Increased Mitochondrial Protein Levels and Bioenergetics in the Musculus Rectus Femoris of Wfs1-Deficient Mice.

Wfs1 deficiency leads to a progressive loss of plasma insulin concentration, which should reduce the consumption of glucose in insulin-dependent tissues, causing a variety of changes in intracellular energy metabolism. Our objective here was to assess the changes in the amount and function of mitochondrial proteins in different muscles of Wfs1-deficient mice. Mitochondrial functions were assayed by high-resolution oxygraphy of permeabilized muscle fibers; the protein amount was evaluated by liquid chromatography tandem mass spectrometry (LC/MS/MS) analysis and mRNA levels of the uncoupler proteins UCP2 and UCP3 by real-time PCR; and citrate synthase (CS) activity was determined spectrophotometrically in muscle homogenates. Compared to controls, there were no changes in proton leak and citrate synthase activity in the heart and m. soleus tissues of Wfs1-deficient mice, but significantly higher levels of both of these factors were observed in the m. rectus femoris; mitochondrial proteins and mRNA of UCP2 were also higher in the m. rectus femoris. ADP-stimulated state 3 respiration was lower in the m. soleus, remained unchanged in the heart, and was higher in the m. rectus femoris. The mitochondrial protein amount and activity are higher in Wfs1-deficient mice, as are mitochondrial proton leak and oxygen consumption in m. rectus femoris. These changes in muscle metabolism may be important for identifying the mechanisms responsible for Wolfram syndrome and diabetes.

Dilation of human atria: increased diffusion restrictions for ADP, overexpression of hexokinase 2 and its coupling to oxidative phosphorylation in cardiomyocytes.

Cardiac energy metabolism with emphasis on mitochondria was addressed in atrial tissue from patients with overload-induced atrial dilation. Structural remodeling of dilated (D) atria manifested as intracellular accumulation of fibrillar aggregates, lipofuscin, signs of myolysis and autophagy. Despite impaired complex I dependent respiration and increased diffusion restriction for ADP, no changes regarding adenylate and creatine kinase occurred. We observed 7-fold overexpression of HK2 gene in D atria with concomitant 2-fold greater activation of mitochondrial oxygen consumption by glucose, which might represent an adaption to increased energy requirements and impaired mitochondrial function by effectively joining glycolysis and oxidative phosphorylation.

Impaired oxidative phosphorylation in overtrained rat myocardium.

The present study was undertaken to characterize and review the changes in energy metabolism in rat myocardium in response to chronic exhaustive exercise. It was shown that a treadmill exercise program applied for six weeks led the rats into a state characterized by decreased performance, loss of body weight and enhanced muscle catabolism, indicating development of overtraining syndrome. Electron microscopy revealed disintegration of the cardiomyocyte structure, cellular swelling and appearance of peroxisomes. Respirometric assessment of mitochondria in saponin-permeabilized cells in situ revealed a decreased rate of oxidative phosphorylation (OXPHOS) due to diminished control over it by ADP and impaired functional coupling of adenylate kinase to OXPHOS. In parallel, reduced tissue content of cytochrome c was observed, which could limit the maximal rate of OXPHOS. The results are discussed with respect to relationships between the volume of work and corresponding energy metabolism. It is concluded that overtraining syndrome is not restricted to skeletal muscle but can affect cardiac muscle as well.

Distinct organization of energy metabolism in HL-1 cardiac cell line and cardiomyocytes.

Expression and function of creatine kinase (CK), adenylate kinase (AK) and hexokinase (HK) isoforms in relation to their roles in regulation of oxidative phosphorylation (OXPHOS) and intracellular energy transfer were assessed in beating (B) and non-beating (NB) cardiac HL-l cell lines and adult rat cardiomyocytes or myocardium. In both types of HL-1 cells, the AK2, CKB, HK1 and HK2 genes were expressed at higher levels than the CKM, CKMT2 and AK1 genes. Contrary to the saponin-permeabilized cardiomyocytes the OXPHOS was coupled to mitochondrial AK and HK but not to mitochondrial CK, and neither direct transfer of adenine nucleotides between CaMgATPases and mitochondria nor functional coupling between CK-MM and CaMgATPases was observed in permeabilized HL-1 cells. The HL-1 cells also exhibited deficient complex I of the respiratory chain. In conclusion, contrary to cardiomyocytes where mitochondria and CaMgATPases are organized into tight complexes which ensure effective energy transfer and feedback signaling between these structures via specialized pathways mediated by CK and AK isoforms and direct adenine nucleotide channeling, these complexes do not exist in HL-1 cells due to less organized energy metabolism.

Oxidative phosphorylation and its coupling to mitochondrial creatine and adenylate kinases in human gastric mucosa.

Energy metabolism in gastrobiopsy specimens of the antral and corpus mucosa, treated with saponin to permeabilize the cells, was studied in patients with gastric diseases. The results show twice lower oxidative capacity in the antral mucosa than in the corpus mucosa and the relative deficiency of antral mitochondria in complex I. The mucosal cells expressed mitochondrial and cytosolic isoforms of creatine kinase and adenylate kinase (AK). Creatine (20 mM) and AMP (2 mM) markedly stimulated mitochondrial respiration in the presence of submaximal ADP or ATP concentrations, and creatine reduced apparent Km for ADP in stimulation of respiration, which indicates the functional coupling of mitochondrial kinases to oxidative phosphorylation. Addition of exogenous cytochrome c increased ADP-dependent respiration, and the large-scale cytochrome c effect (>or=20%) was associated with suppressed stimulation of respiration by creatine and AMP in the mucosal preparations. These results point to the impaired mitochondrial outer membrane, probably attributed to the pathogenic effects of Helicobacter pylori. Compared with the corpus mucosa, the antral mucosa exhibited greater sensitivity to such type of injury as the prevalence of the large-scale cytochrome c effect was twice higher among the latter specimens. Active chronic gastritis was associated with decreased respiratory capacity of the corpus mucosa but with its increase in the antral mucosa. In conclusion, human gastric mucosal cells express the mitochondrial and cytosolic isoforms of CK and AK participating in intracellular energy transfer systems. Gastric mucosa disease is associated with the altered functions of these systems and oxidative phosphorylation.

Compartmentation of energy metabolism in atrial myocardium of patients undergoing cardiac surgery.

The parameters of oxidative phosphorylation and its interaction with creatine kinase (CK)- and adenylate kinase (AK)-phosphotransfer networks in situ were studied in skinned atrial fibers from 59 patients undergoing coronary artery bypass surgery, valve replacement/correction and atrial septal defect correction. In atria, the mitochondrial CK and AK are effectively coupled to oxidative phosphorylation, the MM-CK is coupled to ATPases and there exists a direct transfer of adenine nucleotides between mitochondria and ATPases. Elimination of cytoplasmic ADP with exogenous pyruvate kinase was not associated with a blockade of the stimulatory effects of creatine and AMP on respiration, neither could it abolish the coupling of MM-CK to ATPases and direct transfer of adenine nucleotides. Thus, atrial energy metabolism is compartmentalized so that mitochondria form functional complexes with adjacent ATPases. These complexes isolate a part of cellular adenine nucleotides from their cytoplasmic pool for participating in energy transfer via CK- and AK-networks, and/or direct exchange. Compared to atria in sinus rhythm, the fibrillating atria were larger and exhibited increased succinate-dependent respiration relative to glutamate-dependent respiration and augmented proton leak. Thus, alterations in mitochondrial oxidative phosphorylation may contribute to pathogenesis of atrial fibrillation.