Degradation of tight junction proteins in meprin betatransfected kidney cells subjected to hypoxia

Abstract

Tight junctions prevent paracellular leakage in epithelial cells. Meprins, metalloproteinases that are abundantly expressed in the brush border membranes of proximal kidney tubules, have been implicated in the pathology of ischemia reperfusion (IR) induced kidney injury. Disruption of the meprin [beta] gene, or pretreatment with the meprin inhibitor, actinonin, both protect mice from IR‐induced renal injury. The mechanism by which meprins cause kidney injury is not fully understood. The goal of the current study was to determine if hypoxia activates meprins leading to degradation of the tight junction proteins. Meprin β transfected MDCK cells were depleted of oxygen by exposure to cobalt chloride. Non‐transfected MDCK cells were used as controls. Proteins were extracted and fractionated into cytosolic‐, nuclear‐ and membrane‐enriched fractions. Western blot analysis was used to quantify the levels and fragmentation of occludin and E‐cadherin in the membrane‐enriched protein fractions. A time‐dependent degradation of both E‐cadherin and occludin was observed in the cobalt chloride treated meprin β transfected cells but not in non‐transfected control cells. This suggests that hypoxia triggers activation of meprin B, leading to degradation of the two tight junction proteins. Meprin degradation of tight junction proteins may be partly responsible for the renal injury observed in IR.