Thrombin induces ischemic LTP (iLTP): implications for synaptic plasticity in the acute phase of ischemic stroke

Abstract

Acute brain ischemia modifies synaptic plasticity by inducing ischemic long-term potentiation (iLTP) of synaptic transmission through the activation of N-Methyl-D-aspartate receptors (NMDAR). Thrombin, a blood coagulation factor, affects synaptic plasticity in an NMDAR dependent manner. Since its activity and concentration is increased in brain tissue upon acute stroke, we sought to clarify whether thrombin could mediate iLTP through the activation of its receptor Protease-Activated receptor 1 (PAR1). Extracellular recordings were obtained in CA1 region of hippocampal slices from C57BL/6 mice. In vitro ischemia was induced by acute (3 minutes) oxygen and glucose deprivation (OGD). A specific ex vivo enzymatic assay was employed to assess thrombin activity in hippocampal slices, while OGD-induced changes in prothrombin mRNA levels were assessed by (RT)qPCR. Upon OGD, thrombin activity increased in hippocampal slices. A robust potentiation of excitatory synaptic strength was detected, which occluded the ability to induce further LTP. Inhibition of either thrombin or its receptor PAR1 blocked iLTP and restored the physiological, stimulus induced LTP. Our study provides important insights on the early changes occurring at excitatory synapses after ischemia and indicates the thrombin/PAR1 pathway as a novel target for developing therapeutic strategies to restore synaptic function in the acute phase of ischemic stroke.

Nafamostat Mesilate Improves Neurological Outcome and Axonal Regeneration after Stroke in Rats

“…It has been reported that thrombin, plasmin and kallikrein promote neuron injury and exacerbate glutamate neurotoxicity directly or indirectly [5,6]. For instance, thrombin induces ischemic long-term potentiation (LTP) in hypoxia-treated neurons, impairs the normal LTP [7] and perturbs neurite outgrowth; plasmin contributes to ischemia-induced neuron death [8]; and kallikrein 6 exacerbates glutamate neurotoxicity, implying that serine proteases could be potential targets for neuro-protection following stroke.…”

A Linear Temporal Increase in Thrombin Activity and Loss of Its Receptor in Mouse Brain following Ischemic Stroke

“…In contrast, in brain slices that are subjected to ischemic conditions such as OGD, no circulating coagulation factors are involved and the time points examined were somewhat shorter. Thrombin that is generated in the brain cells rises (14, 15) and as a result PAR1, its own receptor, may first increase as a complementary step, but these receptors are then cleaved and internalized leading to reduced levels. It is hypothesized that inhibiting the levels of thrombin during acute stroke will normalize PAR1 levels at the 2–24 hour time frame.…”

“…Activation of this receptor by low concentrations of thrombin may have neuroprotective effects, while at higher concentrations thrombin has deleterious effects (7–11). In the setting of an acute ischemic stroke, high thrombin levels have been detected in the infarct area, possibly as a consequence of blood–brain barrier opening (12, 13) or as a result of its local synthesis in the brain (14, 15) or both. Functionally, thrombin has been shown to cause synaptic dysfunction (15–19) and later, on vascular disruption, inflammatory response and neuronal damage (20–22), through the activation of PAR1 (13, 20).…”

“…In the setting of an acute ischemic stroke, high thrombin levels have been detected in the infarct area, possibly as a consequence of blood–brain barrier opening (12, 13) or as a result of its local synthesis in the brain (14, 15) or both. Functionally, thrombin has been shown to cause synaptic dysfunction (15–19) and later, on vascular disruption, inflammatory response and neuronal damage (20–22), through the activation of PAR1 (13, 20). Indeed, the toxic effects of thrombin in the central nervous system have been shown in various ischemia models where neuroprotection could be achieved by PAR1 deletion (22).…”

Protective and detrimental effects of neuroectodermal cell–derived tissue factor in mouse models of stroke

“…High levels of prothrombin mRNA expression and thrombin activity have been detected in brain tissue after acute ischemic stroke (36, 37). In addition, thrombin has been shown to cause synaptic dysfunction, and thrombin activity was associated with neuronal damage (38, 39). Furthermore, thrombin-dependent fibrin deposition and platelet activation can lead to microvascular thrombosis during both the ischemia and reperfusion phase, leading to the expansion of the initial infarct.…”