Microgliosis is a hallmark of Alzheimer’s disease (AD) and is associated with inflammatory activation of microglia. Discovery of new molecules capable of mitigating the inflammatory response may provide a viable means to treat AD. Somatostatin receptor subtype-4 (SST4) shows particular promise as a treatment target for AD given its microglia and neuronal localization in the brain. A SST4 agonist has the potential to lessen microglia inflammatory activity. This research evaluated the novel SST4 agonist SM-I-26 in its ability to modulate microglia inflammatory responses and enhance mechanisms affiliated with the breakdown of amyloid-beta peptide (Aβ).
The selective and high affinity SST4 agonist SM-I-26 was evaluated in BV2 mouse microglia cells concurrent with inflammatory challenge via lipopolysaccharide (LPS) treatment. After plating for 24 hrs., cells were treated for another 24 hrs. with SM-I-26 (0, 10, 1000 nM) against LPS (0, 10, 100 ng/mL). Cell viability/proliferation (alamarBlue assay), nitrite (surrogate of nitric oxide, Griess assay) output in media, and mRNA expression (RT-qPCR) of genes associated with SST4, inflammation, Aβ phagocytosis, and Aβ degrading enzymes were measured. Two-way ANOVAs with Tukey post-hoc tests were used to determine significance (α= 0.05).
SM-I-26 decreased BV-2 cell viability/proliferation, while LPS increased viability/proliferation. A significant interaction between LPS and SM-I-26 was found on mean nitrite. Within no LPS, mean nitrite was similar across all concentrations of SM-I-26. With 10 ng/ml LPS, nitrite output trended towards a decrease with both 10 and 1000 nM SM-I-26 compared to vehicle. Within 100 ng/ml LPS, both 10 and 1000 nM SM-I-26 significantly decreased nitrite compared to vehicle control.
The mRNA expression of key genes associated with microglia inflammation, SST4, function, and Aβ clearance were next evaluated. A significant interaction was found between SM-I-26 and LPS for Sst4. Sst4 mRNA expression increased with SM-I-26 treatment under both basal and inflammatory conditions.
The Aβ degrading enzymes Neprilysin and insulin degrading enzyme showed no changes in mRNA expression across treatments. However, SM-I-26 treatment significantly increased angiotensin converting enzyme mRNA expression under basal conditions at highest concentration of SM-I-26. Similar upregulation pattern was observed for endothelin converting enzyme-1, while endothelin converting enzyme-2 showed a decline with treatment.
Interactions were found for macrophage scavenger receptor-1 (Msr1) and triggering receptor expressed on myeloid cells-1 (Trem1). Increased expression of Msr1 by SM-I-26 under non-inflammatory and 10 ng/mL LPS-stimulated conditions implicate enhanced capacity to clear Aβ. The SM-I-26 dose-dependently downregulated Trem1, identifying potential beneficial effects on anti-inflammatory pathways. SM-I-26 treatment increased catalase with and without LPS, but not their interactions. This overexpression of catalase could be neuroprotective against Aβ toxicity.
Significant interactions were found between SM-I-26 and LPS for tumor necrosis factor-α (Tnf-α) and interleukin-1β (IL1β). The 1000 nM SM-I-26 significantly decreased Tnf-α mRNA expression under basal and inflammatory conditions, with 10 nM SM-I-26 decreasing Tnf-α only with the highest LPS concentration. The 10 and 1000 nM SM-I-26 decreased IL-1β expression at the highest LPS concentration. The 10 nM SM-I-26 decreased interleukin-6 with low and high dose LPS treatment. The anti-inflammatory cytokine interleukin-10 was upregulated by 10 nM SM-I-26 under both basal and inflammatory conditions, but not at the higher 1000 nM concentration. Data indicates a dose-range viability respective to effects on cytokines.
These results show treatment with SST4 agonist SM-I-26 exerts an anti-inflammatory and antioxidant activity in microglia with capacity to modulate cell surface proteins associated with Aβ phagocytosis. Treatment with SST4 agonist SM-I-26 generally shifted the activation state of the LPS challenged BV-2 microglia from a pro-inflammatory M1 state to anti-inflammatory/pro-phagocytic M2 state. Data support potential use of SST4 agonist for AD treatment.
|Advisor:||Witt, Kenneth A.|
|Commitee:||Sandoval, Karin E., Schober, Joseph|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 81/3(E), Masters Abstracts International|
|Subjects:||Pharmaceutical sciences, Pharmacology|
|Keywords:||Alzheimer's disease, Enzymes, Inflammation, Microglia, Somatostatin receptor|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be