Transforming growth factor-beta signalling in brain disorders.

Transforming growth factor-beta (TGF-beta) has been characterized as an injury-related factor, based on the observation that it is strongly up-regulated in many acute or chronic central nervous system disorders. TGF-beta is generally thought to be neuroprotective and several mechanisms have been proposed to explain this beneficial action. For instance, TGF-beta protects neurons against the potentiating effect of tissue-type plasminogen activator on NMDA receptor-mediated excitotoxicity, by up-regulating type-1 plasminogen activator inhibitor expression in astrocytes. TGF-beta has also anti-apoptotic properties, through a recruitment of a mitogen-activated protein kinase pathway and a concomitant activation of anti-apoptotic members of the Bcl-2 family. These multiple mechanisms might reflect the pleiotropic nature of TGF-beta, reinforcing the potential therapeutic value of this cytokine in several central nervous system disorders.