Functional changes of the NADH respiratory chain in rat-liver mitochondria and the content changes of high-energy phosphate groups in rat liver and heart during the early phase of burn injury

Locally activated mitophagy contributes to a "built-in" protection against early burn-wound progression in rats

AIMS

Deep burn-wounds undergo a dynamic progression in the initial or periburn area after insults, and the zone of stasis is the crucial region suffering the deterioration, considered as salvageable. Few studies explored the role of mitochondria in this process. This study is to clarify a possible "built-in" protection of mitophagy.

MAIN METHODS

A classic "comb" scald rat model was established. Histological and blood-flow observation were processed based on hematoxylin-eosin staining and laser analysis. Oxidative and apoptotic status were analyzed by commercial kits. Transmission-electron microscope, immunofluorescence staining, and western blot were applied to detect the mitophagy in the zone of stasis and potential regulators. Adenovirus-based gene-silence contributed to determine the role of HIF-1α as a regulatory mediator.

KEY FINDINGS

We found that burn-caused typical ischemia and histological deterioration in the zone of stasis, in parallel with increases in oxidative stress and apoptosis. Mitochondrial damage was involved in the aforementioned changes. Furthermore, we detected mitophagy in burn-wounds, which was contradictory to the burn-wound conversion. HIF-1α expression was closely related to the level of mitophagy, while BNIP3 and PARKIN are involved downstream.

SIGNIFICANCE

We demonstrate that burn-induced mitochondrial impairment contributes to the mobilization of injurious mechanisms in the zone of stasis and that mitophagy provides a beneficial way to protect against burn-wound progression via the elimination of damaged mitochondria. Our findings offer insights into mitochondrial quality control in burn-wound progression and suggest the novel concept that HIF-1α may be a therapeutic target due to its possible regulation on BNIP3- or PARKIN-mediated mitophagy.

Pathological Responses of Cardiac Mitochondria to Burn Trauma

Despite advances in treatment and care, burn trauma remains the fourth most common type of traumatic injury. Burn-induced cardiac failure is a key factor for patient mortality, especially during the initial post-burn period (the first 24 to 48 h). Mitochondria, among the most important subcellular organelles in cardiomyocytes, are a central player in determining the severity of myocardial damage. Defects in mitochondrial function and structure are involved in pathogenesis of numerous myocardial injuries and cardiovascular diseases. In this article, we comprehensively review the current findings on cardiac mitochondrial pathological changes and summarize burn-impaired mitochondrial respiration capacity and energy supply, induced mitochondrial oxidative stress, and increased cell death. The molecular mechanisms underlying these alterations are discussed, along with the possible influence of other biological variables. We hope this review will provide useful information to explore potential therapeutic approaches that target mitochondria for cardiac protection following burn injury.

Burn Trauma Acutely Increases the Respiratory Capacity and Function of Liver Mitochondria

BACKGROUND

A complete understanding of the role of the liver in burn-induced hypermetabolism is lacking. We investigated the acute effect of severe burn trauma on liver mitochondrial respiratory capacity and coupling control as well as the signaling events underlying these alterations.

METHODS

Male BALB/c mice (8-12 weeks) received full-thickness scald burns on ∼30% of the body surface. Liver tissue was harvested 24 h postinjury. Mitochondrial respiration was determined by high-resolution respirometry. Citrate synthase activity was determined as a proxy of mitochondrial density. Male Sprague-Dawley rats received full-thickness scald burns to ∼60% of the body surface. Serum was collected 24 h postinjury. HepG2 cells were cultured with serum-enriched media from either sham- or burn-treated rats. Protein levels were analyzed via western blot.

RESULTS

Mass-specific (P = 0.01) and mitochondrial-specific (P = 0.01) respiration coupled to ATP production significantly increased in the liver after burn. The respiratory control ratio for ADP (P = 0.04) and the mitochondrial flux control ratio (P = 0.03) were elevated in the liver of burned animals. Complex III and Complex IV protein abundance in the liver increased after burn by 17% and 14%, respectively. Exposure of HepG2 cells to serum from burned rats increased the pAMPKα:AMPKα ratio (P < 0.001) and levels of SIRT1 (P = 0.01), Nrf2 (P < 0.001), and PGC1α (P = 0.02).

CONCLUSIONS

Severe burn trauma augments respiratory capacity and function of liver mitochondria, adaptations that augment ATP production. This response may be mediated by systemic factors that activate signaling proteins responsible for regulating cellular energy metabolism and mitochondrial biogenesis.

Differential acute and chronic effects of burn trauma on murine skeletal muscle bioenergetics

Altered skeletal muscle mitochondrial function contributes to the pathophysiological stress response to burns. However, the acute and chronic impact of burn trauma on skeletal muscle bioenergetics remains poorly understood. Here, we determined the temporal relationship between burn trauma and mitochondrial function in murine skeletal muscle local to and distal from burn wounds. Male BALB/c mice (8-10 weeks old) were burned by submersion of the dorsum in water (∼ 95 °C) to create a full thickness burn on ∼ 30% of the body. Skeletal muscle was harvested spinotrapezius underneath burn wounds (local) and the quadriceps (distal) of sham and burn treated mice at 3h, 24h, 4d and 10d post-injury. Mitochondrial respiration was determined in permeabilized myofiber bundles by high-resolution respirometry. Caspase 9 and caspase 3 protein concentration were determined by western blot. In muscle local to burn wounds, respiration coupled to ATP production was significantly diminished at 3h and 24h post-injury (P<0.001), as was mitochondrial coupling control (P<0.001). There was a 5- (P<0.05) and 8-fold (P<0.001) increase in respiration in response to cytochrome at 3h and 24h post burn, respectively, indicating damage to the outer mitochondrial membranes. Moreover, we also observed greater active caspase 9 and caspase 3 in muscle local to burn wounds, indicating the induction of apoptosis. Distal muscle mitochondrial function was unaltered by burn trauma until 10d post burn, where both respiratory capacity (P<0.05) and coupling control (P<0.05) were significantly lower than sham. These data highlight a differential response in muscle mitochondrial function to burn trauma, where the timing, degree and mode of dysfunction are dependent on whether the muscle is local or distal to the burn wound.

Temporal changes in cellular energy following burn injury

Availability of ADP is a predominant influence on respiratory control. Associated with severe burn injury is an increase in energy expenditure. The purpose of this study was to determine the temporal changes in ATP, ADP, NAD, and NADH following severe burn and thereby assess any related alterations in respiratory control and energy deficit. During isoflurane anesthesia and following intraperitoneal injection of saline, 32 mice were flame burned at 40% body surface area. Twelve mice served as controls. At 12, 24, 72, and 168 h post-burn, groups of mice underwent celiotomy with determination of hepatic surface blood flow using laser Doppler and oxygen saturation using pulse oximetry. Biopsies of liver were then frozen in liquid nitrogen for subsequent quantification of ATP, ADP, AMP, NAD, and NADH by HPLC. Mortality was 12.5% at 72 h post-burn and 25% at 1 week. Oxygen saturation and hepatic surface blood flow remained similar to control values throughout the week after burn. ATP, ADP, and energy charge decreased progressively following burn reaching a significant decrease from unburned controls at 72 h. Availability of NADH remained statistically similar to unburned controls throughout the week after burn. These results demonstrate that despite maintenance of baseline oxygen delivery, there was a nadir in ATP and ADP availability and energy charge in the liver at 72 h after burn. This finding supports the concept of a limitation in phosphorylation after injury. Availability of NADH remained at or above pre-burn concentrations suggesting that the rate of fuel oxidation was not a limiting factor for ongoing oxidative phosphorylation for energy.

The effects of thermal injury on mitochondrial oxygen consumption and the glycerol phosphate shuttle

Since many of the physiologic adaptations to postburn hypermetabolism must be related to alterations in mitochondrial function, the effects of thermal injury on rat liver mitochondrial oxygen consumption were studied. A 60% full-thickness thermal injury was found to cause a significant increase in mitochondrial oxygen consumption, peaking at postburn day 12, without the loss of respiratory control. The same thermal injury was also found to cause a significant increase in glycerol-3-phosphate dehydrogenase (GPD) activity, which also peaks at postburn day 12. The increase in GPD activity and the resultant increase in the flow through the glycerol phosphate shuttle might be related to the increase of postburn mitochondrial oxygen consumption. It is also shown that although the loss of respiratory control could also be a contributing factor to postburn hypermetabolism at postburn days 15 and 18, this was not observed during the early days after thermal injury.

Catecholamines: important factors in the increase of oxidative phosphorylation coupling in rat-liver mitochondria during the early phase of burn injury

Thirty minutes after Sprague-Dawley rats had been injected subcutaneously with epinephrine or norepinephrine, the respiratory control ratio (RCR), the rate of O2 consumption in state 3 and the rate of ATP formation in liver mitochondria succinate respiratory chain were increased. The rate of O2 consumption in state 4 was increased or only slightly increased. When the rats were injected with the adrenergic blocking agents, timolol or phenoxybenzamine, 1 h before the burn, the activities of the succinate respiratory chain was partly inhibited 30 min postburn. Compared with our previous results, it can be suggested that catecholamines may play an important role in the increase of oxidative phosphorylation coupling in the early phase of burn injury.