Distribution of glia maturation factor-like activity in organs and cells

Mitogenic and morphogenic effects of a bovine salivary gland extract on astrocytes and fibroblasts

The presence of mitogenic and morphogenic activity in extracts of bovine salivary (parotid) glands is reported. The crude and partially purified extracts stimulated cultured rat cerebellar cells (astrocytes) and skin fibroblasts to undergo morphogenesis. The incorporation of [3H]thymidine was also stimulated in astrocytes, skin fibroblasts, and established fibroblastic cell lines. Growth-promoting activity was also demonstrated. The expression of maximum mitogenic activity in skin fibroblast cultures, but not kidney fibroblast cultures, required the presence of serum. The biological activity had an apparent native molecular weight greater than 230,000, was heat-sensitive, trypsin-resistant, and slightly sensitive to the action of papain.

Endogenous immunoreactive glia maturation factor-like molecule in astrocytes and glioma cells

Using the monoclonal antibody G2-09 raised against bovine glia maturation factor (GMF), we conducted a survey of GMF-like immunoreactivity in various cell types. Of all the normal and neoplastic cells tested, only extracts from astroblasts, gliomas, Schwann cells and schwannomas, but not their conditioned media, possessed endogenous GMF-like immunoreactivity. The presence of immunoreactive GMF correlated well with GMF bioactivity. Using the same monoclonal antibody, the GMF-like factor in astroblasts and C6 glioma cells was characterized by immunofluorescence, immunoadsorption and immunoblotting. Immunofluorescence confirmed the intracellular location of GMF. Immunoadsorption completely eliminated the GMF-like bioactivity from the cell extracts. Immunoblotting identified a protein band having a mol. wt. of 14,000 Da. Thus, the evidence strongly supports the argument that the GMF-like factor in astroblasts and C6 cells is identical with GMF from the bovine brain. In order to explain the fact that astroblasts and C6 cells are both the source and targets of GMF, we propose the hypothesis that GMF functions as an injury signal, being released from the injured glia and serving as a stimulant for gliosis in the neighboring intact glia.

Distribution of immunoreactive glia maturation factor-like molecule in organs and tissues

Using the monoclonal antibody G2-09 raised against bovine glia maturation factor (GMF), we screened various rat organs and tissues for GMF-like immunoreactivity. In the adult animal, with the exception of the heart, GMF was found exclusively in the nervous system, with the cerebellum exhibiting higher specific activity than other brain regions. The nature of the immunoactivity in the heart is presently unclear. None of the body fluids collected from humans, including serum and cerebrospinal fluid, possessed detectable GMF immunoactivity. A phylogenetic comparison revealed the presence of GMF in the brain of al vertebrates studied, from fish to primates. GMF was absent from bacteria and yeast. An ontogenetic study on rats showed the highest GMF level in the fetal brain, with a gradual but steady decrease after birth. However, a substantial amount of GMF persisted even in older animals. GMF was localized in astrocytes and Bergmann glia in the rat brain, using immunostaining at the light microscopic level.

Autocrine regulation of glial proliferation and differentiation: the induction of cytodifferentiation of postmitotic normal glioblast by growth-promoting factor from astrocytoma cell

A growth-promoting factor (GPF) from astrocytoma cells (GA-1) cultured in serum-free medium (N2) exerted on normal glioblasts proliferative and differentiation-promoting effects, which have been observed in glia maturation factor (GMF) stimulation. The serum-free conditioned media of GA-1 provoked DNA synthesis of glioblasts, and subsequently elicited a morphological differentiation characterized by the extrusion of processes as well as biochemical changes including an increased cellular level of glia fibrillary acidic protein (GFA protein), S-100 protein, and alpha-enolase. The transforming growth factor activity was also found in the media. Partially purified GPF had a molecular weight range of 7100-10,000 Mr and acidic isoelectric point (pH 4.6), and showed a susceptibility to heat treatment and denaturation at low and high pHs. The present results and the findings accumulated from our previous studies on gliotrophic growth factors provide a general concept of the growth and differentiation regulations of normal or neoplastic glial cells by growth factors through autocrine systems.

Glia maturation factor influences recovery from injury in neonatal rat brains

Newborn rats were injured with a puncture wound in one cerebral hemisphere. Experimental animals were treated with three i.p. injections of Glia Maturation Factor (GMF) at daily intervals starting from the time of injury, whereas control littermates were treated with equivalent amounts of bovine serum albumin. At 25 days old the size of the cerebral cortex at the plane of injury was measured on representative brain sections. In control rats the injured side was 18% smaller than the normal side whereas in GMF-treated animals the difference was only 1%. The results suggest a possible regulatory role of GMF in promoting tissue recovery from brain damage.

The induction of glial proliferation by an astrocytoma-derived growth factor resembling glia maturation factor

Glia maturation factor (GMF)-like activity which induces DNA synthesis and morphological differentiation of density-inhibited glioblasts was detected in various glial tumor cells. A polypeptide from C6 cells (rat astrocytoma) which has a molecular weight range of 40,000-50,000 showed the highest activity. This factor also induced DNA synthesis in glioma cells (354A and LRM55) and fibroblast (Swiss 3T3). The activity was susceptible to heat treatment at 70 degrees C for 5 min, or to proteases such as trypsin, chymotrypsin, papain, and subtilisin, but it was devoid of esteropeptidase activity. The isoelectric point was found to be 5.3. Subcellular fractionation localized the activity in cytosomal and microsomal fractions. These properties closely resemble those of GMF from pig and bovine brain.