Profiling Epithelial Sodium Channel (ENaC) Expression in the Human Kidney, a Possible Marker for Hypertension
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Hypertension is a key factor risk for several conditions including heart attack, stroke and kidney failure. Hypertension is defined as sustained blood pressure at or above 140 mmHg and 90 mmHg for systolic and diastolic, respectively. Reabsorption of Na by the epithelial Na channel (ENaC) in the cortical collecting duct of the kidney yields the final adjustment to renal Na balance since there are no appreciable further downstream transport systems for Na. This process puts ENaC in a critical position to influence Na balance and its expression as a risk for hypertension. Even though the identification of several molecular variants of ENaC subunits has been possible, there are no consistent finding of the in vivo expression of these variants in humans and any association between the levels of these subunits and channel regulators such as aldosterone. The current study aims at exploring the expression of identified ENaC subunits as well as variants of &agr; and δ subunits in the human kidney. We also characterize the profile of expression in a family with 21-Hydroxylase Deficiency which causes aldosterone deficiency and salt wasting, as a mean for understanding the effects of aldosterone on expression. Urine was collected from two groups of individuals. The first group donors had no prior acute or chronic illnesses. The second group of donors was a family that has 21-Hydroxylase Deficiency. Exosomes were chosen as means of obtaining mRNA. Exosomes were isolated from urine by use of established methods with modification. mRNA was then extracted and reverse transcribed followed by use of q-PCR with gene specific primers. We demonstrated that α, β, γ and δ ENaC subunits are expressed in the human kidney. Further, α 728 which is a long form of a subunit was also expressed. The results showed variable expression of ENaC subunits between healthy and 21–Hydroxylase Deficiency individuals. It was established that the two groups did not show differences in their expression of the β subunit. We also observed that mRNA levels of γ and δ 802 were different in healthy and 21- Hydroxylase Deficiency individuals indicating that they may be subject to regulation by aldosterone. The mRNA level of g ENaC was 3 fold higher in healthy individuals than 21-Hydroxylase Deficiency individuals. This likely indicates that aldosterone acts on synthesis of γENaC mRNA with a 3 fold range. δ 802 ENaC message levels were 1.5 fold higher in 21-Hydroxylase Deficiency Individuals; this may indicate high activity of δ subunit in human kidney as means for compensating for salt wasting. These results represent the first human in vivo evidence for ENaC subunit expression and the range of regulation of subunit message by aldosterone.