HSPG2 and pulmonary arterial hypertension: Another possible mechanism for the pulmonary-hypertension-promoting abilities of HIMF has been found: HIMF increases intracellular calcium levels in the human pulmonary artery smooth muscle cells via the PLC signaling pathway in an IP3 and tyrosine phosphorylation-dependent manner, which ultimately leads to constriction of the pulmonary vasculature [13].