Propionic Acid Induces Gliosis and Neuro-inflammation through Modulation of PTEN/AKT Pathway in Autism Spectrum Disorder
Authors: Saleh A Naser
Aseela Samsam
Latifa S Abdelli
Journal: Scientific Reports (2019)
Discipline: Multidisciplinary
Keywords: Autism spectrum disorder; Glia over-proliferation; Neuro-inflammation; Gastrointestinal symptoms; Propionic acid
Affiliations: Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA., Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA. .

Abstract:  Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by glia over-proliferation, neuro-inflammation, perturbed neural circuitry, and gastrointestinal symptoms. The role of gut dys-biosis in ASD is intriguing and should be elucidated. We investigated the effect of Propionic acid (PPA), a short-chain fatty acid (SCFA) and a product of dys-biotic ASD gut, on human neural stem cells (hNSCs) proliferation, differentiation and inflammation. hNSCs proliferated to 66 neuropsheres when exposed to PPA versus 45 in control. The neurosphere diameter also increased at day 10 post PPA treatment to (Mean: 193.47 um ± SEM: 6.673 um) versus (154.16 um ± 9.95 um) in control, p &lt; 0.001. Pre-treatment with β-HB, SCFA receptor inhibitor, hindered neurosphere expansion (p &lt; 0.001). While hNSCs spontaneously differentiated to (48.38% ± 6.08%) neurons (Tubulin-IIIβ positive) and (46.63% ± 2.5%) glia (GFAP positive), PPA treatment drastically shifted differentiation to 80% GFAP cells (p &lt; 0.05). Following 2 mM PPA exposure, TNF-α transcription increased 4.98 fold and the cytokine increased 3.29 fold compared to control (P &lt; 0.001). Likewise, GPR41 (PPA receptor) and pro-survival p-Akt protein were elevated (p &lt; 0.001). PTEN (Akt inhibitor) level decreased to (0.42 ug/ul ± 0.04 ug/ul) at 2 mM PPA compared to (0.83 ug/ul ± 0.09 ug/ul) in control (p &lt; 0.001). PPA at 2 mM decreased neurite outgrowth to (80.70 um ± 5.5 um) compared to (194.93 um ± 19.7 um) in control. Clearly, the data supports a significant role for PPA in modulating hNSC patterning leading to gliosis, disturbed neuro-circuitry, and inflammatory response as seen in ASD. 

Retracted: No

PubPeer comments:
 Could the authors examine the images marked in Figures 1A (top) and 7 (bottom) below and confirm the apparent repetitions are intentional? *** ![file] *** ![file] , 
 #1 Thanks for the valuable comments. Yes it was intentional to show (by representative images) that PPA interaction with the receptor was specific and the blocking was very effective. The quantitative values for each experiment are mentioned in the result section. Briefly, In Figure 1, the Neurosphere average diameter (um) in cells treated with u03b2-HB (inhibitor)+PPA was 56.53 + -4.7 which was so similar to untreated control cells (58.46 + - 4.1) even after 10 days incubation compared to cells treated with PPA (193.5 + -6.6). Keep in mind that the cells were treated with the inhibitor for 24 hours and then with PPA until day 10. It seems that the inhibitor freezes the time on the cells and completely block any PPA action. This confirmed to us that PPA entry mechanism is through GPR41. Since the images were intended to be a representative of the findings, we chose to show the image from the control cells to clearly make our point that the inhibitor treatment will leave the cells as is, despite any PPA follow up treatment. This could suggest that PPA- specific inhibitors could be considered, in the future, to block intestinal absorption of PPA, etc. Similarly, in Figure 7, we used representative images to reflect on our neurite outgrowth quantitative data which we conducted on 10 to 15 neurites per treatment setting. Our data clearly showed that, u03b2-HB blocked the effect of PPA (Panel 7A-c). Specifically, u03b2-HB pre-treatment followed by PPA (7A-c) resulted in neurite outgrowth measurements so similar to the untreated cells. We are glad that the point was noted, PPA negative effect can be prevented! , 
 Regarding the response on Figure 1, u201cSince the images were intended to be a representative of the findings, we chose to show the image from the control cells to clearly make our point that the inhibitor treatment will leave the cells as is, despite any PPA follow up treatment.u201d Do the authors *not* believe it is misleading to label untreated cells as if they were treated cells? Misrepresentation of experimental results is generally considered research misconduct. Perhaps the authors should contact the journal editors to see if they agree with you. ,