prostaglandin-a1 and Nerve-Degeneration

We have previously reported that prostaglandin A(1) (PGA(1)) reduces infarct size in rodent models of focal ischemia. This study seeks to elucidate the possible molecular mechanisms underlying PGA(1)'s neuroprotective effects against ischemic injury. Rats were subjected to permanent middle cerebral artery occlusion (pMCAO) by intraluminal suture blockade. PGA(1) was injected intracerebroventricularly (icv) immediately after ischemic onset. Western blot analysis was employed to determine alterations in IkappaBalpha, pIKKalpha, and peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Immunohistochemistry was used to confirm the nuclear translocation of nuclear factor-kappaB (NF-kappaB) p65 and the expression of PPAR-gamma. RT-PCR was used to detect levels of c-Myc mRNA. The contribution of PPAR-gamma to PGA(1)'s neuroprotection was evaluated by pretreatment with the PPAR-gamma irreversible antagonist GW9662. A brief increase in pIKKalpha levels and rapid reduction in IkappaBalpha were observed after ischemia. PGA(1) blocked ischemia-induced increases in pIKKalpha levels and reversed the decline in IkappaBalpha levels. Ischemia-induced nuclear translocation of NF-kappaB p65 was attenuated by PGA(1). PGA(1) also repressed the ischemia-induced increase in expression of NF-kappaB target gene c-Myc mRNA. Immunohistochemistry demonstrated an increase in PPAR-gamma immunoreactivity in the nucleus of striatal cells at 3 hr after pMCAO. Western blot analysis revealed that the expression of PPAR-gamma protein significantly increased at 12 hr and peaked at 24 hr. PGA(1) enhanced the ischemia-triggered induction of PPAR-gamma protein. Pretreatment with the irreversible PPAR-gamma antagonist GW9662 attenuated PGA(1)'s neuroprotection against ischemia. These findings suggest that PGA(1)-mediated neuroprotective effect against ischemia appears to be associated with blocking NF-kappaB activation and likely with up-regulating PPAR-gamma expression.

Topics: Active Transport, Cell Nucleus; Anilides; Animals; Brain Infarction; Brain Ischemia; Corpus Striatum; Cytoprotection; Disease Models, Animal; I-kappa B Proteins; Infarction, Middle Cerebral Artery; Male; Nerve Degeneration; Neuroprotective Agents; NF-kappa B; PPAR gamma; Prostaglandins A; Proto-Oncogene Proteins c-myc; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transcription Factor RelA; Up-Regulation

Prostaglandin E2 (PGE2), one product of inflammatory reactions, and PGA1, which is formed during PGE2 extraction, induce degeneration in adenosine 3',5'-cyclic monophosphate (cAMP)-induced differentiated neuroblastoma (NB) cells in culture. The mechanisms of action of PGE2 on neurodegeneration are not well understood. To investigate this, we have utilized PGA(1), which mimics the effect of PGE2 and is very stable in solution. We have assayed selected markers of oxidative stress such as heme oxygenase-1 (HO-1), catalase, glutathione peroxidase (GPx1), mitochondrial superoxide dismutase (Mn-SOD-2) and cytosolic superoxide dismutase (Cu/Zn-SOD-1). The results showed that the treatment of differentiated NB cells with PGA1 for a period of 48 hr increased the expression of HO-1 and catalase, decreased the expression of GPx1 and Mn-SOD-2, and did not change the expression of Cu/Zn-SOD-1 as measured by gene array and confirmed by real-time PCR. The protein levels of HO-1 and GPx1 increased; however, the protein level of Mn-SOD-2 decreased and the levels of catalase and Cu/Zn-SOD-1 did not change as determined by Western blot. The increases in the levels of HO-1 and GPx1 reflected an adaptive response to increased oxidative stress, whereas decrease in the level of Mn-SOD-2 may make cells more sensitive to oxidative damage. These data suggest that one of the mechanisms of action of PGA1 on neurodegeneration may involve increased oxidative stress. This was supported further by the fact that a mixture of antioxidants (alpha-tocopherol, vitamin C, selenomethionine, and reduced glutathione), but not the individual antioxidants, reduced the level of PGA1-induced degeneration in differentiated NB cells. The addition of a single antioxidant at two or four times the concentration used in the mixture was toxic.

Topics: Adaptation, Physiological; Animals; Antioxidants; Catalase; Cell Differentiation; Cell Line, Tumor; Glutathione Peroxidase; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Membrane Proteins; Mice; Nerve Degeneration; Neurons; Oxidative Stress; Prostaglandins A; Superoxide Dismutase

Inflammatory reactions are considered one of the important etiologic factors in the pathogenesis of Alzheimer's disease (AD). Prostaglandins such as PGE2 and PGA1 and free radicals are some of the agents released during inflammatory reactions, and they are neurotoxic. The mechanisms of their action are not well understood. Increased levels of beta-amyloid fragments (Abeta40 and Abeta42), generated through cleavage of amyloid precursor protein (APP), oxidative stress, and proteasome inhibition, are also associated with neurodegeneration in AD brains. Therefore, we investigated the effect of PGs and oxidative stress on the degeneration and viability of cyclic AMP-induced differentiated NB cells overexpressing wild-type APP (NBP2-PN46) under the control of the CMV promotor in comparison with differentiated vector (NBP2-PN1) or parent (NBP2) control cells. Results showed that differentiated NBP2-PN46 cells exhibited enhanced spontaneous degeneration and decreased viability in comparison with differentiated control cells, without changing the level of Abeta40 and Abeta42. PGA1 or PGE2 treatment of differentiated cells caused increased degeneration and reduced viability in all three cell lines. These effects of PGs are not due to alterations in the levels of vector-derived APP mRNA or human APP holoprotein, secreted levels of Abeta40 and Abeta42, or proteasome activity. H2O2 or SIN-1 (an NO donor) treatment did not change vector-derived APP mRNA levels, but H2O2 reduced the level of human APP protein more than SIN-1. Furthermore, SIN-1 increased the secreted level of Abeta40, but not of Abeta42, whereas H2O2 had no effect on the level of secreted Abeta fragments. Both H2O2 and SIN-1 inhibited proteasome activity in the intact cells. The failure of neurotoxins to alter APP mRNA levels could be due to the fact that they do not affect CMV promoter activity. These results suggest that the mechanisms of action of PGs on neurodegeneration are different from those of H2O2 and SIN-1 and that the mechanisms of neurotoxicity of H2O2 and SIN-1 are, at least in part, different from each other.

Topics: Amyloid beta-Protein Precursor; Animals; Cell Differentiation; Cell Line; Cell Survival; Dinoprostone; Dose-Response Relationship, Drug; Down-Regulation; Gene Expression Regulation; Humans; Hydrogen Peroxide; Mice; Nerve Degeneration; Neuroblastoma; Neurotoxins; Nitric Oxide; Prostaglandins A; Tumor Cells, Cultured