Adenosine A_2B Receptor Antagonism Interferes with TGF-β Cellular Signaling Through SMAD2/-3 and p65-Nf-κB in Podocytes and Protects from Phenotypical Transformation in Experimental Diabetic Glomerulopathy

Studies have emphasized alleviating fibrogenesis through interference with adenosine signaling in experimental diabetic nephropathy. We found that the in vivo antagonism of the adenosine A_2B receptor (A_2BAR) using MRS1754 in diabetic rats impedes the diabetes-induced glomerular expression of the mesenchymal-like transformation markers Snail and α-SMA, while the loss of the epithelial podocyte-specific proteins nephrin and ZO-1 was prevented. Furthermore, the production of MCP-1, CCL3, TGF-β, and the transcript levels of inflammatory mediators was reduced by A_2BAR antagonism. Using human podocytes in vitro, we demonstrated that A_2BAR antagonism affected the TGF-β-induced activation of SMAD2/-3, as evidenced by the attenuated phosphorylation of SMAD2/-3 and decreased SMAD3 occupancy at target gene promoters following the MRS1754 treatment. Moreover, the non-canonical activation of p65-NF-κB, the primary inflammatory signaling pathway downstream of TGF-β, and the expression of Snail were also reduced by MRS1754. We conclude that an A_2BAR blockade interferes with the pathogenic TGF-β signaling cascade responsible for the phenotypical transformation of podocytes, thereby alleviating diabetic glomerulopathy.