Purinergic signaling induces thrombospondin-1 expression in astrocytes

Abstract

Thrombospondin (TSP)-1, a multidomain glycoprotein, is secreted from astrocytes and promotes synaptogenesis. However, little is known about the mechanisms regulating its expression and release. In this article, we report that purinergic signaling participates in the production and secretion of TSP-1. Treatment of primary cultures of rat cortical astrocytes with extracellular ATP caused an increase in TSP-1 expression in a time-and concentration-dependent manner and was inhibited by antagonists of P2 and P1 purinergic receptors. Agonist studies revealed that UTP, but not 2,3-O-(4-benzoyl)benzoyl-ATP, 2-methylthio-ADP, adenosine, or 5-N-ethyl-carboxamidoadenosine, caused a significant increase in TSP-1 expression. In addition, release of TSP-1 was stimulated by ATP and UTP but not by 2-methylthio-ADP or adenosine. Additional studies indicated that P2Y 4 receptors stimulate both TSP-1 expression and release. P2Y receptors are coupled to protein kinase cascades, and signaling studies demonstrated that blockade of mitogen-activated protein kinases or Akt inhibited ATP-and UTPinduced TSP-1 expression. Using an in vitro model of CNS trauma that stimulates release of ATP, we found that TSP-1 expression increased after mechanical strain and was completely blocked by a P2 receptor antagonist and by inhibition of p38͞mitogen-activated protein kinase and Akt, thereby indicating a major role for P2 receptor͞protein kinase signaling in TSP-1 expression induced by trauma. We conclude that TSP-1 expression can be regulated by activation of P2Y receptors, particularly P2Y 4, coupled to protein kinase signaling pathways and suggest that purinergic signaling may be an important factor in TSP-1-mediated cell-matrix and cell-cell interactions such as those occurring during development and repair.neuron-glia interaction ͉ traumatic injury ͉ nucleotide receptors ͉ gliosis ͉ protein kinase R ecent evidence has shifted the focus on astrocytes from primarily a passive role involved in homeostasis to a more active role in a number of key physiological and pathological interactions with neurons (1-4). One of the ways in which astrocytes can interact with neurons is by the expression or release of recognition molecules. Thrombospondins (TSPs) are large multimeric, multidomain glycoproteins that participate in cell-cell and cell-matrix interactions (5). TSPs are expressed in many tissues, but their importance in the CNS is just beginning to be understood. For instance, two recent studies have focused attention on the role of TSPs in CNS development and repair. Christopherson et al. (6) showed that application of purified TSP-1, TSP-2, or astrocyte-conditioned medium was sufficient to increase the number of synapses in retinal ganglion cells and that these synapses were presynaptically active. In addition, Lin et al. (7) reported that after ischemia, increased levels of TSP-1 were localized in astrocytes and endothelial cells near blood vessels. These studies indicate the importance of TSPs in synapse formation during development and in remo...

Astrocytes promote peripheral nerve injury-induced reactive synaptogenesis in the neonatal CNS

“…These results indicate that RB-2 partially blocks reactive synaptogenesis. This is in line with in vitro studies showing that ATP-induced TSP-1 expression in cultured astrocytes is not completely blocked by RB-2 (Tran and Neary 2006).…”

“…ATP is released from various sources (Franke et al 2006;Vizi et al 2001), including the damaged cells (Fields and Stevens 2000). ATP activates purinergic receptors of astrocytes so that astrocytes switch from quiescent (resting) to reactive status (Collazos-Castro and Nieto-Sampedro 2001; Tran and Neary 2006). Reactive astrocytes release soluble factors such as TSPs (Christopherson et al 2005;Tran and Neary 2006), cholesterol (Slezak and Pfrieger 2003), and other factors (see for review Pfrieger 2010;Stevens 2008).…”

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