Upregulation of nuclear-encoded mitochondrial LON protease in HAART-treated HIV-positive patients with lipodystrophy: implications for the pathogenesis of the disease

BACKGROUND: HAART can provoke metabolic changes and body fat redistribution, resulting in lipodystrophy, a side effect significantly involving mitochondrial function. Mitochondrial DNA (mtDNA) depletion caused by nucleosidic reverse transcription inhibitors is supposed to be a crucial mechanism in the pathogenesis of mitochondrial damages. METHODS: In adipose tissue from 22 HIV-positive patients with lipodystrophy and 20 healthy controls, we analyzed gene expression by microarray analysis and real-time PCR. The most upregulated gene was further studied in the human adipocytic cell line SW872 by real-time PCR, western blot, transient transfection assays and flow cytometry. RESULTS: We identified 18 genes differently expressed between lipodystrophy patients and controls, and focused our attention on the nuclear-encoded mitochondrial protease LON, essential in mtDNA maintenance. In SW872 cells, treatment with stavudine (d4T) doubled LON levels, in parallel with mtDNA depletion. As d4T increased reactive oxygen species (ROS) intracellular content, we measured LON in presence of deoxyribose, which causes oxidative stress but not mtDNA depletion, and observed LON upregulation. Ethidium bromide, which markedly depletes mtDNA, did not alter LON levels. The antioxidant glutathione inhibited the increase of intracellular ROS and the increase in LON caused by d4T or deoxyribose. CONCLUSION: LON upregulation was due to d4T-induced ROS production, rather than due to mtDNA depletion, and represents a response to an oxidative stress. Other mechanisms than mtDNA depletion thus exist that explain nucleosidic reverse transcription inhibitors toxicity. This observation provides a rationale for possible therapeutic interventions aimed at reducing intracellular ROS content in patients assuming HAART.