Comparison of metabolic effects of mitochondrial dysfunctions in the context of vulnerability to fatigue : computer simulation study

In recent years, the accumulation of phosphate ions and the increase in acidity have been described as crucial metabolic fatigue-leading factors that disturb muscle fiber contractions. This fact is especially important in the context of mitochondrial dysfunctions in which excessive fatigue is one of the possible symptoms. However, little is known about the precise fatigue-inducing thresholds of work intensity in mitochondrial dysfunctions of various types and at various stages of their severity. Possible interactions of additional factors such as disturbances in electrolyte concentrations (i.e. magnesium ions) were also not precisely defined. One of the best-suited tools for this kind of problem is systems biology, which enables modeling of metabolic pathways. In this research, a computer model of working skeletal muscle was adapted. The relationship between the decrease in oxidative phosphorylation and the workload shows a linear dependence for dysfunctions that evenly disturb the activity of each element of the pathway (which is equivalent to the decrease in mitochondrial mass). In case of dysfunctions that disrupt only one element of the pathway, the relationship between fatigue threshold and exercise intensity is exponential, but with higher threshold deficiency values. Muscle phosphate levels were the most vulnerable to disruptions of complex III and ATP synthase. Surprisingly, disruptions of the ATP/ADP exchanger emerged as equally disruptive and capable of significantly increasing phosphate concentrations also in the rest state, whereas the impact of the impairment of the phosphate transporter was negligible. Perturbations in magnesium concentration also did not show a significant effect in any of these models