Age modulates the nitric oxide system response in the ischemic cerebellum.

To determine whether age influences the nitric oxide system response to ischemia in the cerebellum, we have analyzed the levels of nitrogen oxides (NOx) and the expression of the different nitric oxide synthase isoforms (NOS) in mature adult (4-5 months old) and aged rats (24-27 months old) subjected to a transient global ischemia/reperfusion (I/R) model. We also analyzed the nitrated proteins and the glial fibrillary acidic protein (GFAP) expression. NOx concentration in adult rats, which more than doubled the values found in the aged rats, decreased after the ischemia and reperfusion. However, in the aged animals, these NOx levels did not significantly change after I/R. Constitutive isoforms were first down-regulated in the ischemic period, in both adult and aged animals. However, after 6 h of reperfusion, these isoforms were up-regulated, but only in aged rats. After I/R, iNOS was up-regulated in adults but down-regulated in the aged rats. Hence, after an episode of transient global ischemia and reperfusion, the aged cerebellum maintains a balanced NO production, silencing the iNOS isoform and inducing a weak expression of nNOS and eNOS; this allows NO physiological functions while avoiding possible undesirable effects such as the nitrative damage or astrocyte activation.

Steatosis recovery after treatment with a balanced sunflower or olive oil-based diet: involvement of perisinusoidal stellate cells.

AIM: To analyze the relationship between perisinusoidal stellate cell (PSC) activation and the dietary fat quantity and composition in the treatment of hepatic steatosis. METHODS: Using an experimental rat model of steatosis based on the intake of a hyperlipidic diet (14% fat as olive oil or sunflower oil, HL-O and HL-S, respectively), we analyzed the liver's capability of recovery after the treatment with a normal-lipidic diet (5% fat as olive oil or sunflower oil, NL-O and NL-S, respectively) by immunocytochemical and Western blot analysis of glial fibrillary acidic protein (GFAP) expression in PSCs, collagen quantification and serum aminotransferase determination. RESULTS: The fatty infiltration in the steatotic livers decreased after the treatment with both NL diets, indicating liver recovery. This decrease was accompanied with a lower collagen deposition and aminotransferase level as well as changes in the PSC population that increased the GFAP expression. The above-mentioned effects were more pronounced in animals fed on NL-O based diet. CONCLUSION: Treatment with a balanced diet enriched in olive oil contributes to the liver recovery from a steatotic process. The PSC phenotype is a marker of this hepatic-recovery model.

Immunohistochemistry of neuronal nitric oxide synthase and protein nitration in the striatum of the aged rat.

To ascertain the possible implications of the nitric oxide (NO*) producing system in striatal senescence, and by using immunohistochemistry and image-processing approaches, we describe the presence of the enzyme nitric oxide synthase (NOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and nitrotyrosine-derived complexes (N-Tyr) in the striatum of adult and aged rats. The results showed neuronal NOS immunoreactive (nNOS-IR) aspiny medium-sized neurons and nervous fibres in both age groups, with no variation in the percentage of immunoreactive area but a significant decrease in the intensity and in the number of somata with age, which were not related to the observed increase with age of the striatal bundles of the white matter. In addition, NADPH-d activity was detected in neurons with morphology similar to that of the nNOS-IR cells; a decrease in the percentage of area per field and in the number of cells, but an increase in the intensity of staining for the NADPH-d histochemical marker, were detected with age. The number of neuronal NADPH-d somata was higher than for the nNOS-IR ones in both age groups. Moreover, N-Tyr-IR complexes were observed in cells (neurons and glia) and fibres, with a significant increase in the percentage of the area of immunoreaction, related to the increase of white matter, but a decrease in intensity for the aged group. On the other hand, we did not detect the inducible isoform (iNOS) either in adult or in aged rats. Taken together, these results support the contention that NADPH-d staining is not such an unambiguous marker for nNOS, and that increased protein nitration may participate in striatal aging.

Age-related changes of the nitric oxide system in the rat brain.

This work examines the age-related changes of the NO pathway in the central nervous system (CNS), analyzing nitric oxide synthase (NOS) isoform expression, the level of nitrotyrosine-modified proteins, and the NOS activity in the cerebral cortex, decorticated brain (basal ganglia, thalamus, hypothalamus, tegtum and tegmentum) and cerebellum of young, adult and aged rats. Our data demonstrate that the different NOS isoforms are not uniformly expressed across the CNS. In this sense, the nNOS and eNOS isoenzymes are expressed mainly in the cerebellum and decorticated brain, respectively, while the iNOS isoenzyme shows the highest level in cerebellum. Concerning age, in the cerebral cortex nNOS significantly increased its expression only in adult animals; meanwhile, in the cerebellum the eNOS expression decreased whereas iNOS increased in adult and aged rats. No age-related changes in any isoform were found in decorticated brain. NOS activity, determined by nitrate plus nitrite quantification, registered the highest levels in the cerebellum, where the significant increase detected with aging was probably related to iNOS activity. The number of nitrotyrosine-modified immunoreactive bands differed among regions; thus, the highest number was detected in the decorticated brain while the cerebellum showed the least number of bands. Finally, bulk protein nitration increased in cerebral cortex only in adult animal. No changes were found in the decorticated brain, and the decrease detected in the cerebellum of aged animals was not significant. According to these results, the NO pathway is differently modified with age in the three CNS regions analyzed.

Postnatal changes in the nitric oxide system of the rat cerebral cortex after hypoxia during delivery.

The impact of hypoxia in utero during delivery was correlated with the immunocytochemistry, expression and activity of the neuronal (nNOS) and inducible (iNOS) isoforms of the nitric oxide synthase enzyme as well as with the reactivity and expression of nitrotyrosine as a marker of protein nitration during early postnatal development of the cortex. The expression of nNOS in both normal and hypoxic animals increased during the first few postnatal days, reaching a peak at day P5, but a higher expression was consistently found in hypoxic brain. This expression decreased progressively from P7 to P20, but was more prominent in the hypoxic group. Immunoreactivity for iNOS was also higher in the cortex of the hypoxic rats and was more evident between days P0 and P5, decreasing dramatically between P10 and P20 in both groups of rats. Two nitrated proteins of 52 and 38 kDa, were also identified. Nitration of the 52-kDa protein was more intense in the hypoxic animals than in the controls, increasing from P0 to P7 and then decreasing progressively to P20. The 38-kDa nitrated protein was seen only from P10 to P20, and its expression was more intense in control than in the hypoxic group. These results suggest that the NO system may be involved in neuronal maturation and cortical plasticity over postnatal development. Overproduction of NO in the brain of hypoxic animals may constitute an effort to re-establish normal blood flow and may also trigger a cascade of free-radical reactions, leading to modifications in the cortical plasticity.

Proteomic characterization of nitrated cell targets after hypobaric hypoxia and reoxygenation in rat brain.

This study analyzes the nitrated protein profile of the rat-brain cortex in a model of hypoxia/reoxygenation, identifying the nitrated proteins and assessing spot changes. The proteins identified were grouped into categories, according to their function: 1) metabolism: pyruvate kinase (PK), α-enolase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), phosphoglycerate mutase 1 (PGAM1), and glutamine synthetase (GS); 2) cytoskeletal proteins: α-tubulin, ß-tubulin, γ-actin, and glial fibrillary acidic protein (GFAP); 3) chaperones: heat-shock protein 71kDa (HSP71); and 4) carrier proteins: voltage-dependent anion-selective channel protein 1 (VDAC-1) and Atp6v1a. PK, α-enolase, and GS nitration rates were upregulated, increasing progressively during reoxygenation and peaking at 24h. GAPDH and PGAM1 nitration levels fell after hypoxia/reoxygenation. α-Tubulin, ß-tubulin, γ-actin, and GFAP nitration rates augmented at 24h, but diminished at 5d. HSP71 suffered from nitration immediately after hypoxia, but not during reoxygenation. VDAC-1 tyrosine nitration was identified only in the control group, whereas detectable Atp6v1a nitration levels were observed only immediately after hypoxia. The data have been deposited to the ProteomeXchange with identifier PXD001049. Our findings suggest a hypothetically crucial linkage between nitration-related protein modifications and metabolic and cell-structure alterations. These changes are probably needed for the remodeling and plasticity processes activated by the hypoxic brain response. BIOLOGICAL SIGNIFICANCE: For the first time the spectrum of nitrated proteins in the hypoxic brain as well as its changes during reoxygenation are described. Our findings suggest a hypothetically crucial linkage between nitration-related protein modifications and metabolic and cell-structure alterations. These changes are probably needed for the remodeling and plasticity processes activated by the hypoxic brain response. The biological relevance of these findings is linked to the important role developed by the signaling molecule NO in the hypoxic brain, and could be interpreted in two different but complementary ways: first, as a mechanism of damage due to nitration impacts over some key proteins affecting its structure and function; and second, as a regulation mechanism involved in the hypoxic response. Hence, based on the modified proteins identified and their functions, it would be possible to design new tools and therapies to prevent brain damage in low-oxygen-pressure atmospheres.

Acute hypoxia-induced depletion of striatal nitric oxide synthase pathway.

Hypoxia-induced alteration of nitric oxide (NO) production may lead to brain disease, especially in the areas most sensitive to oxygen deficiency, such as the striatum. To date, the behaviour of the striatal NO pathway under hypoxia/reoxygenation remains unknown and its elucidation constitutes the aim of this work. Wistar rats were submitted to hypoxia (20min) and analyzed after 0h, 24h, and 5 days of reoxygenation. Expression, activity, and location of the NO synthase (NOS) isoforms (neuronal, endothelial, and inducible) as well as nitrated protein expression were analyzed in the rat striatum. NO levels were indirectly quantified as nitrates and nitrites (NO(x)), which act as NO-generating molecules. NOS isoform mRNA levels remained unaltered in hypoxic groups vs. normoxic control. However, quantification of immunoreaction showed a significant decrease in eNOS and nNOS after hypoxia. While in situ NOS activity and NO(x) levels fell, levels of nitrotyrosine-modified proteins rose throughout the reoxygenation period. Our data revealed the great complexity of the NO pathway, showing that both acute hypoxia and the successive recovery period down-regulated the NOS system in the rat striatum. However, under hypoxia/reoxygenation NO may be produced in a NOS-independent way from the NO-storage molecules, compensating for the hypoxia-reduced NOS activity.