Control of bovine pyruvate carboxylase expression by saturated and unsaturated fatty acids and impact on fatty acid metabolism

Abstract Text:

Metabolic fates of fatty acids (FA) in tissue may be influenced by extracellular FA concentration and profile. Previous work demonstrates an ability of C18:3n-3 cis to ameliorate C16:0- or C18:0-induced depression of pyruvate carboxylase (PC) mRNA expression. Pyruvate carboxylase catalyzes oxaloacetate (OAA) synthesis and connects gluconeogenesis from lactate and FA metabolism. Our objective was to determine the effects of a copresence of saturated and unsaturated FA on cellular partitioning of [1-¹⁴C]C16:0 metabolism to CO₂ or acid-soluble products (ASP) in Madin-Darby bovine kidney (MDBK) cells and the role of PC in this relationship. We hypothesized that the ratio of saturated to unsaturated FA pretreatments regulates [1-¹⁴C]C16:0 partitioning to CO₂ or ASP. Cells were exposed for 21h pretreatments to either individual FA, C16:0, C18:0, C18:1n-9 cis or C18:3n-3 cis, or to FA combinations in 10:90, 25:75, 50:50, 75:25 or 90:10 ratios for combinations of C16:0: C18:3n-3 cis or C18:0: C18:3n-3 cis or C18:1n-9 cis: C18:3n-3 cis. Total pretreatment FA concentration was 1.0 mM. Following pretreatment, cells were incubated in the presence of 1.0 mM [1-¹⁴C]C16:0 for 3h to determine the rate of metabolism to CO₂ and ASP per h ∙ µg DNA^-1. Pretreatments of either C16:0 or C18:0 alone significantly (P < 0.01) depressed subsequent oxidation of [1-¹⁴C]C16:0 to ASP by 62.7% and 41.2%, respectively, compared to C18:3n-3 cis pretreatments. Similar patterns were observed for [1-¹⁴C]C16:0 oxidation to CO₂. Expression of PC mRNA significantly decreased (P < 0.05) with exposure to either C16:0 or C18:0, compared to either C18:3n-3 cis exposure or control. Expression of cytosolic phosphoenolpyruvate carboxykinase (PCK1) mRNA followed a similar pattern. Pearson’s coefficient correlations were determined for PC mRNA expression and rate of [1-¹⁴C]C16:0 metabolism to CO₂ or ASP, and for PCK1 mRNA expression and rate of [1-¹⁴C]C16:0 metabolism to CO₂ or ASP. Production of CO₂ from [1-¹⁴C]C16:0 positively correlated (r = 0.63; P < 0.05) with PC expression, while ASP production from [1-¹⁴C]C16:0 only tended to correlate (r = 0.51; 0.05 < P < 0.10) with PC mRNA expression. Production of CO₂ or ASP from [1-¹⁴C]C16:0 both positively correlated (r = 0.80; r = 0.69, respectively; P < 0.05) with PCK1 expression. Results show a regulation of FA metabolism in response to saturated and unsaturated FA pretreatments. Cellular oxidative capacity can help determine the response to physiological factors, including FA, which increase during the metabolically stressful transition period in dairy cows.

Keywords:

fatty acid oxidation, ketogenesis, pyruvate carboxylase