As immune responses in the CNS are highly regulated, cell-specific differences in IFNγ signaling may be integral in dictating the outcome of host cell responses. In comparing the response of IFNγ-treated primary neurons to control MEF, we observed that neurons demonstrated lower basal expression of both STAT1 and STAT3, the primary signal transducers responsible for IFNγ signaling. Following IFNγ treatment of these cell populations, we noted muted and delayed STAT1 phosphorylation, no detectable STAT3 phosphorylation, and a 3-10-fold lower level of representative IFNγ-responsive gene transcripts. Moreover, in response to a brief pulse of IFNγ, a steady increase in STAT1 phosphorylation and IFNγ gene expression over 48 h was observed in neurons, as compared to rapid attenuation in MEF. These distinct response kinetics in IFNγ-stimulated neurons may reflect modifications in the IFNγ negative feedback loop, which may provide a mechanism for the cellspecific heterogeneity of responses to IFNγ.

BackgroundPrimary cilia are small non-motile microtubule and cell membrane protrusions expressed on most vertebrate cells, including cortical and hippocampal neurons. These small organelles serve as sensory structures sampling the extracellular environment and reprogramming the transcriptional machinery in response to environmental change. Primary cilia are decorated with a variety of receptor proteins and are necessary for specific signaling cascades such as the Sonic hedgehog (Shh) pathway. Disrupting cilia structure or function results in a spectrum of diseases collectively referred to as ciliopathies. Common to human ciliopathies is cognitive impairment, a symptom also observed in Alzheimer’s disease (AD). One hallmark of AD is accumulation of senile plaques composed of neurotoxic Amyloid-β (Aβ) peptide. The Aβ peptide is generated by the proteolytic cleavage of the amyloid precursor protein (APP). We set out to determine if Aβ affects primary cilia structure and the Shh signaling cascade.MethodsWe utilized in vitro cell-based assays in combination with fluorescent confocal microscopy to address our study goals. Shh signaling and cilia structure was studied using two different cell lines, mouse NIH3T3 and human HeLa cells. To investigate how Aβ levels affect Shh signaling and cilia structure in these cells, we utilized naturally secreted Aβ as well as synthetic Aβ. Effects on Shh signaling were assessed by luciferase activity while cilia structure was analyzed by fluorescent microscopy.ResultsHere, we report that APP localizes to primary cilia and Aβ treatment results in distorted primary cilia structure. In addition, we demonstrate that Aβ treatment interrupts canonical Shh signal transduction.ConclusionsOverall, our study illustrates that Aβ can alter primary cilia structure suggesting that elevated Aβ levels, like those observed in AD patients, could have similar effects on neuronal primary cilia in the brain. Additionally, our study suggests that Aβ impairs the Shh signaling pathway. Together our findings shed light on two novel targets for future AD therapeutics.Electronic supplementary materialThe online version of this article (10.1186/s13630-018-0059-y) contains supplementary material, which is available to authorized users.

Background: Sterols can alter APP metabolism. Results: Cyclopamine, a phytosterol, alters APP-CTF degradation rate, decreases APP-CTF bioavailability for ␥-secretase cleavage, and reduces A␤ and AICD generation. Conclusion: Cyclopamine decreases A␤ and AICD production by altering APP-CTF retrograde trafficking. Significance: Cyclopamine is a novel modulator of APP metabolism and trafficking, which can illuminate new avenues for Alzheimer disease treatment.

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