Differential Developmental Deficits in Retinal Function in the Absence of either Protein Tyrosine Sulfotransferase-1 or -2

To investigate the role(s) of protein-tyrosine sulfation in the retina and to determine the differential role(s) of tyrosylprotein sulfotransferases (TPST) 1 and 2 in vision, retinal function and structure were examined in mice lacking TPST-1 or TPST-2. Despite the normal histologic retinal appearance in both Tpst1−/− and Tpst2−/− mice, retinal function was compromised during early development. However, Tpst1−/− retinas became electrophysiologically normal by postnatal day 90 while Tpst2−/− mice did not functionally normalize with age. Ultrastructurally, the absence of TPST-1 or TPST-2 caused minor reductions in neuronal plexus. These results demonstrate the functional importance of protein-tyrosine sulfation for proper development of the retina and suggest that the different phenotypes resulting from elimination of either TPST-1 or -2 may reflect differential expression patterns or levels of the enzymes. Furthermore, single knock-out mice of either TPST-1 or -2 did not phenocopy mice with double-knockout of both TPSTs, suggesting that the functions of the TPSTs are at least partially redundant, which points to the functional importance of these enzymes in the retina

Differential responsiveness of late passage C-6 glial cells and advanced passages of astrocytes derived from aged mouse cerebral hemispheres to cytokines and growth factors: Glutamine synthetase activity

In this study, we were interested to compare the responsiveness to growth factors, NGF, b-FGF and EGF and cytokines, IL-1 beta, and TNF-alpha, in late passages (74-79) C6 glial cells committed astrocytes and astrocytes of advanced passages (26-28) in cultures derived from aged mouse cerebral hemispheres (MACH). Cultures were grown in either DMEM or chemically defined medium (CDM/TIPS) in order to test the effects of growth factors or cytokines. The activity of glutamine synthetase (GS), a marker for astrocytes, was used as a test parameter. We found that treatment with growth factors increased GS activity in both glial cell culture systems with the exception of EGF in C-6 glial cells. Treatment with cytokines markedly decreased GS activity in the late passage C6 glial cells whereas only TNF-alpha had a similar effect on MACH astrocytes. In view of the generally opposite effects of growth factors and cytokines on GS activity, we speculate that these molecules which are also endogenously present in glial cells may play a role in the maintenance of cellular homeostasis

Stimulation of glutamine synthetase activity by excitatory amino acids in astrocyte cultures derived from aged mouse cerebral hemispheres may be associated with non-N-methyl-d-aspartate receptor activation

We have been using glial cells derived from aged mouse cerebral hemispheres (MACH) at several passages to study the responsiveness of astrocytes to microenvironmental signals in culture. In the present study, we examined the effects of excitatory amino acids on the activity of glutamine synthetase, a marker for astrocytes. MACH glia cell passages 25 to 29 were used. Culture groups were Dulbecco’s modified Eagle’s medium + 10% fetal bovine serum (control); glutamate 100 mu M; gamma-amino-3-hydroxy-5-methyl isoxazole-4-propionic acid (AMPA) 50 mu M; kainic acid 10 mu M; N-methyl-D-aspartate (NMDA) 10 mu M. In all treated groups glutamine synthetase activity was significantly higher than in controls. We speculate that this increase represents an enhanced differentiation of immature astrocytes. In a second series, we examined the effects of glutamate receptor antagonists on glutamine synthetase activity as follows. MACH cultures were treated with glutamate 100 mu M in combination with either L(+)-2-amino-3-phosphonopropionic acid (L-AP3; 50 mu M); D(-)-2-amino-5-phosphonopentanoic acid (D-AP5; 50 mu M) or 6,7-dinitroquinoxaline-2,3-dione (DNQX; 50 mu M). The increase in GS activity produced by glutamate was inhibited by the nonselective NMDA receptor antagonist, DNQX, but not by the metabotropic receptor antagonist, L-AP3 or a selective NMDA receptor antagonist, D-APS. We also found that in cultures treated with glutamate, a number of astrocytes resembled ‘’reactive astrocytes” morphologically. These astrocytes were absent in cultures treated with glutamate + DNQX. The findings provide supportive evidence that astrocytes from aged mouse cerebral hemispheres respond to excitatory amino acids and that this response is mediated by non-NMDA receptor activation. Copyright (C) 1996 ISDN