Role of purinergic signalling and cytokines in the ischaemic stroke

Oddział Neurologiczny, Wojewódzki Szpital Zespolony w Toruniu

AKTUALN NEUROL 2012, 12 (4), p. 205–214
ABSTRACT

Inflammation plays an important role in the aetiology of various diseases of the central nervous system including the stroke. Accumulating evidence indicates that inflammation in the central nervous system is controlled by purinergic signalling. The mediators of purinergic signalling are extracellular nucleotides (e.g. ATP, ADP, UTP and UDP) and adenosine that act via activation of P2 and P1 purinergic receptors, respectively. The activation of P2 and P1 receptors is regulated by the enzymes ectonucleotidases that hydrolyse either extracellular nucleotides or adenosine. This review focuses on the role of purinergic signalling in the ischaemic stroke. We and others have demonstrated the presence of nucleotides and adenosine in the cerebrospinal fluid. We have also shown that the concentration of ATP and other nucleotides is increased in cerebrospinal fluid of patients with ischaemic stroke. Evidence suggests that the activation of P2 and P1 receptors have an opposite role in the ischaemic stroke, i.e. while the nucleoside adenosine exert neuroprotective effects, nucleotides generally promote the proinflammatory and apoptotic responses. P2X7, P2Y2, P2Y6, P2Y11 and P2Y12 are proposed to be involved in the central nervous system inflammation as they are expressed in the brain and their activation is known to control the key inflammatory processes such as release of inflammatory mediators (e.g. cytokines, NO), migration of leukocytes, phagocytosis, apoptosis and thrombosis. The activation of P2 receptors can also increase the release of excitatory neurotransmitters that further exacerbate the inflammatory response. Three cytokines whose release is controlled by P2 receptors have a major role in the ischaemic stroke, namely tumour necrosis factor alpha (TNF-α), interleukin 1 (IL-1) and interleukin 6 (IL-6). By promoting inflammation and thrombosis, these proinflammatory cytokines contribute to the increase in lesion size and thus functional impairment of the affected tissue. Cytokines as well as extracellular nucleotides are involved in leukocyte migration to lesions. By their adherence to endothelium, leukocytes impair cerebral blood circulation and thus exacerbate damage to the brain. The hydrolysis of nucleotides to adenosine by the ectonucleotidases leads to deactivation of proinflammatory responses. Similar effect can also be obtained with P2X7 and IL-1 receptor antagonists that are presently under clinical development and investigation.

Keywords: nucleotides, nucleosides, cytokines, purinergic receptors, ischaemic stroke