Abstract Body: Introduction: Salt sensitivity of blood pressure, a significant risk factor for cardiovascular morbidity and mortality affects 50% of the hypertensive and 25% of the normotensive population. Previously, we showed that immune cells play a role in salt-sensitive hypertension, but the specific mechanisms are not fully understood. Expression of the Immediate early response 3 (IER3) gene is induced by varying forms of cellular stress and proinflammatory cytokines, but its role in salt-sensitive hypertension is unknown. We hypothesize that high dietary salt activates IER3 expression via proinflammatory signaling to contribute to salt-sensitive hypertension.
Method: To test the hypothesis, we conducted bulk RNA sequencing analysis on isolated human monocytes with and without high salt. Following this, In vivo studies were conducted on hypertensive patients using the rigorous Weinberger protocol, followed by single-cell transcriptome profiling using RNA-Seq analysis in peripheral blood mononuclear cells (PBMCs).
Results: Bulk RNA-sequencing data show increased expressions of ER stress markers: PERK, (707 ± 43.61 vs 919.54 ± 89.30, p=0.0400), IRE-1a (1766.55± 136.88 vs 3016.55 ± 638.44, p= 0.0128), ATF4 (5216.09 ± 343.86 vs 7566 ± 549.17, p= 0.0014); the NFKB subunits: p65 (2578.82 ± 206.08 vs 4610.82 ± 347.29, p= <0.0001), p50 (4812.09 ± 473.23 vs 5680.54 ± 602.85, p= 0.0879); and IER3 (10146.64 ± 2868.74 vs 19009.09 ± 5343.53, p=0.0759) in high salt treated monocytes compared to normal salt treated monocytes. Transcriptomic analysis show that IER3 expression changes dynamically with blood pressure (Diastolic Blood Pressure (DBP): r= -0.641, p=0.0074; Mean arterial pressure (MAP): r= -0.6321, p=0.0086; Pulse Pressure (PP): r=0.5033, p=0.0468) in salt-sensitive (SS) but not salt-resistant (SR) patients. Furthermore, changes in blood pressure positively correlated with NFKB2 (SBP: r=0.5276, p=0.0357; DBP: r=0.5366, p=0.0321; MAP: r=0.5872, p=0.0168) in salt-sensitive, but not salt-resistant patients. To validate these findings, we isolated CD11c+ cells from Sv129 mice and treated them with high salt. Western immunoblotting confirmed increased production of the ER stress chaperone GRP78; NFkB p65 and IER3 in high salt treated cells compared to normal salt treated cells.
Conclusions: Our findings suggest an interplay between ER stress, NFkB and IER3 in salt-sensitive hypertension. These agree with previous literature that suggest that IER3 is a NFkB dependent gene.