Salt-induced phosphoproteomic changes in the subfornical organ in rats with chronic kidney disease

Subfornical organ (SFO) is vital in chronic kidney disease (CKD) progression caused by high salt levels. The current study investigated the effects of high salt on phosphoproteomic changes in SFO in CKD rats. 5/6 nephrectomized rats were fed a normal-salt diet (0.4%) (NC group) or a high-salt diet (4%) (HC group) for three weeks, while sham-operated rats were fed a normal-salt diet (0.4%) (NS group). For phosphoproteomic analysis of SFO in different groups, TiO₂ enrichment, isobaric tags for relative and absolute quantification (iTRAQ) labeling, and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used. There were 6808 distinct phosphopeptides found, which corresponded to 2661 phosphoproteins. NC group had 168 upregulated and 250 downregulated phosphopeptides compared to NS group. Comparison to NC group, HC group had 154 upregulated and 124 downregulated phosphopeptides. Growth associated protein 43 (GAP43) and heat shock protein 27 (Hsp27) were significantly upregulated phosphoproteins and may protect against high-salt damage. Differential phosphoproteins with tight functional connection were synapse proteins and microtubule-associated proteins, implying that high-salt diet disrupted brain’s structure and function. Furthermore, differential phosphoproteins in HC/NC comparison group were annotated to participate in GABAergic synapse signaling pathway and aldosterone synthesis and secretion, which attenuated inhibitory neurotransmitter effects and increased sympathetic nerve activity (SNA). This large scale phosphoproteomic profiling of SFO sheds light on how salt aggravates CKD <i>via</i> the central nervous system.