Cardiovascular disease (CVD) is one of the contributing factors to more than one-third of human mortality and the leading cause of death worldwide. The death of cardiac myocyte is a fundamental ...pathological process in cardiac pathologies caused by various heart diseases, including myocardial infarction. Thus, strategies for replacing fibrotic tissue in the infarcted region with functional myocardium have long been a goal of cardiovascular research. This review begins by briefly discussing a variety of somatic stem- and progenitor-cell populations that were frequently studied in early investigations of regenerative myocardial therapy and then focuses primarily on pluripotent stem cells (PSCs), especially induced-pluripotent stem cells (iPSCs), which have emerged as perhaps the most promising source of cardiomyocytes for both therapeutic applications and drug testing. We also describe attempts to generate cardiomyocytes directly from cardiac fibroblasts (i.e., transdifferentiation), which, if successful, may enable the pool of endogenous cardiac fibroblasts to be used as an in-situ source of cardiomyocytes for myocardial repair.
Diabetes mellitus is currently a major public health problem. A common complication of diabetes is cardiac dysfunction, which is recognized as a microvascular disease that leads to morbidity and ...mortality in diabetic patients. While ischemic events are commonly observed in diabetic patients, the risk for developing heart failure is also increased, independent of the severity of coronary artery disease and hypertension. This diabetes-associated clinical entity is considered a distinct disease process referred to as "diabetic cardiomyopathy". However, it is not clear how diabetes promotes cardiac dysfunction. Vascular endothelial dysfunction is thought to be one of the key risk factors. The impact of diabetes on the endothelium involves several alterations, including hyperglycemia, fatty acid oxidation, reduced nitric oxide (NO), oxidative stress, inflammatory activation, and altered barrier function. The current review provides an update on mechanisms that specifically target endothelial dysfunction, which may lead to diabetic cardiomyopathy.
Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, with septic cardiomyopathy being a common and severe complication. Despite its significant clinical ...impact, the molecular mechanisms underlying sepsis-induced cardiomyopathy (SICM) remain incompletely understood. In this study, we performed a comparative analysis of whole transcriptome profiles using RNA sequencing in mouse hearts in two widely used mouse models of septic cardiomyopathy. CLP-induced sepsis was achieved by surgical cecal ligation and puncture, while LPS-induced sepsis was induced using a 5 mg/kg intraperitoneal (IP) injection of lipopolysaccharide (LPS). For consistency, we utilized sham-operated mice as the control for septic models. Our aim was to identify key genes and pathways involved in the development of septic cardiomyopathy and to evaluate the similarities and differences between the two models. Our findings demonstrated that both the CLP and lipopolysaccharide LPS methods could induce septic heart dysfunction within 24 h. We identified common transcriptional regulatory regions in the septic hearts of both models, such as Nfkb1, Sp1, and Jun. Moreover, differentially expressed genes (DEGs) in comparison to control were involved in shared pathways, including regulation of inflammatory response, regulation of reactive oxygen species metabolic process, and the JAK-STAT signaling pathway. However, each model presented distinctive whole transcriptome expression profiles and potentially diverse pathways contributing to sepsis-induced heart failure. This extensive comparison enhances our understanding of the molecular basis of septic cardiomyopathy, providing invaluable insights. Accordingly, our study also contributes to the pursuit of effective and personalized treatment strategies for SICM, highlighting the importance of considering the specific causative factors.
Hexokinase‐II (HKII) is highly expressed in the heart and can bind to the mitochondrial outer membrane. Since cardiac hypertrophy is associated with a substrate switch from fatty acid to glucose, we ...hypothesized that a reduction in HKII would decrease cardiac hypertrophy after pressure overload. Contrary to our hypothesis, heterozygous HKII‐deficient (HKII+/−) mice displayed increased hypertrophy and fibrosis in response to pressure overload. The mechanism behind this phenomenon involves increased levels of reactive oxygen species (ROS), as HKII knockdown increased ROS accumulation, and treatment with the antioxidant N‐acetylcysteine (NAC) abrogated the exaggerated response. HKII mitochondrial binding is also important for the hypertrophic effects, as HKII dissociation from the mitochondria resulted in de novo hypertrophy, which was also attenuated by NAC. Further studies showed that the increase in ROS levels in response to HKII knockdown or mitochondrial dissociation is mediated through increased mitochondrial permeability and not by a significant change in antioxidant defenses. Overall, these data suggest that HKII and its mitochondrial binding negatively regulate cardiac hypertrophy by decreasing ROS production via mitochondrial permeability.
RATIONALE:Heme plays a critical role in gas exchange, mitochondrial energy production, and antioxidant defense in cardiovascular system. The mitochondrial transporter ATP-binding cassette (ABC) B10 ...has been suggested to export heme out of the mitochondria and is required for normal hemoglobinization of erythropoietic cells and protection against ischemia–reperfusion injury in the heart; however, its primary function has not been established.
OBJECTIVE:The aim of this study was to identify the function of ABCB10 in heme synthesis in cardiac cells.
METHODS AND RESULTS:Knockdown of ABCB10 in cardiac myoblasts significantly reduced heme levels and the activities of heme-containing proteins, whereas supplementation with δ-aminolevulinic acid reversed these defects. Overexpression of mitochondrial δ-aminolevulinic acid synthase 2, the rate-limiting enzyme upstream of δ-aminolevulinic acid export, failed to restore heme levels in cells with ABCB10 downregulation. ABCB10 and heme levels were increased by hypoxia, and reversal of ABCB10 upregulation caused oxidative stress and cell death. Furthermore, ABCB10 knockdown in neonatal rat cardiomyocytes resulted in a significant delay of calcium removal from the cytoplasm, suggesting a relaxation defect. Finally, ABCB10 expression and heme levels were altered in failing human hearts and mice with ischemic cardiomyopathy.
CONCLUSIONS:ABCB10 plays a critical role in heme synthesis pathway by facilitating δ-aminolevulinic acid production or export from the mitochondria. In contrast to previous reports, we show that ABCB10 is not a heme exporter and instead is required for the early mitochondrial steps of heme biosynthesis.
Hexokinases (HKs) catalyze the first step in glucose metabolism. Of the three mammalian 100-kDa HK isoforms, HKI and II can bind to mitochondria and protect against cell death. HKIII does not bind ...mitochondria, and little is known about its regulation or cytoprotective effects. We studied the regulation of HKIII at the transcriptional and protein levels and investigated its role in cellular protection.
We show that like HKII, HKIII expression is regulated by hypoxia, but other factors that regulate HKII expression have no effect on HKIII levels. This transcriptional regulation is partially dependent on hypoxia-inducible factor (HIF) signaling. We also demonstrate regulation at the protein level, as mutations in putative N-terminal substrate binding residues altered C-terminal catalytic activity, suggesting that HKIII activity is governed, in part, by interactions between these two domains. Overexpression of HKIII reduced oxidant-induced cell death, increased ATP levels, decreased the production of reactive oxygen species (ROS), and preserved mitochondrial membrane potential. HKIII overexpression was also associated with higher levels of transcription factors that regulate mitochondrial biogenesis, and greater total mitochondrial DNA content. Attempts to target HKIII to the mitochondria by replacing its N-terminal 32-amino-acid sequence with the mitochondrial-targeting sequence of HKII led to protein aggregation, suggesting that this region is necessary to maintain proper protein folding and solubility.
These results suggest that HKIII is regulated by hypoxia and there are functional interactions between its two halves. Furthermore, HKIII exerts protective effects against oxidative stress, perhaps by increasing ATP levels, reducing oxidant-induced ROS production, preserving mitochondrial membrane potential, and increasing mitochondrial biogenesis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ischaemic heart disease limits oxygen and metabolic substrate availability to the heart, resulting in tissue death. Here, we demonstrate that the AMP-activated protein kinase (AMPK)-related protein ...Snf1-related kinase (SNRK) decreases cardiac metabolic substrate usage and mitochondrial uncoupling, and protects against ischaemia/reperfusion. Hearts from transgenic mice overexpressing SNRK have decreased glucose and palmitate metabolism and oxygen consumption, but maintained power and function. They also exhibit decreased uncoupling protein 3 (UCP3) and mitochondrial uncoupling. Conversely, Snrk knockout mouse hearts have increased glucose and palmitate oxidation and UCP3. SNRK knockdown in cardiac cells decreases mitochondrial efficiency, which is abolished with UCP3 knockdown. We show that Tribbles homologue 3 (Trib3) binds to SNRK, and downregulates UCP3 through PPARα. Finally, SNRK is increased in cardiomyopathy patients, and SNRK reduces infarct size after ischaemia/reperfusion. SNRK also decreases cardiac cell death in a UCP3-dependent manner. Our results suggest that SNRK improves cardiac mitochondrial efficiency and ischaemic protection.
RATIONALE:Cardiomyocytes switch substrate utilization from fatty acid to glucose under ischemic conditions; however, it is unknown how perturbations in glycolytic enzymes affect cardiac response to ...ischemia/reperfusion (I/R). Hexokinase (HK)II is a HK isoform that is expressed in the heart and can bind to the mitochondrial outer membrane.
OBJECTIVE:We sought to define how HKII and its binding to mitochondria play a role in cardiac response and remodeling after I/R.
METHODS AND RESULTS:We first showed that HKII levels and its binding to mitochondria are reduced 2 days after I/R. We then subjected the hearts of wild-type and heterozygote HKII knockout (HKII) mice to I/R by coronary ligation. At baseline, HKII mice have normal cardiac function; however, they display lower systolic function after I/R compared to wild-type animals. The mechanism appears to be through an increase in cardiomyocyte death and fibrosis and a reduction in angiogenesis; the latter is through a decrease in hypoxia-inducible factor–dependent pathway signaling in cardiomyocytes. HKII mitochondrial binding is also critical for cardiomyocyte survival, because its displacement in tissue culture with a synthetic peptide increases cell death. Our results also suggest that HKII may be important for the remodeling of the viable cardiac tissue because its modulation in vitro alters cellular energy levels, O2 consumption, and contractility.
CONCLUSIONS:These results suggest that reduction in HKII levels causes altered remodeling of the heart in I/R by increasing cell death and fibrosis and reducing angiogenesis and that mitochondrial binding is needed for protection of cardiomyocytes.
Heme is an essential iron-containing molecule for cardiovascular physiology, but in excess it may increase oxidative stress. Failing human hearts have increased heme levels, with upregulation of the ...rate-limiting enzyme in heme synthesis, δ-aminolevulinic acid synthase 2 (ALAS2), which is normally not expressed in cardiomyocytes. We hypothesized that increased heme accumulation (through cardiac overexpression of ALAS2) leads to increased oxidative stress and cell death in the heart.
We first showed that ALAS2 and heme levels are increased in the hearts of mice subjected to coronary ligation. To determine the causative role of increased heme in the development of heart failure, we generated transgenic mice with cardiac-specific overexpression of ALAS2. While ALAS2 transgenic mice have normal cardiac function at baseline, their hearts display increased heme content, higher oxidative stress, exacerbated cell death, and worsened cardiac function after coronary ligation compared to nontransgenic littermates. We confirmed in cultured cardiomyoblasts that the increased oxidative stress and cell death observed with ALAS2 overexpression is mediated by increased heme accumulation. Furthermore, knockdown of ALAS2 in cultured cardiomyoblasts exposed to hypoxia reversed the increases in heme content and cell death. Administration of the mitochondrial antioxidant MitoTempo to ALAS2-overexpressing cardiomyoblasts normalized the elevated oxidative stress and cell death levels to baseline, indicating that the effects of increased ALAS2 and heme are through elevated mitochondrial oxidative stress. The clinical relevance of these findings was supported by the finding of increased ALAS2 induction and heme accumulation in failing human hearts from patients with ischemic cardiomyopathy compared to nonischemic cardiomyopathy.
Heme accumulation is detrimental to cardiac function under ischemic conditions, and reducing heme in the heart may be a novel approach for protection against the development of heart failure.
RATIONALE:Isoforms I and II of the glycolytic enzyme hexokinase (HKI and HKII) are known to associate with mitochondria. It is unknown whether mitochondria-bound hexokinase is mandatory for ischemic ...preconditioning and normal functioning of the intact, beating heart.
OBJECTIVE:We hypothesized that reducing mitochondrial hexokinase would abrogate ischemic preconditioning and disrupt myocardial function.
METHODS AND RESULTS:Ex vivo perfused HKII hearts exhibited increased cell death after ischemia and reperfusion injury compared with wild-type hearts; however, ischemic preconditioning was unaffected. To investigate acute reductions in mitochondrial HKII levels, wild-type hearts were treated with a TAT control peptide or a TAT-HK peptide that contained the binding motif of HKII to mitochondria, thereby disrupting the mitochondrial HKII association. Mitochondrial hexokinase was determined by HKI and HKII immunogold labeling and electron microscopy analysis. Low-dose (200 nmol/L) TAT-HK treatment significantly decreased mitochondrial HKII levels without affecting baseline cardiac function but dramatically increased ischemia-reperfusion injury and prevented the protective effects of ischemic preconditioning. Treatment for 15 minutes with high-dose (10 μmol/L) TAT-HK resulted in acute mitochondrial depolarization, mitochondrial swelling, profound contractile impairment, and severe cardiac disintegration. The detrimental effects of TAT-HK treatment were mimicked by mitochondrial membrane depolarization after mild mitochondrial uncoupling that did not cause direct mitochondrial permeability transition opening.
CONCLUSIONS:Acute low-dose dissociation of HKII from mitochondria in heart prevented ischemic preconditioning, whereas high-dose HKII dissociation caused cessation of cardiac contraction and tissue disruption, likely through an acute mitochondrial membrane depolarization mechanism. The results suggest that the association of HKII with mitochondria is essential for the protective effects of ischemic preconditioning and normal cardiac function through maintenance of mitochondrial potential.
PDF
