The STC2-PAPP-A-IGFBP4-IGF1 axis and its associations to mortality and CVD in T2D.

Objective: Physiologically, pregnancy-associated plasma protein-A (PAPP-A) serves to liberate bound IGF1 by enzymatic cleavage of IGF-binding proteins (IGFBPs), IGFBP4 in particular. Clinically, PAPP-A has been linked to cardiovascular disease (CVD). Stanniocalcin-2 (STC2) is a natural inhibitor of PAPP-A enzymatic activity, but its association with CVD is unsettled. Therefore, we examined associations between the STC2-PAPP-A-IGFBP4-IGF1 axis and all-cause mortality and CVD in patients with type 2 diabetes (T2D). Design: We followed 1284 participants with T2D from the ADDITION trial for 5 years. Methods: Circulating concentrations of STC2, PAPP-A, total and intact IGFBP4 and IGF1 and -2 were measured at inclusion. End-points were all-cause mortality and a composite CVD event: death from CVD, myocardial infarction, stroke, revascularisation or amputation. Survival analysis was performed by Cox proportional hazards model. Results: During follow-up, 179 subjects presented with an event. After multivariable adjustment, higher levels of STC2, PAPP-A, as well as intact and total IGFBP4, were associated with all-cause mortality; STC2: hazard ratio (HR) = 1.84 (1.09-3.12) (95% CI); P = 0.023, PAPP-A: HR = 2.81 (1.98-3.98); P < 0.001, intact IGFBP4: HR = 1.43 (1.11-1.85); P = 0.006 and total IGFBP4: HR = 3.06 (1.91-4.91); P < 0.001. Higher PAPP-A levels were also associated with CVD events: HR = 1.74 (1.16-2.62); P = 0.008, whereas lower IGF1 levels were associated with all-cause mortality: HR = 0.51 (0.34-0.76); P = 0.001. Conclusions: This study supports that PAPP-A promotes CVD and increases mortality. However, STC2 is also associated with mortality. Given that STC2 inhibits the enzymatic effects of PAPP-A, we speculate that STC2 either serves to counteract harmful PAPP-A actions or possesses effects independently of the PAPP-A-IGF1 axis. Significance statement: PAPP-A has pro-atherosclerotic effects and exerts these most likely through IGF1. IGF1 is regulated by the STC2-PAPP-A-IGFBP4-IGF1 axis, where STC2, an irreversible inhibitor of PAPP-A, has been shown to reduce the development of atherosclerotic lesions in mice. We examined the association of this axis to mortality and CVD in T2D. We demonstrated an association between PAPP-A and CVD. All components of the STC2-PAPP-A-IGFBP4-IGF1 axis were associated with mortality and it is novel that STC2 was associated with mortality in T2D. Our study supports that inhibition of PAPP-A may be a new approach to reducing mortality and CVD. Whether modification of STC2 could serve as potential intervention warrants further investigation.