AMP-activated protein kinase α1-sensitive activation of AP-1 in cardiomyocytes

Cardiomyocyte-targeting exosomes from sulforaphane-treated fibroblasts affords cardioprotection in infarcted rats

BACKGROUND

Exosomes (EXOs), tiny extracellular vesicles that facilitate cell-cell communication, are being explored as a heart failure treatment, although the features of the cell source restrict their efficacy. Fibroblasts the most prevalent non-myocyte heart cells, release poor cardioprotective EXOs. A noninvasive method for manufacturing fibroblast-derived exosomes (F-EXOs) that target cardiomyocytes and slow cardiac remodeling is expected. As a cardioprotective isothiocyanate, sulforaphane (SFN)-induced F-EXOs (SFN-F-EXOs) should recapitulate its anti-remodeling properties.

METHODS

Exosomes from low-dose SFN (3 μM/7 days)-treated NIH/3T3 murine cells were examined for number, size, and protein composition. Fluorescence microscopy, RT-qPCR, and western blot assessed cell size, oxidative stress, AcH4 levels, hypertrophic gene expression, and caspase-3 activation in angiotensin II (AngII)-stressed HL-1 murine cardiomyocytes 12 h-treated with various EXOs. The uptake of fluorescently-labeled EXOs was also measured in cardiomyocytes. The cardiac function of infarcted male Wistar rats intramyocardially injected with different EXOs (1·10¹²) was examined by echocardiography. Left ventricular infarct size, hypertrophy, and capillary density were measured.

RESULTS

Sustained treatment of NIH/3T3 with non-toxic SFN concentration significantly enhances the release of CD81 + EXOs rich in TSG101 (Tumor susceptibility gene 101) and Hsp70 (Heat Shock Protein 70), and containing maspin, an endogenous histone deacetylase 1 inhibitor. SFN-F-EXOs counteract angiotensin II (AngII)-induced hypertrophy and apoptosis in murine HL-1 cardiomyocytes enhancing SERCA2a (sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a) levels more effectively than F-EXOs. In stressed cardiomyocytes, SFN-F-EXOs boost AcH4 levels by 30% (p < 0.05) and significantly reduce oxidative stress more than F-EXOs. Fluorescence microscopy showed that mouse cardiomyocytes take in SFN-F-EXOs ~ threefold more than F-EXOs. Compared to vehicle-injected infarcted hearts, SFN-F-EXOs reduce hypertrophy, scar size, and improve contractility.

CONCLUSIONS

Long-term low-dose SFN treatment of fibroblasts enhances the release of anti-remodeling cardiomyocyte-targeted F-EXOs, which effectively prevent the onset of HF. The proposed method opens a new avenue for large-scale production of cardioprotective exosomes for clinical application using allogeneic fibroblasts.

Human milk oligosaccharide 2'-fucosyllactose promotes melanin degradation via the autophagic AMPK-ULK1 signaling axis

There is still an unmet need for development of safer antimelanogenic or melanin-degrading agents for skin hyperpigmentation, induced by intrinsic or extrinsic factors including aging or ultraviolet irradiation. Owing to the relatively low cytotoxicity compared with other chemical materials, several studies have explored the role of 2'-fucosyllactose (2'-FL), the most dominant component of human milk oligosaccharides. Here, we showed that 2'-FL reduced melanin levels in both melanocytic cells and a human skin equivalent three-dimensional in vitro model. Regarding the cellular and molecular mechanism, 2'-FL induced LC3I conversion into LC3II, an autophagy activation marker, followed by the formation of LC3II⁺/PMEL⁺ autophagosomes. Comparative transcriptome analysis provided a comprehensive understanding for the up- and downstream cellular processes and signaling pathways of the AMPK–ULK1 signaling axis triggered by 2'-FL treatment. Moreover, 2'-FL activated the phosphorylation of AMPK at Thr172 and of ULK1 at Ser555, which were readily reversed in the presence of dorsomorphin, a specific AMPK inhibitor, with consequent reduction of the 2'-FL-mediated hypopigmentation. Taken together, these findings demonstrate that 2'-FL promotes melanin degradation by inducing autophagy through the AMPK–ULK1 axis. Hence, 2'-FL may represent a new natural melanin-degrading agent for hyperpigmentation.

Circulating uromodulin inhibits vascular calcification by interfering with pro-inflammatory cytokine signalling

AIMS

Uromodulin is produced exclusively in the kidney and secreted into both urine and blood. Serum levels of uromodulin are correlated with kidney function and reduced in chronic kidney disease (CKD) patients, but physiological functions of serum uromodulin are still elusive. This study investigated the role of uromodulin in medial vascular calcification, a key factor associated with cardiovascular events and mortality in CKD patients.

METHODS AND RESULTS

Experiments were performed in primary human (HAoSMCs) and mouse (MOVAS) aortic smooth muscle cells, cholecalciferol overload and subtotal nephrectomy mouse models and serum from CKD patients. In three independent cohorts of CKD patients, serum uromodulin concentrations were inversely correlated with serum calcification propensity. Uromodulin supplementation reduced phosphate-induced osteo-/chondrogenic transdifferentiation and calcification of HAoSMCs. In human serum, pro-inflammatory cytokines tumour necrosis factor α (TNFα) and interleukin-1β (IL-1β) co-immunoprecipitated with uromodulin. Uromodulin inhibited TNFα and IL-1β-induced osteo-/chondrogenic signalling and activation of the transcription factor nuclear factor kappa-light-chain-enhancer of activated β cells (NF-kB) as well as phosphate-induced NF-kB-dependent transcriptional activity in HAoSMCs. In vivo, adeno-associated virus (AAV)-mediated overexpression of uromodulin ameliorated vascular calcification in mice with cholecalciferol overload. Conversely, cholecalciferol overload-induced vascular calcification was aggravated in uromodulin-deficient mice. In contrast, uromodulin overexpression failed to reduce vascular calcification during renal failure in mice. Carbamylated uromodulin was detected in serum of CKD patients and uromodulin carbamylation inhibited its anti-calcific properties in vitro.

CONCLUSIONS

Uromodulin counteracts vascular osteo-/chondrogenic transdifferentiation and calcification, at least in part, through interference with cytokine-dependent pro-calcific signalling. In CKD, reduction and carbamylation of uromodulin may contribute to vascular pathology.

Impact of C-reactive protein on osteo-/chondrogenic transdifferentiation and calcification of vascular smooth muscle cells

Medial vascular calcification occurs during the aging process and is strongly accelerated by chronic kidney disease (CKD). Elevated C-reactive protein (CRP) levels are associated with vascular calcification, cardiovascular events and mortality in CKD patients. CRP is an important promoter of vascular inflammation. Inflammatory processes are critically involved in initiation and progression of vascular calcification. Thus, the present study explored a possible impact of CRP on vascular calcification. We found that CRP promoted osteo-/chondrogenic transdifferentiation and aggravated phosphate-induced osteo-/chondrogenic transdifferentiation and calcification of primary human aortic smooth muscle cells (HAoSMCs). These effects were paralleled by increased cellular oxidative stress and corresponding pro-calcific downstream-signaling. Antioxidants or p38 MAPK inhibition suppressed CRP-induced osteo-/chondrogenic signaling and mineralization. Furthermore, silencing of Fc fragment of IgG receptor IIa (FCGR2A) blunted the pro-calcific effects of CRP. Vascular CRP expression was increased in the klotho-hypomorphic mouse model of aging as well as in HAoSMCs during calcifying conditions. In conclusion, CRP augments osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells through mechanisms involving FCGR2A-dependent induction of oxidative stress. Thus, systemic inflammation may actively contribute to the progression of vascular calcification.

Systems biology identifies cytosolic PLA2 as a target in vascular calcification treatment

Although cardiovascular disease (CVD) is the leading cause of morbimortality worldwide, promising new drug candidates are lacking. We compared the arterial high-resolution proteome of patients with advanced versus early-stage CVD to predict, from a library of small bioactive molecules, drug candidates able to reverse this disease signature. Of the approximately 4000 identified proteins, 100 proteins were upregulated and 52 were downregulated in advanced-stage CVD. Arachidonyl trifluoromethyl ketone (AACOCF3), a cytosolic phospholipase A2 (cPLA2) inhibitor was predicted as the top drug able to reverse the advanced-stage CVD signature. Vascular cPLA2 expression was increased in patients with advanced-stage CVD. Treatment with AACOCF3 significantly reduced vascular calcification in a cholecalciferol-overload mouse model and inhibited osteoinductive signaling in vivo and in vitro in human aortic smooth muscle cells. In conclusion, using a systems biology approach, we have identified a potentially new compound that prevented typical vascular calcification in CVD in vivo. Apart from the clear effect of this approach in CVD, such strategy should also be able to generate novel drug candidates in other complex diseases.

Expression of the Alternative Oxidase Influences Jun N-Terminal Kinase Signaling and Cell Migration

Downregulation of Jun N-terminal kinase (JNK) signaling inhibits cell migration in diverse model systems. In Drosophila pupal development, attenuated JNK signaling in the thoracic dorsal epithelium leads to defective midline closure, resulting in cleft thorax. Here we report that concomitant expression of the Ciona intestinalis alternative oxidase (AOX) was able to compensate for JNK pathway downregulation, substantially correcting the cleft thorax phenotype. AOX expression also promoted wound-healing behavior and single-cell migration in immortalized mouse embryonic fibroblasts (iMEFs), counteracting the effect of JNK pathway inhibition. However, AOX was not able to rescue developmental phenotypes resulting from knockdown of the AP-1 transcription factor, the canonical target of JNK, nor its targets and had no effect on AP-1-dependent transcription. The migration of AOX-expressing iMEFs in the wound-healing assay was differentially stimulated by antimycin A, which redirects respiratory electron flow through AOX, altering the balance between mitochondrial ATP and heat production. Since other treatments affecting mitochondrial ATP did not stimulate wound healing, we propose increased mitochondrial heat production as the most likely primary mechanism of action of AOX in promoting cell migration in these various contexts.

AMP-Activated Protein Kinase (AMPK)-Dependent Regulation of Renal Transport

AMP-activated kinase (AMPK) is a serine/threonine kinase that is expressed in most cells and activated by a high cellular AMP/ATP ratio (indicating energy deficiency) or by Ca²⁺. In general, AMPK turns on energy-generating pathways (e.g., glucose uptake, glycolysis, fatty acid oxidation) and stops energy-consuming processes (e.g., lipogenesis, glycogenesis), thereby helping cells survive low energy states. The functional element of the kidney, the nephron, consists of the glomerulus, where the primary urine is filtered, and the proximal tubule, Henle's loop, the distal tubule, and the collecting duct. In the tubular system of the kidney, the composition of primary urine is modified by the reabsorption and secretion of ions and molecules to yield final excreted urine. The underlying membrane transport processes are mainly energy-consuming (active transport) and in some cases passive. Since active transport accounts for a large part of the cell's ATP demands, it is an important target for AMPK. Here, we review the AMPK-dependent regulation of membrane transport along nephron segments and discuss physiological and pathophysiological implications.

Role of PKB/SGK-dependent phosphorylation of GSK-3α/β in vascular calcification during cholecalciferol overload in mice

Medial vascular calcification is a highly regulated process involving osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells. Both, protein kinase B (PKB) and serum- and glucocorticoid-inducible kinase 1 (SGK1) are involved in the intracellular signaling of vascular calcification and both phosphorylate and inactivate glycogen synthase kinase 3 (GSK-3). The present study explored whether PKB/SGK-dependent phosphorylation of GSK-3α/β is involved in vascular calcification. Experiments were performed in Gsk-3α/β double knockin mice lacking functional PKB/SGK phosphorylation sites (gsk-3^KI) and corresponding wild-type mice (gsk-3^WT) following high-dosed cholecalciferol treatment as well as ex vivo in aortic ring explants from gsk-3^KI and gsk-3^WT mice treated without and with phosphate. In gsk-3^WT mice, high-dosed cholecalciferol induced vascular calcification and aortic osteo-/chondrogenic signaling, shown by increased expression of osteogenic markers Msx2, Cbfa1 and tissue-nonspecific alkaline phosphatase (Alpl). All these effects were suppressed in aortic tissue from gsk-3^KI mice. Cholecalciferol decreased aortic Gsk-3α/β phosphorylation (Ser^21/9) in gsk-3^WT mice, while no phosphorylation was observed in gsk-3^KI mice. Moreover, the mRNA expression of type III sodium-dependent phosphate transporter (Pit1) and plasminogen activator inhibitor 1 (Pai1) was increased following cholecalciferol treatment in aortic tissue of gsk-3^WT mice, effects again blunted in gsk-3^KI mice. In addition, phosphate treatment induced mineral deposition and osteogenic markers expression in aortic ring explants from gsk-3^WT mice, effects reduced in aortic ring explants from gsk-3^KI mice. In conclusion, vascular PKB/SGK-dependent phosphorylation of GSK-3α/β contributes to the osteoinductive signaling leading to vascular calcification.

Zinc Inhibits Phosphate-Induced Vascular Calcification through TNFAIP3-Mediated Suppression of NF-κB

Background The high cardiovascular morbidity and mortality of patients with CKD may result in large part from medial vascular calcification, a process promoted by hyperphosphatemia and involving osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). Reduced serum zinc levels have frequently been observed in patients with CKD, but the functional relevance of this remains unclear.Methods We performed experiments in primary human aortic VSMCs; klotho-hypomorphic (kl/kl), subtotal nephrectomy, and cholecalciferol-overload mouse calcification models; and serum samples from patients with CKD.Results In cultured VSMCs, treatment with zinc sulfate (ZnSO₄) blunted phosphate-induced calcification, osteo-/chondrogenic signaling, and NF-κB activation. ZnSO₄ increased the abundance of zinc-finger protein TNF-α-induced protein 3 (TNFAIP3, also known as A20), a suppressor of the NF-κB pathway, by zinc-sensing receptor ZnR/GPR39-dependent upregulation of TNFAIP3 gene expression. Silencing of TNFAIP3 in VSMCs blunted the anticalcific effects of ZnSO₄ under high phosphate conditions. kl/kl mice showed reduced plasma zinc levels, and ZnSO₄ supplementation strongly blunted vascular calcification and aortic osteoinduction and upregulated aortic Tnfaip3 expression. ZnSO₄ ameliorated vascular calcification in mice with chronic renal failure and mice with cholecalciferol overload. In patients with CKD, serum zinc concentrations inversely correlated with serum calcification propensity. Finally, ZnSO₄ ameliorated the osteoinductive effects of uremic serum in VSMCs.Conclusions Zinc supplementation ameliorates phosphate-induced osteo-/chondrogenic transdifferentiation of VSMCs and vascular calcification through an active cellular mechanism resulting from GPR39-dependent induction of TNFAIP3 and subsequent suppression of the NF-κB pathway. Zinc supplementation may be a simple treatment to reduce the burden of vascular calcification in CKD.

AMPKα2 Protects Against the Development of Heart Failure by Enhancing Mitophagy via PINK1 Phosphorylation

RATIONALE

Mitochondrial dysfunction plays an important role in heart failure (HF). However, the molecular mechanisms regulating mitochondrial functions via selective mitochondrial autophagy (mitophagy) are poorly understood.

OBJECTIVE

We sought to determine the role of AMPK (AMP-activated protein kinase) in selective mitophagy during HF.

METHODS AND RESULTS

An isoform shift from AMPKα2 to AMPKα1 was observed in failing heart samples from HF patients and transverse aortic constriction-induced mice, accompanied by decreased mitophagy and mitochondrial function. The recombinant adeno-associated virus Serotype 9-mediated overexpression of AMPKα2 in mouse hearts prevented the development of transverse aortic constriction-induced chronic HF by increasing mitophagy and improving mitochondrial function. In contrast, AMPKα2^-/- mutant mice exhibited an exacerbation of the early progression of transverse aortic constriction-induced HF via decreases in cardiac mitophagy. In isolated adult mouse cardiomyocytes, AMPKα2 overexpression mechanistically rescued the impairment of mitophagy after phenylephrine stimulation for 24 hours. Genetic knockdown of AMPKα2, but not AMPKα1, by short interfering RNA suppressed the early phase (6 hours) of phenylephrine-induced compensatory increases in mitophagy. Furthermore, AMPKα2 specifically interacted with phosphorylated PINK1 (PTEN-induced putative kinase 1) at Ser495 after phenylephrine stimulation. Subsequently, phosphorylated PINK1 recruited the E3 ubiquitin ligase, Parkin, to depolarized mitochondria, and then enhanced the role of the PINK1-Parkin-SQSTM1 (sequestosome-1) pathway involved in cardiac mitophagy. This increase in cardiac mitophagy was accompanied by the elimination of damaged mitochondria, improvement in mitochondrial function, decrease in reactive oxygen species production, and apoptosis of cardiomyocytes. Finally, Ala mutation of PINK1 at Ser495 partially suppressed AMPKα2 overexpression-induced mitophagy and improvement of mitochondrial function in phenylephrine-stimulated cardiomyocytes, whereas Asp (phosphorylation mimic) mutation promoted mitophagy after phenylephrine stimulation.

CONCLUSIONS

In failing hearts, the dominant AMPKα isoform switched from AMPKα2 to AMPKα1, which accelerated HF. The results show that phosphorylation of Ser495 in PINK1 by AMPKα2 was essential for efficient mitophagy to prevent the progression of HF.

AMPK and cardiac remodelling

Cardiac remodelling is generally accepted as a critical process in the progression of heart failure. Myocyte hypertrophy, inflammatory responses and cardiac fibrosis are the main pathological changes associated with cardiac remodelling. AMP-activated protein kinase (AMPK) is known as an energy sensor and a regulator of cardiac metabolism under normal and ischaemic conditions. Additionally, AMPK has been shown to play roles in cardiac remodelling extending well beyond metabolic regulation. In this review, we discuss the currently defined roles of AMPK in cardiac remodelling and summarize the effects of AMPK on cardiac hypertrophy, inflammatory responses and fibrosis and the molecular mechanisms underlying these effects. In addition, we discuss some pharmacological activators of AMPK that are promising treatments for cardiac remodelling.

Angiotensin II affects inflammation mechanisms via AMPK-related signalling pathways in HL-1 atrial myocytes

Inflammation is a common cause of cardiac arrhythmia. Angiotensin ІІ (Ang ІІ) is a major contributing factor in the pathogenesis of cardiac inflammation; however, its underlying molecular mechanism remains unclear. Here, we explored the effect of Ang ІІ on inflammatory mechanisms and oxidative stress using HL-1 atrial myocytes. We showed that Ang ІІ activated c-Jun N-terminal kinase (JNK) phosphorylation and other inflammatory markers, such as transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α). Ang ІІ decreased oxygen consumption rate, which resulted in reactive oxygen species (ROS) generation and inhibition of ROS blocked Ang II-mediated JNK phosphorylation and TGF-β1 induction. Ang ІІ induced the expression of its specific receptor, AT1R. Ang II-induced intracellular calcium production associated with Ang ІІ-mediated signalling pathways. In addition, the generated ROS and calcium stimulated AMPK phosphorylation. Inhibiting AMPK blocked Ang II-mediated JNK and TGF-β signalling pathways. Ang ІІ concentration, along with TGF-β1 and tumor necrosis factor-α levels, was slightly increased in plasma of patients with atrial fibrillation. Taken together, these results suggest that Ang ІІ induces inflammation mechanisms through an AMPK-related signalling pathway. Our results provide new molecular targets for the development of therapeutics for inflammation-related conditions, such as atrial fibrillation.