Passive regulation of water transport through simple epithelia by the activity of LI-cadherin
Zellbiologie
Zusammenfassung der Projektergebnisse
LI-cadherin is a so called 7D-cadherin which is, under physiological conditions, expressed in the intestine and colon in human and other species. 7D-cadherins are exceptional members of the cadherin superfamily, a family of calcium dependent cell-adhesion proteins, which are characterised by seven extracelular cadherin repeats (EC1-EC7) and a small cytosolic domain. LI-cadherin acts as a functional Ca2+-dependent adhesion molecule, linking neighboring cells. Although a lot of biophysical and biochemical parameters were determined in the last time and its dysregulation was found in a variety of diseases, the physiological role of LI-cadherin is still enigmatic. Using molecular modeling based on the sequence similarity of the EC1 of E-cadherin (epithelial cadherin) and LI-cadherin, we could identify an amino acid sequence which is involved in LI-cadherin trans interaction. A synthetic peptide of this AA-sequence could be shown to bind to LI-cadherin and inhibits trans-interaction on purified LI-cadherin molecules as well as on cultured enterocytes (CACO2-cells). We measured the water transport through a monolayer of CACO2 cells grown on transwell filters. Normally water is transported from the luminal side to the basal compartment even under hypertonic conditions at the luminal side. However, if LI-cadherin trans-interaction is inhibited by use of our peptide, the water transport is impaired or even reversed in the case of hypertonic conditions while no effect can be observed in the isotonic or hypotonic case. This is in line with a recently published model predicting LI-cadherin to keep the width of the intercellular cleft (IC) small. In this narrow cleft a high osmolarity can be achieved due to ion pumps yielding a standing osmotic gradient that allows water absorption from the gut even if the feces is highly hypertonic. This effect could be mathematically modelled and it could be shown, that the lateral intercellular cleft, i.e. the space between the cells which is normally bridged by LI-cadherin molecules is important for osmotically driven water transport. If LI-cadherin trans-interaction is turned of physiologically or pathologically, the lateral intercellular cleft becomes wider and therefore the volume increases. Ion pumps, which are energy dependent transporting proteins located in the lateral and basal membrane can no longer increase the osmotic active concentration of ions in the intercellular cleft to a level, where water transport into the interstitium against an osmotic gradient is possible. However, in the case of hypotonic gut content, a widening of the lateral intercellular cleft is advantageous to reduce hydrodynamic drag and thereby facilitates water transport at large rates. Our findings shine some more light onto the physiological and pathological function of LI-cadherin and suggest it to be an interesting target for pharmacology. First because dysregulation of water absorption in the gut is a severe problem within several diseases and second, as LI-cadherin is pathologically expressed in different tumours. The found peptide might be a starting point for the development of drugs to target LI-cadherin directly. During the project we tried to unravel and understand cellular processes that modulate (LI-)cadherin activity. In this line we found that for different cadherins zinc, extracellular pH and the cholesterolcontent of the plasma membrane are of particular interest. Especially in the nervous system and in the vascular system these factors might play an important physiological role for neuronal plasticity or for inflammatory responses.
Projektbezogene Publikationen (Auswahl)
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Different pH-dependencies of the two synaptic adhesion molecules N-cadherin and cadherin-11 and the possible functional implication for long-term potentiation. Synapse. 2013 Oct;67(10):705–15
Baumgartner W, Osmanagic A, Gebhard M, Kraemer S, Golenhofen N
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Possible roles of LI-Cadherin in the formation and maintenance of the intestinal epithelial barrier. Tissue Barriers. 2013 Jan 1(1);1:1–10
Baumgartner W
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Localization of VE-cadherin in plasmalemmal cholesterol rich microdomains and the effects of cholesterol depletion on VE-cadherin mediated cell-cell adhesion. Biochim Biophys Acta. 2014 Oct 2
Baumgartner W, Weth A, Gutberlet J, Harms G, Groschner K
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N-cadherinmediated cell adhesion is regulated by extracellular Zn(2+). Metallomics. 2015 Jan 12
Heiliger E, Osmanagic A, Haase H, Golenhofen N, Grabrucker AM, Weth A, et al.
