Isoform-selective 5'-AMP-activated protein kinase-dependent preconditioning mechanisms to prevent postischemic leukocyte-endothelial cell adhesive interactions

Targeting Adrenergic Receptors in Metabolic Therapies for Heart Failure

The heart has a reduced capacity to generate sufficient energy when failing, resulting in an energy-starved condition with diminished functions. Studies have identified numerous changes in metabolic pathways in the failing heart that result in reduced oxidation of both glucose and fatty acid substrates, defects in mitochondrial functions and oxidative phosphorylation, and inefficient substrate utilization for the ATP that is produced. Recent early-phase clinical studies indicate that inhibitors of fatty acid oxidation and antioxidants that target the mitochondria may improve heart function during failure by increasing compensatory glucose oxidation. Adrenergic receptors (α₁ and β) are a key sympathetic nervous system regulator that controls cardiac function. β-AR blockers are an established treatment for heart failure and α_1A-AR agonists have potential therapeutic benefit. Besides regulating inotropy and chronotropy, α₁- and β-adrenergic receptors also regulate metabolic functions in the heart that underlie many cardiac benefits. This review will highlight recent studies that describe how adrenergic receptor-mediated metabolic pathways may be able to restore cardiac energetics to non-failing levels that may offer promising therapeutic strategies.

Dental follicle stem cells rescue the regenerative capacity of inflamed rat dental pulp through a paracrine pathway

Background

Pulpitis is a common dental disease characterized by sustained inflammation and impaired pulp self-repair. Mesenchymal stem cell-based minimally invasive vital pulp therapy (MSC-miVPT) is a potential treatment method, but its application is limited by the difficulty in acquiring MSCs. We recently revealed the immunomodulatory effects of rat dental follicle stem cells (rDFSCs) on acute lung injury. The present study focused on the paracrine effects of rDFSCs on the inflammation and regeneration of rat injured dental pulp to detect whether DFSCs are a potential candidate for MSC-miVPT.

Methods

Conditioned medium from rDFSCs (rDFSC-CM) was applied to lipopolysaccharide (LPS)-induced inflammatory rat dental pulp cells (rDPCs). The inflammation and regeneration of rDPCs were detected by RT-qPCR, Western blotting, immunofluorescence staining, Cell Counting Kit-8 (CCK-8) assay, flow cytometry, wound-healing assay, and Masson’s staining. The effects of rDFSC-CM on inflamed rat dental pulp were further evaluated by hematoxylin-eosin and immunohistochemical staining.

Results

rDFSC-CM downregulated the ERK1/2 and NF-κB signaling pathways, which resulted in suppression of the expression of IL-1β, IL-6, and TNF-α and promotion of the expression of IL-4 and TGF-β, and these findings lead to the attenuation of rDPC inflammation. rDFSC-CM enhanced the in vitro proliferation, migration, and odontogenic differentiation of inflammatory rDPCs and their in vivo ectopic dentinogenesis. Furthermore, rDFSC-CM inhibited inflammatory cell infiltration in rat pulpitis and triggered Runx2 expression in some of the odontoblast-like cells surrounding the injured site, and these effects were conducive to the repair of inflamed dental pulp.

Conclusions

rDFSC-CM exhibits therapeutic potential by rescuing the regeneration of the inflamed rat dental pulp through an immunomodulatory mechanism, indicating the application prospects of DFSCs in biological regenerative endodontics.

Artemisinin alleviates atherosclerotic lesion by reducing macrophage inflammation via regulation of AMPK/NF-κB/NLRP3 inflammasomes pathway

There is increasing evidence that atherosclerosis is the significant risk factor for cardiovascular diseases, which are the leading causes of morbidity and mortality worldwide. Artemisinin is a natural endoperoxides quiterpene lactone compound in Artemisia annua L with vasculoprotective effects. The primary aim of this study was to investigate whether artemisinin could be conferred an anti-atherosclerotic effect in high-fat diet (HFD)-fed ApoE^-/- mice and explore the possible mechanism. We found that treatment with artemisinin (50 and 100 mg/kg) effectively ameliorated atherosclerotic lesions, such as foam cell formation, hyperplasia and fibrosis in the aortic intima. Atherosclerotic mice treated with artemisinin showed reduced inflammation by up-regulating adenosine 5'-monophosphate (AMP) activated protein kinase (AMPK) activation and by down-regulating nuclear factor-κB (NF-κB) phosphorylation and nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome expression in the aortas. In addition, artemisinin was found to promote AMPK activity in macrophages and its anti-inflammatory effect was neutralised by AMPK silence using specific siRNA. In conclusion, we demonstrate that artemisinin may protect the aortas from atherosclerotic lesions by suppression of inflammatory reaction via AMPK/NF-κB/NLRP3 inflammasomes signalling in macrophages.

Ethanol's Effects on Transient Receptor Potential Channel Expression in Brain Microvascular Endothelial Cells

Ethanol (EtOH), the main ingredient in alcoholic beverages, is well known for its behavioral, physiological, and immunosuppressive effects. There is evidence that EtOH acts through protein targets to exert its physiological effects; however, the mechanisms underlying EtOH's effects on inflammatory processes, particularly at the blood-brain barrier (BBB), are still poorly understood. Transient receptor potential (TRP) channels, the vanguards of human sensory systems, are novel molecular receptors significantly affected by EtOH, and are heavily expressed in brain microvascular endothelial cells (BMVECs), one of the cellular constituents of the BBB. EtOH's actions on endothelial TRP channels could affect intracellular Ca²⁺ and Mg²⁺ dynamics, which mediate leukocyte adhesion to endothelial cells and endothelial permeability at the BBB, thus altering immune and inflammatory responses. We examined the basal expression profiles of all 29 known mammalian TRP channels in mouse BMVECs and determined both EtOH concentration- and time-dependent effects on TRP expression using a PCR array. We also generated an in vitro BBB model to examine the involvement of a chosen TRP channel, TRP melastatin 7 (TRPM7), in EtOH-mediated alteration of BBB permeability. With the exception of the akyrin subfamily, members of five TRP subfamilies were expressed in mouse BMVECs, and their expression levels were modulated by EtOH in a concentration-dependent manner. In the in vitro BBB model, TRPM7 antagonists further enhanced EtOH-mediated alteration of BBB permeability. Because of the diversity of TRP channels in BMVECs that regulate cellular processes, EtOH can affect Ca²⁺/Mg²⁺ signaling, immune responses, lysosomal functions as well as BBB integrity.

Exacerbated cardiac fibrosis induced by β-adrenergic activation in old mice due to decreased AMPK activity

Senescent hearts exhibit defective responses to β-adrenergic receptor (β-AR) over-activation upon stress, leading to more severe pathological cardiac remodelling. However, the underlying mechanisms remain unclear. Here, we investigated the role of adenosine monophosphate-activated protein kinase (AMPK) in protecting against ageing-associated cardiac remodelling in mice upon β-AR over-activation. 10-week-old (young) and 18-month-old (old) mice were subcutaneously injected with the β-AR agonist isoproterenol (ISO; 5 mg/kg). More extensive cardiac fibrosis was found in old mice upon ISO exposure than in young mice. Meanwhile, ISO treatment decreased AMPK activity and increased β-arrestin 1, but not β-arrestin 2, expression, and the effects of ISO on AMPK and β-arrestin 1 were greater in old mice than in young mice. Similarly, young AMPKα2-knockout (KO) mice showed more extensive cardiac fibrosis upon ISO exposure than that was observed in age-matched wild-type (WT) littermates. The extent of cardiac fibrosis in WT old mice was similar to that in young KO mice. Additionally, AMPK activities were decreased and β-arrestin 1 expression increased in KO mice. In contrast, the AMPK activator metformin decreased β-arrestin 1 expression and attenuated cardiac fibrosis in both young and old mice upon ISO exposure. In conclusion, more severe cardiac fibrosis is induced by ISO in old mice than in young mice. A decrease in AMPK activity, which further increases β-arrestin 1 expression, is the central mechanism underlying the ageing-related cardiac fibrosis induced by ISO. The AMPK activator metformin is a promising therapeutic agent for treating ageing-related cardiac remodelling upon β-AR over-activation.

AMP-Activated Protein Kinase: An Ubiquitous Signaling Pathway With Key Roles in the Cardiovascular System

The AMP-activated protein kinase (AMPK) is a key regulator of cellular and whole-body energy homeostasis, which acts to restore energy homoeostasis whenever cellular energy charge is depleted. Over the last 2 decades, it has become apparent that AMPK regulates several other cellular functions and has specific roles in cardiovascular tissues, acting to regulate cardiac metabolism and contractile function, as well as promoting anticontractile, anti-inflammatory, and antiatherogenic actions in blood vessels. In this review, we discuss the role of AMPK in the cardiovascular system, including the molecular basis of mutations in AMPK that alter cardiac physiology and the proposed mechanisms by which AMPK regulates vascular function under physiological and pathophysiological conditions.

Soluble guanylate cyclase activation during ischemic injury in mice protects against postischemic inflammation at the mitochondrial level

The aim was to determine whether treatment with BAY 60-2770, a selective activator of oxidized soluble guanylate cyclase (sGC), near the end of an ischemic event would prevent postischemic inflammation and mitochondrial dysfunction in wild-type (WT) and heme oxygenase-1 KO (HO-1(-/-)) mice. This protocol prevented increases in leukocyte rolling (LR) and adhesion (LA) to intestinal venules along with elevated TNFα and circulating neutrophil levels that accompany ischemia-reperfusion (I/R) in both animal models. We further hypothesized that a component of BAY 60-2770 treatment involves maintenance of mitochondrial membrane integrity during I/R. Measurements on isolated enterocytes of calcein fluorescence (mitochondrial permeability) and JC-1 fluorescence ratio (mitochondrial membrane potential) were reduced by I/R, indicating formation of mitochondrial permeability transition pores (mPTP). These effects were abrogated by BAY 60-2770 as well as cyclosporin A and SB-216763, which prevented mPTP opening and inhibited glycogen synthase kinase-3β (GSK-3β), respectively. Western blots of WT and HO-1(-/-) enterocytes indicated that GSK-3β phosphorylation on Ser(9) (inhibitory site) was reduced by half following I/R alone (increased GSK-3β activity) and increased by one-third (reduced GSK-3β activity) following BAY 60-2770. Other investigators have associated phosphorylation of the GSK-3β substrate cyclophilin D (pCyPD) with mPTP formation. We observed a 60% increase in pCyPD after I/R, whereas BAY 60-2770 treatment of sham and I/R groups reduced pCyPD by about 20%. In conclusion, selective activation of oxidized sGC of WT and HO-1(-/-) during ischemia protects against I/R-induced inflammation and preserves mucosal integrity in part by reducing pCyPD production and mPTP formation.

The new 4-O-methylhonokiol analog GS12021 inhibits inflammation and macrophage chemotaxis: role of AMP-activated protein kinase α activation

Preventing pathologic tissue inflammation is key to treating obesity-induced insulin resistance and type 2 diabetes. Previously, we synthesized a series of methylhonokiol analogs and reported that compounds with a carbamate structure had inhibitory function against cyclooxygenase-2 in a cell-free enzyme assay. However, whether these compounds could inhibit the expression of inflammatory genes in macrophages has not been investigated. Here, we found that a new 4-O-methylhonokiol analog, 3′,5-diallyl-4′-methoxy-[1,1′-biphenyl]-2-yl morpholine-4-carboxylate (GS12021) inhibited LPS- or TNFα-stimulated inflammation in macrophages and adipocytes, respectively. LPS-induced phosphorylation of nuclear factor-kappa B (NF-κB)/p65 was significantly decreased, whereas NF-κB luciferase activities were slightly inhibited, by GS12021 treatment in RAW 264.7 cells. Either mitogen-activated protein kinase phosphorylation or AP-1 luciferase activity was not altered by GS12021. GS12021 increased the phosphorylation of AMP-activated protein kinase (AMPK) α and the expression of sirtuin (SIRT) 1. Inhibition of mRNA expression of inflammatory genes by GS12021 was abolished in AMPKα1-knockdown cells, but not in SIRT1 knockout cells, demonstrating that GS12021 exerts anti-inflammatory effects through AMPKα activation. The transwell migration assay results showed that GS12021 treatment of macrophages prevented the cell migration promoted by incubation with conditioned medium obtained from adipocytes. GS12021 suppression of p65 phosphorylation and macrophage chemotaxis were preserved in AMPKα1-knockdown cells, indicating AMPK is not required for these functions of GS12021. Identification of this novel methylhonokiol analog could enable studies of the structure-activity relationship of this class of compounds and further evaluation of its in vivo potential for the treatment of insulin-resistant states and other chronic inflammatory diseases.

Ischemic preconditioning provides neuroprotection by induction of AMP-activated protein kinase-dependent autophagy in a rat model of ischemic stroke

Accumulating evidence suggests that ischemic preconditioning (IPC) increases cerebral tolerance to the subsequent ischemic exposure. However, the underlying mechanisms are still not fully understood. In the present study, we tested the hypothesis that AMP-activated protein kinase (AMPK)-dependent autophagy contributed to the neuroprotection of IPC in rats with permanent cerebral ischemia. Male Sprague-Dawley rats were pretreated with vehicle, compound C (an AMPK inhibitor), or 3-methyladenine (3-MA, an autophagy inhibitor) and then were subjected to IPC induced by a 10-min middle cerebral artery occlusion. Afterward, the brain AMPK activity and autophagy biomarkers were measured. At 24 h after IPC, permanent cerebral ischemia was induced in these rats, and infarct volume, neurological deficits as well as cell apoptosis were evaluated 24 h later. We demonstrated that IPC activated AMPK and induced autophagy in the brain, which was accompanied by a reduction of infract volume, neurological deficits, and cell apoptosis after cerebral ischemia. Meanwhile, the IPC-induced autophagy was inhibited by compound C while the neuroprotection of IPC was abolished by compound C or 3-MA. These findings suggest that AMPK-mediated autophagy contributes to the neuroprotection of IPC, highlighting AMPK as a therapeutic target for stroke prevention and treatment.

Macrophage migration inhibitory factor in myocardial ischaemia/reperfusion injury

Acute myocardial infarction (AMI) remains one of the leading causes of death in the developed world. There is emerging evidence that the cytokine macrophage migration inhibitory factor (MIF) is a crucial player in AMI. Cardioprotection by MIF is likely to be a multifactorial phenomenon mediated by receptor-mediated signalling processes, intracellular protein-protein interactions, and enzymatic redox regulation. Co-ordinating several pathways in the ischaemic heart, MIF contributes to receptor-mediated regulation of cardioprotective AMP-activated protein kinase signalling, inhibition of pro-apoptotic cascades, and the reduction of oxidative stress in the post-ischaemic heart. Moreover, the cardioprotective properties of MIF are modulated by S-nitros(yl)ation. These effects in the pathophysiology of myocardial ischaemia/reperfusion injury qualify MIF as a promising therapeutic target in the future. We here summarize the findings of experimental and clinical studies and emphasize the therapeutic potential of MIF in AMI.

Observation of mesenteric microcirculatory disturbance in rat by laser oblique scanning optical microscopy

Ischemia-reperfusion (I/R) injury model has been widely applied to the study of microcirculation disturbance. In this work, we used laser oblique scanning optical microscopy (LOSOM) to observe the microcirculation system in the mesentery of rat model. Utilizing a localized point-scanning detection scheme, high-contrast images of leukocytes were obtained. The extended detection capability facilitated both the automatic in vivo cell counting and the accurate measurement of the rolling velocity of leukocytes. Statistical analysis of the different treatment groups suggested that the distinction between I/R and sham groups with time lapse is significant.

Mitochondria and AMP-activated protein kinase-dependent mechanism of efferocytosis

Defective clearance of apoptotic cells is frequently associated with perpetuation of inflammatory conditions. Our results show a rapid activation of AMP-activated kinase (AMPK) in macrophages upon exposure to apoptotic cells or lysophosphatidylcholine, a specific phospholipid that is produced and released from dying cells. AMPK activation resulted from inhibition of mitochondrial oxygen consumption and ATP production and further depended on Ca(2+) mobilization and mitochondrial reactive oxygen species generation. Once activated, AMPK increased microtubule synthesis and chemokinesis and provided adaptation to energy demand during tracking and engulfment. Uptake of apoptotic cells was increased in lungs of mice that received lysophosphatidylcholine. Furthermore, inhibition of AMPK diminished clearance of apoptotic thymocytes in vitro and in dexamethasone-treated mice. Taken together, we conclude that the mitochondrial AMPK axis is a sensor and enhancer of tracking and removal of apoptotic cell, processes crucial to resolution of inflammatory conditions and a return to tissue homeostasis.

Preconditioning with soluble guanylate cyclase activation prevents postischemic inflammation and reduces nitrate tolerance in heme oxygenase-1 knockout mice

Previously we have shown that, unlike wild-type mice (WT), heme oxygenase-1 knockout (HO-1-/-) mice developed nitrate tolerance and were not protected from inflammation caused by ischemia-reperfusion (I/R) when preconditioned with a H2S donor. We hypothesized that stimulation (with BAY 41-2272) or activation (with BAY 60-2770) of soluble guanylate cyclase (sGC) would precondition HO-1-/- mice against an inflammatory effect of I/R and increase arterial nitrate responses. Intravital fluorescence microscopy was used to visualize leukocyte rolling and adhesion to postcapillary venules of the small intestine in anesthetized mice. Relaxation to ACh and BAY compounds was measured on superior mesenteric arteries isolated after I/R protocols. Preconditioning with either BAY compound 10 min (early phase) or 24 h (late phase) before I/R reduced postischemic leukocyte rolling and adhesion to sham control levels and increased superior mesenteric artery responses to ACh, sodium nitroprusside, and BAY 41-2272 in WT and HO-1-/- mice. Late-phase preconditioning with BAY 60-2770 was maintained in HO-1-/- and endothelial nitric oxide synthase knockout mice pretreated with an inhibitor (dl-propargylglycine) of enzymatically produced H2S. Pretreatment with BAY compounds also prevented the I/R increase in small intestinal TNF-α. We speculate that increasing sGC activity and related PKG acts downstream to H2S and disrupts signaling processes triggered by I/R in part by maintaining low cellular Ca²⁺. In addition, BAY preconditioning did not increase sGC levels, yet increased the response to agents that act on reduced heme-containing sGC. Collectively these actions would contribute to increased nitrate sensitivity and vascular function.

Exploiting the anti-inflammatory effects of AMP-activated protein kinase activation

INTRODUCTION

AMP-activated protein kinase (AMPK) is the downstream component of a serine/threonine protein kinase cascade involved in the regulation of metabolism. Many studies have also revealed that AMPK activation can exert significant anti-inflammatory and immunosuppressive effects in a variety of cell types and models of inflammatory/autoimmune disease. Because metformin, an AMPK activator that is a favored first-line therapeutic option for type 2 diabetes, may confer benefits in chronic inflammatory diseases and cancers independent of its ability to normalize blood glucose, there is now considerable interest in identifying and exploiting AMPK's anti-inflammatory effects.

AREAS COVERED

The authors provide a background to AMPK signaling and describe the pro-inflammatory signaling pathways and processes shown to be regulated by AMPK activation.

EXPERT OPINION

Identification of AMPK subunits responsible for specific anti-inflammatory effects, and a molecular understanding of the mechanisms involved, will be necessary to exploit AMPK pathway activation in acute and chronic inflammatory disease settings while minimizing adverse reactions due to deregulation of AMPK's wide-ranging effects on metabolism.

Moderate ethanol ingestion and cardiovascular protection: from epidemiologic associations to cellular mechanisms

While ethanol intake at high levels (3-4 or more drinks), either in acute (occasional binge drinking) or chronic (daily) settings, increases the risk for myocardial infarction and stroke, an inverse relationship between regular consumption of alcoholic beverages at light to moderate levels (1-2 drinks per day) and cardiovascular risk has been consistently noted in a large number of epidemiologic studies. Although initially attributed to polyphenolic antioxidants in red wine, subsequent work has established that the ethanol component contributes to the beneficial effects associated with moderate intake of alcoholic beverages regardless of type (red versus white wine, beer, spirits). Concerns have been raised with regard to interpretation of epidemiologic evidence for this association including heterogeneity of the reference groups examined in many studies, different lifestyles of moderate drinkers versus abstainers, and favorable risk profiles in moderate drinkers. However, better controlled epidemiologic studies and especially work conducted in animal models and cell culture systems have substantiated this association and clearly established a cause and effect relationship between alcohol consumption and reductions in tissue injury induced by ischemia/reperfusion (I/R), respectively. The aims of this review are to summarize the epidemiologic evidence supporting the effectiveness of ethanol ingestion in reducing the likelihood of adverse cardiovascular events such as myocardial infarction and ischemic stroke, even in patients with co-existing risk factors, to discuss the ideal quantities, drinking patterns, and types of alcoholic beverages that confer protective effects in the cardiovascular system, and to review the findings of recent experimental studies directed at uncovering the mechanisms that underlie the cardiovascular protective effects of antecedent ethanol ingestion. Mechanistic interrogation of the signaling pathways invoked by antecedent ethanol ingestion may point the way towards development of new therapeutic approaches that mimic the powerful protective effects of socially relevant alcohol intake to limit I/R injury, but minimize the negative psychosocial impact and pathologic outcomes that also accompany consumption of ethanol.

AMP-Activated Protein Kinase Suppresses Endothelial Cell Inflammation Through Phosphorylation of Transcriptional Coactivator p300

Objective—

Considerable evidence supports the early involvement of monocyte/macrophage recruitment to activated endothelial cells by leukocyte adhesion molecules during atherogenesis. AMP-activated protein kinase (AMPK) is highly expressed in vascular endothelial cells, but its impact on monocyte adhesion and the related mechanisms are not fully understood. The present study was designed to evaluate the impact of and gain mechanistic insight into the signaling coupling AMPK function to the antiinflammatory response.

Methods and Results—

5-Aminoimidazole-4-carboxamide-1-β- d -ribonucleotide (AICAR) treatment or overexpression of constitutively active AMPK markedly reduced human monocytic human acute monocytic leukemia cell line-1 cell adhesion and the expression of vascular cell adhesion molecule-1 in tumor necrosis factor-α–activated human aortic endothelial cells. Furthermore, AICAR or constitutively active AMPK overexpression strongly inhibited the histone acetyltransferase activity of the transcriptional coactivator p300 by phosphorylation of Ser89, which in turn decreased tumor necrosis factor-α-activated p300-mediated acetylation of nuclear factor-κB p65 on Lys221 and reduced the DNA binding activity of nuclear factor-κB by inhibiting its recruitment to its target gene promoters. AMPK phosphorylates the transcriptional coactivator p300 via the atypical protein kinase Cι/λ.

Conclusion—

Our findings demonstrate that transcriptional coactivator p300 phosphorylation at Ser89 by AMPK is critical for the therapeutic effect of AMPK and may be a potential target for pharmaceutical intervention in inflammatory diseases such as atherosclerosis.