Animal studies and clinical observations demonstrate a strong link between salt-sensitive (SS) hypertension (HTN) and circadian clock regulation, underscoring the importance of this interaction for understanding cardiovascular and kidney diseases. Although rodent models are widely used to study HTN and kidney diseases, tissue collection is almost always performed during the daytime, when rodents are inactive. As a result, our understanding of the underlying mechanisms is based primarily on data from the inactive period. To address this critical gap, we performed detailed transcriptomic and proteomic analyses of kidney cortices collected during both the active (2 am) and inactive (2 pm) periods, under normal and high-salt conditions. Kidneys from 8-week-old male Dahl SS rats, fed either a high-salt (HS, 4% NaCl) or a normal salt (NS, 0.4% NaCl) diet for 3 weeks, were perfused and collected at the endpoint for RNA-sequencing, proteomics, and phosphoproteomics (N=4-6 per group). Qiagen Ingenuity Pathway Analysis, STRING, and Phosphomatics software were used for functional predictions. On the NS diet, the kidney cortex showed 2,320 differentially expressed genes (DEGs) between the active and inactive periods. In contrast, only 490 DEGs were significantly reduced under an HS diet. HS diet also decreased the number of DEGs related to “circadian rhythm regulation”, including Bmal1, one of the core clock proteins, which was significantly upregulated in NS-fed rats (log2FC 3.7, active vs. inactive). Next, we sought to identify upstream regulators common to both the NS- and HS-fed groups that act in opposite directions within each dietary challenge. Prl (Prolactin) was predicted to be inhibited in NS-fed rats and activated in HS-fed rats in the active period compared to the inactive period. In contrast, Nr3c1 (glucocorticoid receptor) had opposite effects across the two diet groups. PRL, NR3C1, and their downstream DEGs were predicted to have a significant protein-protein interaction (enrichment p-value 3.69 x 10-12), with “response to lipid” (FDR 4.22 x 10-8) as a top biological process related to the network. NS-fed SS rats showed increased expression of the kinase Pdk4, which deactivates the pyruvate dehydrogenase complex (PDC), resulting in a switch in energy substrate use between lipids and carbohydrates. NS-fed SS rats also decreased Pdp2 (phosphatase that activates PDC) levels during the active period compared to the inactive period. In contrast, HS-fed rats showed no difference in Pdk4 but increased Pdp2. Contrary to transcriptomic findings, phosphoproteomics showed increased phosphorylation at S-293 of PD during the active period (vs. the inactive period) in HS-fed rats, suggesting a possible decoupling at the post-translational level. In conclusion, HS loading markedly blunted time-of-day-driven transcriptomic changes in the renal cortex. These disruptions are predicted to affect key metabolic processes, including PDC remodeling, suggesting a shift in energy utilization under HS conditions. This research was supported by American Heart Association 25POST1375066 and USF Hypertension and Kidney Research Center Early Stage Investigator grants (to LDV). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Dissanayake et al. (Fri,) studied this question.