CHANGES IN mRNA LEVELS OF INTRACELLULAR FATTY ACID METABOLISM REGULATORS IN HUMAN HEPATOMA HepG2 CELLS FOLLOWING THEIR TREATMENT WITH NON-ESTERIFIED FATTY ACIDS AND DEHYDROEPIANDROSTERONE

Miroslav Rypka,Kateřina Červenková,Lenka Uherková,Kateřina Bogdanová,Hana Poczatková,Jaroslav Veselý

doi:10.5507/bp.2005.034

Abstract

The effects of non-esterified fatty acids (NEFA) and hormone dehydroepiandrosterone (DHEA) on the levels of mRNAs of protein kinase C (PKC) -delta and -epsilon isoforms and those of liver fatty acid binding protein (L-FABP) were investigated in the human hepatoma HepG2 cell line. The cells were kept in low-serum, low-albumin medium during experiments. Low FA levels (100 microM) and time intervals of 4 h and 20 h were used. In these conditions, the saturated (palmitic, stearic) and monounsaturated (oleic) acids rather selectively stimulated PKC-epsilon mRNA levels. Unexpectedly, we found that these acids also suppressed liver fatty-acid binding protein (L-FABP) mRNA levels. DHEA in pharmacological doses (100 microM) produced a significant increase in PKC-delta and -epsilon mRNA levels. Although molecular mechanisms underlying the identified changes have not been investigated in this paper, our findings emphasize that NEFA-induced modulation of mRNA levels of key signalling components represent an additional mechanism for how the ambient NEFA can influence metabolic homeostasis in cells.

Highlights

The mechanisms by which ambient non-esterified fatty acids (NEFA) alter gene expression in cells are largely unknown
The protein kinase C (PKC) family of intracellular serine/threonine protein kinases that plays a prominent role in a number of signalling pathways regulating cell metabolism, growth, and death has been implicated in mediating FA-induced modulation of gene expression
HepG2 cells were incubated in the presence of palmitic, stearic, and oleic acids to evaluate whether the mRNA levels of intracellular FA metabolism regulators is influenced by ambient NEFA applied in low concentrations

Summary

Introduction

The mechanisms by which ambient non-esterified fatty acids (NEFA) alter gene expression in cells are largely unknown. Activation of PKC isoenzymes by ambient FA has been evidenced previously[22] and interpreted as a result of the combined action of elevated intracellular long-chain acyl CoA (LCAC) derivatives that can give rise to diacylglycerol (DAG), a known potent activator of PKCs, accumulation of Ca2+, and/or of NEFA themselves.[22,23,24] Using lipid infusions in rats in vivo, Lam et al.[25] have identified the n-PKC-δ isoform as a potential important player in sustained insulin resistance induced by NEFA in this organ At variance with this finding, Samuel et al.[26] have demonstrated abundance of the n-PKC-ε isoform, but not the PKC-δ isoform, in liver cell membranes from high-fat fed animals. Recent studies have indicated that in obese subjects with type 2 diabetes, the activity of various PKC isoforms is higher than in controls.[27,28]

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Results

Conclusion