Mechanical Stretch-Induced Protection against Myocardial Ischemia-Reperfusion Injury Involves AMP-Activated Protein Kinase

Deciphering the dynamics: Exploring the impact of mechanical forces on histone acetylation

Living cells navigate a complex landscape of mechanical cues that influence their behavior and fate, originating from both internal and external sources. At the molecular level, the translation of these physical stimuli into cellular responses relies on the intricate coordination of mechanosensors and transducers, ultimately impacting chromatin compaction and gene expression. Notably, epigenetic modifications on histone tails govern the accessibility of gene-regulatory sites, thereby regulating gene expression. Among these modifications, histone acetylation emerges as particularly responsive to the mechanical microenvironment, exerting significant control over cellular activities. However, the precise role of histone acetylation in mechanosensing and transduction remains elusive due to the complexity of the acetylation network. To address this gap, our aim is to systematically explore the key regulators of histone acetylation and their multifaceted roles in response to biomechanical stimuli. In this review, we initially introduce the ubiquitous force experienced by cells and then explore the dynamic alterations in histone acetylation and its associated co-factors, including HDACs, HATs, and acetyl-CoA, in response to these biomechanical cues. Furthermore, we delve into the intricate interactions between histone acetylation and mechanosensors/mechanotransducers, offering a comprehensive analysis. Ultimately, this review aims to provide a holistic understanding of the nuanced interplay between histone acetylation and mechanical forces within an academic framework.

Oxidative stress and related metabolic alterations are induced in ex situ perfusion of donated hearts regardless of the ventricular load or leukocyte depletion

We sought to determine the role of donor blood circulating leukocytes in mediating oxidative stress and inflammation during normothermic ex situ heart perfusion (ESHP). Normothermic ESHP allows preservation of donated heart in a perfused, dynamic state, preventing ischemia. However, the cardiac function declines during ESHP, limiting the potential of this method for improvement of the outcomes of transplantation and expanding the donor pool. Extracorporeal circulation-related oxidative stress plays a critical role in the functional decline of the donor heart. Hearts from domestic pigs were perfused in working mode (WM, whole blood-based or leukocyte-depleted blood-based perfusate) or nonworking mode. Markers of oxidative stress and responsive glucose anabolic pathways were induced in the myocardium regardless of left ventricular load. Myocardial function during ESHP as well as cardioprotective mechanisms were preserved better in WM. Leukocyte-depleted perfusate did not attenuate tissue oxidative stress or perfusate proinflammatory cytokines and did not improve functional preservation. Although ESHP is associated with ongoing oxidative stress and metabolic alteration in the myocardium, preserved cardioprotective mechanisms in WM may exert beneficial effects. Leukocyte depletion of the perfusate may not attenuate inflammation and oxidative stress effectively or improve the functional preservation of the heart during ESHP.

Immunity and Stress Responses Are Induced During Ex Situ Heart Perfusion

BACKGROUND

Ex situ heart perfusion (ESHP) preserves the donated heart in a perfused, beating condition preventing cold storage-related ischemia and provides a platform to evaluate myocardial viability during preservation. However, myocardial function declines gradually during ESHP. Extracorporeal circulation systems are associated with the induction of systemic inflammatory and stress responses. Our aim was to evaluate the incidence of inflammation and induction of endoplasmic reticulum stress responses during an extended period of ESHP.

METHODS

Cardiac function, myocardial tissue injury, markers of inflammation, oxidative stress, and endoplasmic reticulum stress were assessed in healthy pig hearts, perfused for 12 hours either in nonworking mode (non-WM=7) or working mode (WM, n=6).

RESULTS

Cardiac function declined during ESHP but was significantly better preserved in the hearts perfused in WM (median 11-hour cardiac index/1-hour cardiac index: WM=27% versus non-WM=9.5%, P=0.022). Myocardial markers of endoplasmic reticulum stress were expressed higher in ESHP hearts compared with in vivo samples. The proinflammatory cytokines and oxidized low-density lipoprotein significantly increased in the perfusate throughout the perfusion in both perfusion groups. The left ventricular expression of the cytokines and malondialdehyde was induced in non-WM, whereas it was not different between WM and in vivo.

CONCLUSIONS

Myocardial function declines during ESHP regardless of perfusion mode. However, ESHP in WM may lead to superior preservation of myocardial function and viability. Both inflammation and endoplasmic reticulum stress responses are significantly induced during ESHP and may contribute to the myocardial functional decline, representing a potential therapeutic target to improve the clinical donor heart preservation.

Novel Potentials of the DPP-4 Inhibitor Sitagliptin against Ischemia-Reperfusion (I/R) Injury in Rat Ex-Vivo Heart Model

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a class of oral anti-diabetic drugs, implicated in pleiotropic secondary cardioprotective effects. The aim of the study was to unveil the unknown and possible cardioprotective targets that can be exerted by sitagliptin (Sitg) against ischemia-reperfusion (I/R) injury. Male wistar rats received 2 weeks’ Sitg oral treatment of different doses (25, 50, 100, and 150 mg/kg/day), or saline as a Control. Hearts were then isolated and subjected to two different I/R injury protocols: 10 min perfusion, 45 min regional ischemia, and 120 min reperfusion for infarct size (IS) measurement, or: 10 min perfusion, 45 min regional ischemia and 10 min reperfusion for biochemical analysis: nitric oxide synthases (NOSs) and DPP-4 activity, glucagon-like peptide-1 (GLP-1), Calcium, transient receptor potential vanilloid (TRPV)-1 and calcitonin gene-related peptide (CGRP) levels, transient receptor potential canonical (TRPC)-1 and e-NOS protein expression. NOS inhibitor (l-NAME) and TRPV-1 inhibitor (Capsazepine) were utilized to confirm the implication of both signaling mechanisms in DPP-4 inhibition-induced at the level of IS. Findings show that Sitg (50 mg) resulted in significant decrease in IS and DPP-4 activity, and significant increase in GLP-1, NOS activity, e-NOS expression, TRPV-1 level and TRPC-1 expression, compared to controls. Results of CGRP are in line with TRPV-1, as a downstream regulatory effect. NOS system and transient receptor potential (TRP) channels can contribute to DPP-4 inhibition-mediated cardioprotection against I/R injury using Sitagliptin.

Transposable elements, placental development, and oocyte activation: Cellular stress and AMPK links jumping genes with the creation of human life

Transposable elements (TEs), also known as "jumping genes", are DNA sequences first described by Nobel laureate Barbara McClintock that comprise nearly half of the human genome and are able to transpose or move from one genomic location to another. As McClintock also noted that a genome "shock" or stress may induce TE activation and transposition, accumulating evidence suggests that cellular stress (e.g. mediated by increases in intracellular reactive oxygen species [ROS] and calcium [Ca2+], etc.) induces TE mobilization in several model organisms and L1s (a member of the retrotransposon class of TEs) are active and capable of retrotransposition in human oocytes, human sperm, and in human neural progenitor cells. Cellular stress also plays a critical role in human placental development, with cytotrophoblast (CTB) differentiation leading to the formation of the syncytiotrophoblast (STB), a cellular layer that facilitates nutrient and gas exchange between the mother and the fetus. Syncytin-1, a protein that promotes fusion of CTB cells and is necessary for STB formation, and its receptor is found in human sperm and human oocytes, respectively, and increases in ROS and Ca2+ promote trophoblast differentiation and syncytin-1 expression. Cellular stress is also essential in promoting human oocyte maturation and activation which, similar to TE mobilization, can be induced by compounds that increase intracellular Ca2+ and ROS levels. AMPK is a master metabolic regulator activated by increases in ROS, Ca2+, and/or an AMP(ADP)/ATP ratio increase, etc. as well as compounds that induce L1 mobilization in human cells. AMPK knockdown inhibits trophoblast differentiation and AMPK-activating compounds that promote L1 mobility also enhance trophoblast differentiation. Cellular stressors that induce TE mobilization (e.g. heat shock) also promote oocyte maturation in an AMPK-dependent manner and the antibiotic ionomycin activates AMPK, promotes TE activation, and induces human oocyte activation, producing normal, healthy children. Metformin promotes AMPK-dependent telomerase activation (critical for telomere maintenance) and induces activation of the endonuclease RAG1 (promotes DNA cleavage and transposition) via AMPK. Both RAG1 and telomerase are derived from TEs. It is our hypothesis that cellular stress and AMPK links TE activation and transposition with placental development and oocyte activation, facilitating both human genome evolution and the creation of all human life. We also propose the novel observation that various cellular stress-inducing compounds (e.g. metformin, resveratrol, etc.) may facilitate beneficial TE activation and transposition and enhance fertilization and embryological development through a common mechanism of AMPK activation.

AMPK-dependent nitric oxide release provides contractile support during hyperosmotic stress

In different pathological situations, cardiac cells undergo hyperosmotic stress (HS) and cell shrinkage. This change in cellular volume has been associated with contractile dysfunction and cell death. Given that nitric oxide (NO) is a well-recognized modulator of cardiac contractility and cell survival, we evaluated whether HS increases NO production and its impact on the negative inotropic effect observed during this type of stress. Superfusing cardiac myocytes with a hypertonic solution (HS: 440 mOsm) decreased cell volume and increased NO-sensitive DAF-FM fluorescence compared with myocytes superfused with an isotonic solution (IS: 309 mOsm). When cells were exposed to HS in addition to different inhibitors: L-NAME (NO synthase inhibitor), nitroguanidine (nNOS inhibitor), and Wortmannin (eNOS inhibitor) cell shrinkage occurred in the absence of NO release, suggesting that HS activates nNOS and eNOS. Consistently, western blot analysis demonstrated that maintaining cardiac myocytes in HS promotes phosphorylation and thus, activation of nNOS and eNOS compared to myocytes maintained in IS. HS-induced nNOS and eNOS activation and NO production were also prevented by AMPK inhibition with Dorsomorphin (DORSO). In addition, the HS-induced negative inotropic effect was exacerbated in the presence of either L-NAME, DORSO, ODQ (guanylate cyclase inhibitor), or KT5823 (PKG inhibitor), suggesting that NO provides contractile support via a cGMP/PKG-dependent mechanism. Our findings suggest a novel mechanism of AMPK-dependent NO release in cardiac myocytes with putative pathophysiological relevance determined, at least in part, by its capability to reduce the extent of contractile dysfunction associated with hyperosmotic stress.

Hearts lacking plasma membrane KATP channels display changes in basal aerobic metabolic substrate preference and AMPK activity

Cardiac ATP-sensitive K+ (KATP) channels couple changes in cellular metabolism to membrane excitability and are activated during metabolic stress, although under basal aerobic conditions, KATP channels are thought to be predominately closed. Despite intense research into the roles of KATP channels during metabolic stress, their contribution to aerobic basal cardiac metabolism has not been previously investigated. Hearts from Kir6.2+/+ and Kir6.2−/− mice were perfused in working mode, and rates of glycolysis, fatty acid oxidation, and glucose oxidation were measured. Changes in activation/expression of proteins regulating metabolism were probed by Western blot analysis. Despite cardiac mechanical function and metabolic efficiency being similar in both groups, hearts from Kir6.2−/− mice displayed an approximately twofold increase in fatty acid oxidation and a 0.45-fold reduction in glycolytic rates but similar glucose oxidation rates compared with hearts from Kir6.2+/+ mice. Kir6.2−/− hearts also possessed elevated levels of activated AMP-activated protein kinase (AMPK), higher glycogen content, and reduced mitochondrial density. Moreover, activation of AMPK by isoproterenol or diazoxide was significantly blunted in Kir6.2−/− hearts. These data indicate that KATP channel ablation alters aerobic basal cardiac metabolism. The observed increase in fatty acid oxidation and decreased glycolysis before any metabolic insult may contribute to the poor recovery observed in Kir6.2−/− hearts in response to exercise or ischemia-reperfusion injury. Therefore, KATP channels may play an important role in the regulation of cardiac metabolism through AMPK signaling.

NEW & NOTEWORTHY In this study, we show that genetic ablation of plasma membrane ATP-sensitive K+ channels results in pronounced changes in cardiac metabolic substrate preference and AMP-activated protein kinase activity. These results suggest that ATP-sensitive K+ channels may play a novel role in regulating metabolism in addition to their well-documented effects on ionic homeostasis during periods of stress.

Adenosine monophosphate-activated protein kinase activation and suppression of inflammatory response by cell stretching in rabbit synovial fibroblasts

Joint mobilization is known to be beneficial in osteoarthritis (OA) patients. This study aimed to investigate the effect of stretching on adenosine monophosphate-activated protein kinase (AMPK) activity and its role in modulating inflammation in rabbit synovial fibroblasts. Uniaxial stretching of isolated rabbit synovial fibroblasts for ten min was performed. Stretching-induced AMPK activation, its underlying mechanism, and its anti-inflammatory effect were investigated using Western blot. Static stretching at 20 % of initial length resulted in AMPK activation characterized by expression of phosphorylated AMPK and phosphorylated acetyl-Co A carboxylase. AMP-activated protein kinase phosphorylation peaked 1 h after stretching and declined toward resting activity. Using cell viability assays, static stretching did not appear to cause cellular damage. Activation of AMPK involves Ca²⁺ influx via a mechanosensitive L-type Ca²⁺ channel, which subsequently raises intracellular Ca²⁺ and activates AMPK via Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ). Interestingly, stretching suppressed TNFα-induced expression of COX-2, iNOS, and phosphorylated NF-κB. These effects were prevented by pretreatment with compound C, an AMPK inhibitor. These results suggest that mechanical stretching suppressed inflammatory responses in synovial fibroblasts via a L-type Ca²⁺-channel-CaMKKβ-AMPK-dependent pathway which may underlie joint mobilization's ability to alleviate OA symptoms.

Gadolinium and ruthenium red attenuate remote hind limb preconditioning-induced cardioprotection: possible role of TRP and especially TRPV channels

Remote ischemic preconditioning is a well reported therapeutic strategy that induces cardioprotective effects but the underlying intracellular mechanisms have not been widely explored. The current study was designed to investigate the involvement of TRP and especially TRPV channels in remote hind limb preconditioning-induced cardioprotection. Remote hind limb preconditioning stimulus (4 alternate cycles of inflation and deflation of 5 min each) was delivered using a blood pressure cuff tied on the hind limb of the anesthetized rat. Using Langendorff's system, the heart was perfused and subjected to 30-min ischemia and 120-min reperfusion. The myocardial injury was assessed by measuring infarct size, lactate dehydrogenase (LDH), creatine kinase (CK), LVDP, +dp/dtmax, -dp/dtmin, heart rate, and coronary flow rate. Gadolinium, TRP blocker, and ruthenium red, TRPV channel blocker, were employed as pharmacological tools. Remote hind limb preconditioning significantly reduced the infarct size, LDH release, CK release and improved coronary flow rate, hemodynamic parameters including LVDP, +dp/dtmax, -dp/dtmin, and heart rate. However, gadolinium (7.5 and 15 mg kg(-1)) and ruthenium red (4 and 8 mg kg(-1)) significantly attenuated the cardioprotective effects suggesting the involvement of TRP especially TRPV channels in mediating remote hind limb preconditioning-induced cardioprotection. Remote hind limb preconditioning stimulus possibly activates TRPV channels on the heart or sensory nerve fibers innervating the heart to induce cardioprotective effects. Alternatively, remote hind limb preconditioning stimulus may also activate the mechanosensitive TRP and especially TRPV channels on the sensory nerve fibers innervating the skeletal muscles to trigger cardioprotective neurogenic signaling cascade. The cardioprotective effects of remote hind limb preconditioning may be mediated via activation of mechanosensitive TRP and especially TRPV channels.

Pretreatment with low-dose gadolinium chloride attenuates myocardial ischemia/reperfusion injury in rats

AIM

We have shown that low-dose gadolinium chloride (GdCl3) abolishes arachidonic acid (AA)-induced increase of cytoplasmic Ca(2+), which is known to play a crucial role in myocardial ischemia/reperfusion (I/R) injury. The present study sought to determine whether low-dose GdCl3 pretreatment protected rat myocardium against I/R injury in vitro and in vivo.

METHODS

Cultured neonatal rat ventricular myocytes (NRVMs) were treated with GdCl3 or nifedipine, followed by exposure to anoxia/reoxygenation (A/R). Cell apoptosis was detected; the levels of related signaling molecules were assessed. SD rats were intravenously injected with GdCl3 or nifedipine. Thirty min after the administration the rats were subjected to LAD coronary artery ligation followed by reperfusion. Infarction size, the release of serum myocardial injury markers and AA were measured; cell apoptosis and related molecules were assessed.

RESULTS

In A/R-treated NRVMs, pretreatment with GdCl3 (2.5, 5, 10 μmol/L) dose-dependently inhibited caspase-3 activation, death receptor-related molecules DR5/Fas/FADD/caspase-8 expression, cytochrome c release, AA release and sustained cytoplasmic Ca(2+) increases induced by exogenous AA. In I/R-treated rats, pre-administration of GdCl3 (10 mg/kg) significantly reduced the infarct size, and the serum levels of CK-MB, cardiac troponin-I, LDH and AA. Pre-administration of GdCl3 also significantly decreased the number of apoptotic cells, caspase-3 activity, death receptor-related molecules (DR5/Fas/FADD) expression and cytochrome c release in heart tissues. The positive control drug nifedipine produced comparable cardioprotective effects in vitro and in vivo.

CONCLUSION

Pretreatment with low-dose GdCl3 significantly attenuates I/R-induced myocardial apoptosis in rats by suppressing activation of both death receptor and mitochondria-mediated pathways.

Dystrophin-glycoprotein complex regulates muscle nitric oxide production through mechanoregulation of AMPK signaling

Patients deficient in dystrophin, a protein that links the cytoskeleton to the extracellular matrix via the dystrophin-glycoprotein complex (DGC), exhibit muscular dystrophy, cardiomyopathy, and impaired muscle nitric oxide (NO) production. We used live-cell NO imaging and in vitro cyclic stretch of isolated adult mouse cardiomyocytes as a model system to investigate if and how the DGC directly regulates the mechanical activation of muscle NO signaling. Acute activation of NO synthesis by mechanical stretch was impaired in dystrophin-deficient mdx cardiomyocytes, accompanied by loss of stretch-induced neuronal NO synthase (nNOS) S1412 phosphorylation. Intriguingly, stretch induced the acute activation of AMP-activated protein kinase (AMPK) in normal cardiomyocytes but not in mdx cardiomyocytes, and specific inhibition of AMPK was sufficient to attenuate mechanoactivation of NO production. Therefore, we tested whether direct pharmacologic activation of AMPK could bypass defective mechanical signaling to restore nNOS activity in dystrophin-deficient cardiomyocytes. Indeed, activation of AMPK with 5-aminoimidazole-4-carboxamide riboside or salicylate increased nNOS S1412 phosphorylation and was sufficient to enhance NO production in mdx cardiomyocytes. We conclude that the DGC promotes the mechanical activation of cardiac nNOS by acting as a mechanosensor to regulate AMPK activity, and that pharmacologic AMPK activation may be a suitable therapeutic strategy for restoring nNOS activity in dystrophin-deficient hearts and muscle.

Dystrophin-glycoprotein complex regulates muscle nitric oxide production through mechanoregulation of AMPK signaling

Patients deficient in dystrophin, a protein that links the cytoskeleton to the extracellular matrix via the dystrophin-glycoprotein complex (DGC), exhibit muscular dystrophy, cardiomyopathy, and impaired muscle nitric oxide (NO) production. We used live-cell NO imaging and in vitro cyclic stretch of isolated adult mouse cardiomyocytes as a model system to investigate if and how the DGC directly regulates the mechanical activation of muscle NO signaling. Acute activation of NO synthesis by mechanical stretch was impaired in dystrophin-deficient mdx cardiomyocytes, accompanied by loss of stretch-induced neuronal NO synthase (nNOS) S1412 phosphorylation. Intriguingly, stretch induced the acute activation of AMP-activated protein kinase (AMPK) in normal cardiomyocytes but not in mdx cardiomyocytes, and specific inhibition of AMPK was sufficient to attenuate mechanoactivation of NO production. Therefore, we tested whether direct pharmacologic activation of AMPK could bypass defective mechanical signaling to restore nNOS activity in dystrophin-deficient cardiomyocytes. Indeed, activation of AMPK with 5-aminoimidazole-4-carboxamide riboside or salicylate increased nNOS S1412 phosphorylation and was sufficient to enhance NO production in mdx cardiomyocytes. We conclude that the DGC promotes the mechanical activation of cardiac nNOS by acting as a mechanosensor to regulate AMPK activity, and that pharmacologic AMPK activation may be a suitable therapeutic strategy for restoring nNOS activity in dystrophin-deficient hearts and muscle.