Ubiquitin proteasome system (UPS) activation in the cardiac hypertrophy of hyperthyroidism

The role of the immunoproteasome in cardiovascular disease

The ubiquitinproteasome system (UPS) is the main mechanism responsible for the intracellular degradation of misfolded or damaged proteins. Under inflammatory conditions, the immunoproteasome, an isoform of the proteasome, can be induced, enhancing the antigen-presenting function of the UPS. Furthermore, the immunoproteasome also serves nonimmune functions, such as maintaining protein homeostasis and regulating signalling pathways, and is involved in the pathophysiological processes of various cardiovascular diseases (CVDs). This review aims to provide a comprehensive summary of the current research on the involvement of the immunoproteasome in cardiovascular diseases, with the ultimate goal of identifying novel strategies for the treatment of these conditions.

Baicalin inhibits pressure overload-induced cardiac hypertrophy by regulating the SIRT3-dependent signaling pathway

BACKGROUND

The conserved sirtuin protein sirtuin 3 (SIRT3) is a vital protective protein for cardiac hypertrophy. Inhibition of SIRT3 accelerated the development of heart hypertrophy. On the other hand, myocardial hypertrophy was prevented by overexpressing SIRT3. SIRT3 has been proposed as a potential therapeutic target for managing or averting heart hypertrophy. Baicalin, a flavonoid extracted from the Scutellaria baicalensis plant, has anti-cardiovascular properties, including protection against cardiac hypertrophy. However, the molecular mechanism of the anti-hypertrophic effect of baicalin is not well known.

PURPOSE

In this study, we aim to investigate the effect of baicalin on cardiac hypertrophy and explored its underlying molecular mechanisms.

STUDY-DESIGN/METHODS

Abdominal aortic constriction (AAC)-induced mouse cardiac hypertrophy and angiotensin II (Ang II)-induced cardiomyocyte hypertrophy models were established. After baicalin treatment, cardiac hypertrophy was monitored by detecting the expression of hypertrophic genes and cell surface area. Echocardiogram was performed to check the heart function in vivo. Moreover, the protein expression of the SIRT3-dependent pathway was detected by Western blotting.

RESULTS

In this work, we demonstrated that baicalin might suppress the cell surface area and the expression of the Ang II -induced myosin heavy chain β (β-MHC), brain natriuretic polypeptide (BNP), and atrial natriuretic factor (ANF). Additionally, it reduced the AAC rats' hypertrophic impact. We also found that baicalin prevents cardiac hypertrophy by regulating SIRT3/LKB1/AMPK signaling pathway. Moreover, we showed that baicalin upregulated the SIRT3 protein expression by inhibiting proteasome and by the activation of 20 S proteasome subunit beta type-5 (PSMB5).

CONCLUSION

These results offer the first proof that baicalin inhibits cardiac hypertrophy due to its effect on the SIRT3-dependent signaling pathway, indicating its potential for treating cardiac hypertrophy and heart failure. The present study provides a preliminary experimental basis for the clinical application of baicalin and baicalin-like compounds.

Cardiac Metabolism in Heart Failure and Implications for Uremic Cardiomyopathy

Chronic kidney disease is associated with an increased risk for the development and progression of cardiovascular disorders including hypertension, dyslipidemia, and coronary artery disease. Chronic kidney disease may also affect the myocardium through complex systemic changes, resulting in structural remodeling such as hypertrophy and fibrosis, as well as impairments in both diastolic and systolic function. These cardiac changes in the setting of chronic kidney disease define a specific cardiomyopathic phenotype known as uremic cardiomyopathy. Cardiac function is tightly linked to its metabolism, and research over the past 3 decades has revealed significant metabolic remodeling in the myocardium during the development of heart failure. Because the concept of uremic cardiomyopathy has only been recognized in recent years, there are limited data on metabolism in the uremic heart. Nonetheless, recent findings suggest overlapping mechanisms with heart failure. This work reviews key features of metabolic remodeling in the failing heart in the general population and extends this to patients with chronic kidney disease. The knowledge of similarities and differences in cardiac metabolism between heart failure and uremic cardiomyopathy may help identify new targets for mechanistic and therapeutic research on uremic cardiomyopathy.

Metformin attenuates angiotensin II-induced cardiomyocyte hypertrophy by upregulating the MuRF1 and MAFbx pathway

Pathological cardiac hypertrophy induced by aging and neurohumoral activation, such as angiotensin II (Ang II) activation, is an independent risk factor for heart failure. The muscle really interesting new gene-finger protein-1 (MuRF1) and muscle atrophy F-box (MAFbx) pathway has been previously reported to be an important mechanism underlying the pathogenesis of cardiac hypertrophy. Metformin is currently the first-line blood glucose-lowering agent that can be useful for the treatment of cardiovascular diseases. However, the potential role of metformin in the modulation of MuRF1 and MAFbx in cardiomyocyte hypertrophy remains poorly understood. The present study used H9c2 cells, a cardiomyocyte cell model. The surface area of cultured rat H9c2 myoblasts was measured and the expression levels of MuRF1 and MAFbx were quantified using western blot or reverse transcription-quantitative PCR. H9c2 cells were transfected with MuRF1 and MAFbx small interfering (si) RNA. The present study revealed that Ang II treatment significantly increased the cell surface area of model cardiomyocytes. Additionally, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) mRNA and protein expression was increased following this treatment. Ang II also downregulated MuRF1 and MAFbx protein and mRNA expression. In the H9C2, treatment with metformin attenuated hypertrophic remodeling. In addition, expression of ANP and BNP was significantly reduced in metformin-treated H9C2 cells. The results indicated that metformin increased the activity of MuRF1 and MAFbx and upregulated their expression, the knockdown of which resulted in deteriorative Ang II-induced cell hypertrophy, even following treatment with metformin. Taken together, data from the present study suggest that metformin can prevent cardiac hypertrophy through the MuRF1 and MAFbx pathways.

Prognostic role of hypothyroidism and low free-triiodothyronine levels in patients hospitalized with acute heart failure

Low thyroid function has been widely recognized as a potential cause of heart failure (HF), but the evidence about a possible association with in-hospital, all-cause mortality in patients with acute HF (AHF) is not consistent. This study sought to investigate the prevalence and prognostic role of hypothyroidism, overt and subclinical, and of low free-triiodothyronine (fT3) levels in patients hospitalized with AHF. We retrospectively analyzed consecutive 1018 patients who were hospitalized for AHF in a single academic medical center [Fondazione Policlinico A.Gemelli IRCCS, Rome, Italy] between January 1st 2016, and December 31st 2018. Patients were divided into three groups: normal thyroid function (n = 798), subclinical hypothyroidism (n = 105), and overt hypothyroidism (n = 115). The outcome was in-hospital, all-cause mortality. Patients were 81 years of age, 55% were females and nearly two-thirds of the patients were on New York Heart Association functional class III. The three most common cardiovascular comorbidities were coronary artery disease, hypertension, and atrial fibrillation with no differences across the three groups. Overall, 138 patients (14%) died during the hospital stay. The mortality rate was 27% among patients with overt hypothyroid, 17% among those with subclinical hypothyroidism, and 11% among euthyroid patients (p < 0.001). At a multivariate Cox regression model, overt hypothyroidism (HR 2.1, 95% CI 1.4-3.2) and fT3 levels < 1.8 pg/mL (HR 3.4, 95% CI 2.3-5.1) were associated with an increased likelihood of in-hospital death. No association was found with subclinical hypothyroidism. Among patients hospitalized with AHF, overt hypothyroidism and low fT3 levels are independent predictors of all-cause mortality during the hospital stay.

The endocrinological component and signaling pathways associated to cardiac hypertrophy

Although myocardial growth corresponds to an adaptive response to maintain cardiac contractile function, the cardiac hypertrophy is a condition that occurs in many cardiovascular diseases and typically precedes the onset of heart failure. Different endocrine factors such as thyroid hormones, insulin, insulin-like growth factor 1 (IGF-1), angiotensin II (Ang II), endothelin (ET-1), catecholamines, estrogen, among others represent important stimuli to cardiomyocyte hypertrophy. Thus, numerous endocrine disorders manifested as changes in the local environment or multiple organ systems are especially important in the context of progression from cardiac hypertrophy to heart failure. Based on that information, this review summarizes experimental findings regarding the influence of such hormones upon signalling pathways associated with cardiac hypertrophy. Understanding mechanisms through which hormones differentially regulate cardiac hypertrophy could open ways to obtain therapeutic approaches that contribute to prevent or delay the onset of heart failure related to endocrine diseases.

Tripartite motif 10 regulates cardiac hypertrophy by targeting the PTEN/AKT pathway

The pathogenesis of cardiac hypertrophy is tightly associated with activation of intracellular hypertrophic signalling pathways, which leads to the synthesis of various proteins. Tripartite motif 10 (TRIM10) is an E3 ligase with important functions in protein quality control. However, its role in cardiac hypertrophy was unclear. In this study, neonatal rat cardiomyocytes (NRCMs) and TRIM10-knockout mice were subjected to phenylephrine (PE) stimulation or transverse aortic constriction (TAC) to induce cardiac hypertrophy in vitro and in vivo, respectively. Trim10 expression was significantly increased in hypertrophied murine hearts and PE-stimulated NRCMs. Knockdown of TRIM10 in NRCMs alleviated PE-induced changes in the size of cardiomyocytes and hypertrophy gene expression, whereas TRIM10 overexpression aggravated these changes. These results were further verified in TRIM10-knockout mice. Mechanistically, we found that TRIM10 knockout or knockdown decreased AKT phosphorylation. Furthermore, we found that TRIM10 knockout or knockdown increased ubiquitination of phosphatase and tensin homolog (PTEN), which negatively regulated AKT activation. The results of this study reveal the involvement of TRIM10 in pathological cardiac hypertrophy, which may occur by prompting of PTEN ubiquitination and subsequent activation of AKT signalling. Therefore, TRIM10 may be a promising target for treatment of cardiac hypertrophy.

Effect of endostatin overexpression on angiotensin II-induced cardiac hypertrophy in rats

Background:

Endostatin, a biologically active fragment of collagen XVIII, has been observed in patients with ischemic heart disease. The aim of the present study was to investigate whether endostatin overexpression could attenuate cardiac hypertrophy by inhibiting the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) signaling pathway.

Methods:

This study was examined in vivo in rats and in vitro in primary neonatal rat cardiomyocytes treated with angiotensin (Ang) II to model cardiac hypertrophy. Twenty-four male Sprague-Dawley rats were randomized into adenovirus (Ad)-green fluorescent protein, Ang II, Ad-endostatin, and Ang II + Ad-endostatin groups (n = 6 in each group). Four weeks later, all the rats were weighed and sacrificed after transthoracic echocardiography. Cardiac function was evaluated by transthoracic echocardiography, cardiomyocyte size was evaluated by hematoxylin-eosin staining. Levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were evaluated by quantitative reverse-transcription polymerase chain reaction or Western blotting, PKA level was evaluated by Western blotting, and cAMP level was evaluated by enzyme-linked immunosorbent assay. Statistical significance among multiple groups was evaluated by one-way analysis of variance.

Results:

Endostatin overexpression reduced the increases in left ventricle (LV) mass (P = 0.0063), LV mass/body weight (BW) (P = 0.0013), interventricular septal thickness (IVS) in diastole (P = 0.0013), IVS in systole (P = 0.0056), left ventricular posterior wall thickness (LVPW) in diastole (P = 0.0291), LVPW in systole (P = 0.0080), heart weight (HW) (P = 0.0138), HW/BW (P = 0.0001), and HW/tibial length (P = 0.0372) in Ang II-treated rats. In addition, endostatin overexpression reduced cardiomyocyte cross-sectional area expansion, and reduced the levels of ANP and BNP in Ang II-treated rats (P = 0.0251 and 0.0477 for messenger RNA [mRNA]), and primary neonatal rat cardiomyocytes (P = 0.0188 and P = 0.0024 for mRNA; P = 0.0023 and 0.0013 for protein, respectively). Additionally, endostatin overexpression reduced the increase of cAMP (P = 0.0054) and PKA (P = 0.0328) levels in cardiomyocytes treated with Ang II. Treatment with cAMP reversed the effects of endostatin overexpression on ANP (P = 0.0263) and BNP (P = 0.0322) levels in cardiomyocytes induced by Ang II.

Conclusion:

Endostatin overexpression could alleviate cardiac hypertrophy by inhibiting the cAMP-PKA signaling pathway.

Impact of hyperthyroidism on cardiac hypertrophy

The cardiac growth process (hypertrophy) is a crucial phenomenon conserved across a wide array of species and it is critically involved in maintenance of cardiac homeostasis. This process enables organism adaptation to changes of systemic demand and occurs due to a plethora of responses, depending on the type of signal or stimuli received. The growth of cardiac muscle cells in response to environmental conditions depends on the type, strength and duration of stimuli, and results in adaptive physiologic response or non-adaptive pathologic response. Thyroid hormones (TH) have a direct effect on the heart and induce a cardiac hypertrophy phenotype, which may evolve to heart failure. In this review, we summarize the literature on TH function in heart presenting results from experimental studies. We discuss the mechanistic aspects of TH associated with cardiac myocyte hypertrophy, increased cardiac myocyte contractility and electrical remodeling as well as the signaling pathways associated. In addition to classical crosstalk with the Sympathetic Nervous System (SNS), emerging work points to the new endocrine interaction between TH and Renin-Angiotensin System (RAS) is also explored. Given the inflammatory potential of the angiotensin II peptide, this new interaction may open the door for new therapeutic approaches that target key mechanisms responsible for TH-induced cardiac hypertrophy.

Sphingolipid Mediators of Myocardial Pathology

Cardiomyopathy is the leading cause of mortality worldwide. While the causes of cardiomyopathy continue to be elucidated, current evidence suggests that aberrant bioactive lipid signaling plays a crucial role as a component of cardiac pathophysiology. Sphingolipids have been implicated in the pathophysiology of cardiovascular disease, as they regulate numerous cellular processes that occur in primary and secondary cardiomyopathies. Experimental evidence gathered over the last few decades from both in vitro and in vivo model systems indicates that inhibitors of sphingolipid synthesis attenuate a variety of cardiomyopathic symptoms. In this review, we focus on various cardiomyopathies in which sphingolipids have been implicated and the potential therapeutic benefits that could be gained by targeting sphingolipid metabolism.