Cardiac Fas-Dependent and Mitochondria-Dependent Apoptosis after Chronic Cocaine Abuse

To evaluate whether chronic cocaine abuse will increase cardiac Fas-dependent and mitochondria-dependent apoptotic pathways, thirty-two male Wistar rats at 3–4 months of age were randomly divided into a vehicle-treated group (phosphate-buffered saline, PBS, 0.5 mL, SQ per day) and a cocaine-treated group (Cocaine, 10 mg/kg, SQ per day). After 3 months of treatment, the excised left ventricles were measured by H&E staining, Western blotting, DAPI staining and TUNEL assays. More cardiac TUNEL-positive apoptotic cells were observed in the Cocaine group than the PBS group. Protein levels of TNF-alpha, Fas ligand, Fas death receptor, FADD, activated caspase-8, and activated caspase-3 (Fas-dependent apoptosis) extracted from excised hearts in the Cocaine group were significantly increased, compared to the PBS group. Protein levels of cardiac Bax, cytosolic cytochrome c, t-Bid-to-Bid, Bak-to-Bcl-xL, Bax-to-Bcl-2 ratio, activated caspase-9, and activated caspase-3 (mitochondria-dependent apoptosis) were significantly increased in the Cocaine group, compared to the PBS group. Chronic cocaine exposure appeared to activate the cardiac Fas-dependent and mitochondria-dependent apoptosis, which may indicate a possible mechanism for the development of cardiac abnormalities in humans with chronic cocaine abuse.     

Molecular Mechanisms of Cardiotoxicity Induced by ErbB Receptor Inhibitor Cancer Therapeutics

The introduction of the so-called “targeted therapies”, particularly those drugs that inhibit the activity of tyrosine kinases, has represented a remarkable progress in the treatment of cancer. Although these drugs improve survival rates in cancer, significant cardiotoxicity, manifesting as left vertricular dysfunction and/or heart failure, has emerged. The ErbB receptor tyrosine kinases are being pursued as therapeutic targets because of their important roles in normal physiology and in cancer. Besides the fact that the ErbB receptors are indispensable during development and in normal adult physiology, epidermal growth factor (EGFR) and ErbB2 in particular have been implicated in the development of many human cancers. This review focuses on the rationale for targeting members of ErbB receptor family and numerous agents that are in use for inhibiting the pathway. We summarize the current knowledge on the physiological role of ErbB signaling in the ventricle and on structural aspects of ErbB receptor activation in cancer and cardiac cells. We examine the underlying mechanisms that result in on-target or off-target cardiotoxicities of ErbB inhibitors, which can influence the design of future anticancer therapies.     

Induction of Apoptosis by PQ1, a Gap Junction Enhancer that Upregulates Connexin 43 and Activates the MAPK Signaling Pathway in Mammary Carcinoma Cells

The mechanism of gap junction enhancer (PQ1) induced cytotoxicity is thought to be attributed to the change in connexin 43 (Cx43) expression; therefore, the effects of Cx43 modulation in cell survival were investigated in mammary carcinoma cells (FMC2u) derived from a malignant neoplasm of a female FVB/N-Tg(MMTV-PyVT)634Mul/J (PyVT) transgenic mouse. PQ1 was determined to have an IC₅₀ of 6.5 µM in FMC2u cells, while inducing an upregulation in Cx43 expression. The effects of Cx43 modulation in FMC2u cell survival was determined through transfection experiments with Cx43 cDNA, which induced an elevated level of protein expression similar to that seen with PQ1 exposure, or siRNA to silence Cx43 protein expression. Overexpression or silencing of Cx43 led to a reduction or an increase in cell viability, respectively. The mitogen-activated protein kinase (MAPK) family has been implicated in the regulation of cell survival and cell death; therefore, the gap junctional intercellular communication (GJIC)-independent function of PQ1 and Cx43 in the Raf/Mitogen-activated protein kinase/ERK kinase/extracellular-signal-regulated kinase (Raf-MEK-ERK) cascade of cellular survival and p38 MAPK-dependent pathway of apoptosis were explored. PQ1 treatment activated p44/42 MAPK, while the overexpression of Cx43 resulted in a reduced expression. This suggests that PQ1 affects the Raf-MEK-ERK cascade independent of Cx43 upregulation. Both overexpression of Cx43 and PQ1 treatment stimulated an increase in the phosphorylated form of p38-MAPK, reduced levels of the anti-apoptotic protein Bcl-2, and increased the cleavage of pro-caspase-3. Silencing of Cx43 protein expression led to a reduction in the phosphorylation of p38-MAPK and an increase in Bcl-2 expression. The mechanism behind PQ1-induced cytotoxicity in FMC2u mammary carcinoma cells is thought to be attributed to the change in Cx43 expression. Furthermore, PQ1-induced apoptosis through the upregulation of Cx43 may depend on p38 MAPK, highlighting that the effect of PQ1 on gap junctions as well as cellular survival via a MAPK-dependent pathway.     

Cardiac Ablation of Rheb1 Induces Impaired Heart Growth,Endoplasmic Reticulum-Associated Apoptosis and Heart Failure in Infant Mice

Ras homologue enriched in brain 1 (Rheb1) plays an important role in a variety of cellular processes. In this study, we investigate the role of Rheb1 in the post-natal heart. We found that deletion of the gene responsible for production of Rheb1 from cardiomyocytes of post-natal mice resulted in malignant arrhythmias, heart failure, and premature death of these mice. In addition, heart growth impairment, aberrant metabolism relative gene expression, and increased cardiomyocyte apoptosis were observed in Rheb1-knockout mice prior to the development of heart failure and arrhythmias. Also, protein kinase B (PKB/Akt) signaling was enhanced in Rheb1-knockout mice, and removal of phosphatase and tensin homolog (Pten) significantly prolonged the survival of Rheb1-knockouts. Furthermore, signaling via the mammalian target of rapamycin complex 1 (mTORC1) was abolished and C/EBP homologous protein (CHOP) and phosphorylation levels of c-Jun N-terminal kinase (JNK) were increased in Rheb1 mutant mice. In conclusion, this study demonstrates that Rheb1 is important for maintaining cardiac function in post-natal mice via regulation of mTORC1 activity and stress on the endoplasmic reticulum. Moreover, activation of Akt signaling helps to improve the survival of mice with advanced heart failure. Thus, this study provides direct evidence that Rheb1 performs multiple important functions in the heart of the post-natal mouse. Enhancing Akt activity improves the survival of infant mice with advanced heart failure.