ABSTRACT
Astrocytes are functionally diverse glial cells that maintain blood-brain barrier (BBB) integrity, provide metabolic and trophic support, and react to pathogens or harmful stimuli through inflammatory response. Impairment of astrocyte functions has been implicated in hepatic encephalopathy (HE), a neurological complication associated with hyperammonemia. Although hyperammonemia is more common in adults, ammonia gliotoxicity has been mainly studied in cultured astrocytes derived from neonate animals. However, these cells can sense and respond to stimuli in different ways from astrocytes obtained from adult animals. Thus, the aim of this study was to investigate the direct effects of ammonia on astrocyte cultures obtained from adult rats compared with those obtained from neonate rats. Our main findings pointed that ammonia increased the gene expression of proteins associated with BBB permeability, in addition to cause an inflammatory response and decrease the release of trophic factors, which were dependent on p38 mitogen-activated protein kinase (p38 MAPK)/nuclear factor κB (NFκB) pathways and aquaporin 4, in both neonatal and mature astrocytes. Considering the age, mature astrocytes presented an overall increase of the expression of inflammatory signaling components and a decrease of the expression of cytoprotective pathways, compared with neonatal astrocytes. Importantly, ammonia exposure in mature astrocytes potentiated the expression of the senescence marker p21, inflammatory response, activation of p38 MAPK/NFκB pathways, and the decrease of cytoprotective pathways. In this regard, ammonia can trigger and/or accelerate the inflammaging of mature astrocytes, a phenomenon characterized by an age-related chronic and low-grade inflammation, which may be implicated in HE neurological symptoms.
Subject(s)
Astrocytes/metabolism , Blood-Brain Barrier/metabolism , Hepatic Encephalopathy/metabolism , Neuroglia/metabolism , Oxidative Stress/drug effects , Animals , Animals, Newborn , Cells, Cultured , Hyperammonemia/metabolism , Male , NF-kappa B/metabolism , Rats, WistarABSTRACT
The givenname "Paola" of the author Paola Haack Amaral Roppa (Roppa, P.H.A.) should be corrected to read Ricardo Haack Amaral Roppa (Roppa, R.H.A.) as presented above.
ABSTRACT
Resveratrol, a natural polyphenolic compound, has been studied as a neuroprotective molecule. Our group has demonstrated that such effect is closely associated with modulation of glial functionality, but the underlying mechanisms are not fully understood. Because astrocytes actively participate in the brain inflammatory response, and activation of adenosine receptors can attenuate inflammatory processes, the aim of this study was to investigate the role of adenosine receptors as a mechanism for resveratrol glioprotection, particularly regarding to neuroinflammation. Therefore, primary astrocyte cultures were co-incubated with resveratrol and selective antagonists of A1, A2A, and A3 adenosine receptors, as well as with caffeine (a non-selective adenosine receptor antagonist), and then challenged with bacterial inflammogen lipopolysaccharide (LPS). Caffeine and selective adenosine receptor antagonists abolished the anti-inflammatory effect of resveratrol. In accordance with these effects, resveratrol prevented LPS-induced decrease in mRNA levels of adenosine receptors. Resveratrol could also prevent the activation of pro-inflammatory signaling pathways, such as nuclear factor κB (NFκB) and p38 mitogen-activated protein kinase (p38 MAPK) in a mechanism dependent on adenosine receptors. Conversely, trophic factors and protective signaling pathways, including sirtuin 1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and phosphoinositide 3-kinase (PI3K)/Akt were positively modulated by resveratrol in both LPS-stimulated and unstimulated astrocytes, but adenosine receptor antagonism did not abrogate all effects of resveratrol. To our knowledge, our data provide the first evidence that adenosine receptors are involved in the anti-inflammatory activity of resveratrol in astrocytes, thus exerting an important role for resveratrol-mediated glioprotection.
