Meprin β activity modulates downstream mediators of the protein kinase A (PKA) signaling pathway in ischemia/reperfusion induced acute kidney injury
Authors: Ahmed Faihaa Abedelrahman , Mwiza Jean‐Marie Vianney , Sedighi Rashin , Fernander Mizpha , Yahaya Ismaila , Ongeri Elimelda Moige 
Published: November 2023

Meprins are metalloproteases that are abundantly expressed in the brush border membranes (BBM) of proximal kidney tubules. The levels of expression and the localization of meprins are associated with different types of renal injury, including ischemia‐reperfusion (IR)‐induced acute kidney injury (AKI) and diabetic nephropathy (DN). Meprins could play a role in inducing AKI through multiple cellular and molecular mechanisms, which are not fully understood. In vitro studies have shown that meprins are capable of proteolytically processing and/or degrading a variety of protein substrates. These substrates include bioactive proteins, pro‐inflammatory cytokines, and signaling molecules. Previous work from our lab showed that proteolytic processing of the catalytic subunit of protein kinase A (PKA C) by meprins occurs in vivo when AKI was induced by IR. In vitro studies with purified isoforms of PKA C further demonstrated that cleaving of PKA C by meprins significantly reduces the PKA C kinase activity, which could potentially impact downstream targets of the protein kinase A (PKA) signaling pathway and hypoxia response genes. The goal of the current study was to determine how meprin expression/activity affects downstream mediators of the PKA signaling pathway in IR‐induced acute kidney injury. To this end, IR was induced in 12‐week old wild‐type (WT) and meprin β knockout (βKO) mice on a C57BL/6 background by unilateral clamping of the renal artery for 27 minutes followed by 6 h of reperfusion. Blood samples were collected at 0 and 6 h post‐IR and centrifuged to obtain plasma. For biochemical assessment of kidney function, enzyme‐linked immunosorbent assays (ELISA) were used to determine the plasma levels of two protein markers of kidney injury, namely; cystatin C, and neutrophil gelatinase‐associated lipocalin (NGAL). The mice were then sacrificed, and kidney tissue collected and processed for proteomic analysis. Proteins were extracted from kidney tissue and fractionated into BBM‐, cytosolic‐, and nuclear‐enriched fractions. Western blot analysis was used to determine the levels of heat shock protein 27 (Hsp27), phospho‐PKA C, extracellular signal‐regulated kinase (ERK), and hypoxia inducible factor 1α (HIF‐1α) in the cytosolic and nuclear‐enriched protein fractions. Statistical analysis utilized 2‐way ANOVA (GraphPad Prism). Our data showed that meprin β enhanced kidney injury as indicated by levels of NGAL and cystatin C. Western blot analysis demonstrated increased nuclear levels HIF 1α at 6 h post‐IR, confirming induction of hypoxia. The levels of Hsp27 were higher in kidneys from WT mice subjected to IR‐induced kidney injury when compared with the meprin β deficient counterparts. The levels of phospho‐PKA C in cytosolic‐enriched fraction of WT kidneys decreased following IR. This decrease was not observed in meprin β deficient mice. In contrast, the levels of ERK in cytosolic and nuclear‐ enriched fractions increased significantly in both WT and meprin βKO kidneys following IR. These results indicate that meprin expression/activity impacts the levels of downstream targets of the PKA signaling pathway which could modulate hypoxia response genes.Support or Funding InformationThis study was supported by the National Institutes of Health (NIH)/National Institute of General Medical Sciences (NIGMS) under Award Number SC3GM102049 to Elimelda Moige Ongeri. Faihaa Ahmed is supported by the RISE program under NIH/NIGMS Grant # R25GM076162 to Goldie S Byrd