Abstract
Mitochondria are particularly susceptible to increased formation of reactive oxygen and nitrogen species in the cell that can occur in response to pathological and xenobiotic stimuli. Proteomics can give insights into both mechanism of pathology and adaptation to stress. Herein we report the use of proteomics to evaluate alterations in the levels of mitochondrial proteins following chronic ethanol exposure in an animal model. Forty-three proteins showed differential expression, 13 increased and 30 decreased, as a consequence of chronic ethanol. Of these proteins, 25 were not previously known to be affected by chronic ethanol emphasizing the power of proteomic approaches in revealing global responses to stress. Both nuclear and mitochondrially encoded gene products of the oxidative phosphorylation complexes in mitochondria from ethanol-fed rats were decreased suggesting an assembly defect in this integrated metabolic pathway. Moreover mtDNA damage was increased by ethanol demonstrating that the effects of ethanol consumption extend beyond the proteome to encompass mtDNA. Taken together, we have demonstrated that chronic ethanol consumption extends to a modification of the mitochondrial proteome far broader than realized previously. These data also suggest that the response of mitochondria to stress may not involve non-discriminate changes in the proteome but is restricted to those metabolic pathways that have a direct role in a specific pathology.
Highlights
Lier studies by Cunningham and colleagues [18, 19] have demonstrated that ethanol consumption decreases the synthesis of the 13 mitochondrially encoded proteins that comprise respiratory complexes I, III, and IV and the ATP synthase
Global alterations in mitochondrial protein levels and mtDNA damage were studied in a well characterized rodent model of chronic ethanol feeding [32] that is known to cause hepatic mitochondrial dysfunction [12, 13] and oxidative and nitrosative stress [5, 33] in the early stage of the disease process. Using both the proteomic approaches described above, alterations in the levels of proteins involved in -oxidation of fatty acids and the oxidative phosphorylation system were found in mitochondria isolated from the livers of rats chronically exposed to ethanol
This preparation does contain some minor contamination from other nonmitochondrial membrane sources but is functionally viable for the periods needed for respiratory measurement and proteomics
Summary
Lier studies by Cunningham and colleagues [18, 19] have demonstrated that ethanol consumption decreases the synthesis of the 13 mitochondrially encoded proteins that comprise respiratory complexes I, III, and IV and the ATP synthase. This is important because it will enable probing the molecular basis of the observation that chronic ethanol consumption decreases the functioning of the oxidative phosphorylation system [12, 13] In this investigation, global alterations in mitochondrial protein levels and mtDNA damage were studied in a well characterized rodent model of chronic ethanol feeding [32] that is known to cause hepatic mitochondrial dysfunction [12, 13] and oxidative and nitrosative stress [5, 33] in the early stage of the disease process. The results from these proteomic analyses reveal that the response of liver to chronic ethanol exposure is a complex process the number of changes in proteins is limited to a specific group of metabolic pathways
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