Increased neuroimmune gene induction, microglial and astrocyte activation, and neurodegeneration in post-mortem human alcoholic brain
Information from abstracts and lay language summaries is embargoed until the conclusion of the scientific presentation.
761—Neuroinflammation: Disease Models
Wednesday, November 15, 2017, 1:00 pm - 5:00 pm
761.05 Increased neuroimmune gene induction, microglial and astrocyte activation, and neurodegeneration in post-mortem human alcoholic brain
Location: Halls A-C
*L. QIN, R. P. VETRENO, F. T. CREWS; Bowles Ctr. Alcohol Studies, Univ. North Carolina, Sch. Med., Chapel Hill, NC
Abstract Body: Induction of proinflammatory cytokine, chemokine and oxidative stress genes is associated with microglial activation and neurodegeneration. In the current study, real-time PCR and immunohistochemistry were used to study cytokine, chemokine, and oxidase gene expression as well as markers for microglia, astrocytes and neurodegeneration in postmortem human orbital frontal cortex (OFC) samples from moderate drinking controls and alcoholics. In the alcoholic OFC, we found significant increases in mRNA levels of cytokines (TNFα [349%], IL-1β [157%], IL-6 [220%]), chemokines (MCP1 [175%], MCP2 [371%], MCP3 [157%], MCP4 [290%], IL-8 [306%], RANTES [137%]), and oxidative enzymes (COX-2 [158%], NOX2 [272%], NOX3 [206%], NOX4 [215%]), compared to moderate drinking control subjects. We observed a comparable increase in the expression of various cytokine and chemokine receptors in the post-mortem human alcoholic OFC. Assessment of glial morphology and neurodegeneration revealed increased staining and enlarged Iba-1-immunoreactive (+IR) microglia indicative of microglial activation in the post-mortem alcoholic OFC while control subjects showed resting microglia. Similarly, staining with the astrocytic marker GFAP revealed activated astrocytes in the alcoholic OFC. Expression of activated caspase-3+IR was increased in the alcoholic OFC, compared to the moderate drinking controls. Glial activation was positively associated with expression of several of the proinflammatory cytokines, chemokines, and oxidases. Further, age of drinking onset was highly correlated with expression of several of these neuroimmune genes as well as expression of Iba-1, GFAP, and activated caspase-3. Together, these data suggest that the upregulation of proinflammatory cytokines, chemokines and oxidases in the post-mortem human alcoholic OFC could contribute to chronic alcohol-induced microglial and astroglial activation as well as neurodegeneration.
Lay Language Summary: Our research focuses on neuroimmune signaling in brain and how it contributes to the development of alcoholism (i.e., alcohol use disorders). Neuroimmune signaling refers to cytokines and other signals initially discovered as immune signaling molecules that have recently been found to be active in brain. In preclinical animal studies, alcohol, e.g. ethanol, exposure has been found to increase the expression of neuroimmune genes in brain and to regulate alcohol drinking, alcohol induced changes in brain and to induce neurodegeneration. Preclinical studies also found that alcohol induced increases in neuroimmune gene expression persist for long periods, perhaps permanently, following chronic alcohol abuse. This led to the hypotheses that neuroimmune signaling in brain contributes to the development and persistence of alcoholism. Although studies support this hypothesis there are multiple neuroimmune genes that work through complex signaling cascades and it is not clear how they contribute and/or if there are key neuroimmune signals involved in development of alcoholism among the many neuroimmune genes. In this study, we measured the expression of neuroimmune genes in post-mortem orbitofrontal cortex (OFC) tissue samples from alcoholic and moderate drinking control subjects. The OFC, which is involved in decision making and predicting the future outcome of decisions, is compromised in alcoholism consistent with a loss of prefrontal cortical function. We found significant increases in gene expression of proinflammatory cytokines (e.g., tumor necrosis factor alpha and interleukin 6) and chemokines (e.g., monocyte chemoattractant proteins). In addition, we found increased gene expression of proinflammatory oxidases, including NADPH oxidase and COX2, which are associated with immune responses. Ibuprofen and aspirin are known inhibitors of COX and this contributes to their anti-inflammatory actions. In some cases, neuroimmune gene expression correlated with lifetime alcohol consumption and age of drinking onset, both of which suggest persistently increased neuroimmune gene expression during development and continuing throughout life in alcoholics. Since alcoholism is a chronic relapsing disease that varies across individuals in timing and duration, the finding that lifetime alcohol consumption correlates with neuroimmune gene expression suggests permanent increases are induced by alcohol exposure. In the brain, the neuroimmune system is largely composed of glial cells including microglia and astrocytes, which support neuron function, regulate neuroplasticity, and have multiple other brain functions including expression of neuroimmune genes. We used markers of microglia (Iba1 and CD68) and astrocytes (GFAP) to label glial cells in brain to investigate whether alcohol causes glial activation. Glial morphology revealed increased staining and enlarged Iba-1-immunoreactive (+IR) and CD68+IR microglia indicative of microglial activation in the post-mortem alcoholic OFC while control subjects showed resting microglia. Similarly, staining with the astrocytic marker GFAP revealed activated astrocytes in the alcoholic OFC. Glial activation is an indicator of neurodegeneration. To more directly investigate neurodegeneration, we assessed activated caspase-3, a marker of neuronal cell death. We also found increased expression of this marker of neuronal death suggesting neuroimmune gene expression and glial activation are increasing neurodegeneration in alcoholism. Glial activation was positively correlated with expression of several proinflammatory cytokines, chemokines, and oxidases. Further, age of drinking onset was highly correlated with expression of neuroimmune genes as well as glial activation and cell death markers. It is possible that the loss of OFC function due to increased neuroimmune gene expression, glial activation and neuronal degeneration contribute to the poor decisions that underlie alcohol abuse and alcohol use disorders. (Supported by NIAAA of NIH).
Neuroscience 2017 (47th annual meeting of the Society for Neuroscience)Exit