Chronic ethanol consumption upregulates the cytosolic and plasma membrane sialidase genes, but downregulates lysosomal membrane sialidase gene in rat liver

Abstract

We have previously shown that chronic ethanol feeding stimulates liver cytosolic sialidase (CS) and plasma membrane sialidase (PMS), whereas it decreases lysosomal membrane sialidase (LMS) activities with concomitant alterations in their relative synthetic rate in rat. To understand the molecular mechanism(s) for these changes, we have evaluated the effect of ethanol administration in male Wistar rats as a function of increasing dietary ethanol concentration after 8 weeks of pair-feeding on (i) the expression of CS, PMS, and LMS genes by real-time quantitative polymerase chain reaction method; (ii) their relative transcription rates by nuclear run-on assay; and (iii) the actual amount of these sialidase proteins in the liver fractions of the respective groups by Western blot method. We have demonstrated that the animals fed with 10.6%, 20.8%, and 36% of total calories as ethanol showed a 20% ( P < .05), 34% ( P < .01), and 69% ( P < .01) increase in CS mRNA level, and 22% ( P < .05), 26% ( P < .01), and 47% ( P < .01) increase in PMS mRNA level, but a decrease in LMS mRNA level by 35% ( P < .05), 50% ( P < .01), and 80% ( P < .01), respectively, as compared to controls. Western blot analyses of CS, PMS, and LMS in the liver subfractions showed that changes in protein levels of CS, LMS, and PMS were consistent with the corresponding changes in the respective mRNA levels. Thus, the upregulation of CS and PMS, but not LMS which is downregulated by chronic ethanol, may account for the appearance of asialoconjugates in alcoholics.