Signaling crosstalk between Dipeptidyl Peptidase 4 and Angiotensin II-AT1R plays a role in proximal tubule NHE3 regulation and salt sensitive hypertension
Authors: Martins Flavia , Allada Rohit , Ren Jing , Girardi Adriana , Nistala Ravi 
Published: May 2023

Background: Salt sensitivity to hypertension occurs in 50-60% of all hypertensive patients and is more common in overweight/obese, females and aging population. In salt sensitive hypertension, the renin-angiotensin system (RAS) is known to play a major role and in particular, Angiotensin II (Ang II) regulation of the sodium hydrogen exchanger (NHE3) in the proximal tubule may mediate the pathophysiology. Dipeptidyl peptidase 4 (DPP4), an exopeptidase expressed abundantly on the brush border, binds to NHE3 and DPP4 inhibition reduces NHE3-mediated sodium reabsorption in proximal tubule cells. Interestingly, we observed both in vitro and in vivo that Ang II stimulates DPP4 activity. However, the mechanisms mediating the interplay between Ang II and DPP4 and its role in NHE3 regulation remain unknown. Therefore, we hypothesized that Ang II stimulation of DPP4 activity via crosstalk between AT1R and DPP4 may account for NHE3 modulation and, consequently, salt-sensitive hypertension. Methods: To address this hypothesis, we stimulated OK-AT1R (stable expressing rat AT1R) proximal tubule cells with Ang II (10-8 to 10-10 M), OKP cells with Ang II 10-8 M and microperfused rat nephrons (Ang II 10-10 M). In addition, sodium balance studies were conducted on DPP4-/- mice with high salt (1% sodium choride in drinking water) and low salt (0.02% in diet) Results: In OK-AT1R cells, we observed a dose-dependent increase in DPP4 activity, which was inhibited with AT1R blockade, and a battery of kinase inhibitors, including those for Src, PI3K, mTOR, S6K, ERK, and EGFR. Blockade with the DPP4 inhibitor MK-0626 not only suppressed DPP4 activity but partially suppressed Ang II-mediated signaling via EGFR, src, PI3K, mTOR and S6K. Further dissection of the pathways revealed that the blockade of src, which binds to both AT1R and DPP4, mimicked many of the effects of AT1R and DPP4 blockade. Mechanistically, blockade of motor proteins myosin II and myosin VI, which have been shown to redistribute with DPP4 and NHE3 along the microvilli microdomains, did not inhibit Ang II-induced DPP4 activity suggesting other mechanisms (phosphorylation) may underlie Ang II-DPP4 crosstalk in proximal tubule cells. Importantly, we found that DPP4 inhibition blocked Ang II-mediated stimulation of NHE3 activity (pHi) in vitro (OKP cells) and JHCO3- in vivo (rat nephrons). In addition, we observed that DPP4 gene-deleted mice lose more salt under both high and low salt ingestion and that DPP4 deficiency lowers BP under conditions of high salt, suggesting that DPP4 may regulate salt-sensitive hypertension. In conclusion, Ang II-AT1R and DPP4 likely crosstalk via binding to src and/or PI3-K, and inhibition of DPP4 suppresses Ang II-AT1R signaling and downstream effectors, including NHE3. Moreover, inhibition of signaling downstream of AT1R can suppress DPP4 activity, suggesting that AT1R and DPP4 act in concert but not via subcellular redistribution via motor proteins. The Sao Paulo Research Foundation - FAPESP (2021/14534-3), Sao Paulo, SP, Brazil to Flavia Martins and Dr. Adriana Girardi; NIH/NIDDK - K08 DK115886 to Dr. Ravi Nistala This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.