β-adrenergic activation may promote myosin light chain kinase degradation through calpain in pressure overload-induced cardiac hypertrophy: β-adrenergic activation results in MLCK degradation

Action and therapeutic targets of myosin light chain kinase, an important cardiovascular signaling mechanism

The global incidence of cardiac diseases is increasing, imposing a substantial socioeconomic burden on healthcare systems. The pathogenesis of cardiovascular disease is complex and not fully understood, and the physiological function of the heart is inextricably linked to well-regulated cardiac muscle movement. Myosin light chain kinase (MLCK) is essential for myocardial contraction and diastole, cardiac electrophysiological homeostasis, vasoconstriction of vascular nerves and blood pressure regulation. In this sense, MLCK appears to be an attractive therapeutic target for cardiac diseases. MLCK participates in myocardial cell movement and migration through diverse pathways, including regulation of calcium homeostasis, activation of myosin light chain phosphorylation, and stimulation of vascular smooth muscle cell contraction or relaxation. Recently, phosphorylation of myosin light chains has been shown to be closely associated with the activation of myocardial exercise signaling, and MLCK mediates systolic and diastolic functions of the heart through the interaction of myosin thick filaments and actin thin filaments. It works by upholding the integrity of the cytoskeleton, modifying the conformation of the myosin head, and modulating innervation. MLCK governs vasoconstriction and diastolic function and is associated with the activation of adrenergic and sympathetic nervous systems, extracellular transport, endothelial permeability, and the regulation of nitric oxide and angiotensin II. Additionally, MLCK plays a crucial role in the process of cardiac aging. Multiple natural products/phytochemicals and chemical compounds, such as quercetin, cyclosporin, and ML-7 hydrochloride, have been shown to regulate cardiomyocyte MLCK. The MLCK-modifying capacity of these compounds should be considered in designing novel therapeutic agents. This review summarizes the mechanism of action of MLCK in the cardiovascular system and the therapeutic potential of reported chemical compounds in cardiac diseases by modifying MLCK processes.

The beneficial role of exercise in preventing doxorubicin-induced cardiotoxicity

Doxorubicin is a highly effective chemotherapeutic agent widely used to treat a variety of cancers. However, the clinical application of doxorubicin is limited due to its adverse effects on several tissues. One of the most serious side effects of doxorubicin is cardiotoxicity, which results in life-threatening heart damage, leading to reduced cancer treatment success and survival rate. Doxorubicin-induced cardiotoxicity results from cellular toxicity, including increased oxidative stress, apoptosis, and activated proteolytic systems. Exercise training has emerged as a non-pharmacological intervention to prevent cardiotoxicity during and after chemotherapy. Exercise training stimulates numerous physiological adaptations in the heart that promote cardioprotective effects against doxorubicin-induced cardiotoxicity. Understanding the mechanisms responsible for exercise-induced cardioprotection is important to develop therapeutic approaches for cancer patients and survivors. In this report, we review the cardiotoxic effects of doxorubicin and discuss the current understanding of exercise-induced cardioprotection in hearts from doxorubicin-treated animals.

Smilax glabra Roxb. flavonoids protect against pathological cardiac hypertrophy by inhibiting the Raf/MEK/ERK pathway: In vivo and in vitro studies

ETHNOPHARMACOLOGICAL RELEVANCE

Smilax glabra Roxb., the dry rhizome of Sarsaparilla, which is also known as Tu fuling (TFL) in China, is a well-known traditional CHINESE medicine that is widely used for detoxication, relieving dampness and as a diuretic. We have previously shown that the extracted TFL flavonoids (designated TFLF) possess anti-cardiac hypertrophy effects in vitro. However, the anti-cardiac hypertrophy effects of TFLF in vivo and the underlying mechanisms remain to be elucidated.

AIM OF THE STUDY

To reveal the underlying therapeutic mechanism of TFLF on cardiac hypertrophy by using transverse aortic constriction (TAC) model and cellular assays in vitro.

MATERIAL & METHODS

Cardiac hypertrophy was replicated by TAC surgery in rats or by isoprenaline treatment of rat H9C2 myocardial cells in vitro. Cardiac structure and function were evaluated by echocardiographic and hemodynamic examinations in vivo and histological analysis of tissues ex vivo. Biochemical kits and quantitative PCR were used to analyze markers of cardiac hypertrophy. Expression and phosphorylation of key proteins in the Raf/MEK/ERK pathway were quantified by Western blotting. We further confirmed our findings in H9C2 rat cardiomyocytes treated with isoprenaline and the ERK inhibitor in vitro.

RESULTS

TFLF attenuated cardiac hypertrophy and fibrosis and improved cardiac dysfunction in TAC rats. TFLF treatment induced a strong reduction in serum NT-proBNP levels. Cardiac hypertrophy marker gene (ANP, BNP and β-MHC) expression and the phosphorylation levels of c-Raf and ERK1/2 were decreased by TFLF treatment. TFLF also protected H9C2 cells from isoprenaline-induced hypertrophy in vitro via a similar molecular mechanism as that observed in the rat heart. Moreover, pretreatment with TRLF and the ERK inhibitor further inhibited the mRNA overexpression of hypertrophic genes in vitro.

CONCLUSIONS

TFLFs may protect against pathological cardiac hypertrophy via negative regulation of the Raf/MEK/ERK pathway. Thus, TFLFs are implicated as a potential pharmacological agent for treating cardiac hypertrophy in clinical practice.

Calpains as Potential Therapeutic Targets for Myocardial Hypertrophy

Despite advances in its treatment, heart failure remains a major cause of morbidity and mortality, evidencing an urgent need for novel mechanism-based targets and strategies. Myocardial hypertrophy, caused by a wide variety of chronic stress stimuli, represents an independent risk factor for the development of heart failure, and its prevention constitutes a clinical objective. Recent studies performed in preclinical animal models support the contribution of the Ca²⁺-dependent cysteine proteases calpains in regulating the hypertrophic process and highlight the feasibility of their long-term inhibition as a pharmacological strategy. In this review, we discuss the existing evidence implicating calpains in the development of cardiac hypertrophy, as well as the latest advances in unraveling the underlying mechanisms. Finally, we provide an updated overview of calpain inhibitors that have been explored in preclinical models of cardiac hypertrophy and the progress made in developing new compounds that may serve for testing the efficacy of calpain inhibition in the treatment of pathological cardiac hypertrophy.

Regulation of myosin light-chain phosphorylation and its roles in cardiovascular physiology and pathophysiology

The regulation of muscle contraction is a critical function in the cardiovascular system, and abnormalities may be life-threatening or cause illness. The common basic mechanism in muscle contraction is the interaction between the protein filaments myosin and actin. Although this interaction is primarily regulated by intracellular Ca²⁺, the primary targets and intracellular signaling pathways differ in vascular smooth muscle and cardiac muscle. Phosphorylation of the myosin regulatory light chain (RLC) is a primary molecular switch for smooth muscle contraction. The equilibrium between phosphorylated and unphosphorylated RLC is dynamically achieved through two enzymes, myosin light chain kinase, a Ca²⁺-dependent enzyme, and myosin phosphatase, which modifies the Ca²⁺ sensitivity of contractions. In cardiac muscle, the primary target protein for Ca²⁺ is troponin C on thin filaments; however, RLC phosphorylation also plays a modulatory role in contraction. This review summarizes recent advances in our understanding of the regulation, physiological function, and pathophysiological involvement of RLC phosphorylation in smooth and cardiac muscles.

Calpain-Mediated Mitochondrial Damage: An Emerging Mechanism Contributing to Cardiac Disease

Calpains belong to the family of calcium-dependent cysteine proteases expressed ubiquitously in mammals and many other organisms. Activation of calpain is observed in diseased hearts and is implicated in cardiac cell death, hypertrophy, fibrosis, and inflammation. However, the underlying mechanisms remain incompletely understood. Recent studies have revealed that calpains target and impair mitochondria in cardiac disease. The objective of this review is to discuss the role of calpains in mediating mitochondrial damage and the underlying mechanisms, and to evaluate whether targeted inhibition of mitochondrial calpain is a potential strategy in treating cardiac disease. We expect to describe the wealth of new evidence surrounding calpain-mediated mitochondrial damage to facilitate future mechanistic studies and therapy development for cardiac disease.