**Acknowledgements**

through redistribution of components via fusion events, selective degradation of proteins by mitochondrial proteases, and proteasomal elimination of some outer mitochondrial membrane proteins. Some studies suggest that inner mitochondrial membrane proteins, especially oxidative phosphorylation constituents, may be primarily cleared via mitophagy. There is more to discuss, especially communication between intracellular organelles (mitochondria and endoplasmic reticulum) and oxidative phosphorylation events in mitochondria in relation to redox network, apoptosis/necrosis or mitophagy. These appear to be key players in

Maintenance of mitochondrial function and energy/redox homeostasis requires both generation of newly synthesized and elimination of dysfunctional mitochondria. Taken together, age-dependent decline of mitophagy inhibits removal of dysfunctional or redundant mitochondria as well as impairs mitochondrial biogenesis. It results to progressive mitochondrial accretion and consequently, deterioration of cardiomyocytes function. At present it is pointed out that the steady-state amounts of structural damage accumulated during life are relatively small. However, changes in the redox state reflected by the decline in redox potential,

tous. Activities of ETC complexes revealed that the most affected throughout aging was complex IV, in contrast to relatively small age-related changes in complex II. These non-uniform changes in ETC enzyme complexes may lead to altered electron transfer through the chain, leading to impairment of ATP synthesis and overall functionality of cardiomyocytes during aging. The ability of the main regulatory Krebs cycle enzymes to supplement NADH to ETC was altered in senescent mitochondria. ICDH and KGDH had only half activity in senescent mitochondria; however ICDH was not affected in group of 14 months old. This might sup-

 was also significantly affected. Decrease in GSH levels indicates low GSH/GSSG ratio leading to more oxidized environment in senescent cardiomyocytes but 14-month old hearts were able to maintain basal levels of adult mitochondria. Despite the variations in enzyme activities, the overall proteomic analyses revealed only 12 significantly affected proteins during aging. All these were more or less deprived but question is what is responsible for such a changes. Are these proteins really relevant? Is change in protein amount important? These

Specific marker of senescence was yet not identified, but evaluating a series of markers can help to define the senescent state. Senescent cells have greater proportion of protein content, which might be modulated by several PTMs. If these protein modifications are connected to functional consequences and protein-protein interactions are revealed, link may lead to the solution. Unfortunately, the proteome is much more complicated than the genome. To fit all the proteins together with their different characteristics in various pathways and cellular compartments is almost infeasible. At present, various nutritional, pharmacological and genetic interventions have higher or lower specificity, but are not devoid of potential problems that

and other questions are waiting for us and other researchers to be answered.

and level of protein modifications are significant and ubiqui-

in senescent cardiac myocytes where peroxiredoxin 2 ability to trap

cardiomyocytes survival during aging.

**4. Conclusions**

76 Mitochondrial Diseases

increases in production of H2

port promotion of H2

H2 O2 O2

O2

This work was supported by the project APVV-15-0107 and the project "Competence Center for Research and Development in the field of Diagnostics and Therapy of Oncological diseases", ITMS: 26220220153, co-financed from EU sources. We thank Mrs. Zdena Cetlova for technical assistance.
