Hypertension, the number one risk factor for heart failure development, is one of the largest unmet medical needs in cardiovascular medicine. New evidence positions Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation as a driver of hypertension-induced cardiac remodeling. However, it remains to be elucidated what the precise effect of localisation-dependent activation is. Our most recent data show that the spatio-temporal CaMKII activation profile is crucial for determining whether it takes a protective or maladaptive role. Namely, its activation in the cytoplasm and on the nuclear envelope can speed up calcium uptake and release from cellular calcium stores on a beat-to-beat basis, while activation in the nucleoplasm triggers maladaptive gene signaling. We therefore performed subcellular immunocytochemistry analysis directed against phosphorylated CaMKII (pCaMKII) in isolated cardiomyocytes from hypertensive Dahl-salt sensitive rats at two disease stages. Additionally, we treated a subset of cells with the beta-adrenergic agonist isoprenaline to investigate the effect of short term stress induction. We observed lower pCaMKII levels in the nucleoplasm of early-stage hypertensive rats, while levels in the cytoplasm and at the nuclear envelope remained unchanged compared to age-matched control rats. Late-stage hypertension resulted in elevated pCaMKII levels in the cytoplasm, at the nuclear envelope and in the nucleoplasm. Upon short-term beta-adrenergic stimulation activation of CaMKII in the cytoplasm and at the nuclear envelope of both groups increased, while only hypertensive rats responded with elevated pCaMKII levels in the nucleoplasm. Taken together, our findings indicate that the spatio-specific CaMKII activation profile is altered in hypertension-induced cardiac remodeling and dependent on the disease stage. Further, hypertension escalates the response of CaMKII to beta-adrenergic stimulation in the nucleoplasm. These findings will provide new evidence to develop better therapeutic strategies fine-tuning spatio-specific CaMKII activation.

Excessive β-adrenergic stimulation and tachycardia are potent triggers of cardiac remodeling; however, their exact cellular effects remain elusive. Here, we sought to determine the potency of β-adrenergic stimulation and tachycardia to modulate gene expression profiles of cardiomyocytes. Using neonatal rat ventricular cardiomyocytes, we showed that tachycardia caused a significant upregulation of sodium–calcium exchanger (NCX) and the activation of calcium/calmodulin-dependent kinase II (CaMKII) in the nuclear region. Acute isoprenaline treatment ameliorated NCX-upregulation and potentiated CaMKII activity, specifically on the sarcoplasmic reticulum and the nuclear envelope, while preincubation with the β-blocker propranolol abolished both isoprenaline-mediated effects. On a transcriptional level, screening for hypertrophy-related genes revealed tachycardia-induced upregulation of interleukin-6 receptor (IL6R). While isoprenaline prevented this effect, pharmacological intervention with propranolol or NCX inhibitor ORM-10962 demonstrated that simultaneous CaMKII activation on the subcellular Ca2+ stores and prevention of NCX upregulation are needed for keeping IL6R activation low. Finally, using hypertensive Dahl salt-sensitive rats, we showed that blunted β-adrenergic signaling is associated with NCX upregulation and enhanced IL6R signaling. We therefore propose a previously unrecognized protective role of β-adrenergic signaling, which is compromised in cardiac pathologies, in preventing IL6R overactivation under increased workload. A better understanding of these processes may contribute to refinement of therapeutic options for patients receiving β-blockers.

Background: The insulin-like growth factor 1 (IGF1) pathway is a key regulator of cellular metabolism and aging. Although its inhibition promotes longevity across species, the effect of attenuated IGF1 signaling on cardiac aging remains controversial. Methods: We performed a lifelong study to assess cardiac health and lifespan in 2 cardiomyocyte-specific transgenic mouse models with enhanced versus reduced IGF1 receptor (IGF1R) signaling. Male mice with human IGF1R overexpression or dominant negative phosphoinositide 3-kinase mutation were examined at different life stages by echocardiography, invasive hemodynamics, and treadmill coupled to indirect calorimetry. In vitro assays included cardiac histology, mitochondrial respiration, ATP synthesis, autophagic flux, and targeted metabolome profiling, and immunoblots of key IGF1R downstream targets in mouse and human explanted failing and nonfailing hearts, as well. Results: Young mice with increased IGF1R signaling exhibited superior cardiac function that progressively declined with aging in an accelerated fashion compared with wild-type animals, resulting in heart failure and a reduced lifespan. In contrast, mice with low cardiac IGF1R signaling exhibited inferior cardiac function early in life, but superior cardiac performance during aging, and increased maximum lifespan, as well. Mechanistically, the late-life detrimental effects of IGF1R activation correlated with suppressed autophagic flux and impaired oxidative phosphorylation in the heart. Low IGF1R activity consistently improved myocardial bioenergetics and function of the aging heart in an autophagy-dependent manner. In humans, failing hearts, but not those with compensated hypertrophy, displayed exaggerated IGF1R expression and signaling activity. Conclusions: Our findings indicate that the relationship between IGF1R signaling and cardiac health is not linear, but rather biphasic. Hence, pharmacological inhibitors of the IGF1 pathway, albeit unsuitable for young individuals, might be worth considering in older adults.

Heart failure with preserved ejection fraction (HFpEF) is a highly prevalent and intractable form of cardiac decompensation commonly associated with diastolic dysfunction. Here, we show that diastolic dysfunction in patients with HFpEF is associated with a cardiac deficit in nicotinamide adenine dinucleotide (NAD(+)). Elevating NAD(+) by oral supplementation of its precursor, nicotinamide, improved diastolic dysfunction induced by aging (in 2-year-old C57BL/6J mice), hypertension (in Dahl salt-sensitive rats), or cardiometabolic syndrome (in ZSF1 obese rats). This effect was mediated partly through alleviated systemic comorbidities and enhanced myocardial bioenergetics. Simultaneously, nicotinamide directly improved cardiomyocyte passive stiffness and calcium-dependent active relaxation through increased deacetylation of titin and the sarcoplasmic reticulum calcium adenosine triphosphatase 2a, respectively. In a long-term human cohort study, high dietary intake of naturally occurring NAD(+) precursors was associated with lower blood pressure and reduced risk of cardiac mortality. Collectively, these results suggest NAD(+) precursors, and especially nicotinamide, as potential therapeutic agents to treat diastolic dysfunction and HFpEF in humans.