REGIONAL DIFFERENCES IN RESPONSIVENESS OF ADULT CNS AXONS TO GRAFTS OF CELLS EXPRESSING HUMAN NEUROTROPHIN-3

Neurotrophin 3 (NT3) belongs to the neurotrophin family, which also in cludes nerve growth factor, brain-derived neurotrophic factor, and neu rotrophin 4/5. NT3 mRNA is widely expressed in the rodent nervous syst em, but the physiological function of the native protein is still uncl ear. Genetically modified cell lines that produce physiological amount s of NT3 can provide a useful tool in the elucidation of the NT3 effec ts in the adult central nervous system (CNS). Genetically modified rat primary skin fibroblasts expressing and secreting human NT3 (hNT3) we re prepared and characterized. In vitro, cell lines derived from diffe rent retroviral constructs expressed hNT3 mRNA, as determined by PCR a nd RNA blot analysis. Secretion of biologically active hNT3 was confir med by specific elicitation of neurite outgrowth from cultured chick p rimary sympathetic and sensory neurons and from rat fetal locus coerul eus neurons in the presence of hNT3-producing cell conditioned media. In vivo implanted fibroblasts survived well up to the maximal experime ntal time points of 6 weeks (brain) and 4 weeks (spinal cord) and cont inued to express hNT3 mRNA in vivo. As early as 2 weeks postgrafting, specific sprouting of host sensory neurites in response to hNT3-produc ing grafts was observed in the spinal cord. In contrast, hNT3-producin g cerebral grafts did not induce a sprouting response different from t hat observed with control grafts. These findings establish the existen ce of a regionally different responsiveness of the CNS axons to local hNT3 overexpression. (C) 1995 Academic Press, Inc.