Quantification of protein expression for several matrix metalloproteinases (MMPs) previously implicated in the degradation of arterial elastic and collagen fibers, vascular stiffening12,48–51 and the development of PAH52 revealed increased expression of the gelatinase MMP9, the macrophage elastase MMP12, and the interstitial collagenase MMP13 in PAs of PH-LHD patients, but importantly also in part in LHD w/o PH patients with MMP9 just missing (p = 0.093) and MMP13 reaching the level of significance (Fig. 2d). Here, MMP9 is linked to gonorrhea.