The pathologic accumulation and aggregation of α-synuclein (α-syn) underlies Parkinson's disease (PD). The molecular mechanisms by which pathologic α-syn causes neurodegeneration in PD are not known. ...Here, we found that pathologic α-syn activates poly(adenosine 5'-diphosphate-ribose) (PAR) polymerase-1 (PARP-1), and PAR generation accelerates the formation of pathologic α-syn, resulting in cell death via parthanatos. PARP inhibitors or genetic deletion of PARP-1 prevented pathologic α-syn toxicity. In a feed-forward loop, PAR converted pathologic α-syn to a more toxic strain. PAR levels were increased in the cerebrospinal fluid and brains of patients with PD, suggesting that PARP activation plays a role in PD pathogenesis. Thus, strategies aimed at inhibiting PARP-1 activation could hold promise as a disease-modifying therapy to prevent the loss of dopamine neurons in PD.
c-Abl is activated in the brain of Parkinson's disease (PD) patients and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice where it inhibits parkin through tyrosine ...phosphorylation leading to the accumulation of parkin substrates, and neuronal cell death. In the present study, we evaluated the in vivo efficacy of nilotinib, a brain penetrant c-Abl inhibitor, in the acute MPTP-induced model of PD. Our results show that administration of nilotinib reduces c-Abl activation and the levels of the parkin substrate, PARIS, resulting in prevention of dopamine (DA) neuron loss and behavioral deficits following MPTP intoxication. On the other hand, we observe no reduction in the tyrosine phosphorylation of parkin and the parkin substrate, AIMP2 suggesting that the protective effect of nilotinib may, in part, be parkin-independent or to the pharmacodynamics properties of nilotinib. This study provides a strong rationale for testing other brain permeable c-Abl inhibitors as potential therapeutic agents for the treatment of PD.
Upon activation, microglia and astrocytes produce a number of proinflammatory molecules that participate in the pathophysiology of several neurodegenerative disorders. This study explores the ...anti-inflammatory property of cinnamon metabolite sodium benzoate (NaB) in microglia and astrocytes. NaB, but not sodium formate, was found to inhibit LPS-induced expression of inducible NO synthase (iNOS), proinflammatory cytokines (TNF-alpha and IL-1beta) and surface markers (CD11b, CD11c, and CD68) in mouse microglia. Similarly, NaB also inhibited fibrillar amyloid beta (Abeta)-, prion peptide-, double-stranded RNA (polyinosinic-polycytidylic acid)-, HIV-1 Tat-, 1-methyl-4-phenylpyridinium(+)-, IL-1beta-, and IL-12 p40(2)-induced microglial expression of iNOS. In addition to microglia, NaB also suppressed the expression of iNOS in mouse peritoneal macrophages and primary human astrocytes. Inhibition of NF-kappaB activation by NaB suggests that NaB exerts its anti-inflammatory effect through the inhibition of NF-kappaB. Although NaB reduced the level of cholesterol in vivo in mice, reversal of the inhibitory effect of NaB on iNOS expression, and NF-kappaB activation by hydroxymethylglutaryl-CoA, mevalonate, and farnesyl pyrophosphate, but not cholesterol and ubiquinone, suggests that depletion of intermediates, but not end products, of the mevalonate pathway is involved in the anti-inflammatory effect of NaB. Furthermore, we demonstrate that an inhibitor of p21(ras) farnesyl protein transferase suppressed the expression of iNOS, that activation of p21(ras) alone was sufficient to induce the expression of iNOS, and that NaB suppressed the activation of p21(ras) in microglia. These results highlight a novel anti-inflammatory role of NaB via modulation of the mevalonate pathway and p21(ras).
Increased expression of glial fibrillary acidic protein (GFAP) represents astroglial activation and gliosis during neurodegeneration. However, the molecular mechanism behind increased expression of ...GFAP in astrocytes is poorly understood. The present study was undertaken to explore the role of nitric oxide (NO) in the expression of GFAP. Bacterial lipopolysachharides (LPSs) induced the production of NO and the expression of GFAP in mouse primary astrocytes. Either a scavenger of NO 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) or an inhibitor of inducible nitric oxide synthase l-N6-(I-iminoethyl)-lysine hydrochloride blocked this induction of GFAP expression. Similarly, other inducers of NO production such as interferon-gamma, interleukin-1beta, human immunodeficiency virus type 1 gp120, fibrillar amyloid beta peptides, and double-stranded RNA (polyinosinic-polycytidilic acid) also induced the expression of GFAP through NO. The role of NO in the expression of GFAP was supported further by increased expression of GFAP by S-nitroso glutathione (GSNO), an NO donor. Interestingly, inhibition of nuclear factor kappaB (NF-kappaB) suppressed LPS- but not GSNO-induced expression of GFAP, suggesting that NO does not require NF-kappaB to induce GFAP and that NF-kappaB functions upstream of NO production. However, inhibition of LPS- and GSNO-induced expression of GFAP either by NS-2028 a specific inhibitor of guanylate cyclase (GC) or by KT5823 a specific inhibitor of cGMP-activated protein kinase (PKG), and induction of GFAP expression by either 8-Br cGMP (a cell-permeable cGMP analog) or MY-5445 (a specific inhibitor of cGMP phosphodiesterase) suggests that NO induces GFAP via GC-cGMP-PKG. This study illustrates a novel biological role of NO in regulating the expression of GFAP in astrocytes through the GC-cGMP-PKG pathway that may participate in the pathogenesis of neurodegenerative disorders.
Neuroinflammation and oxidative stress underlie the pathogenesis of various neurodegenerative disorders. Here we demonstrate that sodium phenylbutyrate (NaPB), an FDA-approved therapy for reducing ...plasma ammonia and glutamine in urea cycle disorders, can suppress both proinflammatory molecules and reactive oxygen species (ROS) in activated glial cells. Interestingly, NaPB also decreased the level of cholesterol but involved only intermediates, not the end product of cholesterol biosynthesis pathway for these functions. While inhibitors of both geranylgeranyl transferase (GGTI) and farnesyl transferase (FTI) inhibited the activation of NF-κB, inhibitor of GGTI, but not FTI, suppressed the production of ROS. Accordingly, a dominant-negative mutant of p21(rac), but not p21(ras), attenuated the production of ROS from activated microglia. Inhibition of both p21(ras) and p21(rac) activation by NaPB in microglial cells suggests that NaPB exerts anti-inflammatory and antioxidative effects via inhibition of these small G proteins. Consistently, we found activation of both p21(ras) and p21(rac)in vivo in the substantia nigra of acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Oral administration of NaPB reduced nigral activation of p21(ras) and p21(rac), protected nigral reduced glutathione, attenuated nigral activation of NF-κB, inhibited nigral expression of proinflammatory molecules, and suppressed nigral activation of glial cells. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. Consistently, FTI and GGTI also protected nigrostriata in MPTP-intoxicated mice. Furthermore, NaPB also halted the disease progression in a chronic MPTP mouse model. These results identify novel mode of action of NaPB and suggest that NaPB may be of therapeutic benefit for neurodegenerative disorders.
Mutations in PTEN-induced putative kinase 1 (PINK1) and parkin cause autosomal-recessive Parkinson’s disease through a common pathway involving mitochondrial quality control. Parkin inactivation ...leads to accumulation of the parkin interacting substrate (PARIS, ZNF746) that plays an important role in dopamine cell loss through repression of proliferator-activated receptor gamma coactivator-1-alpha (PGC-1α) promoter activity. Here, we show that PARIS links PINK1 and parkin in a common pathway that regulates dopaminergic neuron survival. PINK1 interacts with and phosphorylates serines 322 and 613 of PARIS to control its ubiquitination and clearance by parkin. PINK1 phosphorylation of PARIS alleviates PARIS toxicity, as well as repression of PGC-1α promoter activity. Conditional knockdown of PINK1 in adult mouse brains leads to a progressive loss of dopaminergic neurons in the substantia nigra that is dependent on PARIS. Altogether, these results uncover a function of PINK1 to direct parkin-PARIS-regulated PGC-1α expression and dopaminergic neuronal survival.
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•PARIS is a PINK1 substrate•PINK1 phosphorylation of PARIS primes it for parkin ubiquitination and degradation•PINK1 controls PARIS-regulated PGC-1α levels and dopamine neuron survival•Conditional knockdown of PINK1 leads to PARIS-dependent loss of dopamine neurons
Lee et al. demonstrate that PARIS is a common substrate of PINK1 and parkin. PINK1 phosphorylation of PARIS primes it for ubiquitination and clearance by parkin. Thus, dysfunction of either PINK1 or parkin converges on PARIS accumulation, which leads to PGC-1α repression and dopamine neuron loss.
Aggregation of misfolded α-synuclein (α-syn) is the major component of Lewy bodies and neurites in Parkinson's disease (PD) and related α-synucleinopathies. Some α-syn mutations (e.g., A53T) in ...familial PD recapitulate the α-syn pathology in transgenic mice, which supports the importance of pathologic α-syn in driving the pathogenesis of α-synucleinopathies. Lymphocyte activation gene 3 (Lag3) is a receptor of α-syn fibrils facilitating pathologic α-syn spread; however, the role of Lag3 in mediating the pathogenesis in α-syn transgenic mice is not clear. Here, we report that depletion of Lag3 in human α-syn A53T transgenic (hA53T) mice significantly reduces the level of detergent-insoluble α-syn aggregates and phosphorylated ser129 α-syn, and inhibits activation of microglia and astrocytes. The absence of Lag3 significantly delays disease progression and reduces the behavioral deficits in hA53T transgenic mice leading to prolonged survival. Taken together, these results show that Lag3 contributes to the pathogenesis in the α-syn A53T transgenic mouse model.
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