Urokinase‐type plasminogen activator modulates mammalian circadian clock phase regulation in tissue‐type plasminogen activator knockout mice

摘要

Abstract Glutamate phase shifts the circadian clock in the mammalian suprachiasmatic nucleus (SCN ) by activatingNMDA receptors. Tissuetype plasminogen activator (tPA ) gates phase shifts by activating plasmin to generate m(ature) BDNF, which binds TrkB receptors allowing clock phase shifts. Here, we investigate phase shifting intPA knockout (tPA / ; B6.129S2Plattm1Mlg /J) mice, and identify urokinasetype plasminogen activator (uPA ) as an additional circadian clock regulator. Behavioral activity rhythms intPA / mice entrain to a lightdark (LD ) cycle and phase shift in response to nocturnal light pulses with no apparent loss in sensitivity. When theLD cycle is inverted,tPA / mice take significantly longer to entrain than C57BL/6J wildtype (WT ) mice.SCN brain slices fromtPA / mice exhibit entrained neuronal activity rhythms and phase shift in response to nocturnal glutamate with no change in dosedependency. Pretreating slices with thetPA /uPA inhibitor, plasminogen activator inhibitor1 (PAI 1), inhibits glutamateinduced phase delays intPA / slices. Selective inhibition ofuPA withUK 122 prevents glutamateinduced phase resetting intPA / but notWT SCN slices.tPA expression is higher at night than the day inWT SCN , whileuPA expression remains constant inWT andtPA / slices. Caseinplasminogen zymography reveals that neithertPA noruPA total proteolytic activity is under circadian control inWT ortPA / SCN . Finally,tPA / SCN tissue has lowermBDNF levels thanWT tissue, whileUK 122 does not affectmBDNF levels in either strain. Together, these results suggest that eithertPA oruPA can support photic/glutamatergic phase shifts of theSCN circadian clock, possibly acting through distinct mechanisms.