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Increasing evidence nowadays is showing that obesity by itself, independent of other comorbidities like diabetes and hypertension, is associated with renal functional changes and structural damage. Intentional weight loss demonstrates beneficial reduction in proteinuria and albuminuria in patients with mild to moderate chronic kidney disease, particularly those whose renal damage is likely induced by obesity. The safety of some weight loss interventions, particularly the use of high-protein diets and/or medications, is questionable in this population due to the lack of well-designed randomized controlled studies reporting on their efficacy or harm. Bariatric surgery showed the most promising results with regards to ameliorating glomerular hyperfiltration and albuminuria albeit with a modest risk of increased perioperative complications with advanced stages of chronic kidney disease (CKD).

Mammalian Na+/H+ exchangers (NHEs) are a family of transport proteins (NHE1-NHE5). To date, the cellular and subcellular localization of NHE4 has not been characterized using immunochemical techniques. We purified a fusion protein containing a portion of rat NHE4 (amino acids 565-675) to use as immunogen. A monoclonal antibody (11H11) was selected by ELISA. It reacted specifically with both the fusion protein and to a 60- to 65-kDa polypeptide expressed in NHE4-transfected LAP1 cells. By Western blot analysis, NHE4 was identified as a 65- to 70-kDa protein that was expressed most abundantly in stomach and in multiple additional epithelial and nonepithelial rat tissues including skeletal muscle, heart, kidney, uterus, and liver. Subcellular localization of NHE4 in the kidney was evaluated by Western blot analysis of membrane fractions isolated by Percoll gradient centrifugation. NHE4 was found to cofractionate with the basolateral markers NHE1 and Na+-K+-ATPase rather than the luminal marker gamma-glutamyl transferase. In stomach, NHE4 was detected by immunoperoxidase labeling on the basolateral membrane of cells at the base of the gastric gland. We conclude that NHE4 is a 65- to 70-kDa protein with a broad tissue distribution. In two types of epithelial cells, kidney and stomach, NHE4 is localized to the basolateral membrane.

Previous immunochemical studies have shown that NHE3 is an apical Na+/H+ exchanger in some renal epithelia. The purpose of the present study was to develop high-affinity, isoform-specific monoclonal antibodies (MAbs) that would be useful for carrying out high-resolution immunocytochemical studies of NHE3 in the adult and neonatal mammalian kidney. Three MAbs were developed to a fusion protein containing amino acids 702-832 of rabbit NHE3. Specificity was established by immunoblotting membranes from NHE-deficient LAP cells that had been transfected with either NHE1,-2, -3, or -4. With the use of high-resolution immunocytochemical techniques, NHE3 was found in vesicles in the apical cytoplasm of proximal tubule cells, as well as in the apical plasma membrane of the proximal tubule, and in both the thin and thick limbs of the loop of Henle. When localized in the 1-day-old rat kidney, NHE3 was first detected in the late stages of the S-shaped body. In later stages of nephron development, the pattern of NHE3 staining was similar to that seen in the adult. This study demonstrates 1) the specificity of three MAbs for Na+/H+ exchanger isoform NHE3; 2) NHE3 is present in an intracellular vesicular compartment in cells of the proximal tubule, consistent with possible regulation by membrane recycling; and 3) NHE3 is expressed on the apical membrane in early stages of the developing nephron.