Zidovudine-Mediated Autophagy Inhibition Enhances Mitochondrial Toxicity in Muscle Cells.

Nucleoside reverse transcriptase inhibitors (NRTI), such as zidovudine (AZT), are constituents of HIV-1 therapy and are used for the prevention of mother-to-child transmission. Prolonged thymidine analogue exposure has been associated with mitochondrial toxicities to heart, liver, and skeletal muscle. We hypothesized that the thymidine analogue AZT might interfere with autophagy in myocytes, a lysosomal degradation pathway implicated in the regulation of mitochondrial recycling, cell survival, and the pathogenesis of myodegenerative diseases. The impact of AZT and lamivudine (3TC) on C2C12 myocyte autophagy was studied using various methods based on LC3-green fluorescent protein overexpression or LC3 staining in combination with Western blotting, flow cytometry, and confocal and electron microscopy. Lysosomal and mitochondrial functions were studied using appropriate staining for lysosomal mass, acidity, cathepsin activity, as well as mitochondrial mass and membrane potential in combination with flow cytometry and confocal microscopy. AZT, but not 3TC, exerted a significant dose- and time-dependent inhibitory effect on late stages of autophagosome maturation, which was reversible upon mTOR inhibition. Inhibition of late autophagy at therapeutic drug concentrations led to dysfunctional mitochondrial accumulation with membrane hyperpolarization and increased reactive oxygen species (ROS) generation and, ultimately, compromised cell viability. These AZT effects could be readily replicated by pharmacological and genetic inhibition of myocyte autophagy and, most importantly, could be rescued by pharmacological stimulation of autophagolysosomal biogenesis. Our data suggest that the thymidine analogue AZT inhibits autophagy in myocytes, which in turn leads to the accumulation of dysfunctional mitochondria with increased ROS generation and compromised cell viability. This novel mechanism could contribute to our understanding of the long-term side effects of antiviral agents.

Histone deacetylase inhibitors induce apoptosis in myeloid leukemia by suppressing autophagy.

Histone deacetylase (HDAC) inhibitors (HDACis) are well-characterized anti-cancer agents with promising results in clinical trials. However, mechanistically little is known regarding their selectivity in killing malignant cells while sparing normal cells. Gene expression-based chemical genomics identified HDACis as being particularly potent against Down syndrome-associated myeloid leukemia (DS-AMKL) blasts. Investigating the antileukemic function of HDACis revealed their transcriptional and post-translational regulation of key autophagic proteins, including ATG7. This leads to suppression of autophagy, a lysosomal degradation process that can protect cells against damaged or unnecessary organelles and protein aggregates. DS-AMKL cells exhibit low baseline autophagy due to mammalian target of rapamycin (mTOR) activation. Consequently, HDAC inhibition repressed autophagy below a critical threshold, which resulted in accumulation of mitochondria, production of reactive oxygen species, DNA damage and apoptosis. Those HDACi-mediated effects could be reverted upon autophagy activation or aggravated upon further pharmacological or genetic inhibition. Our findings were further extended to other major acute myeloid leukemia subgroups with low basal level autophagy. The constitutive suppression of autophagy due to mTOR activation represents an inherent difference between cancer and normal cells. Thus, via autophagy suppression, HDACis deprive cells of an essential pro-survival mechanism, which translates into an attractive strategy to specifically target cancer cells.

HIV-therapy associated lipodystrophy: experimental and clinical evidence for the pathogenesis and treatment.

The introduction of highly active antiretroviral therapy (HAART) including nucleoside reverse transcriptase inhibitors (NRTI) and protease inhibitors (PI) has dramatically improved the morbidity and mortality in HIV-infected patients. Unfortunately, HAART has been associated with several side effects among which the development of lipodystrophy syndrome remains a major clinical issue. It is characterized by fat redistribution dominated by peripheral fat loss and complex metabolic alterations including dyslipidemia and insulin resistance. Dissection of the pathogenesis of the lipodystrophy syndrome is hampered by several factors: all HIV-patients receiving HAART have a chronic and often advanced illness with impact on metabolism and energy homeostasis. Secondly, almost all patients are receiving various combinations of drugs that simultaneously reduce viral replication and restore the immune system. Recently, more detailed clinical studies, experiments using animal models and in vitro systems have been successfully used to elucidate important pathogenic aspects. At the same time, partial reversion of fat loss and metabolic disturbances in HIV-patients could be achieved by omitting components of HAART or administration of metabolically active drugs. Here, we will summarize the current knowledge about the molecular alterations that are induced by antiretroviral therapy and possibly contribute to the lipodystrophy syndrome. Specific attention will be given to the role of NRTI and PI on adipocyte development, function, and mitochondrial integrity leading to fat loss, fat accumulation, and increase of serum lipids.