Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, C110
Increased expression of transforming growth factor-β1 alters synaptic structure in vivo and regulates neuronal activity in vitro
J. J. Bae1,3, A. Martinez-Canabal2,4, P. W. Frankland2,4, W. Lu1,3
1. Physiology, University of Toronto, Toronto, Ontario, Canada. 2. Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada. 3. Clinical and Integrative Biology, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada. 4. Neurosciences and Mental Health, Hospital for Sick Children, Toronto, Ontario, Canada.
Transforming growth factor-beta 1 (TGF-β1) is a multifunctional injury-related cytokine that orchestrates key events of development, disease and repair (Gomes et al. 2005). Secreted by both neurons and glial cells in the central nervous system (CNS), increased expression of TGF-β1 is associated with neurological diseases and brain trauma (Buckwalter et al. 2004). To date, its role in the regulation of synaptic structures and transmission in the mammalian CNS remains unclear. To investigate the effects of chronic over-secretion of TGF-β1 on the structural and functional properties of neural cells, we used transgenic mice (T64) that over-express active form of TGF-β1 in hippocampal and cortical astrocytes. Immunohistochemical analysis demonstrated that in comparison with wild-type (WT) littermate controls, the number of cells in T64 mice expressing glial fibrillary acidic protein (GFAP, astrocyte marker), and CD11b (microglia marker) increased significantly in the hippocampus and cortex. Notably, large immuno-clusters of synaptophysin (presynaptic protein) and calbindin-D28K (CaBP, calcium binding protein) positive immunoreactivity of neurons were, respectively, decreased in the CA3 region and the dentate gyrus through to the mossy fiber terminals. Decrease in CaBP and increase in GFAP protein levels in the T64 model were confirmed. Cultured primary astrocytes from T64 mice show higher rate in proliferation and more elongated cell bodies and processes when compared with WT controls. To examine the effect of TGF-β1 alone in the regulation of neuronal functions, we cultured hippocampal neurons from WT rat embryos in the presence or absence of TGF-β1 (4.0 ng/ml, 7-12 days). Voltage-clamp recordings in these cultured neurons revealed that TGF-β1 significantly increased the amplitudes of voltage-gated K+ currents, Na+ currents and glutamate-induced currents (p<0.05, Student’s t-test) in treated cells. Taken together, our results suggest that chronically increased expression of TGF-β1 may activate glia and induce alterations in synaptic structures of surrounding neuronal populations. Further, TGF-β1 alone appears, at least in culture condition, to increase neuronal activity.
Where applicable, experiments conform with Society ethical requirements