Inhibition of prothrombin kringle-2-induced inflammation by minocycline protects dopaminergic neurons in the substantia nigra in vivo

Abstract

Prothrombin kringle-2 (pKr-2), a domain of prothrombin, can cause the degeneration of mesencephalic dopaminergic neurons through microglial activation. However, the chemical products that inhibit pKr-2-induced inflammatory activities in the brain are still not well known. The present study investigated whether minocycline, a semisynthetic tetracycline derivative, could inhibit pKr-2-induced microglial activation and prevent the loss of nigral dopaminergic (DA) neurons in vivo. To address this question, rats were administered a unilateral injection of pKr-2 in the substantia nigra in the presence or absence of minocycline. Our results show that pKr-2 induces the production of proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and inducible nitric oxide synthase from the activated microglia. In parallel, 7 days after pKr-2 injection, tyrosine hydroxylase immunocytochemical analysis and western blot analysis showed a significant loss of nigral DA neurons. This neurotoxicity was antagonized by minocycline and the observed neuroprotective effects were associated with the ability of minocycline to suppress the expression of tumor necrosis factor-α, interleukin-1β, and nitric oxide synthase. These results suggest that minocycline may be promising as a potential therapeutic agent for the prevention of DA neuronal degeneration associated with pKr-2-induced microglial activation.

Protection of nigral dopaminergic neurons by AAV1 transduction with Rheb(S16H) against neurotoxic inflammation in vivo

“…To examine whether nigral transduction with AAV1-Rheb(S16H) protects the nigrostriatal DA projection from neurotoxic inflammation, we unilaterally injected pKr-2, which has been previously reported to be an endogenous microglial activator, 9 , 25 , 26 , 27 into the SN at 3 weeks after AAV1-GFP and AAV1-Rheb(S16H) administration. The mice treated with pKr-2-alone and pKr-2 in the presence of GFP were used as controls for comparisons withRheb(S16H)-induced neuroprotection.…”

“…To investigate whether the induction of Rheb(S16H) expression in DA neurons affects pKr-2-induced microglial activation, which induces neurotoxic inflammation in the nigrostriatal DA system, 9 , 25 , 26 , 27 we evaluated the levels of activated microglia-produced pro-inflammatory cytokines, such as TNF-α and IL-1β, in the SN. As shown in the double-immunofluorescence staining, there were apparent increases in TNF-α and IL-1β expression levels within Iba1-positive microglia in the SN at 1 day after pKr-2 treatment ( Figure 4a ).…”

“… 5 , 6 , 7 , 8 Recently, we also reported that upregulation of pKr-2, which is an endogenous microglial activator, could induce the degeneration of nigrostriatal DA projections in the adult brain through production of pro-inflammatory cytokines such as TNF-α and IL-1β from activated microglia. 9 , 25 , 26 , 27 These reports suggest that the control of microglial activation, which induces neurotoxic events, may be useful for protecting nigral DA neurons in the adult brain. Numerous studies have focused on the mechanisms of neurotoxic inflammation inhibition that are involved in activated microglia and have shown that their control could result in the neuroprotection of nigral DA neurons.…”

“…Numerous studies have focused on the mechanisms of neurotoxic inflammation inhibition that are involved in activated microglia and have shown that their control could result in the neuroprotection of nigral DA neurons. 5 , 6 , 7 , 8 , 9 , 25 , 26 , 27 , 32 However, whether there is a specific treatment that can induce neuroprotective effects without the control of neuroinflammation in a neurotoxic inflammatory environment, thereby providing direct protection against neurotoxic inflammation in the adult brain, is still unknown.…”

Naringin: A Protector of the Nigrostriatal Dopaminergic Projection

“…Under neuropathological conditions, microglia are activated in response to DA neuronal damages, and activated microglia could produce various potentially neurotoxic molecules, including inducible nitric oxide synthase (iNOS) and proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) [9, 10, 11, 12, 13]. iNOS and proinflammatory cytokines may be involved in nigrostriatal DA neuronal death [12, 13]. Moreover, increasing evidence suggests that activated microglia generate reactive oxygen species, resulting in oxidative stress to DA neurons in the substantia nigra of Parkinson's disease patients and animal models of Parkinson's disease generated by administration of 1-methyl-4-phenylpyridinium (MPP + ) [9].…”