DFG Research Training Group "TJ-Train" (GRK 2318/2)
Tight junctions and their proteins
Molecular features and actions in health and disease

Project A3     1st cohort  3rd cohort

Prof. Dr. Michael Fromm    &   Priv.-Doz. Dr. Jörg Piontek

Clinical Physiology / Nutritional Medicine, Campus Benjamin Franklin,
Charité - Universitätsmedizin Berlin

Structural conditions of claudin-based water and cation channels

Project A3, 2nd cohort:

Functional-structural relationship of paracellular channels and barriers formed by claudin-2 and claudin-3

Background: Our group has discovered that clusters of the tight junction (TJ) protein claudin-2 forms paracellular channels for small cations and also for water. In contrast, claudin-3 does not form channels but contributes to barrier function of the TJ. For the present project, we want to examine the interaction and tight junction strand distribution of claudin-2/claudin-2, claudin-3/claudin-3, and potential claudin-2/claudin-3 clusters. For this, we will generate hybrid claudin-2/claudin-3 cluster expressing cell lines and investigate their properties with regard to their paracellular water permeability using a proprietary method for measuring water transport in cell culture monolayers.

Hypothesis: In vector controls of cell cultures with high claudin-2 expression the TJ properties are mainly determined by the formation of "pure" pores based on claudin-2, which allow cations and water to pass. After claudin-3 transfection, a combined expression and interaction of claudin-2 and claudin-3 should predominate. Although claudin-2/claudin-3 hybrid pores could still be water-permeable they should have a reduced charge density within the pore. This would reduce cation permeability while maintaining water permeability.

Work plan: (A) Generation of stable epithelial cell clones with defined high or low claudin-2 expression as controls and additional defined expression rates of claudin-3. (B) Verification of the transfections and validation of the desired constancy of other claudins and aquaporins in the Western blot with densitometric evaluation. (C) Investigation of the localization and clustering of claudin-2 and -3 in an confocal and super-resolution microscope, in parallel to structure modeling studies performed in the partner project A2. (D) Freeze-fracture electron microscopy of tight junction strands of the different clones with subsequent morphometric evaluation. (E) Measurement of water permeability of the generated clones in comparison to the corresponding controls. The general goal of the project is to understand the structural prerequisites for claudin-based water and cation channels.

2nd cohort PhD doctoral student

Fabián Martínez-Perafán

1st cohort PhD doctoral student

Carlos Ayala-Torres
29.04.21: Doctoral examination passed, Dr. rer. nat. (PhD), Freie Universität Berlin, magna cum laude

  • Ayala-Torres C, Krug SM, Rosenthal R*, Fromm M* (*shared last authorship) (2021) Angulin-1 (LSR) affects paracellular water transport, however only in tight epithelial cells. Int. J. Mol. Sci. 22: 7827 (25 pages). doi: 10.3390/ijms22157827 (IF 6.2)

  • Ayala-Torres C, Krug SM, Schulzke JD, Rosenthal R*, Fromm M* (*shared last authorship) (2019) Tricellulin effect on paracellular water transport. Int. J. Mol. Sci. 20 (22): 5700 (15 pages) [PubMed] [WebPage] [PDF] (IF 4.6)

  • Rosenthal R, Günzel D, Piontek J, Krug SM, Ayala-Torres C, Hempel C, Theune D, Fromm M (2020) Claudin-15 forms a water channel through the tight junction with distinct function compared to claudin-2. Acta Physiol. 228(1): e13334 (15 pages) [PubMed] [WebPage] [PDF]  (°IF 6.3)

Participation with project A3

Priv.-Doz. Dr. Rita Rosenthal 

Priv.-Doz. Dr. Susanne M. Krug 

Project-related publications

If a paper is not accessible, please mail to .

  1. Piontek J, Krug SM, Protze J, Krause G, Fromm M (2020) Molecular architecture and assembly of the tight junction backbone. BBA Biomembranes 1862(7): 183279 (15 pages) [PubMed] [WebPage] [PDF] [Supplement] (Review)

  2. Rosenthal R, Czichos C, Theune D, Günzel D, Schulzke JD, Fromm M (2017) Water channels and barriers formed by claudins. Ann. N.Y. Acad. Sci. 1397: 100-109 [PubMed] [WebPage] [PDF] (Review)

  3. Fromm M, Piontek J, Rosenthal R, Günzel D, Krug SM (2017) Tight junctions of the proximal tubule and their channel proteins. Pflügers Arch. 469(7-8): 877-887 [PubMed] [WebPage] [PDF] (Review)

  4. Rosenthal R, Günzel D, Krug SM, Schulzke JD, Fromm M, Yu ASL (2017) Claudin-2-mediated cation and water transport share a common pore. Acta Physiol. 219(2): 521-536 [PubMed] [WebPage] [PDF]

  5. Milatz S, Krug SM, Rosenthal R, Günzel D, Müller D, Schulzke JD, Amasheh S*, Fromm M* (*shared last authorship) (2010) Claudin-3 acts as a sealing component of the tight junction for ions of either charge and uncharged solutes. Biochim. Biophys. Acta Biomembr. 1798: 2048-2057

  6. Milatz S, Piontek J, Schulzke JD, Blasig IE, Fromm M, Günzel D (2015) Probing the cis-arrangement of prototype tight junction proteins claudin-1 and claudin-3. Biochem. J. 468(3): 449-458

  7. Rosenthal R, Milatz S, Krug SM, Oelrich B, Schulzke JD, Amasheh S, Günzel D, Fromm M (2010) Claudin-2, a component of the tight junction, forms a paracellular water channel. J. Cell Sci. 123(11): 1913-1921 [PubMed] [WebPage] [PDF] [Supplement]

  8. 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]

  9. Yu ASL, Cheng MH, Angelow S, Günzel D, Kanzawa SA, Schneeberger EE, Fromm M, Coalson RD (2009) Molecular basis for cation selectivity in claudin-2-based paracellular pores: Identification of an electrostatic interaction site. J. Gen. Physiol. 133(1): 111-127 [PubMed] [WebPage] [PDF]

  10. Amasheh S, Meiri N, Gitter AH, Schöneberg T, Mankertz J, Schulzke JD, Fromm M (2002) Claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells. J. Cell Sci. 115(24): 4969-4976 [PubMed] [WebPage] [PDF]