Asae Shintani

Tissue Distribution and Immunocytochemical Localization of Neurotrophin‐3 in the Brain and Peripheral Tissues of Rats

Abstract: The tissue distribution of neurotrophin‐3 (NT‐3) was investigated in rats at 1 month of age using a newly established, sensitive two‐site enzyme immunoassay system for NT‐3, as well as the immunocytochemical localization of this protein. The immunoassay for NT‐3 enabled us to quantify NT‐3 at levels > 3 pg per assay. In the rat brain, NT‐3 was detectable only in the olfactory bulb (0.54 ng/g wet weight), cerebellum (0.71 ng/g), septum (0.91 ng/g), and hippocampus (6.3 ng/g). By contrast, NT‐3 was widely distributed in peripheral tissues. Appreciable levels of NT‐3 were also found in the thymus (31 ng/g), heart (38 ng/g), diaphragm (21 ng/g), liver (45 ng/g), pancreas (892 ng/g), spleen (133 ng/g), kidney (40 ng/g), and adrenal gland (46 ng/g). An antibody specific for NT‐3 bound to pyramidal cells in the CA2‐CA4 regions of the hippocampus, to A cells in the islets of Langerhans in the pancreas, to unidentified cells in the red pulp of the spleen, to liver cells, and to muscle fibers in the diaphragm from rats at 1 month of age. Molecular masses of NT‐3‐immunoreactive proteins in the hippocampus and pancreas were 14 and 12 kDa, respectively. Thus, in rats, NT‐3 was detected in restricted regions of the brain and in the visceral targets of the nodose ganglia at high concentrations. Our present results suggest that NT‐3 not only functions as a classical target‐derived neurotrophic factor but also can play other roles.

Production, purification and characterization of biologically active recombinant human nerve growth factor

The human NGF gene was isolated and inserted downstream from murine leukemia virus LTR in a plasmid having dihydrofolate reductase cDNA. The expression plasmid was introduced into CHO cells. Selection of the transformants for the resistance to methotrexate gave a CHO cell line which produced human NGF at a level of 4 mg/L in the culture medium. The recombinant human NGF was purified to near homogeneity from the culture supernatant. The NH2-terminal amino acid sequence, the COOH-terminal amino acid (Ala), and the amino acid composition of the human NGF were identical to those deduced from the nucleotide sequence of the human NGF gene. The recombinant human NGF was composed of 120 amino acid residues. Three disulfide linkages were determined to be Cys15-Cys80, Cys-58-Cys108, and Cys68-Cys110; the locations were identical to those in the mouse 2.5S NGF molecule. The specific biological activity of the recombinant human NGF was comparable with that of authentic mouse 2.5S NGF as determined by stimulation of neurite outgrowth from PC12 cells.

Developmental changes of neurotrophin-3 level in the mouse brain detected by a highly sensitive enzyme immunoassay

Levels of neurotrophin-3 (NT-3) in the mouse brain were measured by a highly sensitive enzyme immunoassay (EIA). The monoclonal antibody, 3W3, was labeled with beta-galactosidase, followed by measurement of galactosidase activity. The detection limit of the EIA system was 0.4 pg/well (4 pg/ml). At 1 and 8 weeks of age, the highest level of NT-3 was detected in the hippocampus, a relatively high level also observed in the cerebellum. In contrast, in the cortex, the striatum, the diencephalon, the midbrain, and the brainstem, NT-3 levels were low. Furthermore, we examined the developmental changes of NT-3 level in the hippocampus and the cerebellum. In the hippocampus, the NT-3 levels were more than 20 ng/g tissue from 1 week to 14 weeks of age, but at 20 weeks of age the level decreased to about half. In the cerebellum, although the NT-3 level was high at 1 week of age, the levels were gradually decreased to one-fourth by 20 weeks of age. In peripheral tissues, a large amount of NT-3 protein was observed in the heart.

Purification and characterization of biologically active recombinant human neurotrophin-3 produced by expression of a chimera gene in Chinese hamster ovary cells

In order to obtain high-level expression of recombinant human neurotrophin-3 (NT-3), we constructed several types of expression plasmids and examined several cell lines for expression of the human NT-3 gene. The highest level production of the recombinant protein was attained in Chinese hamster ovary cells transfected with an expression plasmid that contains a chimera gene encoding the human nerve growth factor (NGF) prepro-region and human NT-3 mature-region under control of a murine leukemia virus-derived long terminal repeat (MuLV-LTR). This cell line can produce more than 1 mg recombinant human NT-3/1 conditioned medium. The recombinant protein was purified to apparent homogeneity with a cation exchange column, a gel filtration column and a reversed-phase HPLC column with a recovery of about 30%. The purified NT-3, at a concentration as low as 0.2 ng/ml, induced neurite out-growth in neurons prepared from 8-day-old chick embryonic dorsal root ganglia; however, it showed little neurotrophic effect on rat PC12 pheochromocytoma cells, which are known to be NGF-responding cells. In addition, this protein promoted colony formation by human peripheral blood lymphocytes in soft agar culture.