Chronic ethanol feeding causes depression of mitochondrial elongation factor Tu in the rat liver: implications for the mitochondrial ribosome

Abstract

Chronic ethanol feeding is known to negatively impact hepatic energy metabolism. Previous studies have indicated that the underlying lesion responsible for this may lie at the level of the mitoribosome. The aim of this study was to characterize the structure of the hepatic mitoribosome in alcoholic male rats and their isocalorically paired controls. Our experiments revealed that chronic ethanol feeding resulted in a significant depletion of both structural (death-associated protein 3) and functional [elongation factor thermo unstable (EF-Tu)] mitoribosomal proteins. In addition, significant increases were found in nucleotide elongation factor thermo stable (EF-Ts) and structural mitochondrial ribosomal protein L12 (MRPL12). The increase in MRPL12 was found to correlate with an increase in the levels of the 39S large mitoribosomal subunit. These changes were accompanied by decreased levels of nuclear- and mitochondrially encoded respiratory subunits, decreased amounts of intact respiratory complexes, decreased hepatic ATP levels, and depressed mitochondrial translation. Mathematical modeling of ethanol-mediated changes in EF-Tu and EF-Ts using prederived kinetic data predicted that the ethanol-mediated decrease in EF-Tu levels could completely account for the impaired mitochondrial protein synthesis. In conclusion, chronic ethanol feeding results in a depletion of mitochondrial EF-Tu levels within the liver that is mathematically predicted to be responsible for the impaired mitochondrial protein synthesis seen in alcoholic animals.

The effect of chronic alcohol consumption on mitochondrial calcium handling in hepatocytes

“…Long-term alcohol consumption decreased the levels of nuclear-encoded polypeptide subunits involved in the assembly of mitochondrial complex I (NDUFB8 and NDUFA9) and a mitochondrially encoded core subunit of complex IV (MTCO1, Figure 1D,E and Table 2). Alcohol-dependent decreases in these subunits has been reported in previous studies [15,16]. The loss of these polypeptide chains was associated with an approximately 40% decrease in cellular ATP levels (Figure 1F).…”

“…Taken together, these data confirm that our animal model reproduces some of the key features of experimentally induced alcoholic fatty liver disease including fat accumulation, decreases in polypeptide subunits that are assembled into mitochondrial respiratory chain complexes I and IV [15,16], compromised capacity to synthesize ATP [9,13] and activation of mitochondrial stress responses [1]. The increase in VDAC protein was unexpected as previous studies had not detected significant changes in the levels of VDAC protein after alcohol feeding [16,41]. We do not have an explanation for this discrepancy.…”

“…Sprague-Dawley rats were maintained on a Lieber-DeCarli alcohol-containing liquid diet for 60 ± 5 days prior to isolation of hepatocytes. This length of ethanol feeding has been shown to induce alcoholic fatty liver disease and mitochondrial dysfunction including decreases in the protein abundance of all complexes involved in oxidative phosphorylation except complex II [2,14–16]. The data shown in Figure 1 validate that the hepatocytes from alcohol-fed rats used in this study also show signs of steatosis and mitochondrial injury.…”

“…Mitochondrial elongation and swelling is an early manifestation of alcohol-induced liver injury, which precedes or is concomitant with alcoholic steatosis [6–8]. Moreover, the abundance and activity of mitochondrial respiratory complexes (I, III and IV) are decreased by chronic ethanol feeding resulting in lower rates of oxidative phosphorylation and lower levels of cellular ATP production [1,2,9–16].…”

Ethanol alters gene expression and cell organization during optic vesicle evagination

“…Vacuoles and mitochondria are involved in ethanol detoxification (review in Manzo-Avalos and Saavedra-Molina, 2010 ). Moreover, ethanol releases free radicals from mitochondria ( Robin et al, 2005 ) and reduces their function ( Weiser et al, 2011 ). All together these alterations could result in the lack of change in cell morphology.…”