Znaczenie cyklooksygenaz w neurotoksyczności peptydów amyloidu β w chorobie Alzheimera

Przewlekłe procesy zapalne odgrywają istotną rolę w przebiegu choroby Alzheimera (ChA). Dotychczas uważano, że rozwijają się one w odpowiedzi na zewnątrzkomórkowe agregaty peptydów amyloidu β (Aβ) odkładające się w mózgu chorych na ChA. Badania epidemiologiczne wykazały, że długotrwałe stosowanie niesteroidowych leków przeciwzapalnych (NLPZ) zmniejsza ryzyko zachorowania na ChA. Leki te są inhibitorami cyklooksygenaz (COX), enzymów syntetyzujących eikozanoidy, główny składnik odpowiedzi zapalnej w organizmie. Najnowsze badania przyniosły dwa zaskakujące odkrycia: 1) toksyczną formą Aβ nie są agregaty, lecz raczej oligomery Aβ, występujące zarówno wewnątrzkomórkowe, jak i zewnątrzkomórkowo; 2) aktywacja COX-2 zachodzi na wczesnych etapach rozwoju ChA i poprzedza powstawanie blaszek starczych oraz aktywację mikrogleju. Odkrycia te wskazują na możliwy udział COX w toksyczności peptydów Aβ w komórkach nerwowych w I fazie ChA, a nie tylko w rozwoju odpowiedzi zapalnej w komórkach glejowych w zaawansowanym stadium choroby. Uzyskane wyniki wskazują na konieczność dalszych badań nad rolą COX w patogenezie/patomechanizmie ChA

α-Synuclein induced cell death in mouse hippocampal (HT22) cells is mediated by nitric oxide-dependent activation of caspase-3

AbstractOur previous studies indicated that exogenous α-synuclein (ASN) activates neuronal nitric oxide (NO) synthase (nNOS) in rat brain slices. The present study, carried out on immortalized hippocampal neuronal cells (HT22), was designed to extend the previous results by showing the molecular pathway of NO-mediated cell death induced by exogenous ASN. Extracellular ASN (10μM) was found to stimulate nitric oxide synthase (NOS) and increase caspase-3 activity in HT22 cells, leading to poly(ADP-ribose) polymerase (PARP-1) cleavage. The inhibitor of Ca2+-dependent NOS (N-nitro-l-arginine, 100μM) prevented ASN-evoked caspase-3 activation and PARP-1 degradation. ASN exposure resulted in apoptotic death of HT22 cells and this effect was reversed by inhibition of NO synthesis and caspase-3 activity. Our results demonstrated that extracellular ASN induces neuronal cell death by NO-mediated caspase-3 activation

Insights into mitochondrial dysfunction: aging, amyloid-β, and tau-A deleterious trio

Significance: Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder mainly affecting elderly individuals. The pathology of AD is characterized by amyloid plaques (aggregates of amyloid-β [Aβ]) and neurofibrillary tangles (aggregates of tau), but the mechanisms underlying this dysfunction are still partially unclear. Recent Advances: A growing body of evidence supports mitochondrial dysfunction as a prominent and early, chronic oxidative stress-associated event that contributes to synaptic abnormalities and, ultimately, selective neuronal degeneration in AD. Critical Issues: In this review, we discuss on the one hand whether mitochondrial decline observed in brain aging is a determinant event in the onset of AD and on the other hand the close interrelationship of this organelle with Aβ and tau in the pathogenic process underlying AD. Moreover, we summarize evidence from aging and Alzheimer models showing that the harmful trio "aging, Aβ, and tau protein" triggers mitochondrial dysfunction through a number of pathways, such as impairment of oxidative phosphorylation (OXPHOS), elevation of reactive oxygen species production, and interaction with mitochondrial proteins, contributing to the development and progression of the disease. Future Directions: The aging process may weaken the mitochondrial OXPHOS system in a more general way over many years providing a basis for the specific and destructive effects of Aβ and tau. Establishing strategies involving efforts to protect cells at the mitochondrial level by stabilizing or restoring mitochondrial function and energy homeostasis appears to be challenging, but very promising route on the horizon

Lipoxygenases and Poly(ADP-Ribose) Polymerase in Amyloid Beta Cytotoxicity

The 12/15-lipoxygenase(s) (LOX), poly(ADP-ribose) polymerase (PARP-1) activity and mitochondrial apoptosis inducing factor (AIF) protein in the amyloid β (Aβ) toxicity were investigated in PC12 cells that express either wild-type (APPwt) or double Swedish mutation (APPsw) forms of human Aβ precursor protein. Different levels of Aβ secretion and free radicals formation characterize these cells. The results demonstrated a relationship between the Aβ levels and LOX protein expression and activity. High Aβ concentration in APPsw cells correlated with a significant increase in free radicals and LOX activation, which leads to translocation of p65/NF-κB into the nucleus. An increase in AIF expression in mitochondria was observed concurrently with inhibition of PARP-1 activity in the nuclear fraction of APPsw cells. We suggested that AIF accumulation in mitochondria may be involved in adaptive/protective processes. However, inhibition of PARP-1 may be responsible for the disturbances in transcription and DNA repair as well as the degeneration of APP cells. Under conditions of increased nitrosative stress, evoked by the nitric oxide donor, sodium nitroprusside (SNP, 0.5 mM), 70–80% of all cells types died after 24 h, significantly more in APPsw cells. There was no further significant change in mitochondrial AIF level and PARP-1 activity compared to corresponding non-treated cells. Only one exception was observed in PC12 control, where SNP significantly inhibits PARP-1 activity. Moreover, SNP significantly activated gene expression for 12/15-LOX in all types of investigated cells. Inhibitors of all LOX isoforms and specific inhibitor of 12-LOX enhanced the survival of cells that were subjected to SNP. We conclude that the LOX pathways may play a role in Aβ toxicity and in nitrosative-stress-induced cell death and that inhibition of these pathways offers novel protective strategies

Age-related alteration of poly(ADP-ribose) polymerase activity in different parts of the brain.

Poly(ADP-ribose) polymerase (PARP) is a conserved enzyme involved in the regulation of DNA repair and genome stability. The role of PARP during aging is not well known. In this study PARP activity was investigated in nuclear fractions from hippocampus, cerebellum, and cerebral cortex of adult (4 months), old adult (14 months) and aged (24-27 months) rats. Concomitantly, the free radical evoked lipid peroxidation was estimated as thiobarbituric acid reactive substances (TBARS). The specific activity of PARP in adult brain was about 25, 21 and 16 pmol/mg protein per min in hippocampus, cerebellum and cerebral cortex, respectively. The enzyme activity was higher in all investigated parts of the brain of old adults. In aged animals PARP activity was lower in hippocampus by about 50%, and was unchanged in cerebral cortex and in cerebellum comparing to adult rats. The concentration of TBARS was the same in all parts of the brain and remained unchanged during aging. There is no direct correlation between PARP activity and free radical evoked lipid peroxidation during brain aging. The lowered enzyme activity in aged hippocampus may decrease DNA repair capacity which subsequently may be responsible for the higher vulnerability of hippocampal neurons to different toxic insults

Effect of amyloid beta peptide on poly(ADP-ribose) polymerase activity in adult and aged rat hippocampus.

It is suggested that the fibrillar amyloid beta peptide (Aβ) in brain plays a direct role in neurodegeneration in Alzheimer's disease, probably through activation of reactive oxygen species formation. Free radicals and numerous neurotoxins elicit DNA damage that subsequently activates poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30). In this study the effect of neurotoxic fragment (25-35) of full length Aβ peptide on PARP activity in adult and aged rat hippocampus was investigated. In adult (4 month old) rat hippocampus the Aβ 25-35 peptide significantly enhanced PARP activity by about 80% but had no effect on PARP activity in cerebral cortex and in hippocampus from aged (24-27 month old) rats. The effect of Aβ peptide was reduced by half by the nitric oxide synthase inhibitor N-nitro-L-arginine. Stimulation of glutamate receptor(s) itself enhanced PARP activity by about 80% in adult hippocampus. However, Aβ 25-35 did not exert any additional stimulatory effect. These results indicate that Aβ, through NO and probably other free radicals, induces activation of DNA bound PARP activity exclusively in adult but not in aged hippocampus

The role of synthetic ligand of PPARα in regulation of transcription of genes related to mitochondria biogenesis and dynamic in an animal model of Alzheimer’s disease

Peroxisome proliferator-activated receptors α (PPARα) are members of the nuclear receptors family and a very potent transcription factor engaged in the regulation of lipid and energy metabolism. Recent data suggest that PPARα could play an important role in the pathomechanism of Alzheimer’s disease (AD) and other neuropsychiatric disorders. This study focused on the effect of a synthetic ligand of PPARα, GW7647 on the transcription of genes encoding proteins of mitochondria biogenesis and dynamics in the brain of AD mice. The experiments were carried out using 12-month-old female FVB-Tg mice with the V717I mutation of amyloid precursor protein (APP + ) and mice without the transgene (APP – ). Moreover, APP + and APP – mice were treated for 14 days with GW7647 administered subcutaneously with a dose 5 mg/kg b.w. Brain cortex was used and qRT-PCR was performed. Our data indicated that GW7647 upregulated the expression of genes encoding proteins of mitochondria biogenesis in ADTg mice. GW7647 enhanced the level of mRNA of Ppargc1, Nrf2 and Tfam in APP + as compared to APP – mice treated with GW7647. Moreover, our studies demonstrated that GW7647 had no effect on genes that regulate mitochondria fission and fusion of ADTg mice as correlated to mice without the transgene. Our results indicate that the ligand of PPARα, GW7647 may exert a promising neuroprotective effect through the regulation of transcription of genes coding proteins of mitochondria biogenesis. These data suggest that activation of PPARα at an early stage of AD could be a helpful strategy for slowing the progression of neurodegeneration

Current View on PPAR-α and Its Relation to Neurosteroids in Alzheimer’s Disease and Other Neuropsychiatric Disorders: Promising Targets in a Therapeutic Strategy

Peroxisome proliferator-activated receptors (PPARs) may play an important role in the pathomechanism/pathogenesis of Alzheimer’s disease (AD) and several other neurological/neuropsychiatric disorders. AD leads to progressive alterations in the redox state, ion homeostasis, lipids, and protein metabolism. Significant alterations in molecular processes and the functioning of several signaling pathways result in the degeneration and death of synapses and neuronal cells, leading to the most severe dementia. Peroxisome proliferator-activated receptor alpha (PPAR-α) is among the processes affected by AD; it regulates the transcription of genes related to the metabolism of cholesterol, fatty acids, other lipids and neurotransmission, mitochondria biogenesis, and function. PPAR-α is involved in the cholesterol transport to mitochondria, the substrate for neurosteroid biosynthesis. PPAR-α-coding enzymes, such as sulfotransferases, which are responsible for neurosteroid sulfation. The relation between PPAR-α and cholesterol/neurosteroids may have a significant impact on the course and progression of neurodegeneration/neuroprotection processes. Unfortunately, despite many years of intensive studies, the pathogenesis of AD is unknown and therapy for AD and other neurodegenerative diseases is symptomatic, presenting a significant goal and challenge today. This review presents recent achievements in therapeutic approaches for AD, which are targeting PPAR-α and its relation to cholesterol and neurosteroids in AD and neuropsychiatric disorders