Structure–function relationships in feedback regulation of energy fluxes in vivo in health and disease: Mitochondrial Interactosome

Abstract

The aim of this review is to analyze the results of experimental research of mechanisms of regulation of mitochondrial respiration in cardiac and skeletal muscle cells in vivo obtained by using the permeabilized cell technique. Such an analysis in the framework of Molecular Systems Bioenergetics shows that the mechanisms of regulation of energy fluxes depend on the structural organization of the cells and interaction of mitochondria with cytoskeletal elements. Two types of cells of cardiac phenotype with very different structures were analyzed: adult cardiomyocytes and continuously dividing cancerous HL-1 cells. In cardiomyocytes mitochondria are arranged very regularly, and show rapid configuration changes of inner membrane but no fusion or fission, diffusion of ADP and ATP is restricted mostly at the level of mitochondrial outer membrane due to an interaction of heterodimeric tubulin with voltage dependent anion channel, VDAC. VDAC with associated tubulin forms a supercomplex, Mitochondrial Interactosome, with mitochondrial creatine kinase, MtCK, which is structurally and functionally coupled to ATP synthasome. Due to selectively limited permeability of VDAC for adenine nucleotides, mitochondrial respiration rate depends almost linearly upon the changes of cytoplasmic ADP concentration in their physiological range. Functional coupling of MtCK with ATP synthasome amplifies this signal by recycling adenine nucleotides in mitochondria coupled to effective phosphocreatine synthesis. In cancerous HL-1 cells this complex is significantly modified: tubulin is replaced by hexokinase and MtCK is lacking, resulting in direct utilization of mitochondrial ATP for glycolytic lactate production and in this way contributing in the mechanism of the Warburg effect. Systemic analysis of changes in the integrated system of energy metabolism is also helpful for better understanding of pathogenesis of many other diseases.

Mitochondrial functional specialization in glycolytic and oxidative muscle fibers: tailoring the organelle for optimal function

“…3A) (72,95). This configuration provides the physical proximity between mitochondria and SR-Ca 2ϩ /MF-Mg 2ϩ ATPases that is required to observe ICEUs (72,84,93,95). In contrast, in fast-glycolytic muscle fibers in which mitochondria are less abundant, mostly located at the level of Z-lines with no trans A-band branches (72), the spatial configuration is less compatible with the formation of ICEUs (72,95).…”

“…This is mainly based on the observation that disruption of the OMM using a well-controlled hypo-osmotic shock lowers the K m for ADP to the values observed in isolated mitochondria and in mitochondria from fast-glycolytic fibers (57). The molecular mechanisms underlying fiber type-specific OMM permeability to ADP are currently unknown but could involve differences in the conductance and isoform expression of voltage-dependent anion channel (VDACs), which are responsible for the transport of a number of solutes across the MOM including adenylates (24,32,53,57,60,93,96,97). Furthermore, recent evidence demonstrates that mitochondrial affinity for ADP is modulated by the contractile state of myofibers (76), with contraction lowering the K m for ADP.…”

“…Indeed, functional units, termed intracellular energetic units (ICEUs), have been well described in the heart (16,50,84,93,95,102), and some evidence for their existence in the soleus muscle has been obtained (102). Within these ICEUs, ATP and ADP are focally released and directly transferred by channeling between mitochondria on the one hand, and sarcoplasmic reticulum (SR)-Ca 2ϩ and myofibrillar (MF-Mg 2ϩ ) ATPases on the other hand (16,50,84,93,95,102). Three lines of evidence, obtained in permeabilized fibers, have led to this conclusion.…”

“…One of the most striking differences between mitochondria from fast-glycolytic and slowoxidative fibers concerns the sensitivity of respiration to ADP, and the mechanisms coupling mitochondrial ATP supply to subcellular sites of ATP consumption (53, 57, 93, 96 -98). These properties were largely uncovered following the development of saponin-permeabilized fibers, which allowed study of mitochondria in a relatively preserved cytoarchitectural environment (58,93,98). Using this approach, several studies, including ours, have shown that mitochondria in slow-oxidative muscles, such as the heart and the soleus, display an apparent K m (Michaelis-Menten constant) for exogenous ADP in range of 200 -500 M, which is approximately 10-fold higher than K m values measured in isolated mitochondria (53,57,96,97).…”

Structure-based Analysis of VDAC1 Protein

“…VDAC1 regulates mitochondrial membrane permeability to ions and small molecules, such as Na ϩ , K ϩ , Ca 2ϩ , Cl Ϫ , ATP, NADH, succinate, and malate (1)(2)(3). It is now also recognized that VDAC1 is involved in many physiological and pathophysiological processes, including Ca 2ϩ homeostasis (2,3), energy metabolism (1)(2)(3)(4)(5), and cell apoptosis (2-4, 6 -8).…”