Comparison of protein expression in kidney tubular apical and basolateral membranes in young and old rats

Abstract

Na‐H Exchanger Regulatory Factor Isoform 1 (NHERF1) is critical for the expression of epithelial signaling complexes. We previously demonstrated loss of NHERF1 expression in kidney apical (BBM) and basolateral (BLM) membranes from old (22 m, O) compared to young (4 m, Y) rats, but the effect of NHERF1 loss on expression of kidney epithelial transporters is unknown. We hypothesize that loss of NHERF1 expression in aging will result in differential expression of ion transporting proteins in the BBM and BLM. To address this hypothesis, we compared protein expression and phosphorylation in BBM and BLM from Y and O female F344 rat kidneys using proteomic analysis. We identified 1331 differentially expressed proteins of which 18 were differentially phosphorylated in BBM and BLM from O animals as compared to Y animals. NHERF1 expression significantly decreased in BBM and BLM from O animals. Phosphoproteomic analysis identified phosphorylation of Ser276 on NHERF1 in membranes from Y animals. An additional phosphorylation at Ser285 on NHERF1 was identified in O animals. Expression of NKA a1, NpT2c, NHE3, NBCe1, g‐glutamyl peptidase, and ezrin were significantly decreased in membranes from old animals as compared to young animals. These data suggest that age‐related alterations in ion homeostasis may result from changes in transporter expression and from loss of normal hormonal regulatory pathways. Supported by NIH.