Mechanisms of regulation of mitochondrial H+ leak and thermogenesis

Project Summary
Mitochondria control cell metabolism by converting nutrients into an electrochemical gradient of protons (H+)
across the inner mitochondrial membrane (IMM) to generate ATP, the currency of the cell, and heat (called
mitochondrial thermogenesis). A precise balance in the distribution of H+ between the two forms of energy
production, ATP and heat, defines the metabolic homeostasis of the cell. Brown fat and beige fat mitochondria
specialize in the production of heat via the uncoupling protein 1 (UCP1). However, even in other tissues,
mitochondrial thermogenesis accounts for 25% of total mitochondrial energy production and can therefore have
a considerable impact on the physiology of the entire body. Mitochondrial thermogenesis is not only essential for
maintaining core body temperature, it is also the process by which excess calories are burned to prevent diet-
induced obesity. In addition, it reduces the production of reactive oxygen species (ROS) by the mitochondria to
protect cells from oxidative damage. In addition, chemical uncouplers such as 2,4-dinitrophenol (DNP), which
are believed to increase H+ leak independently of proteins, are the most effective anti-obesity drugs to date.
Thus, mitochondrial thermogenesis is a powerful regulator of cellular metabolism, and a mechanistic
understanding of this fundamental process will help in the development of therapeutic strategies to
combat many pathologies associated with mitochondrial dysfunction, including metabolic syndrome
and age-related disorders. Unfortunately, the precise molecular mechanisms that control the acute activation
of thermogenesis in the mitochondria are poorly defined. This lack of information is largely due to a dearth of
methods for direct measurement of H+ currents across the IMM. The development of a methodology based on
the patch-clamp technique allows for the first time the direct study of H+ leak through the IMM of each tissue and
the first biophysical characterization of mitochondrial transporters, such as UCP1 and the ADP/ATP transporter
(AAC), which are the mediators of this H+ leak. This unique approach now provides an unprecedented high-
resolution direct functional analysis of 1) the mitochondrial ion channels and transporters responsible for
mitochondrial thermogenesis and 2) the mechanisms of action of chemical uncouplers such as DNP. Using the
new mitochondrial patch-clamp assay combined with modern cellular and molecular techniques, this
research project will provide new insights into the mechanisms that control the thermogenic capacity of
the mitochondria and how they can be targeted for therapeutic purposes.

Grant Number: 5R35GM143097-05
NIH Institute/Center: NIH
Principal Investigator: Ambre Bertholet