Secretion of Matrix Metalloproteinase-9 from Astrocytes by Inhibition of Tonic P2Y14-Receptor-Mediated Signal(s)

Abstract

Glial cells have various important roles in regulation of brain functions. For such events, extracellular nucleotides/P2 receptors have central roles. Although there have been huge amount of literature about activation of P2 receptors and glial functions, little is known about what happens in glia or the brain if glial P2 receptor is inhibited. Here we show that the inhibition of P2 receptors in astrocytes, the most abundant glial cells and cause a constitutive release of nucleotides, resulted in secretion of metalloproteinase-9 (MMP-9), a metal-dependent endopeptidase that degrades extracellular matrix molecules and is important in regulation of brain remodeling. When cultured astrocytes were treated with apyrase (ecto-nucleotidase), reactive blue 2 (P2 receptor antagonist), and pertussis toxin, they secreted MMP-9, suggesting that Gi-coupled P2Y receptor-mediated signals constitutively suppress the production of MMP-9. Among Gi-coupled P2Y receptors, we found that an inhibition of P2Y(14) receptor, a receptor for nucleotide-sugars such as UDP-glucose, is responsible for the production of MMP-9 by pharmacological and molecular biochemical analysis. As for the mechanisms, the inhibition of P2Y(14) receptors resulted in the release of tumor necrosis factor (TNF)-α which then acted on astrocytes to induce MMP-9. Taken together, our results suggest that the constitutive releases of nucleotide-sugars in astrocytes should play an important role in maintaining the normal status of the cell, through Gi-coupled P2Y(14) receptors, and when the signal is removed, the cells start to release TNF-α, which then acts on astrocytes in a feedback fashion to boost MMP-9 synthesis and secretion.

UDP-Sugars as Extracellular Signaling Molecules: Cellular and Physiologic Consequences of P2Y14 Receptor Activation

“…Cultured rat primary astrocytes and murine microglia N9 cells express P2Y 14 R mRNA, and addition of 100 mM UDP-glucose to rat astrocytes resulted in transient elevation of intracellular calcium (Fumagalli et al, 2003;Bianco et al, 2005). More recently, Kinoshita et al (2013) reported that UDP-glucose-promoted Ca 21 signaling was reduced by ∼50% in astrocytes transfected with P2Y 14 R siRNA, although the extent of P2Y 14 R suppression was not reported. In the absence of exogenous agonists, P2Y 14 R siRNA-transfected cells displayed increased release of tumor necrosis factor-a (TNFa) and expression of matrix metalloprotease-9 (MMP-9), suggesting that astrocyte remodeling events are suppressed by constitutively active P2Y 14 R (Kinoshita et al, 2013).…”

The two-hit hypothesis for neuroinflammation: role of exogenous ATP in modulating inflammation in the brain

“…In fact soluble Aβ 1-42 itself induces ATP release, auto-stimulating P2Y 4 receptors in microglia, thus mediating its own clearance. Degradation of extracellular amyloid peptides is also performed by metallopeptidases such as matrix metalloproteinase 9 (MMP-9), whose secretion is upregulated following inhibition of the tonically active P2Y 14 receptors (Kinoshita et al, 2013). These reports suggest that the loss of P2Y 2 and P2Y 4 receptors or an overactivation of P2Y 1 and P2Y 14 receptors alter the steady state levels of amyloid peptides leading to AD.…”

P2Y receptors in Alzheimer's disease

“…Treatment of astrocytes with apyrase, RB2 or PTX, also increased expression of cytokine‐induced neutrophil chemoattractant‐3, TNF‐α, tissue inhibitory metalloproteinase (TIMP)‐1 and monocyte chemoattractant protein‐1 (MCP‐1). While TIMP‐1 is known to bind MMP‐9 and inhibit its proteolytic activity (Hernandez‐Guillamon et al., ), TNF‐α induces MMP‐9 release from astrocytes in vitro (Kinoshita et al., ). These findings suggest a protective role of the P2Y 14 R in AD via suppressing MMP‐9 expression.…”