Physiological and pathophysiological implications of osteopontin and the diagnostic utility of the protein in kidney diseases

Abstract

Introduction and objective. Osteopontin (OPN) is a protein playing many pleiotropic both physiological and pathophysiological roles in various organs. The paper briefly characterizes both the positive and negative roles of OPN, with particular emphasis on the role of the protein in kidney functioning. Brief description of the state of knowledge. As its name suggests, OPN is a protein mainly regulating bone homeostasis, but it also participates in the pathogenesis of inflammation, neoplasm, atherosclerosis and vascular calcification. OPN is also an important protein involved in kidney physiology. Its main physiological function is to act as an inhibitor of the crystallization of urine mineral components and to prevent kidney stones formation. OPN is also overproduced in various kidney pathologies (tubulointerstitial fibrosis, crescending glomerulonephritis, cyclosporine or diabetic nephropathy, renal ischemia reperfusion injury), and both experimental and clinical studies suggest that OPN may exert either a protective or detrimental effect on kidneys. Conclusions. Considering the OPN role in kidneys, the protein is currently proposed as one of novel laboratory biomarkers for renal function. OPN, along with the other proteins found in the urine in various kidney diseases (neutrophil gelatinaseassociated lipocalin-1, kidney injury molecule-1, and fatty acid binding protein) is a part of the laboratory panel that will be gradually introduced into common laboratory practice.