How Does Circadian Rhythm Impact Salt Sensitivity of Blood Pressure in Mice? A Study in Two Close C57Bl/6 Substrains

Background Mouse transgenesis has provided the unique opportunity to investigate mechanisms underlying sodium kidney reabsorption as well as end organ damage. However, understanding mouse background and the experimental conditions effects on phenotypic readouts of engineered mouse lines such as blood pressure presents a challenge. Despite the ability to generate high sodium and chloride plasma levels during high-salt diet, observed changes in blood pressure are not consistent between wild-type background strains and studies. Methods The present work was designed in an attempt to determine guidelines in the field of saltinduced hypertension by recording continuously blood pressure by telemetry in mice submitted to different sodium and potassium loaded diets and changing experimental conditions in both C57BL/6N and C57BL/6J mice strain (Normal salt vs. Low salt vs. High-salt/normal potassium vs. High salt/low potassium, standard vs. modified light cycle, Non-invasive tail cuff blood pressure vs. telemetry). Results In this study, we have shown that, despite a strong blood pressure (BP) basal difference between C57BL/6N and C57BL/6J mice, High salt/normal potassium diet increases BP and heart rate during the active phase only (dark period) in the same extent in both strains. On the other hand, while potassium level has no effect on salt-induced hypertension in C57BL/6N mice, high-salt/low potassium diet amplifies the effect of the high-salt challenge only in C57BL/6J mice. Indeed, in this condition, salt-induced hypertension can also be detected during light period even though this BP increase is lower compared to the one occurring during the dark period. Finally, from a methodological perspective, light cycle inversion has no effect on this circadian BP phenotype and tail-cuff method is less sensitive than telemetry to detect BP phenotypes due to salt challenges. Conclusions Therefore, to carry investigations on salt-induced hypertension in mice, chronic telemetry and studies in the active phase are essential prerequisites

Novel cross-talk within the IKK family controls innate immunity

International audienceMembers of the IκB kinase (IKK) family play a central role in innate immunity by inducing NFκB- and IRF-dependent gene transcription programmes required for the production of pro-inflammatory cytokines and interferons. However, the molecular mechanisms that activate these protein kinases and their complement of physiological substrates remain poorly defined. Using MRT67307, a novel inhibitor of IKKε/TBK1 and BI605906, a novel inhibitor of IKKβ, we demonstrate that two different signalling pathways participate in the activation of the IKK-related protein kinases by ligands that activate the IL-1, TLR3 and TLR4 receptors. One signalling pathway is mediated by the canonical IKKs, which directly phosphorylate and activate IKKε and TBK1, whereas the second pathway appears to culminate in the autocatalytic activation of the IKK-related kinases. In contrast, the TNFα-induced activation of the IKK-related kinases is mediated solely by the canonical IKKs. In turn, the IKK-related kinases phosphorylate the catalytic subunits of the canonical IKKs and their regulatory subunit NEMO, which is associated with reduced IKKα/β activity and NFκB-dependent gene transcription. We also show that the canonical IKKs and the IKK-related kinases not only have unique physiological substrates, such as IκBα, p105 and RelA (IKKα and IKKβ) and IRF3 (IKKε and TBK1), but also have several substrates in common, including the catalytic and regulatory (NEMO and TANK) subunits of the IKKs themselves. Taken together, our studies reveal that the canonical IKKs and the IKK-related kinases regulate each other by an intricate network involving phosphorylation of their catalytic and regulatory (NEMO, TANK) subunits to balance their activities during innate immunity

Effects of various salt challenges on mean blood pressure and heart rate in C57BL/6N male mice.

<p>Mice were monitored with telemetry and placed in a standard (A, C) or modified light/dark cycle (B, D). NS = normal salt diet (n = 12 and n = 17, for the standard and modified light cycle respectively), LS = low salt diet (n = 11 and n = 15, for the standard and modified light cycle respectively), HS = high Na⁺/normal K⁺ diet (n = 5 and n = 6, for the standard and modified light cycle respectively). One-way ANOVA per light phase followed by Tukey’s post-hoc test; *: p<0.05 compared to NS diet.</p

p38 mitogen-activated protein kinase inhibition ameliorates angiotensin II-induced target organ damage

We investigated whether or not p38 mitogen-activated protein kinase inhibition ameliorates angiotensin II-induced target organ damage. We used double transgenic rats harboring both human renin and angiotensinogen genes (dTGRs). dTGR, with or without p38 inhibitor (BIRB796; 30 mg/kg per day in the diet), and nontransgenic Sprague-Dawley rats were studied in 2 protocols. In protocol 1 (week 7), systolic blood pressure of untreated dTGRs was 204+/-4 mm Hg, but partially reduced after BIRB796 treatment (166+/-7 mm Hg), whereas Sprague-Dawley rats were normotensive. The cardiac hypertrophy index was unchanged in untreated and BIRB796-treated dTGRs. The beta-myosin heavy chain expression of BIRB796-treated hearts was significantly lower in BIRB796 compared with dTGRs, indicating a delayed switch to the fetal isoform. BIRB796 treatment significantly reduced cardiac fibrosis, connective tissue growth factor, tumor necrosis factor-alpha, interleukin-6, and macrophage infiltration. Albuminuria was not reduced in BIRB796-treated dTGRs. Tubular and glomerular damage with tumor necrosis factor-alpha expression was unaltered, although serum creatinine and cystatin C were normalized. Renal macrophage infiltration, fibrosis, and vessel damage were reduced. In protocol 2 (week 8), we focused on mortality and arrhythmogenic electrical remodeling. Mortality of untreated dTGRs was 100% but was reduced to 10% in the BIRB796 group. Cardiac magnetic field mapping showed prolongation of depolarization and repolarization in untreated dTGRs compared with Sprague-Dawley rats with a partial reduction by BIRB796. Programmed electrical stimulation elicited ventricular tachycardias in 81% of untreated dTGRs but only in 48% of BIRB796-treated dTGRs. In conclusion, BIRB796 improved survival, target organ damage, and arrhythmogenic potential in angiotensin II-induced target organ damage

Comparison between C57BL/6N and C57BL/6J for their mean blood pressure and heart rate responses to various salt challenges.

<p>Mice were monitored with telemetry during the dark (A, B) and light (C) periods of a modified light/dark cycle. NS = normal salt diet (n = 17 and n = 17, for C57BL/6N and C57BL/6J respectively), LS = low salt diet (n = 15 and n = 17, for C57BL/6N and C57BL/6J respectively), HS = high Na⁺/normal K⁺ diet (n = 8 and n = 8, for C57BL/6N and C57BL/6J respectively) and HS/LK = high Na⁺/low K⁺ diet (n = 6 and n = 9, for C57BL/6N and C57BL/6J respectively). One-way ANOVA per light phase followed by Tukey’s post-hoc test; *: p<0.05 compared to NS diet; #: p<0.05 HS/LK compared to HS.</p

Effect of high salt diets on the circadian blood pressure variations in C57BL/6N and C57BL/6J mice under a reverse light/dark cycle.

<p>2.5 days continuous telemetric recordings of systolic blood pressure after 2 weeks of NS, HS or HS/LK diet challenge. A) n = 8 per group B) n = 6 per group C) n = 8 per group D) n = 9 per group. Two-way ANOVA followed by Sidak’s post-hoc test *: p<0.05 for interaction.</p

Sodium and potassium levels in urine and plasma in C57BL/6N.

<p>Sodium and potassium levels in urine and plasma in C57BL/6N.</p