Involvement of β1 integrin in microglial chemotaxis and proliferation on fibronectin: Different regulations by ADP through PKA

Abstract

Microglia are immune cells in the brain; their activation, migration, and proliferation have pivotal roles in brain injuries and diseases. Microglia are known to attach firmly to fibronectin, the upregulation of which is associated with several pathological conditions in the CNS, through beta1 integrin and become activated. Extracellular nucleotides can serve as potent signaling molecules. Recently, ATP and ADP were revealed to possess chemoattractive properties to microglia via Gi-coupled P2Y receptors. In the present study, we report that the ADP-induced chemotaxis of microglia is mediated by P2Y12/13 receptors and is beta1 integrin-dependent in the presence of fibronectin. Signals from P2Y12/13 receptors also cause beta1 integrin translocation to the membrane ruffle regions, but this redistribution was lost when the intracellular cyclic AMP (cAMP) was increased by forskolin or dibutyryl cAMP. This inhibitory effect of cAMP-elevating agents did not appear when microglia were co-incubated with a protein kinase A (PKA) inhibitor, KT-5720, suggesting that PKA is a negative regulator of the beta1 integrin translocation. We also show that the engagement of beta1 integrin enhanced microglial proliferation. Signals from P2Y12/13 receptors attenuated the proliferation, whereas ADP itself had no effect on microglial growth. Furthermore, beta1 integrin-induced proliferation is positively regulated by the cAMP-dependent PKA. Together, these results indicate the involvement of beta1 integrin in microglial proliferation and chemotaxis, both of which have clinical importance. The data also suggest that PKA is inversely involved in these two cellular functions.

Involvement of vasodilator-stimulated phosphoprotein in UDP-induced microglial actin aggregation via PKC- and Rho-dependent pathways

“…Some reports stated that the activation of P2Y 12 receptors leads to altered cellular morphology and motility in microglia. ATP/ ADP act on their cognate receptor P2Y 12 , leading to actin aggregation, microglial chemotaxis and process extension [5,6,8,9,44]. In a recent study, it was reported that the phosphorylation of VASP is involved in ADP-induced ruffling and protrusion formation in the BV2 microglial cell line [11].…”

“…This research also showed that the accumulation of VASP at the phagocytic cup was abolished by inhibition of RhoGTPase. VASP phosphorylation induced by the UDPactivated P2Y 6 receptor may serve as the driving force for the dynamic processes of movement in microglial phagocytosis.…”

“…Microglia express ionotropic P2X 4,7 and metabotropic P2Y 6,12 receptors [1]. We previously showed that extracellular adenosine 5′-triphosphate (ATP) and adenosine 5′-diphosphate (ADP) induce membrane ruffling and chemotaxis by activation of P2Y 12 receptors in microglia [1,[5][6][7]. Activation of the P2Y 12 receptor also causes integrin-dependent microglial process extension [8].…”

“…These studies indicate the prominent role of P2Y 12 receptor activation in microglial motility. We also reported that P2Y 6 receptor activation stimulated by its ligand uridine 5′-diphosphate (UDP) induced dynamic cytoskeletal arrangement and process movement in microglia, resulting in increase of microsphere phagocytosis [1]. Although the actin cytoskeletal rearrangement occurred in both cases of cellular movements, chemotaxis and phagocytosis, the signaling pathway of cytoskeletal regulation by P2 receptors in microglia remains to be understood.…”

Regulation of death and survival in astrocytes by ADP activating P2Y1 and P2Y12 receptors

“…clopidogrel (also known as Plavix) and ticlopidine [1,[4][5][6], which must be metabolized in vivo prior to receptor inhibition. Recently, the wide distribution of P2Y 12 mRNA in human, mouse, and rat brain tissues was reported [7,8], and the evidence indicates that this receptor is associated with astrocyte function. However, the role of the P2Y 12 receptor in brain function is largely unclear.…”