Possible involvement of glial cell line-derived neurotrophic factor and its receptor, GFRα1, in survival and maturation of thymocytes

The glial cell line-derived neurotrophic factor (GDNF) and its receptors (GFR) play important roles in the promotion of survival and differentiation of central and peripheral neuronal populations. We show that GFRα1, a component of GDNF receptor, was expressed in thymocytes at an early stage of thymocyte-development and was involved in the survival of thymocyte precursors. GFRα1 and GDNF were expressed in thymus, but not in spleen or lymph nodes in adult mice. During embryonic thymocyte development, GFRα1 was predominantly expressed on thymocytes from days 14.5 to 16.5 of gestation, and thereafter its expression gradually declined. In adult thymus, GFRα1 was expressed only on CD4^-CD8^- double-negative (DN) thymocytes, but not on CD4⁺CD8⁺ double-positive or single-positive thymocytes. It was strongly expressed on RAG2^-/- thymocytes arrested at the DN stage, and its expression was reduced during their differentiation after in vivo anti-CD3 antibody stimulation. Additionally, fetal thymocyte precursors grew in serum-free medium of the fetal thymus organ culture system in the presence of recombinant GDNF (rGDNF), while the cells without rGDNF died. These results suggested that GDNF/GFRα1 are involved in the survival of both the nervous system and DN immature thymocytes.