DFG Research Training Group "TJ-Train" (GRK 2318)
The tricellular TJ (tTJ) is considered to form a structural weak point of the barrier-forming TJ network (13). Passage of medium-sized and large molecules might be facilitated in this region in diseased states. Tricellulin plays a critical role for barrier formation against macromolecule passage but the general processes and concepts behind are widely unknown. In first studies with human colon biopsies we have shown that tricellulin is downregulated in the inflammatory bowel disease (IBD) ulcerative colitis and the tTJ is opened (3). We hypothesize that this causes luminal pathogens to pass which then support the inflammatory process (5, 10). A role of other proteins, which are located at the tTJ, e.g. angulins (LSR, ILDR1, ILDR2) (1), as well as for occludin might be assumed.
Our thesis topics comprise characterizing the tTJ proteins regarding their distinct function in IBD development and their regulation, as well as analyzing pathways of large-molecule passage across the bicellular and the tricellular TJ. The projects will cover regulation of macromolecule passage via the tricellular tight junction and functional characterization of tricellular tight junction proteins involved in IBD.
Besides standard molecular biological techniques to analyze expression and localization changes of tTJ proteins in IBD compared to control patients, overexpression and knockdown clones of the respective tTJ proteins are going to be generated and analyzed (13). Methods are Ussing chamber techniques including flux measurements and two-path impedance spectroscopy (14), confocal microscopic methods and visualization of macromolecule passage (9) as well as ultrastructural analysis using freeze fracture electron microscopy (7). Analysis of regulatory pathways include cytokine and inhibitor treatments of intestinal epithelial cell lines, followed by protein and RNA level evaluation as well as promotor analysis.
In summary, our specific thesis projects for two doctoral students (1 PhD and 1 MD) are:
- Regulation of macromolecule passage via the tricellular tight junction.
- Functional characterization of tricellular tight junction proteins involved in IBD.
PhD doctoral student
MD doctoral student
Conrad MP*, Piontek J* (*shared first authorship), Günzel D, Fromm M, Krug SM (2016) Molecular basis of claudin-17 anion selectivity. Cell. Mol. Life Sci. 73(1): 185-200 [PubMed] [WebPage] [PDF] [Supplement]
Demehri FR*, Krug SM* (*shared first authorship), Feng Y, Lee IM, Schulzke JD, Teitelbaum DH (2016) Tight junction ultrastructure alterations in a mouse model of enteral nutrient deprivation. Dig. Dis. Sci. 61(6): 1524-1533 [PubMed] [WebPage] [PDF]
Yang S*, Krug SM* (*shared first authorship), Heitmann J, Hu L, Reinhold AK, Sauer S, Bosten J, Sommer C, Fromm M, Brack A*, Rittner HL* (*shared last authorship) (2016) Analgesic drug delivery via recombinant tissue plasminogen activator and mRNA-183-triggered opening of the blood-nerve barrier. Biomaterials 82: 20-33 [PubMed] [WebPage] [PDF] [Supplement]
Richter JF, Schmauder R, Krug SM, Gebert A, Schumann M (2016) A novel method for imaging sites of paracellular passage of macromolecules in epithelial sheets. J. Contr. Release 229: 70-79 [PubMed] [WebPage] [PDF] [Supplement] [Movie S1] [Movie S2]
Krug SM, Amasheh M, Dittmann I, Christoffel I, Fromm M, Amasheh S (2013) Sodium caprate as an enhancer of macromolecule permeation across tricellular tight junctions of intestinal cells. Biomaterials 34(1): 275-282 [PubMed] [WebPage] [PDF]
Westphal JK, Dörfel MJ, Krug SM, Cording JD, Piontek J, Blasig IE, Tauber R, Fromm M, Huber O (2010) Tricellulin forms homomeric and heteromeric tight junctional complexes. Cell. Mol. Life Sci. 67(12): 2057-2068 [PubMed] [WebPage] [PDF] [Supplement]
Krug SM, Amasheh S, Richter JF, Milatz S, Günzel D, Westphal JK, Huber O, Schulzke JD, Fromm M (2009) Tricellulin forms a barrier to macromolecules in tricellular tight junctions without affecting ion permeability. Mol. Biol. Cell 20: 3713-3724 [PubMed] [WebPage] [PDF] [Supplement text] [Supplement video]
Krug SM, Fromm M, Günzel D (2009) Two-path impedance spectroscopy for measuring paracellular and transcellular epithelial resistance. Biophys. J. 97(8): 2202-2211 [PubMed] [WebPage] [PDF] [Supplement]