Thrombin‐activated microglia contribute to death of dopaminergic neurons in rat mesencephalic cultures: Dual roles of mitogen‐activated protein kinase signaling pathways

Abstract

This study evaluated the role of thrombin-activated microglia in the neurodegeneration of mesencephalic cultures. Immunocytochemical and biochemical evidence indicated that in co-cultures consisting of rat cortical microglia and mesencephalic neurons, thrombin led to nonselective loss of mesencephalic neurons. Accompanying neurodegeneration, microglial activation was obvious, evidenced by expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-1beta, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) and by increasing production of TNF-alpha and nitric oxide (NO). In mesencephalic neurons treated with conditioned media (CM) taken from thrombin-activated microglia, the number of dopaminergic neurons was significantly attenuated. The neurotoxicity of the CM was diminished when it was derived from microglia co-treated with thrombin and either an extracellular signal-regulated kinase 1/2 (ERK1/2) pathway inhibitor (PD98059) or a p38-mitogen-activated protein kinase (p38-MAPK) inhibitor (SB203580). Moreover, jun N-terminal kinase (JNK) and p38-MAPK were activated in mesencephalic neurons treated with CM of thrombin-activated microglia. Inhibition of JNK and p38-MAPK rescued the dopaminergic neurons. Collectively, these results indicate that thrombin-activated microglia induce neurodegeneration in cultured mesencephalic neurons and that the MAPKs actively participate in both microglial activation and neurodegeneration. The present data carefully suggest that microglial activation triggered by thrombin may be involved in the neuropathological processes of dopaminergic neuronal cell death that occur in Parkinson's disease.

The effect of thrombin on a 6-hydroxydopamine model of Parkinson's disease depends on timing

“…While the role of thrombin in the pathogenesis of human PD remains to be determined, several studies have found that thrombin at high doses (∼20 U) can damage dopaminergic neurons in vivo [5,8,9] and in vitro [40 U/mL; [9,25]]. Here, however, we provide data indicating that a much lower dose of thrombin (1 U) can, when given at the time of a 6-OHDA lesion, increase behavioral deficits.…”

“…Experiments using doses in addition to 1 or ∼20 U of thrombin will be required to more fully characterize the dose response relationship of the effects of thrombin on the nigrostriatal dopamine system. Microglial activation has been found to be an important mechanism by which thrombin could damage dopaminergic neurons [8,10,25]. While the direct contribution of microglia to the pathogenesis of PD has remained a controversial topic, a great deal of research suggests that they do indeed play a role [38].…”

“…High doses of thrombin (∼20 U) can lead to degeneration of dopaminergic neurons in the substantia nigra, although cell-type specificity is still unclear [5,9]. This effect is likely mediated by cell death pathways involving microglial activation [5,8,10,25]. It is also interesting that intracerebral hemorrhage (with resultant thrombin production) in or near the nigrostriatal tract, has been found to produce L-DOPA responsive behavioral deficits similar to those observed in PD [19,30].…”

Genome-wide association study confirms extant PD risk loci among the Dutch

“…46 In addition, the frequency of various HLA antigens was increased in patients with PD and in patients dying from postencephalitic PD. [53][54][55] Although PD is clearly not an autoimmune disorder, the occurrence of a localized attack of microglia during the disease course has been demonstrated with epidemiological, 56,57 animal model 58,59 and cell culture [60][61][62] approaches. Zhang et al 63 reported that aggregated a-synuclein activates microglia which, as a consequence, are toxic toward cultured dopaminergic neurons.…”

Thrombin-induced microglial activation contributes to the degeneration of nigral dopaminergic neurons in vivo

“…Previously, Lee and Debeir reported that thrombin was directly toxic to dopaminergic neurons in mesencephalic cultures containing few of microglia. Choi's results suggested that thrombin could activate microglia in vivo and this microglial activation could mediate degeneration of dopaminergic neurons in the SN by increased expression of inducible nitric-oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and proinflammatory cytokines from activated microglia [5][6][7][8][9][10] . However, there is no substantial evidence ob-serving the effect of thrombin on the degeneration of dopaminergic neurons in the longer survival time of rats.…”