Clonal hematopoiesis of indeterminate potential is associated with acute kidney injury

Age is a predominant risk factor for acute kidney injury (AKI), yet the biological mechanisms underlying this risk are largely unknown. Clonal hematopoiesis of indeterminate potential (CHIP) confers increased risk for several chronic diseases associated with aging. Here we sought to test whether CHIP increases the risk of AKI. In three population-based epidemiology cohorts, we found that CHIP was associated with a greater risk of incident AKI, which was more pronounced in patients with AKI requiring dialysis and in individuals with somatic mutations in genes other than DNMT3A, including mutations in TET2 and JAK2. Mendelian randomization analyses supported a causal role for CHIP in promoting AKI. Non-DNMT3A-CHIP was also associated with a nonresolving pattern of injury in patients with AKI. To gain mechanistic insight, we evaluated the role of Tet2-CHIP and Jak2V617F-CHIP in two mouse models of AKI. In both models, CHIP was associated with more severe AKI, greater renal proinflammatory macrophage infiltration and greater post-AKI kidney fibrosis. In summary, this work establishes CHIP as a genetic mechanism conferring impaired kidney function recovery after AKI via an aberrant inflammatory response mediated by renal macrophages.

LNK/SH2B3 loss of function increases susceptibility to murine and human atrial fibrillation

AIMS

The lymphocyte adaptor protein (LNK) is a negative regulator of cytokine and growth factor signaling. The rs3184504 variant in SH2B3 reduces LNK function and is linked to cardiovascular, inflammatory, and hematologic disorders including stroke. In mice, deletion of Lnk causes inflammation and oxidative stress. We hypothesized that Lnk-/- mice are susceptible to atrial fibrillation (AF) and that rs3184504 is associated with AF and AF-related stroke in humans. During inflammation, reactive lipid dicarbonyls are a major component of oxidative injury, and we further hypothesized that these mediators are critical drivers of the AF substrate in Lnk-/- mice.

METHODS AND RESULTS

Lnk-/- or wild-type (WT) mice were treated with vehicle or 2-hydroxybenzylamine (2-HOBA), a dicarbonyl scavenger, for 3 months. Compared to WT, Lnk-/- mice displayed increased AF duration that was prevented by 2-HOBA. In the Lnk-/- atria, action potentials were prolonged with reduced transient outward K+ current, increased late Na+ current, and reduced peak Na+ current, proarrhythmic effects that were inhibited by 2-HOBA. Mitochondrial dysfunction, especially for complex I, was evident in Lnk-/- atria, while scavenging lipid dicarbonyls prevented this abnormality. Tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were elevated in Lnk-/- plasma and atrial tissue, respectively, both of which caused electrical and bioenergetic remodeling in vitro. Inhibition of soluble TNF-α prevented electrical remodeling and AF susceptibility, while IL-1β inhibition improved mitochondrial respiration but had no effect on AF susceptibility. In a large database of genotyped patients, rs3184504 was associated with AF, as well as AF-related stroke.

CONCLUSIONS

These findings identify a novel role for LNK in the pathophysiology of AF in both experimental mice and in humans. Moreover, reactive lipid dicarbonyls are critical to the inflammatory AF substrate in Lnk-/- mice and mediate the proarrhythmic effects of pro-inflammatory cytokines, primarily through electrical remodeling.

Natriuretic Peptide Oligomers Cause Proarrhythmic Metabolic and Electrophysiological Effects in Atrial Myocytes

BACKGROUND

With aging, the human atrium invariably develops amyloid composed of ANP (atrial natriuretic peptide) and BNP (B-type natriuretic peptide). Preamyloid oligomers are the primary cytotoxic species in amyloidosis, and they accumulate in the atrium during human hypertension and a murine hypertensive model of atrial fibrillation susceptibility. We tested the hypothesis that preamyloid oligomers derived from natriuretic peptides cause cytotoxic and electrophysiological effects in atrial cells that promote arrhythmia susceptibility and that oligomer formation is enhanced for a mutant form of ANP linked to familial atrial fibrillation.

METHODS

Oligomerization was assessed by Western blot analysis. Bioenergic profiling was performed using the Seahorse platform. Mitochondrial dynamics were investigated with immunostaining and gene expression quantitated using quantitative reverse transcription polymerase chain reaction. Action potentials and ionic currents were recorded using patch-clamp methods and intracellular calcium measured using Fura-2.

RESULTS

Oligomer formation was markedly accelerated for mutant ANP (mutANP) compared with WT (wild type) ANP. Oligomers derived from ANP, BNP, and mutANP suppressed mitochondrial function in atrial HL-1 cardiomyocytes, associated with increased superoxide generation and reduced biogenesis, while monomers had no effects. In hypertensive mice, atrial cardiomyocytes displayed reduced action potential duration and maximal dV/dT of phase 0, with an elevated resting membrane potential, compared with normotensive mice. Similar changes were observed when atrial cells were exposed to oligomers. mutANP monomers produced similar electrophysiological effects as mutANP oligomers, likely due to accelerated oligomer formation, while ANP and BNP monomers did not. Oligomers decreased Na⁺ current, inward rectifier K⁺ current, and L-type Ca⁺⁺ current, while increasing sustained and transient outward K⁺ currents, to account for these effects.

CONCLUSIONS

These findings provide compelling evidence that natriuretic peptide oligomers are novel mediators of atrial arrhythmia susceptibility. Moreover, the accelerated oligomerization by mutANP supports a role for these mediators in the pathophysiology of this mutation in atrial fibrillation.

Optimizing transesophageal atrial pacing in mice to detect atrial fibrillation

Mice are routinely used to investigate molecular mechanisms underlying the atrial fibrillation (AF) substrate. We sought to optimize transesophageal rapid atrial pacing (RAP) protocols for the detection of AF susceptibility in mouse models. Hypertensive and control C57Bl/6J mice were subjected to burst RAP at a fixed stimulus amplitude. The role of parasympathetic involvement in pacing-related atrioventricular (AV) block and AF was examined using an intraperitoneal injection of atropine. In a crossover study, burst and decremental RAP at twice diastolic threshold were compared for induction of AV block during pacing. The efficacy of burst and decremental RAP to elicit an AF phenotype was subsequently investigated in mice deficient in the lymphocyte adaptor protein (Lnk-/-) resulting in systemic inflammation, or the paired-like homeodomain-2 transcription factor (Pitx2+/-) as a positive control. When pacing at a fixed stimulus intensity, pacing-induced AV block with AF induction occurred frequently, so that there was no difference in AF burden between hypertensive and control mice. These effects were prevented by atropine administration, implicating parasympathetic activation due to ganglionic stimulation as the etiology. When mice with AV block during pacing were eliminated from the analysis, male Lnk-/- mice displayed an AF phenotype only during burst RAP compared with controls, whereas male Pitx2+/- mice showed AF susceptibility during burst and decremental RAP. Notably, Lnk-/- and Pitx2+/- females exhibited no AF phenotype. Our data support the conclusion that multiple parameters should be used to ascertain AF inducibility and facilitate reproducibility across models and studies.NEW & NOTEWORTHY Methods were developed to optimize transesophageal rapid atrial pacing (RAP) to detect AF susceptibility in new and established mouse models. High stimulus intensity and pacing rates caused parasympathetic stimulation, with pacing-induced AV block and excessive AF induction in normal mice. For a given model, pacing at twice TH enabled improved phenotype discrimination in a pacing mode and sex-specific manner. Transesophageal RAP should be individually optimized when developing a mouse model of AF.