Induction by Hydrocortisone of Glutamine Synthetase in Mouse Primary Astrocyte Cultures

Abstract

Glutamine synthetase activity was investigated in developing primary astroglial cultures established from newborn mouse cerebral hemispheres. Between the 2nd and 4th week of culture there was little change in activity under our standard culturing conditions; however, when hydrocortisone (10 microM) was added to the cultures for 48 h, the enzyme activity increased two- to fourfold, depending upon the age of the culture, with maximum response in 2-week-old cultures. The addition of dibutyryl cyclic AMP (dBcAMP) to the culture medium caused morphological differentiation of the astroglial cells but eliminated the response of the cells to hydrocortisone. Culturing in elevated serum levels, which delays morphological differentiation and inhibits astroglial cytodifferentiation after exposure to dBcAMP, shifted the time of maximal response to hydrocortisone from 2 to 3 weeks and prevented the abolishment of glutamine synthetase induction by dBcAMP. The induction of glutamine synthetase by hydrocortisone was prevented by actinomycin D (0.5 microgram/ml), indicating its dependence upon RNA and protein synthesis. The present work thus confirms reports in the literature that hydrocortisone induces glutamine synthetase in neural tissues, but differs from the findings of Moscona and co-workers in the chick retina that intact tissues are required for the induction to occur.

Glutamate and Glutamine Metabolism and Compartmentation in Astrocytes

“…The relative homogeneity of the mouse astrocyte preparation is reflected by the observation that practi cally all individual astrocytes in these cultures stain for glutamine synthetase [8]. This is in contrast to the finding by Hallermayer et al [9] that only a fraction of the cells stain for this enzyme.…”

“…This is in contrast to the finding by Hallermayer et al [9] that only a fraction of the cells stain for this enzyme. Obviously the homogeneity with respect to glutamine synthetase, reported by Juurlink et al [8] does not indicate that the mouse cultures could not be functionally heterogeneous in other respects.…”

Astrocytes in the aging brain

“…Both astrocytes and oligodendrocytes express a variety of hormone receptors, particularly receptors for glucocorticoids, mineralocorticoids, and the sex hormones androgen, estrogen (ER␣ and -␤), and progesterone (Melcangi et al, 1999). Activated steroid receptors regulate astrocytic expression of growth factors (Jurgen and Lehner, 1995), GFAP and glutamine synthetase (Juurlink et al, 1981;Laping et al, 1994;Rozovsky et al, 1995), proteins that regulate ion channel function (Yarowski et al, 1994;Bohn et al, 1994) and inhibit proliferation (Gould et al, 1992;Crossin et al, 1997). Estrogen has positive effects on calcium signaling; estrogen pretreatment of cultures of cortical astrocytes results in a severalfold increase in the extent of calcium wave propagation.…”

Developmental Expression of Glial Fibrillary Acidic Protein and Glutamine Synthetase in Serum-Free Aggregating Cell Cultures of Fetal Rat Telencephalon

“…Jorgensen, Psychochemistry Institute, University of Copenhagen, Denmark [21], was applied first, followed by swine anti rabbit immunoglobulins bound to tetramethylrhodamine isothiocyanate isomer R (Dakopatts, 1:25). The sections were washed several times in PBS and then treated with a monoclonal anti-GFAP antiserum (BioYeda, 1:800).…”