Abstract
Claudin-5 determines the sealing properties of blood-brain barrier tight junctions and its function is impaired in neurodegenerative and neuroinflammatory disorders. Focusing on the contribution of claudin-5 to the trans-interaction within the tight junction seal, we used Xenopus laevis oocytes as an expression system. Cells were clustered and challenged in a novel approach for the analysis of claudin interaction. We evaluated the strengthening effect of claudin-5 to cell-cell-connection in comparison to claudin-3. Application of a hydrostatic pressure impulse on clustered control oocyte pairs revealed a reduction of contact areas. In contrast, combinations with both oocytes expressing claudins maintained an enhanced connection between the cells (cldn5–cldn5, cldn3–cldn3). Strength of interaction was increased by both claudin-3 and claudin-5. This novel approach allowed an analysis of single claudins contributing to tight junction integrity, characterizing homophilic and hetrophilic trans-interaction of claudins. To test a new screening approach for barrier effectors, exemplarily, this 2-cell model of oocytes was used to analyze the effect of the absorption enhancer sodium caprate on the oocyte pairs.
Highlights
Claudin-5 is strongly expressed in capillary endothelia and dominates the tight junction (TJ) of the blood-brain barrier (BBB) as the expression is >100 times higher compared to any other claudin (Ohtsuki et al, 2007)
Claudin5 causes a stronger barrier in brain capillaries than in other tissues (Reinhold and Rittner, 2017) and its function is impaired in neurodegenerative and neuroinflammatory disorders (Greene et al, 2019)
All samples from three individual animals (d1–d3) revealed claudin5 specific signals at 23 kDa, whereas RNAse-free waterinjected oocytes showed no specific signal for claudin-5 expression (Figure 2A)
Summary
The tight junction protein family is crucial for cell physiology as lack or impairment is associated with diseases and dysfunction of many organs and tissues, as shown e.g., in the inner ear (Wilcox et al, 2001; Florian et al, 2003), kidney (Konrad et al, 2006; Günzel et al, 2009), gastrointestinal tract (Resnick et al, 2005; Amasheh et al, 2009), epidermis (Furuse et al, 2002; Tebbe et al, 2002), and brain capillaries (Nitta et al, 2003; Wolburg et al, 2003). Claudin-5 is strongly expressed in capillary endothelia and dominates the tight junction (TJ) of the blood-brain barrier (BBB) as the expression is >100 times higher compared to any other claudin (Ohtsuki et al, 2007). It is expressed in a variety of epithelial tissues including lung (Soini, 2011), exocrine tissues (Comper et al, 2009), intestinal (Garcia-Hernandez et al, 2017), and urinary tract (Koda et al, 2011). The BBB is protective, it limits the therapeutic options as drugs are hindered to permeate this barrier
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