Mechanism of beta 2 adrenergic receptor (β2AR) agonist in regulation of inflammation in Parkinson’s disease

• Author / Creator

  Monika, .

• Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by degeneration of dopaminergic neurons (DA-neurons) which are primarily present within a region of the brain called as substantia nigra (SN). Several studies suggest that the etiology of the PD includes destructive chronic inflammation within the mid-brain that also contributes to the progressive neurodegeneration. Microglia are the principle immune cells of the central nervous system (CNS) and play an important role in CNS homeostasis. The presence of activated glial cells, the participation of innate immune system, increased inflammatory molecules such as cytokines and chemokines, and increased oxidative stress and reactive oxygen species are the main neuroinflammatory characteristics present in neurodegenerative disorders including PD.
  Previously, we have found that the use of a long-acting β2-AR (β2-adrenergic receptor) agonist, Salmeterol functions in part to inhibit the inflammatory response of activated microglial cells, and in this thesis, I have sought to discover the underlying mechanisms of the immunoregulatory effects of β2-AR agonists on microglial cells using several molecular approaches. β2-ARs belong to the G protein-coupled seven transmembrane receptor superfamily and microglial cells a high density of these β2-ARs on their cell surface. Activation of β2-AR by Salmeterol and other β2-AR agonists initiate intracellular signaling pathways either via G proteins or through β-arrestins. In the present set of studies that constitute my thesis, I have investigated the signaling pathways and anti-inflammatory effects of Salmeterol that regulates the response of microglial cells to inflammatory stimuli that can explain the ability of these β2-AR to protect DA-neurons against inflammation and progressive degeneration.
  In initial studies, we have found that pre-treatment with Salmeterol suppresses production and release of pro-inflammatory mediators such as TNF-α, IL-1β and nitric oxide at both the protein and mRNA levels in LPS-stimulated BV2 cells. Salmeterol appears to mediate this anti-inflammatory effect by inhibiting the NF-κB signaling pathway via suppressing the phosphorylation of TAK1 and degradation of IκBα. Furthermore, Salmeterol reduces nuclear translocation of NF-κB, thereby suppresses the production of these and other inflammatory mediators. Salmeterol appears to function by increasing the expression of β-arrestin2, suppressing TAK1/TAB1 interaction, and enhancing the interaction between TAB1 and β-arrestin2. Conversely, the silencing of β-arrestin2 abrogates the anti-inflammatory effects of Salmeterol in LPS-stimulated BV2 cells. These findings suggest that the anti-inflammatory properties of Salmeterol are dependent on the non-canonical or β-arrestin2-dependent pathway of GPCR signaling.
  In further studies, we found that Salmeterol inhibits the production of other LPS-induced pro-inflammatory mediators of M1 phenotype such as IL-(interleukin) 18, IL-6, pro-inflammatory chemokines (CCL2, CCL3, CCL4) and reactive oxygen species from BV2 cells. Interestingly, treatment with Salmeterol and other 2-AR agonists robustly enhanced the production of the regulatory anti-inflammatory cytokine IL-10 from LPS-activated BV2 cells. In addition, Salmeterol upregulates the expression of arginase-1 and CXCL14. In contrast, the silencing of the transcription factor Creb abrogates the Salmeterol-mediated production of IL-10 in LPS-activated BV2 cells, but silencing of β-arrestin2 with Arrb2 siRNA did not. In conclusion, these findings suggest that the Salmeterol-induced conversion of LPS-activated microglial cells from an M1- to M2-like phenotype by β2-AR agonists involves activation of the classical cAMP/PKA/CREB signaling pathway. Furthermore, we have performed RNA-sequencing to determine the effect of Salmeterol on global gene expression in LPS-activated BV2 microglia. Results from differential gene expression analysis show that pattern of inflammatory genes up-regulated by LPS stimulation, including cytokines, chemokines and transcription factors, was significantly altered by pre-treatment with Salmeterol. In addition, other neurodegenerative disease-related genes were modified by treatment with Salmeterol in activated microglia.
  Finally, I also tested whether the anti-inflammatory properties of Salmeterol can be used to target other chronic inflammatory diseases such as periodontitis (an oral-inflammatory disease). Results from this study showed that Salmeterol exerts similar anti-inflammatory effects on murine macrophages and human monocytes stimulated by PgLPS (LPS from Porphyromonas gingivalis). Similar to our studies on microglia, Salmeterol suppresses production and release of pro-inflammatory mediators via inhibiting the NF-κB and MAPK signaling pathway. My results suggest the efficacy in using Salmeterol and other β2-AR agonists in the treatment of chronic inflammatory disorders.

• Subjects / Keywords

  • Parkinson's disease
  • Adrenergic receptor
  • Neuroinflammation

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-bdqm-y581

• License

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