Osteopontin-mediated myocardial fibrosis in heart failure: a role for lysyl oxidase?

We investigated whether the pro-fibrotic matricellular protein osteopontin (OPN) is associated with the enzymes involved in the extracellular synthesis of fibril-forming collagen type I (i.e. procollagen C-proteinase, PCP) and its cross-linking to form insoluble fibrils (i.e. lysyl oxidase, LOX) in heart failure (HF) of hypertensive origin. OPN, PCP, and LOX were assessed by histochemical and molecular methods in the myocardium of 21 patients with hypertensive heart disease (HHD) and HF. Whereas the myocardial expression of OPN was very scarce in control hearts (n 10), it was highly expressed in HF patients (P 0.0001). OPN was directly correlated with LOX (r 0.460, P 0.041), insoluble collagen (r 0.534, P 0.015), pulmonary capillary wedge pressure (r 0.558; P 0.009), and left-ventricular (LV) chamber stiffness (r 0.458, P 0.037), and inversely correlated with LV ejection fraction (r 0.513, P 0.017) in all patients. OPN did not correlate with PCP and other parameters assessing collagen synthesis by fibroblasts or degradation by matrix metalloproteinases. In vitro studies showed that OPN significantly (P 0.05) increases the expression and activity of LOX in human cardiac and dermal fibroblasts. An excess of OPN is associated with increased LOX and insoluble collagen, as well as with LV stiffness and systolic dysfunction in patients with HHD and HF. In addition, OPN up-regulates LOX in human fibroblasts. It is suggested that the OPNLOX axis might facilitate the formation of insoluble collagen (i.e. stiff and resistant to degradation) and the subsequent alteration in LV mechanical properties and function in patients with HHD and HF.