[Semaphorin and osteoporosis.]

Although Semaphorins were originally identified as neuronal axon guidance molecules, recent research has revealed the functions of Semaphorins in many organs, tissues and cells. Among Semaphorin family members, Semaphorin 3A(Sema3A)and Sema4D are highly expressed in bone cells and play critical roles in the regulation of bone homeostasis. Other semaphorins and their receptors are also shown to be involved in bone metabolism. In contrast, the function of Semaphorins expressed in lung is not well understood althogh many of Semaphorins are highly expressed in lung among various tissues examined. As growing evidence reveals that the link between chronic obstructive pulmonary disease(COPD)and osteoporosis, the crosstalk between bone and lung through Semaphorin signaling should be investigated.