Do Sweeteners Affect the Expression of (Pro)renin Receptors in the Rat Kidney?

Abstract

Excess amounts of sugars can cause diabetes and chronic kidney diseases. Recently stevia and saccharin have been used to lower calorie intake and reduce blood sugar. Aqueous extracts of stevia may reduce blood pressure and could be a useful hypotensive agent. The mechanism has not yet been determined but may relate to the renin angiotensin system (RAS). A key protein in the system is the (Pro)renin receptor (PRR) that binds both renin and prorenin. PRR may lead to upregulation of genes associated with hypertension and chronic kidney disease. Recent studies have shown that sweeteners affect RAS; however their effect on PRR is unknown. PRR is a transmembrane protein with a large extracellular domain. The extracellular domain can be cleaved in the Golgi by furin to make a soluble form of PRR. Additionally the mRNA of PRR has a long 3′UTR and may be targeted by microRNAs. We performed a preliminary study to test the effect of sweeteners on PRR expression in the rat kidney. Rats were fed standard Osmolite diets with supplements of sucrose, stevia or saccharin. Kidneys were obtained and small RNAs and mRNAs were purified from the tissues using the mirVana kit. Then the expression of PRR mRNA was measured. At the mRNA level, PRR mRNA expressions were not statistically different in the experimental samples versus the control sample. Then we tested the expression of miRNAs that can potentially target PRR protein expression. miRNA‐132 showed a decrease in expression in the stevia and saccharin samples; however, these samples were not statistically different from the control samples. miRNA‐152 was found to be expressed in the rat kidney and showed the same trend as miRNA‐132. Saccharin and stevia samples did not show any statistical differences from the control. This suggests that sweeteners do not affect PRR mRNA expression or the expression of miRNAs that might target PRR protein expression. In the third study, PRR protein expression was measured in the samples using Western blotting. The blot showed the presence of both intact and soluble PRR proteins. The blot suggested a significant decrease in the protein expression of the soluble PRR in the kidneys of rats fed stevia and sucrose. Increased levels of sPRR have been associated with increased hypotensive affects. However, more samples will be tested to further determine if sPRR is further downregulated or unregulated in the saccharin, stevia and sucrose diets. Our preliminary study indicates that sweeteners may play a role in the regulation of soluble PRR that may further affect kidney diseases.Support or Funding Information2013 and 2014 Minnesota State University, Mankato Foundation Grants