Increased levels of adenosine and ecto 5'-nucleotidase (CD73) activity precede renal alterations in experimental diabetic rats

The pathogenesis of diabetic nephropathy (DN) has not been clearly established, making diagnosis and patient management difficult. Recent studies using experimental diabetic models have implicated adenosine signaling with renal cells dysfunction. Therefore, the study of the biochemical mechanisms that regulate extracellular adenosine availability during DN is of emerging interest. Using streptozotocin-induced diabetic rats we demonstrated that urinary levels of adenosine were early increased. Further analyses showed an increased expression of the ecto 5'-nucleotidase (CD73), which hydrolyzes AMP to adenosine, at the renal proximal tubules and a higher enzymatic activity in tubule extracts. These changes precede the signs of diabetic kidney injury recognized by significant proteinuria, morphological alterations and the presence of the renal fibrosis markers alpha smooth muscle actin and fibronectin, collagen deposits and thickening of the glomerular basement membrane. In the proximal tubule cell line HK2 we identified TGF-β as a key modulator of CD73 activity. Importantly, the increased activity of CD73 could be screened in urinary sediments from diabetic rats. In conclusion, the increase of CD73 activity is a key component in the production of high levels of adenosine and emerges as a new tool for the early diagnosis of tubular injury in diabetic kidney disease.