The role of multifunctional adhesion molecules in spermatogenesis and sperm function: Lessons from hemostasis and defense?

The functional maintenance of the vascular endothelial cell barrier depends on different homo- and heterotypic adhesion systems involving tight junctions, junctional adhesion proteins, and cadherins. Upon inflammatory responses, vessel wall-dependent adhesion and transmigration of leukocytes involves the subtle orchestration of intercellular adhesion receptors and their counter-ligands on each cell type. Following tissue injury, the hemostatic/wound-healing process relies on various cell-associated adhesion receptors (particularly integrins) on platelets and vascular cells as well as on extracellular matrix (ECM) proteins to warrant sealing of the wound. In particular, integrin-binding ECM adhesion molecules mediate firm anchorage as well as cellular motility in cooperation with pericellular proteolytic systems. Accumulating evidence indicates that such cell-anchored and ECM adhesion proteins, which are crucial in vascular defense processes, are also expressed in the testicular epithelium and in gametes to mediate the timely events of spermatid movement during spermatogenesis in the testis and to contribute to the various phases of the fertilization process, culminating in sperm-oocyte fusion, respectively. We explore the multifunctional roles of junctional adhesion molecules, nectins, integrins, ECM proteins, and others beyond their role in defense and hemostasis as important contributors in spermatogenesis and sperm function.