Diabetes downregulates renal adenosine A2A receptors in an experimental model of hypertension

Abstract

Studies on diabetic nephropathy rarely take into account that the co-existence of diabetes and hypertension is frequent and further aggravates the prognosis of renal dysfunction. Adenosine can activate four subtypes of adenosine receptors (A1, A2A, A2B and A3) and has been implicated in diabetic nephropathy. However, it is not known if, in hypertensive conditions, diabetes alters the presence/distribution profile of renal adenosine receptors. The aim of this work was to describe the presence/distribution profile of the four adenosine receptors in six renal structures (superficial/deep glomeruli, proximal/distal tubules, loop of Henle, collecting tubule) of the hypertensive kidney and to evaluate whether it is altered by diabetes. Immunoreactivities against the adenosine receptors were analyzed in six renal structures from spontaneously hypertensive rats (SHR, the control group) and from SHR rats with diabetes induced by streptozotocyin (SHR-STZ group). Data showed, for the first time, that all adenosine receptors were present in the kidney of SHR rats, although the distribution pattern was specific for each adenosine receptor subtype. Also, induction of diabetes in the SHR was associated with downregulation of adenosine A2A receptors, which might be relevant for the development of hypertensive diabetic nephropathy. This study highlights the adenosine A2A receptors as a potential target to explore to prevent and/or treat early diabetes-induced hyperfiltration, at least in hypertensive conditions.

Fig 1. Negative controls of kidney transversal sections from SHR animals.

Representative photomicrographs of kidney sections from 4 SHR rats incubated in parallel with 10% normal horse serum instead of the primary antibody to assess the level of background ascribed to nonspecific binding of the secondary antibody. A clean background was obtained in superficial (SG) and deep (DG) glomeruli, proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) or collecting tubule (CT). Scale bar: 20 μm.

Fig 2. Immunoreactivity against the adenosine A₁ and A₃ receptors in the SHR control group.

Representative photomicrographs of kidney sections from 4 SHR control rats incubated with a primary antibody against the adenosine A₁ (left panels) and A₃ (right panels) receptors. The six renal structures studied in separate are represented: superficial (SG) and deep glomeruli (DG), proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Scale bars: 20 μm.

Fig 3. Immunoreactivity against the adenosine A_2A and A_2B receptors receptors in the SHR control group.

Representative photomicrographs of kidney sections from 4 SHR control rats incubated with a primary antibody against the adenosine A_2A (left panels) and A_2B (right panels) receptors. The six renal structures studied in separate are represented: superficial (SG) and deep glomeruli (DG), proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Scale bars: 20 μm.

Fig 4. Quantitative immunostaining for A₁, A_2A, A_2B, and A₃ adenosine receptors in the renal structures from SHR control rats.

Quantitative analysis of the immunostaining (staining fractional area in percentage of the tissue total area; using the SACAIA method) for the adenosine A₁, A_2A, A_2B, and A₃ receptors in the six renal structures from SHR control rats. Superficial (SG) and deep (DG) glomeruli, proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Values are median and 25th-75th percentiles (P25-P75) from 4 rats. * p<0.05 vs corresponding PCT; ^# p<0.05 vs corresponding DG; ^§ p<0.05 vs corresponding SG and DG; ^& p<0.05 vs corresponding LH.

Fig 5. Immunoreactivity against the adenosine A₁ and A₃ receptors in rats simultaneously having hypertension and diabetes.

Representative photomicrographs of kidney sections from 4 SHR-STZ rats incubated with a primary antibody against the adenosine A₁ (left panels) and A₃ (right panels) receptors. The six renal structures studied in separate are represented: superficial (SG) and deep glomeruli (DG), proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Scale bars: 20 μm.

Fig 6. Quantitative immunostaining for A₁, A_2A, A_2B, and A₃ adenosine receptors in the renal structures from SHR-STZ rats.

Quantitative analysis of the immunostaining (staining fractional area in percentage of the tissue total area; using the SACAIA method) for the adenosine A₁, A_2A, A_2B, and A₃ receptors in the six renal structures from SHR-STZ rats. Superficial (SG) and deep (DG) glomeruli, proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Values are median and 25th-75th percentiles (P25-P75) from 4 rats. * p<0.05 vs corresponding PCT; ^# p<0.05 vs corresponding DG; ^§ p<0.05 vs corresponding SG and DG; ^& p<0.05 vs corresponding LH.

Fig 7. Immunoreactivity against the adenosine A_2A and A_2B receptors in rats simultaneously having hypertension and diabetes.

Representative photomicrographs of kidney sections from 4 SHR-STZ rats incubated with a primary antibody against the adenosine A_2A (left panels) and A_2B (right panels) receptors. The six renal structures studied in separate are represented: superficial (SG) and deep glomeruli (DG), proximal (PCT) and distal (DCT) convoluted tubule, loop of Henle (LH) and collecting tubule (CT). Scale bars: 20 μm.