MPC inhibition induces ATP utilization by lipid cycling.Figure 5(A,B) Effect of UK5099 on energy expenditure contributed by ATP demand and by mitochondrial proton leak in non-stimulated brown adipocytes. Primary brown adipocytes were pre-treated with vehicle (DMSO) or 100 nM UK5099 for 2 hours. OCR were measured in respirometry media supplemented with 5 mM glucose and 3 mM glutamine in the presence of vehicle or UK5099. Oligomycin A (Oligo; 4 µM), mitochondrial uncoupler FCCP (2 µM) and antimycin A (AA; 4 µM) were injected where indicated. (A) Representative OCR traces averaging 6 technical replicates. (B) Quantification of mitochondrial proton leak and ATP-linked OCR (oligomycin sensitive) as measured in (A) from n=9 individual experiments. Data were normalized to vehicle for each individual experiment. (C) To determine the contribution of ATP demand to increased energy expenditure under UK5099 cells were permeabilized and cytosolic ADP concentrations were clamped. OCR were measured in the presence of 5 mM pyruvate, 3 mM malate, 0.1 mM palmitoyl-CoA, 0.5 mM carnitine and 5 mM ADP. Cells were treated with either 100 nM, 1 µM or 10 µM UK5099. Data shows maximal state 3 OCR normalized to maximal complex 4 activity from n=3 individual experiments. (D) Schematic representation of lipid cycling. HK, hexokinase; PFK, phosphofructokinase; ATGL, adipose triglyceride lipase; ACS, Acyl-CoA synthetase; TAG, triacylglyceride; DAG, diacylglyceride; MAG, monoacylglyceride; LPA, lysophosphatidic acid; FFA, free fatty acid; G3P, glycerol-3-phosphate (E) Effect of MPC inhibition on glycerol 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) generation. G3P/DHAP is used as a measure of acylglycerol synthesis. Brown adipocytes were treated with either vehicle, 100 nM UK5099 or 1 µM norepinephrine (NE) for 24 h from n=4 individual experiments. (F,G) Contribution of lipolysis to UK5099 induced energy demand. Primary brown adipocytes were pre-treated with either vehicle (DMSO), 100 nM UK5099, 40 µM Atglistatin or a combination of Atglistatin with UK5099 for 2 h. OCR were measured in respirometry media supplemented with 5 mM glucose and 3 mM glutamine in the presence of vehicle, UK5099, or Atglistatin. (F) Quantification of non-stimulated OCR from n=4 individual experiments. (G) Quantification of ATP-linked respiration from n=4 individual experiments. Data were normalized to vehicle for each individual experiment. (H,I) Contribution of TAG synthesis to UK5099 induced energy demand. Primary brown adipocytes were pre-treated with either vehicle (DMSO), 100 nM UK5099, 1 µM DGAT1 and 1 µM DGAT2 or a combination of DGAT1/2 inhibitors with UK5099 for 2 h. OCR were measured in respirometry media supplemented with 5 mM glucose and 3 mM glutamine in the presence of vehicle, UK5099, DGAT1/2 inhibitors, or UK5099 + DGAT1/2 inhibitors. (H) Quantification of non-stimulated OCR from n=6 individual experiments. (I) Quantification of ATP-linked OCR from n=6 individual experiments. Data were normalized to vehicle for each individual experiment. (J,K) Contribution of ACS to UK5099 induced energy demand. Primary brown adipocytes were pre-treated with either vehicle (DMSO), 100 nM UK5099, 5 µM Triacsin C or a combination of 5 µM Triacsin C with UK5099 for 2 h. OCR were measured in respirometry media supplemented with 5 mM glucose and 3 mM glutamine in the presence of vehicle, UK5099, Triacsin C, or UK5099 + Triacsin C. (J) Quantification of non-stimulated OCR from n=4 individual experiments. (K) Quantification of ATP-linked OCR from n=4 individual experiments. Data were normalized to vehicle for each individual experiment.