Sodium 4-Phenylbutyrate Attenuates Myocardial Reperfusion Injury by Reducing the Unfolded Protein Response

Activation of adenosine A2B receptor alleviates myocardial ischemia-reperfusion injury by inhibiting endoplasmic reticulum stress and restoring autophagy flux

Myocardial ischemia-reperfusion injury (MIRI) poses a significant threat to patients with coronary heart disease. Adenosine A2A receptors have been known as a protective role in MIRI by regulating autophagy, so we assumed that activation of adenosine A2B receptor (A2BAR) might exert a similar effect during MIRI and underlying mechanism be related to proteostasis maintenance as well. In situ hearts were subjected to 30 min of ischemia and 120 min of reperfusion (IR), while invitro cardiomyocytes from neonatal rats experienced 6 h of oxygen-glucose deprivation followed by 12 h of reoxygenation (OGDR). Initially, we observed that post-ischemia-reperfusion induced autophagy flux blockade and ERS both in vivo and in vitro, evident through the increased expression of p62, LC3II, and BIP, which indicated the deteriorated proteostasis. We used a selective A2BAR agonist, Bay 60-6583, to explore the positive effects of A2BAR on cardiomyocytes and found that A2BAR activation rescued damaged cardiac function and morphological changes in the IR group and improved frail cell viability in the OGDR group. The A2BAR agonist also alleviated the blockage of autophagic flux, coupled with augmented ERS in the IR/OGDR group, which was reassured by using an autophagy inhibitor chloroquine (CQ) and ERS inhibitor (4-PBA) in vitro. Additionally, considering cAMP/PKA as a well-known downstream effector of A2BAR, we utilized H89, a selective PKA inhibitor. We observed that the positive efficacy of Bay 60-6583 was inhibited by H89. Collectively, our findings demonstrate that the A2BAR/cAMP/PKA signaling pathway exerts a protective role in MIRI by mitigating impaired autophagic flux and excessive ERS.

Traditional Therapeutics and Potential Epidrugs for CVD: Why Not Both?

Cardiovascular disease (CVD) is the leading cause of death worldwide. In addition to the high mortality rate, people suffering from CVD often endure difficulties with physical activities and productivity that significantly affect their quality of life. The high prevalence of debilitating risk factors such as obesity, type 2 diabetes mellitus, smoking, hypertension, and hyperlipidemia only predicts a bleak future. Current traditional CVD interventions offer temporary respite; however, they compound the severe economic strain of health-related expenditures. Furthermore, these therapeutics can be prescribed indefinitely. Recent advances in the field of epigenetics have generated new treatment options by confronting CVD at an epigenetic level. This involves modulating gene expression by altering the organization of our genome rather than altering the DNA sequence itself. Epigenetic changes are heritable, reversible, and influenced by environmental factors such as medications. As CVD is physiologically and pathologically diverse in nature, epigenetic interventions can offer a ray of hope to replace or be combined with traditional therapeutics to provide the prospect of addressing more than just the symptoms of CVD. This review discusses various risk factors contributing to CVD, perspectives of current traditional medications in practice, and a focus on potential epigenetic therapeutics to be used as alternatives.

Sodium arsenite-induced cytotoxicity is regulated by BNIP3L/Nix-mediated endoplasmic reticulum stress responses and CCPG1-mediated endoplasmic reticulum-phagy

We elucidated the BNIP3L/Nix and SQSTM1/p62 molecular mechanisms in sodium arsenite (NaAR)-induced cytotoxicity. Considerable changes in the morphology and adhesion of H460 cells were observed in response to varying NaAR concentrations. NaAR exposure induced DNA damage-mediated apoptosis and Nix accumulation via proteasome inhibition. Nix targets the endoplasmic reticulum (ER), inducing ER stress responses. p62 and Nix were colocalized and their expressions were inversely correlated. Autophagy inhibition upregulated Nix, p62, cell cycle progression gene 1 (CCPG1), heme oxygenase (HO)- 1, and calnexin expression. Nix knockdown decreased the NaAR-induced ER stress and microtubule-associated protein 1 A/1B light-chain 3 (LC3) B-II levels and increased the CCPG1 and calnexin levels. p62 knockdown upregulated Nix, LC3-II, and CCPG1 expressions and the ER stress responses, indicating that p62 regulates Nix levels. Nix downstream pathways were mitigated by Ca²⁺ chelators. We demonstrate the critical roles of Nix and p62 in ER stress and ER-phagy in response to NaAR.

Effects of Tauroursodeoxycholic Acid and 4-Phenylbutyric Acid on Selenium Distribution in Mice Model with Type 1 Diabetes

The effect of selenium on diabetes is significant. As pharmaceutical chaperones, tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid (4-PBA) can effectively improve the oxidative stress of the endoplasmic reticulum. This study established a mice model with type 1 diabetes (T1D) to evaluate the effects of pharmaceutical chaperones on selenium distribution. Streptozotocin was used to induce Friend virus B-type mice to establish a T1D mice model. Mice were administered with TUDCA or 4-PBA. Selenium levels in different tissues were measured by inductively coupled plasma-mass spectroscopy (ICP-MS). After treatment with TUDCA and 4-PBA, related laboratory findings such as glucose and glycated serum protein were significantly reduced and were closer to normal levels. At 2 weeks, 4-PBA normalized selenium levels in the heart, and 4-PBA and TUDCA maintained the selenium in the liver, kidney, and muscle at normal. At 2 months, 4-PBA and TUDCA maintained the selenium in the heart, liver, and kidney at normal levels. The serum selenium had a positive correlation with zinc and copper in the diabetes group and the control group, while the serum selenium had no significant association with magnesium and calcium at 2 weeks and 2 months. TUDCA and 4-PBA have crucial effects on selenium distribution in diabetic mice, and further research is needed to research their internal mechanisms.

The long and winding road to target protein misfolding in cardiovascular diseases

BACKGROUND

In the last decades, cardiovascular diseases (CVD) have remained the first leading cause of mortality and morbidity in the world. Although several therapeutic approaches have been introduced in the past, the development of novel treatments remains an important research goal, which is hampered by the lack of understanding of key mechanisms and targets. Emerging evidences in recent years indicate the involvement of misfolded proteins aggregation and the derailment of protein quality control in the pathogenesis of cardiovascular diseases. Several potential interventions targeting protein quality control have been translated from the bench to the bedside to effectively employ the misfolded proteins as promising therapeutic targets for cardiac diseases, but with trivial results.

DESIGN

In this review, we describe the recent progresses in preclinical and clinical studies of protein misfolding and compromised protein quality control by selecting and reporting studies focusing on cardiovascular diseases including cardiomyopathies, cardiac amyloidosis, atherosclerosis, atrial fibrillation and thrombosis.

RESULTS

In preclinical models, modulators of several molecular targets (eg heat shock proteins, unfolded protein response, ubiquitin protein system, autophagy and histone deacetylases) have been tested in various conditions with promising results although lacking an adequate transition towards clinical setting.

CONCLUSIONS

At present, no therapeutic strategies have been reported to attenuate proteotoxicity in patients with CVD due to a lack of specific biomarkers for pinpointing upstream events in protein folding defects at a subclinical stage of the diseases requiring an intensive collaboration between basic scientists and clinicians.

Crocetin alleviates myocardial ischemia/reperfusion injury by regulating inflammation and the unfolded protein response

Crocetin, a natural compound, has been demonstrated to exhibit beneficial effects in cardiovascular diseases. Previous studies demonstrated that crocetin reduced ischemia/reperfusion (I/R) injury by attenuating cytotoxicity and cellular apoptosis. However, the previous mechanistic studies did not fully elucidate its pharmacological effects on cardiac damage, especially I/R injury. The present study verified its cardioprotective effects in a Langendorff perfusion system, an ex vivo model of I/R. It was demonstrated that crocetin significantly attenuated the activities of pro-inflammatory cytokines and nuclear factor erythroid-2 related factor 2 (Nrf2)/heme oxygenase-1 signaling. The present study provided novel insight that crocetin regulated the unfolded protein response (UPR) and decreased associated protein levels to protect the heart. Furthermore, it was identified that Nrf2 played a key role in the cardioprotective effect of crocetin by attenuating inflammation and the UPR.

Increased ER Stress After Experimental Ischemic Optic Neuropathy and Improved RGC and Oligodendrocyte Survival After Treatment With Chemical Chaperon

Purpose

Increased endoplasmic reticulum (ER) stress is one of the earliest subcellular changes in neuro-ophthalmic diseases. In this study, we investigated the expression of key molecules in the ER stress pathways following nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults over 50, and assessed the impact of chemical chaperon 4-phenylbutyric acid (4-PBA) in vivo.

Methods

We induced AION using photochemical thrombosis in adult mice and performed histologic analyses of key molecules in the ER stress pathway in the retina and optic nerve. We also assessed the effects of daily intraperitoneal injections of 4-PBA after AION.

Results

In the retina at baseline, there was low proapoptotic transcriptional regulator C/EBP homologous protein (CHOP) and high prosurvival chaperon glucose-regulated protein 78 (GRP78) expression in retinal ganglion cells (RGCs). One day after AION, there was significantly increased CHOP and reduced GRP78 expressions in the ganglion cell layer. In the optic nerve at baseline, there was little CHOP and high GRP78 expression. One day after AION, there was significantly increased CHOP and no change in GRP78 expression. Treatment immediately after AION using daily intraperitoneal injection of chemical chaperone 4-PBA for 19 days significantly rescued Brn3A⁺ RGCs and Olig2⁺ optic nerve oligodendrocytes.

Conclusions

We showed for the first time that acute AION resulted in increased ER stress and differential expression of ER stress markers CHOP and GRP78 in the retina and optic nerve. Rescue of RGCs and oligodendrocytes with 4-PBA provides support for ER stress reduction as possible treatment for AION.

Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43

Healthy cardiomyocytes are electrically coupled at the intercalated discs by gap junctions. In infarcted hearts, adverse gap-junctional remodeling occurs in the border zone, where cardiomyocytes are chemically and electrically influenced by myofibroblasts. The physical movement of these contacts remains unquantified. Using scanning ion conductance microscopy, we show that intercellular contacts between cardiomyocytes and myofibroblasts are highly dynamic, mainly owing to the edge dynamics (lamellipodia) of the myofibroblasts. Decreasing the amount of functional connexin-43 (Cx43) at the membrane through Cx43 silencing, suppression of Cx43 trafficking, or hypoxia-induced Cx43 internalization attenuates heterocellular contact dynamism. However, we found decreased dynamism and stabilized membrane contacts when cellular coupling was strengthened using 4-phenylbutyrate (4PB). Fluorescent-dye transfer between cells showed that the extent of functional coupling between the 2 cell types correlated with contact dynamism. Intercellular calcein transfer from myofibroblasts to cardiomyocytes is reduced after myofibroblast-specific Cx43 down-regulation. Conversely, 4PB-treated myofibroblasts increased their functional coupling to cardiomyocytes. Consistent with lamellipodia-mediated contacts, latrunculin-B decreases dynamism, lowers physical communication between heterocellular pairs, and reduces Cx43 intensity in contact regions. Our data show that heterocellular cardiomyocyte-myofibroblast contacts exhibit high dynamism. Therefore, Cx43 is a potential target for prevention of aberrant cardiomyocyte coupling and myofibroblast proliferation in the infarct border zone.-Schultz, F., Swiatlowska, P., Alvarez-Laviada, A., Sanchez-Alonso, J. L., Song, Q., de Vries, A. A. F., Pijnappels, D. A., Ongstad, E., Braga, V. M. M., Entcheva, E., Gourdie, R. G., Miragoli, M., Gorelik, J. Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43.

Endogenous muscle atrophy F-box is involved in the development of cardiac rupture after myocardial infarction

Muscle atrophy F-box (MAFbx/atrogin-1), an E3 ubiquitin ligase, is a crucial mediator of skeletal muscle atrophy and cardiac hypertrophy in response to pressure overload and exercise. The role of MAFbx in the regulation of cardiac remodeling after myocardial infarction (MI) remains unclear. Permanent coronary ligation of the left coronary artery was performed on MAFbx knockout (KO) and wild-type (WT) mice and MAFbx expression in the WT mice was shown to be significantly increased in the left ventricles after MI. The mortality rate due to post-MI cardiac rupture was significantly decreased in MAFbx KO mice compared to that in the WT mice. DNA microarray and mRNA expression analyses revealed that the upregulation of genes involved in inflammatory processes and cell motility of leukocytes and neutrophils, including Mmp9, Il1b, Cxcl2, and Nlrp3, was significantly attenuated in MAFbx KO mice 1 day after MI. MAFbx downregulation inhibited nuclear factor-κB (Nfkb) activation after MI. Flow cytometry results demonstrated that the myocardial infiltration of neutrophils was suppressed in MAFbx KO mice 1 day after MI. Nlrp3 and Il1b protein levels were decreased in MAFbx KO mice compared with those in the WT mice. MAFbx downregulation significantly attenuated Tnfa-induced Cxcl2, Il1b, and Nlrp3 expression in cardiomyocytes. We conclude that MAFbx plays an important role in the mediation of excessive inflammation, including neutrophil infiltration, inflammasome formation, and production of proinflammatory cytokines through the activation of Nfkb, promoting cardiac rupture after MI.

Hypothesis: role for ammonia neutralization in the prevention and reversal of heart failure

Ammonia plays a central role in the life and death of all living organisms and has been studied for over 100 yr. Ammonia is necessary for growth and development, but it is toxic in excess, and, as a result, differing methods of ammonia neutralization have evolved. After physiological and pathological stress to the heart, tissue ammonia levels rise. Local ammonia neutralization may be inadequate, and excess ammonia may exert its toxic effects. Phenylbutyrate (PBA), which is Federal Drug Administration approved for the treatment of elevated blood ammonia in urea cycle disorders, provides an accessory pathway for ammonia excretion. Recently, PBA has also been found to prevent specific cardiomyopathies. The central theme presents the hypothesis that stress to the myocardium from a variety of environmental sources causes injury, cell death, necrosis, and ammonia production. Ammonia, if not neutralized, exerts downstream toxic effects. Here, data are presented showing that neutralization with PBA alone and PBA combined with angiotensin-converting enzyme inhibition prevent and reverse pathophysiology associated with specific cardiomyopathies. NEW & NOTEWORTHY Ammonia produced after myocardial injury is hypothesized to be an upstream stress contributing to the pathophysiology of heart failure, effects that may be attenuated by a documented ammonia-reducing treatment. Reversal of heart failure can be achieved using an angiotensin-converting enzyme inhibitor combined with an ammonia-reducing treatment.

Endogenous Selenoprotein P, a Liver-Derived Secretory Protein, Mediates Myocardial Ischemia/Reperfusion Injury in Mice

Selenoprotein P (SeP), a liver-derived secretory protein, functions as a selenium supply protein in the body. SeP has been reported to be associated with insulin resistance in humans through serial analysis of gene expression. Recently, SeP has been found to inhibit vascular endothelial growth factor-stimulated cell proliferation in human umbilical vein endothelial cells, and impair angiogenesis in a mouse hind limb model. In this study, the role of SeP in ischemia/reperfusion (I/R) injury has been investigated. SeP knockout (KO) and littermate wild-type (WT) mice were subjected to 30 min of myocardial ischemia followed by 24 h of reperfusion. The myocardial infarct area/area at risk (IA/AAR), evaluated using Evans blue (EB) and 2,3,5-triphenyltetrazolium chloride (TTC) staining, was significantly smaller in SeP KO mice than in WT mice. The number of terminal de-oxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive nuclei was significantly lower in SeP KO mice than in WT mice. In addition, caspase-3 activation was reduced in SeP KO mice compared to that in WT mice. Furthermore, phosphoinositide 3-kinase/Akt and Erk levels were examined for the reperfusion injury salvage kinase (RISK) pathway. Interestingly, SeP KO significantly increased the phosphorylation of IGF-1, Akt, and Erk compared to that in WT mice after I/R. Finally, I/R-induced myocardial IA/AAR was significantly increased in SeP KO mice overexpressing SeP in the liver compared to other SeP KO mice. These results, together, suggest that inhibition of SeP protects the heart from I/R injury through upregulation of the RISK pathway.