In a screening campaign to find biotargets related to acute cardiovascular diseases, we identified a novel biomarker candidate, dipeptidyl peptidase 3 (DPP3).
DPP3 is a ubiquitously expressed, cytosolic, zinc-dependent metallopeptidase that sequentially cleaves dipeptides from the N-terminus of various bioactive substrates , such as angiotensins and enkephalins.
Despite the first identification of DPP3 more than 50 years ago , the exact physiological role of intracellular DPP3 remains unclear considering that its currently known substrates are extracellular bioactive peptides.
The most prominent substrate of DPP3 is angiotensin II (Ang II) – the main effector of the renin-angiotensin system (RAS). The RAS is activated in cardiovascular diseases and Ang II, in particular, has been shown to modulate many cardiovascular functions including blood pressure control and cardiac remodeling [3, 4]. Recently, it was shown that DPP3 degrades Ang II in vivo, reducing blood pressure in hypertensive mice . The release of DPP3 from dying cells and DPP3’s potential implications in blood pressure regulation and pain modulation, based on its extracellular substrate specificity (Ang II and enkephalins), lead us to develop a blood-based immunoassay to quantify DPP3 in the bloodstream.
“These results indicate that high cDPP3 levels directly affect heart and kidney hemodynamics, resulting in organ dysfunction .”
Using our immunoassay, we determined the normal circulating DPP3 levels in the blood of healthy volunteers, which we refer to as cDPP3 to differentiate it from intracellular DPP3. Using this as a reference value, we first observed an increase of cDPP3 levels in severely ill septic patients. Furthermore, high cDPP3 levels were associated with disease severity and high short-term mortality risk .
Additional studies in cardiogenic shock patients showed that high cDPP3 levels are associated with heart and kidney dysfunction within 48h, need of vasopressor therapy within 96 h, high rates of refractory shock and high short-term mortality [7,8]. We also observed that dynamic changes of cDPP3 levels during the first 24h were significantly associated with outcome. Patients that showed a decrease in cDPP3 levels in 24h had lower risk of refractory shock, organ failure and mortality in comparison to patients that kept their cDPP3 levels high [7,8].
In order to understand if cDPP3 directly causes organ dysfunction, we natively purified DPP3 from human blood cell lysate  and intravenously injected it in healthy mice. Upon DPP3 injection, we reported impaired heart function within 15 min and reduction of kidney function within 60 min. These results indicate that high cDPP3 levels directly affect heart and kidney hemodynamics, resulting in organ dysfunction . Our current model suggests that, upon cell death, DPP3 is released in the extracellular space and reaches the bloodstream. This leads to uncontrolled degradation of DPP3 substrates, such as Ang II and enkephalin, and consequent organ dysfunction. Our results provide solid evidence that DPP3 is not only a powerful biomarker for short-term organ dysfunction and disease severity but also a druggable target.
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