Recent advances regarding commensals in the gastrointestinal tract point to an intimate “accessory” organ status. To study the cross-talk that an accessory organ must have, the Piletz laboratory began in 2014 developing a three-dimensional (3D) in vitro co-culture model system, whereby two differentiated cell lines are juxtaposed along with “luminal” contents. The model uses differentiated C2BBe1 cell line enterocytes grown to confluency on polycarbonate filters with 0.4 µm pores over-layered atop SH-SY5Y cell line neurons to study cross-talk from either the lumen-side or the neuron-side. The focus is on an endogenous molecule, agmatine (1-amino-4-guanidobutane), made by gut bacteria at millimolar concentrations in the mucosa of the small intestine—yet in the brain known to be a neurotransmitter. Starting with each individual cell line in standard mono-cultures, agmatine was added at varying doses and varying times to replicate what is essentially dogma to the agmatine field, that of being anti-proliferative to all mammalian cells. Above 1 mM agmatine, the predicted anti-proliferative response was realized as a non-toxic, non-divisional state sustained for at least 4 days from single dosing. Moving to the 3D co-culture system, wherein the C2BBe1 cells were differentiated as per high transepithelial electrical resistance (TEER) over a 24-hour equilibration period, it was expected that agmatine would again be anti-proliferative. Yet, apical agmatine appeared to exert a pro-proliferative effect starting as low as 0.002 mM. A parallel decline in metabolism per SH-SY5Y cell was found using the color dye reaction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). It was therefore hypothesized that apical agmatine had caused the C2BBe1 cells to secrete a growth signal(s) impacting the underlying SH-SY5Y cells; and to test this, conditioned basal media collected from just C2BBe1 cells grown 4 days in the presence of apical 2 mM agmatine was taken to replace the media of naïve SH-SY5Y cells growing in log phase mono-cultures. The expectation was that growth factors would be carried over, but to the contrary, an anti-proliferative response emerged from the conditioned media, mirroring the earlier studies with agmatine in mono-cultures. Cellular lysates were also prepared from treated cells exposed for 24 h to 2 mM agmatine, and these were probed on immune-blots to assess if any of 32 common receptor tyrosine kinases had phosphorylated /activated post-addition of apical mM agmatine. No evidence was obtained that agmatine (mM apical) had elicited such flags of cell activation. Next, the 3D co-culture condition was re-run for longer periods and with more controls, and from this came the realization that the model had hidden the existence of an anti-proliferative response from the C2BBe1 cells before agmatine was even added. In short, the starting hypothesis was disproven, but in doing so it was realized that micromolar apical agmatine is able to rejuvenate a cytostasis rendered by the C2BBe1 co-culturing. Two fundamentally different mechanisms must be invoked by agmatine, because the concentrations of agmatine at which these two processes occurred were 500-fold different (0.002 mM for the reversal of cytostasis vs. 1 mM for anti-proliferative, respectively). In summary, any microbial dysbiosis involving agmatine-producing bacteria is likely to act through two molecular signaling mechanisms from the “accessory” organ bacteria to enteric nervous system.
|Advisor:||Piletz, John E.|
|Commitee:||Bourassa, Erick A., Reiken, Angela W.|
|School Location:||United States -- Mississippi|
|Source:||MAI 57/04M(E), Masters Abstracts International|
|Subjects:||Neurosciences, Cellular biology, Developmental biology|
|Keywords:||Agmatine, Caco-2, Co-culture, Enteric nervous sytem, Probiotics, SH-SY5Y|
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