Purpose of review
Galectins, a family of evolutionarily conserved glycan-binding proteins, are involved in the regulation of multiple cellular processes (e.g. immunity, apoptosis, cellular signaling, development, angiogenesis and cellular growth) and diseases (e.g. chronic inflammation, autoimmunity, cancer, infection). We discuss here how galectins contribute to the development of specialized microenvironmental niches during hematopoiesis.
Recent findings
An expanding set of data strengthens a role of galectins in hematopoietic differentiation, particularly by setting specific interactions between hematopoietic and stromal cells: galectin-5 is found in reticulocytes and erythroblastic islands suggesting a major role during erythropoiesis; galectin-1 and 3 are involved in thymocyte apoptosis, signaling and intrathymic migration; galectin-1 plays critical roles in pre-BII cells development. Moreover, expression of galectins-1 and 10 are differentially expressed during T-regulatory cell development. Various galectins (3, 4, 5, 9) have been reported to be regulated during myelopoiesis and traffic into intracellular compartments, dictating the cellular distribution of specific glycoproteins and glycosphingolipids.
Summary
The abundance of galectins in both extracellular and intracellular compartments, their multifunctional properties and ability to form supramolecular signaling complexes with specific glycoconjugates, make these glycan-binding proteins excellent candidates to mediate interactions between hematopoietic cells and the stromal microenvironment. Their secretion by one of the cellular partners can modulate adhesive properties by cross-linking specific glycoconjugates present on stromal or hematopoietic cells, by favoring the formation of synapses or by creating glycoprotein lattices on the surface of different cell types. Their divergent specificities and affinities for various glycoproteins contribute to the multiplicity of their cellular interactions.
