E-cadherin and claudin-4 expression has circadian rhythm in adult rat kidney

Urinary sodium excretion varies during the day. It is unknown whether expression levels of cell-cell junctions in the kidney are dynamic and associated with urinary sodium excretion.

Adult Sprague Dawley rats were fed ad libitum or exclusively during the day, or kept under fasting condition. We measured expression levels of Per2, E-cadherin and claudin-4 as representative molecules of the peripheral circadian clock, adherens junctions and tight junctions, respectively. We also measured sodium concentration in urine. Effects of aldosterone on expression levels of Per2 and claudin-4 were also studied. To see proliferating cells in the kidney, rats were labeled with 5-bromo-2'-deoxyuridine.

In rats fed ad libitum, Per2, E-cadherin and claudin-4 mRNA showed robust circadian oscillation: the correlation coefficients (R values) of the cosinor fitting curves with a 24-hour cycle were 0.928, 0.999 and 0.983, respectively. Oscillation phases of these molecules shifted in response to restricted feeding (R=0.922, R=0.815 and R=0.821, respectively). E-cadherin and claudin-4 proteins also oscillated circadianly under ad libitum feeding (R=0.851 and R=0.999, respectively), which shifted in response to the restricted feeding (R=0.811 and R=0.985, respectively). Urinary sodium excretion was low when protein levels of E-cadherin and claudin-4 were high. Aldosterone or cell division did not account for mRNA oscillation of claudin-4 or E-cadherin in the kidney.

Expression of E-cadherin and claudin-4 has a circadian rhythm. The dynamic change in protein levels of E-cadherin and claudin-4 seems to coincide with that in the level of sodium excretion.