CD73-Dependent Generation of Adenosine and Endothelial Adora2b Signaling Attenuate Diabetic Nephropathy

Abstract

Nucleotide phosphohydrolysis by the ecto-59-nucleotidase (CD73) is the main source for extracellular generation of adenosine. Extracellular adenosine subsequently signals through four distinct adenosine A receptors (Adora1, Adora2a, Adora2b, or Adora3). Here, we hypothesized a functional role for CD73-dependent generation and concomitant signaling of extracellular adenosine during diabetic nephropathy. CD73 transcript and protein levels were elevated in the kidneys of diabetic mice. Genetic deletion of CD73 was associated with more severe diabetic nephropathy, whereas treatment with soluble nucleotidase was therapeutic. Transcript levels of renal adenosine receptors showed a selective induction of Adora2b during diabetic nephropathy. In a transgenic reporter mouse, Adora2b expression localized to the vasculature and increased after treatment with streptozotocin. Adora2b 2/2 mice experienced more severe diabetic nephropathy, and studies in mice with tissue-specific deletion of Adora2b in tubular epithelia or vascular endothelia implicated endothelial Adora2b signaling in protection from diabetic nephropathy. Finally, treatment with a selective Adora2b agonist (BAY 60-6583) conveyed potent protection from diabetes-associated kidney disease. Taken together, these findings implicate CD73-dependent production of extracellular adenosine and endothelial Adora2b signaling in kidney protection during diabetic nephropathy.

Adenosine signalling in diabetes mellitus—pathophysiology and therapeutic considerations

“…137 Production of adenosine, via CD73, is protective against diabetic nephropathy; 138 indeed, mice lacking CD73 exhibit a more severe form of renal dysfunction following induction of diabetes mellitus than wild-type littermates. 138 This study also found a selective induction of A 2B adenosine receptors in the vasculature, and use of mice with global or tissue-specific knockout of the A 2B adenosine receptor revealed that the protective role exerted by CD73-derived adenosine was mediated by endothelial A 2B adenosine receptor signalling. 138 The discrepancies regarding the harmful versus protective roles of A 2B adenosine receptors in the various studies are probably due to the different experimental approaches, such as the use of A 2B adenosine receptor knockout mice compared with p harmacological blockade of A 2B a denosine receptors in rats.…”

The Dark Side of Extracellular ATP in Kidney Diseases

“…39 More recently, the genetic deletions of the adenosine A 2B receptor and of CD73 (a key enzyme that produces extracellular adenosine) in mice have been found to be associated with more severe diabetic nephropathy. 40 Increased eATP signaling via P2X 4 R due to hyperglycemia induces activation of the NLRP3 inflammasome, thus stimulating IL-1b and IL-18 release, with development of tubulointerstitial inflammation 41,42 (Table 2). Two studies revealed that in individuals with type 2 diabetes and diabetic nephropathy, P2X 4 R, P2X 7 R, and NLPR3 are upregulated compared with controls, and that tubular P2X 4 R expression colocalized in confocal analysis with NLRP3, IL-1b, and IL-18 expression.…”

The role of adenosine receptors A2A and A2B signaling in renal fibrosis

“…73 CD73 expression and adenosine are also elevated in diabetic mice. 74 Expression and activity of the equilibrative nucleoside transporters ENT-1 and -2 are reduced in diabetic rats, 75 indicating a tendency for extracellular adenosine accumulation in hyperglycemia. Concurrently, hyperglycemia upregulates expression of hypoxia-inducible factor1a, 76 which in turn upregulates expression of A 2B R 77 on mesangial cells and podocytes.…”

“…However, it has been reported recently that the absence of endothelial A 2B R is associated with increased vascular endothelial growth factor levels and more severe diabetic nephropathy in a model of streptozotocin-induced diabetes. 74 This highlights the complexity in understanding the variable effects of different cells that express the A 2B R in diabetes. Of interest, Tak et al 74 further demonstrated that infusion of BAY 60-6583 (previously recognized as an agonist of the A 2B R) in a mouse model of streptozotocin-induced diabetes and in genetically diabetic Akita (Ins2 þ / À ) mice reduced the development of diabetic nephropathy.…”

“…74 This highlights the complexity in understanding the variable effects of different cells that express the A 2B R in diabetes. Of interest, Tak et al 74 further demonstrated that infusion of BAY 60-6583 (previously recognized as an agonist of the A 2B R) in a mouse model of streptozotocin-induced diabetes and in genetically diabetic Akita (Ins2 þ / À ) mice reduced the development of diabetic nephropathy. Recent studies from Müller's laboratory in Germany 81 have demonstrated that, in the presence of high levels of adenosine, BAY 60-6583 acts as an antagonist of the A 2B R. So perhaps, in the diabetic mouse models above 74 in which adenosine levels are inherently high, infusion of BAY 60-6583 may have led to the inhibition of the A 2B R and subsequent protection from diabetic nephropathy.…”