Exosomes derived from grapes communicate with intestinal stem cells

Posted by Kasra

I worked on exosomes for some time, so I have written about them and other secreted vesicles every now and then. I still try to follow up the research in the field and get excited with the new findings, methods and applications. Here is exciting work by by Ju et al.  where they study the interaction between grape (yes the fruit) exosomes with mouse intestinal cells.

They purified exosome-like vesicles from grapes that they bought from grocery stores. Given to mice, the exosomes appeared to be absorbed by intestinal stem cells present in the intestinal crypts. Interestingly, the authors show that picking up these vesicles induce the Wnt/β-Catenin pathway. Generally, activation of this pathway promotes proliferation of stem cells. Ju et al. show grape exosomes induce proliferation of stem cells by putting stem cells together with the vesicles ex vivo and looking at crypt formation in organoids. Finally, to provide a health-related application for their vesicles, the authors show that grape exosomes protect mice and delay death in a murine colitis model. This can be because the vesicles induce proliferation of the stem cells and thus enhance tissue regeneration to revert the damage caused by colitis.

Formation of crypts from a single intestinal stem cell ex vivo is quickened when exposed to grape exosomes. From Ju et al. Molecular Therpay 2013

Formation of crypts from a single intestinal stem cell ex vivo is quickened when exposed to grape exosomes. From Ju et al. 11 June 2013;doi: 0.1038/mt.2013.64

This study contains so many buzz-words, I could think of terrible ways by which it can be mis-interpretted by media: grapes heal gut disease, nano-particles in fruit protect against gut disease, … As the authors say in the first paragraphs of the paper, this study is a proof of concept and there is still a lot more to learn. Thankfully, they show enough evidence to tickle other scientists to look at application of plant-derived exosomes and exosome-like vesicles as means for drug delivery and therapy. For one thing, plants-derived products are available in higher abundance compared to their animal-derived counterparts and can be cheaper to purify in commercial quantities.  Also, humans have been exposed to them (maybe not in such high concentrations) for millions of years, so they are no strangers to the gut cells.

Ju S, Mu J, Dokland T, Zhuang X, Wang Q, Jiang H, Xiang X, Deng ZB, Wang B, Zhang L, Roth M, Welti R, Mobley J, Jun Y, Miller D, & Zhang HG (2013). Grape Exosome-like Nanoparticles Induce Intestinal Stem Cells and Protect Mice From DSS-Induced Colitis. Molecular therapy : the journal of the American Society of Gene Therapy PMID: 23752315

ResearchBlogging.org

Tracking exosomes in vivo

Posted by: Kasra

Application of exosomes for therapeutic, especially as drug delivery agents has been always an interest. However, there is limited knowledge on how these vesicles interact with the variety of the cells inside the body and how does the body react to their presence.

Takahashi et al. have used exosomes released by a melanoma cell line that also produces Gaussia luciferase (gLuc) to shed some light on this question. They intravenously injected the chemiluminescent exosomes into mice and watched how they go around in the body. Benefiting from the strong chemiluminescence of gLuc, they used in vivo imaging systems to visualize the localization of exosomes in the mouse during time. Surprisingly, they observed that exosomes were cleared from the serum very rapidly, with less than 5% remaining 5 minutes after administration. Also, the organs taking most shares of the exosomes were the liver and later the lungs. In the discussion, the authors mention that the reason for rapid clearance of exosomes from the serum could be unspecific interactions of the vesicles with blood cells. Exosomes express a multitude of adhesion proteins on their surface, allowing them to potentially bind various kinds of cells. We are far from fully understanding the dynamics of cell adhesion. But maybe careful engineering of proteins expressed on exosome surface could help in that direction, besides making progress in development of better targeted exosome therapeutics.

Tracking of localization of exosomes after intravenous injection. From Takahashi et al. J Biotechnol. 2013 Apr 2. pii: S0168-1656(13)00164-8. doi: 10.1016/j.jbiotec.2013.03.013

Tracking of localization of exosomes after intravenous injection. From Takahashi et al. J Biotechnol. 2013 Apr 2. pii: S0168-1656(13)00164-8. doi: 10.1016/j.jbiotec.2013.03.013

Takahashi Y, Nishikawa M, Shinotsuka H, Matsui Y, Ohara S, Imai T, & Takakura Y (2013). Visualization and in vivo tracking of the exosomes of murine melanoma B16-BL6 cells in mice after intravenous injection. Journal of biotechnology PMID: 23562828

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Communication between intestinal commensal bacteria and the host via membrane vesicles

Posted by Kasra

Releasing outer membrane vesicles or OMVs of by bacteria can be considered one of their protein secretion pathways. This pathway is especially important for carrying messages to longer distances than what other mechanisms such as type III secretion system can do.

Although the gut is largely colonized, there is not much of direct cell to cell contact between the microbiota and the host cells due to presence of a thick mucosal layer and other factors. In a recent study, Shen et al. show that bacterial OMVs can make up for this distance and allow for communication between the microbiota and host. They show that orally administered OMVs collected from Bacteroides fragilis can protect mice from chemically induced colitis. Furthermore, they show that this protection is dependent on presence of a capsular polysaccharide (PSA) on the OMV surface. Shen et al. suggest that PSA-containing OMVs are picked up by dendritic cells and induce IL-10 production, thus ameliorating colitis. Specifically, they show that production of IL-10 by DCs is dependent on recognition of PSA by TLR2. Therefore, stimulation of TLR2 by B. fragilis OMVs leads to tolerance instead of inflammation, which is necessary for homeostatic maintenance of the gut.

 

Top shows B. fragilis releasing OMVs. Bottom shows purified B. fragilis OMVs from wildtype and non-PSA producing strains. From Shen et al. Cell host & Microbe. Oct. 2012

Shen Y, Torchia ML, Lawson GW, Karp CL, Ashwell JD, & Mazmanian SK (2012). Outer membrane vesicles of a human commensal mediate immune regulation and disease protection. Cell host & microbe, 12 (4), 509-20 PMID: 22999859

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Exploitation of host microvesicles by Trypanosoma cruzi

Posted by Kasra

Studying mechanisms of parasitism teaches us a lot about the host physiology as well as parasite pathogenicity. Millions of years of co-evolution have adapted the parasites to exploit various homeostatic and pathologic processes of the host for their benefit. A nice example is recent study on the protozoan parasite Trypanosoma cruzi and its exploitation of host microvesicles. T. cruzi, is the causative agent of Chagas disease in Southern America’s and similar to other parasites has a complicated life-cycle. Once injected into the mammalian host, it toggles between an intracellular and bloodstream stage. In the blood-stream, among all, the parasite should fight complement-mediated lysis and inside the host cells it should avoid being killed by activated immune cells. Cestari et al. show how the parasite is able to get help from host-released microvesicles for survival in both of these stages.

Microvesicles or plasma membrane vesicles or (PMVs) are relatively large (between 200-500nm, compared to exosomes that are between 40-100nm) exovesicles released by eukaryotic cells. Not much is known about their part in homeostasis, but they have been shown to play roles in cancer and infections. More research on their role in disease can help us tell what they do in normal conditions.

Microvesicles released from THP-1 cells, Cestari et al. 2012, J Immunology

Cestari et al. show that contact between T. cruzi metacyclic trypomastigotes and THP-1 induces a rapid augmentation in release of microvesicles from THP-1 cells in an apoptosis independent manner. They suggest that the cytoplasmic trigger for release of microvesicles is a transient increase in Ca2+ levels. Interestingly, they show that these vesicles are able to save the parasite from complement mediated lysis by binding C3 convertase on the parasite surface and inhibiting C3 cleavage.

Although they do not look at the complete content of the microvesicles, Cestari et al. show that microvesicles contain TGF-β, a generally antiproliferative and antiactivatory cytokine. Levels of TGF- β are not surprisingly different in microvesicles from different cell origins. However, once present together with the parasite, they allow a stronger infection of Vero cells (an epithelial cell line). They show that pre-incubation with microvesicles allows for a stronger T. cruzi infection and this effect is specifically due to TGF- β. This can be important for parasitism, since they have also suggested that mice infected with T. cruzi have higher levels of microvesicles in their bloodstream compared to normal mice.

Like any other exciting piece of research, this study raises a lot of questions. For instance, why is there an increase in microvesicle release following contact with T. cruzi? Is this a common effect with other pathogens or eukaryotic parasites? What is the role of these vesicles when they are not being exploited? What other cytokines/signaling proteins do they contain? What do they do? What are their target cells? And so on. I am very eager to read the follow-up papers and learn more about this method of cell-cell communication.

Cestari I, Ansa-Addo E, Deolindo P, Inal JM, & Ramirez MI (2012). Trypanosoma cruzi Immune Evasion Mediated by Host Cell-Derived Microvesicles. Journal of immunology (Baltimore, Md. : 1950), 188 (4), 1942-52 PMID: 22262654

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