Activated Alpha 2-Macroglobulin Is A Novel Mediator Of Mesangial Cell Profibrotic Signaling In Diabetic Kidney Disease

Diabetic kidney disease (DKD) is caused by the overproduction of extracellular matrix proteins (ECM) by glomerular mesangial cells (MCs). We previously showed that high glucose (HG) induces cell surface translocation of GRP78 (csGRP78), mediating PI3K/Akt activation and downstream ECM production. Activated alpha 2-macroglobulin (alpha 2M*) is a ligand known to initiate this signaling cascade. Importantly, increased alpha 2M was observed in diabetic patients' serum, saliva, and glomeruli. Primary MCs were used to assess HG responses. The role of alpha 2M* was assessed using siRNA, a neutralizing antibody and inhibitory peptide. Kidneys from type 1 diabetic Akita and CD1 mice and human DKD patients were stained for alpha 2M/alpha 2M*. alpha 2M transcript and protein were significantly increased with HG in vitro and in vivo in diabetic kidneys. A similar increase in alpha 2M* was seen in media and kidneys, where it localized to the mesangium. No appreciable alpha 2M* was seen in normal kidneys. Knockdown or neutralization of alpha 2M/alpha 2M* inhibited HG-induced profibrotic signaling (Akt activation) and matrix/cytokine upregulation (collagen IV, fibronectin, CTGF, and TGF beta 1). In patients with established DKD, urinary alpha 2M* and TGF beta 1 levels were correlated. These data reveal an important role for alpha 2M* in the pathogenesis of DKD and support further investigation as a potential novel therapeutic target.