Differential Effects of Gram-positive and Gram-negative Inflammatory Stimuli on the Expression and Function of Energy Substrate Transporters in Human Mammary Epithelial cells
Manthena, Uma Lakshmi
Mastitis is often bacterial in origin. Lipoteichoic acid (LTA) and lipopolysaccharide (LPS), endotoxins from gram-positive and gram-negative bacteria, respectively, are potent inducers of mammary gland inflammation. Inflammation can alter expression of transporters responsible for transport of substrates important in synthesis of milk constituents and cellular metabolic energy. Since, gram-positive and gram-negative bacterial infections cause a different clinical course of mastitis, I investigated whether LTA and LPS differentially alter proton-coupled (MCT1) and sodium-coupled monocarboxylate transporter (SMCT1, SMCT2) expression and functional outcomes of altered expression. Human mammary epithelial cells (MCF-12A) were incubated with 1 microgram/mL LPS or LTA for 6, 12 and 24 hours and mRNA expression of TNF-alpha, IL-1β, IL-6, MCT1, SMCT1, and SMCT2 were measured using Quantitative RT-PCR. LPS decreased SMCT1, but increased SMCT2 expression after 6 h, while LTA increased MCT1 expression at 6 h, followed by gradual decrease in expression until 24 h. To know whether such differential changes in transporter expression by LPS and LTA could cause changes in cellular energy production, I quantified creatine (Cr) and high-energy phosphate substrates (CrP, ATP, ADP, AMP) and oxygen consumption rates using HPLC and Hansatech oxygen electrode, respectively. At 12 h, LPS increased concentrations of Cr, CrP, ATP and ADP, whereas LTA caused changes in CrP and ADP concentrations relative to control. Both LPS and LTA decreased oxygen consumption rates after 12 h. Furthermore, to know whether changes in transporter expression lead to differences in substrate availability, I performed uptake studies for carnitine using radiolabelled tritium L-carnitine. LPS and LTA challenge did not affect the affinity, but caused a 2-3-fold increase in maximal activity (Vmax) of carnitine transport. Although increases in Vmax were not significant, the increase in Vmax after 12 h exposure by LPS and LTA corresponds to changes in mRNA expression of the OCTN2 transporter (previously reported in the laboratory). In conclusion, LPS and LTA differentially alter mRNA expression of transporters, which leads to changes in cellular energy levels and oxygen consumption rates and possibly to changes in the functional activity of transporters. Whether such differences contribute to the different clinical course of mastitis warrants further investigation.
DegreeMaster of Science (M.Sc.)
DepartmentPharmacy and Nutrition
CommitteeLohmann, Katharina; Hendrick, Steven; Penner, Gregory
Copyright DateAugust 2012
Mammary Gland Inflammation, LPS and LTA Differentially Alter Transporter Expression in MCF-12A cells, Monocarboxylate Transporters