Identification of a Mitochondrial Target of Thiazolidinedione Insulin Sensitizers (mTOT)—Relationship to Newly Identified Mitochondrial Pyruvate Carrier Proteins

Abstract

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 13C-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.

MitoNEET-dependent formation of intermitochondrial junctions

“…Although it was later revealed that the main mitochondrial binding site of pioglitazone was the Mpc mitochondrial pyruvate carrier complex (6), this initial observation launched a series of studies to unravel the molecular function of the mNEET protein. mNEET belongs to a family of three proteins exhibiting a CDGSH domain, together with miner1 and miner2.…”

The Mitochondrial Pyruvate Carrier and Metabolic Regulation

“…TZD activation of the energy status-sensing, catabolism driver AMP-activated protein kinase (AMPK) [26], is also mimicked by UK5099. In another report, MCP1 and MCP2 were identified as mitochondrial proteins that could be chemically crosslinked to TZD [27] in a manner that could be blocked by UK5099. These authors also showed that TZDs altered the incorporation of 13 C-labeled carbon from glucose into acetyl CoA.…”

Treating fatty liver disease by modulating mitochondrial pyruvate metabolism

“…A new mitochondrial drug target has been identified that provides an opportunity to treat metabolic diseases by changing the way pyruvate is metabolized, and this may have implications for treating diseases as diverse as Parkinson's disease and liver disease. Mitochondrial target of thiazolidinediones (mTOT)1, 2, 3 modulators have been selected for their ability to bind to and modulate the activity of the mTOT, which was subsequently identified as the mitochondrial pyruvate carrier (MPC). The MPC is a heterologous complex composed of two proteins, MPC1 and MPC2, in the inner mitochondrial membrane 4, 5.…”