Calpain activation and CaMKIV reduction in spinal cords from hSOD1G93A mouse model.

Amyotrophic Lateral Sclerosis (ALS), a severe neurodegenerative disease, affects the upper and lower motor neurons in the brain and spinal cord. In some studies, ALS disease progression has been associated with an increase in calcium-dependent degeneration processes. Motoneurons are specifically vulnerable to sustained membrane depolarization and excessive elevation of intracellular calcium concentration. The present study analyzed intracellular events in embryonic motoneurons and adult spinal cords of the hSOD1G93A ALS mouse model. We observed activation of calpain, a calcium-dependent cysteine protease that degrades a variety of substrates, and a reduction in calcium-calmodulin dependent protein kinase type IV (CaMKIV) levels in protein extracts from spinal cords obtained at several time-points of hSOD1G93A mice disease progression. However, in cultured embryonic motoneurons these differences between controls and hSOD1G93A mutants are not evident. Our results support the hypothesis that age-dependent changes in calcium homeostasis and resulting events, e.g., calpain activation and CaMKIV processing, are involved in ALS pathogenesis.

Nuclear factor-κB2/p100 promotes endometrial carcinoma cell survival under hypoxia in a HIF-1α independent manner.

Endometrial carcinoma (EC) is a common female cancer, treated mainly by surgery and adjuvant radiotherapy. Relapse following treatment is associated with increased risk of metastases. Hypoxia, a common microenvironment in solid tumors, correlates with malignant progression, rendering tumors resistant to ionizing therapy. Hence, we assessed here the immunohistochemical expression of hypoxia-inducible factor-1α (HIF-1α) and members of the NF-κB family in 82 primary EC and 10 post-radiation recurrences of EC. Post-radiation recurrences were highly hypoxic, with a higher expression of HIF-1α and also RelA (p65) and p52 when compared with primary EC. We next investigated the effects of hypoxia on EC cell lines. We found that EC cell lines are highly resistant to hypoxia-induced apoptosis. We thus focused on the molecular mechanisms involved in conferring hypoxic cell death resistance. We show that in addition to the classical NF-κB, hypoxia activates the alternative NF-κB pathway. To characterize the upstream kinases involved in the activation of these pathways, we used lentiviral-mediated knockdown and mouse embryonic fibroblasts lacking IKKα and IKKß kinases. Both IKKα and IKKß kinases are required for RelA (p65) and p100 accumulation, whereas p52 processing under hypoxia is IKKα dependent. Furthermore, Ishikawa endometrial cell line harboring either RelA (p65) or p52 short-hairpin RNA was sensitive to hypoxia-induced cell death, indicating that, in addition to the known prosurvival role of RelA (p65) under hypoxia, alternative NF-κB pathway also enhances hypoxic survival of EC cells. Interestingly, although HIF-1α controlled classical NF-κB activation pathway and survival under hypoxia through RelA (p65) nuclear accumulation, the alternative pathway was HIF-1α independent. These findings have important clinical implications for the improvement of EC prognosis before radiotherapy.

Developmental silencing and independency from E2F of apoptotic gene expression in postmitotic tissues.

The involvement of caspases in postmitotic cell death is controversial. Here we report that adult brain and heart are devoid of many key pro-apoptotic proteins due to a progressive postnatal silencing event involving a reduction of their transcript levels. E2F has been shown to control cell cycle progression and to be transcriptional activator of apoptotic genes. However, our data demonstrate that apoptotic gene expression in heart, brain and liver, as well as cardiac and neuronal apoptotic gene silencing during development, are E2F-independent events. Therefore, the genes regulating caspase-dependent cell death are expressed in embryonic organs in an E2F-independent manner and a developmental-related silencing event represses these genes in postmitotic adult tissues.

EndoG links Bnip3-induced mitochondrial damage and caspase-independent DNA fragmentation in ischemic cardiomyocytes.

Mitochondrial dysfunction, caspase activation and caspase-dependent DNA fragmentation are involved in cell damage in many tissues. However, differentiated cardiomyocytes repress the expression of the canonical apoptotic pathway and their death during ischemia is caspase-independent. The atypical BH3-only protein Bnip3 is involved in the process leading to caspase-independent DNA fragmentation in cardiomyocytes. However, the pathway by which DNA degradation ensues following Bnip3 activation is not resolved. To identify the mechanism involved, we analyzed the interdependence of Bnip3, Nix and EndoG in mitochondrial damage and DNA fragmentation during experimental ischemia in neonatal rat ventricular cardiomyocytes. Our results show that the expression of EndoG and Bnip3 increases in the heart throughout development, while the caspase-dependent machinery is silenced. TUNEL-positive DNA damage, which depends on caspase activity in other cells, is caspase-independent in ischemic cardiomyocytes and ischemia-induced DNA high and low molecular weight fragmentation is blocked by repressing EndoG expression. Ischemia-induced EndoG translocation and DNA degradation are prevented by silencing the expression of Bnip3, but not Nix, or by overexpressing Bcl-x(L). These data establish a link between Bnip3 and EndoG-dependent, TUNEL-positive, DNA fragmentation in ischemic cardiomyocytes in the absence of caspases, defining an alternative cell death pathway in postmitotic cells.

Switch from caspase-dependent to caspase-independent death during heart development: essential role of endonuclease G in ischemia-induced DNA processing of differentiated cardiomyocytes.

Differentiated cardiomyocytes are resistant to caspase-dependent cell death; however, the mechanisms involved are still uncertain. We previously reported that low Apaf1 expression partially accounts for cardiomyocyte resistance to apoptosis. Here, we extend the knowledge on the molecular basis of cardiac resistance to caspase activation by showing that the whole caspase-dependent pathway is silenced during heart development. Experimental ischemia triggers caspase activation in embryonic cardiomyocytes and proliferating fibroblasts, but not in neonatal and adult cardiomyocytes. Ischemia induces the release of the proapoptotic factors cytochrome c, truncated-AIF, and EndoG from mitochondria in postnatal cardiomyocytes in the absence of caspase activation. On the one hand, lentiviral-driven knockdown of EndoG shows that this gene is essential for ischemia-induced DNA degradation in neonatal cardiomyocytes, but not in proliferating fibroblasts; on the other hand, the AIF gene is essential for high molecular DNA cleavage in fibroblasts, but not in postmitotic cardiomyocytes, where it plays a prosurvival role during reoxygenation. These results show the switch from caspase-dependent to caspase-independent death pathways after cardiac cell differentiation, and disclose the relevance of EndoG in the caspase-independent DNA processing of differentiated cardiomyocytes.

Bcl-2 is a key factor for cardiac fibroblast resistance to programmed cell death.

Cardiac fibroblasts play an essential role in the physiology of the heart. These produce extracellular matrix proteins and synthesize angiogenic and cardioprotective factors. Although fibroblasts of cardiac origin are known to be resistant to apoptosis and to remain metabolically active in situations compromising cell survival, the underlying mechanisms are unknown. Here, we report that cardiac fibroblasts were more resistant than dermal or pulmonary fibroblasts to mitochondria-dependent cell death. Cytochrome c release was blocked in cardiac fibroblasts but not in dermal fibroblasts treated with staurosporine, etoposide, serum deprivation, or simulated ischemia, precluding caspase-3 activation and DNA fragmentation. Resistance to apoptosis of cardiac fibroblasts correlated with the expression of the anti-apoptotic protein Bcl-2, whereas skin and lung fibroblasts did not express detectable levels of this protein. Bcl-x(L,) Bax, and Bak were expressed at similar levels in cardiac, dermal, and lung fibroblasts. In addition, the death of cardiac fibroblasts during hypoxia was not associated with the cleavage of Bid but rather with Bcl-2 disappearance, suggesting the requirement of the mitochondrial apoptotic machinery to execute death receptor-induced programmed cell death. Knockdown of bcl-2 expression by siRNA in cardiac fibroblasts increased their apoptotic response to staurosporine, serum, and glucose deprivation and to simulated ischemia. Moreover, dermal fibroblasts overexpressing Bcl-2 achieved a similar level of resistance to these stimuli as cardiac fibroblasts. Thus, our data demonstrate that Bcl-2 is an important effector of heart fibroblast resistance to apoptosis and highlight a probable mechanism for promoting survival advantage in fibroblasts of cardiac origin.