Role of astroglial α7 nicotinic acetylcholine receptors in neuroinflammation and oxidative stress

Title:
Role of astroglial α7 nicotinic acetylcholine receptors in neuroinflammation and oxidative stress
Creator:
Patel, Hiral B. (Author)
Contributor:
Loring, Ralph H. (Advisor)
Dunah, Anthone (Committee member)
Miller, Greg (Committee member)
Gatley, John (Committee member)
Brenhouse, Heather (Committee member)
Language:
English
Publisher:
Boston, Massachusetts : Northeastern University, December 2016
Date Awarded:
December 2016
Date Accepted:
December 2016
Type of resource:
Text
Genre:
Dissertations
Format:
electronic
Digital origin:
born digital
Abstract/Description:
α7 nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the central nervous system (CNS) and periphery. Within the CNS, these receptors are expressed in neurons and glia cells, and are actively involved in learning, memory and attention. A majority of the studies evaluating the role of α7nAchRs in the CNS have focused on neurons. However, these receptors are also present on astrocytes, which represent 20-40% of the brain cells and are key regulators of neuroinflammation and oxidative stress in several neurodegenerative diseases including Alzheimer's disease, Parkinson's disease or amyotrophic lateral sclerosis. Less evidence exists regarding the potential anti-inflammatory properties of these receptors in astrocytes. Therefore, we evaluated the role of α7 nAChR activation in both in vitro and in vivo models of neuroinflammation and aimed to elucidate the molecular mechanism of anti-inflammatory and anti-oxidant properties of these receptors in astrocytes.

We observed that treatment with α7 nAChR agonists, GTS21 and PNU282987, significantly reduced lipopolysaccharide (LPS)-mediated secretion of the inflammatory cytokines in a dose dependent manner in astrocytes and this effect was reversed by pharmacological inhibition of α7 nAChR with the antagonist methyllycaconitine (MLA) and by knocking down α7 nAChR expression with short hairpin RNA suggesting specificity of the response. Further, we assessed the effect of α7 nAchR agonist on activation of NF--κB, which is a transcription factor involved in regulating inflammatory responses. We observed that α7 nAChR activation blocked LPS mediated NF--κB nuclear translocation in astrocytes indicating that the observed anti-inflammatory effect may be mediated through NF--κB pathway. We further tested the antioxidant effect of astroglial α7 nAChR through modulation of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) pathway, which is a member of the NF-E2 family of basic region leucine-zipper transcription factors and responds to oxidative and electrophilic stress by regulating antioxidant responsive genes. We demonstrated that treatment with α7 nAChR agonists up regulated canonical Nrf2 antioxidant genes and proteins suggesting antioxidant properties of α7 nAchR in astrocytes. Interestingly, α7 nAchR activation in astrocyte cultures from Nrf2 knockout mice not only showed reduction of the anti-oxidant response, but also the anti-inflammatory response in the in vitro inflammation model; highlighting the possibility that cross-talk between the Nrf2 and NF-kB pathways may be responsible for the observed anti-inflammatory properties of α7 nAchR. Using an astrocyte conditioned media approach; we demonstrated reduction in neuronal apoptosis measured by apoptotic marker caspase 3/7 when astrocytes were pre-treated with α7 nAchR agonists. Finally, in an in vivo neuroinflammation model using LPS in NF-kB luciferase reporter mice, we demonstrated reduction with GTS21 treatment in NF-kB activity using whole body imaging and ex vivo brain imaging. We also observed significant reduction in gene expression of pro-inflammatory cytokines and increase in Nrf2 target genes with GTS21 treatment in liver and brain tissues.

In conclusion, our results suggest that activating astroglial α7 nAChRs may have a role in neuroprotection by decreasing inflammation and oxidative stress, and therefore could have therapeutic implication for disease modifying treatments of neurodegenerative diseases.
Subjects and keywords:
nicotinic acetylcholine receptors
neuroprotection
inflammation
DOI:
https://doi.org/10.17760/D20274193
Permanent Link:
http://hdl.handle.net/2047/D20274193
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