Identification of a mitochondrial target of thiazolidinedione insulin sensitizers (mTOT)--relationship to newly identified mitochondrial pyruvate carrier proteins.

Thiazolidinedione (TZD) insulin sensitizers have the potential to effectively treat a number of human diseases, however the currently available agents have dose-limiting side effects that are mediated via activation of the transcription factor PPARγ. We have recently shown PPARγ-independent actions of TZD insulin sensitizers, but the molecular target of these molecules remained to be identified. Here we use a photo-catalyzable drug analog probe and mass spectrometry-based proteomics to identify a previously uncharacterized mitochondrial complex that specifically recognizes TZDs. These studies identify two well-conserved proteins previously known as brain protein 44 (BRP44) and BRP44 Like (BRP44L), which recently have been renamed Mpc2 and Mpc1 to signify their function as a mitochondrial pyruvate carrier complex. Knockdown of Mpc1 or Mpc2 in Drosophila melanogaster or pre-incubation with UK5099, an inhibitor of pyruvate transport, blocks the crosslinking of mitochondrial membranes by the TZD probe. Knockdown of these proteins in Drosophila also led to increased hemolymph glucose and blocked drug action. In isolated brown adipose tissue (BAT) cells, MSDC-0602, a PPARγ-sparing TZD, altered the incorporation of (13)C-labeled carbon from glucose into acetyl CoA. These results identify Mpc1 and Mpc2 as components of the mitochondrial target of TZDs (mTOT) and suggest that understanding the modulation of this complex, which appears to regulate pyruvate entry into the mitochondria, may provide a viable target for insulin sensitizing pharmacology

Identification of a mitochondrial target of thiazolidinedione insulin sensitizers (mTOT)--relationship to newly identified mitochondrial pyruvate carrier proteins.

Thiazolidinedione (TZD) insulin sensitizers have the potential to effectively treat a number of human diseases, however the currently available agents have dose-limiting side effects that are mediated via activation of the transcription factor PPARγ. We have recently shown PPARγ-independent actions of TZD insulin sensitizers, but the molecular target of these molecules remained to be identified. Here we use a photo-catalyzable drug analog probe and mass spectrometry-based proteomics to identify a previously uncharacterized mitochondrial complex that specifically recognizes TZDs. These studies identify two well-conserved proteins previously known as brain protein 44 (BRP44) and BRP44 Like (BRP44L), which recently have been renamed Mpc2 and Mpc1 to signify their function as a mitochondrial pyruvate carrier complex. Knockdown of Mpc1 or Mpc2 in Drosophila melanogaster or pre-incubation with UK5099, an inhibitor of pyruvate transport, blocks the crosslinking of mitochondrial membranes by the TZD probe. Knockdown of these proteins in Drosophila also led to increased hemolymph glucose and blocked drug action. In isolated brown adipose tissue (BAT) cells, MSDC-0602, a PPARγ-sparing TZD, altered the incorporation of (13)C-labeled carbon from glucose into acetyl CoA. These results identify Mpc1 and Mpc2 as components of the mitochondrial target of TZDs (mTOT) and suggest that understanding the modulation of this complex, which appears to regulate pyruvate entry into the mitochondria, may provide a viable target for insulin sensitizing pharmacology

Crosslinking of the <i>Drosophila</i> ortholog in wild type and knockdown lines.

<p>(<b>A</b>) Wild-type larvae and adult flies were homogenized and mitochondrial pellets were crosslinked with and without the addition of MSDC-0160 as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061551#pone-0061551-g001" target="_blank">figure 1</a>. The autoradiograms of the resulting image of the specifically crosslinked proteins are shown for the flies on the left side compared to mouse liver in the lane on the right. (<b>B</b>) Fly stocks carrying RNAi constructs were crossed to Act-GAL4 driver and progeny tissues were processed and crosslinked as described in the text. Lanes marked “1” were from knockdowns of CG9399, lanes marked “4” were from knockdowns of CG14290, the other lanes were either unrelated genes or control strains. Two separate knockdown lines are represented. The complete list of the strains is shown in the text. Red arrows indicate reduced crosslinking of the specific CG9399 protein (BRP44 ortholog). (<b>C</b>) Membrane samples from CG9399 and CG14290 KD as in B were subjected to Western blot analysis for either the CG9399 (left) or CG14290 protein (right).</p