Periostin: The bone and beyond.

In recent years the relationship between bone, metabolism and many pathophysiologic mechanisms involving other organs and the immune system, was increasingly apparent. This observation concerns vitamin D, osteopontin and periostin (PO). PO is expressed in the periosteum of long bones but also in many other tissues and organs, including heart, kidney, skin and lungs, being enhanced by mechanical stress or injury. PO has a relevant physiological function in promoting injury repair in a large number of tissues. However, its overexpression was observed in different diseases characterized by inflammation, fibrosis and tumorigenesis. Here we review the current knowledge on the role of PO in physiologic and pathologic pathways of different diseases. A specific focus regards the correlation between the level of PO and lung diseases and the identification of PO also as an inflammatory key effector in asthma, strongly associated with airways eosinophilia. In fact PO seems to be a useful biomarker of "Th2-high" asthma compared to "Th2-low" asthma phenotype and a predictor of response to therapeutic agents. Currently, a growing number of studies suggests a possible role of PO as a new diagnostic marker and/or therapeutic target for different diseases and its usefulness in clinical practice should be supported and confirmed by further and larger studies.