital. Infants <1 year old with tetralogy of Fallot, ventricular septal defect, or atrioventricular septal defect who underwent surgical repair 2012-2020 and had stored plasma samples in our biorepository were screened for inclusion. Patients with mechanical ventilation before surgery were excluded. Patients were divided into quartiles based on postoperative duration of mechanical ventilation (control <25th percentile, study >75th percentile). Preoperative and 48-hour postoperative samples for each cohort (20 patients each) were tested for PRG4 level using enzyme-linked immunosorbent assay (ELISA) technique.

Results

Study group had lower lung compliance, higher mean airway pressure and higher oxygen need postoperative when compared to control group. Plasma PRG4 levels before surgery and 48 hours postoperative were lower in study group compared to control group (P=0.0232 preoperative; P=0.0016 postoperative). Plasma PRG4 levels were compared preoperative to PRG4 levels postoperative in both group, there was no statistically significant difference (study group: P=0.0869; control group: P=0.6500).

Conclusions

Lower levels of plasma PRG4 is associated with longer duration of mechanical ventilation, worse ventilator compliance and higher oxygen requirement after cardiac surgery in our patient population. Further validation of this finding in a larger and more diverse patient population is necessary prior to its application at the bedside.

Effect of disulfide bonding and multimerization on proteoglycan 4's cartilage boundary lubricating ability and adsorption

PURPOSE

The objectives of this study were to assess the cartilage boundary lubricating ability of (1) nonreduced (NR) disulfide-bonded proteoglycan 4 (PRG4) multimers versus PRG4 monomers and (2) NR versus reduced and alkylated (R/A) PRG4 monomers and to assess (3) the ability of NR PRG4 multimers versus monomers to adsorb to an articular cartilage surface.

MATERIALS AND METHODS

PRG4 was separated into two preparations, PRG4 multimer enriched (PRG4Multi+) and PRG4 multimer deficient (PRG4Multi-), using size exclusion chromatography (SEC) and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The cartilage boundary lubricating ability of PRG4Multi+ and PRG4Multi- was compared at a physiological concentration (450 μg/mL) and assessed over a range of concentrations (45, 150, and 450 μg/mL). R/A and NR PRG4Multi- were evaluated at 450 μg/mL. Immunohistochemistry with anti-PRG4 antibody 4D6 was performed to visualize the adsorption of PRG4 preparations to the surface of articular cartilage explants.

RESULTS

Separation into enriched populations of PRG4Multi+ and PRG4Multi- was achieved using SEC and was confirmed by SDS-PAGE. PRG4Multi+ and PRG4Multi- both functioned as effective friction-reducing cartilage boundary lubricants at 450 μg/mL, with PRG4Multi+ being more effective than PRG4Multi-. PRG4Multi+ lubricated in a dose-dependent manner, however, PRG4Multi- did not. R/A PRG4Multi- lubricated similar to NR PRG4Multi-. PRG4-containing solutions showed 4D6 immunoreactivity at the articular surface; the immunoreactive intensity of PRG4Multi+ appeared to be similar to SF, whereas PRG4Multi- appeared to have less intensity.

CONCLUSIONS

These results demonstrate that the intermolecular disulfide-bonded multimeric structure of PRG4 is important for its ability to adsorb to a cartilage surface and function as a boundary lubricant. These findings contribute to a greater understanding of the molecular basis of cartilage boundary lubrication of PRG4. Elucidating the PRG4 structure-lubrication function relationship will further contribute to the understanding of PRG4's role in diarthrodial joint homeostasis and disease.